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1999 | show all back to the top of all publications back to the year overview Watson, E, Kunert, N, Putzar, R, Maas, H, Hiermaier SFour-view split-image fragment tracking in hypervelocity impact experiments 2020 Int J Impact Eng , issue : 135» show abstract « hide abstract Abstract Fragmentation is a significant phenomenon caused by hypervelocity impact and has applications in orbital debris and planetary impact research, among many others. In particular, the velocity distribution of fragments created by hypervelocity impact is not thoroughly understood. In this paper, we present an experimental setup and analysis method for tracking and measuring individual fragment velocities in 3D. The setup uses two synchronized high-speed cameras with split images, yielding four views, to record image sequences of the in-flight fragments. We analyze the image sequences by identifying fragments and their trajectories in each view, matching the fragments found in different views, and finally triangulating for their 3D positions. The result is a method able to measure fragments’ 3D velocities in the highly transient hypervelocity process. Ganzenmüller G, Plappert DMechanical Properties of a Unidirectional Basalt-Fiber/Epoxy Composite 2020 J. Compos. Sci. , volume : 4, issue : 3, page : 101
Download file Oliveira, P, May, M, Panzera, T, Scarpa, F, Hiermaier SReinforced biobased adhesive for eco-friendly sandwich panels 2020 Int J Adhes Adhes , issue : 98, page : 102550» show abstract « hide abstract Abstract This work describes the development of a bio-polyurethane (bio-PU) adhesive made from castor oil plant to be used in sustainable (eco-friendly) sandwich panels made from recycled plastic waste. Low-cost fillers, such as Portland cement and recycled rubber particles are incorporated into the biopolymer to modify its mechanical behaviour. Epoxy is also used to benchmark the mechanical performance of the reinforced biopolymer described in this work. A full factorial design is performed to identify the effects of the types of adhesive, particles and their weight fraction on the mechanical and physical properties of hybrid panels. Single lap and adapted T-peel tests are used to assess the adhesion of the polymers to the aluminium surfaces. The inclusion of 3 wt% cement particles in the biopolymer provides a significant increase in the tensile strength and stiffness compared to the pristine bio-PU. Other properties that benefit from that amount of reinforcement in the bio-adhesive are the impact resistance and reduction of density and porosity compared to higher fractions of inclusions. Despite its lower mechanical properties, the biopolymer with rubber particles provides however an increase of the single lap shear strength, the opposite of what happens when using the reinforced epoxy polymer. The T-peel test also highlights the higher bonding affinity of the biopolymer to the sustainable sandwich core; that indicates the promise of using this biopolymer-reinforced adhesive in secondary and sustainable applications. Pfaff, A., Bierdel, M., Hoschke, K., Wickert, M., Riedel, W., Hiermaier, S.Resource analysis model and validation for selective laser melting, constituting the potential of lightweight design for material efficiency 2020 Sustainable production and consumption 21 , issue : 21, pages : 182 - 191» show abstract « hide abstract Abstract Selective Laser Melting (SLM) offers significant potential for a sustainable way of production. Raw material in form of metallic powder can directly be reused and the selective nature of the process offers new potential for resource economization. We introduce a mathematical model, which allows conclusions about the influence of parameters like part volume (influenced by lightweight design) and exposure parameters onto the resource consumption in an SLM process. For this purpose, time and energy consumption are classified in process shares as a function of volume and process parameters. The introduced approach is validated by experimental methods under the consideration of part volume, exposure parameters and batch size. While the approach shall be independent of the manufactured material, the experiments are executed for the aluminum alloy AlSi10Mg. The measurements quantify the impact of the part volume and process parameters on the resource consumption and provide recommendations for improvements regarding an increased material efficiency. Additionally, the established model can be used to analyze manufacturing costs for single parts or series productions. The results illustrate the importance of lightweight design methods for an efficient and sustainable production by powder bed fusion methods like SLM. back to the year overview Ganzenmüller, Georg, Plappert, David, Trippel, Antonina, Hiermaier, StefanA Split-Hopkinson Tension Bar study on the dynamic strength of basalt-fibre composites 2019 Compos Part B-eng , pages : 310 - 319» show abstract « hide abstract Abstract This paper investigates the strain rate sensitivity of laminated composites made of plies of unidirectional basalt fibres and epoxy resin. We consider laminates with quasi-isotropic [0∘,−45∘,+45∘,90∘]s and orthogonal [+45∘,−45∘]4 layup. A Split-Hopkinson Tension Bar is used to generate accurate stress/strain data at elevated rates of strain of ≈3 × 102/s. Moderate strain rate effects are observed with strength increase of ≈3.5% per decade of increased loading rate for both laminate types. Ganzenmüller, Georg, Patil, Sankalp, Maurer, Michael, Sauer, Martin, Jung, Markus, Hiermaier, StefanA simple glassy polymer model 2019 Journal of dynamic behavior of materials , issue : 3, pages : 331 - 343» show abstract « hide abstract Abstract This work presents a simple and robust material model, suitable for dynamic simulations of glassy polymers such as Polycarbonate. The new model reduces the complex stress/strain behavior and its dependence on strain rate and temperature to a simple set of characteristics. Utilizing a time–temperature superposition principle, these characteristics serve as input for a purely empirical fitting approach, which provides an accurate representation of the material behaviour over a wide range of strain rates and temperatures. Calibration data including failure at high rates is obtained using a split Hopkinson tension bar. To demonstrate the applicability of the new model, it is parameterized using high strain rate data and its simulation predictions compared to a gas gun impact experiment wherein a Polycarbonate plate is subjected to the impact of a steel sphere at temperatures between 23–80 °C and 56–75 m/s. Schäfer, Frank, Kenkmann, Thomas, Hiermaier, StefanObituary for a brilliant materials scientist - on Klaus Thoma's death 2019 Meteorit Planet Sci , issue : 1, pages : 254 - 255 Watson, Erkai, Gulde, Max, Kortmann, Lukas, Higashide, Masumi, Schäfer, Frank, Hiermaier, StefanOptical fragment tracking in hypervelocity impact experiments 2019 Acta Astronaut , pages : 111 - 117» show abstract « hide abstract Abstract In-orbit impacts between satellites and space debris lead to varying degrees of fragmentation, ranging anywhere from minor damage to complete breakups. In this paper, we describe an experimental measurement approach for studying fragmentation caused by hypervelocity impact in the laboratory. We investigate impacts on thin aluminum bumper plates with the goal of measuring individual fragment velocities and sizes generated by hypervelocity impact. The experimental setup, commonly used in fluid dynamics for Particle Tracking Velocimetry, consists of using a laser plane and high-speed video camera to track the motion of debris fragments. We describe the fragment tracking algorithm and demonstrate its ability to determine fragment velocity and sizes in specific hypervelocity impact experiments performed at Fraunhofer EMI. The measurement technique enables quantitative data, at an unprecedented level of detail, to be measured from hypervelocity impact fragmentation experiments in the lab, which can be applied to understanding the effects of satellite collisions and improving breakup models. Sandoval Murillo, José Luis, Osen, Raffael, Hiermaier, Stefan, Ganzenmüller, GeorgTowards understanding the mechanism of fibrous texture formation during high-moisture extrusion of meat substitutes 2019 J Food Eng , pages : 8 - 20» show abstract « hide abstract Abstract This paper investigates the physical mechanisms of structure formation during high-moisture extrusion of vegetable proteins. Our model starts from the observation that extrudates with fibrous, meat-like structures exhibit water-rich and protein-rich domains. The origin and structure of these domains is attributed to a spinodal phase-separation process which occurs upon cooling of the extrudate. We investigate the process using continuum-mechanics simulations, considering the combined effects of viscous flow, thermal diffusivity, and the mixing thermodynamics of water and protein. This multi-physics problem is numerically solved using an unconventional mesh-free approach, the material point method (MPM), combined with the Cahn- Hilliard model of phase separation. The method incorporates both Eulerian and Lagrangian aspects, and is well suited to model multicomponent flows of history-dependent materials. Our simulations show that fiber-like structures are obtained when the ratio of phase separation rate, heat conduction rate, and flow rate are matched within a narrow window. Our results predict that the shape of the temperature profile within the cooling channel determines the structure of the phase-separated state. These findings suggest that the physical mechanism which causes fibrous structure formation is given by spinodal phase separation under the influence of a temperature gradient. Häring, Ivo, Ramin, Malte von, Stottmeister, Alexander, Schäfer, Johannes, Vogelbacher, Georg, Brombacher, Bernd, Pfeiffer, Mercy, Restayn, Elena-Maria, Ross, Katharina, Schneider, Johannes, Hiermaier, StefanValidated 3D spatial stepwise quantitative hazard, risk and resilience analysis and management of explosive events in urban areas 2019 European journal for security research 4 , issue : 1, pages : 93 - 129» show abstract « hide abstract Abstract Urban physical security and resilience with respect to accidental and intentional explosive events are an increasing issue regarding civil safety and security of modern societies and their citizens. Examples include industrial on-site explosions, gas explosions or terrorist attacks. In particular, multiple, simultaneous and maliciously time-coordinated events are an increasing event type such as complex attack events consisting of targeted combinations of improvised explosive devices. The paper presents a comprehensive, tailorable and stepwise process. This includes methodologies for scenario, hazard, damage, exposure, event frequency, risk and resilience analysis that have been developed, refined and praxis-tested over decades. The focus is on a summarizing description of the modern best practice approach, the validation efforts undertaken for each step as well as two detailed case studies for exemplary presentation and overall validation. In a comprehensive table, the present approach is compared with other state-of-the-art approaches. The paper shows a refined process how to systematically improve resilience when using the tool, in particular through barriers at explosive sites and at exposed sites of various geometries. Furthermore, along the presentation a set of quality requirements regarding explosive event risk and resilience analyses are provided as collected over the years from the in-field, user group and engineering science perspective as well as a broad outlook on extension options for the future. back to the year overview Laessig, Torsten, May, Michael, Heisserer, Ulrich, Riedel, Werner, Bagusat, Frank, Werff, Harm van der, Hiermaier, StefanEffect of consolidation pressure on the impact behavior of UHMWPE composites 2018 Compos Part B-eng , volume : 147, pages : 47 - 55» show abstract « hide abstract Abstract For the first time, the influence of the manufacturing process on the dynamic performance of ultra-high molecular weight polyethylene (UHMWPE, Dyneema® HB26) composites is investigated. The material is significantly influenced by the hot-pressing parameters temperature and pressure. The ballistic resistance and shock wave behavior was characterized for the UHMWPE composite consolidated with three different pressures. In the case of UHMWPE composites, higher consolidation pressures result in a better ballistic performance. The shock wave behavior converges to high-density polyethylene (HDPE). Based on these observations, an analytical approach is proposed describing the equation of state as a function of consolidation pressure. Kenkmann, Thomas, Deutsch, Alex, Thoma, Klaus, Ebert, Matthias, Poelchau, Michael, Buhl, Elmar, Carl, Eva-Regine, Danilewsky, Andreas, Dresen, Georg, Dufresne, Anja, Durr, Nathanaël, Ehm, Lars, Grosse, Christian, Gulde, Max, Güldemeister, Nicole, Hamann, Christopher, Hecht, Lutz, Hiermaier, Stefan, Hoerth, Tobias, Kowitz, Astrid, Langenhorst, Falko, Lexow, Bernd, Liermann, Hanns-Peter, Luther, Robert, Mansfeld, Ulrich, Moser, Dorothee, Raith, Manuel, Reimold, Wolf Uwe, Sauer, Martin, Schäfer, Frank, Schmitt, Ralf Thomas, Sommer, Frank, Wilk, Jakob, Winkler, Rebecca, Wünnemann, KaiExperimental impact cratering: A summary of the major results of the MEMIN research unit 2018 Meteoritics & planetary science , volume : 53, issue : 8, pages : 1543 - 1568» show abstract « hide abstract Abstract This paper reviews major findings of the Multidisciplinary Experimental and Modeling Impact Crater Research Network (MEMIN). MEMIN is a consortium, funded from 2009 till 2017 by the German Research Foundation, and is aimed at investigating impact cratering processes by experimental and modeling approaches. The vision of this network has been to comprehensively quantify impact processes by conducting a strictly controlled experimental campaign at the laboratory scale, together with a multidisciplinary analytical approach. Central to MEMIN has been the use of powerful two‐stage light‐gas accelerators capable of producing impact craters in the decimeter size range in solid rocks that allowed detailed spatial analyses of petrophysical, structural, and geochemical changes in target rocks and ejecta. In addition, explosive setups, membrane‐driven diamond anvil cells, as well as laser irradiation and split Hopkinson pressure bar technologies have been used to study the response of minerals and rocks to shock and dynamic loading as well as high‐temperature conditions. We used Seeberger sandstone, Taunus quartzite, Carrara marble, and Weibern tuff as major target rock types. In concert with the experiments we conducted mesoscale numerical simulations of shock wave propagation in heterogeneous rocks resolving the complex response of grains and pores to compressive, shear, and tensile loading and macroscale modeling of crater formation and fracturing. Major results comprise (1) projectile–target interaction, (2) various aspects of shock metamorphism with special focus on low shock pressures and effects of target porosity and water saturation, (3) crater morphologies and cratering efficiencies in various nonporous and porous lithologies, (4) in situ target damage, (5) ejecta dynamics, and (6) geophysical survey of experimental craters. Durr, Nathanael, Sauer, Martin, Hiermaier, StefanMesoscale investigation of dynamic fracture in quartzite and sandstone and homogenization to macroscale 2018 Int J Solids Struct , volume : 144-145, pages : 160 - 179» show abstract « hide abstract Abstract The work presented here is part of the MEMIN (Multidisciplinary Experimental and Modeling Impact Research Network) project, which is devoted to the experimental and numerical investigation of the effects of meteorite impact on geological materials from laboratory scale to natural scale. In general, high velocity impacts on rock material causes fractures in the target that may lead to spallation of material near surfaces. While spallation effects are of great importance for laboratory scale craters, they are much less significant in natural craters. Therefore, they need to be taken into account when comparing natural craters with laboratory craters, particularly, when scaling laws that provide relationships between laboratory and natural craters shall be developed. This scale bridging requires realistic quantification of spallation effects, which can be done with numerical methods if appropriate material models exist. For this purpose, we investigate dynamic fracture in quartzite and sandstone. We present a new methodology to derive three dimensional macroscale material data from one-dimensional dynamic fracture experiments, namely Hopkinson-Bar experiments in the spallation configuration, using a new mesoscale simulation model. Simulations are conducted with the in-house hydrocode SOPHIA. Mesoscopic material parameters are identified from a parameter study such that simulated macroscopic failure quantities conform to experimentally measured data. The calibrated mesoscale model is then subjected to a set of multiaxial load cases in order to derive macroscopic yield and failure parameters using averaging techniques. The results can be directly used to calibrate macroscale material models for dynamic fracture and will support the predictability of laboratory craters and, in particular, of spallation effects. Fischer, Kai, Hiermaier, Stefan, Riedel, Werner, Haering, IvoMorphology dependent assessment of resilience for urban areas 2018 Sustainability , volume : 10, pages : 1 - 14» show abstract « hide abstract Abstract The formation of new threats and the increasing complexity of urban built infrastructures underline the need for more robust and sustainable systems, which are able to cope with adverse events. Achieving sustainability requires the strengthening of resilience. Currently, a comprehensive approach for the quantification of resilience of urban infrastructure is missing. Within this paper, a new generalized mathematical framework is presented. A clear definition of terms and their interaction builds the basis of this resilience assessment scheme. Classical risk-based as well as additional components are aligned along the timeline before, during and after disruptive events, to quantify the susceptibility, the vulnerability and the response and recovery behavior of complex systems for multiple threat scenarios. The approach allows the evaluation of complete urban surroundings and enables a quantitative comparison with other development plans or cities. A comprehensive resilience framework should cover at least preparation, prevention, protection, response and recovery. The presented approach determines respective indicators and provides decision support, which enhancement measures are more effective. Hence, the framework quantifies for instance, if it is better to avoid a hazardous event or to tolerate an event with an increased robustness. An application example is given to assess different urban forms, i.e., morphologies, with consideration of multiple adverse events, like terrorist attacks or earthquakes, and multiple buildings. Each urban object includes a certain number of attributes, like the object use, the construction type, the time-dependent number of persons and the value, to derive different performance targets. The assessment results in the identification of weak spots with respect to single resilience indicators. Based on the generalized mathematical formulation and suitable combination of indicators, this approach can quantify the resilience of urban morphologies, independent of possible single threat types and threat locations. Haering, Ivo, Ramin, Malte vo, Stottmeister, Alexander, Schaefer, Johannes, Vogelbacher, Georg, Brombacher, Bernd, Pfeiffer, Mercy, Restayn, Elena-Maria, Ross, Katharina, Schneider, Johannes, Hiermaier, StefanValidated 3D spatial stepwise quantitative hazard, risk and resilience analysis and management of explosive events in urban areas 2018 European Journal of security research , volume : Online First, pages : 1 - 37» show abstract « hide abstract Abstract Urban physical security and resilience with respect to accidental and intentional explosive events are an increasing issue regarding civil safety and security of modern societies and their citizens. Examples include industrial on-site explosions, gas explosions or terrorist attacks. In particular, multiple, simultaneous and maliciously time-coordinated events are an increasing event type such as complex attack events consisting of targeted combinations of improvised explosive devices. The paper presents a comprehensive, tailorable and stepwise process. This includes methodologies for scenario, hazard, damage, exposure, event frequency, risk and resilience analysis that have been developed, refined and praxis-tested over decades. The focus is on a summarizing description of the modern best practice approach, the validation efforts undertaken for each step as well as two detailed case studies for exemplary presentation and overall validation. In a comprehensive table, the present approach is compared with other state-of-the-art approaches. The paper shows a refined process how to systematically improve resilience when using the tool, in particular through barriers at explosive sites and at exposed sites of various geometries. Furthermore, along the presentation a set of quality requirements regarding explosive event risk and resilience analyses are provided as collected over the years from the in-field, user group and engineering science perspective as well as a broad outlook on extension options for the future. back to the year overview Durr, Nathanael, Sauer, Martin, Hiermaier, StefanA numerical study on mesoscale simulation of quartzite and sandstone under shock loading 2017 International Journal of Impact Engineering , volume : 108, page : 16» show abstract « hide abstract Abstract In this paper, we present two numerical models for the mesoscale (grain scale) simulation of planar shock waves in quartzite and sandstone using the in-house hydrocode SOPHIA. The models are compared in terms of their capability to represent physical mechanisms, such as phase transitions in
quartz and pore collapse in sandstone, and they are validated by comparison to literature data. The study is part of the MEMIN (Multidisciplinary Experimental and Modeling Impact Research Network) project, which is devoted to the experimental and numerical investigation of the effects of meteorite
impact on geological materials from laboratory scale to natural scale. The first model is based on the Smoothed Particle Hydrodynamics (SPH) method. Simulations with rather simplified structures in planar symmetry are presented. The model is used to investigate basic effects of porosity, pore
geometry and water saturation. The second model presented is a more detailed, three-dimensional Finite Element (FE) model. With this model, the effects of grain anisotropy and different types of shear strength modeling are studied. In a parameter study, we investigate the influence of these
parameters on shock Hugoniot relations, such as shock velocity (Us) vs. particle velocity (Up) and compressive longitudinal stress (sL) vs. Up. Finally, the models are compared and the specific advantages and disadvantages of the different modeling variants are outlined. Ganzenmueller, Georg, Blaum, E., Mohrmann, Deborah, Langhof, T., Plappert, D., Ledford, Noah, Paul, Hanna, Hiermaier, StefanA simplified design for a Split-Hopkinson tension bar with long pulse duration 2017 Procedia Engineering , volume : 197, pages : 109 - 118» show abstract « hide abstract Abstract This paper presents a simplified design for a Split-Hopkinson Tension Bar (SHTB) which allows for pulse durations exceeding one millisecond. This testing apparatus is intended for material characterization requiring large amounts of elongation, necessitated either by large specimen dimensions,
or large strains to failure. The design proposed here can be assembled from off the shelve components without the need for specialized machining tools. The simple mechanical design is accompanied by a comparatively low-cost, yet high-speed, means of independently measuring specimen strain using a
fast line scan camera. The performance of this SHTB implementation is demonstrated by obtaining intermediate strain rate results for tensile yield strength of Polycarbonate in an unprecedented quality. Ganzenmueller, Georg, Blaum, E., Mohrmann, Deborah, Langhof, T., Plappert, D., Ledford, Noah, Paul, Hanna, Hiermaier, StefanA simplified design for a Split-Hopkinson tension bar with long pulse duration 2017 Procedia Engineering , volume : 197, pages : 109 - 118» show abstract « hide abstract Abstract This paper presents a simplified design for a Split-Hopkinson Tension Bar (SHTB) which allows for pulse durations exceeding one millisecond. This testing apparatus is intended for material characterization requiring large amounts of elongation, necessitated either by large specimen dimensions,
or large strains to failure. The design proposed here can be assembled from off the shelve components without the need for specialized machining tools. The simple mechanical design is accompanied by a comparatively low-cost, yet high-speed, means of independently measuring specimen strain using a
fast line scan camera. The performance of this SHTB implementation is demonstrated by obtaining intermediate strain rate results for tensile yield strength of Polycarbonate in an unprecedented quality. Dlugosch, Michael, Fritsch, Jens, Lukaszewicz, Dirk, Hiermaier, StefanExperimental investigation and evaluation of numerical modeling approaches for hybrid-FRP-steel sections under impact loading for the application in automotive crash-structures 2017 Composite structures , volume : 174, pages : 338 - 347» show abstract « hide abstract Abstract A large body of work has studied the energy absorption of metallic and composite tubes undergoing crushing. Similarly, reinforcements of metallic structures with composites have also been studied. By contrast, composite tubes with metallic reinforcements (composite-intensive) have not been
investigated, although they may offer benefits in terms of robustness or cost over both composite as well as metallic tubes. Here, composite materials with metallic reinforcements were tested under dynamic axial loading in order to study the effects of major design parameters on the energy
absorption and load uniformity behavior. Significant benefits could be identified, particularly when considering cost aspects. Two numerical approaches for modeling the adhesive interface between the two discrete material phases were evaluated in terms of accuracy and efficiency in crash
simulations. The simplified modeling technique comprising two layers of shell elements rigidly tied at the interface proved to be generally applicable to the evaluation of structural concepts in an early vehicle development stage. Watson, Erkai, Gulde, Max, Hiermaier, StefanFragment tracking in hypervelocity impact experiments 2017 Procedia Engineering , volume : 204, pages : 170 - 177» show abstract « hide abstract Abstract Space debris impacts of in-orbit satellites cause varying degrees of fragmentation, ranging from minor damage to catastrophic breakup. In this paper, we introduce an experimental measurement approach for studying the fragmentation effects of hypervelocity impact in the laboratory. We
demonstrate this method by investigating a hypervelocity impact on a thin aluminum bumper plates and tracking individual fragments in the debris clouds. The setup involves a thin laser plane illuminating the debris cloud fragments, which are recorded with a high-speed video camera. The image
sequence is analyzed, yielding spatio-temporal information about each fragment in the debris cloud. This allows individual fragment size and velocity information, previously not available, to be calculated. Watson, Erkai, Gulde, Max, Hiermaier, StefanFragment tracking in hypervelocity impact experiments 2017 Procedia Engineering , volume : 204, pages : 170 - 177» show abstract « hide abstract Abstract Space debris impacts of in-orbit satellites cause varying degrees of fragmentation, ranging from minor damage to catastrophic breakup. In this paper, we introduce an experimental measurement approach for studying the fragmentation effects of hypervelocity impact in the laboratory. We
demonstrate this method by investigating a hypervelocity impact on a thin aluminum bumper plates and tracking individual fragments in the debris clouds. The setup involves a thin laser plane illuminating the debris cloud fragments, which are recorded with a high-speed video camera. The image
sequence is analyzed, yielding spatio-temporal information about each fragment in the debris cloud. This allows individual fragment size and velocity information, previously not available, to be calculated. Hoerth, T., Bagusat, F., Hiermaier, S.Hugoniot data of Seeberger sandstone up to 7 GPa 2017 International Journal of Impact Engineering , volume : 99, pages : 122 - 130» show abstract « hide abstract Abstract Planar-plate impact tests were carried out for the measurement of Hugoniot data of dry Seeberger sandstone in the pressure range of up to 7 GPa. A special inverse testing method suitable for rock targets was applied together with a laser interferometer for the measurement of the free-surface
velocity of the target plate required for the calculation of the particle velocity (up) and the shock wave velocity (US) in the sandstone specimen. In our measurement range (impact velocity between about 50m/s and about 1300 m/s), the US - up data show significant scattering. The travel times of the
impact-induced shock waves indicate that pore crushing occurs. A strong dependance of the US - up data on the test batch selected for the impact experiments and, thus, on the mining location was observed. This dependance is greater than the scattering of the individual data sets. Dlugosch, Michael, Volk, Maximilian, Lukaszewicz, Dirk, Fritsch, Jens, Hiermaier, StefanSuitability assessments for advanced composite-metal hybrid material systems in automotive crash structural applications 2017 International journal of automotive composites : IJAutoC , volume : 3, pages : 14 - 28» show abstract « hide abstract Abstract The application of hybrid material systems composed of advanced composites and metals in automotive crash structural applications holds significant potential in terms of lightweighting and functional improvements. This paper proposes a comprehensive methodology to assess the suitability of
vehicle body components for the application of hybrid material systems by analysing superimposed numerical crash simulation data of conventional steel bodies-in-white. The loading anisotropy and the global deformation are presented as two suitability criteria including an evaluation methodology to
eventually select suitable hybrid material systems in the transition from conventional to enhanced material employment and vehicle structure design. Additionally, the methodology provides novel insights into the global structural loading by simultaneously considering multiple crash load cases. back to the year overview Isakov, M., May, M., Hiermaier, S., Kuokkala, V.-T.A model for the strain rate dependent plasticity of a metastable austenitic stainless steel 2016 Materials and design , volume : 106, pages : 258 - 272» show abstract « hide abstract Abstract A continuum material model is developed for the dynamic plastic deformation behavior of metastable austenitic stainless steel EN 1.4318-2B. An incremental approach in both experimental testing and in the model is used to distinguish between the direct effects of strain rate and the macroscopic
adiabatic heating effects. In the model a set of evolution equations is integrated over the deformation path, which makes the model flexible in terms of changes in the strain rate and material temperature. The strain-induced phase transformation from austenite to a'-martensite is accounted for with
evolution equations based on the Olson-Cohen transformation model. In order to describe the phase transformation accurately during dynamic loading, the original model is modified by adding instantaneous strain rate sensitivity to the a'-transformation rate. Comparison with experimental results shows
that the model can be used to describe the strain rate and temperature dependent behavior of a metastable austenitic alloy with a reasonable number of material parameters. Finally, the model gives realistic results in a set of validation experiments. Andricevic, N., Duddeck, F., Hiermaier, S.A novel approach for the assessment of robustness of vehicle structures under crash 2016 International journal of crashworthiness , volume : 21, page : 15» show abstract « hide abstract Abstract The use of numerical optimisation in vehicle development aiming at designing increasingly lighter vehicle structures may lead to a highly sensitive behaviour in terms of crashworthiness. Methods for the analysis of robustness have been introduced to account for the impact of varying input
parameters, possibly detecting undesired deformation modes due to bifurcations. The objective of this paper is to introduce an index for the quantitative assessment of robustness of vehicle structures under crash. The novel approach is applied to axially impacted extrusion profiles as well as to an
assembly of extrusion profiles under varying input parameters. It was found that the new Robustness Index accurately reflects the findings from state-of-the-art methods of robustness analysis, enabling an objective and transparent overall assessment of robustness prior to a potential in-depth
analysis. Cadoni, E., Couque, H., Hiermaier, S.Editorial 2016 European physical journal special topics , volume : 225, page : 229 Dlugosch, M., Lukaszewicz, D., Fritsch, J., Hiermaier, S.Experimental investigation of hybrid material systems consisting of advanced composites and sheet metal 2016 Composite structures , volume : 152, pages : 840 - 849» show abstract « hide abstract Abstract Previous studies have identified composite-metal hybrid material systems in automotive crash structural applications as a possible solution to meet the demands of both ambitious efficiency goals and increasingly strict vehicle safety requirements. The purpose of this study is to experimentally
identify basic principles, which define the material systems' properties such as the stiffness and strength as well as major parameter effects on a coupon scale. A further aim is to compare these findings to common approaches such as the rule-of-mixture theory and define analytical models able to
predict these properties based on a set of parameter values. While there is a strong dominance of the steel phase, the experiments generally confirm the rule-of-mixture theory. Some effects might have to be considered when designing hybrid material systems for technical applications, such as the
shift of the special neutral plane in asymmetric layups or a changed failure mode for different loading directions. The analytical models presented do match the experimental results, although the complex interaction between the material phases is not fully analyzed. Ganzenmueller, G., Sauer, M., May, M., Hiermaier, S.Hourglass control for Smooth Particle Hydrodynamics removes tensile and rank-deficiency instabilities : Hourglass control for SPH 2016 European physical journal special topics , volume : 225, pages : 385 - 395» show abstract « hide abstract Abstract We present a stabilization scheme for elastoplastic Smooth-Particle Hydrodynamics (SPH) which overcomes two major challenges: (i) the tensile instability inherent to the updated Lagrangian approach is suppressed and (ii) the rank-deficiency instability inherent to the nodal integration
approach is cured. To achieve these goals, lessons learned from the Finite-Element Method are transferred to SPH. In particular, an analogue of hourglass control is derived for SPH, which locally linearizes the deformation field to obtain stable and accurate solutions, without the need to resort to
stabilization via excessive artificial viscosity. The resulting SPH scheme combines the ability of updated Lagrangian SPH to model truly large deformations with the accuracy and stability needed to faithfully perform simulations. This claim is supported by the analysis of problematic cases and the
simulation of an impact scenario. Fischer, Kai, Haering, Ivo, Riedel, Werner, Vogelbacher, Georg, Hiermaier, StefanSusceptibility, vulnerability, and averaged risk analysis for resilience enhancement of urban areas 2016 International journal of protective structures , volume : 7, pages : 45 - 76» show abstract « hide abstract Abstract The dynamic growth and evolution of urban areas generate new challenges for safety and security driving societal, economic, and ecological developments at local and worldwide levels. Cities comprise a high degree of critical infrastructure with an increasing complexity and interdependency. In
addition, modified and new threats ranging from natural to man-made and malicious hazards ask for more robust and sustainable cities. This work combines and extends existing empirical, engineering, and simulative methods to define and determine quantities for resilience assessment of urban areas in
a comprehensive approach. Based on a multitude of possible events in a city quarter with a larger number of infrastructures, susceptibilities, vulnerabilities, and averaged risks are analyzed in a systematic and quantitative way. The use of an established empirical-historical database gives first
insights to identify susceptible elements or endangered areas in the considered urban environments. It is coupled to an approach for consequences where state-of-the-art physical-engineering hazard and damage propagation and quantification models are integrated forvulnerability assessment. The
consideration of multiple threats and multiple possible locations cumulates in an object- and location-dependent quantification of averaged risks to visualize the most critical regions and infrastructure aspects indensely populated areas. In this article, the approach is exemplarily applied to
terroristic threats. The integration of the three-dimensional visualized approach into existing risk assessment and management processes will help to create cities that are more resilient. back to the year overview Laessig, T., Nguyen, L., May, M., Riedel, W., Heisserer, U., Werff, H. van der, Hiermaier, S.A non-linear orthotropic hydrocode model for ultra-high molecular weight polyethylene in impact simulations 2015 International Journal of Impact Engineering , volume : 75, pages : 110 - 122» show abstract « hide abstract Abstract This paper presents detailed experimental characterization of quasi-static anisotropic directional strength properties as well as the shock behavior of ultra-high molecular weight polyethylene (UHMWPE) for the development of an advanced material model for this class of materials. Specifically,
we consider Dyneema� HB26 - pressed from uni-directional (UD) tapes in a 0/90� stacking sequence. A material model based on a constitutive law with orthotropic, non-linear strength, shock response, composite failure and softening criteria is presented. A set of material parameters is derived for
applications in hydrocodes (here: ANSYS AUTODYN). High- and hypervelocity impact tests with different impact velocities are used for preliminary validation and discussion of the predictive capabilities in view of future application. Laessig, T., Bagusat, F., May, M., Hiermaier, S.Analysis of the shock response of UHMWPE composites using the inverse planar plate impact test and the shock reverberation technique 2015 International Journal of Impact Engineering , volume : 86, pages : 240 - 248» show abstract « hide abstract Abstract Ultra-high molecular-weight polyethylene (UHMWPE) composites are commonly used in ballistic protection systems. In order to understand the behavior under shock conditions, dynamic material properties were recently measured by inverse planar plate impact tests providing US-uP-data for particle
velocities from 170 m/s up to 900 m/s. In this paper the previously known data range is extended at both ends. On the one hand, inverse flyer plate tests were performed at impact velocities less than 200 m/s in order to assess potential effects of porosity. On the other hand, the
mechanical response under extremely high pressures was determined using the shock reverberation technique. //For low shock pressures no effect of porosity was identified. For high shock pressures, the available data range was extended by a factor of 3. For the whole range of velocities and
pressures, the slope of the US-uP relationship indicates a slight concave curvature. Isakov, M., Hiermaier, S., Kuokkala, V.-T.Effect of strain rate on the martensitic transformation during plastic deformation of an austenitic stainless steel 2015 Metallurgical and materials transactions. A , volume : 46, page : 4» show abstract « hide abstract Abstract The effect of strain rate on the plastic deformation and phase transformation behavior of metastable austenitic stainless steel EN 1.4318 was studied. Strain rate jump tests were used to distinguish the direct effects of strain rate from the effects of adiabatic heating. Test results are
analyzed from the viewpoint of both stress- and strain-induced martensitic transformation. Vignjevic, R., Hughes, K., Vuyst, T. de, Djordevic, N., Campbell, J., Stojkovic, M., Gulavani, O., Hiermaier, S.Lagrangian analysis led design of a shock recovery plate impact experiment 2015 International Journal of Impact Engineering , volume : 77, pages : 16 - 29» show abstract « hide abstract Abstract Shock recovery techniques, such as the flyer-plate impact test, are used to examine a material that has been subjected to a single well-defined shock, followed by a single release wave. One of the key requirements of this type of technique is that the process should be such that any change
found in the sample after recovery, can only be attributed to the shock process alone. Therefore, the principal problem for a test specimen-fixture assembly is that it is designed such that the loading history of the recovered specimen is known. This has motivated this research through the analysis
led design of a shock recovery experiment. The choice of Lagrangian Finite Element Analysis for this design work was driven by the method's ability to accurately track history variables (for plastic deformation) and treat contact interactions which are crucial in this problem. //Starting from an
initial configuration, LS-Dyna has been used to analyse in detail the resulting wave propagation to ensure the generation of a uniaxial strain state in the specimen through Lagrangian distance-time diagrams. These iso-maps enabled the identification of potential shortcomings with the initial design,
in terms of the transmission of contact and the influence of radial release waves at the different boundaries between specimen and supporting fixture rings. //The benefits of using Lagrangian Finite Element Analysis for this design work are its ability to track history variables (for plastic
deformation) and contact treatment. Based on these findings, a new configuration was developed, which consists of an array of concentric rings that support the specimen. During shock formation in the specimen, these rings progressively transfer the loading in the impact direction and radially away
from the specimen, acting as momentum traps and preventing unwanted release waves from affecting the strain state experienced by the specimen. //Comparing distance time diagrams between original and proposed configurations, a design sensitivity analysis was performed, where the new geometry resulted
in a decrease of both the residual velocity (−38%) and radial displacement (−27%) of the target when compared to the original setup. Ganzenmueller, G.C., Hiermaier, S., May, M.On the similarity of meshless discretizations of Peridynamics and Smooth-Particle Hydrodynamics 2015 Computers and Structures , volume : 150, pages : 71 - 78» show abstract « hide abstract Abstract This paper discusses the similarity of meshless discretizations of Peridynamics and Smooth-Particle-Hydrodynamics (SPH), if Peridynamics is applied to classical material models based on the deformation gradient. We show that the discretized equations of both methods coincide if nodal
integration is used. This equivalence implies that Peridynamics reduces to an old meshless method and all instability problems of collocation-type particle methods apply. These instabilities arise as a consequence of the nodal integration scheme, which causes rank-deficiency and leads to spurious
zero-energy modes. As a result of the demonstrated equivalence to SPH, enhanced implementations of Peridynamics should employ more accurate integration schemes. May, Michael, Hesebeck, Olaf, Marzi, Stephan H., Boehme, Wolfgang, Lienhard, Joerg, Kilchert, Sebastian, Brede, Markus, Hiermaier, StefanRate dependent behavior of crash-optimized adhesives - experimental characterization, model development, and simulation 2015 Engineering fracture mechanics , volume : 133, pages : 112 - 137» show abstract « hide abstract Abstract The mechanical properties of crash-optimized adhesive BETAMATE 1496V are characterized over a wide range of strain rates. The information gathered from the mechanical tests are used for developing a fully rate-dependent constitutive law for cohesive interface elements considering both, the
strain rate dependency of the initiation stress and the strain rate dependency of the fracture toughness. The model is calibrated and verified against experimental data for tapered double cantilever beam (TDCB) and tapered end notched flexure (TENF) tests. Finally, the model is validated against
quasi-static and dynamic experimental results on an adhesively bonded T-joint. The numerical predictions show good correlation with the experimental results. back to the year overview May, M., Nossek, M., Petrinic, N., Hiermaier, S., Thoma, K.Adaptive multi-scale modeling of high velocity impact on composite panels 2014 Composites. Part A, Applied science and manufacturing , volume : 58» show abstract « hide abstract Abstract A computationally efficient adaptive multi-scale methodology for modeling composites under high rates of loading is proposed. The physically based model relies on micromechanical properties of the constituents only. The adaptive algorithm switches between two different constitutive laws.
Initially, the material response is calculated based on effective linear-elastic, orthotropic material properties at the ply scale which are calculated using the rule of mixtures. A modified Hashin-Rotem criterion is then used to identify the switch to a more accurate micromechanical analysis based
on the generalized method of cells (GMC). The methodology is verified by simulating tensile tests on laminates with different stacking sequences. Finally the model validated against experimental data for high-velocity impact on quasi-isotropic composite targets taken from the literature in order to
illustrate the efficiency and accuracy of the proposed methodology. Isakov, Matti, Hiermaier, Stefan, Kuokkala, Veli-TapaniImproved specimen recovery in tensile split Hopkinson bar 2014 Philosophical Transactions of the Royal Society of London. Series A , volume : 372, page : Art. 20130194» show abstract « hide abstract Abstract This paper presents an improved specimen recovery method for the tensile split Hopkinson bar (TSHB) technique. The method is based on the trapping of residual stress waves with the use of momentum trap bars. As is well known, successful momentum trapping in TSHB is highly sensitive to
experimental uncertainties, especially on the incident bar side of the set-up. However, as is demonstrated in this paper, significant improvement in the reliability of specimen recovery is obtained by using two momentum trap bars in contact with the incident bar. This makes the trapping of the
reflected wave insensitive to striker speed and removes the need for a precision set gap between the incident bar and the momentum trap. May, M., Voss, H., Hiermaier, S.Predictive modeling of damage and failure in adhesively bonded metallic joints using cohesive interface elements 2014 International journal of adhesion and adhesives , volume : 49» show abstract « hide abstract Abstract A rate-dependent constitutive law for cohesive interface elements is introduced for the adhesive considering both, the rate dependency of the initiation stress and the rate dependency of the fracture toughness. The model is calibrated with experimental data available from the literature and
validated against novel quasi-static and dynamic experimental results on an adhesively bonded T-joint made from high strength steel DP-K 30/50 and crash-optimized adhesive BETAMATE 1496V. The numerical predictions show an excellent correlation with the experimental results. back to the year overview Gueldemeister, N., Wuennemann, K., Durr, N., Hiermaier, S.Propagation of impact-induced shock waves in porous sandstone using mesoscale modeling 2013 Meteoritics & planetary science , volume : 48» show abstract « hide abstract Abstract Generation and propagation of shock waves by meteorite impact is significantly affected by material properties such as porosity, water content, and strength. The objective of this work was to quantify processes related to the shock-induced compaction of pore space by numerical modeling, and
compare the results with data obtained in the framework of the Multidisciplinary Experimental and Modeling Impact Research Network (MEMIN) impact experiments. We use mesoscale models resolving the collapse of individual pores to validate macroscopic (homogenized) approaches describing the bulk
behavior of porous and water-saturated materials in large-scale models of crater formation, and to quantify localized shock amplification as a result of pore space crushing. We carried out a suite of numerical models of planar shock wave propagation through a well-defined area (the ""sample"") of
porous and/or water-saturated material. The porous sample is either represented by a homogeneous unit where porosity is treated as a state variable (macroscale model) and water content by an equation of state for mixed material (ANEOS) or by a defined number of individually resolved pores (mesoscale
model). We varied porosity and water content and measured thermodynamic parameters such as shock wave velocity and particle velocity on meso- and macroscales in separate simulations. The mesoscale models provide additional data on the heterogeneous distribution of peak shock pressures as a
consequence of the complex superposition of reflecting rarefaction waves and shock waves originating from the crushing of pores. We quantify the bulk effect of porosity, the reduction in shock pressure, in terms of Hugoniot data as a function of porosity, water content, and strength of a quartzite
matrix. We find a good agreement between meso-, macroscale models and Hugoniot data from shock experiments. We also propose a combination of a porosity compaction model (?-? model) that was previously only used for porous materials and the ANEOS for water-saturated quartzite (all pore space is
filled with water) to describe the behavior of partially water-saturated material during shock compression. Localized amplification of shock pressures results from pore collapse and can reach as much as four times the average shock pressure in the porous sample. This may explain the often observed
localized high shock pressure phases next to more or less unshocked grains in impactites and meteorites. back to the year overview May, M., Kilchert, S., Hiermaier, S.3D modeling of fracture in brittle isotropic materials using a novel algorithm for the determination of the fracture plane orientation and crack surface area 2012 Finite Elements in Analysis and Design , volume : 56, pages : 32 - 40» show abstract « hide abstract Abstract A user defined material model for simulation of brittle fracture in isotropic materials was implemented into the explicit FE code Abaqus/Explicit. The model uses a methodology for calculating the orientation of the fracture plane in isotropic materials in 3D space using an analytical approach.
Knowing the orientation of the fracture plane, the cross-sectional area of the fracture surface can in a hexagonal element can be calculated. Regularization is then achieved using the size of the fracture plane. The model is first tested on single-element tests and then applied to more complex test
cases such as a short bar with chevron notch or micromechanical analyses of composite materials. The numerical predictions correlate well with experimental evidence from the literature. Ganzenmueller, G.C., Hiermaier, S., Steinhauser, M.O.Consistent temperature coupling with thermal fluctuations of smooth particle hydrodynamics and molecular dynamics 2012 PLoS one. Online journal , volume : 7, page : Art. e51989, 11» show abstract « hide abstract Abstract We propose a thermodynamically consistent and energy-conserving temperature coupling scheme between the atomistic and the continuum domain. The coupling scheme links the two domains using the DPDE (Dissipative Particle Dynamics at constant Energy) thermostat and is designed to handle strong
temperature gradients across the atomistic/continuum domain interface. The fundamentally different definitions of temperature in the continuum and atomistic domain - internal energy and heat capacity versus particle velocity - are accounted for in a straightforward and conceptually intuitive way by
the DPDE thermostat. We verify the here-proposed scheme using a fluid, which is simultaneously represented as a continuum using Smooth Particle Hydrodynamics, and as an atomistically resolved liquid using Molecular Dynamics. In the case of equilibrium contact between both domains, we show that the
correct microscopic equilibrium properties of the atomistic fluid are obtained. As an example of a strong non-equilibrium situation, we consider the propagation of a steady shock-wave from the continuum domain into the atomistic domain, and show that the coupling scheme conserves both energy and
shock-wave dynamics. To demonstrate the applicability of our scheme to real systems, we consider shock loading of a phospholipid bilayer immersed in water in a multi-scale simulation, an interesting topic of biological relevance. Boljen, M., Hiermaier, S.Continuum constitutive modeling of woven fabrics 2012 European physical journal special topics , volume : 206, pages : 149 - 161» show abstract « hide abstract Abstract The constitutive behavior of woven fabrics is significantly influenced by distinctive yarn interactions at the fabric mesoscale. Since, in most cases, an explicit discretization at yarn level is not desirable due to the related computational effort, an improved computational approach is
proposed using a simple, but powerful kinematic model linked to the deformation of a representative volume cell (RVC) at the fabric mesoscale. The constitutive model is validated experimentally for three different fabric materials and implemented as user-defined subroutine in the explicit
finite-element code LS-DYNA. The model includes an enhanced formulation for rate-dependent, dissipative shear properties. Ganzenmueller, G.C., Hiermaier, S., Steinhauser, M.O.Energy-based coupling of smooth particle hydrodynamics and molecular dynamics with thermal fluctuations 2012 European physical journal special topics , volume : 206, pages : 51 - 60» show abstract « hide abstract Abstract We propose a thermodynamically consistent and energy conserving coupling scheme between the atomistic and the continuum domain. The coupling scheme links the two domains using the DPDE (Dissipative Particle Dynamics at constant Energy) thermostat and is designed to handle strong temperature
gradients across the atomistic/continuum domain interface. The fundamentally different definitions of temperature in the continuum and atomistic domain - internal energy and heat capacity versus particle velocity - are accounted for in a straightforward and conceptually intuitive way by the DPDE
thermostat. We verify the here proposed scheme using a fluid, which is simultaneously represented as a continuum using Smooth Particle Hydrodynamics, and as an atomistically resolved liquid using Molecular Dynamics. In the case of equilibrium contact between both domains, we show that the correct
microscopic equilibrium properties of the atomistic fluid are obtained. As an example of a strong non-equilibrium situation, we consider the propagation of a steady shock-wave from the continuum domain into the atomistic domain, and show that the coupling scheme conserves both energy and shock-wave
dynamics. Hiermaier, S., Huberth, F.Volume dilatation in a polycarbonate blend at varying strain rates 2012 European physical journal special topics , volume : 206, pages : 173 - 181» show abstract « hide abstract Abstract Impact loaded polymers show a variety of strain-rate dependent mechanical properties in their elastic, plastic and failure behaviour. In contrast to purely crystalline materials, the volume of polymeric materials can significantly change under irreversible deformations. In this paper,
uni-axial tensile tests were performed in order to measure the dilatation in the Polycarbonate-Acrylnitril-Butadien-Styrol (PC-ABS) Bayblend T65. The accumulation of dilatation was measured at deformation speeds of 0. 1 and 500 [mm/s]. Instrumented with a pair of two high-speed cameras, volume
segments in the samples were observed. The change in volume was quantified as relation between the deformed and initial volumes of the segments. It was observed that the measured dilatations are of great significance for the constitutive models. This is specifically demonstrated through comparisons
of stress-strain relations derived from the two camera-perspectives with isochoric relations based on s ingle-surface observations of the same experiments. back to the year overview Ganzenmueller, G.C., Hiermaier, S., Steinhauser, M.O.Shock-wave induced damage in lipid bilayers: A dissipative particle dynamics simulation study 2011 Soft matter , volume : 7, pages : 4307 - 4317» show abstract « hide abstract Abstract The effects of shock-wave impact on the damage of lipid bilayer membranes are investigated with dissipative particle simulations at constant energy (DPDE). A coarse-grained model for the phospholipid bilayer in aqueous environment is employed, which models single lipids as short chains
consisting of a hydrophilic head and two hydrophobic tail beads. Water is modeled by mapping four H2O molecules to one water bead. Using the DPDE method enables us to faithfully simulate the non-equilibrium shock-wave process with a coarse-grained model as the correct heat capacity can be recovered.
At equilibrium, we obtain self-stabilizing bilayer structures that exhibit bending stiffness and compression modulus comparable to experimental measurements under physiological conditions. We study in detail the damage behavior of the coarse-grained lipid bilayer upon high-speed shock-wave impact as
a function of shock impact velocity and bilayer stability. A single damage parameter based on an orientation dependent correlation function is introduced. We observe that mechanical bilayer stability has only small influence on the resulting damage after shock-wave impact, and inertial effects play
almost no role. At shock-front velocities below less than or similar to 3000 ms(-1), we observe reversible damage, whereas for speeds greater than or similar to 3900 ms(-1) no such recovery, or self-repair of the bilayer, could be observed. back to the year overview Hiermaier, S., Meenken, T.Characterization of low-impedance materials at elevated strain rates 2010 The journal of strain analysis for engineering design , volume : 45, pages : 401 - 409» show abstract « hide abstract Abstract Experimental characterization of materials at elevated strain rates of the order of 10(3) s(-1) is typically performed by Hopkinson-bar-type facilities. The specific nature of Hopkinson bar tests is that a specimen is loaded by waves. As both the input and output bars are often made from
high-impedance metallic materials, the ratio between transmitted and reflected wave components is very poor in the case of low-impedance specimen materials such as rubbers and foams. That poor wave transmission brings with it a limited quality of the signal-to-noise ratio. Changing the bar materials
(e.g. to polycarbonate) is of little help because of the related viscous effects. A further deficiency of the wave-driven Hopkinson bar test for many rubber and foam applications is the comparably small amount of compression that is achievable. Maximum compressions of 95 per cent and above, often
expected for damping and energy absorption applications, are out of the range of most Hopkinson bar set-ups. In order to overcome these deficiencies, first a split Hopkinson pressure bar (SHPB) facility was equipped with polyvinylidenefluoride (PVDF) thin-film sensors. Second, a direct-impact set-up
for low-impedance materials was developed and calibrated at the Ernst Mach Institute (EMI). With the PVDF gauges, the range of application both for the SHPB and for the new set-up was enhanced. This is demonstrated with an SHPB-based investigation of stress homogeneity in polyurethane (PU)
specimens. The direct-impact facility made it possible to derive the stress-strain relations for PU-rubber up to strain rates in the range of several 10(3) s(-1). Maximum compressions of more than 95 per cent were achieved. The paper describes the limitations of a classic SHPB set-up applied to
low-impedance materials. The problem of stress homogeneity is addressed, and a set-up for a new direct-impact facility is presented. As an example application, a Confor-Blue foam, typically used for automotive crash-test dummies, is characterized at strain rates between 160 and 1115 s(-1). back to the year overview Steinhauser, M.O., Hiermaier, S.A review of computational methods in materials science : Examples from shock-wave and polymer physics 2009 International journal of molecular sciences , volume : 10, pages : 5135 - 5216» show abstract « hide abstract Abstract This review discusses several computational methods used on different length and time scales for the simulation of material behavior. First, the importance of physical modeling and its relation to computer simulation on multiscales is discussed. Then, computational methods used on different
scales are shortly reviewed, before we focus on the molecular dynamics (MD) method. Here we survey in a tutorial-like fashion some key issues including several MD optimization techniques. Thereafter, computational examples for the capabilities of numerical simulations in materials research are
discussed. We focus on recent results of shock wave simulations of a solid which are based on two different modeling approaches and we discuss their respective assets and drawbacks with a view to their application on multiscales. Then, the prospects of computer simulations on the molecular length
scale using coarse-grained MD methods are covered by means of examples pertaining to complex topological polymer structures including star-polymers, biomacromolecules such as polyelectrolytes and polymers with intrinsic stiffness. This review ends by highlighting new emerging interdisciplinary
applications of computational methods in the field of medical engineering where the application of concepts of polymer physics and of shock waves to biological systems holds a lot of promise for improving medical applications such as extracorporeal shock wave lithotripsy or tumor treatment. back to the year overview Schaefer, F., Hiermaier, S., Schneider, E.Ballistic limit equation for the normal impact of unyawed ellipsoid-shaped projectiles on aluminium Whipple Shields 2005 Science and Technology Series , volume : 109, pages : 291 - 308» show abstract « hide abstract Abstract In this study, an approach to cope with the impactor shape in ballistic limit assessment of Whipple shields is presented. A ballistic limit equation (BLE) for impacts of ellipsoid-shaped projectiles on Whipple Shields was derived from existing and thoroughly verified BLEs which were originally
developed to yield the critical projectile diameter of spherical projectiles impacting on aluminium Whipple shields. The derived equation was validated by hypervelocity impact tests and numerical simulations. The Whipple Shields had a bumper thickness of 1.0 mm and backwall thicknesses of 3.0 mm and
4.0 mm, respectively, placed at a stand-off of 200 mm and 150 mm, respectively, from the bumper. The total number of impact tests on Whipple Shields performed was 39, covering shape factors of around 0.4, 1.0, and 1.53. Projectile masses amounted to between 0.18 g and 0.32 g. Impact velocities
ranged between 0.85 km/s and 6.76 km/s. The numerical simulations of hypervelocity impacts on Whipple Shields with spherical and prolate shaped projectiles (f=1.53) covered the velocity range up to 13 km/s which is not accessible to experimental testing. 8 numerical simulation runs were performed.
The BLE can be used to predict the critical projectile mass for a given projectile shape for normal and unyawed impact on aluminium Whipple Shields as a function of impact velocity. Teng, X., Wierzbicki, T., Hiermaier, S., Rohr, I.Numerical prediction of fracture in the Taylor test 2005 International Journal of Solids and Structures , volume : 42, pages : 2929 - 2948 back to the year overview Thoma, K., Schaefer, F., Hiermaier, S., Schneider, E.An approach to achieve progress in spacecraft shielding 2004 Advances in Space Research , volume : 34, pages : 1063 - 1075» show abstract « hide abstract Abstract Progress in shield design against space debris can be achieved only when a combined approach based on several tools is used. This approach depends on the combined application of advanced numerical methods, specific material models and experimental determination of input parameters for these
models. Examples of experimental methods for material characterization are given, covering the range from quasi static to very high strain rates for materials like Nextel and carbon fiber-reinforced materials. Mesh free numerical methods have extraordinary capabilities in the simulation of extreme
material behaviour including complete failure with phase changes, combined with shock wave phenomena and the interaction with structural components. In this paper the benefits from combining numerical methods, material modelling and detailed experimental studies for shield design are demonstrated.
The following examples are given: (1) Development of a material model for Nextel and Kevlar-Epoxy to enable numerical simulation of hypervelocity impacts on complex heavy protection shields for the International Space Station. (2) The influence of projectile shape on protection performance of
Whipple Shields and how experimental problems in accelerating such shapes can be overcome by systematic numerical simulation. (3) The benefits of using metallic foams in "sandwich bumper shields" for spacecraft and how to approach systematic characterization of such materials. back to the year overview Clegg, R.A., White, D.M., Hayhurst, C., Riedel, W., Harwick, W., Hiermaier, S.Advanced numerical models and material characterisation techniques for composite materials subject to impact and shock wave loading 2003 Journal de physique. 4, Colloque , volume : 110, pages : 311 - 316» show abstract « hide abstract Abstract The development and validation of an advanced material model for orthotropic materials, such as fibre reinforced composites, is described. The model is specifically designed to facilitate the numerical simulation of impact and shock wave propagation through orthotropic materials and the
prediction of subsequent material damage. Initial development of the model concentrated on correctly representing shock wave propagation in composite materials under high and hypervelocity impact conditions. This work has now been extended to further concentrate on the development of improved
numerical models and material characterisation techniques for the prediction of damage, including residual strength, in fibre reinforced composite materials. The work is focussed on Kevlar-epoxy however materials such as CFRP are also being considered. The paper describes our most recent activities
in relation to the implementation of advanced material modelling options in this area. These enable refined non-liner directional characteristics of composite materials to be modelled, in addition to the correct thermodynamic response under shock wave loading. The numerical work is backed by an
extensive experimental programme covering a wide range of static and dynamic tests to facilitate derivation of model input data and to validate the predicted material response. Finally, the capability of the developing composite material model is discussed in relation to a hypervelocity impact
problem. Hiermaier, S.J., Schaefer, F.K.Simulation of ellipsoidal projectile impact on whipple shields 2003 International Journal of Impact Engineering , volume : 29, pages : 333 - 343 back to the year overview Thoma, K., Riedel, W., Schaefer, F., Hiermaier, S.Status and perspectives in protective design 2000 Space debris , volume : 2, pages : 201 - 224» show abstract « hide abstract Abstract Starting with an introduction into the field of hypervelocity impacts, an overview over current research in the area of protection against space debris is given. Trends and strategies to further develop know-how in protection technology are then discussed. One purpose is to demonstrate that
improvements in shield efficiency can be expected. To achieve this aim, a strategy is outlined which tries to avoid the adjustment of numerical and material parameters by fits to penetration experiments. Instead, it is suggested to determine material parameters from carefully selected laboratory
tests, covering a broad range of strains, strain rates and stress states. Knowledge of the dynamic material behaviour can then be used for the development of new shield concepts by means of numerical simulation. back to the year overview Hayhurst, C.J., Hiermaier, S.J., Clegg, R.A., Riedel, W., Lambert, M.Development of material models for Nextel and Kevlar-epoxy for high pressures and strain rates 1999 International Journal of Impact Engineering , volume : 23, pages : 365 - 376 Hiermaier, S., Schaefer, F.Hypervelocity impact fragment clogh-pressure gas numerical and experimental investigations 1999 International Journal of Impact Engineering , volume : 23, pages : 391 - 400
Books Years: 2009 |
2008 | show all back to the top of all publications back to the year overview Springer, Berlin Predictive modeling of dynamic processes : A tribute to Professor Klaus Thoma ISBN : 978-1-4419-0726-4 Hiermaier, S back to the year overview Springer US, Berlin Structures under crash and impact : Continuum mechanics, discretization and experimental characterization ISBN : 978-0-387-73862-8 Hiermaier, S.J.
Book chapters Years: 2019 |
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2009 | show all back to the top of all publications back to the year overview Hiermaier, Stefan, Scharte, Benjamin, Fischer, KaiResilience Engineering: Chances and challenges for a comprehensive concept In : Handbook on resilience of socio-technical systems 2019, Cheltenham: Elgar, 2019 , Ruth, Matthias, pages : 155 - 166, Ruth, Matthias, ISBN : 978-1-78643-936-9» show abstract « hide abstract Abstract Ever more complex socio-technical systems enable modern societies to profit from most technological developments in everyday life. New means of communication and transport, cheap energy and supply goods as well as stable global business opportunities are the basis for the comfortable environment many modern civilizations have to offer. The related technological innovations involve manifold interdependencies and complexities in the system behavior never known before. As a consequence, safe operation of critical infrastructure and secure environment for societies have to face a new quality of challenges demanding for new approaches in safety and security research. back to the year overview Haering, Ivo, Scharte, Benjamin, Stolz, Alexander, Leismann, Tobias, Hiermaier, StefanResilience engineering and quantification for sustainable systems development and assessment: Socio-technical systems and critical infrastructure In : IRGC Resource Guide on Resilience. Online resource 2016, IRGC Resource Guide on Resilience. Online resource , Online im WWW, page : 9, Online im WWW, back to the year overview Laessig, T., Riedel, W., Heisserer, U., Werff, H. van der, May, M., Hiermaier, S.Numerical sensitivity studies of a UHMWPE composite for ballistic protection In : Structures under shock and impact 2014, Structures under shock and impact , WIT Press, Southampton, pages : 371 - 381, WIT Press, Southampton, ISBN : 978-1-84564-796-4» show abstract « hide abstract Abstract Ultra-high molecular weight polyethylene (UHMWPE) has a high potential for ballistic armor applications due to the excellent weight specific strength inherent to this type of material. In this paper, a non-linear orthotropic material model for the UHMWPE, based on the product DYNEEMA� HB26, is
used for assessing the influence of the material properties on the ballistic performance. The model, implemented in the commercial hydrocode ANSYS AUTODYN uses initially linear-orthotropic elasticity, subsequent non-linear strain hardening, multiple stress-based composite failure criteria and
post-failure softening. The strength model is coupled with a polynomial equation of state. An experimentally supported material data set for UHMWPE, presented before, is used as a baseline for the numerical studies on high velocity impact. Parameter sensitivities are studied for these impact
situations. The numerical predictions are compared to available experimental data over a wide range of impact velocities (1 km/s up to 6 km/s). The objective of this paper is to assess the influence of different material parameters on the predictive capability of high velocity impact simulations and
subsequently provide guidelines for the required experimental characterization of UHMWPE under shock loading. back to the year overview Hiermaier, StefanCrashverhalten von Polymerwerkstoffen In : Handbuch Leichtbau 2011, Handbuch Leichtbau , Hanser, Muenchen, Hanser, Muenchen, ISBN : 978-3-446-42267-4 back to the year overview Haase, T., Thoma, K., Hiermaier, S.Selbstheilende Polymere In : Festschrift zum 60. Geburtstag von Univ.-Prof. Dr.-Ing. Ingbert Mangerig 2010, Festschrift zum 60. Geburtstag von Univ.-Prof. Dr.-Ing. Ingbert Mangerig , Universit�t der Bundeswehr Muenchen, Institut fuer Mechanik und Statik, Neubiberg, Universit�t der Bundeswehr Muenchen, Institut fuer Mechanik und Statik, Neubiberg, back to the year overview Hiermaier, S.Hypervelocity impact induced shockwaves and related equations of state In : Predictive modeling of dynamic processes 2009, Predictive modeling of dynamic processes , Springer, Berlin, pages : 333 - 348, Springer, Berlin, ISBN : 978-1-4419-0726-4» show abstract « hide abstract Abstract Precondition for stable shock wave propagation is a convex Equation of State (EoS) in terms of pressure and volume. The first mathematical proof for the existence and dependence of shock waves on that non-linearity was derived by Bethe [1]. In this introductory chapter,
Talks Years: 2018 | show all back to the top of all publications back to the year overview Laessig, Torsten, Bagusat, Frank, Pfändler, Siegfried, May, Michael, Riedel, Werner, Heisserer, Ulrich, Werff, Harm van der, Sauer, Martin, Hiermaier, StefanInfluence of the consolidation pressure on the shock wave propagation in UHMWPE composites 2018 1st World Conference on Advanced Materials for Defense (AuxDefense 2018), Lisbon, Portugal, September 3 and 4, 2018
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1998 | show all back to the top of all publications back to the year overview Dlugosch, Michael, Fritsch, Jens, Hiermaier, Stefan, Lukaszewicz, DirkEfficiency-driven model simplifications in crash simulations of FRP-metal hybrid material systems in automotive body structures 2019 International Conference on Simulation Process and Data Management (SPDM) 2019, Quebec A world of engineering simulation. NWC 2019, NAFEMS World Congress : 17-20 June, Quebec City, Canada : incorporating SPDM, International Conference Simulation Process & Data Management : summary of pr , International Association for the Engineering Analysis Community -NAFEMS-:, page : 21» show abstract « hide abstract Abstract Growingly stringent CO2-emission regulations lead to increased efforts to explore novel multi-material systems for effective lightweight design solutions. These often exhibit a complex internal architecture including interfaces between the discrete material phases. Particularly in highly nonlinear crash simulations of complex structures, model fidelity is a key aspect in the trade-off considerations between accurate predictive capabilities of a modeling technique and the resources needed for model development as well as computationally producing and processing solutions. The present study investigates various model simplification strategies for Finite Element (FE)-simulations of automotive crash structural concepts composed of fiber-reinforced plastics (FRP)-metal hybrid material systems in view of the conflicts invoked by strict model efficiency requirements. This particularly implies the modeling resolution of the FRP phase and different modeling techniques for the adhesive interface between the material phases and the respective implications on the predictive qualities of the simulation results. All results are compared to hardware experiments of hybrid generic structural components under crash loading conducted by the authors. The results show, that the model fidelity in the FRP phase does generally have a strong correlation with the predictive capabilities of the overall simulation. Comparing the simulation and the experimental data of generic components shows that explicitly modeling the cohesive behavior at the adhesive interface is not only more complex, it is also not necessarily bound to produce more accurate results than a simple modeling approach using rigid tie connections. In terms of computational efficiency however, the tie modeling approach does not decrease the computational time solving the model, which limits potential efficiency benefits to the reduced modeling complexity and the omission of the adhesive’s characterization process.
Download file Fischer, Kai, Hiermaier, Stefan, Riedel, Werner, Häring, IvoStatistical driven vulnerability assessment for the resilience quantification of urban areas 2019 13th International Conference on Applications of Statistics and Probability in Civil Engineering (ICASP), ICASP 2019, Seoul Online resource : Seoul, South Korea, May 26-30, 2019 Seoul, 2019 http://s-space.snu.ac.kr/handle/10371/142934 Paper 26, 8 S. , volume : 26, page : 8» show abstract « hide abstract Abstract The formation of new threats and the increasing complexity of infrastructure elements underline the need for more robust and sustainable systems, which are able to cope with adverse events. Achieving sustainability requires the increase of resilience. Currently, a comprehensive approach for the quantification of resilience is missing. Within this paper, a new generalized mathematical framework is presented to assess the resilience of complex systems, like urban areas. A clear definition of terms and their interaction builds the basis of this assessment scheme. Risk-based approaches are extended with the dimension of time, to quantify the susceptibility, the vulnerability and the recovery behavior of complex systems for multiple threat scenarios. Engineering approaches are applied to assess expected damage effects and are combined with statistical methods to weight the probability of occurrence and the exposition of the investigated system to the source of disruptive events. Resilience is covered by indicators for preparation, prevention, protection, response and recovery. The presented approach is able to determine these indicators and provides decision support, which enhancement measures are more effective. Hence, the framework quantifies, if it is better to avoid a hazardous event or to tolerate an event with an increased robustness, for example. An application example assesses urban areas with consideration of multiple adverse events, like terrorist attacks or earthquakes, and multiple buildings. Each urban object includes a certain number of attributes, like the object use, the construction type, the time-dependent number of persons and the value to derive different performance targets. The assessment results in the identification of weak-spots through the evaluation of single resilience indicators. back to the year overview Ledford, Noah, Paul, Hanna, Isakov, Matti, Hiermaier, StefanHigh rate loading of hybrid joints in a Split Hopkinson Tension Bar 2018 International Conference on the Mechanical and Physical Behaviour of Materials under Dynamic Loading (DYMAT)/Arcachon EPJ Web of Conferences , volume : 183» show abstract « hide abstract Abstract Bonded joints are nowadays seen as one of the preferred joining methods in aerospace applications. However, the difficulty in certifying bond strength and the relatively low energy absorption capability of the joint are barriers to widespread adoption. The use of a hybrid joint, that is, the combination of a mechanical and a bonded joint, allows for a fail-safe design and offers improved performance of the joint. The quasi-static properties of hybrid joints have been investigated by a number of researchers. In contrast, the high rate loading regime has been only sparsely investigated. In this work, hybrid joints are tested in quasi-static and high rate loading in order to analyze their loading rate dependence. The hybrid joint studied is a composite-aluminum double lap shear joint with Sikaforce 7752 adhesive and Hi-Lite-315 countersunk titanium bolts. In order to quantitatively analyze the high rate behavior of the hybrid joints and their respective sub-components, additional tests are carried out on simply bonded and simply bolted specimens. The high rate characterization was performed with a Split Hopkinson Tension Bar. The main challenges for these tests are the relatively large specimen size and complex specimen geometry needed to properly characterize the joint behavior, which both are in contradiction with the assumptions of the classical Split Hopkinson Bar-analysis. In this paper we describe an approach to solve these challenges based on an elastic wave analysis of the system. Watson, Erkai, Maas, Hans-Gerd, Schaefer, Frank, Hiermaier, StefanTrajectory based 3D fragment tracking in hypervelocity impact experiments 2018 Symposium "Towards Photogrammetry 2020"/Riva del Garda ISPRS, 2018 (The International Archives of the Photogrammetry, Remote Sensing and Spatial Information Sciences XLII-2 , volume : XLII-2» show abstract « hide abstract Abstract Collisions between space debris and satellites in Earth’s orbits are not only catastrophic to the satellite, but also create thousands of newfragments, exacerbating the space debris problem. One challenge in understanding the space debris environment is the lack of data onfragmentation and breakup caused by hypervelocity impacts. In this paper, we present an experimental measurement technique capableof recording 3D position and velocity data of fragments produced by hypervelocity impact experiments in the lab. The experimentalsetup uses stereo high-speed cameras to record debris fragments generated by a hypervelocity impact. Fragments are identified andtracked by searching along trajectory lines and outliers are filtered in 4D space (3D + time) with RANSAC. The method is demonstratedon a hypervelocity impact experiment at 3.2 km/s and fragment velocities and positions are measured. The results demonstrate thatthe method is very robust in its ability to identify and track fragments from the low resolution and noisy images typical of high-speedrecording. Hoschke, Klaus, Pfaff, Aron, Fleig, Luisa, Bierdel, Marius, Jaecklein, Martin, Riedel, Werner, Hiermaier, StefanA parametric mesostructural approach for robust design of additive manufacturing parts 2018 Fraunhofer Direct Digital Manufacturing Conference (DDMC)/Berlin Fraunhofer Direct Digital Manufacturing Conference DDMC 2018 , volume : 1» show abstract « hide abstract Abstract Additive Manufacturing (AM) allows for production of potentially complex design solutions and motivates the use of Structural Optimization tools in product development to chase the structural limit of a design problem and its solution concept. Scratching on the limits of the material strength, design solutions can lack robustness concerning simplifications in model assumptions and uncertainties. However, the design freedom with AM can also actively be used to enhance robustness and reliability of solutions. To this end, an approach is presented that introduces Parametric Mesostructures into selective areas of the Additive Design. Structural members and coherent mechanical characteristics of these mesostructures can significantly reduce local stress peaks and can account for uncertainties, e.g. direction of load application. Their design is motivated by Structural Optimization and analysis results. Implementation of the approach is demonstrated and discussed on the example of a structural aircraft component. Ganzenmüller, Georg, Langhof, Timo, Hiermaier, StefanA constant acoustic impedance mount for sheet-type specimens in the tensile Split-Hopkinson Bar 2018 International Conference on the Mechanical and Physical Behaviour of Materials under Dynamic Loading (DYMAT) <12, 2018, Arcachon> Les Ulis: EDP Sciences, 2018 (EPJ Web of Conferences 183) ISBN: 978-2-7598-9053-8 Art. 02064, 4 S. , page : 4» show abstract « hide abstract Abstract This paper addresses a problem well-known amongst practitioners of the Split-Hopkinson Tension Bar method: attaching a flat test specimen made from sheet material to the cylindrical input-and output bars. To date, slotting the bar ends and gluing the specimens into these ends with high-strength adhesives is the gold standard. However, this approach is not universally applicable because some materials are difficult to bond, and the adhesion surface is limited by the bar diameter, meaning that only small width specimens can be tested. In contrast, the hitherto published mechanical clamping mechanisms typically introduce excessive additional mass into the Split-Hopkinson system which detrimentally affects wave propagation and thus causes errors in the stress-strain signals. We circumvent this problem by designing a mechanical clamping device which has the same acoustic impedance as the bar material and is suitable to securely attach specimens with a width larger than the bar diameter. The benefits of our new clamping device are demonstrated by reporting tensile stress-strain data for Polycarbonate at high strain rates. The data is free from unwanted oscillations and enables accurate determination of dynamic strength and stiffness. Hoschke, Klaus, Pfaff, Aron, Fleig, Luisa, Bierdel, Marius, Jaecklein, Martin, Riedel, Werner, Hiermaier, StefanA parametric mesostructural approach for robust design of additive manufacturing parts 2018 Fraunhofer Direct Digital Manufacturing Conference, DDMC 2018 , Fraunhofer Verlag, Stuttgart, page : 6» show abstract « hide abstract Abstract Additive Manufacturing (AM) allows for production of potentially complex design solutions and motivates the use of Structural Optimization tools in product development to chase the structural limit of a design problem and its solution concept. Scratching on the limits of the material strength,
design solutions can lack robustness concerning simplifications in model assumptions and uncertainties. However, the design freedom with AM can also actively be used to enhance robustness and reliability of solutions. To this end, an approach is presented that introduces Parametric Mesostructures
into selective areas of the Additive Design. Structural members and coherent mechanical characteristics of these mesostructures can significantly reduce local stress peaks and can account for uncertainties, e.g. direction of load application. Their design is motivated by Structural Optimization and
analysis results. Implementation of the approach is demonstrated and discussed on the example of a structural aircraft component. back to the year overview Watson, Erkai, Gulde, Max, Schaefer, Frank, Hiermaier, StefanOptical fragment tracking in hypervelocity impact experiments 2017 International Astronautical Congress (IAC)/Adelaide 68th International Astronautical Congress (IAC 2017): Unlocking Imagination, Fostering Innovation and Strengthening Security , volume : 6, pages : 3585 - 3592» show abstract « hide abstract Abstract In-orbit impacts between satellites and space debris lead to varying degrees of fragmentation, ranging anywhere from minor damage to complete breakups. In this paper, we describe an experimental measurement approach for studying the fragmentation effects of hypervelocity impact in the laboratory. We investigate hypervelocity impacts on a thin aluminum bumper plates and track individual fragments in the debris clouds with an innovative algorithm that bases matches on trajectories instead of features. The experimental setup involves recording the debris cloud fragments illuminated by a thin laser plane with a high-speed video camera. The image sequence is analyzed, yielding spatio-temporal information about each fragment in the debris cloud. This allows individual fragment size and velocity information, to directly measured. Dlugosch, Michael, Spiegelhalter, Bastian, Soot, Thomas, Lukaszewicz, Dirk, Fritsch, Jens, Hiermaier, StefanPotentials of optical damage assessment techniques in automotive crash-concepts composed of FRP-steel hybrid material systems 2017 12th International Conference on Damage Assessment of Structures, DAMAS 2017. Proceedings , IOP, London, page : Art. 012044, 13» show abstract « hide abstract Abstract With car manufacturers simultaneously facing increasing passive safety and efficiency requirements, FRP-metal hybrid material systems are one way to design lightweight and crashworthy vehicle structures. Generic automotive hybrid structural concepts have been tested under crash loading
conditions. In order to assess the state of overall damage and structural integrity, and primarily to validate simulation data, several NDT techniques have been assessed regarding their potential to detect common damage mechanisms in such hybrid systems. Significant potentials were found
particularly in combining 3D-topography laser scanning and X-Ray imaging results. Ultrasonic testing proved to be limited by the signal coupling quality on damaged or curved surfaces. back to the year overview Dlugosch, M., Ihle, J., Lukaszewicz, D., Fritsch, J., Hiermaier, S.Experimental investigation of automotive components consisting of hybrid FRP-metal material systems under crash loading 2016 2. Internationale Konferenz Euro Hybrid - Materials and Structures 2016. Proceedings , Institut fuer Verbundwerkstoffe -IVW-, Kaiserslautern, Kaiserslautern, pages : 63 - 68» show abstract « hide abstract Abstract In the course of a strong trend towards automotive material diversification, hybrid material systems could offer solutions to design lightweight body-in-white structures particularly subject to crash loads in order to meet the demands of both ambitious efficiency goals and increasingly strict
vehicle safety requirements. Hybrid material systems consisting of glass- and carbon fiber reinforced plastics and sheet steel are tested under axial impact loading and analyzed regarding their qualitative behavior and relevant crash metrics. The study shows the complex behavior of those material
systems and the interaction between the material phases resulting in a complex system of parameter effects and interdependencies. Generally, the hybrid specimens studied indicated their applicability in automotive crash structures by exhibiting comparable results to pure FRP materials while
simultaneously being potentially more compatible and cost efficient. Klomfass, A., Stolz, A., Hiermaier, S.Improved explosion consequence analysis with combined CFD and damage models 2016 15th International Symposium on Loss Prevention and Safety Promotion in the Process Industries 2016. Proceedings , AIDIC, Mailand, pages : 109 - 114» show abstract « hide abstract Abstract The most-widely used approach to explosion consequence analysis is the classical engineering method based on the combination of TNT equivalence, scaled distances and overpressure-based damage levels. This approach rests on established and easily comprehensible elements and permits a fast
assessment of explosion consequences. There are however several limitations inherent in this approach. In contrast, a simulation-based approach using computational fluid dynamics (CFD) and structural dynamics (CSD) methods permits an analysis with a high level of detail regarding both the prediction
of the explosive loads and the caused damage. This comes at the cost of complex simulation models which require expert knowledge, intense validation and a high computational effort. To bridge the gap between the classical simplified approach and the CFD/CSD based methods, we have developed a
specialized CFD tool, the APOLLO Blastsimulator, with a built-in library of experimentally validated damage models and blast-injury models suitable for an improved explosion consequence analysis. The high resolution CFD tool uses globally and locally adaptive Cartesian grids and includes models for
TNT detonations as well as gas detonations. The built-in damage models are based on experimentally validated single-degree-of-freedom (SDOF) representations of structural components. This paper gives a brief review on the classical approaches and their limitations and an overview on the concepts
used in the APOLLO Blastsimulator and the SDOF damage models. For an exemplary explosion scenario the results obtained with different explosive source and damage models are compared. Klomfass, A., Stolz, A., Hiermaier, S.Improved explosion consequence analysis with combined CFD and damage models 2016 15th International Symposium on Loss Prevention and Safety Promotion in the Process Industries 2016. Proceedings , AIDIC, Mailand, pages : 109 - 114» show abstract « hide abstract Abstract The most-widely used approach to explosion consequence analysis is the classical engineering method based on the combination of TNT equivalence, scaled distances and overpressure-based damage levels. This approach rests on established and easily comprehensible elements and permits a fast
assessment of explosion consequences. There are however several limitations inherent in this approach. In contrast, a simulation-based approach using computational fluid dynamics (CFD) and structural dynamics (CSD) methods permits an analysis with a high level of detail regarding both the prediction
of the explosive loads and the caused damage. This comes at the cost of complex simulation models which require expert knowledge, intense validation and a high computational effort. To bridge the gap between the classical simplified approach and the CFD/CSD based methods, we have developed a
specialized CFD tool, the APOLLO Blastsimulator, with a built-in library of experimentally validated damage models and blast-injury models suitable for an improved explosion consequence analysis. The high resolution CFD tool uses globally and locally adaptive Cartesian grids and includes models for
TNT detonations as well as gas detonations. The built-in damage models are based on experimentally validated single-degree-of-freedom (SDOF) representations of structural components. This paper gives a brief review on the classical approaches and their limitations and an overview on the concepts
used in the APOLLO Blastsimulator and the SDOF damage models. For an exemplary explosion scenario the results obtained with different explosive source and damage models are compared. Haering, Ivo, Scharte, Benjamin, Hiermaier, StefanTowards a novel and applicable approach for Resilience Engineering 2016 6th International Disaster and Risk Conference, IDRC 2016. Extended Abstracts , GRF, Davos, pages : 272 - 276» show abstract « hide abstract Abstract Resilience Engineering can provide society and its critical infrastructure and systems with means, methods and technologies to overcome disruptions with as less harm as possible. In this context it is of utmost importance to identify ways to strengthen the adaptive capacity of up to complex
socio technical systems. We try to establish Resilience Engineering as away of thinking that enables engineers to use their scientific expertise, creative ingenuity and help society to develop tools to handle all kinds of adverse events properly - from critical system disruptions, natural disasters,
global terrorism to large-scale infrastructure failure. For that purpose, we suggest to deliberately limit the scope of Resilience Engineering towards engineering, i.e. mainly technological solutions, in contrast to the main body of Resilience Engineering literature. By that we try to pave the way
for the next generation of engineers dealing with the extension from risk analysis and management towards resilience thinking. In short, Resilience Engineering means preserving critical functionality, ensuring graceful degradation and enabling fast recovery of systems with the help of engineered
generic capabilities as well as customized technological solutions when the systems witness problems, unexpected disruptions or unexampled events. One central aspect of Resilience Engineering is the ability to quantify and measure resilience. Only adequate and valid indicators will give us the
chance for comparatively and absolutely analyzing various systems with respect to their specific resilience. Finally, we need to be able to develop advanced methods for modelling and simulating, in particular for complex systems and their resilience towards adverse events. The presentation will hint
at opportunities and research necessities for developing a new and integrated approach to model, simulate and improve the resilience of complex, interdependent, sociotechnical systems. back to the year overview Hiermaier, S.Foreword. DYMAT 2015 - 11th International Conference on the Mechanical and Physical Behaviour of Materials under Dynamic Loading 2015 DYMAT 2015, 11th International Conference on the Mechanical and Physical Behaviour of Materials under Dynamic Loading , EDP Sciences, Les Ulis, page : Art. 00001, 1 Ganzenmueller, G., Hiermaier, S., May, M.Improvements to the prototype micro-brittle model of peridynamics 2015 Meshfree Methods for Partial Differential Equations VII , Springer International Publishing, Cham, pages : 163 - 183» show abstract « hide abstract Abstract This paper assesses the accuracy and convergence of the bond-based Peridynamic model with brittle failure, known as the prototype micro-brittle (PMB) model. We investigate the discrete equations of this model, suitable for numerical implementation. It is shown that the widely used
discretization approach incurs rather large errors. Motivated by this observation, a correction is proposed, which significantly increases the accuracy by cancelling errors associated with the discretization. As an additional result, we derive equations to treat the interactions between differently
sized particles, i.e., a non-homogeneous discretization spacing. This presents an important step forward for the applicability of the PMB model to complex geometries, where it is desired to model interesting parts with a fine resolution (small particle spacings) and other parts with a coarse
resolution in order to gain numerical efficiency. Validation of the corrected Peridynamic model is performed by comparing longitudinal sound wave propagation velocities with exact theoretical results. We find that the corrected approach correctly reproduces the sound wave velocity, while the
original approach severely overestimates this quantity. Additionally, we present simulations for a crack growth problem which can be analytically solved within the framework of Linear Elastic Fracture Mechanics Theory. We find that the corrected Peridynamics model is capable of quantitatively
reproducing crack initiation and propagation. Dlugosch, M., Lukaszewicz, D., Fritsch, J., Hiermaier, S.Mechanical characterization of hybrid material systems consisting of sheet metal and advanced composites 2015 20th International Conference on Composite Materials, ICCM 2015. Proceedings. Online resource , pages : Paper 4213 - 5, 16» show abstract « hide abstract Abstract Strip-shaped hybrid coupon specimens comprised of steel and glass/carbon fiber reinforced plastics are tested under quasistatic tension and 3-point-bending. The effects of major material and design parameters (steel and fiber type, laminate thickness and layup) on the stiffness, strength and
the specific energy absorption are assessed. Furthermore, hybrid mechanisms resulting from the mutual interaction of both constituent materials are presented. Although anticipated effects on the hybrid specimens' stiffness and strength are widely confirmed, the fiber type for example exhibits a
distinctly smaller impact than expected. The specimens' loading and failure behavior is rather dominated by the type of steel and its characteristics. Thus, glass fiber reinforced hybrid variants generally keep up with carbon fiber reinforced hybrid variants in terms of mechanical properties.
Considering the difference in price, this is of particular interest for hybrid mid or high volume crash structural applications. As hybrid mechanism, a distinct extension of the maximum strain is observed for both composites (up to 48 %) and steel (up to 23 %) when joined in a hybrid specimen and
tested under tensile loads. Furthermore, having composites on the rather pressure loaded side in 3-point-bending results in a 26 %-increase in mass specific energy absorption (compared to reverse loading) due to an enhanced composite failure mode and the stabilizing effect of the steel strip. Dlugosch, M., Fritsch, J., Lukaszewicz, D., Hiermaier, S.New method to analyze numerical crash simulation data to assess the suitability of hybrid composite structures in automotive applications 2015 30. American Society for Composites 2015. Proceedings. CD-ROM , DEStech Publications, Lancaster, Pa., page : Paper 1554, 15» show abstract « hide abstract Abstract In order to enhance development processes for multi material vehicle architecture concepts involving composites or hybrid composite-metal material systems a method is presented that aims to rationalize engineering judgements by means of quantifiable criteria for the suitability of a certain
hybrid material system for a particular structural application. A number of significant crash load cases for a structure is considered simultaneously by superimposing the output data of several numerical crash simulations and defining criteria to qualify the suitability of a particular hybrid
material system. The work introduced here focusses on the analysis of the global anisotropy of the crash loading situation as an indicator for a rather composite- or metal-intensive hybrid material system. The definition of the anisotropy criterion and the implementation of the method into the
development infrastructure of automotive engineering is presented. A first step validation using simple flat coupon specimen simulations shows reasonable results and proves the applicability of the method. back to the year overview Hiermaier, S.Integrated experimental-numerical characterization of geological materials under shock and impact 2013 Rock Dynamics and Applications. State of the Art , CRC Press, Hoboken, pages : 71 - 76» show abstract « hide abstract Abstract Scientific investigation of transient processes and engineering design of structures for dynamic loading conditions are still a great challenge. Other than quasi-static loading conditions a dynamic application of loads by impact or blast leads to additional effects that enhance the complexity
of the thermo-mechanical material behavior. They can be reduced to two basic phenomena: first, the strain rate dependent change of mechanical behavior and, secondly, the evolution and propagation of shock waves. In order to understand the structural behavior under transient loading conditions, the
involved materials need to be characterized by material tests. Mathematical formulations are needed for the description of both the strain rate dependent deviatoric behavior and the non-linear Equation of State responsible for the shock wave formation. Implemented into numerical codes these
constitutive equations allow for a predictive simulation of the structural behavior. Sometimes nume rical simulation itself can be used to derive material properties. This is the case when for example the material is composed of two or more constituents for which the individual thermo-mechanical
properties are known. Modeling the composite material as specimens and application of loads that may be outside the load types applicable in experiments leads to additional results not achievable in a pure experimental approach. Therefore, an integrated experimental-numerical approach for the
characterization of materials under transient loading conditions is more and more preferred if predictive capabilities are needed for the highly complex phenomena observed in the related structural applications of interest. Durr, N., Sauer, M., Gueldemeister, N., Wuennemann, K., Hiermaier, S.Mesoscale Investigation of Shock Wave Effects in Dry and Water-saturated Sandstone 2013 12th Hypervelocity Impact Symposium, HVIS 2012. Proceedings , Elsevier, Amsterdam» show abstract « hide abstract Abstract In this paper, the behavior of natural sandstone under hypervelocity impact is investigated numerically. Sandstone essentially consists of cemented quartz grains, it can be generally considered as a polygranular structure with air or water-filled pores. In order to study the influence of pores
and water filling on the behavior of sandstone under shock loading, a numerical investigation at the mesoscale is performed. We explicitly resolve pores and the closure of pores in a homogeneous and isotropic quartz matrix. The quartz matrix is described with an equation of state and a strength
model; the pore geometry is simplified. Two-dimensional planar shock simulations are conducted in order to analyze effects of quartz strength and water-saturation on pore crushing. Averaging is used to perform a macroscale analysis of the dependencies of pressure and shock velocity on particle
velocity. The simulation results shall enhance the basis for the development of accurate macroscale sandstone models that take the water content into account. Durr, N., Sauer, M., Gueldemeister, N., Wuennemann, K., Hiermaier, S.Mesoscale Investigation of Shock Wave Effects in Dry and Water-saturated Sandstone 2013 12th Hypervelocity Impact Symposium, HVIS 2012. Proceedings , Elsevier, Amsterdam» show abstract « hide abstract Abstract In this paper, the behavior of natural sandstone under hypervelocity impact is investigated numerically. Sandstone essentially consists of cemented quartz grains, it can be generally considered as a polygranular structure with air or water-filled pores. In order to study the influence of pores
and water filling on the behavior of sandstone under shock loading, a numerical investigation at the mesoscale is performed. We explicitly resolve pores and the closure of pores in a homogeneous and isotropic quartz matrix. The quartz matrix is described with an equation of state and a strength
model; the pore geometry is simplified. Two-dimensional planar shock simulations are conducted in order to analyze effects of quartz strength and water-saturation on pore crushing. Averaging is used to perform a macroscale analysis of the dependencies of pressure and shock velocity on particle
velocity. The simulation results shall enhance the basis for the development of accurate macroscale sandstone models that take the water content into account. back to the year overview Hiermaier, S., Kilchert, S., May, M.Modellierung des Einflusses von Unregelmaessigkeiten in der Mikrostruktur auf das Versagen von UD-Composites 2012 Berechnung und Simulation - Anwendungen, Entwicklungen, Trends , NAFEMS Deutschland, Bernau am Chiemsee Steinhauser, M., Ganzenmueller, G., Hiermaier, S.Multiscale modeling and simulation of shock-wave impact failure in hard and soft matter 2012 28th International Symposium on Shock Waves 2011. Vol.1 , Springer, Berlin, pages : 803 - 808» show abstract « hide abstract Abstract Understanding the mechanisms of failure in materials on various length- and time scales is a prerequisite for the design of new materials with desired superior properties such as high toughness or strength. On the macroscopic scale, many materials such as concrete or ceramics may be viewed as
being homogeneous; however, on the scale of a few microns these materials often exhibit an inhomogeneous polyhedral granular structure which is known to influence its macroscopic mechanical and optical properties, see e.g. Steinhauser [1]. back to the year overview May, M., Nossek, M., Hiermaier, S.A multi-scale methodology for the evaluation of different fiber-matrix combinations using the generalized method of cells 2011 Seminar Progress in Simulating Composites 2011 , NAFEMS Deutschland, Bernau am Chiemsee May, M., Nossek, M., Petrinic, N., Hiermaier, S.A new rate dependent cohesive zone model for impact applications 2011 Composites 2011, 3rd ECCOMAS Thematic Conference on the Mechanical Response of Composites. Proceedings , Leibniz Universit�t, Institut fuer Statik und Dynamik, Hannover back to the year overview Hiermaier, S., Riedel, W., Thoma, K.Tragwerke unter Anprall und Explosion - Experimentelle und numerische Methoden zur Auslegung 2010 Zuverlaessigkeit und Robustheit von Tragwerken. 14. Dresdner Baustatik-Seminar 2010 , Technische Universitaet Dresden, Dresden Riedel, W., Hiermaier, S., Thoma, K.Transient stress and failure analysis of impact experiments with ceramics 2010 3rd International Conference on Science and Technology of Advanced Ceramics, STAC 2009 , Elsevier, Amsterdam, pages : 139 - 147» show abstract « hide abstract Abstract At Ernst-Mach-Institut (EMI), ductile and brittle materials are studied both experimentally and numerically with the focus on shock and impact loading and associated damage effects. Experimental investigations using plate impact, edge-on impact, penetration and perforation on light gas
accelerators provide input for numerical studies and allow verification of constitutive models. Hydrocodes are the standard numerical tool for the simulation of transient processes and basis of the modelling in the present paper. Besides use of commercial codes with mesh-based Lagrangean and
Eulerian spatial discretization, an own meshfree SPH code has been developed at EMI. Edge-on impact experiments, plate impact tests and deep penetration in confined targets are simulated to study different loading histories and failure conditions. Significantly different material models based on
continuum damage approaches as well as microstatistical modelling of inhomogeneities have been implemented. Their performances in reproducing damage fracture patterns and continued fragment loading in different ceramic types are analysed and compared to edge-on impact experiments. Riedel, W., Hiermaier, S., Thoma, K.Transient stress and failure analysis of impact experiments with ceramics 2010 3rd International Conference on Science and Technology of Advanced Ceramics, STAC 2009 , Elsevier, Amsterdam, pages : 139 - 147» show abstract « hide abstract Abstract At Ernst-Mach-Institut (EMI), ductile and brittle materials are studied both experimentally and numerically with the focus on shock and impact loading and associated damage effects. Experimental investigations using plate impact, edge-on impact, penetration and perforation on light gas
accelerators provide input for numerical studies and allow verification of constitutive models. Hydrocodes are the standard numerical tool for the simulation of transient processes and basis of the modelling in the present paper. Besides use of commercial codes with mesh-based Lagrangean and
Eulerian spatial discretization, an own meshfree SPH code has been developed at EMI. Edge-on impact experiments, plate impact tests and deep penetration in confined targets are simulated to study different loading histories and failure conditions. Significantly different material models based on
continuum damage approaches as well as microstatistical modelling of inhomogeneities have been implemented. Their performances in reproducing damage fracture patterns and continued fragment loading in different ceramic types are analysed and compared to edge-on impact experiments. back to the year overview Fritsch, J., Hiermaier, S., Strobl, G.Characterizing and modeling the non-linear visco-elastoplastic tensile deformation properties of a glass fiber reinforced polypropylene 2009 DYFP 2009, the 14th International Conference on Deformation, Yield and Fracture of Polymers. Book of abstracts , Technische Universiteit Eindhoven, Eindhoven, pages : 187 - 190 Fritsch, J., Hiermaier, S., Strobl, G.Characterizing and modeling the non-linear viscoelastic tensile deformation of a glass fiber reinforced polypropylene 2009 Sixteenth International Conference on Composite Materials with Regular Papers, ICCM 2007 , Elsevier, Amsterdam, pages : 2460 - 2466» show abstract « hide abstract Abstract On the basis of comprehensive experimental investigations on a long glass fiber reinforced polypropylene (PP-LGF) a novel rheological material model is developed. It features a decomposition of the stress into a time independent quasi-static and a time and strain dependent viscous
contribution. Furthermore it allows for plastic deformations starting from the very beginning of straining and is thereby able to reproduce the absence of a purely linear elastic domain going along with the nonexistence of a defined yield point, characteristic for many fiber reinforced thermoplastic
polymers. In order to approach the true quasi-static material behavior, various tensile tests were carried out. The viscous material behavior was deduced from a series of stress relaxation experiments and is described by Eyring's equation with strain dependent viscosity parameters. Fritsch, J., Hiermaier, S., Strobl, G.Characterizing and modeling the non-linear viscoelastic tensile deformation of a glass fiber reinforced polypropylene 2009 Sixteenth International Conference on Composite Materials with Regular Papers, ICCM 2007 , Elsevier, Amsterdam, pages : 2460 - 2466» show abstract « hide abstract Abstract On the basis of comprehensive experimental investigations on a long glass fiber reinforced polypropylene (PP-LGF) a novel rheological material model is developed. It features a decomposition of the stress into a time independent quasi-static and a time and strain dependent viscous
contribution. Furthermore it allows for plastic deformations starting from the very beginning of straining and is thereby able to reproduce the absence of a purely linear elastic domain going along with the nonexistence of a defined yield point, characteristic for many fiber reinforced thermoplastic
polymers. In order to approach the true quasi-static material behavior, various tensile tests were carried out. The viscous material behavior was deduced from a series of stress relaxation experiments and is described by Eyring's equation with strain dependent viscosity parameters. back to the year overview Ryan, S., Schaefer, F., Guyot, M., Hiermaier, S., Lambert, M.Characterizing the transient response of CFRP/Al HC spacecraft structures induced by space debris impact at hypervelocity 2008 Hypervelocity impact. Proceedings of the 2007 symposium , Elsevier, Amsterdam, pages : 1756 - 1763» show abstract « hide abstract Abstract To quantify the disturbance induced by the impact of micrometeoroid and space debris particles at hypervelocity on vibration-sensitive CFRP/Al HC SP satellite platforms a method is presented which uses experimentally validated hydrocode models to characterize the impact-induced transient wave
in the local structure. Key features of the transient waveform are simplified by a mathematical function which is expressed in terms of impactor momentum. Evolution of the transient waveform is characterized using multiple measurement gauges located on the sandwich panel facesheets outside the area
of mechanical damage. The characterization is then used to extrapolate the elastic waveform back to the impact location. The elastic-equivalent excitation of a CFRP/Al HC SP is defined in terms of force with respect to time for application in finite element: structural codes for propagation of the
local disturbance to vibration-sensitive locations (i.e. measurement devices). Ryan, S., Schaefer, F., Guyot, M., Hiermaier, S., Lambert, M.Characterizing the transient response of CFRP/Al HC spacecraft structures induced by space debris impact at hypervelocity 2008 Hypervelocity impact. Proceedings of the 2007 symposium , Elsevier, Amsterdam, pages : 1756 - 1763» show abstract « hide abstract Abstract To quantify the disturbance induced by the impact of micrometeoroid and space debris particles at hypervelocity on vibration-sensitive CFRP/Al HC SP satellite platforms a method is presented which uses experimentally validated hydrocode models to characterize the impact-induced transient wave
in the local structure. Key features of the transient waveform are simplified by a mathematical function which is expressed in terms of impactor momentum. Evolution of the transient waveform is characterized using multiple measurement gauges located on the sandwich panel facesheets outside the area
of mechanical damage. The characterization is then used to extrapolate the elastic waveform back to the impact location. The elastic-equivalent excitation of a CFRP/Al HC SP is defined in terms of force with respect to time for application in finite element: structural codes for propagation of the
local disturbance to vibration-sensitive locations (i.e. measurement devices). Hiermaier, S.Hydrocodes - Simulation tool of choice for transient processes 2008 3. Workshop "Bau-Protect" Buildings and Utilities Protection , Universit�t der Bundeswehr Muenchen, Institut fuer Mechanik und Statik, Neubiberg, pages : 21 - 22 Hiermaier, S., Gebbeken, N.Numerical methods for dynamic processes 2008 3. Workshop "Bau-Protect" Buildings and Utilities Protection , Universit�t der Bundeswehr Muenchen, Institut fuer Mechanik und Statik, Neubiberg, pages : 17 - 18 Vergniaud, J.B., Guyot, M., Lambert, M., Schaefer, F., Ryan, S., Hiermaier, S., Taylor, E.Structural vibrations induced by HVI - Application to the Gaia spacecraft 2008 Hypervelocity impact. Proceedings of the 2007 symposium , Elsevier, Amsterdam, pages : 1836 - 1843» show abstract « hide abstract Abstract Given the growing stability needed for spacecraft in operation to ensure functioning of future instruments whose sensitivity requires an important technological step, perturbations encounter in orbital conditions that used to be negligible, become today an issue. This is the case of
micrometeorite impacts whose energy could induce modal response of the flexible structure and imply a dynamic response of the spacecraft which could probably be disturbing for the instrument functioning. The impact environment that could be encountered by the spacecraft is preliminary studied before
the definition of test to recreate the excitation with light-gas gun. Experiments are made on samples of structure representative of the ongoing Gaia astrometric mission project. Response of the structure is recorded to be correlated to finite elements model of the sample. The excitation is then
extrapolated to orbital conditions and to Gaia finite elements model. The final perturbation is compared to the specification. The main conclusion is that for daily impact event, dynamic response of the structure will not disturb Gaia functioning. Nevertheless, for a yearly impact event, the
astrometric mission will largely be disturbed by the dynamic response of the structure to the impact. Vergniaud, J.B., Guyot, M., Lambert, M., Schaefer, F., Ryan, S., Hiermaier, S., Taylor, E.Structural vibrations induced by HVI - Application to the Gaia spacecraft 2008 Hypervelocity impact. Proceedings of the 2007 symposium , Elsevier, Amsterdam, pages : 1836 - 1843» show abstract « hide abstract Abstract Given the growing stability needed for spacecraft in operation to ensure functioning of future instruments whose sensitivity requires an important technological step, perturbations encounter in orbital conditions that used to be negligible, become today an issue. This is the case of
micrometeorite impacts whose energy could induce modal response of the flexible structure and imply a dynamic response of the spacecraft which could probably be disturbing for the instrument functioning. The impact environment that could be encountered by the spacecraft is preliminary studied before
the definition of test to recreate the excitation with light-gas gun. Experiments are made on samples of structure representative of the ongoing Gaia astrometric mission project. Response of the structure is recorded to be correlated to finite elements model of the sample. The excitation is then
extrapolated to orbital conditions and to Gaia finite elements model. The final perturbation is compared to the specification. The main conclusion is that for daily impact event, dynamic response of the structure will not disturb Gaia functioning. Nevertheless, for a yearly impact event, the
astrometric mission will largely be disturbed by the dynamic response of the structure to the impact. back to the year overview Huberth, F., Hiermaier, S.Experimental parameter identification for material models including deformation induced volume dilation for thermoplastic materials 2007 Experimental Analysis of Nano and Engineering Materials and Structures. Proceedings of the 13th International Conference on Experimental Mechanics 2007 , Springer Netherland, Dordrecht, pages : 293 - 294» show abstract « hide abstract Abstract Simulation of structures made from thermoplastic materials under crash loads including large deformations and failure is still a challenge for most existing numerical tools. To model the complex mechanical behaviour of thermoplastic materials new models have been developed. To reproduce the
mechanical behaviour in the simulation, model parameters for each material have to be identified by experimental testing. Hiermaier, S., Wicklein, M.Zellulare Werkstoffe in der Crashsimulation : Charakterisierung und numerische Simulation 2007 Polyurethan 2007. Automotive - Bauen - Daemmen - Komfort - Struktur , VDI Verlag, Duesseldorf back to the year overview Ryan, S., Schaefer, F., Spencer, G., Hiermaier, S., Guyot, M., Lambert, M.An excitation function for hypervelocity impact-induced wave propagation in satellite structures 2006 57th International Astronautical Congress, IAC 2006 , Curran, Red Hook, NY, pages : 3838 - 3846» show abstract « hide abstract Abstract An empirical excitation function which defines the elastic excitation of a satellite wall-representative Aluminum plate from impact of a projectile at hypervelocity is derived empirically from experimentally validated hydrocode simulations. The resulting function is intended for application in
a structural finite element model code to assess the perturbation effects of small micrometeoroid and space debris impacts on highly stiffened satellite structures. This will enable the risk that these impacts pose on a future generation of ESA scientific satellite missions employing ultra-sensitive
equipment to be quantified. The excitation function has been empirically derived from simulated velocity measurements made at various offsets from the impact location. The measured velocity waveforms have been simplified in terms of its frequency content in mind of its end-point application in
structural codes, and this simplified velocity waveform has been extrapolated to the impact o rigin. The resulting empirical function is polynomial-exponential decay in form, and defines a point-source velocity-time input for structural codes. Boljen, M., Harwick, W., Rohr, I., Hiermaier, S.Characterisation and numerical simulation of twill and satin weaves of fabrics made of p-Aramid under static and dynamic loading 2006 DYMAT 2006, 8th International Conference on Mechanical and Physical Behaviour of Materials under Dynamic Loading , EDP Sciences, Les Ulis, pages : 345 - 352» show abstract « hide abstract Abstract The aim of this work is to numerically model two representative twill and satin weaves on a mesoscopical level in order to reveal weave specific yarn interactions. These mesoscopical models that explicitly depict each participating yarn are subjected to uniaxial tension, quasi-static biaxial
tension and pure shear loading. The material response of both weaves will be investigated and compared to experimental results performed earlier by Rohr and Harwick. Boljen, M., Harwick, W., Rohr, I., Hiermaier, S.Characterisation and numerical simulation of twill and satin weaves of fabrics made of p-Aramid under static and dynamic loading 2006 DYMAT 2006, 8th International Conference on Mechanical and Physical Behaviour of Materials under Dynamic Loading , EDP Sciences, Les Ulis, pages : 345 - 352» show abstract « hide abstract Abstract The aim of this work is to numerically model two representative twill and satin weaves on a mesoscopical level in order to reveal weave specific yarn interactions. These mesoscopical models that explicitly depict each participating yarn are subjected to uniaxial tension, quasi-static biaxial
tension and pure shear loading. The material response of both weaves will be investigated and compared to experimental results performed earlier by Rohr and Harwick. Hiermaier, S.Hydrocodes - Simulation transienter Vorgaenge mit expliziter Zeitintegration 2006 2. Workshop "BAU-PROTECT" 2006. Sicherheit der baulichen Infrastruktur vor au�ergewoehnlichen Einwirkungen , Univ. der Bundeswehr Muenchen, Muenchen Huberth, F., Gerster, T., Guth, S., Hiermaier, S.Kunststoffe in der Crashsimulation - Eine Betrachtung aus experimenteller Sicht unter Beruecksichtigung numerischer Problemstellungen 2006 Fortschritte der Kennwertermittlung fuer Forschung und Praxis. Tagung Werkstoffpruefung 2006 , Verlag Stahleisen, Duesseldorf, pages : 91 - 96 Meenken, T., Hiermaier, S.Large strain dynamic compression for soft materials using a direct impact experiment 2006 DYMAT 2006, 8th International Conference on Mechanical and Physical Behaviour of Materials under Dynamic Loading , EDP Sciences, Les Ulis, pages : 653 - 659 Huberth, F., Hiermaier, S.Materialmodelle im Vergleich mit experimentell bestimmten Werkstoffverhalten 2006 24th CADFEM Users' Meeting 2006. CD-ROM , CAD-FEM GmbH, Grafing, Muenchen Hiermaier, S., Gebbeken, N.Numerische Berechnungsverfahren fuer dynamische Prozesse 2006 2. Workshop "BAU-PROTECT" 2006. Sicherheit der baulichen Infrastruktur vor au�ergewoehnlichen Einwirkungen , Univ. der Bundeswehr Muenchen, Muenchen Huberth, F., Hiermaier, S.Verrippte Bauteile - Kugelimpaktversuche und Simulationsergebnisse mit LS-DYNA 2006 5. LS-DYNA Anwenderforum 2006 , DYNAmore GmbH, Stuttgart, Ulm, page : 10 back to the year overview Huberth, F., Hiermaier, S., Neumann, M.Material models for polymers under crash loads existing LS-DYNA models and perspectives 2005 4. LS-DYNA Anwenderforum 2005 , DYNAmore GmbH, Stuttgart, Stuttgart, pages : H - I Nossek, M., Sauer, M., Riedel, W., Hiermaier, S.Simulation des Energieaufnahmevermoegens von CFK-Strukturen bei Belastungen in der Laminatebene 2005 Leichtbau als interdisziplin�re und branchenuebergreifende Herausforderung , LC-Verlag, Landshut, pages : 53 - 66 Wicklein, M., Hiermaier, S., Thoma, K.Simulation of cellular aluminium: Crash and impact 2005 Cellular metals and polymers, CMaP 2004 , Trans Tech Publications, Uetikon-Zuerich, pages : 111 - 114 back to the year overview Schaefer, F., Hiermaier, S., Schneider, E.Ballistic limit equation for the normal impact of unyawed ellipsoid-shaped projectiles on aluminium whipple shields 2004 Space Debris and Space Traffic Management Symposium 2003 , Univelt, San Diego, Calif., pages : 291 - 308 Sindelar, R., Riedel, W., Schaeuble, R., Thielicke, B., Hiermaier, S.Failure mechanisms in layered composite materials for compressed hydrogen tanks 2004 FISITA World Automotive Congress 2004. Conference proceedings. CD-ROM , International Federation of Automobile Techniques Engineers -FISITA-, Barcelona» show abstract « hide abstract Abstract Storage systems for compressed hydrogen used in automotive applications are internally sealed by a diffusion barrier made of polyethylene or aluminium reinforced by a layer of several millimetres thick carbon fiber composite. A layer of impact resistant glass fiber covers the pressure vessel
against external impact damage on the carbon shell. For safety reasons tank systems are qualified by several standardized tests. The main reason for these tests is to ensure that nocatas trophic failure of the tank could occur. Investigation on catastrophic failure of high performance composite
materials was undertaken by testing and numerical simulation. Here the influence of preload during penetration of the laminate was investigated. A report of the current research is given. back to the year overview Hiermaier, S., Sauer, M.Adaptive FE-Meshfree-Modelling for Impacts of Liquid Filled Vessels on Thin Walled Structures 2003 Applied Mechanics and Biomedical Technology , pages : 43 - 48» show abstract « hide abstract Abstract A principal approach to simulate the airplane impact and the collapse of World Trade Center North Tower has been shown by Quan and Birnbaum [4]. Using the general purpose hydrocode AUTODYN the impact damage, fire induced strength reduction and progressive collapse were investigated. Both for
the fuel propagation after tank break up and the thermodynamic burn processes assumptions have been taken. It is the aim of this paper to focus on the numerical aspects of simulating the fluid propagation after vessel break up. The release of a fluid out of a broken vessel after impact is not easily
represented in a numerical simulation as the fluid flow and its interaction with structures can not be modelled using Lagrangian type element formulations. These elements, typically applied for structural analyses, fail under massive deformation and usually need then to be taken out of the
simulation. Typical fluid dynamic discretization methods, so called Eulerian grids, would have to cover the whole space potentially being reached by the fluid flow and are therefore inefficient in a large three dimensional simulation. As an alternative method a coupled discretization using Lagrange
elements and Lagrange type meshfree methods is proposed here. Meshfree methods have been introduced to structural dynamics more then ten years ago specifically to simulate processes including large deformation [1]. Originally developed as pure meshfree code, the EMI SOPHIA [3] provides now a new
form of adaptivity that allows for more efficiency and accuracy. This is achieved by the use of finite elements as long as deformation is capable for the elements. At definable strain or failure thresholds any element can be transformed into one or more meshfree particles. This way, mass and volume
of the original elements are conserved. As the particles interact with each other as well as with the remaining elements, all physical processes can be modelled continuously. The purpose of this study was to contribute to numerical simulation of the airplane impacts into the World Trade Center. It
includes impact simulations of cylindrical vessels filled with water against thin walled rectangular shaped bars. It shows that coupled discretizations and specifically an adaptive FE-meshfree discretization offer the flexibility needed to gain both accuracy and efficiency in the simulation. Wicklein, M., Sauer, M., Klomfass, A., Hiermaier, S., Thoma, K.Mesomechanical simulation of cellular aluminium 2003 Cellular metals: Manufacture, properties, applications , MIT-Verlag, Berlin, pages : 369 - 374 back to the year overview Corley, J., Riedel, W., Hiermaier, S., Weidemaier, P., Thoma, K.A combined experimental/computational approach for assessing the high strain rate response of high explosive simulants and other viscoelastic particulate composite materials 2002 Shock compression of condensed matter 2001. Pt.1 , American Institut of Physics, Melville, NY, pages : 705 - 708 Hiermaier, S., Sauer, M., Peter, J., Thoma, K.Modeling the continuum/discrete transition using adaptive meshfree methods 2002 Fifth World Congress on Computational Mechanics 2002. Book of abstracts. Vol.2 , TU Wien, Wien, page : 190 Hiermaier, S., Sauer, M., Thoma, K.Predictive crash simulation using adaptive finite methods 2002 Berechnung und Simulation im Fahrzeugbau , VDI-Verlag, Duesseldorf, pages : 27 - 38 Rohr, I., Hiermaier, S., Thoma, K.The erosion process during KE-Penetration: New experiments to investigate material behaviour 2002 20th International Symposium on Ballistics 2002. Proceedings. Vol.2: Terminal ballistics , DEStech Publications, Lancaster, Pa., pages : 1175 - 1181 back to the year overview Thoma, K., Riedel, W., Schaefer, F., Hiermaier, S.Hypervelocity impacts and protection 2001 Third European Conference on Space Debris 2001. Proceedings. Vol.2 , ESA Publications Division, Noordwijk, pages : 555 - 568 Palmieri, D., Schaefer, F., Hiermaier, S., Lambert, M.Numerical simulation of non-perforating impacts on shielded gas-filled pressure vessels 2001 Hypervelocity impact , Pergamon, Oxford, pages : 591 - 602 Heider, N., Hiermaier, S.Numerical simulation of the performance of tandem warheads 2001 19th International Symposium on Ballistics 2001. Proceedings. Vol.3: Warhead mechanics, vulnerability modeling , pages : 1493 - 1499 Schaefer, F., Herrwerth, M., Hiermaier, S., Schneider, E.Shape effects in hypervelocity impact on semi-infinite metallic targets 2001 Hypervelocity impact , Pergamon, Oxford, pages : 699 - 712 back to the year overview Thoma, K., Hiermaier, S., Riedel, W.Beton unter dynamischer Beanspruchung: Materialmodellierung, Messung von Parametern und numerische Simulation 1998 10. Forum Bauinformatik - Junge Wissenschaftler forschen , VDI-Verlag, Duesseldorf» show abstract « hide abstract Abstract Zur Berechnung von kurzzeitdynamischen Vorgaengen wie Impakt und explosiver Belastung werden Finite-Element-Programm vom Typ 'Hydrocodes' verwendet. Durch inkrementelle Stoffgesetze bei expliziter Zeitintegration sind sie zur Modellierung von komplexen Materialverhalten geeignet. Die
mechanischen Eigenschaften von Beton sind von Inhomogenit�t und Porosit�t gepr�gt. In dem Beitrag werden nichtlineare Materialmodelle der Kontinuumsmechanik unter Beruecksichtigung von Sch�digung mit mikromechanischen Ans�tzen verglichen. Die n�tigen Materialparameter werden am Ernst-Mach-Institut in
verschiedenen statischen Credits: SILK Icons by http://www.famfamfam.com/lab/icons/silk/