Freiburg, Germany

The Fraunhofer Institute for High-Speed Dynamics , commonly known as the Ernst Mach Institute and also by the abbreviation Fraunhofer EMI, is a facility of the Fraunhofer Society in Germany. The Institute is based in Freiburg im Breisgau. Its activities are applied research and development in the fields of materials science and high-speed measurement techniques. The Institute also has offices in Efringen-Kirchen and Kandern.The name "Ernst Mach Institute" is named for the physicist Ernst Mach , who first used high-speed photography to visualize ballistic and gas-dynamic processes. Wikipedia.

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Wickert M.,Fraunhofer Institute for High-Speed Dynamics, Ernst-Mach-Institut
Proceedings of SPIE - The International Society for Optical Engineering | Year: 2017

Impact processes are highly transient processes requiring high time resolution for diagnostics techniques. Fraunhofer EMI performs impact and other highly dynamic experiments under laboratory conditions, allowing close-proximity observation of events with the dissipation of high amounts of energy leading to failure of structure and materials upon extreme dynamic loading. High-speed camera techniques have improved massively over the last decades, especially the capability for microsecond video. This development has paralleled the evolvement of the tools for the numerical simulation of impact processes. The presentation reviews many examples from various research projects and shows how the application of high-speed imaging has evolved over the years and how it has brought in-situ insights into the dynamics of impact processes, accompanied by the complementary use of flash X-ray diagnostics. This gives insight into the material response of different classes of materials upon impact and provides a thorough base for modeling dynamic material behavior including failure. © 2017 SPIE.

May M.,Fraunhofer Institute for High-Speed Dynamics, Ernst-Mach-Institut
Composites Part A: Applied Science and Manufacturing | Year: 2016

Composite materials are often subjected to mechanical impact causing delamination. For quasi-static loading, measuring the mode I fracture toughness has been standardized. However, for high-rate loading, additional challenges arise. Consequently, no standard test has yet been defined for measuring the mode I fracture toughness under high rates of loading. This article therefore reviews candidate tests for measuring the high-rate mode I fracture toughness. Strength and weaknesses of different specimen designs and test setups are shown. Different approaches to measuring crack growth and loads are presented. The different approaches are compared and recommendations are provided for measuring the mode I fracture toughness of composites under high rates of loading. © 2015 Elsevier Ltd.

Mechtcherine V.,TU Dresden | Millon O.,Fraunhofer Institute for High-Speed Dynamics, Ernst-Mach-Institut | Butler M.,TU Dresden | Thoma K.,Fraunhofer Institute for High-Speed Dynamics, Ernst-Mach-Institut
Cement and Concrete Composites | Year: 2011

This paper describes the material behaviour of a strain hardening cement-based composite (SHCC) at high strain rates. The results of highly dynamic spall experiments using a Hopkinson bar at strain rates 140-180 s -1 are arrayed against the results of quasi-static uniaxial tensile tests at strain rates of 0.001 s-1. This comparison is based on the values of tensile strength, Young's modulus, and fracture energy of the specimens. In addition, the experimental results of SHCC are related to the characteristic values of other concrete types. Differences in material behaviour are explained by the phenomena of crack formation and fibre pullout resistance. © 2010 Elsevier Ltd.

Krell A.,Fraunhofer Institute for Ceramic Technologies and Systems | Strassburger E.,Fraunhofer Institute for High-Speed Dynamics, Ernst-Mach-Institut
Ceramic Engineering and Science Proceedings | Year: 2013

The study addresses (1) the impact (i) of ceramic microstructures and (ii) of the deformation of the ceramic/backing composite on ceramic fragmentation and resulting projectile erosion, and (2) other materials influences which may affect the abrasive destruction of the penetrator via the mechanical properties of the ceramics (Young's modulus E, hardness, HEL, bending/compressive strength, Klc). Regarding the highly dynamic interaction, the study had to find out whether all mechanical parameters must be dynamically recorded for understanding the ballistic performance. The results show that the ballistic strength of Al2O3 and spinel ceramics and single crystals with different backings (steel, aluminum, glass) is subject to a 3-fold hierarchy of influences: 1. Top priority is the ceramic fragmentation governed by the microstructure and by the dynamic stiffness (not simply by the Young's modulus E) of the ceramic/backing target. These influences also affect the relative importance of dwell and penetration phases. 2. On a middle rank, E and the dynamic stiffness of the ceramic are responsible for the projectile deformation during dwell. 3.On penetration, the abrasive benefit of a high ceramic hardness depends on the size of the ceramic debris, i.e. on ceramic fragmentation; this effect increases the projectile erosion by ceramics with glass backing compared with Al backing. In contrast, all strength data are weakly correlated with the ballistic figure. This hierarchy explains apparently contradictive findings of the past.

May M.,Fraunhofer Institute for High-Speed Dynamics, Ernst-Mach-Institut
Composite Structures | Year: 2015

This paper compares four cohesive zone models for modeling delamination caused by impact on composite materials. The four cohesive zone models differ by the way rate-dependent material properties, such as strength and fracture toughness, are treated. The influence of the cohesive zone model formulation on the prediction of delamination size is evaluated using the numerical example of a dynamic punch test. It is demonstrated that the use of strain-rate dependent material models significantly influences the numerical result. It is also shown that both, the rate-dependent strength and the rate-dependent fracture toughness, must be considered. © 2015 Elsevier Ltd.

Tham R.,Fraunhofer Institute for High-Speed Dynamics, Ernst-Mach-Institut
EPJ Web of Conferences | Year: 2012

In order to characterize materials with respect to their susceptibility to shear band formation at high strain rates, a modified Hopkinson pressure bar apparatus and hat-shaped steel specimens with a shear zone having a width significantly larger than the typical width of adiabatic bands are used. The sample is directly impacted by the striker. The force acting on the sample is measured with a PVDF-gauge between the sample and the output bar. The displacement is recorded with an electro-optical extensometer. The energy absorbed by the shearing process up to failure can be used as a reference for the susceptibility of materials to shear band formation. The method is demonstrated comparing the shear behavior of two high-strength steels with similar metallic structure and strength. Differences were found in the transition region between quasi-static and fully adiabatic shearing conditions where the energy up to rupture differs by 40 %. For fully adiabatic shear band formation, the deformation process of both materials equals. At extreme rates, shear processes are mainly governed by the thermodynamic properties of the materials. On the other hand, strength and structural properties play a role for low and intermediate rates where global and localized shear mechanisms occur in parallel. © Owned by the authors, 2012.

Ganzenmuller G.C.,Fraunhofer Institute for High-Speed Dynamics, Ernst-Mach-Institut | Hiermaier S.,Fraunhofer Institute for High-Speed Dynamics, Ernst-Mach-Institut | Steinhauser M.O.,Fraunhofer Institute for High-Speed Dynamics, Ernst-Mach-Institut
Soft Matter | Year: 2011

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 H 2O 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 ≲ 3000 ms -1, we observe reversible damage, whereas for speeds ≳ 3900 ms -1 no such recovery, or self-repair of the bilayer, could be observed. © 2011 The Royal Society of Chemistry.

Ganzenmuller G.C.,Fraunhofer Institute for High-Speed Dynamics, Ernst-Mach-Institut | Patey G.N.,University of British Columbia
Physical Review Letters | Year: 2010

We report a computer simulation study of an electroneutral mixture of oppositely charged oblate ellipsoids of revolution with aspect ratio A=1/3. In contrast with hard or soft repulsive ellipsoids, which are purely nematic, this system exhibits a smectic-A phase in which charges of equal sign are counterintuitively packed in layers perpendicular to the nematic director. © 2010 The American Physical Society.

Ganzenmuller G.C.,Fraunhofer Institute for High-Speed Dynamics, Ernst-Mach-Institut
Computer Methods in Applied Mechanics and Engineering | Year: 2015

This paper presents a stabilization scheme which addresses the rank-deficiency problem in meshless collocation methods for solid mechanics. Specifically, Smooth-Particle Hydrodynamics (SPH) in the Total Lagrangian formalism is considered. This method is rank-deficient in the sense that the SPH approximation of the deformation gradient is not unique with respect to the positions of the integration points. The non-uniqueness can result in the formation of zero-energy modes. If undetected, these modes can grow and completely dominate the solution. Here, an algorithm is introduced, which effectively suppresses these modes in a fashion similar to hour-glass control mechanisms in Finite-Element methods. Simulations utilizing this control algorithm exhibit much improved stability, accuracy, and error convergence properties. In contrast to an alternative method which eliminates zero-energy modes, namely the use of additional integration points, the here presented algorithm is easy to implement and computationally very efficient. © 2014 Elsevier B.V.

Sauer M.,Fraunhofer Institute for High-Speed Dynamics, Ernst-Mach-Institut
International Journal of Impact Engineering | Year: 2011

This paper presents a numerical study on the simulation of impacts of projectiles on fluid-filled containers. The type of impact investigated leads to hydrodynamic ram (HRAM) and complete failure of the container shell. Two different numerical approaches are compared which are both implemented in a research hydrocode: a pure Lagrangian discretization with Finite Elements (FE) and element erosion, and a coupled adaptive FE/SPH discretization. The numerical results are compared with two reference experiments. The principal phenomenology including the container deformation could be modeled well with both methods. The coupled FE/SPH approach was superior in the reproduction of the projectile's observed residual velocity, it is, however, computationally more expensive.

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