Fraunhofer Institute For Kurzzeitdynamik

Freiburg, Germany

Fraunhofer Institute For Kurzzeitdynamik

Freiburg, Germany
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Bach A.,Schussler Plan Ingenieurgesellschaft | Stolz A.,Fraunhofer Institute For Kurzzeitdynamik | Noldgen M.,Cologne University of Applied Sciences | Thoma K.,Fraunhofer Institute For Kurzzeitdynamik
Beton- und Stahlbetonbau | Year: 2013

Within the design of reinforced concrete against explosive threats only a subjective or a lump safety is currently considered. Therefore the established safety is unknown. For the estimation of the existing safety of present approaches the SDOF approach has been linked to the first order reliability method, which allows for a derivation of the given reliability. Hereby it could be proven that the considered safety is, compared to the claimed reliability of the Eurocode (EC0), deficient. Copyright © 2013 Ernst & Sohn Verlag für Architektur und technische Wissenschaften GmbH & Co. KG, Berlin.

Riedel W.,Fraunhofer Institute For Kurzzeitdynamik | Noldgen M.,Cologne University of Applied Sciences | Stolz A.,Fraunhofer Institute For Kurzzeitdynamik | Wassmann W.,Schussler Plan Ingenieurgesellschaft MbH
Beton- und Stahlbetonbau | Year: 2013

Aircraft impact is taken into account as exceptional load case for exposed critical infrastructure such as nuclear plants and super-rise buildings. This contribution introduces the development and validation of new building concepts based on high performance concretes (HPC, UHPC). A high-rise building [1, 2] and a superstructure for existing nuclear power plants [2, 3] serve as examples with high performance concretes allowing innovative designs. The design methods "Two-Degree-of-Freedom Model" (TDOF, in German ZMS) and Finite Element Methods for transient and structural dynamics are used together with own validation experiments [5, 6] to derive the limit thicknesses of (ultra) high performance concrete elements with fiber reinforcement, protecting the vital zones of the buildings against impact and fire. Copyright © 2013 Ernst & Sohn Verlag für Architektur und technische Wissenschaften GmbH & Co. KG, Berlin.

Hoerth T.,Fraunhofer Institute For Kurzzeitdynamik | Schafer F.,Fraunhofer Institute For Kurzzeitdynamik | Nau S.,Fraunhofer Institute For Kurzzeitdynamik | Kuder J.,Fraunhofer Institute For Kurzzeitdynamik | And 3 more authors.
Journal of Geophysical Research E: Planets | Year: 2014

In the present study we introduce an innovative method for the measurement of impact-induced pressure waves within geological materials. Impact experiments on dry and water-saturated sandstone targets were conducted at a velocity of 4600m/s using 12mm steel projectiles to investigate amplitudes, decay behavior, and speed of the waves propagating through the target material. For this purpose a special kind of piezoresistive sensor capable of recording transient stress pulses within solid brittle materials was developed and calibrated using a Split-Hopkinson pressure bar. Experimental impact parameters (projectile size and speed) were kept constant and yielded reproducible signal curves in terms of rise time and peak amplitudes. Pressure amplitudes decreased by 3 orders of magnitude within the first 250mm (i.e., 42 projectile radii). The attenuation for water-saturated sandstone is higher compared to dry sandstone which is attributed to dissipation effects caused by relative motion between bulk material and interstitial water. The proportion of the impact energy radiated as seismic energy (seismic efficiency) is in the order of 10-3. The present study shows the feasibility of real-time measurements of waves caused by hypervelocity impacts on geological materials. Experiments of this kind lead to a better understanding of the processes in the crater subsurface during a hypervelocity impact. © 2014. American Geophysical Union.

Kupka F.,University of Vienna | Losch M.,Alfred Wegener Institute for Polar and Marine Research | Zaussinger F.,TU Brandenburg | Zweigle T.,Alfred Wegener Institute for Polar and Marine Research | Zweigle T.,Fraunhofer Institute For Kurzzeitdynamik
Meteorologische Zeitschrift | Year: 2015

Fluid stratified by gravitation can be subject to a number of instabilities which eventually lead to a flow that causes enhanced mixing and transport of heat. The special case where a destabilizing temperature gradient counteracts the action of a stabilizing gradient in molecular weight is of interest to astrophysics (inside stars and giant planets) and geophysics (lakes, oceans) as well as to some engineering applications. The detailed dynamics of such a system depend on the molecular diffusivities of heat, momentum, and solute as well as system parameters including the ratio of the two gradients to each other. Further important properties are the formation and merging of well-defined layers in the fluid which cannot be derived from linear stability analysis. Moreover, the physical processes operate on a vast range of length and time scales. This has made the case of semi-convection, where a mean temperature gradient destabilizes the stratification while at the same time the mean molecular gradient tends to stabilize it, a challenge to physical modelling and to numerical hydrodynamical simulation. During the MetStröm project the simulation codes ANTARES and MITgcm have been extended such that they can be used for the simulations of such flows. We present a comparison of effective diffusivities derived from direct numerical simulations. For both stars and the oceanic regimes, the Nusselt numbers (scaled diffusivities) follow similar relationships. Semi-convection quickly becomes inefficient, because the formation of layers limits vertical mixing. In contrast to the complementary saltfingering, these layers tend to damp instabilities so that effective diffusivities of salinity (concentration) are up to two orders of magnitudes smaller than in the former case. © 2015 The authors.

Eaton M.,University of Cardiff | May M.,Fraunhofer Institute For Kurzzeitdynamik | Featherston C.,University of Cardiff | Holford K.,University of Cardiff | And 2 more authors.
Journal of Physics: Conference Series | Year: 2011

Detection and characterisation of damage in composite structures during in-service loading is highly desirable. Acoustic emission (AE) monitoring of composite components offers a highly sensitive method for detecting matrix cracking and delamination damage mechanisms in composites. AE relies on the detection of stress waves that are released during damage propagation and using an array of sensors, damage location may be determined. A methodology for damage characterisation based on measuring the amplitude ratio (MAR) of the two primary lamb wave modes; symmetric (in-plane) and asymmetric (out-of-plane) that propagate in plate like structures has been developed. This paper presents the findings of a series of tensile tests in composite coupons with large central ply blocks. The specimens were monitored using AE sensors throughout loading and once significant AE signals were observed the loading process was stopped. The specimens were removed and subjected to x-ray inspection to assess for any damage. The onset of damage was successfully detected using AE and was identified as being matrix cracking using the MAR methodology. The results were validated with x-ray inspection and a strong correlation was observed between the number of significant AE signals recorded and the number of identified matrix cracks. © 2011 Published under licence by IOP Publishing Ltd.

Anderson Jr. C.E.,Southwest Research Institute | Behner T.,Fraunhofer Institute For Kurzzeitdynamik | Holmquist T.J.,Southwest Research Institute
International Journal of Impact Engineering | Year: 2011

Reverse ballistic experiments were used to investigate confinement, pre-damaged and intact, and rod size effects on penetration of long, gold rods into silicon carbide (SiC-N). Rod diameters were 1.0 mm and 0.75 mm, and lengths were 70 mm and 50 mm, respectively. Within data scatter, penetration velocity was the same for intact (bare or sleeved), pre-damaged (thermally shocked with non-contiguous cracks), and in situ comminuted SiC-N. Penetration velocity was independent of rod diameter within the data scatter. An expression for the penetration velocity versus impact velocity is found using linear regression. It is proposed that the reason there is no difference in the penetration rate between intact and pre-damaged (failed) SiC is because, after the first few microseconds following impact, the rod penetrates failed material in both cases. © 2011 Elsevier Ltd. All rights reserved.

Anderson Jr. C.E.,Southwest Research Institute | Holmquist T.J.,Southwest Research Institute | Orphal D.L.,International Research Associates Inc. | Behner T.,Fraunhofer Institute For Kurzzeitdynamik
International Journal of Applied Ceramic Technology | Year: 2010

We have conducted impact experiments using gold long rods into borosilicate glass and the measured the penetration velocity as a function of impact velocity. At sufficiently low-impact velocities, the glass target resists penetration and there is dwell; dwell is observed to approximately 450 m/s for bare glass. If a copper buffer is placed over the glass to eliminate the impact shock, significant dwell can be seen at impact velocities as high as 890 m/s. These impact velocities correspond to Bernoulli stresses of approximately 2.0 and 7.6 GPa, respectively. The paper describes the experimental data, and summarizes the results and our findings. © 2010 The American Ceramic Society.

Aberg D.,BAE Systems | Hermansson P.,BAE Systems | Sattler A.,Fraunhofer Institute For Kurzzeitdynamik | Rakus D.,Fraunhofer Institute For Kurzzeitdynamik
IEEE Transactions on Plasma Science | Year: 2015

The ignition of LOVA gun propellants at low loading densities is of interest for future gun systems with insensitive modular charges. The ignition system in conventional propellant systems is traditionally optimized for high loading densities. There is a need to be able to control the ignition for the envelop of the system, to reduce unburnt propellant at low loading densities and, at the same time, avoid pressure waves at high loading densities. Plasma ignition is interesting for this application, with the possibility to vary ignition energy and with the plasma plume penetrating deep into the propellant bed to achieve uniform ignition. This paper presents results from plasma ignition experiments in a 45-mm gun system, using NL008, an RDX-based CAB-LOVA propellant. The plasma igniter is a capillary jet type, driven by a pulse-forming network. A zero-dimensional model for the plasma igniter has been developed and will be discussed in the context of the experiments. © 2015 IEEE.

Michal M.,University of Federal Defense Munich | Keuser M.,University of Federal Defense Munich | Millon O.,Fraunhofer Institute For Kurzzeitdynamik
Beton- und Stahlbetonbau | Year: 2016

Bond of concrete and steel under high dynamic loading Against the background of increasing terrorist thread for critical infrastructure, it is necessary to consider the high strain rates related with explosion and impact for the design of structural components. The precondition for this is a realistic characterization of the material behavior. In meso-level the interaction of steel and concrete is described by bond. In order to assess the behavior of structures exposed to high rate loading correctly, even the knowledge of strain rate dependent bond behavior is required. Within the ongoing research project RS1510 at the University of the Bundeswehr München (UniBwM) tests on bond between steel and concrete with a split-hopkinson-bar (SHB) are currently performed in collaboration with the Fraunhofer Institute for High-Speed Dynamics Ernst-Mach Institute (EMI). The results will be used as a basis for the development of a numerical model for the simulation of bond between steel and concrete under high loading rates. After a short survey on bond behavior, the theoretical basis for the testing technology is given and the specific characteristics of the performed push-in tests are explained. The results of the tests show a clear tendency for the rate-dependent increase in bond strength. © 2016 Ernst and Sohn Verlag für Architektur und technische Wissenschaften GmbH and Co. KG, Berlin.

Millon O.,Fraunhofer Institute For Kurzzeitdynamik | Mechtcherine V.,TU Dresden | Thoma K.,Fraunhofer Institute For Kurzzeitdynamik | Butler M.,TU Dresden
Beton- und Stahlbetonbau | Year: 2010

This paper describes the material behaviour of Strain Hardening Cementitious Composite (SHCC) at high strain rates. The results of high dynamic spall experiments using a Hopkinson Bar at strain rates > 140/sec were arrayed against the results of quasistatic, centric tensile tests at strain rates of 0,001/sec. This comparison is based on the parameters of tensile strength, elastic 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 force. © 2010 Ernst & Sohn Verlag für Architektur und technische Wissenschaften GmbH & Co. KG, Berlin.

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