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.
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 |
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.
Verbund von Beton und Bewehrungsstahl bei hoch-dynamischer Belastung [Verbund von Beton und Bewehrungsstahl bei hoch-dynamischer Belastung: Entwicklung einer Konfiguration für Push-In-Versuche am Split-Hopkinson-Bar]
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.
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.