Bulletin of the American Physical Society
18th Biennial Intl. Conference of the APS Topical Group on Shock Compression of Condensed Matter held in conjunction with the 24th Biennial Intl. Conference of the Intl. Association for the Advancement of High Pressure Science and Technology (AIRAPT)
Volume 58, Number 7
Sunday–Friday, July 7–12, 2013; Seattle, Washington
Session K1: ME.3 Inelastic Deformation, Fracture, and Spall II |
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Chair: K.T. Ramesh, Johns Hopkins University Room: Grand Ballroom I |
Tuesday, July 9, 2013 1:45PM - 2:00PM |
K1.00001: Influence of shock loading kinetics on the spall response of copper Juan Escobedo, Darcie Dennis-Koller, Ellen Cerreta, Brian Patterson, Curt Bronkhorst A suite of plate-impact experiments was designed and conducted to examine the influence of loading kinetics on the spall response of high purity copper samples. The density of grain boundaries dynamically loaded and peak compressive stresses (1.5GPa) were held constant for all experiments. The kinetics of the tensile pulses were designed using a hydrodynamic shock-wave propagation code and experimentally achieved by controlling the geometry of copper impactors and targets. Examination of damage fields shows that the total fraction of damage (voids) decreases as the tensile rates increase. In addition, an accompanying larger plastic dissipation, in the form of grain misorientation measured by means of electron backscatter diffraction, is present in the samples deformed at lower tensile rates. These results suggest a time dependent behavior of the processes that convert plastic dissipation into void growth. [Preview Abstract] |
Tuesday, July 9, 2013 2:00PM - 2:15PM |
K1.00002: High temperature impact response of copper Eugene Zaretsky, Gennady Kanel The evolution of elastic-plastic shock waves with the propagation distance has been studied in 99.999-{\%} purity polycrystalline copper. The free surface velocity histories of 0.1 to 2.0 mm thick samples shock-loaded from initial temperatures 300 to 1353 K, have been recorded using VISAR. Experiments confirmed anomalous growth of the HEL value with temperature. With approaching melting temperature the growth becomes stronger while the shape of the elastic precursor wave changes and becomes spike-like. These changes are possibly caused by the increase of the amount of lattice defects near melting. Results of measurements of the precursor decay at different initial temperatures have been converted into relationships between the shear stress and the initial plastic strain rate at the top of the precursor wave. The strain rate was found to decrease over 0.25 to 2-mm precursor traverse from $2\times 10^{6}$ to $6\times 10^{4}$s$^{-1}$ at 1353 K and from $7\times 10^{4}$ to $2.3\times 10^{3}$s$^{-1}$ at 300 K. An analysis of the rise times of the plastic shock waves has shown that for the same level of shear stress, the plastic strain rate at the shock front at 300 K is by a factor of 300 and at 1353 K is by a factor of 30 higher than just behind the elastic precursor front. [Preview Abstract] |
Tuesday, July 9, 2013 2:15PM - 2:30PM |
K1.00003: A Comparison of Multiple Techniques for Determining the Release Behaviour of a Simple FCC Metal Michael Lowe, David Chapman, Steve Rothman, Chris Robinson A shock compression pulse normally consists of a discontinuous rise in stress or pressure followed by a sustained period, if loaded using a technique such as plate impact, and terminated with a release back to ambient conditions over a finite time. Although historically a great body of work has been undertaken on the measurement and characterisation of the rise profile and plateau of many metals, minerals and other materials, the subsequent release phenomenon has tended not to be so vigorously investigated. This release behaviour is a compound effect, normally dependent upon the initial shock loading conditions and the distance within the subject material that the subsequent release effect has travelled. We discuss recent work undertaken on the development and testing of methodologies for investigating the release behaviour. These methods were employed to determine the release behaviour of a commonly available commercial C101 copper, the choice of which was made to minimise experimental complications due to any phase changes, microstructural effects or inherent material strength. [Preview Abstract] |
Tuesday, July 9, 2013 2:30PM - 3:00PM |
K1.00004: On the homogenous nucleation and propagation of dislocations under shock compression Invited Speaker: Hussein Zbib In strong shock regimes, homogenous nucleation of dislocation loops is believed to be the dominant mechanism of plastic deformation. We compare threshold stress for homogenous nucleation calculated by continuum elasticity and standards nucleation theory with multiscale dislocation dynamics plasticity (MDDP) predictions for copper single crystals. Several MDDP homogenous nucleation simulations are then carried out to investigate the state of stress and strain behind the wave front. The results show that the stress filed exhibits an elastic overshoot followed by rapid relaxation such that the1D state of strain is transformed into a 3D state of strain due to plastic flow. Based on MDDP results, we develop models for dislocation density evolution, saturated dislocation density, and stress relaxation time at different pressures. Moreover, an extension of high strain rate Orowan equation that accounts for homogenous nucleation is derived. The dependence of strain rate on the peak pressure shows good agreement with Swegle-Grady scaling law. [Preview Abstract] |
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