Bulletin of the American Physical Society
15th APS Topical Conference on Shock Compression of Condensed Matter
Volume 52, Number 8
Sunday–Friday, June 24–29, 2007; Kohala Coast, Hawaii
Session D3: Inelastic Deformation I |
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Chair: William Proud, University of Cambridge Room: Fairmont Orchid Hotel Plaza I |
Monday, June 25, 2007 3:45PM - 4:00PM |
D3.00001: Embedded Cohesive Elements (ECE) Approach to the Simulation of Spall Fracture Experiment Nicola Bonora, Luca Esposito, Andrew Ruggiero Discrepancies between the calculated and observed velocity vs time plot, relatively to the spall signal portion in terms of both signal amplitude and frequency, in numerical simulations of flyer plate impact test are usually shown. These are often ascribed either to material model or the numerical scheme used. Bonora et al. (2003 )[Bonora N., Ruggiero A. and Milella P.P., 2003, \textit{Fracture energy effect on spall signal}, Proc. of 13$^{th}$ APS SCCM03, Portland, USA] showed that, for ductile metals, these differences can be the imputed to the dissipation process during fracturing due to the viscous separation of spall fracture plane surfaces. In this work that concept has been further developed implementing an \textit{embedded cohesive elements} (ECE) technology into FEM. The ECE method consists in embedding cohesive elements (normal and shear forces only) into standard isoparametric 2D or 3D FEM continuum elements. The cohesive elements remain silent and inactive until the continuum element fails. At failure, the continuum element is removed while the ECE becomes active until the separation energy is dissipated. Here, the methodology is presented and applied to simulate soft spall in ductile metals such as OHFC copper. Results of parametric study on mesh size and cohesive law shape effect are presented. [Preview Abstract] |
Monday, June 25, 2007 4:00PM - 4:15PM |
D3.00002: Modeling Spallation Damage in Laser Driven Flyer Plate Experiments Davis Tonks, Dennis Paisley, Pedro Peralta, Scott Greenfield, Darrin Byler, Shengnian Luo, Damian Swift, Aaron Koskelo The TRIDENT laser at Los Alamos has been used to drive small plate impact experiments. Flyers are typically 8 mm in diameter and 0.1 to 1.0 mm thick, while the targets are 10 mm in diameters and 0.2 to 2.0 mm thick. The sample materials are polycrystalline copper and copper composed of large columnar grains. The latter samples reveal information about damage in single crystals and bi-crystals. This work will focus on simulating these experiments to reveal the stress loading histories and to evaluate damage modeling. As part of the former activity, the damage patterns in recovered samples due to edge effects will be explored with a conventional hydrocode and the TEPLA damage model. A crystal plasticity model in the ABAQUS hyrdocode will be used to assess the damage seen in the columnar samples. Models of void nucleation at special grain locations and dynamical void growth will be explored. [Preview Abstract] |
Monday, June 25, 2007 4:15PM - 4:30PM |
D3.00003: A new cavitation and spall criterion derived from probabilistics aspects of dynamic degradation in ductile materials. Application to tantalum spall behaviour. Gilles Roy, Francois Hild, Herve Trumel, Yves-Patrick Pellegrini Dynamic loadings produce high stress waves leading to the spallation of ductile materials such as aluminium, copper, magnesium or tantalum. The main mechanism used to explain the change in the number of cavities with stress rate is a nucleation inhibition induced by the growth of cavities already nucleated [F. Hild et al., to be submitted to J. App. Phys., 2007]. The dependence of the spall strength and critical time with the loading rate is investigated. The present approach is applied to analyse experimental data on a high purity tantalum grade. [Preview Abstract] |
Monday, June 25, 2007 4:30PM - 4:45PM |
D3.00004: ABSTRACT WITHDRAWN |
Monday, June 25, 2007 4:45PM - 5:00PM |
D3.00005: ABSTRACT WITHDRAWN |
Monday, June 25, 2007 5:00PM - 5:15PM |
D3.00006: Temporal Softening and its Effect upon Spall Strength Victor Skokov Experimental observation has revealed that the effects of shock wave loading are extremely complex, often resulting in morphological changes that result in a hardening of the material. Temporal softening that precedes the aforementioned hardening has also been observed. In Al and Cu, the duration of this softening is on the order of 0.3 to 0.5 $\mu$s. This work has revealed that, at least in some cases, this temporal softening phenomenon is attributable to the formation of complex bi-periodic twin structures. The overall morphology of these structures is rather complex, consisting of what we shall refer to as ``packages,'' with each ``package'' being composed of two sets of parallel twins aligned in a quasi-herringbone pattern. It is probable that the temperature within the ``package'' is much higher than the temperature of the surrounding material during ``package'' formation. The formation of bi-periodic twin structures and concomitant temporal softening has an effect upon spall strength. That effect is explored in the work to be presented. Samples are loaded by short duration pulses (0.3 -- 1 $\mu$s) in such a way that the onset of damage occurs within the period of temporal softening. This has enabled an assessment of the softening effect on spall strength. [Preview Abstract] |
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