Bulletin of the American Physical Society
20th Biennial Conference of the APS Topical Group on Shock Compression of Condensed Matter
Volume 62, Number 9
Sunday–Friday, July 9–14, 2017; St. Louis, Missouri
Session P3: Inelastic Deformations, Fracture and Spall IX |
Hide Abstracts |
Chair: Ivan Oleynik, University of South Florida Room: Grand Ballroom FG |
Wednesday, July 12, 2017 11:15AM - 11:30AM |
P3.00001: Elastic precursor wave decay in shock-compressed aluminum over a wide range of temperature Ryan Austin As a part of broader efforts to understand the dynamic strength of metals, precursor wave decay measurements are well-situated to probe time-dependent flow behavior at relatively high strain rates and low strain levels. Such measurements provide crucial data to help constrain models of underlying deformation mechanisms and microstructure evolution under shock wave loading. In previous work, wave structures were measured in aluminum plate impact experiments performed at temperatures ranging from 300 K to just below the ambient melting point (933 K). These measurements serve as a basis for evaluating and refining a dislocation-based model of high-rate metal plasticity. In the experiments, the precursor wave amplitudes were observed to increase with temperature. This effect is usually explained in terms of the temperature dependence of dislocation phonon scattering (i.e., the linear regime of damped dislocation mobility). However, the model predicts that phonon radiation provides a somewhat stronger damping effect at all temperatures, given the high speeds attained by the dislocations. The combined effects of phonon scattering and radiation then seem to be responsible for the measured precursor amplifications. [Preview Abstract] |
Wednesday, July 12, 2017 11:30AM - 11:45AM |
P3.00002: Towards an improved physical understanding of dynamic plasticity in FCC metals Lewis Lea, Andrew Jardine Above true strain rates of $10^4$ $s^{-1}$, FCC metals begin to exhibit a rapid increase in strength. Attempts at modelling this transition have led to two general theories as to the underlying mechanisms. Firstly, the drift velocity of the dislocations imparting strain has been proposed to become limited by viscous-like scattering with phonons in the metal. Meanwhile, other authors have proposed that the ever reducing timescale of slip gives rise to changes in the evolution of dislocation structure. Regardless of the chosen mathematical framework, the fundamental natures of the two proposed mechanisms provide testable qualitative predictions about material behaviour. In this study we will perform a variety of Hopkinson bar experiments on a OFHC grade copper to provide insight into which of these two mechanisms provides the most sound basis for developing reliable models of high rate metal plasticity. [Preview Abstract] |
Wednesday, July 12, 2017 11:45AM - 12:15PM |
P3.00003: Continuum dislocation-density based models for the dynamic shock response of single-crystal and polycrystalline materials Invited Speaker: Darby Luscher The dynamic thermomechanical responses of polycrystalline materials under shock loading are often dominated by the interaction of defects and interfaces. For example, polymer-bonded explosives (PBX) can initiate under weak shock impacts whose energy, if distributed homogeneously throughout the material, translates to temperature increases that are insufficient to drive the rapid chemistry observed. In such cases, heterogeneous thermomechanical interactions at the mesoscale (i.e. between single-crystal and macroscale) lead to the formation of localized hot spots. Within metals, a prescribed deformation associated with a shock wave may be accommodated by crystallographic slip, provided a sufficient population of mobile dislocations is available. However, if the deformation rate is large enough, there may be an insufficient number of freely mobile dislocations. In these cases, additional dislocations may be nucleated, or alternate mechanisms (e.g. twinning, damage) activated in order to accommodate the deformation. Direct numerical simulation at the mesoscale offers insight into these physical processes that can be invaluable to the development of macroscale constitutive theories, if the mesoscale models adequately represent the anisotropic nonlinear thermomechanical response of individual crystals and their interfaces. This talk will briefly outline a continuum mesoscale modeling framework founded upon local and nonlocal variations of dislocation-density based crystal plasticity theory. The nonlocal theory couples continuum dislocation transport with the local theory. In the latter, dislocation transport is modeled by enforcing dislocation conservation at a slip-system level through the solution of advection-diffusion equations. The configuration of geometrically necessary dislocation density gives rise to a back-stress that inhibits or accentuates the flow of dislocations. Development of the local theory and application to modeling the explosive molecular crystal RDX and polycrystalline PBX will be discussed. The talk will also emphasize recent implementation of the coupled nonlocal model into a 3D shock hydrocode and simulation results for the dynamic response of polycrystalline copper in two and three dimensions. [Preview Abstract] |
Follow Us |
Engage
Become an APS Member |
My APS
Renew Membership |
Information for |
About APSThe American Physical Society (APS) is a non-profit membership organization working to advance the knowledge of physics. |
© 2024 American Physical Society
| All rights reserved | Terms of Use
| Contact Us
Headquarters
1 Physics Ellipse, College Park, MD 20740-3844
(301) 209-3200
Editorial Office
100 Motor Pkwy, Suite 110, Hauppauge, NY 11788
(631) 591-4000
Office of Public Affairs
529 14th St NW, Suite 1050, Washington, D.C. 20045-2001
(202) 662-8700