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 H3: Stress-Strength Measurements I |
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Chair: Tracy Vogler, Sandia National Laboratories Room: Fairmont Orchid Hotel Plaza I |
Tuesday, June 26, 2007 1:45PM - 2:00PM |
H3.00001: Phenomenological viscous-elastic-plastic model of dynamic yield of Cu Olga Ignatova Taken together, the fundamental mechanisms that govern material flow under conditions of intensive loading comprise a multifaceted set, with each facet possessing its own domain of influence. These mechanisms include dislocation multiplication, grain size modification, twinning, and the formation of periodic shear bands during high-rate deformation. Existing flow stress models do not possess the capability of accounting for all of these mechanisms.Existing models are, for the most part, empirical. Those which attempt to account for the fundamental mechanisms responsible for material flow tend to be based on dislocation mechanics. Some include a number of internal state variables to try to account for history-dependent changes in morphology. None accounts for the full complexity of material behavior. An observation that can be made of existing models is that the greater the number of physical mechanisms accounted for, the greater the number of empirical parameters. In this work we present a new phenomenological elastic-viscoplastic flow stress model for M1 copper that accounts for variations in grain size, and does so with a reasonably small set of empirical parameters. [Preview Abstract] |
Tuesday, June 26, 2007 2:00PM - 2:15PM |
H3.00002: Application of Lagrangian Analysis to the Unloading Velocity-Time Signals of Flyer-Plate Experiments James Stolken, Mukul Kumar, Jeffrey Nguyen, Reed Patterson Lagrangian analysis (LA) has been applied to a broad range of dynamic solid-state experiments over the last forty years to infer material constitutive behavior under complex loading conditions and provides the analytical foundation to interpret current state-of-the-art experiments probing both the Equation-of-State and Deformation properties of materials. Using a combination of high-resolution computer hydro-code simulations and gas-gun driven flyer-plate experimental data, a new method of LA is developed that combines the two methods due to D.C. Wallace and P.J. Chen to infer the normal stress and strain response of the material just prior to unloading. This new method of LA is applied to infer the stress-strain response of copper samples of varying grain size. In the case of ductile metals, the results suggest an alternate interpretation of the ``elastic'' unloading response on release as a ``plastic'' reloading wave produced as the result of an elastic transition from compressive to tensile loading. Extensions to ``re-shock'' experiments and the development of three-stepped targets to explore the nature of the ``plastic'' reloading waves are discussed. This work was performed under the auspices of the U.S. Department of Energy by University of California, Lawrence Livermore National Laboratory under Contract W-7405-Eng-48. [Preview Abstract] |
Tuesday, June 26, 2007 2:15PM - 2:30PM |
H3.00003: Longitudinal and Lateral Stress Measurements in Stainless Steel 304 Under 1D Shock Loading G. Whiteman, J.C.F. Millett, R.E. Winter, N.K. Bourne Interest in the behaviour of the common stainless steel grade 304 at high rates of strain is always high due to the materials regular use in industry. Longitudinal and lateral stresses during the shock loading of stainless steel 304 have been measured using manganin stress gauges. The shear strength has been shown to increase with impact stress. Comparison with a pure fcc metal (nickel) shows a significant increase in strength. Strengths are similar to those of mild steel, but the rate of increase with impact stress is much greater in SS304. These results are discussed in terms of structure and degree of alloying. [Preview Abstract] |
Tuesday, June 26, 2007 2:30PM - 2:45PM |
H3.00004: Shear Strength of Aluminum Oxynitride Dattatraya P. Dandekar, Brian A. M Vaughan, William G. Proud Aluminum oxynitride (AlON) is a transparent, polycrystalline cubic spinel. The results of investigations$^{1-4}$ on shock response of AlON permit determination of the equation of state, and shear strength retained under shock compression. Whereas the values of the HEL of AlON holds no surprises, the inelastic response of AlON reported in Ref. 1-4 differ significantly and is stress dependent. The results of Ref. 1-2 show that AlON retains a shear strength of 3 to 4 GPa when shocked up to around 20 GPa, but the results of Ref, 3-4 seem to suggest a possible loss of shear strength when shocked to 16 GPa and beyond. Our analysis examines the observed differences in the inelastic response of AlON reported in these four studies . 1. J. U. Cazamias, et. al., in Fundamental Issues and Applications of Shock-Wave and High Strain Rate Phenomena, Eds. Staudhammer, Murr, and Meyers, Elsevier, NY, 173 (2001). 2. B. A. M. Vaughn, et.al., Shock Physics, Cavendish Laboratory, Report SP/1092 (2001) 3. T. Sekine, et.al., \textit{J. Appl. Phys.} \textbf{94}, 4803 (2003). 4. T. F. Thornhill, et.al., Shock Compression of Matter-2005, Eds. Furnish, Elert, Russell, White, AIP, NY, 143 (2006). [Preview Abstract] |
Tuesday, June 26, 2007 2:45PM - 3:00PM |
H3.00005: Shear strength and HEL's for various geological materials C.H. Braithwaite, W.G. Proud, J.E. Field, A.R. Guest Previous investigations (Braithwaite, Proud and Field: SCCM 2005, pp1435-1438) into geological materials have shown that for some materials no change in slope is seen in the Hugoniot curve up to values of 10 GPa (depending on the rock type). These shock pressures are well above the expected elastic limits of the materials. There is some hysteresis seen in release curves above a certain stress level. By using the plate impact facility it was possible to measure the shear strength of the materials and determine region of the HEL. It is shown that the start of hysterestic behaviour in the release paths does not correspond to the HEL. [Preview Abstract] |
Tuesday, June 26, 2007 3:00PM - 3:15PM |
H3.00006: Shear strength and its variation according to structure in shock-loaded polyethylene Jeremy Millett, Neil Bourne, Eric Brown, George Gray In a recent series of papers, we have made a study of the shock response of a number of polymers, whilst systematically changing their structure, for example side group size (polyethylene, polypropylene and polystyrene) or replacement of hydrogen atoms (polyethylene, polyvinylidene difluoride and polytetrafluoroethylene). In this study, we examine a single polymer, polyethylene in two structural forms -- high molecular weight and cross-linked. In particular, the shock induced shear strength is determined, and the effects of structural variation noted. [Preview Abstract] |
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