Michael E. Nixon

New Anisotropic Constitutive Models For HCP Sheet Forming Simulations

In this paper, we present a new macroscopic isotropic yield criterion expressed in terms of the principal values of the stress deviator that captures the asymmetry in yielding between tension and compression. Comparisons with the results of polycrystalline simulations performed by Hosford and Allen show that this isotropic criterion describes very well the asymmetry in yielding due to activation of twinning. Furthermore, extensions of this criterion to orthotropy are presented. To introduce anisotropy we use two approaches: (a) the generalized invariants approach of Cazacu and Barlat, and (b) the linear transformation approach (Barlat et al.). The ability of the proposed formulations to describe both the asymmetry and anisotropy in yielding of hcp (Mg‐Li) sheet is demonstrated.

Initiation of Polymer Bonded Explosive (PBXN-110) by Combined Shock and Shear Loading

Combined shock and shear loading of explosives has been shown to result in detonation of explosives at input pressures less than those required with a nearly planar shock. In this study, the effect of combined shock and shear loading on PBXN‐110 is investigated. The explosive sample is loaded by a TNT/Octol plane wave lens or a Pentolite pad in contact with a layer of PMMA followed by a cylindrical wave shaper that has one side angled at 45 degrees. The experiment is repeated for different thicknesses of the PMMA layer in order to vary the input pressure. In addition, the experiment is modeled using the Lagrangian finite element hydrocode EPIC, and the results of the experiments are compared with the numerical simulations.