Williams-2014-On the shock stress, substructur.pdf

On the shock stress, substructure evolution, and spall response of commercially pure 1100-O aluminum C.L. Williams a,n, C.Q. Chen b, K.T. Ramesh b, D.P. Dandekar a a U.S. Army Research Laboratory, Aberdeen Proving Ground, MD 21005-5066, USA b The Johns Hopkins University, Baltimore, MD 21218-2681, USA a r t i c l e i n f o Article history: Received 1 July 2014 Received in revised form 3 September 2014 Accepted 5 September 2014 Available online 16 September 2014 Keywords: Shock stress Shock hardening Dynamic recovery Substructure Evolution Recovery a b s t r a c t Plate impact shock and spall recovery experiments were conducted to study the effects of peak shock stress on the substructure evolution and spall response of fully annealed 1100 aluminum. The substructure of the material evolves substantially with increase in peak shock stress ranging from 4 GPa to 9 GPa with dislocation debris uniformly distributed throughout the interior of the subgrain. Observations from substructure evolution in conjunction with spall failure results suggest that ductile fracture by void nucleation, growth, and coalescence was perhaps the dominant fracture mode for shock stresses up to approximately 8.3 GPa. Whereas, beyond 8.3 GPa the material softened possibly due to dislocation reorganization (dynamic recovery) and brittle intergranular fracture by decohesion with isolated pockets of nanovoids was perhaps the dominant fracture mode. The contributions of nanovoids to the dynamic recovery process, if any, were unresolved. Microhardness measurements show an increase in residual hardness throughout the shock stress range studied implying shock hardening up to approximately 8.3 GPa. This observation also suggests that thermal softening was not operative throughout the shock stress range studied. However, dynamic recovery was thermally influenced during shock loading. Published by Elsevier B.V. 1. Introduction Aluminum alloys such as the 2xxx, 5xxx, and 7xxx series are widely used in appl