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Existing and emerging methods in computational mechanics are rarely validated against problems with an unknown outcome. For this reason, Sandia National Laboratories, in partnership with US National Science Foundation and Naval Surface Warfare Center Carderock Division, launched a computational challenge in mid-summer, 2012. Researchers and engineers were invited to predict crack initiation and propagation in a simple but novel geometry fabricated from a common off-the-shelf commercial engineering alloy. The goal of this international Sandia Fracture Challenge was to benchmark the capabilities for the prediction of deformation and damage evolution associated with ductile tearing in structural metals, including physics models, computational methods, and numerical implementations currently available in the computational fracture community. Thirteen teams participated, reporting blind predictions for the outcome of the Challenge. The simulations and experiments were performed independently and kept confidential. The methElectronic supplementary material The online version of this article (doi:10.1007/s10704-013-9904-6) contains supplementary material, which is available to authorized users.Sandia National Laboratories, Albuquerque, NM, USA e-mail: blboyce@sandia.gov ods for fracture prediction taken by the thirteen teams ranged from very simple engineering calculations to complicated multiscale simulations. The wide variation in modeling results showed a striking lack of consistency across research groups in addressing problems of ductile fracture. While some methods were more successful than others, it is clear that the problem of ductile fracture prediction continues to be challenging. Specific areas of deficiency have been identified through this effort. Also, the effort has underscored the need for additional blind prediction-based assessments.

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Metallic sandwich panels with prismatic cores offer the potential for superior blast resistance relative to monolithic plates of equivalent areal density. However, under sufficiently high impulse, severe plastic strains can occur at the junctions of the face sheets and the core members shortly after arrival of the pressure wave but prior to significant deformation elsewhere. The potential consequence is localized shear rupture with minimal plastic dissipation. To characterize this failure mode, a combined experimentalnumerical protocol has been used to ascertain the plastic strain for dynamic shear rupture of ductile metals. The experimental component involves firing cylindrical projectiles through plates of the targeted materials and monitoring changes in projectile velocity during penetration. With appropriate combinations of plate thickness and projectile velocity, penetration occurs through propagation of an annular shear crack. In parallel, a numerical model of dynamic deformation and rupture has been employed to infer the critical strain through comparisons with projectile velocity change measurements. Experiments and analyses have been performed on both 304 stainless steel and superaustenitic AL6XN. Effects of mesh size on the resolution of the predicted strain distribution and the plastic dissipation associated with penetration are addressed.