2ème atelier international
J. Phys. IV France 05 (1995) C4-89-C4-102
Dislocation Mechanisms for Shock-Induced Hot SpotsR.W. Armstrong
Department of Mechanical Engineering, University of Maryland, College Park, MD 20742, U.S.A.
Crystal dislocations provide the ultimate source of localized damage enhancement within solid materials. Vortices are the dislocation counterparts within liquids and gases. For energetic crystals, tubular holes might run along the pre-existent dislocation line lengths and act as shock-induced "in-situ" hot spots. Beyond this consideration, nearly invisible clouds of dislocations are possibly generated at point defects or point defect clusters by the shear stresses at a shock front. Multiple fine scale dislocation movements provide a mechanism for the shock to move to a hydrostatic stress state. Interatomic or intermolecular separations of the order of critical reaction coordinate distances are achievable during the unit dislocation displacements --- without change in material volume. Such nanoscale dislocation predictions connect with microscale experiments in a number of cases where larger scale "defect" considerations are involved. Dislocation pile-ups in slip band avalanches, often associated with cracking, account for very appreciable and localized heating that is deformation rate dependent. Complex dislocation slip band interactions occur within the plastic zones of macroscopic crack tips to control the fracture toughness properties of energetic and related materials.
© EDP Sciences 1995