Stress bridging in a heterogeneous material

The fracture process of a material denoted PBS 9501 sugar mock, a simulant of the PBX 9501 high explosive, was studied using the optical technique of Coherent Gradient Sensing (CGS) interferometry. We found that in the PBS 95 01 sugar mock material, crack initiation and propagation are preceded by th e formation and extension of a sizable stress-bridging zone. Two mechanisms were identified as contributing to the bridging process. One is crystal in terlocking and Friction, and the other is binder stretching. By comparing t he experimental CGS fringe pattern with one simulated using a simple bridgi ng model, we found that the overall behavior of the bridging zone is harden ing, which is consistent with the fact that majority of the bridging region is dominated by a binder stretching mechanism. We conclude that the entire process of stress-bridging initiation and extension, as well as subsequent crack propagation, has to be considered in describing the fracture behavio r of high explosive materials. (C) 2000 Elsevier Science Ltd. All rights re served.