Mechanical changes in materials caused by explosive precompression shock waves and the effects on fragmentation of exploding cylinders

概要

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Explosive driven rapid fracture in a structural body will be preceded by a compression process, and the compression effects on mechanical properties of the materials are clearly important to understand shock-induced failure such as spall or fragmentation phenomena. In this study, incident shock waves in plate specimens of aluminum A2017-T4 and 304 stainless steel are generated by plane detonation waves in the high explosive PETN initiated using wire-row explosion techniques, and the compressed specimens are successfully recovered without severe damages due to the reflected expansion waves with use of momentum trap method. A hydro code, Autodyn-2D is applied to determine test conditions: thicknesses of explosives, attenuators, specimens and momentum traps and to evaluate experimental results, simulating time-histories of stress waves in the layers of the test assembly. Microhardness distributions in cross-sections, tensile strength, fracture ductility and yield stress are measured for the recovered specimens, using miniature tensile and compression test pieces machined from them. They are compared with those of virgin specimens, showing significant increase of hardness, tensile and yield strength and remarkable reduction of elongation and ductility for shocked specimens. The results are taken into consideration for evaluation of experimental fragmentation energy in cylinder explosion tests.