Deformation substructures and terminal properties of explosively-loaded thin-walled stainless-steel cylinders

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Abstract
Thin-walled cylinders of 304 stainless steel were explosively expanded in a constrained system to produce strains ranging from 0.5 to 62%. A flash x-ray technique was employed to measure the strain rates from freely expanding cylinders where the limits of strain rates in this investigation were established as 1.6-4.4 × 104 sec−1. Fracture of the expanded cylinders was detected for strains in excess of 25%, and the number of cracks per unit circumferential length was observed to be roughly proportional to the expansion velocity as predicted by Mott. Scanning electron microscope observations established that a predominant tensile fracture character existed at the outer cylinder wall, in support of the cylindrical stress conditions derived based on the Tresca yield criterion. Direct observations of the terminal substructures in the cylinder walls using transmission electron microscopy showed that a high density of deformation twins and dislocations contributed to the residual hardening. A comparison of the residual defect character and density in the explosively formed 304 stainless-steel cylinders with that previously observed for plane-wave shock-loaded 304 stainless steel at equivalent terminal hardnesses suggests a significant contribution to hardening at high strains in explosively formed stainless steel may arise from an appreciable point defect concentration.

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