High Strain-rate Fracture and Fragmentation of Navy High Density Reactive Material

LT Erik Chamberlain, USN

Abstract: This thesis examines the dynamic fracture and fragmentation of a reactive material under development by the Navy for use in reactive fragment warheads. Several experimental techniques including gas gun impact and explosive launch were used to study the fracture behavior of the Navy’s current high density reactive material (HDRM). HDRM is fabricated via hot isostatic pressing of metal powders into a dense, low-ductility composite. Several unexpected fracture mechanisms, including widespread transgranular fracture of residual zinc particles, were observed in all tests. Tungsten inclusions, meant to enhance the density of HDRM, also appear to be natural nucleation points for failure and frequently appear next to residual pores. The majority of crack surfaces were dominated by failure at residual particle-particle interfaces, with an additional transgranular fracture component that varied with the rate of loading. Recovered fragment distributions of HDRM were reasonably consistent between gun and Hopkinson bar impact tests. Distributions were consistent with a bimodal Mott form with peaks at approximately 100 and 800 μm, well above the original size of constituent powders. The data suggest that removing tungsten may improve survivability of HDRM while retaining desirable fragmentation properties.

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Jul 07, 2015

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