Mechanical Properties Of High Density Reactive Material

LT Robert L. Ross, USN

Abstract: This thesis examines the mechanical properties of the Navy's High Density Reactive Material (HDRM) that is under consideration for use in Navy warheads. HDRM is a metal composite designed to meet the competing requirements of surviving warhead launch but still fragmenting and igniting upon striking a target. In this thesis we report experimental analysis of the hardness, toughness, quasi-static compressive yield stress, and dynamic compressive yield stress of HDRM. The yield strength of HDRM in quasi-static compression is about 330 MPa, increasing to roughly 600 MPa under compressive uniaxial stress at strain rates of 103 s-1. A series of Hopkinson bar impacts were performed and a temperature-independent Johnson Cook type model was used to develop a viscoplasticity model. High strain-rate tests showed a dramatic upturn in the rate-dependence of the dynamic yield strength of HDRM above 102 s-1, which is likely attributable to the zinc component. Izod pendulum impact on notched HDRM samples placed their fracture energy values close to that of a brittle ceramic such as Al2O3. As-received HDRM has a Vickers hardness of about 104, which increases only slightly following 28% strain in a Hopkinson bar at rates of roughly 3500 s-1. Samples recovered from explosive launch, however, show a sizable increase in hardness from the detonation-induced shock. Measurements of the longitudinal and shear wave speeds in HDRM indicate that the Young's modulus is 94 GPa and the Poisson's ratio is 0.24.

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Jul 07, 2015

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