Variations in Hardness with Position In One Dimensionally Recovered Shock Loaded Metals

G Whiteman,I.P Jones,B Pang,D.L Higgins,J.C.F Millett,Y-L Chiu

doi:10.1051/epjconf/201818302013

G Whiteman, I.P Jones + Show 4 more

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The microstructural and mechanical response of materials to shock loading is of the utmost importance in the development of constitutive models for high strain-rate applications. However, unlike a purely mechanical response, to ensure that the microstructure has been generated under conditions of pure one dimensional strain, the target assembly requires both a complex array of momentum traps to prevent lateral releases entering the specimen location from the edges and spall plates to prevent tensile interactions (spall) affecting the microstructure. In this paper, we examine these effects by performing microhardness profiles of shock loaded copper and tantalum samples. In general, variations in hardness both parallel and perpendicular to the shock direction were small indicating successful momentum trapping. Variations in hardness at different locations relative to the impact face are discussed in terms of the initial degree of cold work and the ability to generate and move dislocations in the samples.

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To successfully predict the physical behaviour of materials subjected to dynamic loads requires an understanding of, and ability to simulate, the underlying microscopic processes that govern the macroscopic response
Note in particular that there is no evidence of hardness deviations around the outer edges of these samples, which would be indicative of inadequate release capture across those interfaces
In the case of the cold rolled tantalum shocked to 7.2 GPa, note that there is no evidence of hardness changes around the outer edge, again indicating successful release capture

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Introduction

To successfully predict the physical behaviour of materials subjected to dynamic loads requires an understanding of, and ability to simulate, the underlying microscopic processes that govern the macroscopic response. Shock loading over a period of a few microseconds, over millimetre distances, relevant to many real world applications, requires plate-impact or explosive loading techniques. The viable option for studying microstructural response for these types of test is the post-shock metallographic study of samples, i.e. those which have been through a shock sequence consisting of a loading pulse, potentially a period held at pressure and a release back to ambient conditions. Each of these stages adds its own contributions to the deformation such that the microstructure obtained is cumulative in nature for the full loading/unloading event. This work has been adapted by the current authors to study polycrystalline copper [8,9,10] and tantalum [9, 10]

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