The Behavior of Ni, Ni-60Co, and Ni 3 Al during One-Dimensional Shock Loading
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I.
INTRODUCTION
THE response of materials to high loading rate situations has been a source of much interest since World War II. Typically, this has concentrated in the fields of ballistics and armor development, but more recently applications such as crash test worthiness, high rate forming and machining, satellite protection, and the aerospace industry have also made investigations in this area. In particular, the development of jet turbine engines requires knowledge of the response of materials to impact events of importance to understanding and developing predictive models describing material response under bird strike, foreign object damage, and blade containment loading environments. Shock wave testing of materials can be performed using a variety of techniques including explosive loading, and more commonly using launcher-driven plate impact. This technique uses a flat and parallel flyer plate, which is accelerated down a smooth bore gun either by a powder propellant breech or by using compressed gas. It is impacted onto an equally flat and parallel target plate, which is aligned to the flyer to a tolerance of less than 1 mradian (25 lm over 50 mm or 5 optical fringes). At high impact velocities (100 m s-1 and greater) a planar shock wave is generated, behind which conditions of one-dimensional (1-D) strain prevail (assuming the material is isotropic) until release waves from the edge of the target reach the measurement location. Under these conditions, the strain (e) is accommodated down the impact axis while the strains perpendicular to it are zero due to inertial confinement. As a consequence, there must be a confining stress (r) operating in these directions; thus, ex 6¼ 0 ¼ ey ¼ ez and rx 6¼ ry ¼ rz 6¼ 0
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J.C.F. MILLETT, Senior Scientist, and N.K. BOURNE, Distinguished Scientist, are with the AWE, Aldermaston, Reading RG7 4PR, United Kingdom. G.T. GRAY III, Laboratory Fellow, is with the MST-8, Los Alamos National Laboratory, Los Alamos, NM 87545, USA. Contact e-mail: [email protected] Manuscript submitted September 8, 2007. Article published online December 28, 2007 322—VOLUME 39A, FEBRUARY 2008
where x refers to the loading axis and y and z refer to the orthogonal directions to x. A more complete description of materials under shock loading conditions can be found in the review article of Davison and Graham.[1] The response of any material to external loading, at quasi-static strain rates or the extreme conditions of shock loading, will be governed by the microstructural features it possesses, such as crystalline structure, grain size, second phases, or previous strain history (i.e., dislocation and or twin density). The properties of metallic materials are often manipulated by the addition of alloy elements, and thus the effects of solution strengthening and precipitation hardening have been studied for a great many years. While such research has been performed in great detail for materials designed for applications under more conventional loading regimes, similar work for high-strain rate and im
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