High-pressure, laser-driven deformation of an aluminum alloy
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8/10/04
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High-Pressure, Laser-Driven Deformation of an Aluminum Alloy J.M. McNANEY, M.J. EDWARDS, R. BECKER, K.T. LORENZ, and B.A. REMINGTON Recent development of a laser-based experimental platform allows loading materials to high pressures in the solid state while controlling both strain rate and peak pressure. The drive utilizes momentum transfer from a plasma generated by the introduction of a strong shock in a reservoir of low-Z material. This study looks at the response of a commercial aluminum alloy (6061-T6) subjected to pressures of 18 and 40 GPa at strain rates of 107/s and 5 107/s, respectively. It was found that the depth of the crater formed on the sample surface is a good indicator of the general yield behavior of the material and that a relatively simple strength model prevails under the loading conditions considered here. Metallographic examination of recovered samples showed no evidence of shear-band formation or significant melting due to plasma-surface interactions. Crystal plasticity–based calculations were used to assess the effects of material texture. Lack of shear-band formation during the laser-based drive is rationalized by considering the strain gradient as compared to grain size and texture.
I. INTRODUCTION AND BACKGROUND
II. LASER DRIVE
THERE has been extensive work characterizing material response under shock-loading conditions over the past four to five decades. These studies have generally used gas-gun or high-explosive (HE)–driven impactors to load the material to pressures up to a few tens of gigapascals at strain rates up to 108 s1, with more-usual pressures and strain rates in the range of a few tens of gigapascals and 104 s1, respectively. Over the last few years, lasers[1,2] and the Z-machine (Sandia National Laboratory)[7,8,9] have been used to drive high-pressure shocks, up to 100 GPa, at strain rates of 107 to 108s1. The laser-driven experiments have utilized high-intensity, direct illumination of the material, over nanosecond timescales, to create a shock driven by material ablation, while the Z-machine uses a temporally shaped magnetic pulse to either compress materials directly or accelerate a projectile impactor. More recently, shockless drives based on lasers[3] and HE impactors[4,5,6] have been developed, which allow control over both the drive pressure and strain rate. The current work is in support of a much larger overall effort to measure strength by looking at the growth of Raleigh–Taylor instabilities in solid-state metals under highpressure, high-strain-rate loading conditions.[11] Specifically, the current research considers the use of the laser-generated shockless drive, referred to previously, to investigate the deformation behavior of a commercial aluminum alloy. Of particular interest is the formation of plastic-flow instabilities (shear bands), which strongly affect the continuum behavior of the material, and the interaction of plasma, which is used to generate the pressure pulse, with the sample surface.
A schematic of the
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