Shock Wave Compression of Hardened and Annealed 2024 Aluminum

Abstract

Measurements of the Hugoniot equations of state of hardened and annealed 2024 aluminum at pressures below 50 kbar are presented. The major aim of the experiments was to determine the validity of elastic‐plastic theory, which predicts that, at a given compression, the stress normal to the shock front is larger than the hydrostatic pressure necessary to produce the same compression by an amount equal to two‐thirds the yield strength in simple tension. Oblique shock geometry was employed. Shock and free‐surface velocities were recorded with a streak camera by means of a light‐reflection technique employing the principle of the optical level. This technique provides continuous recording of free‐surface motion with time, an essential requirement because of the existence of a double shock system. The observed elastic wave amplitudes (5.4±0.2 kbar and 0.9±0.2 kbar for hardened and annealed material, respectively) agree within experimental precision with values predicted from static tensile specimen data. The shock wave data, in the range 25–50 kbar, yield one‐dimensional strain isotherms which, while significantly different for the two different hardness conditions, agree within experimental precision with semitheoretical curves based on Bridgman's hydrostatic data to 30 kbar and on simple tension stress‐strain data. No significant strain rate effects are evident. It is concluded that elastic‐plastic theory is valid for the description of plane shock waves in this material.