Hypervelocity Impact -- Material Strength Effects on Crater Formation and Shock Propagation in Three Aluminum Alloys

Abstract

Abstract : The effects of material strength upon the transient response of thick aluminum targets to hypervelocity impact has been studied experimentally. Most experiments involved the normal impact of 2017 aluminum spheres at a velocity of about 7 km/sec. Material strength was varied by employing targets of 1100, 6061, and 7075 aluminum alloys. Flash x-ray techniques were used to measure accurately the rate at which the crater grew during the impact process. Crater growth rates were also measured for 1100 aluminum in four separate ranges of projectile velocity from 2.3 km/sec to 7.0 km/sec. Free surface velocity and Hopkinson fly-off disk techniques were used to measure values of the peak normal stress at various distances from the impact point (between 1 cm and 10 cm) at several related angles away from the projectile trajectory. The measurements of the variation of stress amplitude with distance into the target demonstrated significant non-hydrodynamic stress attenuation believed to be associated with propagation of an elastic relief wave from the rear of the impacting projectile. Numerical calculations yield reasonable agreement with experimental results, but many of the details are in question. Measurement of shock arrival time with quartz disk sensors confirmed the elastic-plastic behavior of the target material.