CHARACTERISTICS OF DEBRIS CLOUDS PRODUCED BY HYPERVELOCITY IMPACT OF ALUMINUM SPHERES WITH THIN ALUMINUM PLATES

Debris clouds produced by the normal impact of aluminum spheres with aluminum bumper plates are shown to consist of an ejecta veil, an external bubble of debris, and a significant internal structure composed of three distinct elements. Effects of variations in bumper-plate thickness, sphere diameter, and impact velocity on the shape and velocity of the elements of the internal structure are described and compared. Three alloys of bumper material and several diameters of 2017-T4 aluminum spheres, ranging from 6.35 mm to 12.70 mm, were used in the tests described in this paper. Test results were sorted into two sets. In the first set, impact velocity was held constant at 6.7 km/s and the bumper-thickness-to-projectile-diameter ratio, t/D, varied from 0.026 to 0.424. In the second set, t/D ratio was held constant at 0.049 and the impact velocity varied from 3.77 km/s to 7.23 km/s. In both sets of test results, debris-cloud properties are shown to scale with projectile diameter. Characteristics of the front element of the debris-cloud internal structure are shown to be sensitive to changes in t/D ratio and impact velocity. A model for the formation of this front element is presented and used to develop a description of a debris cloud consisting of material in the solid-liquid and/or liquid-vapor phases.