Fragmentation-Initiation Threshold for Spheres Impacting at Hypervelocity

Results of impact tests using aluminum bumper sheets ranging from 0.076-mm- to 4.80-mm-thick and impact velocities ranging from 1.98 to 7.19 km/s were used to determine the fragmentation-initiation threshold for aluminum spheres impacting at hypervelocity. This threshold velocity was expressed as a function of the bumper-thickness-to-projectile-diameter ratio (t/D). Tests using 9.53-mm- and 12.70-mm-diameter, 2017-T4 aluminum spheres indicated that the fragmentation-initiation threshold velocity scaled with t/D ratio. Analysis of radiographs from the tests indicated that the material forming the front structure of the debris cloud was produced by quasi one-dimensional loading of the bumper during the initial phase of the impact process.