Study of Initial Conditions in Constant Velocity Impact

Diffraction grating measurements are made of dynamic plastic strain within a few thousandths of an inch from the impact face of 1‐in. diameter, annealed aluminum specimens in free flight undergoing constant velocity impact. From these data it has been established that initial nondispersive shock fronts are present, even in low‐velocity impact. This initial nondispersive front develops in the first ¼ diameter in two sections, each involving ½ the initial kinetic energy; the first section is that of the deviatoric, or shear, component, and the second is associated with the hydrostatic stress. It is shown that the dynamic stress‐strain curves obtained experimentally in annealed aluminum and copper may be computed directly from the theory, using information supplied by the static stress‐strain curve. The von Karman critical velocity for annealed aluminum is found to be a dividing point between two types of initial wave development.