THE LOW-VELOCITY-TO-HYPERVELOCITY PENETRATION TRANSITION FOR IMPACT CRATERS IN METAL TARGETS

Projectile/target behavior for 1100 Al/Cu, soda-lime glass/Cu, soda-li me glass/1100 Al, ferritic stainless steel/Cu, and ferritic stainless steel/1100 Al for spherical (3.18 mm diameter) projectiles at impact v elocities ranging from 0.8 to similar to 6 km s(-1) has been examined by light metallography, SEM, and TEM. At a reference velocity of 1 km s(-1), the crater depth/crater diameter ratio (p/D-c) is observed to b e linearly related to bulk density ratios Co,lp,)liz and elastic modul us ratios (E-p/E-t)(rho(p)/rho(t))(1/2), and to vary from about 0.2 to 2.95. The hypervelocity (u(o) > 5 km s(-1)) threshold value for p/D-c is also shown to be linearly related to these functionalities and ran ges from p/D-c = 0.4 for the 1100 Al/Cu system and 0.85 for the ferrit ic stainless steel/1100 Al system. The residual crater microstructures are all characterized by a zone of dynamic recrystallization at the c rater wall (which thickens with impact velocity), and decreasing dislo cation density beyond this zone; consistent with residual hardness pro files whose amplitudes decrease with distance from the crater wall. Co mputer simulations and validation of these simulations utilizing the r anges of experimentally measured crater geometries with impact velocit y were developed which fairly accurately represented residual crater s hapes and related features. These results also demonstrate the importa nce of appropriate projectile/target strength ratios in computer simul ations; and illustrate the potential for extrapolations to new systems , and for impact velocities well beyond those achievable in the labora tory. (C) 1998 Elsevier Science S.A. All rights reserved.