SURFACE DAMAGE OF POLYMETHYLMETHACRYLATE PLATES BY ICE AND NYLON BALLIMPACTS

A study is described of the impact process and the corresponding surfa ce damage to PMMA (polymethylmethacrylate) targets impacted by ice and nylon spheres. A gas gun system was used to project the spheres and t he impacts were recorded using a high-speed image converter camera (Im acon 792). Special attention was paid to the conditions causing projec tile failure and the surface damage to the target. The experimental re sults show that although the deformation and failure modes for ice and nylon are different, the surface damage to the PMMA target has a simi lar failure pattern, i.e., a central, circular undamaged region surrou nded by an annular damaged region containing many short circumferentia l cracks. Analysis shows that the diameter d of the central undamaged region and the annular damaged area A(m) can be used to characterize t he surface damage which depends on the projectile material, sphere rad ius R, as well as the impact velocity V-0. For a given projectile, two critical impact velocities exist: One is the threshold velocity (V-0) (th), below which no visible surface damage is observed, and another i s the fracture velocity (V-0)(f), above which a plate target is broken . Damage in the annular region is caused by the Rayleigh surface wave in the present experiments. The conditions for the Rayleigh surface wa ve to pass ahead of the expanding edge contact velocity are analyzed. Comparisons between the theoretical predictions and experimental resul ts, including the present study and earlier data, are made for PMMA pl ates impacted by projectiles of different materials (ice, nylon sphere s, and water drops) and at different impact angles. (C) 1995 American Institute of Physics.