ON THE VELOCITY DEPENDENCE OF THE L D EFFECT FOR LONG-ROD PENETRATORS/

At ordnance velocities (1.0-1.9 km/s), there is a pronounced decrease in efficiency, as measured by P/L, when projectiles of larger L/D are used. The influence of L/D on penetration is referred to as the L/D ef fect. We numerically examine the L/D effect at higher velocities, from 2.0 km/s to 4.5 km/s. It is found that as the velocity increases, the re is a change in mechanism for the L/D effect. At ordnance velocities the L/D effect is mostly due to the decay in penetration velocity dur ing the ''steady-state'' region of penetration. At higher velocities, the steady-state region of penetration shows no L/D dependence, and th e L/D effect is due primarily to the penetration of the residual (non- eroding) rod at the end of the penetration event. This change in mecha nism is related to the change in slope of the penetration-versus-impac t velocity ''S-shaped'' curve for eroding projectiles.