On the L/D effect for long-rod penetrators

A common measure of penetration efficiency is given by the depth of penetration P into a semi-infinite target normalized by the original length of the projectile L. It has been known for over 30 years that P/L depends upon the aspect ratio L/D for projectiles with relatively small aspect ratios, e.g. 1 less than or equal to L/D less than or equal to 10. This influence of L/D on penetration is referred to as the LID effect. Although observed, the L/D effect for large aspect ratio rods is not as well documented. Further, published penetration equations have not included the L/D effect for high aspect ratio rods. We have compiled a large quantity of experimental data that permits the quantification of the L/D effect for projectiles with aspect ratios of 10 less than or equal to L/D less than or equal to 30. Numerical simulations reproduce the observed experimental behavior; thus, no new physics is required to explain the phenomenon. The numerical simulations allow investigation of the fundamental mechanics leading to a decrease in penetration efficiency with increasing aspect ratio.