A modified 'Hawkyard's method to predict the deformation of projectiles in Taylor impact tests

Abstract

The shapes of projectiles after Taylor impact tests can be predicted by using simple equations that were proposed by Hawkyard, in which elastic-perfectly plastic materials and instant strain-hardening materials are assumed to represent the projectiles. In order to improve the accuracy, the force on the undeformed volume of the projectile to depend on the strain of the deformed volume. Based on the equation of motion, equations that represent the shape of the deformed projectile by assuming an instant strain-hardening model are developed. In the same way, those assuming an arbitrary continuous stress-strain curve are developed, and the solution of using the power-law hardening rule to represent the stress strain relation is derived. To validate the formulations, Taylor impact tests were conducted, and the deformed shapes of the projectiles were compared with the calculations made by the developed formulations. The lengths of the deformed projectiles are reproduced within several percent by the proposed models using the stress-strain relation obtained from split-Hopkinson bar tests. The proposed models tend to underestimate the diameters of the deformed projectiles around the contact face and to overestimate the diameters of the other part of the deformed projectiles.