Study on impact perforation fracture mechanism in PMMA

Abstract

Many studies on the hypervelocity impact problem in metallic materials have been conducted [1±3]. In these studies, rail guns, powder guns and light gas guns are used to launch projectiles. The correlation of target fracture morphology, absorbed energy, the penetration depth, and the crater diameter=volume with impact velocity is investigated. In the present study, polymeric materials are used as target material. The objective of the present study is to examine the fracture mechanism of polymeric materials by high velocity impact tests and quasistatic perforation tests. A target material is polymethylmethacrylate (PMMA). The target plate sizes are 115 mm3 115 mm and 214 mm 3 214 mm. Thickness of target specimens, t, are 1, 3, 5 and 10 mm. The target specimens are ®xed between two plates with circular holes. The diameters of the holes, D, are 100 mm and 200 mm. The high velocity impact tests and quasi-static perforation tests are impact test and perforation test into a ®xed circular plate. In high velocity impact tests, the experimental apparatus is composed of an air compressor and an air gun. Stainless and PMMA spherical projectiles, whose diameter is ,11 mm are launched by impact testing machine at various velocities up to 200 m sy1. In quasi-static perforation tests, the target specimen is perforated by a steel bar having a spherical head whose diameter is 10 mm. The tests are performed by using a universal testing machine. The cross head speeds are 0.5, 5.0 and 50.0 mm miny1. In high velocity impact tests, four typical fracture forms of targets and PMMA projectiles, respectively, were veri®ed. Fracture forms of targets are de®ned as ricochets, cracks, breaks and perforates. Those for projectiles are de®ned as intact, cracked, broken and shattered. Fig. 1 shows a ballistic phase diagram which indicates the relationships between the impact velocity and the fracture morphology of targets and projectiles. Fig. 2 shows the relation between impact velocity and perforated hole area. It is found that the hole area becomes similar to the maximum section area of the projectile at impact velocities above a certain value. For impact velocities below 100 m sy1, the perforation fracture is dominated by bending deformation. For impact velocities above 100 m sy1, bending deformation is very small before the projectile perforates the target. Fig. 3 shows typical load±displacement curves obtained by quasi-static perforation tests (D ˆ 100 mm, t ˆ 1 mm). It is seen that in this range of