Impact delamination testing of fibre reinforced polymers using Hopkinson Pressure Bars

Abstract

High rate delamination tests are often performed using high speed servo-hydraulic or drop-weight test frames. However, impact induced stress wave propagation in the specimen, load cell and test frame often results in oscillations in the force readings which can obscure specimen response. The Hopkinson Pressure Bar provides a means of measuring impact forces and velocities that accounts for stress wave propagation, but is typically used where forces are relatively high and deflections to failure are relatively low. A modified Hopkinson Pressure Bar apparatus was developed to conduct delamination tests, based on Three Point Bend Test geometry, at impact velocities of the order of 5–10m/s, with specimen deflections to failure approaching 10mm. This apparatus was used to test the delamination response of Glass Fibre reinforced Polypropylene specimens, using the mixed Mode I–Mode II Single Leg Bend delamination test. The shape of the force–deflection curve differed dramatically between quasi-static and impact tests. Finite Element Analysis, using cohesive zone elements to capture delamination, was used to elucidate the different response of the quasi-static and impact delamination tests.