Initiation and propagation toughness of delamination crack under an impactload

A combined experimental and finite element method is developed to determine the interlaminar dynamic fracture toughness. An interlaminar crack is prop agated at very high speed in a double cantilever beam (DCB) specimen made o f two steer strips with a precrack. A special fixture is designed to apply impact load to one cantilever and determine the deflection of the cantileve r-end, initiation time and crack propagation history. The experimental resu lts are used as input data in a FE code to calculate J-integral by the grad ual release of nodal forces to model the propagation of the interlaminar cr ack. The initiation fracture toughness and propagation fracture toughness a re evaluated for interlaminar crack propagating between 850 and 1785 m/s. T he initiation and propagation toughness were found to vary between 90-200 J /m(2) and 2-13 J/m(2) respectively. The technique is extended to study init iation and propagation toughness of interlaminar crack in undirectional FRP laminates. (C) 1998 Elsevier Science Ltd. All rights reserved.