Interfacial crack propagation arising in single-fiber pull-out tests

As a result of the high stress concentrations at the fiber entry point, a failure-stress analysis of pull-out rest data is problematic. As an alternative, the energy release rate is determined by a fracture-mechanics-based analysis in which the interfacial debonding process is studied with the aid of finite elements. The energy release rate is calculated for glass and carbon fibers embedded in a thermoplastic matrix. The influences of thermally induced stresses and of interfacial friction are analysed. It turns out that the thermal stresses result in a large amount of stored strain energy, lending to a remarkable increase of the energy release rate. The dependence of the crack stability on the compliance of the specimen and the testing device, and on the level of interfacial friction has been studied. Furthermore, the experimental findings concerning the change of the force/displacement trace indicating the onset of crack propagation are confirmed. (C) 1997 Published by Elsevier Science Limited.