Novel Test Method for Mixed Mode II and III Interlaminar Fracture Toughness

A novel test method is proposed to evaluate mixed mode II and III interlaminar fracture toughness of composite laminates. The method is a well-improved test method of the split cantilever test method and easy to conduct, while a computational analysis is necessary to specify the critical toughness values. The aim of the test is to obtain mixed mode fracture toughness. The twisting force that exists in the case of the split cantilever test method is avoided by making the specimen symmetric by introducing two symmetrically located delaminations. By the present method, the two cracks grow stably keeping their configuration with the increase of applied displacement, that is, stable self-similar crack growth is realized. The energy release rate can be numerically evaluated from the experimentally obtained data, such as, the applied load (or applied displacement)as well as the crack configuration. The energy release rate varies along the curved crack front and the dependence of the mixed mode critical energy release rate on the ratio of the mode components can be obtained by one test trial. The method can be conveniently used to roughly estimate the failure criterion for mode II and III mixed mode Interlaminar fracture.