Quasi-static modes I, II and mixed modes I/II fracture toughness of two laminate composites: Part I - Testing

In Part I of this study, fracture toughness tests were carried out in modes I, II and mixed modes I/II on two laminate composites. Both composites contain carbon fibers in an epoxy matrix. One laminate is unidirectional and the second is composed of plies fabricated from a twill fabric. The tests were carried out using double cantilever beam, end-notched flexure and mixed mode bending specimens according to ASTM and ISO standards. This is an extensive and complete study of the in-plane, quasi-static fracture toughness (both initiation and resistance) of two material systems. In Part II of this study, micro-computerized tomography carried out on some of the specimens is reported. On the basis of these images, the experimental behavior was related to the micromechanical structure of the materials. In addition, load-displacement curves were simulated numerically by means of a cohesive zone model and the finite element method to gain better insight into the failure behavior observed.