Evaluation of In-Plane Mode II Fracture Toughness in Unidirectional GFRP Using Four-Point Shear Loading Test (Revised Method and Dependence of the Pre-Crack Length)

In-plane Mode II fracture toughness tests on unidirectional GFRP are conducted using a four-point shear loading test method. In the previous paper, the four-point shear loading test method was examined as a simple Model II fracture toughness test. Then the effect of pre-crack length on fracture toughness was investigated. In this study, the same test method is applied to evaluate the Mode II fracture toughness. The dependence of the pre-crack length and the initial failure process are clarified. The results obtained are summarized as follows; (1) It is revealed that the crack opening displacement is much less than the crack relative sliding displacement in the four-point shear loading test. (2) From an analysis of the damage propagation length, it is found that the initiation of the main crack is close to the maximum load point. The initial failure behavior of the unidirectional GFRF subjected to shear loading is clarified. (3) The normalized stress intensity factor concerning an orthotropic body of the unidirectional GFRF is calculated by a finite element method. The mode II fracture toughness is constant irrespective of the pre-crack length.