Since change of compliance as increasing crack length under mode Ⅱ loading is much smaller than that under mode Ⅰ loading, mode Ⅱ delamination fatigue crack propagation behavior near the threshold of FRP laminates had not been investigated until several studies was reported in recent years. In this paper, the test method of mode Ⅱ delamination fatigue was established using end notched flexure specimens. Loading apparatus and computer software were developed in order to determine the threshold. New equation for the relation between compliance and crack length was proposed, where parameters are independent of specimen thickness. Compliance value under fatigue loading was smaller than that under static loading because of the viscoelasticity of the matrix resin and the friction between the crack surfaces over the support of the loading apparatus. These results show the necessity to obtain the relation between compliance and crack length during fatigue test. Since crack propagation rate under mode Ⅱ loading was independent of crack growth in maximum energy release rate-constant test, maximum energy release rate-decreasing test also can be carried out to obtain the conservative fatigue crack growth behavior. Test results gave the sufficiently low crack propagation rate to obtain the fatigue threshold.
