Mixed-mode fatigue failure criteria for adhesively-bonded pultruded GFRP joints

The behavior of adhesively-bonded pultruded GFRP joints under cyclic loading was experimentally investigated. Three specimen types were examined: double cantilever beam, end load split, and mixed-mode bending specimens for Mode I, Mode II, and mixed-Mode I/II loading conditions respectively. The crack length was determined during the fatigue experiments by a dynamic compliance method for DCB specimens and a video extensometer for ELS and MMB specimens. Fatigue experiments were conducted at constant displacement amplitude. A significant difference was found between the quasi-static strain energy release rates and corresponding fatigue threshold values for all the examined cases. A total fatigue life model was used to simulate the fatigue crack growth curve under each mode-mixity. The experimental results and the analytical models were used to establish fatigue mixed-mode fracture failure criteria that can be used for the prediction of the fatigue behavior of other joint configurations comprising the same adhesive and adherends.