Fatigue/fracture characterization of composite bonded joints under mode I, mode II and mixed-mode IÂ +Â II

Experimental and numerical studies of the fatigue/fracture behavior of carbon-epoxy composite bonded joints under pure mode I, pure mode II and mixed-mode I + II loading were performed. The Double Cantilever Beam, End-Notched Flexure and Single-Leg Bending tests were used for fatigue/fracture characterization under high-cycle fatigue loading. Equivalent crack length based procedures were used to evaluate the evolution of strain energy release rates during the tests, avoiding the difficulty associated with monitoring crack length in high-cycle fatigue tests. The modified Paris laws for each loading mode were determined averaging the results issuing from several experimental tests. These experimental laws were used as input in a mixed-mode I + II cohesive zone model appropriate for high-cycle fatigue analysis. The model is based on the modified Paris law and its main feature is the use of a single damage parameter accounting for cumulative damage resulting from static and fatigue loading. Excellent agreement was observed in the region of validity of the modified Paris law between the numerical and averaged experimental laws used as input in the numerical simulation for the three types of fatigue/fracture tests. This result validates the model as a suitable tool to predict fatigue behavior of structural applications involving composite bonded joints.