[In Press] Numerical slow growth damage assessment of an adhesively bonded composite joint under compression through four-point bending

In this study, an extended finite element method (XFEM)-based numerical analysis procedure is developed as part of a framework for assessing damage slow growth behaviors of an adhesively bonded composite joint. This CFRP-CFRP single strap joint is stabilized with an aluminium honeycomb subjected to static compression through four-point bending. The adhesively bonded patch has a 140mm overlap length centered on its 440mm parent structure. The residual strengths are determined using an adhesive element failure criterion and a failure index based on energy release rate for disbonded and delaminated joints. XFEM is utilized to introduce pre-initiated cracks of various lengths and to calculate the energy release rates for each of four failure scenarios. Mesh convergence studies are conducted to acquire appropriate element sizes at crack tip. Additionally, multiple numerical benchmark models to experimental and numerical literatures are devised to validate individual components of the proposed finite element model. Results of the energy release rates for joints with cracks starting at the gap region suggest that a mixed-mode fracture occurs. At small crack lengths, mode-I is relatively low, and mode-II is high. As the crack length increases, mode-I increases, and mode-II gradually decreases. The energy release rates for joints with cracks starting in the taper end show that only a mode-II fracture exists. Finally, slow growth damage could be identified in each of the four damage scenarios. Joints with cracks initiated from the taper end exhibit substantially longer periods of slow growth damage when compared to joints with cracks initiated from the gap region.