Finite element crack propagation of adhesively bonded repaired panels in general mixed-mode conditions

In order to simplify the analyses, in the previously developed mixed-mode fracture analyses of the single-side repaired panels with composite patches, the effect of mode-III was neglected. In those analyses, it was also assumed that the crack-front remains perpendicular to the panel's surfaces during the crack propagation which is in defeat with the experimental observations. In this paper, finite element analyses are performed to investigate the crack propagation of single-side repaired panels using composite patches containing an initial central inclined crack. In these analyses the general mixed-mode fracture conditions of mode I, II and III and the real three-dimensional crack-front are considered in the finite element crack growth modeling. For this purpose, Modified Virtual Crack Closure Technique (MVCCT) is used to calculate the three strain energy release rate components corresponding to various fracture modes at the crack-front. The obtained crack-front shapes at various crack growth steps, crack trajectories at both patched and un-patched sides and life of the repaired panels with various patch lay-ups are discussed.