Prediction of strength of bonded scarf repaired laminate using 3-D virtual crack closure technique
Scarf bonded repair is the most widely used technique to repair composite laminates, especially critical and highly loaded components. This thesis presents the findings from an attempt at the prediction of the strength of scarf repaired laminate under remote in-plane tensile loads using the virtual crack closure technique (VCCT). For accuracy purposes, around the scarf repair which is the region of interest, each composite adherend ply is simulated by an individual layer of three-dimensional solid elements. Instead of assuming any particular failure types, all possible cases including cohesive, interlaminar and interface failures are investigated. Cases where VCCT is combined with progressive failure and others that consider only the progressive failure are also examined. In all considered cases, it is assumed that the adhesive layer is elastic till failure. A linear elastic analysis of pristine scarf repaired laminate model under remote tension revealed that the most critical point which is the failure initiation location in the specimen, is situated in the top ply of the patch at a very small distance from the patch-adhesive interface. This might imply that fracture in the examined scarf repaired composite laminate was initiated within the patch material. The results of VCCT and progressive failure analyses showed that the finite element model that assumes crack location at the patch-adhesive interface and uses interlaminar fracture toughness values gives the best prediction of failure load compared to the experimental data. Also, it was shown that VCCT analysis without progressive failure is capable enough in accurately predicting the strength of the scarf repaired composite laminate.