Focusing on in-service repair to composite laminates of different thicknesses via scarf-repaired method

In terms of in-service components, sometimes it is difficult to undertake repairing with an autoclave due to the structure configurations and repair conditions. In order to conduct in-service soft patch repair, vacuum bagging process can be used. However, for composite materials manufactured in autoclaves, high porosity levels may be induced when cured using vacuum bagging, which harms the mechanical properties of composites. This article aims to use an alternative material which shows better performance than the original one when using vacuum bagging for the patch. Four groups of scarf repaired composites with various laminate thicknesses were fabricated and tested. Experimental results indicate that the failure strengths of different groups are similar and the dominated failure mode is cohesive failure of adhesive, accompanied by partial 45° and 90° matrix cracks of composite patch. In addition, a finite element model was established to predict the failure strength and explain the damage mechanism. The numerical results show good agreement with test results and indicate that matrix cracks of composites initiate before the adhesive failure. Based on the validated model, the effects of overlap patch and 3D defects on the ultimate strength were discussed.