Failure load prediction of laminates repaired with a scarf-bonded patch using the damage zone method

Abstract

The damage zone method (DZM) is an efficient way to predict the failure of composite structures with a minimum of real testing. Particularly, it is useful when the failure mechanism is too complicated to be accurately analyzed by a merely numerical method. The aim of this study was to use the damage zone model to predict the failure load of repaired laminates, in which scarf-bonded joints were used for repair. The model uses a test-based critical damage zone and stress-based failure criteria. A total of 45 carbon-epoxy composite (USN) laminate scarf-repaired specimens were first tested with two different defect sizes, four scarf angles, and three overlap layer sizes. The Tsai-Wu and Tsai-Hill criteria were used for the laminate, and the maximum shear stress criterion for the adhesive was adopted to predict failure onset. The predicted failure loads were compared to test results and a good agreement was obtained with a 9.2% maximum deviation for almost all parameters with the exception of a case with an unrealistically large scarf angle. To verify the feasibility of the DZM for different material, additional 30 repair specimens using other unidirectional carbon-epoxy laminate were then also tested and. the predictions were confirmed by the results of the experiment.