Influence of patch parameters on damage and residual strength of adhesively bonded composite repair under fatigue loading

A progressive fatigue damage analysis method was developed to predict damage propagation and residual strength of the adhesively bonded repairs in composites subjected to constant amplitude cyclic loading. The fatigue damage models of adhesively bonded repairs are respectively established with different shapes of the patches. Based on the theory of the residual strength and residual stiffness in composites, the material property degradation technique for modifying element stiffness and strength and materials ultimate failure criteria were proposed. This program is able to simulate progressive fatigue damage and predict residual strength of the adhesively bonded repairs in composites subjected to constant amplitude cyclic loading with different shapes of the patches. The calculation results of damage model show that the patch shape and size are important fatigue design parameters of adhesively bonded repairs. The effect of repair with tilted square patch is the best than others and the residual strength improves by 27.6 % than the unrepaired composite laminates.