The Residual Compressive Strength Of Stitched Composite Laminates With An Ellipse Delamination

With high specific strength and high specific stiffness, carbon fiber/resin composites have become one of the most important structures used in modern aviation. Fiber breakage,matrix damage and delamination are common failure modes of composites. Delaminationoften occurs as a consequence of the imperfections in the production process, or becauseof the external factors during the usage. Local-buckling is the main reason of structure failure for composites with delamination. Because the traditional composites have low interlaminar toughness, delamination propagation often happens after local-buckling, which can reduce the residual compressive strength. Stitching was developed to improve the interlaminar property. Experiments have shown that delamination caused by impact on stitched composites is smaller than those without stitching, which indicates that stitching can restrain thedelamination.Based on progressive damage method, the compressive behavior of stitched compositelaminates containing an initial ellipse delamination was investigated. To predict the residual compressive strength, a finite element (FE) model was presented by ABAQUS, in which stitching was modeled by truss element and interface between the sub-laminates was modeled with cohesive element. Firstly, by solving the equation of eigenvalues, buckling modes was obtained. Then influence on buckling load was discussed by changing parameters.Secondly, with the buckling modes added to the non-linear analyses as geometrical imperfection, the local-buckling load and residual compressive strength was predicted. During theprogressive damage analyses, three criterions were selected to model the material failures.Finally, both geometrical and stitching parameters were discussed on residual compressivestrength. The results have good agreement with the experimental results, so the method used in this paper is suitable. Comparing with unstitched composites, stitching can increasethe local buckling load, restrain the delamination propagation, and finally increase the residual compressive strength for composites with delamination.