Damage investigation on the adhesively bonded single-lap joints of three-dimensional braided composite and laminates

Adhesive bonding is usually used to fabricate composite structures that are hard to manufacture in one piece, however, their lightweight advantage is usually impaired by low failure strength. For high performance composite structures, bonding properties of joints dominate the failure performance and commonly are the primary target of structural optimization. Both experimental and numerical studies of failure behavior of single-lap joints with three-dimensional braided composite laminate adherends are presented in this paper. First, tensile failure tests were performed on braid-laminates single-lap joints bonded with epoxy resin. Compared with the laminates–laminates single-lap joints, the failure load of the braid–laminates single-lap joints increased by 18.4%. Then, the Finite Element Method (FEM) coupled with cohesive zone models (CZM), considering different value of overlap length (L), was used to perform the detail stress distribution of the overlap sections of SLJs. Further, damage initialization and crack growth of single-lap joints are analyzed in detail to fully characterize the failure process, and both experimental and numerical results lead to the same conclusion. Lastly, the effect of three-dimensional braided adherends’ braiding angle on braid-laminates single-lap joints’ performance was investigated, which provides suggestions for the design and optimization for adhesive bonded composite structures.