Abstract: Carbon Fiber Reinforced Plastics (CFRP) and aluminum alloys were used to prepare the double-lap bonding samples with different overlap lengths. First, a universal testing machine was used to perform tensile tests to obtain the load-displacement curves and failure morphologies of the bonding joints. On this basis, based on the continuous damage mechanics model and the 3D Hashin failure criterion, the damage and evolution of CFRP laminates are simulated, and the cohesion zone model is used to simulate the damage of the adhesive layer and the matrix, and CFRP interlayer stress field distribution and cross-sectional stress field distribution curve are obtained. Finally, the load-displacement curves and failure modes of the double lap joints with different overlap lengths were analyzed, influence of stress distribution of the composite material on the failure morphology was studied, and the failure mechanism of the joints was explored. The results show that when the overlap length increases from 20 mm to 40 mm, the mechanical properties of the adhesive joints improved significantly with the increase of the overlap length; when the overlap length was over 40 mm, its effect gradually decreased. The tensile load leads to larger stress values in the 1 and 2 directions of the matrix near the 90° fiber, and thus stress concentration and shear and peer failure of the joint. The double lap joint is failed when the one side of the joint is subject to shear and peel forces, and the joint becomes unstable instantly as the peeling force causes the failure of the other side of the joint.

Key words: double lap joint, lap length, adhesive, composite material failure, stress distribution