Effect of lap length and stacking sequence on strength and damage behaviors of adhesively bonded CFRP composite laminates

The experimental tensile tests have been performed on adhesively bonded single-lap joints of carbon fiber reinforced polymer(CFRP) composite laminates with different lap lengths and stacking sequences. The relevant mechanical responses and damage behaviors were observed during the test process. Finite element (FE) models were built, in which the intralaminar damage was captured using the continuum damage mechanics (CDM) theory derived from 3D Hashin damage criteria, and the delamination of CFRP composite laminates as well as the failure of adhesive were simulated by cohesive zone model (CZM). The numerical prediction is in a good agreement with the experimental results, which validates the numerical modeling strategy. The effect of lap length and stacking sequence on the bonding strength and damage behaviors was investigated for adhesively bonded joints with single-lap and double-lap configurations. The optimization configuration was obtained using the numerical simulation for adhesively bonded joint of CFRP composite laminates. The results show that the ultimate failure load rises with the increase of the lap length for both single-lap and double-lap configurations, and it finally tends to be a stable value. The failure modes of the joints gradually transform from the shear failure within adhesive film to the delamination within laminates adjacent to the ahesive film. The bonding strength and failure modes also change as the stacking sequence varies, and the optimal stacking sequence is obtained as[0₃/90₃]_{2 s} by comparing and analysing three stacking sequences. When the lap length varies in the range of 5-20 mm, the optimum is obtained as 17 mm for single-lap configuration, and that value is 19.3 mm in the double-lap case. Compared with joint with the lap length of 20 mm, the bonding strengths of adhesively bonding single-lap and double-lap joints are increased by 13.26% and 0.43%, respectively.