Effect of alternating load on residual strength of adhesively bonded CFRP composite-aluminum alloy joints

To provide a reference for the safety design and application of carbon fiber reinforced polymer (CFRP) composites adhesive structure, the fatigue life characteristics and residual strength of adhesively bonded CFRP composite-aluminum alloy butt joint were studied. The special fixture was designed to complete the production and solidification of the joints, and the tensile and shear quasi-static failure strength were tested. On the basis, the fatigue life under different stress levels was tested. The residual strength of the joint under specific load levels after different cycles was obtained and the failure modes are observed and analyzed. The results show that the fatigue stress-number of cycle (S-N) curve of adhesive joints accords with linear function on the single logarithmic coordinate. With the increase of alternating load cycles, the residual strength of the joint decreases, first slowly and then quickly. The decrease is more obvious under the larger load level. The failure modes of joint also changed which from slight fiber tear of CFRP composite transformer into local interfacial failure. Combined with the initial failure criterion obtained by experiment and the fatigue degradation factor, the cohesive zone model is used to simulate the strength attenuation of the adhesive joint under alternating load, and the results show that the model can predict the residual strength of the joint under alternating load effectively.