Revealing the competitive fatigue failure behaviour of CFRP-aluminum two-bolt, double-lap joints

The fatigue failure behaviour of CFRP-metal fastened joints in highly-loaded structures differs from that of CFRP-CFRP or metal-metal fastened joints because of the significant dissimilarity between fatigue damage mechanisms of CFRP and metal materials. In this paper, the competitive fatigue failure behaviour of a CFRP-aluminum two-bolt, double-lap joint was revealed via experiments and a novel numerical prediction method. In the proposed method, fatigue failures of the CFRP and aluminum joined plates were predicted by a novel progressive fatigue damage model and the nominal stress method, respectively. The predicted competitive fatigue life and failure mode of the joint were consistent with the experimental results, which validated the efficiency of the proposed method. It was found that, the collapse failure of the joint is caused by the failure of the CFRP laminate at high loading levels, whereas caused by the failure of the aluminum plate at low loading levels. Furthermore, influences of the thickness ratio of the joined plates on the competing fatigue failure of the joint were determined. Based on the critical thickness ratios corresponding to the transition of failure mode, the fatigue failure mode diagram of the joint was established, which is helpful for the design of the CFRP-aluminum bolted joint.