Fatigue behavior of CFRP/Al adhesive joints — Failure mechanisms study using digital image correlation (DIC) technique

Fatigue failure is one of the main causes of structural failure. Fatigue failure mechanism signifies a critical research issue for better design of the joined parts to enhance endurance and longevity. This study aims to explore the failure mechanisms of a CFRP/aluminum adhesive joint, in which DIC technique is used to record fatigue process in real time. The DIC system took the images at peak and valley phases of equivalent cyclic loads every certain number of cycles which were relative to the stress levels to characterize deformations of the joint. In this way, the whole fatigue testing process was recorded effectively to study the fracture process. The results divulged that the fracture behavior of the joints were opposite between high and low stress levels, implying that design and enhancement strategies of joints should be adopted selectively in accordance with their working conditions. Besides, the characteristics of failure surface could reflect the different fracture behavior effectively. The stiffness degradation of bonding area was characterized, where DIC presents a more effective way to illustrate stiffness of adhesive joints. Based upon the failure mechanism analysis, the fatigue problems of single lap joint were studied and design suggestions were discussed. The study is aimed to gain some new insights into the fatigue failure of CFRP/Al single lap joint. • The stress levels affect the fatigue initial crack and secondary crack initiation ends of CFRP/Al adhesive joints. • Stiffness degradation analysis of the bonding part through the data recorded by DIC system. • Fatigue fracture surface analysis of CFRP/Al adhesive joint with three characteristics regions. • Simple single lap adhesive joint does not play a good role in fatigue resistance.