Multi-stage mechanical behavior and failure mechanism analysis of CFRP/Al single-lap bolted joints with different seawater ageing conditions

This paper aims to investigate the mechanical response behavior of CFRP/Al single-lap bolted joints in marine environment. The joints with four interference fit sizes (0%, 0.42%, 2.14% and 3.02%) were prepared, and fully and half immersed in 3.5% sodium chloride solution with a controlled temperature of 30 °C for four months. Single-lap bearing tests were carried out to evaluate the mechanical behavior and failure mode of the CFRP/Al bolted joints after seawater ageing. Scanning electron microscope (SEM) was used to analyze the environmental damage and failure mechanism of structures. The results show that the critical load-bearing capacity and the maximum friction force at the overlap gradually decreased with the increasing of ageing time, and it was more serious in half immersion ageing environment compared with full immersion. The interference fit significantly improved the mechanical properties of joints, especially for 2.14% interference fit. Environmental damage such as pitting, delamination and fiber-matrix interface debonding was all aggravated with the increasing ageing time but suppressed by interference fit. In addition, the failure modes of structures were bearing failure and shear-out failure of CFRP, and the failure mechanism was delamination for unaged structures, the interlayer shear damage for aged structures.