The mechanical degradation mechanism of CFRP/Al double-lap bolted joints (with and without corrosion protections) after seawater ageing

Dual effects of environmental and mechanical loadings complicate mechanical behaviors of CFRP/Al joints, which significantly influence their reliable applications. This paper aims to reveal the mechanical degradation mechanism of CFRP/Al double-lap bolted joints with two kinds of corrosion protections (epoxy coating and PVC film) after seawater aging. All joints were exposed in the artificial marine environment with 3.5% sodium chloride solution at 30 ℃ for 0–8 weeks. Double-lap bearing tests and material analysis experiments with micro-CT and step profiler were conducted to reveal the environmental damage and mechanical degradation mechanism of aged joints. The results show that compared to epoxy coating, PVC film can better suppress galvanic-corrosion but degrades more the load-bearing capacity of joints due to the reduction of friction coefficient between CFRP and Al. The failure modes of unprotected joints and joints protected with PVC film evolve both from squeezing/shear-out to delamination/cleavage with ageing time, while squeezing is almost the only primary failure mode of joints protected with epoxy-coating. Joints protected with PVC films show more serious failure damage than the ones protected with epoxy-coating, since the epoxy-coating has better protective effect on CFRP laminate and therefore inhibits the deterioration of damage.