To explore the bonding performance and damage progression at the interface between carbon fiber-reinforced polymer (CFRP) and steel under constant amplitude fatigue loading, fourteen CFRP-to-steel single-lap shear joints, fabricated using the nonlinear structural adhesive Araldite 2015, were tested under both static and fatigue loading conditions. The influence of load ratio on failure mode, fatigue life, and bonding performance was examined, shedding light on the damage evolution mechanism at the CFRP-steel interface under fatigue. The CFRP-steel single-lap shear specimens consistently displayed cohesive failure under static and fatigue loading conditions. A decrease in load ratio correlated with a reduction in adhesive residue on the steel surface. Additionally, the fatigue life of an interface was found to decrease with an increase in load ratio, with a linear relationship observed between the logarithm of fatigue life and the load ratio. During fatigue loading, the stiffness at the loading end of the specimen progressively degraded with the accumulation of fatigue cycles, particularly noticeable at higher load ratios. Analysis of CFRP strain distribution and interface shear stress suggested that interface failure under fatigue loading initiated at the loading end and propagated towards the free end as a result of damage accumulation. An increase in the load ratio resulted in higher peak strain and peak shear stress at the CFRP plate during interface failure. The bond-slip response evolved from approximately bilinear at a load ratio of 0.3 to trilinear at a load ratio of 0.8, with the latter showing a more extended platform phase. Stiffness degradation under a single cycle of fatigue loading indicated varying damage accumulation rates; within 67.5 mm from the loading end, the rate was lower compared to regions beyond 67.5 mm, where the rates were approximately the same.
Keywords: carbon fiber-reinforced polymer (CFRP); interfacial bonding performance; load ratio; stiffness; damage accumulation