The fatigue response of environmentally degraded adhesively bonded aluminium structures

Experimental studies have been undertaken investigating the effect of moisture on the fatigue response of adhesively bonded monolithic single lap joints and laminated doublers loaded in bending, both made of the same materials. The joints were aged in deionised water at a temperature of 50 °C for up to 2 years exposure. The backface strain technique was employed to monitor damage initiation and propagation in the joints. The test results show that the fatigue life degraded with increasing moisture content and tended to level off when approaching saturation. The failure surfaces were cohesive in the adhesive. Numerical fatigue modelling has been undertaken to predict the fatigue response of these joints utilising a strain-based fatigue damage law integrated with a bilinear traction-separation cohesive zone model. The residual stresses due to thermal and swelling strain were included in the model. Good agreement was found between the predicted fatigue response and the experimental results.