Fatigue behaviour and damage evolution of single lap bonded joints in composite material

The paper presents the results of an experimental investigation on the fatigue behaviour of single lap bonded joints. Carbon/ epoxy laminates bonded with epoxy adhesive were tested under tension–tension fatigue loading and the effect of overlap length and corner geometry was discussed by using the classical stress-life approach. Significant improvements in fatigue strength can be obtained by adopting long overlap length and spew fillet corner geometry. A careful analysis of the evolution of the fatigue damage was also carried out and it was observed that a significant fraction of the fatigue life of the joint is spent in the nucleation of one or more cracks which then propagate up to failure of the joint. The duration of nucleation process, which can last from 20% up to 70% of the joint life, suggests the need of incorporating this phase in the development of future predictive models. The fatigue crack propagation process is also discussed and the rates of crack propagation evaluated.