A study on fatigue crack propagation in thick composite adhesively bonded joints

► We model the fatigue crack propagation in composite, adhesively bonded lap joints. ► We base the simulation upon fatigue crack growth data obtained using DCB specimens. ► We compare two models allowing for mode mixity, based on the GT and the Geq concept. ► A simplified 2D model with a crack in the adhesive layer provided acceptable results. ► The Geq criterion correlates better with experimental results. The fatigue crack propagation in adhesively bonded, thick composite joints was investigated experimentally using double cantilever beam and single lap joint specimens. The crack growth was modelled using a fracture mechanics model based on finite element models. The parameters of the Paris law were derived from fracture mechanics tests on double cantilever beam joints. The fatigue crack propagation in tapered single lap joints was modelled using these parameters and results compared with fracture observations. In both the fatigue tests on single lap and DCB joints complex crack paths were observed, with a combination of cohesive failure and delaminations. In spite of the complexity of the crack growth behaviour, a numerical model, based on the crack propagation in the adhesive layer only, allowed for predicting the crack growth behaviour observed during fatigue tests on single lap joints with relatively good accuracy.