Fracture of adhesively-bonded pultruded GFRP joints under constant amplitude fatigue loading

The fracture behavior of adhesively-bonded structural joints under tensile constant amplitude fatigue has been investigated. Double-lap joints (DLJs) and stepped-lap joints (SLJs) composed of pultruded GFRP laminates and an epoxy adhesive were examined. Both joint types exhibited a fiber-tear failure with cracks that initiated at the joint edges in the adhesive–laminate interface and then propagated in the laminates’ mat layers. A linear trend of crack growth and compliance was observed for the DLJs whereas a sigmoid trend was found for SLJs. The experimental compliance method was used for the calculation of the maximum strain energy release rate, Gmax, and the incremental polynomial method for the calculation of the crack propagation rate, da/dN. Fatigue crack growth (FCG) curves established for both joint types showed that empirical constants are dependent on the joint configuration. Based on this fatigue life modeling, design allowables that correlate the developed damage with fatigue life were derived.