Fatigue life prediction for dissimilar single-lap bonded joints based on relative displacement of adherents

Abstract

To develop a unified method for evaluating the fatigue strength of adhesive joints, shear tests were conducted under static and fatigue loading conditions on dissimilar single-lap bonded joints composed of A5083P-O and CFRP bonded with a second-generation acrylic adhesive. The cumulative energy dissipated in the adhesive layer, W_d,f, was calculated, and a fracture criterion incorporating loading frequency and mean stress was proposed. Using the fracture stress of 17.9 MPa obtained from shear tests as a reference, fatigue tests were performed under stress ratios of 0.5, 0, and −1, and loading frequencies of 2 Hz and 10 Hz. The resulting τ_a−N_f fatigue curves showed that the predicted number of cycles to failure N_f,pred and experimental values N_f,exp scattered to a Factor of 20 range. An experimental method was established to estimate adhesive strain rate from the relative displacement between adherents across the adhesive layer, enabling calculation of W_d,f. A fracture criterion was derived by fitting the relationship between W_d,f and cumulative cycles to failure N_f,c on a double-logarismic diagram. The main novelty of this study lies in the simplified experimental procedure for estimating adhesive-layer shear strain rate from adherent displacements, which enables practical application of the energy-based criterion. The predicted N_f,c values showed a Factor of 3 agreement with N_f,exp, indicating a sixfold improvement in fatigue life prediction accuracy compared to conventional fatigue curves.