Fatigue fracture criteria in single-lap adhesive joints with cumulative dissipated energy

This study focuses on predicting the fatigue life of structurally bonded joints. Herein, fatigue tests were conducted using single-lap adhesive joints subjected to varying stress ratios (R = − 1.0 and − 0.5) and cyclic frequencies (f = 2, 5, 10, and 20 Hz) with a digital image correlation to measure shear strain in adhesives. The relation between tensile–shear stress and the number of cycles to failure Nf showed a dependence on R and f, which suggested that reduced mean stress and increased f positively impacted fatigue life of single-lap adhesive joints. Cumulative dissipated energy Wd was developed by considering adhesive strain rate owing to cyclic loading, and a fracture criterion Wd–Nf was established to approximate the relation with the number of cycles regardless of the R and f conditions. The fracture criterion established under R = 0.2 was expected to include the relationships between Wd and Nf for other conditions within ranging from 1/3 to 3 times. In a range of 104 to 107 cycles, the prediction accuracy of the fatigue fracture criteria based on the Wd exceeded that of the conventional fatigue curves by approximately three times.