Stress concentrations caused by bond cracks in single-lap adhesive composite joints

Nonlinear finite element analysis was used to study stress fields in single-lap adhesively bonded composite joints containing cracks of different lengths. It was shown that stresses, energy release rates, and stress intensity factors vary nonlinearly with the crack length. However, a near-linear dependence was observed between the stress intensity factors and the load for cracks of constant length. The analysis showed that the critical values of the energy release rates for fast crack propagation in the final stage of fatigue life were 2-3 times lower than the critical energies for the cracks propagating under quasi-static loading.