Crack growth in adhesively bonded joints under quasi-static and fatigue loading

Adhesively bonded joints are attracting increasing interest in the aerospace industry. However, incomplete knowledge of fatigue crack growth in adhesive bonds is a major concern to their application. This thesis investigates several aspects of crack growth in adhesively bonded joints. The influence of adhesive thickness on fatigue crack growth under mode I loading was addressed by a combination of experimental tests and numerical simulations. Increased crack growth was found in thicker specimens. This was explained as a result of increased energy available for crack growth in thicker adhesives, while the crack growth resistance was found not to be affected by the thickness. Formation of micro-cracks promoted by increased plasticity is thought to be the source of increased crack growth. Cohesive zone models were applied to the study of mode I and mode II quasi-static crack growth. A strong dependence on the input parameters was observed. In particular, the effect of viscous regularization on the solution was investigated. A proof of consistency of the viscous solution was proposed. It was shown that a low value of viscosity is needed to obtain consistent results. Finally, disbond arrest in bonded GLARE was studied by means of fatigue tests on bolted cracked lap shear specimens. The experiments evidenced a moderate decrease of the crack growth rate near the bolt. This was further investigated by numerical computations, which showed a significant change of the strain energy release rate around the bolt from mixed mode I/II to almost pure mode II. Outside this region, good predictions of the fatigue crack growth rate could be obtained by a combination of existing models from the literature. Extensive adherent cracking was observed, which led to the conclusion that crack arrest in GLARE comes from a balance of adhesive crack growth retardation and adherent cracking.