Experimental study on the influence of environmental conditions on the fatigue behaviour of adhesive joints

The fatigue behaviour of adhesive joints under the influence of environmental conditions has been the subject of several studies. However, a significant knowledge gap still exists, particularly regarding the understanding of failure mechanisms associated with these phenomena. This research presents a novel investigation into failure modes under varying environmental conditions of adhesively bonded single lap joints (SLJ), particularly focusing on the transition between static and fatigue loading. Utilising numerical simulation and experimental observations, the study offers valuable insights into the failure mode transition and its dependence on the environment. Results shown that, both temperature and humidity reduced the fatigue strength of the joints, mostly for lower fatigue lives, up to 10 times. Fatigue changed the failure mode from cohesive to mixed cohesive–adhesive. Thus, static tests proved inadequate in predicting fatigue fracture path. Adhesive failure area increased with decreasing load level (up to 60%). These phenomena were ascribed to the numerically determined SLJ’s stress concentration. The findings contribute to improving the design of adhesive joints for enhanced fatigue resistance in different environments.