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.

粘合接头在环境条件影响下的疲劳行为一直是多项研究的主题。然而，仍然存在重大的知识差距，特别是在理解与这些现象相关的故障机制方面。本研究对粘合单搭接接头 (SLJ) 在不同环境条件下的失效模式进行了新颖的调查，特别关注静态载荷和疲劳载荷之间的过渡。利用数值模拟和实验观察，该研究为故障模式转换及其对环境的依赖性提供了有价值的见解。

结果表明，温度和湿度均降低了接头的疲劳强度，主要是疲劳寿命降低，最高可达 10 倍。疲劳将失效模式从内聚改变为混合内聚-粘附。因此，静态试验证明不足以预测疲劳断裂路径。粘合剂失效面积随着负载水平的降低而增加（高达 60%）。这些现象归因于数值确定的 SLJ 的应力集中。这些发现有助于改进粘合接头的设计，以增强不同环境下的抗疲劳性。