Effect of temperature on the fatigue performance and failure mechanism of a flexible adhesive butt joint

To study the influence of temperature on the fatigue performance of adhesive structures, polyurethane adhesive was used to make butt joints (BJs). Using an environmental-fatigue coupling loading devices, the temperature points of -40, -10, 20, 50 and 80 degrees C were selected to carry out tension-tension fatigue tests on BJs. The S-N curves of the joints were obtained. The quasi-static and fatigue failure sections of the BJs were observed by macrography and scanning electron microscopy (SEM). The results show that temperature has a significant effect on the quasi-static and fatigue properties of the flexible adhesive. As the temperature increases, the failure strength, failure strain and Young's modulus of the adhesive decrease, and the fatigue performance of BJs decreases gradually. The fatigue failure sections of BJs vary greatly at different temperatures. When the temperature rises, the polymer chain begins to move and the viscoelastic property of the adhesive becomes obvious. Cavitation has obvious effect on the fatigue life of BJs. Fatigue failure is caused by multiple cracks and cavities, leading to localized stress concentration. The functional relationship for the temperature-nominal stress-fatigue life is established, which can provide a reference for fatigue performance prediction of vehicle bonding structures.