The effects of service temperature on the fatigue behavior of a polyurethane adhesive joint

Abstract In order to study the influence of service temperature on the fatigue performance of the adhesive structure, Sikaflex®-265 polyurethane adhesive was used to make thick-adherend shear joints (TASJs) with aluminum alloy. According to the service environment of the vehicle, the temperature points of −40 °C, −10 °C, 20 °C, 50 °C and 80 °C were selected to carry out quasi-static tensile test on the joints, and the change law of failure load and failure displacement with time was analyzed. The variation law of the fatigue frequency and load on the internal temperature of the adhesive layer was analyzed by using the environment-fatigue coupling loading device. The fatigue load levels (60%, 50%, 40%, 30% and 20%) were selected to carry out fatigue tests, the fatigue life curves at different temperatures were analyzed, and the functional relationship of nominal stress-temperature-fatigue fracture cycles was obtained by fitting. The fatigue failure section of the joints at different temperature was analyzed by macrography and scanning electron microscopy (SEM). The results show that the temperature has obvious influence on the quasi-static and fatigue performance of the joints. Since the glass transition temperature (Tg) of the adhesive is −66 °C, the quasi-static failure load and failure displacement of the joints gradually decrease with the increase of temperature. Compared with −40 °C, the failure load and failure displacement decrease by 76.88% and 57.36% respectively at 80 °C. The temperature inside the adhesive layer increases with the increase of the fatigue frequency. With the increase of temperature, the fatigue performance of the joint decreases gradually. The closer the temperature is to the Tg of the adhesive, the larger the fatigue performance decreases. The temperature has obvious effect on the fatigue failure section, and the fatigue failure mechanism may change with the change of temperature. Interface failure is easy to occur at low temperature, and the ligament area of the failure section changes significantly. Cohesive failure is easy to occur at high temperature, and the obvious cracks and convex particles are easy to appear on the failure section.