Effect of cure temperature on the mechanical properties of epoxy-aluminium single lap joints

Mixed adhesive joints combining different stiffnesses and strengths in the same overlap is a good strategy to increase the mechanical properties. For this purpose, different adhesives with distinct curing temperatures are used, whose optimization is crucial to maximize the mechanical performance. In this context, this study considers Araldite (R) AV 4076-1/HY 4076 and Araldite (R) AW 106/HV 953 U adhesives to evaluate the effect of curing temperature on tensile strength, creep and stress relaxation response and fatigue strength of single lap joints. It was possible to conclude that both adhesives exhibited higher static strength, lower stress relaxation and lower creep displacements with increasing curing temperature, but while for the brittle adhesive this trend occurred up to 150 degrees C for the ductile one it was only up to 70 degrees C. After this value, all properties regressed due to the degradation of the ductile adhesive with temperature. Considering values corresponding to 25% of the tensile strength, for example, it was noted that the ductile adhesive relaxes 54.7% more than the fragile one and presents a creep displacement around 95.1% higher. On the other hand, while the fatigue life was shown to be insensitive to the curing temperature for the brittle adhesive, in the case of the ductile one it decreases after 70 degrees C. Therefore, when these adhesives are combined into a mixed adhesive joint, the curing temperature must never exceed 70 degrees C.