Durability of steel joints with ductile adhesive subjected to fatigue tests

The aim of this work is the study of the adhesive joints degradation within the polyurethane-steel and silicone-steel joints from the point of view of their behavior on service and under aging conditions. In order to evaluate the performance of the adhesive, the maximum strength resistance of different types of joints was calculated. This value was compared with the one obtained before the fatigue test. First, the maximum lap shear is determined in the single lap joints, followed by fatigue tests that will be done on the same lap joints with an increasing number of cycles, up to 105. Lap joints will be tested at several percentages values of the maximum lap shear. The material fatigue threshold is obtained from the resulting data. In some cases, and due to the inherent viscoelasticity of the adhesives, the samples may reach the fatigue threshold, and therefore it will not break. In those cases, the determination of damage suffered is performed by lap shear tests. The same procedure was carried out in aged silicone and polyurethanes joints and results were compared with non-aged samples. Finally, an analysis of the surface and morphological modifications, were investigated with scanning electron microscopy (SEM).