Influence of Temperature, Humidity and Load Coupling on Mechanical Properties of Adhesive Joints and Establishment of Creep Model

To study the creep and property degradation behavior of adhesive joints under the coupling action of temperature, humidity and load, polyurethane shear joints were prepared and tested. Different static loads were applied to joints at high temperature (80 °C) and high temperature and humidity (80 °C/95% RH) to test and analyze the creep deformation, and a suitable creep model was established. At the same time, the performance degradation test of the joints under the effect of multifactor coupling was carried out to obtain the variation law of the failure load, and the failure mechanism was discussed based on the failure section. The research shows that the creep strain of the joint at high temperature and humidity was significantly larger than that at high temperature, and the failure fracture time was shorter, in which water molecules played a role of softening and hydrolysis. The viscoelastic multi-integral creep model was used to analyze and predict the creep behavior of the joints. It was found that the creep model could better describe the creep behavior of the joints under uniaxial constant loading. Under the coupling effect of temperature, humidity and load, the failure load decreased with time, and with the increase in static load, the decline range and rate of failure load increased. It was found that the mechanical properties in the high temperature and humidity environment decreased significantly more than those in the high temperature environment. When a static load was applied during creep, cracks easily occurred inside the adhesive layer, and water molecules easily diffused inside the cracks, which increased the decay rate of the mechanical properties. This study provides good theoretical significance and engineering value for the application of polyurethane adhesion structures in rail vehicles.