Experimental testing and finite element analysis of polyurethane adhesive joints under Mode I loading and degradation conditions

The use of adhesive joints in marine environments for extended periods and under adverse environmental conditions leads to accelerated adhesive degradation. Therefore, this study aims to perform a dual analysis, both experimental and FEM, based on steel-polyurethane-steel adhesive joints to evaluate their fracture behaviour in Mode I under degradation conditions caused by accelerated polymer aging, due to the combined effects of moisture (seawater immersion) and high temperature (50 degrees C). Experimental tests provided insights into the moisture concentration profiles within polyurethane, determining its critical concentration (0.61%) and diffusion coefficient (5.105 x 10-13 m2s-1). Additionally, the variation curve of fracture energy versus elongation and the cohesive behaviour law of polyurethane were obtained (maximum stress of 0.32 MPa with a deformation of 0.02 mm). These experimental results enabled the development of an FEM analysis of the polyurethane adhesive joint, allowing for the simulation of the polyurethane-steel interface behaviour under adverse environmental conditions and constant Mode I loading. This approach makes it possible to predict both the failure moment and failure mode of the joint.