Characterization of adhesive ageing using mechanical and electrochemical inspection

Abstract

Two methacrylate adhesives, commonly used in railway applications, were tested before, during and after accelerated humid ageing. First, bulk tensile samples were fabricated in order to perform mechanical characterization before ageing. Then, the samples were placed in a humid environment and the influence of water on the Young's modulus and the tensile strength was determined. In parallel, Electrochemical Impedance Spectroscopy (EIS) measurements were carried out with methacrylate-adhesive-coated aluminum panels in order to extract parameters related to the porosity and adhesion of adhesives which are both dependent on water penetration. Finally, the mechanical characterization of adhesively-bonded lap joints with aluminum substrates was performed before and after accelerated humid ageing. All these experiments allowed to distinguish the two adhesives tested. It was found that the bulk adhesive samples which presented the best mechanical properties before ageing did not guarantee a good bonded-joint behavior after ageing. More importantly, the combination of EIS with mechanical tests allows to significantly reduce very much the number of experiments and, thus, the cost of industrial validation tests.