Evaluating the performance of organic coatings under mechanical stress using electrochemical impedance spectroscopy

Stress in coatings originating from a mechanical load imposed during exploitation is a relatively unexplored field of investigation. Paradoxically, a number of constructions and installations seem to operate under such conditions. The purpose of this work was to investigate the impact of a cyclic mechanical load exerted on coating/metal systems. It was the authors’ aim to verify whether repeated mechanical stress constitutes a significant factor contributing to coating degradation. Epoxy coated St3SAl steel samples were subjected to 21,000 uniaxial strain/release cycles. The maximum force applied assured maintenance within the elastic deformation region of the metal substrate. The state of the protective film was monitored using electrochemical impedance spectroscopy. The coating response to the mechanical load occurred in a three-stage process. The system subjected to the strain/release cycles revealed signs of degradation earlier compared to a non-strained, reference sample.