Determination of fracture toughness of polymer coating using micro-scale digital image correlation technique

This paper presents a comprehensive study on determining the interface adhesive strength of the polymer coating/substrate system to improve its durability. Interfacial stress intensity factors based on the crack tip opening displacement (CTOD) method were theoretically analysed and verified by the finite element simulation. Thereafter, an experimental setup was established with the micro-scale digital image correlation (DIC) method to measure the CTODs and the designed loading fixture for multi-angle loading. The apparent specimen rotation and out-of-plane displacement were significantly restrained in the test, and the measured displacement accuracy of the micro-scale DIC method was approximately 1/10 of the minimum CTOD value. Mixed-mode stress intensity factors and an interfacial failure criterion curve in terms of stress intensity factors were obtained. Furthermore, the test method was applied to evaluate the interfacial fracture toughness of nanoparticle-reinforced epoxy coatings. The experimental results demonstrate that determining the stress intensity factors on the interface of the polymer coating/substrate system based on the CTODs is an effective and reliable approach.