Energy-release rates and opening of cracks in thin barrier coatings on polymer substrates subjected to tensile loading
Marcus Vinícius Tavares da Costa, E. Kristofer Gamstedt
Abstract
Thin barrier coatings on polymer films are used increasingly in various applications. In coatings development, it is of interest to characterise the fracture toughness. The tensile fragmentation test potentially provides data to determine the critical energy-release rate for channelling cracks in the coatings during crack accumulation with increasing strain. Also, the crack-opening of displacement is of importance to predict barrier properties. In this work, a method based on finite-element simulations is presented to predict the energy-release rate and crack-opening displacement. The results are compared with experimental findings for TiO2 and mixed TiO2-Al2O3 coatings, with a thickness down to 4–20 nm, on polymer films. It was found that the non-linear stress–strain behaviour of the polymer substrate material needs to be accounted for in the numerical model, in particular for the high strains close to crack saturation observed in these types of materials. Considering the small scales for the cracks and coating thickness, the predicted crack openings compare favourably with those measured experimentally using high-resolution scanning-electron microscopy.