Mode I fracture toughness determination in Cu/W nano-multilayers on polymer substrate by SEM - Digital Image Correlation

Nanostructured metallic multilayers with carefully designed mechanical and functional properties are omnipresent in cutting edge technological applications. To ensure the mechanical integrity of such coatings, the Mode I critical Stress Intensity Factor KIC is used to quantify their fracture toughness in order to avoid material failure by appropriate design. In this article, we present a novel approach for the KIC determination of thin and ultrathin films on compliant substrate, based on micro-displacement field analysis using Digital Image Correlation within SEM. Using this method, KIC of a Cu/W nano-multilayer with a total coating thickness of 240 nm was determined as K IC = 4.8 ± 0.05 MPa m , showing excellent agreement with the values published for comparable systems in the literature. To verify the validity of the chosen approach, two independent finite element simulations were employed, thus revealing the role and effect of the compliant substrate on the stress and displacement fields arising around the crack tip in thin films.