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 K-IC 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 K-IC determination of thin and ultra thin films on compliant substrate, based on micro-displacement field analysis using Digital Image Correlation within SEM. Using this method, K-IC of a Cu/W nano-multilayer with a total coating thickness of 240 nm was determined as K-IC = 4.8 +/- 0.05 MPa root 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. (c) 2020 Elsevier Ltd. All rights reserved.