Elastic Mismatch Influence on Modes I and II Ratio during Buckling-induced Delamination

Abstract

In the field of modern electronic, medical and aero-space industry there has been an increasing demand on the investigation and development of new materials and their usage as thin films and coatings. To ensure a proper and long-life reliability of the device composed of several micro- and nano-scale thin layers, not only the reliability of used materials has to be engineered, but also the interface stability between the layers must be ensured. Modern thin film applications use the combination of metallic conductive thin films on compliant substrates or hard coatings, connecting two, highly dissimilar materials. Therefore, in order to correctly assess the interface adhesion and fracture criteria, the elastic mismatch between the thin film and substrate must be properly accounted for. A widely used method to measure the adhesion between thin film and substrate is the buckling-induced delamination by Hutchinson and Suo (1992) where the adhesion energy of the thin film is evaluated as a function of the mode-mixity (for mixed-mode I+II) angle. However, a common practice in such measurements is to disregard the elastic mismatch of film and substrate. Recent research showed that the elastic mismatch has significant impact on the value of the mode-mixity angle. Since the dependence of the adhesion energy on the ratio between modes I and II is used for the interface fracture criteria, the errors introduced by disregarding the elastic mismatch influence may lead to errors in estimation of the critical crack driving force. In this study, we apply our model of the influence of the elastic mismatch on several fracture criteria in combination with experimental measurements of three film-substrate systems. Application of a more precise approach with use of the elastic mismatch influence show change in obtained mode I critical crack driving force. Therefore, the presented work highlights the need for precise assessment of the elastic mismatch influence on the mode-mixity when measuring the adhesion of thin films.