Fracture criterion of mixed-mode crack propagation along the interface in nanoscale components

Abstract

To investigate the fracture behavior of mixed-mode interfacial cracking in nanoscale components, three different types of nano-specimens, including the nano-cantilever specimen with a horizontal Cu/SiN interface, the nano-cantilever specimen with a vertical Cu/SiN interface, and the modified double-cantilever-beam (DCB) specimen, are adopted to conduct experiments of crack propagation from a pre-crack tip along the Cu/SiN interface, where the mixed-mode, mode-I dominated and qusai-mode-I interface cracking in nanoscale components are successfully achieved, respectively. Crack propagations from the pre-crack tip along Cu/SiN interface with different mode mixities are in situ TEM observed, and critical load/displacement for the starting of crack propagation are precisely measured. FEM analysis reveals that the interfacial crack propagation is dominated by a nanoscale singular stress field in all specimens, and the mixity of fracture modes varies from 0.27 to 1.28. Critical energy release rates for the starting of crack propagation along the Cu/SiN interface of all specimens are obtained with the compliance method, and the energy release rate linearly increases with the transition of fracture mode from the qusai-mode-I status to the mixed-mode one. Furthermore, the critical normal stress and shear stress show a circular relation, indicating the criterion for evaluating the mixed-mode crack propagation along interface in nanoscale components.