Delamination of Thin Films From Two-Dimensional Interface Flaws at Corners and Edges

Abstract

This paper details the mechanics governing delamination of thin films driven by thermal expansion mismatch from two-dimensional interface flaws. Two scenarios are considered: (i) the edge of the film is concurrent with the edge of the substrate and (ii) the substrate extends past the edge of the film. Fully three-dimensional finite element models are used to analyze semi-circular interface flaws (along the edge) or quarter-circle interface flaws (at the corner of the film) for both scenarios. Results are presented for energy release rates and mode-mixity along two-dimensional crack fronts. For all cases considered, the crack driving force very close to the intersection of the crack front and the edge of the film is substantially larger than that for the interior portions of the crack front. For a given flaw size, the energy release rate along the entire front is higher when the substrate extends past the end of the film. The stress intensity factors are mixed-mode along the entire crack front; the predictions illustrate that the mode III component comprises a substantial contribution to the crack driving force over a significant part of the crack front. The implications of the results on film delamination is discussed in terms of critical flaw sizes, crack front profiles and the influence of the intersection singularity.