Driving force for interface delamination

If a crack lies in the interface between two materials, with the crack edge separating a part of the interface over which the materials are bonded from a part over which the bond has been broken, then the determination of local fields becomes a complex problem. Dundurs (1969) showed that the solutions to problems in plane strain elastostatics which involve two joined homogeneous and isotropic materials depend on the four elastic constants involved in a very special way. The elastic fields depend on the material 

For any fixed value of Di and Poisson ratios in the range 0 the parameter D2 must be in the range — (1 — Di) D2 (l- -Di). Values of the Dundurs parameters for some common substrate-film material combinations are listed in Table 4.1. 

When a crack edge lies within either one of the joined materials, the 

In many particular cases, there is a direct correspondence between the Irwin and Griffith criteria, as was noted above an connection with the result in (4.27). However, the latter criterion has the distinct advantage that the energy release rate can often be determined, or at least estimated, without the need for a complete solution of the boundary value problem for the stress field in the body. For this reason, it is selected as the basis for the present discussion. Many of its special features and numerous extensions of the basic concept will become evident in the sections that follow, in the course of discussing various issues concerned with delamination and fracture in thin film configurations. 

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