An expanding circular delamination front

How is the behavior modified if the delamination front is curved rather than 

Because the outer edge of the annular region at r = a is still at its unrelaxed position, the circumferential strain there is essentially Cm so that 

It is evident from this result that the stress restraining the film has the value (Ta = 0 when a = b, and that it increases monotonically as a/b increases from the value 1. Note also that as5rmptotically approaches unity as 

The value of a at which advance of the delamination front must stop, say ar, is the value at which the Griffith condition 

Farris and Bauer (1988) introduced an experimental approach to measure the separation energy F based on the geometrical configuration under discussion here. Motivated by this approach, the separation energy is expressed as a function of ap in (4.45), rather than the other way around, to anticipate the interpretation of measurements. The material parameters of the film, the film thickness and the mismatch stress are presumably known on the basis of measurements made separately from any delamination experiments. The radius h is controlled in the experiment, and therefore its value is known. Thus, if ap can be observed in an experiment, a value for F can be inferred on the basis of (4.45). 

---