Tensile stress due to island contiguity

A simple expression for the stress generated when islands impinge on each other can be obtained on the basis of this concept. Consider a flat 

Section 8.6.2 within the framework of a particular model which can capture the zipping up process in a realistic way. The model is based on the theory of elastic contact of solids with rounded surfaces known as Hertz contact theory, with the added feature that the contacting surfaces cohere. 

As noted, an estimate of the tensile stress magnitude based on the Hoffman-Nix model often leads to a stress magnitude that is larger than any observed. However, as soon as the stress level reaches the yield stress of a polycrystalline material, glide dislocations can form to modulate the amplitude. This line of reasoning has been discussed in some detail by Machlin (1995) who pointed out that the mechanism as described is athermal except for the possible dependence of yield stress on temperature. At elevated temperatures, mechanisms associated with increased surface mobility of atoms can come into play to diminish the effectiveness of the Hoffman-Nix mechanism in generating stress, and evidence for the influence of such mechanisms is apparent in experimental data. 

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