Critical strain arguments are often used to model the thickness dependence of the strength of thin films on substrates. In these arguments, plastic deformation occurs when the stress in a film is high enough that the strain energy relieved by the introduction of a misfit dislocation is sufficient to generate the line energy of that misfit. Such models typically assume compact dislocation cores. However, experimental evidence suggests that, under certain circumstances, dislocation cores may spread out into the interface between the film and the substrate. If this happens, the energy of the misfit dislocation, and the critical stress needed for its propagation, will be lowered. In this paper, the effect of dislocation core spreading on the critical stress has been modeled. The effects of interface strength, film thickness, and misfit dislocation spacing are considered.
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