Dislocation nucleation in a perfect crystal

The issue of dislocation nucleation in an initially perfect crystal has been studied experimentally by Gouldstone et al. (2001) who used the soap bubble 

In a continuum analysis, Li et al. (2002) adopted an approach whereby the nonlinear elastic response of the material was based on the known homogeneous deformation response of the single crystal of interest. The stress field throughout the performing elastic crystal is then determined incremen- 

Physically, the onset of instabihty at the point is interpreted as the formation of crystal defect there. It should be noted that local instability does not imply global instability of the configuration. If angle between the vectors k and w established in this way is larger than 60°, then the nucleated defect is expected to be a dislocation with slip plane normal k and Burgers vector approximately along w. On the other hand, if the angle between k and w and instability is less than 30°, the nucleated defect would likely be a microcrack or a void. 

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