Producing Dislocations in an Elastic Body Schematic

Hypothetically, one might imagine two ways of producing a dislocation 

In single crystals, dislocations are formed at the free smfaces. Suffice it to say that sites, such as precipitates, dispersed phases, oxides, etc., can all serve as sources for dislocation initiation and generation. Note that an important concept for dislocation generation is the collapse of vacancies to form disc-shaped dislocations, as suggested by Nabarro [41]. 

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