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Plastic Deformation
Frank-Reed Source

· Observations show that new dislocations are created to permit plastic deformation. 
· The observed shear displacements require about 1000 active dislocations on a single slip plane. A source of these dislocations that can emit dislocation loops on a single slip plane is needed.
· Frank and Reed proposed a dislocation source that is illustrated below for an isotropic material.
· The straight segment (a) bows into a loop due to the external forces. This closes on itself, creating a free loop (g) and a new segment that can repeat the process.
From: Barrett, Nix, and Tetelman, "The Principles of Engineering Materials," Prentice Hall (1973)