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Plastic Deformation
Dislocation Model

· The Frenkel ideal crystal model predicts the critical shear stress to be on the order of: τ cr ~ (G/2π) ~ 10 GPa, for a ~ b
· Data for metals shows this value is about 104 x the measured bulk value. A better model is required!
· The dislocation model of yield and plastic deformation is expected to reduce the yield stress by requiring only local bonding changes during the shear slip process.
· The dislocation model is analogous to sliding a carpet across a floor by kicking a ruck from one side of the carpet to the other.

From: Barrett, Nix, and Tetelman, The Principles of Engineering Materials, Prentice Hall (1973)