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Unformatted text preview: MECH 210 081008 Dislocations and Strengthening Mechanisms Deformation by Slip Dislocations: (1) Edge dislocation: Burgers vector ⊥ dislocation line (2) Screw dislocation: Burgers vector // dislocation line • Lattice distortion exists around the dislocation line due the presence of the extra plane of atoms • Lattice distortion results in compressive, tensile, and shear lattice strains around the dislocation lines • Dislocations can exert a repulsive force or a attractive force on each other resulting in movement of dislocations on certain planes under shear stress • Two dislocations can annihilate each other upon meeting under attractive force Slip: The process by which plastic deformation is produced by dislocation motion. • Slip system – preferred plane ( slip plane ) and direction ( slip direction ) for dislocation motion - slip direction is in slip plane - slip directions are crystallographic directions of the highest linear density of atoms - slip planes are the crystallographic planes of the highest planar density of atoms - primary slip system for major crystal structures are - Burgers vectors for FCC, BCC, and HCP crystal structures are expressed, respectively, as , 1 1 1 2 , 1 1 2 〉 〈 = 〉 〈 = a b a b v v and 〉 〈 = 2 1 1 3 a b v- resolved shear stress:...
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- Fall '08
- Deformation, 45°, dislocation motion, 2 grain