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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