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ENGR 240 - 10.17.07

ENGR 240 - 10.17.07 - increased plastic deformation =...

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ENGR 240 – October 17, 2007 Dislocation motion o Bonds break & reform o Figure 8.1 & 8.2 Edge Dislocation Motion is parallel to shear stress Screw Dislocation Motion is perpendicular to shear stress. o Slip Plastic Deformation by dislocation Dislocations move along preferred planes and in preferred directions Slip plane and slip direction form a slip system Slim system depends on crystal structure Occurs along the most densely packed planes and directions Highest linear and planar density It is not easy to break bonds in densely packed planes, but it is easier to break bonds between two densely packed planes o FCC crystal structures in the {1 1 1} family of planes are the most densely packed Triangle that intersects each direction at the reciprocal of 1 (i.e. 1) The amount of plastic deformation increases with the amount of slip
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Unformatted text preview: increased plastic deformation = easier slip o Ductility will increase o FCC, BCC, then HCP have decreasing Plastic deformation in this order FCC is highly symmetric which gives it the highest plastic deformation o HCP has few active slip systems and tend to be brittle Slip in Single Crystals o We apply tensile or compressive stress o Dislocations move or slip in response to shear stresses that result from applied stresses Resolved shear stress τ R o Magnitude of τ R depends on Applied stress Crystal orientation o Slip occurs along most favorable plane and direction Non-uniform deformation o If a single crystal with rectangular geometry and oriented properly, you could get: One face to remain constant in width but the other face would change drastically...
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