EGN 3365 Lecture Notes - Lecture 10: Ductility, Ultimate Tensile Strength, Precipitation Hardening
Document Summary
Metals: dislocation motion easiest, nondirectional bonding, close packed directions for slip (an edge dislocation slides over adjacent plane half-planes of atoms in direction perpendicular to dislocation line which is same as burgess vector direction). Ionic ceramics: motion difficult, ned to avoid nearest neighbor of like sign. If dislocations can"t move, plastic deformation doesn"t occur. Slip system: slip plane is plane on which easiest slippage occurs which is the highest planar densities, slip difections is directions of movement which is highest linear densities. Fcc slip occurs on {111} planes (close packed) in <110> directions (close packed); total of 12 slip systems in fcc, for bcc and hcp there are other slip systems. Stress and dislocation motion: resolved shear stress (tr) results from applied ensile stresses. Condition for dislocation motion: ease of dislocation motion depends on crystallographic orientation [tr>tcrss which will cause crystal to yield] Deformation to occur the applied stress must be greater than or equal to the yield stress.
