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Lecture 13 Dislocations and Friends

# Lecture 13 Dislocations and Friends - Dislocations Weve...

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Dislocations We’ve already covered several things: 1) Basic definition in terms of edge, screw, mixed 2) Burgers vector 3) Partial dislocations 4) Energy & stress/strain field 5) Climb and glide More on types of dislocations I am going to focus on “real” dislocations in materials, as against mathematical combinations which are sometimes used in mechanical modeling to represent what is taking place during plastic deformation. Full Dislocations (done before, included here only for completeness) The Burgers vector corresponds to a lattice vector of the crystal, in almost all conceivable cases of the primitive unit cell. For instance, for fcc this is ½ [110] and for bcc ½ [111]. (For rigor, note use of “[“ and I am assuming the inclusion of the lattice parameter.) In a crystal provided that the Burgers circuit does not cut a defect, the nett Burgers vector has to correspond to a sum of full dislocation Burgers vectors. Partial Dislocation The Burgers vector is not a lattice vector, and the remaining part to complete the circuit is taken up by some other defect. For instance, a stacking fault corresponds to a rigid body translation from ABC A B CA… to ABC B CA… We remove “ A ”, and move down B by 1/3[111]. Since ½[110]=1/3[111]+1/6[11-2] a partial dislocation (Shockley) is associated with a stacking fault.

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Lecture 13 Dislocations and Friends - Dislocations Weve...

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