Lecture note 22 (11-17-2011)

# Lecture note 22 (11-17-2011) - one dislocation on the other...

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1 MAE 581 Advanced Materials Science Lecture note 22 Sample questions of dislocations Question 1: Consider a crystal in the form of a cube of side L containing an edge dislocation of Burgers vector b . if the crystal is subjected to a shear stress σ on the upper and lower faces in the direction of slip, show, by considering energy balance, that the force acting on the dislocation is per unit length. Solution of question 1: Question 2: Assume that there exist two parallel dislocations in a solid material. The character of one is pure edge and the other is pure screw. Consider the interaction between the dislocations and use the corresponding elastic fields in the material to explain whether one dislocation exerts a force on the other. Solution of question 2: The dislocations do not exert any force on each other, since the Peach-Koehler force exerted by

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Unformatted text preview: one dislocation on the other is zero. Consider a “positive” edge dislocation with along the z-direction and b along the x-direction. A glide component of the Peach-Koehler force is exerted on the dislocation provided a nonzero value of is present, and a climb component is exerted provided a nonzero value of is present. This can be confirmed by using Peach-Koehler formula Therefore, the positive edge dislocation has a glide force 2 And a climb force The stress field solution for a screw dislocation provides neither of these (only and are produced). Therefore, a parallel screw dislocation does not exert a force on an edge dislocation. The same conclusion is obtained by considering whether an edge dislocation exerts any force on a screw dislocation....
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Lecture note 22 (11-17-2011) - one dislocation on the other...

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