1. Consider a glide dislocation loop in a crystal subjected to shear stress on planes parallel to the loop as shown below. Determine if the loop expands or moves as a whole. Does the loop remain circular when the stress is applied as shown in the figure below.
2. Consider two parallel dislocations, one as an edge dislocation and the other a screw dislocation. Show that there is force acting between them.
Q3. The following dislocation nodes are observed in fcc crystal. If each of the total dislocations of the (a/2) <110> type are split into Shockley partial dislocations, determine the final configurations of the two nodes following the convention of splitting into Shockley partial dislocations. The sense vectors of the dislocations at the nodes are given by the arrows. All three dislocations are lying in the (111) plane. Use the Thompson tetrahedron given below.
1. Stress field of an edge dislocation along z with Burgers vector in the x-direction and extra plane of atoms along y direction.
With the Burgers vector in the x-direction and sense vector in the z-direction, the stress field of the edge dislocation situated at the origin is given by c'xx -A y(3x2+y2)/r4, ayy=A y(x 2 -y2 )1r4 , axy=Ax(x2-?)/r4, azr=v(axx+yy) Atb/2it(1 -v)
2. Stress field of a screw dislocation
With sense vector and burgers vector are along z-axis, the stress field of the screw dislocation is given by
yz A(1-v)x/?, xz-A(1-v) yIr2
A is same as above with b the burgers vector of the screw dislocation.
3. Peach-Koehler Formula:
F= (b.)xE.
4. Climb force
F= - (kT/V a ) ( bX) In (C/Co)
