Question

The stress I, o and Burger's vector of a dislocation sing ABCDA is shown in the @ Estimate the type of each dislocation 6 How will the dislocation sing move if I is high enough ? ③ How will the discreation sing move if o is high enough ? How will the sing deform? How will the crystal deform? 99 A

Answer 1

Answer: en A Ilshear stres) Normal Shess D . Ś AB > Clockwise souw dislocator Be > positive edge disloc atoz CD > Articleuk wise screw dtlocation DA > Negative edge dislocation B led 7] lo La {] CB in ?] (B ?)

ESTIMATION OF SCPEW DISLOCATION ( due to_) A screen dislocation along the plane ABCDA aris with Burgers vector b is given by Shear stress o=GY : where G is shear modules Elastic Energy Es por unit length of the Screw dislocation. is given by : Gb2717 Es 19b (401 IN 12 . . dir > lower & upper limits for radius. of the Cylindterical 09055 Section to small faction of the total energy. ESTIMATION of Boge Dislocation : An edge dislocation Ę per unit length is given as " / 962 2 . . (-) Denotes the poisson ratio. → Ako perces between two edge. dislocations of equal Sign, but in opposite direction and with a Bergers Vector along the x-aris is given by

21*((-U) ESTIMATION OF I! The upper part of shown figure is gliding along ABCDA Slip plane an edge dislocation meets Obstacles in the form of a pair of precipitate porticles at B ... and c as shown. The applied stress to -> normal force. Tbl Dislocation line, bowing it out between the points B and C. -). This force isi balanced by the parallel component of the dislocation line Tension. 1261 = 27 Some) in 26d. < precipitate - Particle pa Vitamin D kt d-) Distance between B &c. the line tension T is given by T-G62 G> elastic Sheca modulus from above equations we have e=aabsing e

Marinum Stress required to Cause Maximum bowing in the line segment is when it become semi- circular her at o= 90 then T= 26b ABCPA 7 Mixed dislocation shear stress only cause ? deformation - 7> Shear cause deformation o normal won't cause plastik deformation * * Edge Screw After dislocation dislocation Moves Moves Parallel to È perpendicular to B

- If ?' is high then above part of tube will have edge dislocation prominent along plane ABCDA , across Be line > In Burger Vector be with respect to edge dislocation then bs. Before Afleg After Normal stress do not cause plastic deformation It 'o ABCDA direction. is high, then above part is screwed parallel to plane. in clockwise direction when seen from upside The variation of bs is prominent then the be.