DEFECTS IN METALS AND SIMULATION OF MECHANICAL ...

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Fig. 4-4: Edge dislocation in the (1 1 -2) plane while indenting in the Z direction, yielding at a depth of 8 A. Atoms with a co-ordination number less than 8 are shown. All other atoms are removed. Now performing nanoindentation in the same direction as the direction of motion of the edge dislocation in order to show the behavior of the dislocation in such conditions, so we perform nanoindentation in the y direction using the same indenter tip radius and the same indentation velocity; in this case the dislocation moves in the y direction until it recombines with the surface under the indenter as shown in Fig. 4-5 and Fig. 4-6. The motion of the dislocation toward the free surface is associated with the force of its image dislocation or image force; this force is an attraction force and is obtained from the stress of the image dislocation, it arises solely from the change in the elastic energy in the crystal: F y /L= (µb 2 )/ [(4Π (1-ν) l] [ 51 ]. 36
For iron the shear modulus, µ, is 82 Gpa and the burger’s vector, b, is 0.248 nm, l is the distance from the surface 7.5 nm and L is the length of the dislocation 15 nm and poison’s ratio, is 0.29. Therefore, for this simulation Fy/L= 0.0753 N/m. The force exerted by the indenter F i on the dislocation, considering the maximum shear stress under the indenter of around 7Gpa is on the order of Fi/L=105 N/m. Therefore, the motion of the dislocation in the simulation is likely related to the indentation rather than resultant image forces. It also gives an insight on the difference in the velocity of motion of the dislocation which is 273 m/s without the applied stresses of the indenter and around 600m/s when the indenter’s stresses are applied. 37
Page 1 and 2: DEFECTS IN METALS AND SIMULATION OF
Page 3 and 4: ACKNOWLEDGMENTS The time and commit
Page 5 and 6: dislocations on yield load were als
Page 7 and 8: LIST OF TABLES Page Table.2-1: Forc
Page 9 and 10: Fig. 3-2: Defects formation at the
Page 11 and 12: Chapter 1 Motivation The motivation
Page 13 and 14: experiments, the advantage is that
Page 15 and 16: Chapter 2 Vacancies effect on metal
Page 17 and 18: showing no dislocation nucleation b
Page 19 and 20: Fig. 2-3: Force displacement curves
Page 21 and 22: Fig.2-5: Indentation with 0% Vacanc
Page 23 and 24: In Fig. 2-6 a) and b) we can see th
Page 25 and 26: Vacancy concentrations were varied
Page 27 and 28: The load at yielding is also sensit
Page 29 and 30: Fig. 2-9 shows that with a higher s
Page 31 and 32: Atomistic computer simulation techn
Page 33 and 34: Figure 3-1 shows the simulation box
Page 35 and 36: Fig. 3-4a: Defects after the initia
Page 37 and 38: In Fig. 3-5 we can see the evolutio
Page 39 and 40: Fig. 3-6: Fraction Nv/n of survivin
Page 41 and 42: Chapter 4 Dislocations effect on Me
Page 43 and 44: The dislocation was created by remo
Page 45: Fig. 4-3: Edge dislocation in the (
Page 49 and 50: Fig.4-6: Simulatin showing dislocat
Page 51 and 52: Chapter 5 Conclusion Defects in met
Page 53 and 54: [ 14 ] D.F. Bahr, D.E. Kramer, and
Page 55: [ 47 ] H. G. M. Kreuzer and R. Pipp

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