DEFECTS IN METALS AND SIMULATION OF MECHANICAL ...

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800 700 600 Force (nN) 500 400 300 200 100 0 0.05% 0.1% 0 0 5 10 15 20 25 Depth (A) Fig.2-4: Load-depth curves for three vacancies fractions showing decreased yield load with increasing vacancy concentration. Load – displacement relationships for indentations at 100 m/s for the perfect Fe crystal and with vacancy concentrations of 0.05 and 0.1 % are shown in Fig.2-4. In general, the elastic loading is relatively independent of vacancy concentration at these concentrations, as it is expected that vacancies would have no significant effect on the elastic deformation. At a depth of 13 Ǻ the material starts to yield for the three curves; the load drops with increasing penetration depth. This indicates the start of the plastic regime where dislocations are created and start to move. Additionally, at this point the sample exhibits a rise in the temperature from 5 to 13 K, which is physically explained as the result of the motion of dislocations that causes friction and subsequently a rise in the temperature. 10
Fig.2-5: Indentation with 0% Vacancies at a) a depth of 9Ǻ showing atoms with decreased number of nearest neighbors b) View at the yield load with depth13 Ǻ. The large cluster of atoms with co-ordintation numbers less than 8 is representative of dislocation formation. Fig.2-5 shows two snapshots of the atoms at two different depths of the indenter for 0.0% vacancies. To visualize the deformation, Fig. 2-5 only notes atom positions which do not have a coordination number of 8, the typical value for BCC materials. Fig. 2-5(a) shows the surface deflection as a result of the force exerted by the indenter showing no plastic deformation and no 11
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: Fig. 2-3: Force displacement curves
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 and 46: Fig. 4-3: Edge dislocation in the (
Page 47 and 48: For iron the shear modulus, µ, is
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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