DEFECTS IN METALS AND SIMULATION OF MECHANICAL ...

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Fig. 2-9: Hertzain Fit and load displacement curves from simulations for different values of the force constant K (indenter stiffness) The equation used for the Hertzian force displacement fit is: [ 30 ] F is the load, d is the depth inside the sample R is the spherical indenter radius E1, v1 are respectively the elastic modulus and poison’s ratio of the sample E2 and v2 are the elastic modulus and the poison’s ration of the indenter (with k>1000 the indenter is perfectly rigid) 18
Fig. 2-9 shows that with a higher stiffness (k=1000 eV/ Ǻ 2 and above) of the indenter is very close to the Hertzian fit in terms of force and displacement values, which is a proof that the system during nanoindentation behaves as it s supposed to behave during experimental nanoindentation. In summary, the effect of vacancies on the yield load in nanoindentation was studied by molecular dynamics simulations. The results indicate that the presence of vacancies lowers the yield load, and a higher concentration will cause a higher deviation from the yield point with no vacancies following a weak power law relationship. During nanoindentation we can observe that the number of vacancies is going down as the indenter depth is higher. Dislocations begin to form at the yield load and after this point the model behaves plastically. The vacancies are not required to be present at the regions of highest imposed shear stresses to impact the nucleation stress, and as such may be influencing the stress field in the solid as well as participating directly in mechanisms that require additional time or temperature to activate a source. 19
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: The load at yielding is also sensit
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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