The stress-strain curves of single crystals under uniaxial tensile deformation are obtained for the whole deformation process by atomistic molecular statics simulations. Effects of model sizes, boundary conditions, crystal orientations and displacement increment on the stress-strain curves are investigated. Various deformation evidence such as dislocation movement, dislocation piling up and twinning are clearly observed. The deformation and fracture characteristics of and their dependence on the boundary conditions or the stress states are studied.

Classical molecular dynamics simulations of the interaction of edge dislocations with precipitates in a-iron are performed. The critical resolved shear stress (CRSS) is determined for various morphologies of precipitates: pure copper and nickel precipitates, ordered and unordered copper/nickel precipitates, copper and nickel precipitates with substitutional iron atoms, copper precipitates of ellipsoidal shape, and copper precipitates with nickel shells. The dependence of the CRSS on the nature of the precipitate is explained by considering the Burgers vector distribution within the precipitates. It is shown that, except for the ordered precipitates, chemical inhomogeneities of the precipitates lower the CRSS with respect to the precipitates consisting of the pure phases.

The aim of the present work is to investigate by molecular dynamics (MD) calculations the interaction between a moving edge dislocation in an -Fe crystal and a copper precipitate. In the absence of external stresses, two edge dislocations with the same slip plane and opposite Burgers vectors within a perfect -Fe crystal lattice are investigated. In agreement with Frank's rule, the movement of the dislocations under mutual attraction is found and attention is focused on the interaction between one of the dislocations and the Cu precipitate. The critical resolved shear stress of the Fe was calculated and the influence of different sizes of Cu precipitates on the dislocation mobility was studied. The pinning of the dislocation line at the Cu inclusion as derived from the atomistic modelling agrees with previously published continuum theoretical behaviour of pinned dislocations. Therefore, nanosimulation as a way to model precipitation hardening could be established as a useful scientific tool.

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The local structural arrangement of ions around a substitutional Cr3+ ion in sapphire (ruby) has been studied experimentally using extended X‐ray absorption fine structure (EXAFS) in the vicinity of the Cr absorption edge. The findings are compared with an ionic model (Mott‐Littleton) computation using two sets of pairwise potentials. Both the EXAFS results and the computations reveal that when Cr substitutes for an Al ion in sapphire, the surrounding ions relax to an arrangement similar to that for Cr in α‐Cr2O3. Also, most of the structural relaxation is accommodated by the first shell of oxygen and aluminum ions around the substituted Cr3+ ion. The computations also indicate that with applied pressure (tensile and compressive) the ionic positions change self‐similarly and in proportion to the macroscopic strain.