Dislocation Dynamics simulations

Fig. 12.26. Results of mesoscopic dislocation dynamics simulation of dislocation interactions in a strained epitaxial layer (adapted from Schwarz and LeGoues (1997)). The network shown in the figure results from the interaction of dislocations on parallel glide planes.

At the microscale, dislocation dynamics simulations implement the equations of continuum elasticity theory to track the motion and interaction of individual dislocations under an applied stress, leading to the development of a dislocation microstructure and single-crystal plastic deformation. In our multiscale modeling... 

Preliminary Dislocation Dynamics (DD) simulations using the model developed by Verdier et al. provide a plausible scenario for the dislocation patterning occuring during the deformation of ice single crystals based on cross-slip mechanism. The simulated dislocation multiplication mechanism is consistent with the scale invariant pattemings observed experimentally. 

Figure 9.2, Left Structure of a CeOj(l 11) surface as relaxed on a cubic ZrOj(l 11) substrate, generated by dynamic simulation. Zr (light blue), Ce(magenta), oxygen in 2hO,(red), oxygen in CeO,(green). Right Stick representation of a screw-edge dislocation threading through the CeOj layer and the first ZtO sub-layer. From ref. 62, reproduced by permission of the Royal Society of Chemistry.

Mesoscopic computer simulations [27] of the 3-D dislocation dynamics of fatigue hardening reveal that dipoles forming in one half-cycle unzip during the next, unless stabilized to form EDLs via annihilation. This... 

Fig. IX-37. The molecular dynamic simulation of deformation and fracture of two-dimensional crystal a - plastic deformation and formation of a dislocation at elevated temperature (upper portion) and development of brittle crack at low temperature (lower portion) b - simultaneous processes of crack nucleation and foreign atom propagation at elevated temperature (both upper and lower portions)...

Fig. 6. Three snapshots of molecular dynamics simulations of a (10.10) nanotube under axial tension, (a) Formation of a bond rotation defect at T = 2000 K and 10% strain, (b) Plastic flow behavior after ns at T = 3(K)0 K and. 3% strain. The shaded area indicates the migration path of the (5-1) edge dislocation, (c) Nucleation of large open rings and initiation of the brittle relaxation after 1.0 ns at T = 1.300 K and 15% strain. See text.

The method of dislocation dynamics (DD) intends for the modeling of dislocation-based plastic deformation in crystals. It is in the same spirit as atomistic MD simulations, but instead of int aring the equations of motion of particles, it considers evolution of dislocation lines. Modeling these dislocations and their evolution and growth can, in principle, be performed at the atomic scale, but very large numbers need to be modeled to determine their influence at the macroscopic level. 

Formation and Strength of Dislocation Junctions in FCC Metals A Study by Dislocation Dynamics and Atomistic Simulations. 

Usually, experiments and numerical simulations are rather complementary and it may be difficult to make meaningful comparisons. Nevertheless, there are two cases where this can be done. The first one is related to the mobility of non-dissociated dislocations. The computed Peierls stress for the non-dissociated shuffle screw dislocation is 4 GPa, in good agreement with the order of magnitude of the extrapolation at OK of flow stress measurements below 300°C (Section 2.3.2). In addition, the extrapolation at OK of yield stress measurements performed in the medium temperature range fits quite well the computed values of the Peierls stress for glide dislocations. Numerical simulations revealed that the thermally activated motion of non-dissociated screw dislocations was possible at 300 °C under an applied stress of 1.5 GPa, as reported from yield stress measurements (Section 2.3.2). The second case concerns the nucleation of dislocations. Molecular dynamics simulations of the dislocation nucleation from surface steps... 

Dislocation dynamics has been recently applied to minerals such as periclase [443] (Fig. 17) to explore the hardening in this material through interactions and reactions between dislocations gliding in noncoplanar slip systems and olivine [424]. Such simulations may in the future become important tools to predict plasticity based on dislocation geometry for a variety of conditions that cannot be explored experimentally. 

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