Influence of collective effects on the dynamic behavior of a single edge dislocation in a crystal with point defects

The glide of a single edge dislocation in an elastic field of point defects randomly distributed over a crystal is investigated taking into account the influence of the phonon subsystem of the crystal. The force of retardation of the dislocation motion is calculated, and the velocities at which this force has a local maximum and a local minimum are determined. A comparative analysis of the glide of a single dislocation and the glide of a pair of edge dislocations is performed.     

Effect of a high hydrostatic pressure on the dynamic instability of dislocation motion

The effect of a high hydrostatic pressure on the dislocation dipole vibration frequency and the forces of dynamic drag of dislocations by dislocation dipoles and of dislocation pairs by pinned dislocations is studied. Analytical expressions are obtained for the force of dynamic drag of mobile dislocation pairs by pinned dislocations and for the force of drag of isolated dislocations by dislocation dipoles in hydrostatically compressed crystals. Hydrostatic compression leads to a significant increase in these forces. This effect is most pronounced in alkali-halide crystals, where the drag force increases by a factor of 1.5–2.0.     

Influence of the phonon viscosity and dislocation interaction on the glide of a pair of edge dislocations in a crystal with point defects

The motion of a pair of edge dislocations in an elastic field of point defects is investigated taking into account the interaction of dislocations both with each other and with the phonon subsystem of the crystal. It is demonstrated that the retarding force is a nonmonotonic function of the velocity of dislocation glide with two extrema displayed under certain conditions.     

Interaction of point defects with an edge dislocation in the gradient theory of elasticity

Interaction between a point defect and an edge dislocation is studied in the framework of the gradient theory of elasticity. The change in the energy of the system caused by a displacement of the point defect relative to the dislocation line is calculated. The results of the theoretical analysis are used to describe edge dislocation pinning by impurity atoms.     

Dynamic interaction of edge dislocations with point defects and prismatic dislocation loops at high-strain-rate deformation of crystals

The motion of an ensemble of edge dislocations at high-strain-rate deformation of a crystal with a high concentration of prismatic dislocation loops and point defects has been analyzed. It has been shown that, under certain conditions, the drag of an edge dislocation by prismatic dislocation loops has the character of dry friction, and the magnitude of the drag force of the dislocation is determined by the relationship between the concentration of prismatic dislocation loops and the density of mobile dislocations. An increase in the density of mobile dislocations leads to an enhancement of their collective interaction, thus facilitating the overcoming of prismatic dislocation loops by edge dislocations. The total drag force of an edge dislocation is a nonmonotonic function of the concentration of point defects, which, under certain conditions, has a minimum.     

Elastic interaction of dislocation loops and point defects

The elastic interaction energy of a circular dislocation loop with interstitial atoms and vacancies characterized as dilatation or relaxation centres is calculated. Further, the forces which the dislocation loops exert on point defects through elastic interaction are discussed.     

Influence of hydrostatic pressure on the native point defects in wurtzite ZnO: Ab initio calculation

The formation energies and transition energy levels of native point defects in wurtzite ZnO under applied hydrostatic pressure are calculated using the first-principle band-structure methods. We find that the pressure coefficient of the (2+/0) level for oxygen vacancy is larger than that of the (2+/1+) level for zinc interstitial, which demonstrates that the donor level of oxygen vacancy is deeper than that of zinc interstitial, therefore the latter is the more probable electron resource in native n-type ZnO. And the significantly different pressure dependence of the transition levels between them can be used to determine the origin of the green luminescence center in ZnO. Zinc octahedral interstitial and oxygen tetrahedral interstitial configurations became the dominant defects under 5 GPa at their favorable growth conditions, respectively. The formation of defects under applied pressure is the result of fine interplay between internal strains, charges on the defects and applied external pressures.     

Dynamic drag of edge dislocation by circular prismatic loops and point defects

Motion of edge dislocation in the presence of prismatic loops and point defects is studied analytically. It is shown that at certain conditions, the velocity dependence of the drag force has two maximums and two minimums.     

The interaction of a screw dislocation with point defects in bcc iron

In this study, we calculate the interaction energy of intrinsic point defects vacancies and interstitials) with screw dislocations in body-centered cubic iron. First (we calculate the dipole tensor of a defect in the bulk crystal using molecular statics. Using a formulation based on linear elasticity theory, we calculate the interaction energy of the defect and the dislocation using both isotropic and anisotropic strain fields. Second, we perform atomistic calculations using molecular statics methods to directly calculate the interaction energy. Results from these two methods are compared. We verify that continuum methods alone are unable to correctly predict the interactions of defects and dislocations near the core. Although anisotropic theory agrees qualitatively with atomistics far from the core, it cannot predict which dumbbell orientations are stable and any continuum calculations must be used with caution. Spontaneous absorption by the core of both vacancies and dumbbells is seen. This paper demonstrates and discusses the differences between continuum and atomistic calculations of interaction energy between a dislocation core and a point defect.     

Steps on the smectic a liquid crystal surface and their interaction with an edge dislocation

The step on the smectic A surface is modelled using a part of an edge dislocation solution. Then a step-edge dislocation interaction in a finite smectic A sample is calculated and discussed.     

Effect of high hydrostatic pressure and high dynamic pressure on stability and rheological properties of model oil-in-water emulsions

Both static and dynamic high pressure applications provide interesting modifications in food structures which lead to new product formulations. In this study, the effects of two different treatments, high hydrostatic pressure (HHP) and high dynamic pressure (HDP), on oil-in-water emulsions were identified and compared. Microfluidization was selected from among the HDP homogenization techniques. The performance of each process was analyzed in terms of rheological modifications and emulsion stability improvements compared with the coarse emulsions. The stability of the emulsions was determined comparatively by using an analytical photo-centrifuge device employing novel analysis technology. Whey protein isolate (WPI) in combination with a food polysaccharide (xanthan gum, guar gum or locust bean gum) were used as emulsifying and stabilizing ingredients. The effective disruption of oil droplets and the degradation of polysaccharides by the shear forces under high pressure in HDP microfluidization yielded finer emulsions with lower viscosities, leading to distinctive improvements in emulsion stability. On the other hand, improvements in stability obtained with HHP treatment were due to the thickening of the emulsions mainly induced by protein unfolding. The corresponding increases in viscosity were intensified in emulsion formulations containing higher oil content. Apart from these, HHP treatment was found to be relatively more contributive to the enhancements in viscoelastic properties.     

On the vibrational spectrum of a parallel dislocation array

The free vibrations of dislocation arrays of different types (monopole and dipole dislocation walls and a planar dislocation array) have been investigated on the basis of the dispersion equation derived within the self-consistent dynamic theory of dislocations. The relaxation spectrum of a planar dislocation array in the strong damping mode has also been analyzed.     

Analytical methods for the calculation of the elastic interaction of point defects with dislocation loops in hexagonal crystals

The Green’s function method for hexagonal crystals within the Lifshitz–Rosenzweig (1947) and Kröner (1953) approaches has been used to obtain analytical expressions for the energy of elastic interaction of radiation-induced point defects with dislocation loops of three types: the basal edge dislocation loop (cloop), the basal shear dislocation loop, and the edge a-loop (bedding plane {11 20}, Burgers vector b ^D = 1/3〈11 20〉). In the case of the basal edge dislocation loop, a similar expression has been obtained independently by solving the equilibrium equations using the Elliott method. A numerical comparison of the derived expressions for zirconium has demonstrated a complete identity of the results obtained within the approaches considered in this study.     

Elastic interaction of point defects with dislocations

Elastic interaction between dislocation and point defects with spherical symmetry is investigated theoretically by means of the sphere-in-hole model. The interaction energy due to the different elastic moduli of the point defect and matrix is computed and then added to the interaction energy due to the size effect. The force on and the probable position of the point defect is determined. The numerical results for some selected solute atoms are computed by means of available experimental data.The results are compared with other recent papers and some experimental applications are briefly discussed.The author is much indebted to F. Kroupa, CSc., for fruitful discussions and valuable comments.     

Orientational effect of the dynamical interaction of circular dislocation loops with a moving edge dislocation

The glide of an edge dislocation in a crystal containing circular dislocation loops is studied theoretically. An analytical expression is obtained for the drag force exerted on a dislocation by various types of dislocation loops, and it is shown that this force depends significantly on the orientation of the Burgers vector of immobile dislocation loops with respect to the gliding dislocation line. The F _‖/F _⊥ ratio of the drag force for the parallel orientation of the Burgers vectors of the loops with respect to the gliding dislocation line (F _‖) and the drag force for the perpendicular orientation (F _⊥) is equal to K(v/c)², where v is the velocity of the dislocation; c is the velocity of acoustic waves in the crystal; and K is a dimensionless coefficient, whose value is of the order of the ratio of the concentrations of dislocation loops with parallel and perpendicular orientations of the Burgers vector.     

Influence of hydrostatic compression on the sliding of a pair of edge dislocations in metals with a high impurity concentration

The dynamic drag of dislocations by point defects in hydrostatically compressed metals is theoretically investigated. Account is taken of the influence of a high pressure on dislocation-dislocation and dislocation-point defect interactions. It is shown that the pressure dependence of the force causing dynamic drag of dislocations is determined by competition between these interactions.