The stress-driven redistribution of point defects in the vicinity of crack-like singularities

1990 ◽  
Vol 427 (1872) ◽  
pp. 1-23 ◽  
Keyword(s):  
Steady State ◽  
Stress Field ◽  
Grain Boundary ◽  
Point Defect ◽  
Slip Band ◽  
Point Defects ◽  
Elastic Interaction ◽  
Mode Ii ◽  
Fracture Of Materials ◽  
Kinetics Of

The most important term in the energy of the elastic interaction between a crack and a point defect is presented and used to estimate the kinetics of redistribution of point defects in the stress field of an isolated crack under mode II load and a slip band impinging against a grain boundary sink. Our analyses show that the point defects should migrate only to the tip of the crack, whereas they should enter both into the slip band tip and along the adjacent boundary interface. Explicit results are obtained for the concentrations, the number and flux distributions as well as the total numbers segregated in the transient depletion and the steady-state irradiation situation and serve to reinforce previous conclusions regarding the importance of such stress-driven processes in the fracture of materials.

The stress-driven migration of point defects to a crack

1985 ◽  
Vol 397 (1812) ◽  
pp. 121-141 ◽  
Keyword(s):  
Steady State ◽  
Stress Field ◽  
Interaction Energy ◽  
Point Defects ◽  
Elastic Interaction ◽  
Constant Concentration ◽  
Nearby Point ◽  
Loaded Crack ◽  
Solute Atoms ◽  
Kinetics Of

The elastic interaction energy between a crack tip and nearby point defects is derived and used to estimate the kinetics of migration of these defects in the stress field of a loaded crack. Explicit results are obtained for both the transient depletion of solute atoms from an initial constant concentration and the steady state loss of point defects to a crack during irradiation. In the latter situation the migrating defects can be either self-interstitials or vacancies, and attention is drawn to the fact that interstitials should be lost at the tip of the crack whereas vacancies should enter the crack across the surfaces behind the actual tip.

Point Defect Injection Kinetics by N2O Oxidation of Silicon

1997 ◽  
Vol 469 ◽  
Author(s):  
C. Tsamis ◽  
D. N. Kouvatsos ◽  
D. Tsoukalas
Keyword(s):  
Point Defect ◽  
High Temperatures ◽  
Point Defects ◽  
Silicon Substrate ◽  
Oxidation Process ◽  
Stacking Faults ◽  
Defect Injection ◽  
Dry Oxidation ◽  
Kinetics Of

ABSTRACTThe influence of N2O oxidation of silicon on the kinetics of point defects at high temperatures is investigated. Oxidation Stacking Faults (OSF) are used to monitor the interstitials that are generated during the oxidation process. We show that at high temperatures (1050°-1150°C) the supersaturation of self-interstitials in the silicon substrate is enhanced when oxidation is performed in an N2O ambient compared to 100% dry oxidation. This behavior is attributed to the presence of nitrogen at the oxidizing interface. However, at lower temperatures this phenomenon is reversed and oxidation in N2O ambient leads to reduced supersaturation ratios.

scholarly journals Weyl geometry and the nonlinear mechanics of distributed point defects

2012 ◽  
Vol 468 (2148) ◽  
pp. 3902-3922 ◽  
Author(s):  
Arash Yavari ◽  
Alain Goriely
Keyword(s):  
Residual Stress ◽  
Stress Field ◽  
Point Defect ◽  
Point Defects ◽  
Spherical Inclusion ◽  
The Body ◽  
Inclusion Problem ◽  
Spherically Symmetric ◽  
Residual Stress Field ◽  
Defect Distribution

The residual stress field of a nonlinear elastic solid with a spherically symmetric distribution of point defects is obtained explicitly using methods from differential geometry. The material manifold of a solid with distributed point defects—where the body is stress-free—is a flat Weyl manifold, i.e. a manifold with an affine connection that has non-metricity with vanishing traceless part, but both its torsion and curvature tensors vanish. Given a spherically symmetric point defect distribution, we construct its Weyl material manifold using the method of Cartan's moving frames. Having the material manifold, the anelasticity problem is transformed to a nonlinear elasticity problem and reduces the problem of computing the residual stresses to finding an embedding into the Euclidean ambient space. In the case of incompressible neo-Hookean solids, we calculate explicitly this residual stress field. We consider the example of a finite ball and a point defect distribution uniform in a smaller ball and vanishing elsewhere. We show that the residual stress field inside the smaller ball is uniform and hydrostatic. We also prove a nonlinear analogue of Eshelby's celebrated inclusion problem for a spherical inclusion in an isotropic incompressible nonlinear solid.

Influence of Slip Localization on Surface Relief Formation and Grain Boundary Microcrack Nucleation

2011 ◽  
Vol 465 ◽  
pp. 35-40 ◽  
Author(s):  
Maxime Sauzay ◽  
Pierre Evrard ◽  
Karine Bavard
Keyword(s):  
Aspect Ratio ◽  
Stress Field ◽  
Grain Boundary ◽  
Slip Band ◽  
Surface Relief ◽  
Tensile Deformation ◽  
Equivalent Stress ◽  
Slip Bands ◽  
Relief Formation ◽  
Analytical Formulae

Slip localization is often observed in metallic polycrystals after cyclic deformation (persistent slip bands) or pre-irradiation followed by tensile deformation (channels). To evaluate its influence on surface relief formation and grain boundary microcrack nucleation, crystalline finite element (FE) computations are carried out using microstructure inputs (slip band aspect ratio/spacing). Slip bands (low critical resolved shear stress (CRSS)) are embedded in small elastic aggregates. Slip band aspect ratio and neighboring grain orientations influence strongly the surface slips. But only a weak effect of slip band CRSS, spacing and grain boundary orientation is observed. Analytical formulae are deduced which allow an easy prediction of the surface and bulk slips. The computed slips are in agreement with experimental measures (AFM/TEM measures on pre-irradiated austenitic stainless steels and nickel, copper and precipitate-strengthened alloy subjected to cyclic loading). Grain boundary normal stresses are computed for various materials and loading conditions. A square root dependence with respect to the distance to the slip band corner is found similarly to the pile-up stress field. But the equivalent stress intensity factor is considerably lower. Analytical formulae are proposed for predicting the grain boundary normal stress field depending on the microstructure lengths. Finally, an energy balance criterion is applied using the equivalent elastic energy release rate and the surface/grain boundary energies. The predicted macroscopic stresses for microcrack nucleation are compared to the experimental ones.

Grain Boundary Engineering by Application of Mechanical Stresses

2007 ◽  
Vol 558-559 ◽  
pp. 987-992
Author(s):  
Myrjam Winning
Keyword(s):  
Stress Field ◽  
Grain Boundary ◽  
Grain Boundaries ◽  
Mechanical Stress ◽  
Grain Growth ◽  
Microstructure Evolution ◽  
Mechanical Stresses ◽  
Grain Boundary Engineering ◽  
New Approach ◽  
Kinetics Of

It is shown that an externally applied mechanical stress field can change the kinetics of individual grain boundaries. Moreover, such mechanical stresses also have influence on grain growth and recrystallization kinetics and can strongly affect the microstructure evolution, so that the application of mechanical stresses during annealing can be used as a new approach in the field of grain boundary engineering.

Interplay between intrinsic point defects and low-angle grain boundary in bcc tungsten: effects of local stress field

2015 ◽  
Vol 27 (25) ◽  
pp. 255007 ◽  
Author(s):  
Liang-Liang Niu ◽  
Ying Zhang ◽  
Xiaolin Shu ◽  
Shuo Jin ◽  
Hong-Bo Zhou ◽  
...  
Keyword(s):  
Stress Field ◽  
Grain Boundary ◽  
Point Defects ◽  
Local Stress ◽  
Intrinsic Point Defects ◽  
Local Stress Field

Detection of a point defect in a silicon single crystal by high-resolution TEM

1995 ◽  
Vol 53 ◽  
pp. 466-467
Author(s):  
M. Awaji
Keyword(s):  
High Resolution ◽  
Single Crystal ◽  
Point Defect ◽  
Point Defects ◽  
Noise Level ◽  
Dark Field ◽  
Silicon Single Crystal ◽  
High Resolution Image ◽  
Dark Field Imaging ◽  
Field Imaging

It is necessary to improve the resolution, brightness and signal-to-noise ratio(s/n) for the detection and identification of point defects in crystals. In order to observe point defects, multi-beam dark-field imaging is one of the useful methods. Though this method can improve resolution and brightness compared with dark-field imaging by diffuse scattering, the problem of s/n still exists. In order to improve the exposure time due to the low intensity of the dark-field image and the low resolution, we discuss in this paper the bright-field high-resolution image and the corresponding subtracted image with reference to a changing noise level, and examine the possibility for in-situ observation, identification and detection of the movement of a point defect produced in the early stage of damage process by high energy electron bombardment.The high-resolution image contrast of a silicon single crystal in the [10] orientation containing a triple divacancy cluster is calculated using the Cowley-Moodie dynamical theory and for a changing gaussian noise level. This divacancy model was deduced from experimental results obtained by electron spin resonance. The calculation condition was for the lMeV Berkeley ARM operated at 800KeV.

Point Defect Absorption and Dislocation Loop Formation at Grain Boundaries in Hvem-Irradiated Zr and Its Alloys:1. Influence of Solute Addition

1985 ◽  
Vol 43 ◽  
pp. 350-351
Author(s):  
R.A. Herring ◽  
M. Griffiths ◽  
M.H Loretto ◽  
R.E. Smallman
Keyword(s):  
Grain Boundary ◽  
Grain Boundaries ◽  
Point Defect ◽  
Reactor Core ◽  
Solute Concentration ◽  
Nuclear Industry ◽  
Dislocation Loops ◽  
Loop Formation ◽  
Component Material ◽  
Impurity Interaction

Because Zr is used in the nuclear industry to sheath fuel and as structural component material within the reactor core, it is important to understand Zr's point defect properties. In the present work point defect-impurity interaction has been assessed by measuring the influence of grain boundaries on the width of the zone denuded of dislocation loops in a series of irradiated Zr alloys. Electropolished Zr and its alloys have been irradiated using an AEI EM7 HVEM at 1 MeV, ∼675 K and ∼10-6 torr vacuum pressure. During some HVEM irradiations it has been seen that there is a difference in the loop nucleation and growth behaviour adjacent to the grain boundary as compared with the mid-grain region. The width of the region influenced by the presence of the grain boundary should be a function of the irradiation temperature, dose rate, solute concentration and crystallographic orientation.

Kinetic analysis of mechanism of intestinal Na+-dependent sugar transport

1985 ◽  
Vol 248 (5) ◽  
pp. C498-C509 ◽  
Author(s):  
D. Restrepo ◽  
G. A. Kimmich
Keyword(s):  
Experimental Data ◽  
Steady State ◽  
Sugar Transport ◽  
Enzyme Kinetic ◽  
Steady State Distribution ◽  
State Distribution ◽  
Least Squares Fit ◽  
Coupling Stoichiometry ◽  
Rate Limiting ◽  
Kinetics Of

Zero-trans kinetics of Na+-sugar cotransport were investigated. Sugar influx was measured at various sodium and sugar concentrations in K+-loaded cells treated with rotenone and valinomycin. Sugar influx follows Michaelis-Menten kinetics as a function of sugar concentration but not as a function of Na+ concentration. Nine models with 1:1 or 2:1 sodium:sugar stoichiometry were considered. The flux equations for these models were solved assuming steady-state distribution of carrier forms and that translocation across the membrane is rate limiting. Classical enzyme kinetic methods and a least-squares fit of flux equations to the experimental data were used to assess the fit of the different models. Four models can be discarded on this basis. Of the remaining models, we discard two on the basis of the trans sodium dependence and the coupling stoichiometry [G. A. Kimmich and J. Randles, Am. J. Physiol. 247 (Cell Physiol. 16): C74-C82, 1984]. The remaining models are terter ordered mechanisms with sodium debinding first at the trans side. If transfer across the membrane is rate limiting, the binding order can be determined to be sodium:sugar:sodium.

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