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.

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.

Non-equilibrium segregation in metals and alloys

1980 ◽  
Vol 295 (1413) ◽  
pp. 197-207 ◽  
Keyword(s):  
Point Defects ◽  
Driving Force ◽  
Corrosion Behaviour ◽  
Metals And Alloys ◽  
Impurity Atoms ◽  
Solute Atoms ◽  
Kinetics Of ◽  
Practical Implications ◽  
Equilibrium Segregation ◽  
Non Equilibrium

The phenomenon of non-equilibrium segregation of solute and impurity atoms at interfaces in quenched materials is defined and the driving force and kinetics of the segregation are shown to differ significantly from those of reversible equilibrium segregation. Large point defect supersaturations are produced during quenching, irradiation and sintering, and both enrichment and depletion of solute atoms at interfaces, associated with the flow of point defects to sinks, have been observed. Some of the quantitative and qualitative experimental data on non-equilibrium segregation are described and the current understanding of the mechanisms and kinetics are summarized. Finally, some of the practical implications of non-equilibrium segregation, in terms of the effects on the deformation, fracture and mechanical properties, corrosion behaviour and structural stabilities of quenched and irradiated metals and alloys, are outlined and possible methods of inhibiting segregation are suggested.

Stress-Corrosion Cracking and the Interaction Between Crack-Tip Stress Field and Solute Atoms

1970 ◽  
Vol 92 (3) ◽  
pp. 633-638 ◽  
Author(s):  
H. W. Liu
Keyword(s):  
Stress Field ◽  
Stress Corrosion ◽  
Crack Growth ◽  
Stress Corrosion Cracking ◽  
Solute Atom ◽  
Crack Tip ◽  
Elastic Interaction ◽  
Corrosion Cracking ◽  
Solute Atoms ◽  
Crack Tip Stress

Based on the elastic interaction between a solute atom and a tensile crack-tip stress field, a mechanism of stress-corrosion cracking was proposed and analyzed. This elastic interaction provides a potential for solute atoms to migrate toward the tip of a crack. The elastic interaction and the equilibrium concentration of solute atoms near a crack tip were calculated. The solute atom concentration increases rapidly toward the crack tip if the solute atom is interstitial or if it relaxes the crack-tip stress field. The high concentration of solute atoms at the tip of a crack will enhance the reaction between solute and solvent atoms. The weak fracture strength of the reaction product may cause crack growth. Two crack growth models were analyzed: One is based on the assumption of the “homogeneity” of the fracture and deformation properties of a material, and the other takes a structural size of a material into consideration. The proposed models are compared with available data on magnesium-aluminum alloy, 4340 steel, and soda-lime glass.

The effect of electrondonors on the polymerization kinetics of isoprene

1980 ◽  
Vol 45 (12) ◽  
pp. 3338-3346
Author(s):  
Miroslav Kašpar ◽  
Jiří Trekoval
Keyword(s):  
Induction Period ◽  
Ethyl Ether ◽  
Reaction Order ◽  
Propagation Rate ◽  
Reaction Scheme ◽  
Polymerization Kinetics ◽  
Polymerization Rate ◽  
Constant Concentration ◽  
Initial Concentration ◽  
Kinetics Of

The effect of small additions of 1-octene, butyl ethyl ether and triethylamine on the polymerization kinetics of isoprene (2-methyl-1,3-butadiene) in benzene initiated with butyllithium was investigated by employing the GLC analysis. The addition of 1-octane was reflected only in a shorter induction period of the reaction; the effect on the propagation rate was insignificant. With the increasing amount of butyl ethyl ether, the polymerization rate increases linearly, while the reaction order with respect to the concentration of triethylamine is variable and increases from 0.33 to 0.66 with the increasing concentration of the initiator. For a constant concentration of triethylamine, the reaction order with respect to the initial concentration of the initiator was found to vary considerably, reaching even negative values. A reaction scheme was suggested, taking into account the competition between two different solvates of alkyllithium.

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.

Sign in / Sign up

Export Citation Format

Share Document