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2005) Multi-scale simulations of the effects of irradiation-induced voids and helium bubbles on the mechanical properties of aluminium, Philosophical Magazine, 85:4-7, 757-767To link to this article: http://dx.As a result of irradiation, pressurized helium bubbles are observed in large number densities in some metals, which produce mechanical property changes. This paper presents the results of a computational multi-scale study (dislocation dynamics, DD, and molecular dynamics simulations, MD) to quantify the effect of He bubbles on material hardening from the impediment to dislocation motion. The effects of voids were studied using MD, and the effects of He bubbles, with a mean size of 2.5 nm and number densities from 3 Â 10 22 m À3 to 6 Â 10 22 m À3 , were investigated using DD over a range of internal He pressures ranging from 125 to 750 MPa. The MD simulations elucidated the dislocation pinning action of voids and bubbles. Also, within the range of parameters studied, the DD simulations showed a clear, but weak correlation between the number density of He bubbles, and the internal He pressure, on the flow stress of the metal.

Analytical closed-form solutions for the crack tip plastic zone shape have been derived for a semi-infinite crack in an isotropic elastic-perfectly plastic solid under both plane stress and plane strain conditions. Two yield criteria have been applied: the Von Mises and Tresca yield criteria. The solutions have been developed for crack modes I and III (mode II has been published previously). The results, which favorably compare to a limited number of existing experimental and analytical findings, indicate that the Tresca zone is larger in size than the Von Mises zone. Moreover, an interesting observation is that both zones are generally much larger than the ones predicted by classical Irwin and Dugdale-Barenblatt solutions.

Weld overlays have been used to remedy intergranular stress corrosion cracking (IGSCC) in boiling water reactors (BWRs) since the 1980s. Overlays have also been applied in the last few years in pressurized water reactors (PWRs) where primary water stress corrosion cracking (PWSCC) has developed. The weld overlay provides a structural reinforcement with SCC resistant material and favorable residual stresses at the ID of the overlaid component. Leak-before-break (LBB) had been applied to several piping systems in PWRs prior to recognizing the PWSCC susceptibility of Alloy 82/182 welds. The application of the weld overlay changes the geometric configuration of the component and as such, the original LBB evaluation is updated to reflect the new configuration at the susceptible weld. This paper describes a generic leak-before-break (LBB) analysis program which demonstrates that the application of weld overlays always improves LBB margins, relative to un-overlaid, PWSCC susceptible welds when all the other parameters or variables of the analyses (loads, geometry, operating conditions, analysis method, etc…) are kept equal. Analyses are performed using LBB methodology previously approved by the US NRC for weld overlaid components. The analyses are performed for a range of nozzle sizes (from 6″ to 34″) spanning the nominal pipe sizes to which LBB has been commonly applied, using associated representative loads and operating conditions. The analyses are performed for both overlaid and un-overlaid configurations of the same nozzles, and using both fatigue and PWSCC crack morphologies in the leakage rate calculations and the LBB margins are compared to show the benefit of the weld overlays.