Classical thermodynamic approach to void nucleation in irradiated materials
Abstract One of the major problems in building a future fusion power station is the development of suitable structural materials. These materials will be exposed to high energy neutron bombardment, with consequent changes in their mechanical properties – embrittlement, hardening and swelling, for example. A missing link in modelling these effects is an effective treatment of the nucleation of voids under irradiation. These voids are initially stabilised by transmutation helium but, once formed, grow by vacancy accumulation. In this paper, a quasi-chemical model is developed to calculate the entropy of a steel/helium system. Although a substantial contribution from quasi-chemical effects might be expected, the steady state concentrations of dissolved helium are found to be too low for such effects to manifest. The steady state concentration of dissolved helium is low in absolute terms, but the resulting supersaturation is very high, making it reasonable to assume that all available nucleation sites are instantaneously activated.
THEORY OF HELIUM TRANSPORT AND CLUSTERING IN MATERIALS UNDER IRRADIATION
A theoretical model is developed to describe helium transport and clustering during irradiation. Diffusional reactions of helium with vacancies and vacancy clusters, with extended sinks for helium absorption, and direct reactions with displacement producing particles are included. The full description developed is employed in numerical computations. A simpler description is also developed in the limits where certain reactions are unimportant. Analytical expressions for the effective diffusion coeficient of helium are derived. Regimes of the parameter space of dose rate, temperature, helium generation rate, sink strength and other important conditions, where the effective diffusion coefficient is dictated by three different physical processes, are defined. The result is determined by the dominant release mechanism of helium bound in vacancies-thermal detrapping, replacement by the self-interstitial or direct displacement. Results from the full computations and the analytical expressions are compared.
Evaluation of Impact of Yarn Count and Stitch Length on Pilling, Abrasion, Shrinkage and Tightness Factor of 1 ? 1 Rib Cotton Knitted Fabrics
This study investigates the impact of yarn count and stitch length of 100% cotton knitted fabrics. 1 × 1 ribs structured fabrics were used in this research work. The stitch length 2.50 mm, 2.52 mm, 2.60 mm, 2.70 mm, 2.80 mm and 2.96 mm were used of the yarn count of 26Ne, 28Ne and 36Ne. The areal densities of the grey fabrics were in various amounts. The impacts of yarn count and stitch length were measured concerning pilling resistance, abrasion resistance, and shrinkage and tightness factor. The result showed that the fabric pilling grade decreased while number of cycle increased. Abrasion resistance decreased but length wise shrinkage increased despite the fact that the stitch length increased. The results also exposed that the tightness factor of the fabric increased with the increase of the stitch length in both dyeing and washing state and finished state compared to grey state for the yarn count 26Ne and homogeneous result not found for yarn count 28Ne and 36 Ne. Evaluation of Impact of Yarn Count and Stitch Length on Pilling, Abrasion, Shrinkage and Tightness Factor of 1 × 1 Rib Cotton Knitted Fabrics