2012 Volume 6 Issue 4 Pages 278-287
Simplified inelastic design procedures have been required to reduce simulation cost and to shorten the development period for the modern high temperature machines and structures. Stress redistribution locus (SRL) method has been proposed to provide a reasonable solution employing both the elastic Finite Element (FE) analysis and a unique hyperbolic curve. In the SRL method, dimensionless stress and strain that were normalized using the inelastic stress/strain and the corresponding elastic stress/strain were introduced. This methodology is based on the fact that the stress distribution in well deformed or in high temperature components changes with deformation or time and that the dimensionless stress-strain relation traces a kind of the elastic follow-up locus in spite of the constitutive equation of the material. In this paper, FE analyses incorporating plasticity and creep were performed for a tapered nozzle of a reactor vessel under some thermal transient loads. The dimensionless stress-strain relation was compared with a conventional and newly proposed SRL curves. FE analysis results showed there to be a critical point in the tapered nozzle due to the thermal transient load dependant on a descending rate of temperature from the higher temperature in the operation cycle. Whenever a certain amount of inelastic strain in the nozzle is produced in a restricted area, the dimensionless stress-strain relation is depicted inside the presently proposed SRL curve. Thus the appropriate coefficient in the SRL method is found to be greater than the proposed one, and the present criterion guarantees robust structures for complicated components involving inelastic deformation.
