A numerical study of parameters controlling stress redistribution in circular notched specimens during creep

Abstract

In this study, numerical calculations of the creep behaviour of circular notched specimens have been performed with emphasis placed on the role of specimen geometry, material ductility, and the constitutive creep law used for the calculations. In a first order approximation, the calculations performed using primary, secondary, and tertiary-types of constitutive equations result in similar stress distributions for most of the creep life. Therefore, acceptable engineering creep calculations can be performed using a pure Norton-type of constitutive law. In the beginning of creep life, however, there are signifiant differences in calculated stress distributions obtained using primary, secondary, and teriary constitutive laws. Brittle material undergoing primary creep can redistribute stresses faster than a ductile material exhibiting tetriary dominated creep behaviour. Comparing flat plate and cylindrical circular notched specimens it is found that maximum axial stresses are higher for flat plate specimens than for cylindrical specimens. Implications of these results on possible failure mechanisms are discussed.