ESTIMATION OF THE PARAMETER CONTROLLING SHORT-TERM CREEP CRACK GROWTH UNDER COMBINED PRIMARY AND SECONDARY LOADING

摘要

Components in Advanced Gas-Cooled Reactor (AGR) plant operate at temperatures where creep is important. However, for some components the temperature is not sufficiently high for steady state creep conditions to be attained for most of the lifetime. Consequently, defect assessments in such components need to consider creep crack growth controlled by transient or short-term creep conditions at the crack tip. In addition, such components are often subjected to combined primary and secondary loading where creep relaxation of secondary stresses is not complete so that the effect of secondary thermal and residual stresses on creep crack growth needs to be considered throughout the lifetime. In this paper, formulae for the estimation of the short-term creep crack tip characterising parameter C(t) are derived for elastic-plastic-creep material response for combined primary and secondary loading. The formulae are shown to be less conservative in their treatment of crack tip plasticity than existing estimates in the literature, particularly at the times which are relevant to some AGR components. The new formulae are compared with existing estimates, theoretical solutions and with finite element data to provide confidence in their application to AGR plant components.