A computational fatigue analysis of cyclic thermal shock in notched specimens

Thermal shock induced fatigue plays a role in the assessment of the lifetime of different components in the primary cooling circuit of a nuclear plant. In spite of the implementation of substantial and costly safety factors, a few, unexpected cases of fatigue failure have occurred. Here we report on a laboratory experiment which mimics the thermal loading observed in such components. A finite element thermal stress analysis using a calibrated, elasto-plastic, combined kinematic–isotropic cyclic hardening material model is presented. The distribution of transient stresses and strains in the specimens subjected to cyclic thermal shock, are used to predict the number of cycles to crack initiation with a fatigue curve that has been calibrated experimentally with data from equivalent specimens under pure mechanical fatigue. Our results indicate that cyclic thermal shock induced ratcheting occurs locally near the tip of the notch in the specimens, and the potential impact on the number of cycles to crack initiation is explored.