Thermographic detection of fatigue damage of reactor pressure vessel (RPV) steels

An IR (IR) thermography technique, as a nondestructive evaluation technique, was applied to investigate the fatigue damage of reactor pressure vessel (RPV) steels during 20 Hz and 1000 Hz fatigue testing. Five stages of temperature profile were observed: an initial increase of the average specimen temperature, a region of temperature decrease, an equilibrium (steady-state) temperature region, an abrupt increase of the temperature, and a drop of temperature following specimen failure. The relationship between the temperature, stress-strain state, and fatigue behavior is discussed. Both thermodynamic and heat-transfer theories are applied to model the observed temperature variation during fatigue. The stress-strain state of the material has been back-calculated from the observed temperature profiles. The predicted and measured temperature evolutions and mechanical behavior during fatigue were found to be in good agreement. Thermography appears to provide a useful method of investigating the stress-strain behavior during fatigue.