Thermal-imaging technologies for detecting damage during high-cycle fatigue

A high-speed and high-sensitivity thermographic-infrared (IR) imaging system has been used for nondestructive evaluation of specimen-temperature evolutions during high-cycle fatigue experiments. The relationship among the temperature, stress-strain state, and fatigue behavior is discussed. Both thermodynamics and heat-transfer theories are applied to model and quantify the observed temperature variations during fatigue. The predicted and measured temperature evolutions and inelastic strains during fatigue were found to be in good agreement. During fatigue experiments, in-situ observations as well as qualitative and quantitative analyses of Lüders-band evolutions, crack propagation, plastic zones, and final fracture have been performed by thermography, which can open up wide applications of thermography in detecting the in-situ heat-related processes, including mechanical damages and phase transformations, of materials and structural components.