Stress Analyses and Geometry Effects During Cyclic Loading Using Thermography

Abstract

A high-speed and high-sensitivity thermographic-infrared (IR) imaging system has been used to investigate the temperature evolutions of SA533B1 steel specimens during high-cycle fatigue experiments. Both thermodynamics and heat-transfer theories are applied to quantify the relationship between the observed temperature variations and stress–strain states during fatigue. The thermoelastic effect has been utilized to calculate the maximum stress level during fatigue testing. The predicted results matched the experimental data quite well. Different temperature and strain behaviors have been observed between cylindrical and flat specimens during high-cycle fatigue experiments. Explanations have been provided, based on Lüders band evolutions in flat specimens during fatigue, which have been observed in detail by thermography. Numerical methods have been provided to convert the temperature map (thermograph) into heat-dissipation-rate (HDR) map, which illustrates the kinetics of the Lüders-band evolution. Thus, the thermography technology can provide an effective means to “watch” and “quantify” the heat-evolution processes, such as the mechanical-damage behaviors, which can open up new opportunities for in- situ studying mechanical and phase-transformation behaviors in detail.