Experimental Investigation of Factors Influencing the Determination of the Onset of Yielding by Temperature Measurement

Abstract

The cooling of the material during elastic tensile loading is well known as the thermoelastic effect. It is already known that the temperature minimum at the elastic-plastic transition can be used for the determination of the onset of yielding. Conceivable parameters for this have already been presented and investigated. Within this study factors influencing the specimen temperature during tensile loading and unloading are experimentally analyzed to improve the determination approach and the understanding of it. Furthermore, the robustness and repeatability of the measurement and evaluation procedures are analyzed. Therefore, cyclic tensile tests with the mild steel DC06 and the high strength steel CR590Y980T (DP1000) are performed with four PT1000 sensors applied on the specimen. The temperature behavior during elastic loading, elastic-plastic elongation and elastic unloading is separately evaluated. Different strain rates are investigated to better understand the strain-dependent heat development and its influence on the temperature-dependent evaluation. In this way, correlations between strain rate and thermal conduction due to prevailing temperature differences are found and their influence on the temperature-based determination of the onset of yielding is analyzed. Therefore, the yield stress at temperature minimum YSTmin as well as an additional yield stress at zero plastic strain YS0 are evaluated for all experiment settings. In a comprehensive experimental study, the standard deviations are compared and thus conclusions can be drawn about the robustness of the determination methods.