Taylor-Quinney coefficient determination from simultaneous strain and temperature measurements of uniform and localized deformation in tensile tests

Abstract

Experimental determination of the Taylor-Quinney coefficient (TQC), $\beta$, from tensile tests at nominal strain rates of 1.0 s^-1 and 500 s^-1 is presented. Simultaneous full-field measurements of the deformation (strain) and temperature on the surface of the specimens are made throughout the tests, including in the localized region during necking. These measurements provide means to determine the value of the TQC at large strains. Results from testing Inconel 718 show that during the uniform deformation portion of the tests (up to a strain of about 0.15 before necking initiation) the conditions at the center of the specimen's gage section are adiabatic in both strain rates and the TQC can be determined accurately. Large strains and significant increase in temperature are observed in the necking region once it develops. Analysis of the measured data shows that in the 500 s^-1 strain rate test the necking process is sufficiently fast (about 165 μs) such that the center of the necking deforms under adiabatic conditions and the TQC can accurately be determined up to a strain of 0.36. In the 1.0 s^-1 strain rate test, where the necking process lasts much longer (about 110 ms), some heat is conducted away from the center of the necking region and the TQC can accurately be determined only during the uniform deformation up to a strain of 0.15.