Changes in State Variables at Elevated Temperatures

[+] Author and Article Information
Huseyin Sehitoglu

Department of Mechanical and Industrial Engineering, University of Illinois at Urbana-Champaign, Urbana, IL 61801

J. Eng. Mater. Technol 111(2), 192-203 (Apr 01, 1989) (12 pages) doi:10.1115/1.3226453 History: Received February 18, 1988; Online September 15, 2009


Two state variables, strength and internal (back) stress, were determined during cyclic deformation by rapid unloading-reloading experiments. The experiments were performed at different temperatures and strain rates, Considerable increases in strength at low temperatures (20°C–300°C) due to cyclic deformation and due to strain aging were measured. The variation of internal stresses at elevated temperatures (600°C) with strain rate was identified. Regions of high back stress rates were established on stress-back stress diagrams. High strain rates during unload-reload excursions are needed to minimize changes in back stress during measurements. The results (state variables) and the stress-strain response were compared to predictions based on a unified constitutive model. The capabilities of the model under cyclic loading, decrease in strength at high temperatures due to spheroidization, and increase in strength due to strain aging at lower temperatures, were found to be satisfactory. The extension of the unloading-reloading technique to multiaxial loading is outlined.

Copyright © 1989 by ASME
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