Investigations into Taylor-Quinney coefficient determination for a 7000 series aluminium alloy using a novel small specimen test technique

Abstract

Thermo-mechanical coupling is a critical component in the thermodynamics of irreversible processes and is related to the dissipation of thermal energy during plastic straining. The Taylor-Quinney coefficient may be thought of as a ratio between thermally dissipated energy and plastic work, thereby giving insight into the thermo-mechanical coupling term. The inclusion of this parameter in a meaningful way is complicated by the various dependencies that the Taylor-Quinney coefficient may be subject to (e.g. loading rate and temperature). Determination of these dependencies is usually achieved through extensive experimentation, wherein temperature variations are monitored (with reference to an unloaded control sample) in a test piece during mechanical loading. There are practical limitations in full size testing methods however, not least relating to the location of full sized control and loaded samples in an environment chamber/furnace while simultaneously maintaining (control sample) temperature uniformity and high resolution temperature measurement (in the loaded sample). The present work details a method based on a novel small specimen testing technique that is currently under development at the University of Nottingham. A small ring of 7175-T7351 aluminum alloy (approximately 10mm in diameter and 2mm in thickness) is loaded between two pins at room temperature, with the local specimen temperature field monitored during monotonic deformation using an infra-red thermal camera. Experimental results are compared for different pin loading rates (namely 0.1mm/s, 1mm/s, and 10mm/s), with particular emphasis placed on localised temperature variations in areas of expected high plasticity. Differences of approximately 0.6°C were observed between 0.1mm/s and 1mm/s tests, with higher temperatures recorded in the latter. Higher temperatures were also noted at small specimen locations associated with localised plasticity. Fundamental thermal material properties are reported for the 7175 alloy in order to facilitate future analysis and heat equation solution efforts (working towards Taylor-Quinney coefficient determination).

Keywords

• small ring
• taylor-quinney
• aluminium 7175
• thermoplasticity