This paper studies temperature variation phenomenon induced by the thermomechanical effect in aluminum alloys 2024-T3 and 7075-T6 under uniaxial tensile loading. Experimental results show that cooling occurs under elastic deformation. When load yielding is attained the temperature approaches its minimum. Beyond the temperature minimum the slope of the temperature curve inverts and becomes positive as heating occurs under plastic deformation. The point of temperature curve inversion coincides with the point at which the sample's elastic behavior yields to stress and becomes plastic. At strain rates of 2×10-2 s-1-2×10-4 s-1, the amount of temperature drop was found to be reasonably close to the theoretical values, as determined by the standard thermoelastic model. Likewise, within this strain range, the relative difference between the stress value at lowest temperature and the stress value at the yielding point was minimum. Experiments demonstrate that the temperature method of defining yield strength is a valid technique and, moreover, for the aluminum alloys tested, superior to the tensile method, at least within the strain rate range of 2×10-2 s-1-2×10-4 s-1. The curve of experimental estimated thermoelastic factor, Km, showed two different regions when plotted in relation to strain rate. The two regions had inverse slopes and dramatically different curve characteristics. The regions met at a strain rate of about 10-3 s-1, which was also the point of closest approach to the theoretical values.
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