Thermodynamic dislocation theory of high-temperature deformation in aluminum and steel

Abstract

The statistical-thermodynamic dislocation theory developed in previous papers is used here in an analysis of high-temperature deformation of aluminum and steel. Using physics-based parameters that we expect theoretically to be independent of strain rate and temperature, we are able to fit experimental stress-strain curves for three different strain rates and three different temperatures for each of these two materials. Our theoretical curves include yielding transitions at zero strain in agreement with experiment. We find that thermal softening effects are important even at the lowest temperatures and smallest strain rates.

Thermodynamic theory of dislocation-enabled plasticity

“…These curves are for T = 573 K, for three different strain rates 0.25 s −1 , 2.5 s −1 , and 25 s −1 . In [6], we also showed curves for T = 673 K and 773 K at the same three strain rates, as well as analogous results for a steel alloy. We assumed that all nine of the aluminum samples tested by Shi et al were prepared identically, and therefore we used a single set of system parameters obtained by a least-squares fit to the data.…”

“…II, and U 1 and S 1 are the energy and the entropy of all the other configurational degrees of freedom. As before, 6) where γ D is the dislocation energy per unit length; and…”

“…This geometry directly models experiments in which such a slab undergoes simple shear; but it also can be used to describe compression and torsional tests by rescaling the stress and/or the elastic modulus by dimensionless factors of order unity. (See [6].) Assume, as in Sec.…”

“…4. The experimental data shown here is taken from Shi et al [15]; and the theoretical analysis is from [6]. These curves are for T = 573 K, for three different strain rates 0.25 s −1 , 2.5 s −1 , and 25 s −1 .…”

“…4, especially at the largest strain rate, there is clear evidence of thermal softening; the stress decreases at large strains. This effect is even more visible at the higher temperatures discussed in [6]. To account for it, we have used Eq.…”