Large and erratic values for the material parameter d ln [dV / dT] / dsigma have been reported in the past, including (our own) values indistinguishable from zero. Naive theoretical estimates for the parameter suggest that it should be of the order of an inverse Young's modulus, but some groups have reported values as much as 100 times greater, as high as an inverse Yield modulus. This suggests that an explanation for the anomalously high and variable coefficient is that it depends on plastic history. In an effort to resolve the discrepancies we revisit the measurements, but now on specimens with different plastic histories. The times-of-flight of multiply reflected 10 MHz ultrasound pulses in aluminum bars were resolved to within I nanosecond. Variations in natural wavespeeds were measured to within by cross-correlating late echoes received at different temperatures and stresses. Compressive elastic loads were applied on an axis perpendicular to the direction of the longitudinal acoustic wave. as the specimens cooled from 50 degrees C to 20. The specimen with large (10%) plastic pre-strain was found to show a 4% change in d ln V/ dT when applied elastic strain was 0.1%, but the effect was not linear in stress. Consistent with our previous reports, specimens with no significant plastic history showed no discernable coefficient.
