Origin of successful pre-yield stress-relaxation scaling

Determine why Liu et al.’s scaling of stress-relaxation curves obtained before yield succeeds despite the qualitative disconnect between probe reorientation times and mechanical relaxation times in the pre-yield regime.

Background

The paper compares optical probe relaxation times with mechanical relaxation times obtained from the initial stress-relaxation decay. These observables correlate in the post-yield regime but evolve qualitatively differently before yield: probe relaxation times decrease substantially as yield is approached, whereas mechanical relaxation times remain nearly constant.

The authors discuss prior work by Liu et al., who reported that stress-relaxation curves obtained after constant strain rate deformation could be scaled onto a nearly universal decay by rescaling observation time with the preceding deformation rate, including for pre-yield experiments. Because the present measurements show a disconnect between molecular and mechanical relaxation before yield, the authors explicitly state that the reason for the success of Liu et al.’s procedure is unclear. They note that fixing the stress at the beginning of stress relaxation may be relevant, but do not resolve the issue.