In every instance, a “yield stress” was first found as a 2% offset in the total strain. This was considered to represent the commencement of macroscopic work hardening in compression. After the removal of this “microplastic” part, each curve was fitted and smoothed with a 10th‐order polynomial using the MATLAB™ software. In some challenging cases, a higher‐order polynomial (14th) was employed. The smoothing eliminated the fluctuations present in the experimental flow curves and in this way, allowed the differentiation operations.
In order to determine the critical stresses for the initiation of DT and DRX, the strain hardening rate, θ, was calculated by the following expression: