Validity of friction stress σo measurements for high-temperature creep

Abstract

In a recent paper in Metal Science, J. C. Gibeling and W. D. Nix raised a number of important criticisms on the σ₀ or friction stress approach to creep deformation including (a) the validity of the σ₀ measurement technique, (b) the relationship of the measured σ₀ values to the sensitivity of the strain measuring technique and, (c) following work on lead, the point of whether incubation periods, which are an important part of the σ₀ measurement method, always accompany stress reductions. Following a detailed reappraisal of our σ₀ data a number of points have arisen which relate particularly to these three items. This new information is considered in detail but in essence it (a) provides further support for the validity of the σ₀ approach, (b) demonstrates that the σ₀ values are not directly determined by measurement sensitivity, and (c) provides evidence that it is not possible to conclude that incubation periods do not exist in lead on the basis of the limited published data.