Increased Temperature Margins Due to Constraint Loss

Enhanced levels of toughness associated with constraint loss are related to temperature shifts in the ductile-brittle transition curve. An argument to quantify the temperature shift is developed using self-similarity of near-tip stress fields under small-scale yielding combined with scaling techniques developed by Dodds and co-workers [1,2] for cleavage. The change in the yield stress and hence temperature that give the same stress field at failure in constrained and unconstrained fields has been determined. The procedure is illustrated using the data of Sherry et al [3] for A533B pressure vessel steel. The results are consistent with the empirical expressions proposed by Wallin [4], and enable a discussion of the physical implications for the micro-mechanics of cleavage.