Influence of statistical and constraint loss size effects on cleavage fracture toughness in the transition—A single variable experiment and database

Abstract

This paper, which is the first of two parts, describes a comprehensive experimental study to systematically measure constraint loss and statistical size effects on fracture toughness of a typical low alloy pressure vessel steel in the brittle-to-ductile transition. Both of these size effects lead to higher toughness in smaller specimens. Previous studies primarily involved specimens that differed in size, but with self-similar standard geometric configurations, making it difficult to separate constraint loss from statistical size effects. The focus here is on a single-variable database developed for a homogeneous plate section of the decommissioned Shoreham Reactor vessel steel, tested at the 3/4-plate thickness position. Tests were carried out at a common set of conditions and covered a full matrix of specimens with six thicknesses ( B) ranging from 7.9 to 254 mm and four widths ( W) ranging from 6.4 to 50.8 mm. The variations in B were designed to provide readily observable statistical sampling effects, while variations in W result in fracture at deformation conditions ranging from small scale yielding to those involving extensive loss of constraint. A detailed analysis of this database is presented in a companion paper, where physically based models are used to quantify the relative contributions of constraint loss and statistical size effects. The models also provide a general approach to adjusting measured toughness for both testing and applications. The B– W database and analysis also provides a comprehensive independent assessment of some key aspects of the master curve method in the ASTM E 1921 Standard discussed in detail elsewhere. In this paper, we present an empirical analysis that shows a high constraint toughness scaling with B that is reasonably consistent with ASTM E 1921, as well as effects of loss of constraint that occur at much lower deformation levels than reflected in the data censoring limit in ASTM E 1921.