Compatibility of fracture toughness results in the upper shelf region

Fracture toughness has been used for decades nowadays for structure integrity assessment and it is important mechanical characteristic for new materials as well. In the upper shelf region, where stable fracture behavior is observed, concept of J-R curve is widely apply to determine fracture toughness parameter JIc defined by the intersection of the 0.2 mm offset construction line and the J-R curve according to ASTM El 820. Fracture mechanic methods have been well established in the community especially for standard sized specimens but as it was mainly developed for large structures assessment against the brittle failure, standardized specimens are of large size at present. In many cases, such as evaluation of additively manufactured products properties, residual life of in-service components, local properties of components, weld joint, etc., standard specimens are not possible to use due to size requirements. Therefore, small sized specimens are necessary to use for material characterization. Due to constraint effect, the results obtained from standard and small sized specimens may be different. In the current paper, fracture toughness properties are going to be investigated using different sized samples scaled from mini-Charpy or mini-CT specimens to the standard one. Based on experimental results from several structural metals like steels 34CrNiMo6 and 27NiCrMoV 15-6, a procedure leading to the comparable results from small to standard samples will be proposed. (C) 2019 The Authors. Published by Elsevier B.V.