A Mechanistic Modelling Approach to Derive Fracture Toughness Properties from Charpy Impact Energy in the Lower Transition Region

Abstract

This research was undertaken to develop an engineering method for the determination of material fracture toughness, Kmat, from Charpy V-notch impact energy, Uel+pl,LLD. Current structural integrity assessment methodologies for flawed steel structures are premised upon a knowledge of Kmat for a given material. In circumstances when fracture toughness is not available or possible to obtain for an industrial structure Uel+pl,LLD is commonly used to estimate Kmat using empirical correlations. These correlations are necessarily conservative and are potentially inaccurate for some ferritic steels materials.The development of a mechanistic engineering procedure for determining fracture toughness using Uel+pl,LLD within the lower ductile-to-brittle transition of fracture behaviour for ferritic steels would significantly reduce this conservatism and provide increased confidence concerning safety assessments. Increased confidence in Kmat calculations using a new mechanistic approach would also provide a functional use for much Charpy impact test data which are available for structural and nuclear grade steels.The cleavage fracture differences between a single edge notch bend, SE(B), specimen and Charpy specimen were experimentally measured and numerically simulated. A mechanistic correlation was developed using a Weibull stress scaling approach to achieve accurate predictions of cleavage fracture behaviour of SE(B), Charpy V-notch and a range of intermediate geometries between these bounding geometries of interest.This research has developed a new mechanistic procedure to correlate Uel+pl,LLD with an equivalent KJ corresponding to a SE(B) specimen. The correlation was found to be accurate in the lower ductile-to-brittle transition and provided probabilistic predictions of fracture behaviour. The correlation was validated using quasi-static and dynamic experimental test results and provided a linkage with the existing ASTM E 1921-11 master curve methodology for ferritic steels.The research has provided recommendations for how the new approach might be applied in practice within an industrial context, and areas for future work that would develop a more generalised approach for a wider range of ferritic materials are highlighted.

Date of Award	1 Aug 2015
Original language	English
Awarding Institution	The University of Manchester
Supervisor	Andrew Sherry (Supervisor)