The influence of long-range residual stress on the cleavage fracture of ferritic steel

Abstract

This dissertation considers the influence of long-range residual stress on the cleavagefracture of ferritic steel. The existing body of work related to the influence ofmacro scale residual stress on fracture is reviewed. It is shown that although long-rangeresidual stress, resulting from misfits between components of an engineeringstructure, was discussed by a number of researchers in the late 1970s, it wasneither treated comprehensively nor developed by more recent researchers. Consequently, the design of a test rig capable of generating long-range residual stressin a laboratory compact-tension (C(T)) specimen, for the purpose of investigatingthe effects associated with combined residual and applied loading, is described.Results from fracture tests, carried out using this rig in conjunction with ferriticsteel C(T) specimens below the ductile to brittle transition temperature, are presentedand assessed within the context of a whole-structure model. The developmentof this whole-structure model leads to the central thesis that the strength ofa cracked structure containing long-range residual stress is not dependent solelyon the level of residual stress but also on the amount of plastic deformation priorto fracture, the position of the applied load relative to the cracked element and,crucially, on the relative stiffness of the cracked and uncracked parts of the structure.Finally, the treatment of long-range residual stress within the R6 Revision4 structural integrity assessment procedure is considered and a critical specimento rig stiffness ratio is identified, above which classifying a given long-rangeresidual stress as a ‘secondary’ stress leads to a non-conservative estimate of theload carrying ability of the structure.

Date of Award	2010
Original language	English
Awarding Institution	The University of Bristol
Supervisor	David Smith (Supervisor) & Christopher E Truman (Supervisor)