Dr M Roy
Applications accepted all year round
About the Project
This project is part of the EPSRC Centre for Doctoral Training in Materials for Demanding Environments [CDT in M4DE], is sponsored by Rolls-Royce plc. and will commence October 2017.
Background
The defect tolerance assessment of austenitic stainless steel piping and component welds using the methods such as those in the UK R6 procedure [1] often results in failure being estimated to occur by ductile crack initiation when the crack driving force reaches the material’s initiation fracture toughness value commonly designated, KJ0.2. This approach can result in relatively small limiting defect sizes being calculated particularly when elastically calculated thermal stresses are combined with the high weld residual stress levels assumed for non-stress relieved welds. However, in austenitic stainless steel component welds the relatively high fracture toughness and tearing resistance combined with low yield stress would result in extensive plasticity developing and the final failure condition being controlled by plastic collapse rather than by fracture. Consequently, there is a need to develop a greater understanding of the mechanisms involved in the failure of austenitic stainless steel components to enable defect tolerance assessment margins to be better understood.
Project Outline
The project will establish the current state of current practices in the defect tolerance assessment of austenitic stainless steel components and aim to develop improved and less conservative methods by gaining a fundamental understanding of the mechanisms of failure. Some potential areas to be explored are: (a) when the primary and secondary stresses are combined it is likely that the total stress will exceed the yield stress of the material in non-stress relieved welds. Subsequent application of the service loads can induce stress redistribution by shakedown. If the use of the redistributed residual stress can be justified it may allow improved margins to be claimed; (b) the validity of using an initiation fracture toughness value KJ0.2 as there is the potential for loss of constraint when increasing plasticity develops in the ligament ahead of the crack.
About Rolls-Royce
Rolls-Royce is a global business providing power systems for use on land, at sea and in the air. The Group has a balanced business portfolio with leading positions in the civil and defence aerospace, marine and nuclear power generation sectors. Rolls-Royce has substantial investments in developing technology and capabilities that can be applied to products and services in a variety of markets. This project will be carried out in close collaboration with the Civil Nuclear business in Rolls-Royce which provides products and services to both the existing nuclear fleet and new build projects throughout the world.
[1] ‘R6, Assessment of the Integrity of Structures Containing Defects’, EDF Energy Nuclear Generation Limited, Revision 4, Amendment 11 2015.
Funding Notes
This project is funded by the EPSRC, the University of Manchester and Rolls-Royce plc. The successful candidates will have their fees paid in full and will receive an enhanced maintenance stipend of £17,000 p.a.
Funding is available to UK candidates only.
www.m4de.manchester.ac.uk