Use of high strength steels is becoming more popular in offshore structures and ship construction to obtain weight and manufacturing cost savings without sacrificing structural performance. During the material selection for ship hulls, leg structures of mobile offshore units and lifting appliances, high strength steels with yield strength of the order of 690 MPa and beyond in thicknesses up to 220mm are increasingly being adopted.
The toughness of a material obtained from small scale standard fracture mechanics test is used in fracture mechanics based assessments of structures to evaluate flaw tolerance. Where the thickness of the actual structural component is greater than the thickness of the test specimens, it is not certain that the measured fracture toughness from the former can represent the toughness of the latter. Furthermore, is it very well-known that the fracture toughness of the materials decreases as the thickness of the section increases. Consequently any assessment carried out using small scale test results may lead to non-conservative estimates of flaw tolerance.
The aim of this study is hence to develop new, validated correlations for the determination of fracture toughness of thick high strength steel sections based on the material properties obtained from smaller specimens of this material.
This PhD will:
Critically review existing fracture toughness correlations between small scale tests and large scale components for parent materials and welds.
Two steels will be selected for testing purposes. These materials and their welds will be fully characterised at the start of the practical work (i.e. chemical composition, microstructure, tensile tests, Charpy V-notch testing/transition curves, fracture toughness testing etc.).
Fracture toughness testing will be conducted over a range of thicknesses. The proposed work will also include numerical modelling to optimise the testing programme, to analyse constraint of the small and larger scale test specimens, and to compare these results with the constraint in the structure.
The results of testing will be used to test existing correlations and develop improvements or new correlations as appropriate.
In addition to the classical methods of fracture mechanics, it is also proposed to include novel approaches requiring modelling of damage by progressive failure analysis techniques (with which plane stress and plane strain fracture toughness can be predicted based on strain energy) into this programme to predict fracture toughness as a function of thickness numerically.
A number of fully-funded PhD scholarships are available for suitable candidates with a strong interest in fundamental and applied research in the area of structural integrity. Scholarships cover an amount to £16,000 per annum for 3 years, Home/EU tuition fees and support for research. Overseas applicants are welcomed, with total funding capped at £20k/year.
Candidates should have a relevant degree at 2.1 minimum, or an equivalent overseas degree in mechanical, Electrical/Electronics or Civil/Structural Engineering, Material Science, Metallurgy or Physics. Candidates with suitable work experience and strong capacity in numerical modelling and experimental skills are particularly welcome to apply. Overseas applicants should also submit IELTS results (minimum 6.5) if applicable.
To apply, please send your CV and transcript of university study, with a cover letter specifying your interest and research topic to the following email address: [email protected]
Please direct general enquiries to: [email protected]
NSIRC will be a state-of-the-art postgraduate engineering facility established and managed by structural integrity specialist TWI, working closely with lead academic partner Brunel University, the universities of Cambridge, Manchester, Loughborough, Birmingham, Leicester and a number of leading industrial partners. NSIRC aims to deliver cutting edge research and highly qualified personnel to its key industrial partners.
For more information about The National Structural Integrity Research Centre, visit www.nsirc.co.uk