Prediction of Fatigue Limit of Additive Manufactured Materials

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Location/Division: Cambridge

PhD Studentship – Prediction of fatigue limit of additive manufactured materials

Institution National Structural Integrity Research Centre (NSIRC)
PhD Supervisor TBC
Application Deadline 
Funding Availability Fully-funded for UK & EU students, partial funding for overseas students

In fatigue design, it is important to know the fatigue limit of the material to be used in order to avoid fatigue failure.
For conventional metallic materials, with or without cracks, the Kitagawa-Takahashi diagram is often used to predict the fatigue limit. The stress range corresponding to no crack growth increases with decreasing crack size according to linear elastic fracture mechanics until crack size approaches a critical value below which the growth rates of small fatigue cracks cannot be correlated with the stress intensity factor range. There are several existing models predicting fatigue limit of small cracks.
Additive manufactured (AM) materials often contain manufacturing defects such as gas porosity, lack of fusion, inclusions and micro-cracking. Their fatigue behaviour is often found to be different from that of conventional metallic materials due to their heterogeneous microstructure characteristics and manufacturing defects of various types and sizes. Therefore, the models developed for predicting fatigue limit of conventional metallic materials may not be suitable for the AM materials.

Project Outline
This study will contribute to developing models to predict fatigue limit of AM materials with manufacturing defects and to characterise small crack behaviour in these materials.
The study will involve both numerical modelling and fracture mechanics analysis to develop solutions of stress intensity factor for typical defects seen in AM materials. They are often not planar defects and are of different shapes. Models will be developed to characterise the behaviour of small cracks, including threshold crack growth, in AM materials. In addition to collecting relevant fatigue data of AM materials from the literature, fatigue tests will be performed to verify the model proposed.

About Industrial Sponsor
The Lloyd’s Register Foundation funds the advancement of engineer-related education and research and supports work that enhances safety of life at sea, on land and in the air, because life matters. Lloyd’s Register Foundation is partly funded by the profits of their trading arm Lloyd’s Register Group Limited, a global engineering, technical and business services organisation.
NSIRC is a state-of-the-art postgraduate engineering facility established and managed by structural integrity specialist TWI, working closely with, top UK and International Universities and a number of leading industrial partners. NSIRC aims to deliver cutting edge research and highly qualified personnel to its key industrial partners.
About the University
Our research in Materials Engineering and Structural Integrity builds on our historical research strengths at Coventry and adds new research teams through investment and growth. We are part of the newly established University Research Institute for Future Transport and Cities. We aim to be the research partner of choice for key industry sectors including manufacturing, aerospace, and energy. We bring value to our partners by adding value, effecting knowledge transfer, generating intellectual property and fostering new technologies. This is underpinned by our expertise in Metrology, Advanced Experimentation, Residual Stress Analysis, Structural Integrity, and proven models of effective collaboration with academic peers and industrial partners from all over the world.
Our key research themes include:
• advanced analytical, modelling, and experimentation methods
• materials, mechanics and measurement
• non-destructive evaluation, material anomaly detection using evolutionary computing techniques
• residual stress measurement and stress engineering
• structural integrity methods for new materials made by advanced manufacturing processes
We are delighted to have been awarded 15 PhD studentships from NSIRC, with funding support from the BP, LRF and TWI.
Candidate Requirements
Candidates should have a relevant degree at 2.1 minimum, or an equivalent overseas degree in engineering or materials science. 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 7.0) if applicable.
Funding Notes
This project is funded by Lloyds Register Foundation, TWI and Coventry University. The studentship will provide a successful Home/EU student with a stipend of £16k/year and will cover the cost of tuition fees. Non-EU students are also welcome to apply, full studentship will be provided for this project to cover the stipend and tuition fees, subject to availability.