“Engineering is all about solving problems and, rather like crossword puzzles, there’s a lot of fun and intellectual stimulation in finding an optimum solution and testing it,” says Neil James, Professor of Mechanical Engineering.
For the near 20 years that Professor James has been a part of Plymouth University, that willingness to confront challenges in industry and search for answers has been a defining feature of his research. And in one rewarding example, it’s resulted in the collaborative development of an innovative welding technique and commercial platform that has changed the way testing and repair work is carried out on power plants in South Africa, making a major contribution to extending their lifespan and improving safety.
“I’m a mechanical engineer and I’ve been interested in cracking mechanisms since the second year of university,” says Neil, Head of the School of Marine Science and Engineering. “If you’re interested in cracking and failure then you’re interested in materials and their properties and in joining them together. The most common industrial joining process is welding.”
Friction stir welding is a new welding method, differing from fusion welding in its use of a rotating tool applied under pressure to plastically deform and bond materials together, generating much lower and more localised heat. This has major advantages for joint performance and for joining metals that are hard or even impossible to fusion weld. Historically, one of the limitations of friction welding has been the trial and error approach needed to identify the optimum process parameters, such as how much torque is required, and how fast to feed the tool along the weld.
This was the issue facing the engineering sector when Neil began to collaborate in 1998 with Professor Danie Hattingh, a former Plymouth PhD student, who returned to the city on sabbatical leave from Nelson Mandela Metropolitan University (NMMU) to work on friction stir welding and their associated residual stresses. Funded by the Dutch steel and aluminium-making firm, Hoogovens (later acquired by British Steel and latterly part of the Tata Group), the work led to several influential papers that assessed the various influences of tool speed, feed rate and geometry on residual stresses, microstructure and defects, and hence on mechanical and fatigue properties.
The research provided the initial foundation for a range of subsequent joint research projects and well-cited publications. Professor Hattingh returned to South Africa and developed the country’s first friction stir welding platform in 2002.