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profile6AMJuly/August 2017 | MicroscopyandAnalysisAn X-ray visionFrom word go, Professor Phil Withers, Regius Professor of Materials at the UK-based University of Manchester, had a passion for the practical. As a child, he spent a lot of time repairing things, and in his words: "There is a certain satisfaction in understanding how something functions and making it work again, and I don't think I've ever lost that."Drawn to the physical world, he studied the Natural Sciences at the University of Cambridge from 1982, finally specialising in Physics. Realising he simply wasn't interested in 'quarks and far-off galaxies', he opted for a PhD in metal matrix composites.During his doctorate, he spent his Summers at the Risø National Laboratory in Denmark, using neutron diffraction to measure the stresses in each phase within the composites."It was quite exciting to do an experiment inside a nuclear reactor," he recalls. "And in many ways some of my happiest days were cycling from the neutron reactor to the physics department, with a floppy disc the size of an old LP under my arm, thinking I'm actually being paid to do this work."Withers' excitement for practical Materials Science has continued ever since. On finishing his PhD, he accepted a lectureship at the University of Cambridge, where he continued to work with short-fibre metal matrix composites. Crucially, at the time, the young researcher was also spending a lot of time at the UK-based neutron source, ISIS, Rutherford Appleton Facility, measuring the stresses and strains in these composites.Working with a pan-European team of researchers, including colleagues from ISIS as well as the Fracture Research Group at the Open University, he designed and built the world's first instrument to measure engineering strain using neutron diffraction. Dubbed ENGIN, the strain scanner – a time-of-flight neutron diffractometer – used large radial collimators with detector arrays to quickly measure precise elastic strains within small volumes of bulky specimens.For the first time, researchers were able to quickly map residual stresses in 3D in large engineering materials and components.As Withers highlights: "The instrument really sped our research up, we no longer had to waste time setting up experiments and it massively improved the accuracy and rate at which we could work." ENGIN has since served as a blueprint for engineering instruments worldwide, mapping stress fields. And as the researcher points out: "Strain measurements are now taking place all around the world, based on our instrument." Come 1998, and with composite research continuing apace, Withers was offered a Professorship at the Manchester Materials Science Centre. As he puts it: "I loved Cambridge but I do think that some degree of movement is good for you, and the time was right to move on."Failure and stressAt Manchester, he set to work establishing the Unit for Stress and Damage Characterisation, using neutron, and later, Raman and X-ray analysis to primarily understand why materials fail."To [understand materials failure], you need to be able to know the externally applied stresses, the internal residual stresses and the defects within the materials," says Withers. "At this point, I got really interested in using synchrotron X-ray diffraction, to measure the residual stresses, and also X-ray imaging, to find the defects," he adds. "Synchrotron sources are so much brighter than laboratory. X-ray sources meaning we could collect the information so much quicker."As Withers' enthusiasm for X-ray analysis grew, the researcher was also working with the likes of Rolls Royce and BP to better understand how residual stresses in components can cause unexpected, and sometimes catastrophic, failure."If a door handle fails it's frustrating but if an aircraft engine fails, that's In his relentless quest to understand why materials fail, Professor Phil Withers has pioneered the use of neutron and X-ray beams to map stresses and image components. Rebecca Pool reports

profile7euMicroscopyandAnalysis | July/August 2017more significant," he says. "So I have always been interested in structural integrity and the prediction of failure. And I have always focused on where failure really is important, and that includes oil and gas, nuclear and aerospace applications."Working at the European Synchrotron Radiation Facility and later at the newly built, UK-based Diamond Light Source, Withers showed how X-rays could be used to investigate crack and cavity formation in large steel samples. His developments included novel time-lapse experiments to predict failure mechanisms in components, and he also exploited the brilliance of the synchrotron beams to map stress development in welds at very high resolution.In related research, Withers was also using X-ray computed tomography at synchrotrons to study, for example, the growth of corrosion cracks along grain boundaries at micron-resolution. And, importantly, he also pioneered X-ray microscopy, combining diffraction and imaging modes, to glean fracture mechanics detail on the driving forces behind cracks."We were able to use X-rays to not only collect a 3D image, but to create 3D movies where we could, for example, watch the nucleation and growth of defects in components," he says. "This ability to do time-lapse imaging - in-situ - was one of the big things we managed to do at this time."As Withers' X-ray analysis methods progressed at speed, advances in X-ray CT scanners were also coming in thick and fast, meaning an X-ray imaging facility in Manchester was now a real option. This led to the foundation of the Manchester (Henry Moseley) X-ray imaging facility, now regarded as one of the most extensive multi-scale X-ray imaging laboratory in the world.Headed up by Withers, the facility is home to a vast array of instruments, including X-ray CT scanners, tomography systems and microscopes, supported by in-situ equipment. Meanwhile, research is complemented by synchrotron X-ray imaging at ESRF, Diamond Light Source and the Advanced Photon Source. "We can use different methods to study [samples] from a large scale right down to a fine scale," says Withers. "Each length scale provides you with new knowledge as well as strategies to stop a degradation process."And as the researcher highlights, facility users can make some of the fastest and highest resolution X-ray images in the world across a vast range of time-scales. "The X-rays in synchrotrons are very intense, giving us very high-resolution images, very quickly, which is great for capturing fracture in real-time," he says."However, we can use the lower intensity X-rays in our lab to look at, say, longer-term failures," he adds. "We may only take one or two frames a second, but this is good if you are taking time-lapse sequence images of corrosion over many months."But the Manchester X-ray Imaging Facility has not just been about materials failure analysis. According to Withers, his research alone has shed light on the structural performance of bone, structural changes during butterfly pupation and lithium battery degradation, as well as structure-property relationships in artificial skin."We have this wonderful facility here... for example we found ourselves studying parasites in the gut as we could use the same techniques to locate a parasite as we have used to identify a void in a metal matrix composite," he says.Indeed, Withers believes collaboration with other researchers from different areas of Materials Science, and across disciplines, has been paramount to his success. "Some people can spend a lifetime focusing on one topic and they are Tomographic sections from the centre of a C-cored fibre before testing at an intermediate stage and after full fragmentation. A 3D semi-transparent visualisation of a wedge-crack is also shownWithers et al, "Monitoring the Interface in Metal Matrix Composites", ESRF Highlights, 2004spider Computed tomography of Huntsman spiderDunlop et al. "Computed tomography recovers data from historical amber: an example from huntsman spiders", Naturwissenschaften 98, 6: 519-527