Mechanical properties at the microscale
Professor Alfonso Hing Wan Ngan (Croucher Scholarship 1991 and Croucher Fellowship 1992) is a professor in materials engineering at the University of Hong Kong. His research program focuses on understanding the microstructural basis of mechanical properties of materials, electron microscopy for materials engineering, and crystalline defects and their modelling. In addition to having an illustrious research career, Ngan also contributes significantly to the academic development at the University of Hong Kong, as an associate dean of the Faulty of Engineering.
Ngan’s interests in microstructure began as a graduate student at the University of Birmingham, where he used electron microscopy to study the atomic structure in metallic alloys and understand how microstructural variability affects the mechanical properties of materials. It took Ngan only two years and nine months to complete his PhD thesis, which won the Thomas Turner Research Prize for the best thesis in Materials and Metallurgy. After obtaining his PhD, Ngan was eager to explore the theoretical side of materials science. He moved to the University of Oxford to work with Professor David Pettifor, who is a pioneer in materials modelling and theory. Ngan returned to Hong Kong in 1993 and joined the University of Hong Kong as a lecturer in materials science and solid mechanics in the Department of Mechanical Engineering.
At the University of Hong Kong, Ngan has decided to focus on understanding the mechanical behaviour of small materials. Traditionally, a lot is known about materials of macro sizes, for example, what materials should be used to build a bridge, and to what extent the materials can withstand fatigue. “But there is a significant gap in knowledge at the micro scale,” Ngan said, “as most conventional understanding would not apply to materials of about 10 to 50 micrometers in size – about the thickness of a human hair.” A classic example is strength. Most materials science textbooks would say that the strength of a material is independent of its size, meaning that a large beam and a small one made of the same material will break at the same stress. However, this does not apply at the micro scale, at which strength is actually inversely related to size.
Recognising this knowledge gap and the importance of it to the design of small devices, such as the bonded wires in an integrated circuit, Ngan’s research group has focused on understanding the microstructural basis of mechanical properties of small materials using a combination of experimental and theoretical approaches. In 2000, he established Hong Kong’s first laboratory on “nanomechanics”, for experimental measurement of mechanical properties of small materials. More recently, his group has been focusing on developing theoretical models and simulators to predict material properties at the meso-scale. It is well known that defects in the atomic arrangement control the strength of metals, but current simulators cannot deal with the quantity of defects present in materials of micron sizes and beyond – the so-called meso-scale. By designing a tool that simulates the dynamics of the density distribution of defects, rather than the defects themselves, one would be able to handle a lot of defects, and predict how a material of a real size would fail and its residual life.
Professor Alfonso Hing Wan Ngan is Kingboard Professor in Materials Engineering at the University of Hong Kong and an elected Fellow of the Hong Kong Academy of Engineering Sciences, Hong Kong Institution of Engineers, and the Institute of Materials, Minerals and Mining (IMMM) in the UK. His research has won numerous awards, including the Outstanding Young Researcher Award and Outstanding Researcher Award, both at the University of Hong Kong, and the Rosehain Medal and Prize by the IMMM. In 2008, he was conferred a higher doctorate by the University of Birmingham. He obtained his bachelor in engineering at the University of Hong Kong with first class honours.
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