题目：Cutting Mechanics of Soft Materials – The Role of Fracture Toughness
报告人：Prof. Yiu-Wing Mai
(Centre for Advanced Materials Technology, the University of Sydney)
Cutting of soft materials is a common daily life experience (e.g., slicing of meat and cheese) and an essential operation in many industries, healthcare (e.g., surgery) and manufacturing (e.g., paint removal) among them. By measuring the cutting forces of the tool and examining the deformation mechanisms of the workpiece, we can put the cutting process on a strong scientific and technological footing. For it provides an ingenious method to measure the fracture energy, i.e., the specific resistance to cracking, of soft materials like plastics, thin films on substrates and nanocomposites at different cut-depths. The new knowledge gained improves tool design and optimizes cutting conditions to increase the cutting process efficiency with huge economic benefits. For example, cutting with sharp tools will enable the paint industry an effective solution to measure the adhesion energy and scrape paints from metal substrates. It will also provide a unique fracture energy index for food products for correlation with food quality and texture.
In this seminar, we present our recent work on the cutting behaviour of polyolefins with different molecular weights and epoxies with different degree of cross-links. We investigate the effects of rake angle, cut depth, and tool sharpness as well as chip bending on the fracture energy obtained from the cutting theory. Our results show that fracture has a critical role in the formation of the newly cut surface as the chip is separated from the workpiece by the cutting tool. The surface finish after cutting is dependent on the cutting depth and the ratio between fracture energy and yield strength. These new findings provide useful guidance for understanding the machining behaviour of soft materials like polymers.
Professor Yiu-Wing Mai received his undergraduate and postgraduate training in mechanical engineering at the University of Hong Kong, China. He worked previously in the US (University of Michigan and the NIST), the UK (Imperial College) and Hong Kong (CityU, HKU, HKUST and PolyU); and now holds a University Chair in Mechanical Engineering at the University of Sydney.
Prof Mai has made seminal contributions on fracture mechanics and advanced composite materials. His research results have impacted on the developments of asbestos-free fibre cements, testing protocols for essential work of fracture of polymers, and improved composites manufacturing processes. Prof Mai was appointed AM (Order of Australia) in 2010 and is Fellow of the Royal Society, the Royal Academy of Engineering, the Australian Academy of Science, and the Australian Academy of Technological Sciences and Engineering.