报告人：Andy Bushby 教授
时 间：2017年6月27日（星期二）下午 14:30-16:00
地 点：长安校区 理学院383会议室
主 题： Mechanical Properties of Polymers Determined by Nanoindentation
内容简介： The application of polymeric materials in engineering is rapidly increasing, in both bulk and coating form, in technologies from automotive to plastic electronics to medical applications. Determining the mechanical properties is important for structural applications, for high throughput screening of materials and understanding of polymer degradation and aspects of polymer physics. Nanoindentation is a convenient means to determine mechanical properties but the response is dependent on strain, strain rate, strain state and load history. The test method, contact geometry and load cycle can also strongly influence the measured values. In indentation testing, assumptions about the contact area derived from displacement measurements may not hold true, and the induced strain gradients can lead to non-uniform time-dependent responses within the strained volume, making determination of material parameters test dependent. It is often difficult to obtain values equivalent to tensile, flexure or dynamic test methods, with measured indentation modulus values typically a factor of 2 or more too high.
Here we present the results of an inter-comparison study of indentation methods on a range of engineering polymers. Different indentation geometries and test methods are compared to tensile and dynamic data from the same materials. The results show that the choice of indenter geometry, load cycle and analysis method have a large influence on the measured mechanical property values obtained. The results imply that confinement of the polymer within the high pressure beneath the indenter can significantly change the elastic and flow properties, creating apparent differences between test methods. However, comparative values for time-dependent elastic properties can be obtained using appropriate geometries and analysis methods. The work raises fundamental questions about the nature of elastic modulus in polymeric materials.
Dr Andy Bushby
Reader in Materials
Director of SEMS -NPU Collaboration
School of Engineering and Materials Science, Queen Mary University of London
Member of Institute of Physics, Fellow of the Royal Microscopical Society
Dr Bushby's research is centred on the micro- and nano-mechanics of materials and structures. He is a leading expert in the technique of nanoindentation for small-scale mechanical property measurement and contributes to ISO Standards working groups for instrumented indentation. Major research themes include the development of methods using spherical indenters, electromechanical properties of ferroelectric thin films, visco-elastic and composites materials, structure-properties relationships in calcified biological tissues and nano-structured crystalline materials. Fundamental research has focused on the origin of size effects in mechanical properties and has led to new understanding of the strength of nano-structured materials. A long term goal is to exploit the size effect in novel high-strength, lightweight materials through length-scale engineering of their microstructure. Dr Bushby is also the creator and director of Queen Mary’s NanoVision Centre for advanced microscopy. The Centre encourages overlap between different high-resolution microscopy techniques and between scientists from different disciplines. He has developed volume electron microscopy techniques for 3D imaging of biological tissues in collaboration with leading biological imaging groups in the UK.