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whh1235068木虫 (小有名气)
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【原创】美国田纳西大学T.G.Nieh教授系列学术讲座
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国家重点实验室学术讲座 SKL-AMM Seminar 题目/Tiltle： Shear band dynamics and flow serration during deformation of bulk metallic glasses 报告人/Speaker：T.G. Nieh 报告人单位/Affiliation: Department of Material Science and Engineering, The University of Tennessee 日期/Date： 2009年6月11日(周四)/ June 11 (Thursday), 2009 时间/Time： 10:00 – 11:00 AM 报告地点/Location：北科大主楼 353/ 353 Main Building, USTB 报告摘要/Abstact: We conduct uniaxial compression tests on Zr64.13Cu15.75Ni10.12Al10 bulk metallic glass at room temperature using high-sensitivity strain gauges directly attached to test samples to characterize the flow behavior. Displacement-time curves exhibited micron-size serrations (or bursts) after the onset of yielding, apparently associated with discrete shear band formation. The onset of the first burst appears at only about 0.8 σy, where σy is the macroscopic yield strength. Each displacement burst indicates shear band propagation consisting of three steps: acceleration, steady-state, and deceleration. The viscosity of a propagating shear band was found to be relatively low and was, in fact, in a similar range usually measured in the supercooled liquid region. An analysis of the experimental results using a self-consistent Vogel-Fulcher-Tamann (VFT) equation based on free volume model suggested that shear band propagation might be resulted from free volume accumulation. 题目/Tiltle： Microcompression of bulk metallic glasses: understanding and associated challenges 报告人/Speaker：T.G. Nieh 报告人单位/Affiliation: Department of Material Science and Engineering, The University of Tennessee 日期/Date： 2009年6月12日(周五)/ June 12 (Friday), 2009 时间/Time： 10:00 – 11:00 AM 报告地点/Location：北科大主楼 353/ 353 Main Building, USTB 报告摘要/Abstact: In this presentation, the development of compression technique for micro- and nano-scale samples, in particular, bulk metallic glasses, to investigate the effect of length scale on mechanical behavior will be described. Controversies of whether there is a size effect or not will be discussed from recent experiments. The problems and challenges associated with sample preparation, testing, and data interpretation, are to be addressed. Several examples will be given as illustration for these technical issues. If time permits, I will present our recent advances in high-temperature nanoindentation/microcompression: the potential and its limitation. 题目/Tiltle： Comparison of nanoindentation and uniaxial creep of nocrystalline nickel 报告人/Speaker：T.G. Nieh 报告人单位/Affiliation: Department of Material Science and Engineering, The University of Tennessee 期/Date： 2009年6月12日(周五)/ June 12 (Friday), 2009 时间/Time： 15:00 – 16:00 PM报告地点/Location：北科大主楼 353/ 353 Main Building, USTB 报告摘要/Abstact: Nanoindentation creep has been suggested to be a viable technique to evaluate the long-term stability of a mechanical system. In this presentation, I will present our recent results of the creep of nanocrystalline nickel (with a grain size of 14-65 nm) conducted by nanoindentation and microcompression methods. A direct comparison of data obtained from the two techniques will be made. It is found that, despite the fact that the two techniques produce a similar strain rate sensitivity value, nanocrystalline nickel creeps about 100 times faster under nanoindentation as compared to uniaxial condition. An explanation will be offered to reconcile the rate difference. Tai G. Nieh： 1973获台湾成功大学物理学学士学位；1980年获美国斯坦福大学材料科学与工程博士学位。现为美国田纳西大学材料科学与工程系教授，TMS和ASM成员，2003年起成为ISI常被引述的材料科学家。他的研究领域包括复合材料、超塑性材料、轻合金、金属间化合物、耐高温材料、薄膜材料、纳米结构材料、非晶态材料以及生物陶瓷等众多方面。 [ Last edited by hslining on 2009-9-12 at 08:56 ] |
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hslining
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whh1235068
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