Measurement techniques of grain motion and inter-grain structures in dense granular materials |
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| Authors: | YANG Hui ZHANG Guohua WANG Yujie SUN Qicheng |
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| Institution: | 1.School of Optical-Electrical and Computer Engineering, University of Shanghai for Science and Technology, Shanghai 200093, China;2.Department of Physics, University of Science and Technology Beijing, Beijing 100083, China;3.Department of Physics and Astronomy, Shanghai Jiao Tong University, Shanghai 200240, China;4.State Key Laboratory of Hydroscience and Engineering, Tsinghua University, Beijing 100084, China |
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| Abstract: | A dense granular material is composed of a large number of densely packed coarse grains, which is widely encountered in nature, engineering and industries, such as granular debris flows, rock-filled dams, and pebble beds in nuclear reactors. It is a typical many-body system with intrinsic characteristics of structural and dynamic heterogeneities which leads to the complicated macroscopic behavior. By developing the statistic mechanics of structure and dynamics of grains, continuum theories of granular materials can be established and such macroscopic behaviors are then expected to be described. However, it is very difficult to fulfil these objectives because of the limitations of present measurement techniques and theoretical basis. The present measurement techniques are only applicable to study ideal and simple structure problems, and do not work well for granular structures. The shortage of granular structures properties makes the connections between structure and macroscopic properties impossible. Therefore, measurements of heterogeneity in structural and dynamics are the foundation for understanding the complex bulk properties of granular materials. The authors of this paper, from different research institutions, have conducted thorough experimental studies in the past decade, which can be classified into two categories: (1) non-invasive methods, mainly including digital image velocimetry, speckle visibility spectroscopy and Xray-CT, are developed to measure the moment of single grains; (2)response spectrum methods, mainly including volume response spectrum, mechanic response spectrum and acoustic measurements, are developed to directly or indirectly detect the inter-particle contact force. In this paper, we review the fundamental principles of these methods and their limitations, and state-of-the-art studies. Finally, we conclude the paper with our experience sand lessons learned, and provide suggestions for the future work. |
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| Keywords: | granular materials mesoscopic structure structural heterogeneity dynamics heterogeneity non-invasive method response spectrum method acoustic spectrum analysis |
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