Shear band analysis of granular materials considering effects of particle shape
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O R I G I NA L PA P E R
Jianqiu Tian · Enlong Liu · Chuan He
Shear band analysis of granular materials considering effects of particle shape
Received: 26 March 2020 / Revised: 15 June 2020 © Springer-Verlag GmbH Austria, part of Springer Nature 2020
Abstract Biaxial simulation tests with flexible membrane boundaries and Cosserat theory are used to investigate the effect of the particle shape on the properties of a shear band of granular materials. Three kinds of special particle shapes are quantified by the aspect ratio (AR) and the AR values for disks, squared, and elongated grains which are 1.00, 0.88, and 0.50, respectively. The peak and residual stress ratios and dilatancy increase as the AR decreases. A measurement of inclinations and thicknesses of X shear bands based on the porosity is proposed here. For DEM simulation and bifurcation analysis, the predicted maximal inclination of the shear band increases with the AR decreasing. However, the predicted maximal and minimal thicknesses of the shear band for DEM simulation and bifurcation analysis decrease with the AR decreasing. Based on Cosserat theory, a new empirical equation with fewer material constants which describe the relation between the stress ratio and shear strain is proposed, and this equation is in good agreement with DEM data. The predicted particle rotation and displacement in the shear band are both comparing well with DEM data for three kinds of particle shapes. Furthermore, the rotation of a particle in the shear band gradually decreases on successively considering AR = 1.00, 0.88, and 0.50. 1 Introduction In nature and human industry, granular materials are prevalent. The materials in landslides, debris-flow, and ore excavation can be treated as granular materials. The stability and deformation characteristics of granular materials are often controlled by the strain localization, i.e., the shear band, and the strain localization is a typical failure mode of granular materials. The shear bands are generally observed in the laboratory tests [5,17,20,37,39]. Desrues and Viggiani [14] summarized abundant laboratory results of biaxial compression tests, and effects of initial state, specimen size, and grain size on the shear band were discussed. However, properties of the shear band in laboratory tests are obtained with the help of other auxiliary tools, such as digital image correlation techniques, X-ray computed tomography, and stereophotogrammetry. Some properties of the grain, especially the particle shape, in laboratory tests are hard to control. The discrete element method (DEM) developed by Cundall [12] can overcome these shortcomings in laboratory tests, and DEM is proved to be a good tool in the research of granular materials [13]. The shear band is mainly obtained in biaxial simulations, and some researchers [25,28] used the rigid boundary and disks in biaxial compression to discuss the shear band. The flexible membrane boundary instead of a rigid boundary can capture the natural development of the J. Tian · E. Liu (B) · C.He State
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