Structural and topological nature of plasticity in sheared granular materials

• Published in: Nature communications Vol. 9; no. 1; pp. 2911 - 7
• Main Authors: Cao, Yixin, Li, Jindong, Kou, Binquan, Xia, Chengjie, Li, Zhifeng, Chen, Rongchang, Xie, Honglan, Xiao, Tiqiao, Kob, Walter, Hong, Liang, Zhang, Jie, Wang, Yujie
• Format: Journal Article
• Language: English
• Published: London Nature Publishing Group UK 25.07.2018; Nature Publishing Group; Nature Portfolio
• Subjects: 639/301/119; 639/301/923/218; Constitutive models; Deformation; Disclinations; Edge dislocations; Granular materials; Humanities and Social Sciences; Mechanical loading; Mechanics; Mechanics of materials; multidisciplinary; Physics; Plastic deformation; Plastic properties; Plasticity; Plastics; Science; Science (multidisciplinary); Shear bands; Synchrotron radiation
• ISSN: 2041-1723; 2041-1723
• DOI: 10.1038/s41467-018-05329-8

Upon mechanical loading, granular materials yield and undergo plastic deformation. The nature of plastic deformation is essential for the development of the macroscopic constitutive models and the understanding of shear band formation. However, we still do not fully understand the microscopic nature of plastic deformation in disordered granular materials. Here we used synchrotron X-ray tomography technique to track the structural evolutions of three-dimensional granular materials under shear. We establish that highly distorted coplanar tetrahedra are the structural defects responsible for microscopic plasticity in disordered granular packings. The elementary plastic events occur through flip events which correspond to a neighbor switching process among these coplanar tetrahedra (or equivalently as the rotation motion of 4-ring disclinations). These events are discrete in space and possess specific orientations with the principal stress direction. It is a general consensus that the structural defects are the plasticity carriers in amorphous solids, but its microscopic view remains largely unknown. Cao et a. show that highly distorted coplanar tetrahedra act as defects in granular packings, which flip under shear to carry local plasticity.