Linking macro-scale yielding and micro-scale response

Abstract

The nature of the link between macro-scale yield and particle scale interactions is poorly understood. This contribution addresses this knowledge gap using discrete element method (DEM) triaxial test simulations performed with a modified version of the granular LAMMPS code, employing a simplified Hertz-Mindlin contact model. Each sample comprised monodisperse spheres and these samples were sheared from different initial density states. The positions of the yield surfaces were identified from the overall load:deformation behaviour, just as in a laboratory test. The overall sample responses observed in these DEM simulations confirmed that the size and positions of the sub-yield surfaces largely depend upon the sample density. The particle-scale parameters monitored included the coordination number, the second order fabric tensor and the proportion of sliding contacts (the sliding fraction). A correlation was established between the variation in coordination number with strain and stiffness degradation with strain. The sliding fraction data information showed that, in contrast to conventional understanding, the particles start to slide relative to each other even within the linear elastic zone