Influence of gradation range on strong contact network in granular materials

The topology of the granular material in the microscale affects the macroscale mechanical responses. Based on graph theory, the particles can be considered as nodes, and contacts can be considered as links, which form the contact network. Within the contact network, different force thresholds are applied to distinguish the strong and weak networks. This paper focuses on the influence of gradation range on the topological characterizations of the strong contact network in 2D granular materials. Biaxial shearing tests for 6 uniformly graded samples and 1 nonuniformly graded sample are conducted using the discrete element method. Network-based metrics are used to investigate the topology features of the strong contact network with different thresholds for three stress states. It is found that gradation range has little influence on the macroscale mechanical responses and the formation of shear bands for assemblies with different gradations (except for monodisperse assembly). Comparing the network-based metrics for samples with different gradations, only the differences in the value of the metrics are found while the strong networks exhibit a unique variation rule. The critical threshold appears at 1.4 times average contact force, which means the largest cluster can span the boundaries with minimum contacts in the strong contact system. The granular system loses the connections between the boundaries in the confining pressure direction at a smaller threshold compared to the loading direction, and the monodisperse assembly shows a particular topology compared to other samples.