Abstract: The granular materials may have undergone full-domain quasi-uniform failure without significant local damage, i.e., diffuse instability, before reaching the Mohr-Coulomb plastic limit condition. Recent applications of network science tools in granular materials environments have provided interesting and novel insights to study their instability and failure. The numerical tests of the equal volume strain loading path on the granular systems with different initial porosities are carried out by using the discrete element method, it is found that the more loose the initial state of the granular systems, the more likely diffuse instability will occur. Using the theories and tools of network science to analyze the topological structure characteristics and evolution laws of the granular contact networks, it is found that the granular contact networks collapse completely when the diffuse instability of the granular materials occur. The granular system is divided into strong and weak contact systems to construct strong contact sub-networks, weak contact sub-networks and strong-weak contact sub-networks, and study the evolution of network features from the three sub-networks and the complete network. The results show that when the granular materials start to be in an unstable state, the part of contacts from the weak contact system disconnect first, leading to the strong contact system reducing its load-bearing capacity due to the loss of stable support from the weak contact system, and as the loading continues, the system leads to the full collapse of the contact structure through a non-local process of self-organization, i.e. the overall diffuse instability occurs. Therefore, the loss of partial weak contacts that precede the overall instability can be considered as a critical sign of diffuse instability of granular materials.

Key words: granular materials, diffuse instability, complex network, strong and weak contact networks