基于复杂网络的岩土颗粒材料分散性失稳先兆研究

岩土颗粒材料在达到Mohr-Coulomb塑性极限之前可能已经发生了没有明显局部损伤的全域准均匀破坏，即分散性失稳。近年来，网络科学工具在颗粒材料环境中的应用为研究其失稳破坏现象提供了有趣新颖的洞见。采用离散单元法对不同初始密实度的颗粒体系进行等体积应变加载路径的数值试验，发现初始状态越松散的颗粒体系越有可能发生分散性失稳；采用网络科学的理论和方法分析颗粒接触网络的拓扑结构特性和演化规律，发现颗粒材料分散性失稳的结构根源是颗粒接触网络完全崩塌。将颗粒体系划分为强、弱接触系统以构建强接触子网络、弱接触子网络和强?弱接触子网络，研究颗粒接触网络及其3个子网络的特征量演化，结果表明：当颗粒材料开始处于不稳定状态时，易受扰动的弱接触系统的部分接触先失效，导致强接触系统失去其稳定支撑作用而降低承载能力。随着加载的继续，系统通过非局部的自组织过程导致接触结构的全面崩塌，最终触发整体分散性失稳。因此，先于整体失稳的部分弱接触的失效，可视为颗粒材料分散性失稳的关键性临界征兆。

Study on precursors of diffuse instability of granular materials based on complex network theory

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.