基于离散元的岩石断裂尺寸效应及断裂过程区演化特征分析

为了在离散元中研究岩石的非线性断裂过程，基于幂律型位移软化接触模型，针对一系列相似边切槽半圆盘花岗岩的三点弯曲试验进行数值模拟，并分析了其尺寸效应和断裂过程区演化规律。荷载位移曲线的峰后特征表明，随着半圆盘半径的增大，延性破坏逐渐过渡为脆性破坏，而测试结构的强度模拟结果与Baant尺寸效应理论吻合较好。在加载过程中，断裂过程区长度先增大后减小，并在荷载位移曲线的峰后达到最大值，该最大值与结构尺寸密切相关，当试件尺寸足够大，断裂过程区不受边界的约束而充分扩展，可达到饱和长度，而小尺寸试件的断裂过程区扩展会受到边界条件的限制。

Research on Rock Fracture Size Effect and Fracture Process Zone Based on Discrete Element

In order to study the nonlinear fracture process of rock in discrete element method, based on an exponential displacement softening contact model, numerical simulations of three-point bending tests were carried out on a series of geometrically similar edge-cut semicircular granite disks. The size effect of structural strength and the evolutionary characteristic of fracture process zone were analyzed. The shape of post-peak load-displacement curves shows that the gradual transition from ductile failure to brittle failure was observed as the radius of the semicircular disk increases. The simulated structural strengths match well with Baant size effect law. During the loading process, the length of fracture process zone increases at first and then decreases. Besides, it reaches the maximum length after the peak load is reached. This maximum value is highly related to the structural size. When the specimen size is large enough, the extension of fracture process zone is free of boundary and fracture process zone could fully develop to the saturated length. On the contrary, for small specimen, the extension of fracture process zone is restricted by boundary conditions.