考虑初始缺陷的水泥基复合材料细观开裂研究

为了研究微观初始缺陷对水泥稳定碎石基层材料（CTB）细观开裂的影响，基于离散元法（DEM）和随机算法构建了细观非均质随机骨料数值模型，结合参数反演确定了模型细观参数，并引入裂隙网络（DFN）来表征水泥砂浆内部的微观初始缺陷。通过虚拟半圆弯曲（SCB）试验模拟了细观开裂过程，比较分析了数值模拟结果和试验结果，并进一步研究了裂隙密度和宽度对结构细观开裂的影响。结果表明：细观断裂模型的数值模拟结果和试验结果基本吻合，模型能较好地表征细观随机开裂行为；材料的宏观开裂是由于细观损伤的累积导致，宏观裂纹的产生经历了平稳扩展和快速贯通的过程；张力是裂纹演化的驱动力，裂纹通常沿着砂浆与骨料的界面薄弱区进行扩展；微观缺陷显著影响水泥基材料的力学性能和断裂行为，初始裂隙通过诱导微裂纹的扩展与贯穿，降低结构整体强度，但是在一定程度上增大了结构的容许形变，其中20~40 m·m^-2的裂隙密度和0.3~0.45 mm的裂隙宽度对材料强度影响最为显著，施工过程中合理控制裂隙密度和宽度对于提高材料抗裂能力有益。所构建的细观模型可以很好地捕捉微裂纹的扩展和贯穿过程，能够实现对细观断裂的精确模拟，为探索水泥基复合材料的破坏过程和机理提供了一种新的研究手段。

Mesoscale Cracking of Cement-treated Composites with Initial Defects

To investigate the effect of initial microscopic defects on the mesoscopic fracture of cement-treated base (CTB) materials, a mesoscale heterogeneous numerical model was established using the discrete element method (DEM) and randomization method. Experiments were conducted to obtain the model parameters through an inverse analysis. A discrete fracture network (DFN) was then used to characterize the initial microscopic defects in cement mortar during hardening. Based on the established mesoscale DEM model with initial defects, virtual semicircular bending tests were conducted, the results of which show good agreement with the experimental results. In addition, the mesoscale cracking process was simulated, and the influence of the density and width of the DFN on microstructure cracking was analyzed; the proposed model could better characterize the mesoscopic random cracking behavior. The failure of CTB could most likely be due to the accumulation of damages at mesoscopic level. The simulated crack was formed by the aggregation, connection, and expansion of microfractures. Tension is the driving force of crack evolution, and cracks usually extend along weak areas such as the interfaces between mortar and aggregate. The results also show that the initial microscopic defects negatively affect the structural strength but increase the failure allowable deformation. Furthermore, the fracture density of 20-40 m·m^-2 and fracture width of 0.3-0.45 mm have the most significant influence on the material strength. The reasonable control of the initial defect density and width in the construction process is beneficial for improving the anticrack ability of the material. This paper provides a new numerical method for investigating the progressive failure process and failure mechanism of cement-treated composites.