为了从材料细观结构角度研究沥青混凝土的断裂机理,运用离散元程序PFC3D内的“Fish”语言,采用多球相互重叠的方法描述粗集料颗粒的空间不规则形状,结合集料颗粒的随机投放算法和离散元的空隙处理方法,建立了沥青混凝土小梁试件的三维离散元模型；通过室内沥青砂浆单轴压缩试验和劈裂试验,并结合宏观性能与微观力学参数的转化关系,获得了用于离散元模拟的各类微观参数；采用三维离散元程序PFC3D,进行了-10℃和15℃条件下小梁中点弯曲断裂试验的离散元模拟,获得了弯曲断裂曲线；采用与混合料三维离散元结构相同沥青用量、空隙率和级配在室内成型了沥青混合料的小梁试件,并获得了室内实测断裂曲线.研究结果表明:所建立的离散元模型可以充分考虑集料颗粒的不规则形状、集料级配特征和空隙大小；三维离散元方法可以较好地模拟沥青混合料弯曲断裂过程中裂纹起始和扩展的现象,模拟结果与室内实测结果基本相当；三维离散元模拟可以作为研究沥青混合料断裂特征的辅助手段.%In order to reveal the fracture mechanism of asphalt concrete ( AC ) from the viewpoint of microstructure, first, the irregular three-dimension (3D) shape of coarse aggregate particles was described with overlapping spheres, and a 3D discrete element model of a small AC beam specimen was established by using the Fish language provided in the finite element software PFC3D, the random aggregate packing algorithm and the generation method of air voids. Next, the micro-parameters for the discrete element simulation were obtained according to the test re-sults of uniaxial compression and splitting, with the relationship between the macro and the micro mechanical pa-rameters being also considered. Then, the midpoint-bending fracture test of a user-defined 3D AC beam at - 10 and 15 ℃ was simulated with PFC3D and the corresponding fracture curves were obtained. Finally, AC beams with their asphalt dosage, porosity and gradation similar to those of the AC model were frabricated, and some practical fracture curves were obtained in laboratory. The results indicate that the established discrete element model fully considers the irregular shape, the gradation and the porosity of aggregate, so that it is capable of simulating the ini-tiation and propagation of cracks during the bending fracture with high accuracy, and that the 3D discrete element-based simulation can be used as a supplemental tool to evaluate the fracture properties of asphalt mixture.
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