用3D离散元实现Ⅰ/Ⅱ型拉剪混合断裂的模拟

将变形体离散元分别与弥散式旋转裂缝模型和分离式裂缝模型耦合起来,采用上述两种非线性断裂力学模型分析了混凝土、岩石等准脆性材料的Ⅰ/Ⅱ型拉剪混合模式的开裂行为,以实现从连续介质到非连续介质转化的数值模拟。基于变形体离散元方法的界面接触本构关系提出了混凝土Ⅰ/Ⅱ混合型开裂的拉剪分区开裂准则;基于缝面法向开度增大对刚度强度的逐渐折减实现了界面裂缝扩展的模拟。作为数值验证,通过单边切口非对称三点弯梁试验的数值计算与试验结果对比,表明两种断裂力学模型均能够合理预测裂缝的起裂和扩展,在混合形式的荷载条件下,裂缝通常以Ⅰ/Ⅱ型拉剪混合模式起裂,而后以Ⅰ型为控制方式稳定扩展。文末指出,基于离散单元法的分离裂缝模型能够实现系统在外载作用下破坏全过程仿真。

Ⅰ/Ⅱ TENSILE-SHEAR MIXED MODE FRACTURE SIMULATION BY 3D DISCRETE ELEMENT METHOD

For numerical simulation of transition process from continua to discontinua, theⅠ/Ⅱ tensile-shear mixed mode fracture of quasi-brittle materials such as concrete and rock is analyzed by coupling respectively the smeared rotating crack model and the discrete crack model with deformable discrete element method(DEM). The zoning of tensile-shear failure criterion and the gradual reduction of stiffness and strength driven by the normal opening of crack are proposed based on the joint-contact constitutive relationship of deformable discrete element method. The models are applied to analyze the nonsymmetric three-point bending beam with a single-edge notch. The comparison between experimental and numerical results shows that the two nonlinear fracture models are both capable of predicting the initiation and propagation of the crack. It also shows that the crack initiateds withⅠ/Ⅱ tensile-shear mixed mode but steadily propagated predominantly in mode Ⅰ under mixed loading. It is also concluded that the discrete crack model based on DEM is capable of simulating the entire fracture to collapse process of the loaded system.