饱水灰岩巴西试验准静态加载应变率效应研究

通过对饱水灰岩进行不同加载应变率巴西试验、实时声发射监测以及破裂面扫描电镜观察,试验研究了应变率对饱水灰岩强度及破裂机制的影响。结果表明:1饱水对灰岩强度有明显的弱化作用,其拉伸强度值与干燥时相比降低了约15.99%;2声发射特征会受到加载速率的影响,试样中出现最大声发射事件数会随着应变率的增大而增大;3较低应变率(3.0×10-4s-1和9.0×10-4s-1)时灰岩破裂细观机制为沿晶破裂模式,宏观上拉伸强度较低;当应变率增大至1.5×10-3s-1时细观上为沿晶与穿晶耦合断裂模式,宏观上拉伸强度较高,而应变率为1.0×10-2s-1时细观上为穿晶断裂模式,宏观上拉伸强度最高。基于试验结果,采用三维颗粒流(PFC3D)分析了饱水灰岩加速速率效应细观机理。模拟显示,较低应变率下荷载–位移曲线表现为脆性,而随着应变率的提高曲线延性增大。灰岩拉伸强度随着应变率的提高近似线性增大。边界能与拉伸强度呈现为正比关系,灰岩破坏所消耗的能量与微裂纹数均随着应变率增大而增加。

Quasi-static loading strain rate effects on saturated limestone based on Brazilian splitting test

Based on the Brazilian splitting test, real-time acoustic emission (AE) monitoring and SEM observations, the influences of strain rate on tensile strength and deformation failure mechanism of saturated limestone specimens are investigated. The results show that: (1) Compared with the dry specimen, the tensile strength of saturated specimens has a reducing tendency and the decrease extent is about 15.99%. (2) The AE characteristics are also affected by the strain rate, i.e., the number of AE events increases as strain rate increases. (3) When the strain rate is smaller (3.0×10^-4s^-1 and 9.0×10^-4s^-1), the failure mechanism of saturated limestone specimens is that the crack propagates between mineral particles, thus the tensile strength is the smallest. When the strain rate increases to 1.5×10^-3s^-1, the failure mechanism is coupled of being penetrated and penetrating along mineral particles, so the tensile strength is medium. However, when the strain rate equals to 1.0×10^-2s^-1, the failure mechanism begins to penetrate mineral particles, then the tensile strength is the largest. Based on the experimental results, a discrete element method (DEM) PFC^3D is used to analyze the meso-mechanism of strain rate effects. According the simulation results, the following conclusions can be drawn: the load-displacement curves are brittle when the strain rate is small. When the strain rate is high, the load-displacement curves show a ductile response. The tensile strength increases linearly with the increasing strain rate. The boundary energy is positively correlated with the tensile strength, i.e., the larger the boundary, the higher the tensile strength. The energy of sample failure at the high strain rate and the number of micro-cracks are all greater than those at the low rate.