玄武岩三维细观孔隙模型重构与直接拉伸数值试验

Three-dimensional microscopic model reconstruction of basalt and numerical direct tension tests

由于岩石材料的不透明性和多孔隙特性,通过传统的物理试验或数值模拟很难真实体现其内部三维细观结构.本文基于CT扫描技术、边缘检测算法、滤波算法、三维点阵映射与重构算法,构建了可以表征玄武岩试样内部孔隙结构的三维细观非均匀数值模型.结合并行计算进行直接拉伸数值试验,研究了内部孔隙结构特征对试样破坏机制及抗拉强度的影响.研究结果表明:加载初期在试样孔隙处产生初始裂纹,随着荷载的增加初始裂纹逐渐沿横向扩展最终形成宏观拉伸破坏裂纹,并且孔隙含量和分布位置对试样拉伸断裂的位置具有重要影响.随着孔隙率增高,试样破坏过程中的声发射数目和能量逐渐减小.拉伸破坏模式呈现脆性破坏特征,同时孔隙的存在削弱了试样的抗拉强度.

The presence of discontinuities and randomly distributed pores in basalt specimens greatly affects their engineering properties,such as the failure mechanism and strength.Therefore,investigating the mechanical and fracture behaviors of basalt affected by the pre-existing defects is important for underground engineering,mining engineering,foundation engineering,and rock breaking and blasting.Laboratory tests have been widely used to research the failure mechanism of rocks under different conditions.However,it is difficult to clearly show the internal or spatial crack evolution during rock failure process in laboratory tests.Recently,X-ray computerized tomography(CT)and numerical tests have been used to detect the internal microstructures of rock specimens and to study their failure mechanism and strength.In addition,tensile strength is an important mechanical property of rock material.The direct tensile test is theoretically the simplest and most effective method for understanding the tensile behavior of rock.However,it is difficult to carry out in practical condition,because the sample processing and test procedures are complicated,also the experimental process of each sample cannot be repeated and has limited results.Due to the opacity of rocks,it is difficult to examine the three-dimensional internal structures of rocks through traditional physical and numerical experiments.In the present research,a 3 D numerical method was proposed for simulating porous rock failure based on CT technology,the edge detection algorithm,filtering algorithm,and 3 D matrix mapping method.Direct tensile tests were carried out based on the parallel finite element method to study the effect of the porosity and pore distribution on the failure mechanism and tensile strength.The results indicate that initial cracks at the beginning of loading usually occur in pores,and then with the raising of load the initial cracks propagate along the direction perpendicular to the loading direction and eventually form macroscopic tensile cracks.The porosity and pore distribution have significant influences on the position of macroscopic tensile cracks.The acoustic emission(AE)event numbers and the accumulative AE energy are gradually decreased as the porosity increased.In addition,the brittle failure primarily determines the tensile failure mode and the presence of pores weakens the tensile strength of basalt samples.