Abstract Many widely used numerical models of rock fracture based on mesoscale laboratory test characterisation of effective ‘intact’ strength parameters neglect microstructure effects. They therefore cannot explain grain boundary and pore effects on crack propagation and consequently are inadequate for models of rock destruction that exploit point and indentation stresses. Understanding deep drilling processes involving drill-bit buttons and/or water-jetting where rock loading is concentrated in domains with fewer mineral grains will therefore require models with microstructure. To investigate microscale failure mechanisms of granular rocks in diverse scenarios, we target a porous sandstone and introduce a novel workflow consisting of a computerized tomography (CT) based microstructure construction approach and a complementary mechanical numerical approach. The construction approach extracts the realistic rock microstructure and transforms the large voxel number CT-scan data into significantly fewer triangular elements. The finite-discrete element method (FDEM) with grain-based model (GBM) is adopted to solve the mechanics. The microscale failure mechanism of sandstone during the Brazilian test was thoroughly analysed using the numerical results together with the post failure CT-scan test data. The build-up of compressive and tensile stress chains, micro-crack nucleation, local relaxation, chain switching and final crack-path development exploiting pores was illustrated, revealing the micro-to-macro failure mechanism in time and space. Fracture paths in the specimens during Brazilian tensile test were dominated by the pores and the inter-grain boundaries. The tensile strength of the inter-grain joints was estimated to be at least 3.67 times the mesoscale specimen's intact tensile strength, while the pores account for 72.76% of the fracture path. The influence of the cementation distribution and microscale discontinuities was investigated with numerical cases.

中文翻译：

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多孔砂岩的晶粒尺度破坏机制：使用 CT-Scan 微观结构对巴西抗拉强度试验进行的实验和数值 FDEM 研究

摘要 许多广泛使用的基于有效“完整”强度参数的中尺度实验室测试表征的岩石断裂数值模型忽略了微观结构的影响。因此，它们无法解释晶界和孔隙对裂纹扩展的影响，因此不适用于利用点应力和压痕应力的岩石破坏模型。因此，了解涉及钻头按钮和/或水射流的深钻过程，其中岩石载荷集中在矿物颗粒较少的区域，因此需要具有微观结构的模型。研究粒状岩石在不同情况下的微尺度破坏机制，我们针对多孔砂岩并引入了一种新颖的工作流程，该工作流程包括基于计算机断层扫描 (CT) 的微结构构建方法和互补的机械数值方法。该构造方法提取逼真的岩石微观结构，并将大体素数 CT 扫描数据转换为显着更少的三角形元素。采用基于颗粒模型（GBM）的有限离散元法（FDEM）进行力学求解。使用数值结果和破坏后 CT 扫描测试数据，彻底分析了巴西试验期间砂岩的微观破坏机制。说明了压应力链和拉应力链的建立、微裂纹成核、局部松弛、链转换和利用孔隙的最终裂纹路径发展，揭示时空微观到宏观的失效机制。巴西拉伸试验中试样的断裂路径主要是孔隙和晶界。晶粒间接头的拉伸强度估计至少是中尺度试样完整拉伸强度的 3.67 倍，而孔隙占断裂路径的 72.76%。用数值案例研究了胶结分布和微尺度不连续性的影响。