Huang Yiqun, Hu Shaowei, Gu Zi, Sun Yueyang
College of Mechanics and Materials, Hohai University, Nanjing 210098, China.
School of civil Engineering, Chongqing University, Chongqing400044, China.
Materials (Basel). 2019 Jun 14;12(12):1929. doi: 10.3390/ma12121929.
In order to investigate the fracture behavior of concrete mesostructure and reveal the inner failure mechanisms which are hard to obtain from experiments, we develop a 3D numerical model based on the Voronoi tessellation and cohesive elements. Specifically, the Voronoi tessellation is used to generate the aggregates, and the cohesive elements are applied to the interface transition zone (ITZ) and the potential fracture surfaces in the cement matrix. Meanwhile, the mechanical behavior of the fracture surfaces is described by a modified constitutive which considers the slips and friction between fracture surfaces. Through comparing with the experiments, the simulated results show that our model can accurately characterize the fracture pattern, fracture propagation path, and mechanical behaviors of concrete. In addition, we found that the friction on the loading surfaces has a significant effect on the fracture pattern and the strength of concrete. The specimens with low-friction loading surfaces are crushed into separate fragments whereas those with high-friction loading surfaces still remain relatively complete. Also, the strength of concrete decreases with the increase of the specimen height in the high friction-loading surfaces condition. Further, the energy analysis was applied to estimate the restraint impact of loading surfaces restraint on the compressive strength of concrete. It shows that the proportion of the friction work increases with the increase of the restraint degree of loading surfaces, which finally causes a higher compressive strength. Generally, based on the proposed model, we can characterize the complicated fracture behavior of concrete mesostructure, and estimate the inner fracture mode through extracting and analyzing the energies inside the cohesive elements.
为了研究混凝土细观结构的断裂行为，并揭示从实验中难以获得的内部破坏机制，我们基于Voronoi镶嵌和内聚单元开发了一个三维数值模型。具体来说，Voronoi镶嵌用于生成骨料，内聚单元应用于界面过渡区（ITZ）和水泥基体中的潜在断裂面。同时，通过考虑断裂面之间的滑移和摩擦的修正本构模型来描述断裂面的力学行为。通过与实验对比，模拟结果表明我们的模型能够准确地表征混凝土的断裂模式、断裂扩展路径和力学行为。此外，我们发现加载面上的摩擦对混凝土的断裂模式和强度有显著影响。低摩擦加载面的试件被压碎成单独的碎片，而高摩擦加载面的试件仍相对完整。而且，在高摩擦加载面条件下，混凝土强度随试件高度的增加而降低。此外，通过能量分析来评估加载面约束对混凝土抗压强度的约束影响。结果表明，摩擦功的比例随着加载面约束程度的增加而增加，最终导致更高的抗压强度。总体而言，基于所提出的模型，我们可以表征混凝土细观结构复杂的断裂行为，并通过提取和分析内聚单元内部的能量来估计内部断裂模式。
