基于Cosserat近场动力学的纤维混凝土破坏模拟

本文基于Cosserat近场动力学发展了一种纤维混凝土的近场动力学模型，对纤维混凝土的破坏现象进行研究。该模型考察了物质点独立的转动自由度和物质点间的力偶作用，而且有表征微结构尺寸的内禀长度，相比于传统的近场动力学模型，更适合描述纤维混凝土这类胶结颗粒材料的力学行为。本文采用完全离散的方式对纤维进行建模，引入了纤维拔出实验中拔出位移和切应力的关系，并且采用组构张量描述纤维的局部分布。数值算例部分模拟了单纤维拔出实验、带预制裂纹的平板拉伸实验和三点弯曲梁实验。数值结果和已有的数值模型以及实验进行了对比，验证了所提出模型的正确性。此外，本文还调查了微结构对纤维混凝土破坏的影响，数值结果显示Cosserat剪切模量和内禀长度会影响裂纹的局部分布，但是不会改变裂纹的主方向。

Numerical fracture analysis of fiber-reinforced concrete based on the Cosserat peridynamic model

Fiber-reinforced concrete (FRC) is a composite material made up of concrete and fibers. FRC has higher tensile strength and toughness than conventional plain concrete because of the reinforcement of fibers. Understanding the fracture behavior of FRC is vital for its application and design in construction work. The size effect of the FRC experimental specimen affects the accuracy of predicting the mechanical properties because of the micro-structures. Most existing numerical methods are unable to reproduce the complex fracture patterns of FRC, due to the lack of methods to characterize the FRC’s micro-structure. This paper proposes a numerical model of FRC based on the Cosserat peridynamic model and analyzes the crack propagation of FRC. The material points in Cosserat peridynamic model have independent rotational degrees of freedom and have the internal length to represent the size of micro-structure, which is appropriate for describing the mechanical behavior of FRC. The full-discrete method is applied in fiber modeling, and the relation of pullout displacement and shear stress is applied to obtain the peridynamic force between the fibers and the concrete matrix. And a fabric tensor of fiber distribution is defined to represent the local reinforcement and its direction. The proposed model is validated by simulating the single fiber pullout test and the numerical results show consistent with the experimental data and existing numerical results. The tension test of the notched plate and the three-point bending beam test with randomly distributed fibers are simulated to analyze the influences from the micro-structure and the fibers on crack propagation. The results indicate that the influence from micro-structure on the load-displacement curve mainly exists at the post-peak stage and has little impact on the peak value and pre-peak stage. And the micro-structure mainly influences the local damage and has little impact on the main direction of the crack path.