Abstract：Concrete is a widely used artificial composite material. Its damage and fracture properties determine the reliability and safety of many engineering structures. The macroscopic damage and cracking of concrete structures are closely related to their heterogeneous microstructures. When a bottom-notched concrete beam undergoes a three-point bending failure, as the notch position shifts from the center to the edge, the crack initiation location transits from the top of the notch to the bottom center of the beam. In this paper, the intermediately homogenized peridynamic (IH-PD) model and fully homogenized peridynamic (FH-PD) model are used to study the three-point bending fracture of concrete beams. The IH-PD model randomly generates different bond combinations based on the volume fraction of aggregates in concrete and introduces microscale heterogeneities into the model without describing the shape and distribution of aggregates in detail. The IH-PD model applies the simplest material constitutive relationship of a prototype microelastic brittle to mimic the micro-scale brittle nature of concrete. By comparing the relationship between the fracture mode and the notch position obtained by the IH-PD model, the FH-PD model, and from the experimental observation, it is found that only the IH-PD model considering the heterogeneities of concrete, can reproduce the experimental results, indicating that the behavior of the three-point bending fracture mode of notched concrete beams changing with the notch position is mainly related to the microstructures. Note that in the IH-PD model, the horizon size depends on aggregates' size, which benefits from studying the influence of aggregates' size on the fracture mode. The simulation results show that aggregates' size is a factor leading to the size effect of concrete structures' mechanical behavior. In addition, the randomly distributed pores are introduced into the IH-PD model by setting pre-damage, and the influence of concrete porosity on the fracture modes of concrete beams is discussed. The results show that the porosity influents the critical notch position of the fracture mode transition state and has a certain influence on the crack path direction and the roughness of the crack surface.
2022, Vol. 43 
