Mesoscale Fracture Analysis Of Concrete Based On Cohesive Zone Model

Cracks are one of the main diseases of cement concrete.To explore the fracture mechanism of concrete,scholars have established various numerical models based on nonlinear fracture mechanics and continuous damage mechanics to simulate the crack propagation and material stiffness degradation of concrete which is treated as a homogeneous material.However,from the perspective of meso-composition,concrete is considered to be a composite multiphase material composed of cement mortar,aggregate,aggregate-mortar interface,and pores.It exhibits anisotropy,and its fracture performance is related to the composition of internal phases,Intensity,and spatial distribution.To analyze the effect of the internal microstructure of concrete on the fracture behavior of concrete,this paper wrote a two-dimensional aggregate automatic generation program and a batch insertion program for cohesive elements,established a micro-fracture concrete model based on the cohesive zone model.The meso-fracture finite element numerical analyses of small double notches beams and single notch beams were carried out,and the effects of mesostructure and notch on concrete fracture were analyzed.The main research results are as follows:(1)Using python language to write a two-dimensional aggregate automatic generation program to realize the automatic generation of concrete aggregate models with circular,elliptical,and convex polygonal aggregate shapes.At the same time,a batch insertion program of cohesive elements was written to realize the insertion of zero-thickness cohesive elements with traction-separation criteria between solid element grids to simulate potential micro-crack areas and realize the establishment of a meso-fracture concrete model based on the cohesive zone model.(2)The finite element numerical analyses of the mesoscopic modeling of the three-point loading double notches beams were carried out.The whole process of the three-point loading beam fracture was simulated.The effects of meso-structural features such as the porosity,the proportion of aggregate,and the aggregate-mortar interface strength,on the cracking and bearing capacity of beams,were analyzed.The results show that the numerical simulation results of the beam load,the crack shape,and the crack propagation path are consistent with the experimental results,verifying the applicability of the model;as the porosity increases from 0 to 6%,the ultimate bearing capacity of the beam decreases by 24.5%,the initiation breaking load of the beam decreases by 35.9%,and the length of the fracture process area increases by 44.2%.Cracks expand along paths with more pores;as the proportion of aggregate increases from 20% to 50%,the ultimate bearing capacity of the beam increases by17.4%,and the initiation breaking load of the beam increases by 35.3%,the length of the fracture process area increases by 41.5%,and the fracture energy consumed by cracking increases;as the aggregate-mortar interface strength increases from 1.24 MPa to 3.1 MPa,the ultimate bearing capacity of the beam increases by 30.3%,the initiation breaking load of the beam increases by 44.9%,ultimate bearing capacity and the initiation breaking load of the beam linearly increases with the increase in the strength of the aggregate-mortar interface.(3)The finite element numerical analyses of the mesoscopic modeling of the three-point loading single notch beams were carried out,and effects of the position of the notch on the bearing capacity of the beam and the fracture mode of the beam were analyzed.The results show that the distance between the notch and the middle span increasing 0 to 90 mm,the ultimate bearing capacity of the beam increases by 91.5%,and the initiation breaking load of the beam increases by 85.3%,the fracture mode of the single notch concrete beam changes from mode Ⅰ fracture dominance to Ⅰ-Ⅱ mixed-mode fracture dominance,and finally to mode Ⅰ fracture dominance.