Numerical Study On Fracture Damage Of Steel Fiber Reinforced Concrete Based On Extended Finite Element Method

Fracture property is one of the important mechanical properties of steel fiber reinforced concrete?SFRC?.The research on the fracture characteristics of SFRC is of great significance for the study of SFRC materials and structures.This paper studied the fracture and failure problem of C30 SFRC through a mesoscopic numerical model established from the view point of microscopic mechanism,and discussed the influence of the coarse aggregate maximum size,steel fiber length and volume fraction on the fracture energy and the crack evolution process of SFRC.The main content is as follows:1.Through the Micro-scanning electron microscopy experiments,the effects of the coarse aggregate maximum size and the steel fiber length on the thickness of the aggregate-mortar interface and the steel fiber-mortar interface transition zone in steel fiber reinforced concrete have been studied.The results show that the thickness of the transition zone of aggregate-mortar interface increases with the increase of the coarse aggregate maximum size,and the thickness of the transition zone of steel fiber-mortar interface decreases with the increase of the steel fiber length.According to the microscopic experimental results,the thicknesses of the interface of the meso component in the mesoscopic numerical model of steel fiber reinforced concrete were selected to be 0.2 mm.2.In this paper,steel fiber reinforced concrete was regarded as a five-phase composite material composed of coarse aggregate,steel fiber,aggregate-mortar interface,steel fiber-mortar interface and mortar at the mesoscopic level.Through MATLAB software,the Monte Carlo method was used to generate random numbers.Combining the point-line distance calculation and the line-line intersection judgment method,the random distribution of steel fiber and coarse aggregate was realized,and a two-dimensional numerical model of steel fiber reinforced concrete was established.3.Numerical simulations of fracture and failure of steel fiber reinforced concrete have been studied.The crack evolution process of ordinary concrete and steel fiber reinforced concrete is analyzed.The simulation results under the typical working condition of load-deflection curve and load-crack opening displacement curve of the coarse aggregate maximum size and steel fiber length were compared with macroscopic test results.The results show that the numerical calculation results are in good agreement with the macroscopic test results,and the reliability of the model is verified.4.The effects of different coarse aggregate maximum sizes,different steel fiber lengths and different steel fiber volume fractions on the fracture energy and the crack evolution process of steel fiber reinforced concrete have been simulated.The results show that the fracture energy of steel fiber reinforced concrete increases first and then decreases with the increase of the coarse aggregate maximum size,the length of steel fiber and the volume fraction of steel fiber.The crack evolution process of steel fiber reinforced concrete is affected by the coarse aggregate maximum size,the length of steel fiber and the volume fraction of steel fiber.5.The effect of steel fiber length and coarse aggregate maximum size ratio l_f/D_max on the fracture energy gain ratio of steel fiber reinforced concrete was studied.The results show that in the calculation range of this paper,for concrete with D_max=10mm and 20mm,the steel fiber has better effect on the fracture energy of concrete at l_f/D_max=2.5⁴,for concrete with D_max=30mm and 40mm,steel fiber has better effect on the fracture energy of concrete at l_f/D_max=1.5².33.6.In the research scope of this paper,when the maximum aggregate diameter of coarse aggregate is 40mm,the length of steel fiber is 60mm,and the volume fraction of steel fiber is 1.5%,steel fiber has better effect on concrete reinforcement,and steel fiber concrete has the largest fracture energy.