Study On The Meso-damage Evolution Law Of Steel Fiber Orientation Coefficient On Cement-based Composites

Steel fiber reinforced concrete is a new type of material mixed with steel fiber and cement mortar.It is one of the most widely used building materials at present.It can improve the ductility and toughness of concrete and improve the crack resistance of concrete.However,the steel fibers in ordinary steel fiber reinforced concrete are usually randomly distributed due to the pouring and delivery process,which greatly weakens the enhancement effect of steel fibers and reduces the utilization rate of steel fibers.At present,the research on the orientation and distribution of steel fibers is not uncommon,but most of them remain in physical experiments or theoretical analysis,and there are few damage simulation studies at the meso-scale.Based on this,the uniaxial tensile test of steel fiber reinforced concrete is simulated by numerical calculation software.From the perspective of micromechanics,the influence of fiber orientation and distribution on the macroscopic mechanical properties and damage cracking of concrete is analyzed,in order to provide reference for the application and promotion of directional steel fiber reinforced concrete in engineering.The main research contents and results are as follows:(1)By studying the application and working process of Monte Carlo method in steel fiber reinforced concrete,a random aggregate model is established.The heterogeneity of concrete meso-materials was studied,and the random mechanical characteristic model was established by Weibull distribution function and uniform distribution function.In addition,based on the theory of damage mechanics,the common damage constitutive model of concrete in modern models is studied,and the double broken line damage constitutive model of damaged materials is established by secondary development of APDL parametric language in ANSYS finite element software.(2)The numerical calculation model of steel fiber-cement mortar specimens with different steel fiber orientation coefficients was established,and the numerical simulation of uniaxial tensile test was carried out.The influence of the average orientation coefficient of steel fiber on the mechanical properties and damage characteristics of concrete was studied.The results show that the program compiled in this paper is feasible to describe the damage cracking behavior of concrete under uniaxial tensile load.The average orientation coefficient of steel fiber plays a positive role in improving the tensile mechanical properties of concrete,and the enhancement of fiber orientation effect also significantly improves the toughness of concrete.The average direction coefficient of 0.8 is the turning point of the fiber direction effect.In addition,from the microscopic point of view,the enhancement of the orientation effect of steel fiber can effectively inhibit the generation and propagation of cracks and improve the ability of fiber bridging cracks.(3)The effects of different material homogeneity on the tensile mechanical properties and meso-damage cracking of steel fiber-cement mortar specimens were studied.The research shows that the mechanical properties of concrete are closely related to the homogeneity of materials.The increase of material homogeneity can significantly improve the mechanical behavior of steel fiber-cement mortar specimens before peak stress,that is,it has a significant effect on the elastic modulus of the specimens,improves the peak stress and peak strain of the specimens,and has a superimposed enhancement effect with the average direction effect coefficient of steel fiber.However,the change of homogeneity will make its influence on peak stress more saturated,which is negatively correlated with the increase of peak stress.Moreover,the increase of the average direction coefficient of steel fiber will reduce the influence of homogeneity on the peak stress of steel fiber-cement mortar specimens.At the same time,the increase of homogeneity has a certain negative effect on the toughness of steel fiber-cement mortar specimens,but this effect will decrease with the increase of the average direction effect coefficient.In addition,through the study of the meso-element damage law of steel fiber-cement mortar specimens,it is found that the mechanical properties of concrete can be evaluated according to the damage change law of interface elements.(4)The calculation model of steel fiber reinforced concrete with several different geometric aggregates was established.Through the simulation of uniaxial tensile test,the influence factors of average direction coefficient of steel fiber,material homogeneity and aggregate shape on the mechanical behavior and meso damage of concrete were studied.The results show that the change of average directional effect coefficient does not change the mechanical behavior of steel fiber reinforced concrete specimens before peak stress,but increases the peak stress of concrete and improves the softening section after peak stress.In addition,the increase of material homogeneity can weaken the interference of the randomness of the mechanical parameters of the meso-element in the program,and the relationship between the change of homogeneity and the mechanical strength of concrete is similar to that of steel fiber-cement mortar specimens.In addition,the shape of aggregate does not play a decisive role in the mechanical strength of steel fiber reinforced concrete.From the microscopic point of view,the damage of steel fiber reinforced concrete model specimens is mainly concentrated on the aggregate interface layer,which is the main contributor to macroscopic cracks.The increase of average direction coefficient can improve the effect of steel fiber bridging cracks,and the increase of homogeneity has a certain negative impact on the toughness of concrete.In addition,the smoothness of aggregate edge is closely related to the mechanical properties of concrete.