The Numerical Simulation Study On The Damage And Fracture Of Steel Fiber Reinforced Concrete Based On Mesoscopic Scale

In order to research the damage and failure of steel fiber reinforced concrete,a mesoscopic numerical model used to simulate the damage and failure process of steel fiber reinforced concrete was established from the view point of microscopic mechanism in this paper.The failure process was analyzed from the macro and micro perspectives,which obtained the relationship between mechanical properties of steel fiber reinforced concrete and various influencing factors,and then revealed the meso damage and failure rules.Firstly,two dimensional geometric model of steel fiber reinforced concrete was built using MATLAB mathematical software based on the mix proportion theory of concrete and actual mix ratio of steel fiber concrete.In the course of modeling,the vector algorithm was introduced to judge of the intersection between steel fibers as well as the intersection between steel fibers and aggregates.It greatly reduced the computational workload and improved the quality and speed of modeling.The vector intersection judgment method was also applied in combination with the scan sorting algorithm which increased the amount and the speed of the generation of aggregates and steel fibers.Besides,relying on the GUI platform in MATLAB,a two-dimensional modeling software for steel fiber concrete was developed and could simply and rapidly generate the steel fiber concrete plane model by its own operation window.Finally,based on the geometrical model which the aggregate and the steel fiber meet the random distribution as well as the stochastic mechanical parameter model,the mesoscopic numerical model of steel fiber reinforced concrete with mechanical parameter satisfying Weibull distribution was established.Secondly,the steel fiber pull-out test was carried out and obtained load displacement curves of steel fibers with different lengths and shapes.On this basis,the pull-out process of steel fiber was numerically simulated by elasto-brittle damage constitutive model.In the simulation,the interface failure threshold was introduced.When the damage amount exceeds this value,the steel fiber into the sliding stage,and the elastic modulus of interface element was re-assigned at this stage.In accordance with the load curve of slip section of steel fiber in pull-out test,the rigid slip of steel fiber was simulated by elastic deformation of interface element,and the frictional force was simulated by elastic force.The simulation result is satisfying.Based on that,Numerical simulation of pull-out test of single steel fiber with different length was carried out,which obtained the law of interfacial stress transmission of steel fiber.Compared with the load displacement curve of steel fiber obtained from pull-out test and numerical simulation,the numerical results are in good agreement with the experimental results in terms of the peak load,the sliding load,or the load change law,which verified the accuracy of the numerical model proposed in this paper.Thirdly,based on the numerical model of steel fiber reinforced cement mortar,a numerical simulation of uniaxial tension and uniaxial compression was conducted according to the elasto-brittle damage constitutive model.The effects of end friction restraint,steel fiber geometry and steel fiber amount were investigated in the simulation.More importantly,the relationship between macro-mechanical response of steel fiber reinforced mortar specimens and damage of meso-scopic elements under typical loads was established by three aspects of macro-mechanical properties,meso-crack evolution and meso-element damage.It revealed the internal force variation of steel fiber in the damage and failure process as well as obtained the relationship between enhancement,toughening and crack resistance of steel fiber and its size,angle and amount.Finally,in the foundation of two dimensional numerical model of steel fiber reinforced concrete with random distribution of aggregate and steel fiber as well as elasto-brittle damage constitutive theory,the steel fiber reinforced concrete specimens under typical uniaxial tensile,uniaxial compression loading damage failure process was simulated by random mechanical parameters model.The simulation was used to analyse in uniaxial compression process of steel fiber reinforced concrete specimens with different matrix strength,different aggregate shapes and voids respectively.The results show that under the condition of constant geometric parameters,with the increase of the matrix strength,the compressive strength of steel fiber reinforced concrete increases,the brittleness of the samples becomes more obvious,and the damage quantity of aggregate is great;For CF80 high strength steel fiber reinforced concrete,the shape of aggregate has less influence on the mechanical properties of specimens;The damage and failure process of steel fiber reinforced concrete specimens containing pore defects is more complicated.The crack development is more random,not in the simple rules,which is more corresponding to the actual characteristics of steel fiber reinforced concrete.Through the above studies,the meso-scopic numerical model proposed in this paper could effectively simulate steel fiber reinforced concrete damage process.It realized the research of crack initiation,evolution,development in the point of view of meso-mechanics and provided a new research method for damage problems of steel fiber reinforced concrete.