| The addition of a fiber-reinforced phase in concrete can effectively improve its shortcomings,such as easy cracking and brittleness,and expand its application range.At present,the research on fiber-reinforced concrete(FRC)mainly focuses on macro-tests and mainly focuses on single-doped fiber concrete.Macro-test method is simple and feasible,but the influence and failure mechanisms of components in FRC can not be satisfactorily explained.The numerical simulation method offers a fresh approach to studying the mechanical properties of FRC since it can analyze these properties at the microscopic level.Therefore,this paper combines numerical simulation with a laboratory test to analyze the relationship between crack propagation process and macro-failure mode in fiber composite material,and to analyze the damage and failure mechanism of single-doped and hybrid fiber reinforced concrete from micro-level.The bonding mechanism between steel fiber and concrete is revealed through uniaxial pull-out simulation test.The main research work and achievements are as follows:Firstly,in this research,FRC is regarded as a two-phase composite consisting of fiberreinforced phase and concrete matrix at the micro level,and a random distributed FRC numerical model is established by using CDP constitutive relation and ideal elastic-plastic property of fiber.The influence of fiber type and content on the compressive properties of FRC with single fiber addition is analyzed by combining the laboratory test results.The effect of the diameter and distribution angle of steel fibers on the mechanical properties of the matrix under pressure is analyzed extensively,which lays a foundation for the subsequent research of various kinds of steel-reinforced concrete.The numerical simulation and experimental comparison results show that the numerical model can effectively reveal the FRC from the beginning of internal initial damage to the complete destruction of the material.Low modulus PVA and basalt fibers have little effect on the compressive strength of concrete,but their brittleness is improved.High-modulus steel fiber has a significant effect on the reinforcement and toughening of concrete matrix,and the Micro-Mechanical Properties of steel fiber concrete are particularly sensitive to the characteristics of fiber.Secondly,by establishing the micro-finite element model of Hybrid Fiber Reinforced Concrete(HFRC),the mechanical properties and damage-fracture process of HFRC with steel-PVA fibers,steel-basalt fibers and steel-steel fibers of different proportions under monotonous,cyclic and three-point bending loads are simulated.The damage-cracking behavior of composite material and the mechanism of reinforcement,toughening and crack resistance of hybrid fibers to the concrete are further revealed.The results show that the proper mixing ratio of hybrid fibers can produce a positive mixing effect.Different types of fibers complement each other and play their respective roles before and after cracking,reaching the effect of 1+1>2.Finally,the interfacial bonding behavior between steel fiber and concrete is studied.The interfacial transition zone is characterized by cohesion constitutive relation,and the single-axle pull-out numerical model of steel fibers is established to further study and analyze the relationship between pull-out inclination,embedment depth and fiber shape and pull-out force-displacement curve.It is found that the bonding performance between steel fiber and matrix is the best when the distribution angle of steel fiber is between 15 degrees and 40 degrees.Insufficient embedded depth or small size of steel fibers will result in poor tensile properties.The reinforcing mechanism of special-shaped steel fiber on concrete is complex,which significantly increases the maximum pull-out force and energy consumption during pull-out process,thus improving the interfacial bonding performance. |
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