Three-Dimensional Meso-Mechanical Simulation And Analysis Of Concrete Failure

As a typical heterogeneous multiphase composite material,concrete can be seen on the mesoscopic level as composed of coarse aggregate,cement mortar and the interface transition zone between the two.It is of great theoretical and practical significance to study the failure mechanism of concrete by using the three-dimensional solid model.Using ellipsoid and convex polyhedron,a three-dimensional multiphase mesoscopic model of inconformable concrete in interfacial transition zone is established in this paper,and the failure path and failure mechanism of concrete specimens under uniaxial tensile condition are studied.On this basis,the influence of meso-structure characteristics on the macroscopic mechanical properties of concrete is discussed,and the whole process from damage evolution to fracture failure of a three-point bending concrete beam is simulated by using a threedimensional model.Python language and ABAQUS universal finite element software are used to realize the automatic establishment process of the model.The main research work of this paper includes:1.The algorithm of random generation of spherical and ellipsoid aggregates is given.By means of the quadratic matrix of ellipsoid,the precise phase separation method of ellipsoid aggregates is studied.Convex polyhedral aggregates are produced on the basis of spherical aggregates.The aggregates generated are uniform and dense,satisfying the characteristics of the random distribution of aggregates in space.2.The three-dimensional multiphase mesoscopic model of concrete is established,in which the inconsistency characteristics of interface transition zone is considered.The transition surfaces of inner and outer mesh are set to make the mesh of interface transition zone form smooth transition with the mesh of aggregate and mortar.By this means,the number of units is effectively reduced and the calculation efficiency is improved while the calculation accuracy is guaranteed.The validity of the model is verified in comparison with the experimental data.3.The failure process of concrete specimens under uniaxial tensile condition is studied.The advantages and significance of using the three-dimensional method to analyze concrete failure problems are discussed from the perspectives of fracture failure direction,damage evolution path,consistency of macro and micro analysis,and so on.The failure path and damage degree of the ellipsoid aggregate model and the convex polyhedron aggregate model are compared.It is concluded that the cracking point of the convex polyhedron aggregate is at its tip;under the same loading displacement,the damage degree of convex polyhedron aggregate model is less severe.4.The influence of meso-structure characteristics on the macroscopic mechanical properties of concrete under uniaxial tensile condition is investigated,and the results show that:the spatial distribution of aggregates has a great influence on the failure mode and cracking position of concrete;the higher the mortar strength,the smaller the thickness of the interfacial transition zone and the higher the strength of the interfacial transition zone,the higher the overall strength of the model;the mortar strength plays a dominant role in the concrete strength.5.The whole process of damage generation,crack initiation,crack propagation and failure of the three-point bending concrete beam specimen is simulated.The mesoscopic damage evolution path inside the specimen is contrasted with the macroscopic damage fracture path outside the specimen,which reflects the consistency of the results of mesoscopic and macroscopic analysis.The fracture surface of the three-dimensional model is an approximate plane surface formed by the fusion of the various profile fault zones,which is more consistent with the reality.In conclusion,the numerical simulation of concrete failure process based on threedimensional multiphase mesoscopic model in this paper is of preferably theoretical significance to the study of revealing the failure mechanism of concrete.