Investigation On The Damage Behavior Of Cencrete Based On 3D Meso-scale Modeling

Concrete has been widely used in civil engineering,industry,military protection.And it plays an important role especially in major engineering construction.As a combination of natural and artificial materials,concrete has more complex mechanical properties than other single materials due to the different physical and mechanical properties and random spatial distribution of each phase material.In recent years,the research on the micromechanical behavior of concrete has become the focus of researchers.In this paper,the damage mechanical behavior of concrete and its components was studied comprehensively and systematically by using a 3D meso-scale concrete model.The presented research provided the foundation for further understanding the failure mechanism of concrete-like heterogeneous materials and establishing the muliti-scale relationship.The main research works were summarized as follows:A simple and highly efficient method was proposed for constructing realistic mesostructures of concrete based on 3D Voronoi tessellation.The random scaling factor was introduced to generate the random convex polyhedron aggregate by shrinkage;oppositely,the Interfacial transitional zone(ITZ)layer was generated by expanding procedure.In the process,aggregate size and particle number can be counted,as a result,the aggregate quantity and gradation interval were precisely controlled.The geometric defects such as short edges and sharp corners were removed to optimize the geometric shape.The falling process was conducted to simulate the practical vibration process to perfect the spatial distribution of aggregates and increase the aggregate volume content.The corresponding finite element model had good computational robustness and could be solved by nonlinear implicit algorithm.The mechanical behaviour and damage evolution of concrete under static uniaxial,biaxial and triaxial loads were systematically studied by using the plastic-damage material constitutive model.The study revealed the mechanism of damage formation and development from the viewpoint of mesoscopic.The typical failure modes and strength variation rule of concrete were obtained under complex stress conditions.The model had been fully verified in terms of stressstrain response and failure modes.The analysis showed that the damage started from the ITZ after the peak stress and extended to mortar phase,then the damage was connected to each other to form penetrating cracks which leads to the failure of the sample.The failure modes were related to the form of load.Under uniaxial tensile stress(biaxial compression-tension,triaxial compressioncompression-tension),damage developed along the load direction.Cracks were parallel to the compressive stress or perpendicular to the tensile stress direction.Under bidirectional tensile stress(biaxial tension-tension,triaxial compressiontension-tension),oblique cracks were generated.The specimen tended to be tensile shear failure.Under triaxial compressive stress,the development of damage was interlaced.The crack distribution was intersectional grid.Based on the classic Ottosen failure criterion,the gradient descent method which is one of the most common methods in big data dealing was introduced to determine the function parameters by using the simulated multi-axis strength data.On the one hand,the correctness of the simulation is validated again.On the other hand,compared with the classical parameters determined by uniaxial and biaxial results,the fitting accuracy of the failure criterion was improved,which makes it more feasible to the triaxial results.On the premise of ensuring uniform aggregate grading,particle size and distribution,3D meso-scale models with different aggregate volume fractions were established.The increasing aggregate content reduced the overall strength of concrete because of the increase of weakness ITZ content,but it prevented the development of damage,increased the loading area and improved the antisplitting capacity.The relationship between ITZ strength,aggregate volume fraction and concrete strength was established.The mesoscopic model of random material properties was presented.Reserving the multi-phase structure of concrete,the influence of material property distribution of mortar phase was discussed.Besides,the the correlation between material properties and damage distribution was explored.The nonlinear viscoelastic Zhu-Wang-Tang(ZWT)constitutive equation was extended to concrete materials,and the thermal activation damage evolution model was introduced.Based on the 3D meso-scale model,the dynamic simulation of concrete carried under SHPB loading was conducted.The determination method of equation parameters was presented by using the numerical results,and then the rate-dependent constitutive equation with damage modified was given.The research extended the applicability of ZWT equation and provided a foundation for further research on the dynamic constitutive relationship of concrete with high strain rate.