Research On Dynamic Meso-mechanical Properties Of Concrete Based On Voronoi Random Aggregate Model

Concrete is a complex silicate material.As a typical non-homogeneous material,the macroscopic mechanical properties of concrete are related to the mesostructure of concrete.The numerical study of the meso-mechanical properties of concrete can reveal the phenomena that cannot be observed in many physical experiments and explain its failure mechanism.Concrete structures are usually subjected to the quasi-static loads that change very slowly,but in some special cases,the concrete structures are also subjected to the dynamic loads such as earthquakes,impacts,and explosions that affect the concrete structures.In these cases,the dynamic performance of the concrete plays an important role in the destruction of the concrete.Under dynamic loading,the strength and deformation of concrete are significantly different from the strength and deformation of concrete under static loading.Therefore,it is necessary to study the meso-mechanical properties of concrete structures under dynamic loading.With the development of computer technology,more and more researchers began to study the mechanical properties of concrete from the meso level.In this paper,concrete of two-dimensional and three-dimensional Voronoi random aggregate models are established,and the finite element simulation of dynamic uniaxial compression and splitting tensile of concrete specimens is performed from the meso level.The specific research contents and conclusions are as follows:(1)The shape of the Voronoi pattern is similar to that of the concrete aggregate and all have an irregular shape.Therefore,the Voronoi pattern is used to represent the aggregate in the concrete specimen.The APDL program was compiled by MATLAB,the initial model of concrete was generated by ANSYS,meshing and the finite element calculation was performed by LS-DYNA.The dynamic uniaxial compression test and dynamic splitting tensile test of concrete were numerically analyzed.(2)In the dynamic compression test,concrete specimens with the same aggregate volume fraction and different aggregate distribution were analyzed.It was found that although the fracture patterns were different in different specimens,the difference of dynamic compressive strength between different specimens was very small;The analysis of concrete specimens of which aggregate volume fraction was different shows that with the increase of the volume fraction of aggregates in the concrete specimens,the dynamic compressive strength of the specimens is greatly increased;the fracture patterns and the mechanical properties of specimens at the strain rates of 1,0.1,0.01,and 0.001 were analyzed.The results show that when the strain rate of the specimen is 0.001,a small amount of cracks are generated inside the specimen.With the increase of strain rate,the number of internal cracks in the specimen increases significantly and is dispersed throughout the concrete specimen.With the increase of the strain rate of the specimen,the compressive strength of the specimen gradually increases,showing a obvious rate effect.(3)In the dynamic splitting test,the crack forms of plain concrete and single aggregate concrete are analyzed.The numerical simulation results show that the cracks of the plain concrete are generated along the y axis.In the single aggregate model,the aggregates won’t break,so the cracks will bypass the aggregate and continue to pass to the lower part of the specimen.The size and shape of the aggregate have influence on the concrete crack pattern;the fracture patterns and the mechanical properties of specimens at the strain rates of 1,0.1,0.01,and 0.001 were analyzed,the calculation results show that when the specimen strain rate is low,the splitting tensile fracture of the concrete is in the direction perpendicular to the direction of the load,the micro-cracks are mainly along the interface between the aggregate and the mortar and finally form a penetrating crack parallel to the direction of the load.When the specimen strain rate is high,the micro-cracks not only extend down the y-axis,but also produce some bifurcations on both sides of the y-axis.At the same time,as the strain rate of the specimen increases,the tensile strength of the specimen also gradually increases,showing a obvious rate effect.