A Meso-level Numerical Simulation Study On The Split-tension Fracture Of Fully-graded Wet Screened Concrete Wedge

In recent years,the research results show that,due to the in-depth study of the mechanical properties of concrete materials and the rapid development of science and technology,the problem of combining the experimental and numerical simulation of the mechanical properties of concrete has gradually attracted the attention of scholars,but the macro-level research has not taken into account the heterogeneity and locality of the material,in order to better reveal.The fracture mechanism of concrete materials and the study of meso-level have become a heated topic of discussion nowadays.However,there are some doubts and difficulties in the study of meso-level.For example,in order to produce numerical specimens which are in good agreement with the actual specimens so as to achieve reasonable numerical results,on the one hand,it is necessary to select and determine the failure criteria of meso-element and the degradation law of stiffness matrix,on the other hand,it is necessary to determine the selection of mechanical parameters of different phases.At the same time,the number of meso-element is also necessary.In order to improve the efficiency and accuracy of calculation,it is necessary to select appropriate calculation methods.In this paper,concrete is regarded as a three-phase heterogeneous composite material consisting of aggregate,mortar matrix and the interface between them at the mesoscopic level.Based on the existing program,the program for generating numerical specimens is improved and the numerical simulation of concrete deformation and damage fracture process is realized by combining damage mechanics and computational mechanics with finite element software.Specifically,the main work of this paper includes the following parts:(1)In order to generate a numerical model which is in good agreement with the experiment,a random aggregate parameter model is adopted.Based on the existing program,a program for generating wedge splitting model of wet-screened concrete is further proposed.The area ratio of aggregates with different gradations is calculated by Walraven formula,in order to prepare for the subsequent numerical model,and eventually the same height-to-height ratio is generated.The numerical specimens with different heights;(2)Through wedge splitting test and basic mechanical parameters test of five groups of wet-screened concrete specimens with different heights,the change rules of mechanical parameters and related fracture parameters at macro level can be obtained,which paves the way for subsequent numerical simulation.(3)To study the fracture and crack propagation of concrete at the meso-level,it is necessary to assign different mechanical properties to the meso-phases of the material.The macro-parameters obtained from the test can not directly reflect the properties of the meso-phase material.Therefore,in this paper,when studying the properties of the meso-phase material,the stress-strain relationship provided by the Code for the Design of Concrete Structures is used to deduce the suitable stress-strain relationship for calculation.By calculating the relationship between the mechanical parameters of each phase,the plastic damage model built in the finite element calculation software can be used for numerical simulation analysis,and the crack propagation nephograms of numerical specimens with different sizes can be obtained.By comparing the numerical results with the experimental results,it can be seen that the fracture parameters such as fracture toughness and fracture energy of wet-screened concrete have a certain size effect,and the numerical results are in good agreement with the experimental results,which shows that the program used to generate numerical specimens and the calculation of mechanical properties of materials in this paper are basically effective and feasible.