Simulation Of Compressive And Bending Behavior For Concrete Based On The K & C Model And Multiresolution Theory

The most important factor for choosing a material in engineering applications is the macro-mechanical properties of the material,but materials which are widely used in a wide variety of engineering applications such as alloys and composite materials are heterogeneous.For these materials,it is obvious that the macroscopic material behaviors reside in the properties of inner microstructure and their interactions occurring at different length scales.The key point and difficulty of the research is how to faithfully model and describe the influence of the microstructure and their interactions to material behaviors.Concrete,a widely used building material,is a typical heterogeneous material.Regardless the heterogeneous property of concrete and the influence of initial imperfection in hardening process,the classical approaches think concrete is a homogenized continuum material that cause the limitation and insufficiency of understanding the mechanical behaviors of the concrete.While brute-force modeling of all the details of the microstructure using experimental method is too costly,many of the current micro mechanical models have its limitation.It is quite necessary to find a more efficient and accurate multi-scale method researching for real mechanical response of concrete so that it can provide a more clear understanding and powerful foundation for research of concrete in other fields.In this thesis,the finite element models of concrete under uniaxial compression and bending isare established first using the general explicit nonlinear dynamic finite element program LS-DYNA by determining the dimensions,loading conditions and boundary conditions of the two finite element models.Then,the compressive and flexural behavior of concrete is simulated by using the damage theory-based and K&C damage constitutive model.Compared with the test,it is shown that the K&C model can simulate the mechanical behavior of concrete preferablyreasonably well.It is appropriatefeasible to research and ssimulate the mechanical behavior of concrete based on the damage theory.Next,according to the multi-scale characteristics and heterogeneous of concrete,and starting from the perspective of the use of multi-scale method,this thesis uses the advantage of analyzing the multi-scale problem of heterogeneous materials to establish the model of concrete based on the multiresolution theory.The theory is a new method proposed for studying multi-scale properties of hierarchical materials.The basic idea is to decompose the overall deformation of the material to different scales and to superimpose the deformations at different scales.And then the total deformation of the material at the macroscopic level can be concurrently obtained.Heterogeneous material is divided into macroscopic scale and arbitrary number of microscopic scale in the multiresolution theory.Each point has three conventional degrees of freedom at the macro scale.As for microscopic scales,the microscopic physical quantities at the microscopic scale are associated with various kinematic variables and attached to conventional degrees of freedom at the macroscopic scale in the form of extra degrees of freedom.The governing equations can be established by the virtual power principle using the continuum mechanics.And then the multiresolution theory can be formed by combining the governing equations with the constitutive relation of materials.When the preprocessing of the finite element model is completed,FORTRAN program is written for the development of LS-DYNA to achieve the implementation of the solving process of finite element model.The results show that the multiresolution theory has high accuracy in simulating the compressive behavior of concrete.