Reseach On Elastoplastic Damage Model Of High Strength Lightweight Aggregate Concrete

In recent years,with the development of building structures in the direction of super high-rise and large span,higher requirements have been placed on the performance of building materials.As a green building material,high-strength lightweight aggregate concrete has been used more and more widely because of its advantages such as high strength,good heat preservation,good durability and so on.There are significant differences in the damage mechanism compared with ordinary concrete,so the existing numerical methods can not simulate its internal force variation and deformation characteristics well.It has great theoretical and practical values to in-depth study of the mechanical properties of lightweight aggregate concrete materials and establish a material model considering the characteristics of the material hardening,damage,etc.Based on the theory of plastic mechanics and continuum damage mechanics,the elasto-plastic damage constitutive model of lightweight aggregate concrete based on Drucker-Prager yield criterion is derived in this paper.By decoupling plastic strains and damage evolutions,the numerical framework are divided into three parts: elastic predictor,plastic corrector and damage corrector.The algorithm for updating the stress and the corresponding algorithm consistent tangent modulus are provided in this paper.And then the user material subroutine is compiled and verified.The main contents and conclusions are as follows:(1)The Drucker-Prage double plastic yield surface,which is simple and able to describe the yield characteristics of rock materials,is used to describe the yield surface of the lightweight aggregate concrete.The shear yield surface is hyperbolic function and the volume yield surface is elliptical.The two damage variables and the stiffness recovery factor are used to consider the asymmertry of tension and pressure and the unilateral effect.The elastoplastic Helmholtz free energy is determined according to the plastic mechanics of the effective stress space.Thus the release rate of the elastoplastic damage energy is introduced,and the damage criterion in accordance with the thermodynamic principle is established.(2)The plastic part and the damaged part are decoupled,and each component is split into three parts of elastic,plastic and damage.The stress renewal is carried out with the unconditionally stable backward Euler method and the uniform tangent stiffness algorithm is given.Then the FORTRAN programming language is used to compile a material subroutine.(3)The material subroutine is used to simulate the single axial compression cube test block,and the numerical simulation results are compared with the theoretical curve,whichshows the correctness of the subroutine made in this paper.According to the compression test of lightweight aggregate concrete prism with strength grade of LC50,and the finite element model which is consistent with the condition is established.By comparing the simulation and test results,it is proved that the development of the UMAT is correct and the calculation precision meets the requirements.