Research And Application Of Microplane Constitutive Model M7 Based On Nonlocal Theory For Plain Concrete

As a heterogeneous composite material,the complicated and various mechanical properties of concrete,such as inhomogeneity,nonlinearity,strain localization and fracture behavior,are very difficult to be simulated precisely by macroscopic constitutive model.When concrete material is damaged,the deformation is often manifested tend to focus on relatively narrow band,which called a typical strain localization phenomenon in domain of structural nonlinear response.The numerical method for strain localization,an important feature of material damage,has been an important research subject for the simulation and prediction of the phenomenon.While it tends to appear the problem of spurious mesh sensitivity and zero energy dissipation when simulating that phenomenon by traditional continuum damage mechanics.In order to overcome the above problems,based on the general finite element program ABAQUS,which has a strong ability of nonlinear analysis,and its secondary development interface,the microplane model M7 subroutine for calculation stress field of has been developed and combined with nonlocal theory in order to more factually simulate the softening stage of concrete constitutive model and the nonlinear mechanical response of concrete structure under the condition of various stress states.In this paper,the main research works are as follows:(1)With the user subroutine interface VUMAT provided by ABAQUS main program,a subroutine of microplane model M7 for plain concrete based on the latest research of professor Ba?ant has been developed and applied to simulate complex mechanical behaviors of concrete materials.Concrete specimens under uniaxial compression and tension,triaxial compression are simulated with the proposed program.And the reasonableness of the secondary development of the subroutine is validated by comparing the numerical predictions of proposed program with the test results.(2)The results show that the M7 model can simulate the stress-strain full curves of concrete excellently,and be exceptionally well suited for the multiaxial behavior,which laid the foundations for simulating the concrete structure response objectively and factually.(3)This paper combines the microplane model with the recently improved nonlocal approach to study the strain softening and mesh sensitivity induced by strain localization of the concrete rectangular plate and the three point bending beam.And the objective rationality of the microplane model is compared with the nonlocal microplane model for nonlinear analysis of structures.(4)The results show that it is difficult to achieve accurate simulation of concrete structure strain localization only with microplane model,and numerical calculation result appears mesh sensitivity,significantly affected by the differences of mesh.While the nonlocal microplane model considering distance interaction can effectively avoid the problem of finite element mesh sensitivity induced by strain localization,realize the corresponding localization simulation,and ensure the rationality of numerical simulation results.