Study On Macro And Micro Multiscale Mechanical Properties Of Concrete

Two methods of the second development of Abaqus are implemented.The assembler of Fortran language and the Assembler of Python language are implemented at the solver level.The UMAT subroutine based on Fortran language was used for secondary development.The material subroutines of the macroscopic level such as the fully elastic model,the large deformation elastoplastic model and the linear motion hardening model were compiled.Three sets of different sizes of concrete cubes were tested.The mechanical properties are analyzed and the numerical results are in accordance with the corresponding theoretical derivation.It is proved that the three macroscopic constitutive models for secondary development of UMAT subroutine can accurately simulate the macroscopic mechanical properties of concrete members.On the macroscopic level,a point can be regarded as a series of three-phase unit cells that are periodically and repeatedly arranged on the microscopic level.Therefore,the appropriate unit cell is selected,and periodic boundary conditions are established.According to the calculation results of stress and strain at a macro point,the stress and strain values of each cell at the micro scale are derived.According to the homogenization theory,the stress and strain of each daughter cell are averaged,and the stress and strain values of the damaged cell are obtained.The two-dimensional representative volume element is established by Abaqus software,and the program of periodic boundary condition is programmed by Python language.Then the finite element calculation is carried out.During the calculation,the cell always satisfies the displacement and stress Boundary Conditions.Therefore,the second development of the Python Program for Abaqus can quickly add cell periodic boundary conditions to complete the meso-cell mechanical properties.The Composite Periodic Cell plug-in provided by Abaqus software was used to generate three-dimensional meso-cell.By applying boundary conditions in the embedded program,the strain calculated at a point on the macro-level is transformed into a displacement load and applied to the cell model.Under the same load,the smaller the construction size is,the easier it is to be destroyed,but the deformation of the coarse aggregate is smaller because of the larger elastic modulus of the coarse aggregate.The mechanical properties of each cell after homogenization treatment were analyzed,and it was found that the strain value of the cell was in good agreement with the applied strain curve It also shows that the method adopted in this paper can take into account the mechanical properties of different constituent materials in concrete members,and can be used to analyze the failure at the macroscopic level.