Numeralization Of Macroscopic & Microscopic Constitutive Relations And Their Applications In FE Simulation

Hybrid-hardening elastic-plastic constitutive relation and rate-dependent crystal plasticity, describing deformation behaviors of crystalline material from macroscopic and microscopic scales, respectively, disclose material deformation characteristics of anisotropic hardening, plasticity anisotropy and rate dependency. Therefore, these two styles of constitutive models play an irreplaceable role in the research and development of advanced plastic forming theories and technologies. However, the numerical applications of these two styles of models are difficult and their numerical calculation is inefficient. These problems restrict their applications in FE simulation. For this reason, macroscopic and microscopic constitutive theories are studied deeply in this dissertation. As a result, several simplified constitutive models are proposed, suitable treatments are performed to deal with the key problems in the numeralization of these models, and efficient algorithms are developed. Based on these works, user material subroutines for these constitutive models are developed in ABAQUS/Explicit environment. At last, cold ring rolling process is simulated on the basis of these subroutines. A brief introduction to the project and its main achievements and results are as follows.Introducing isotropic hardening coefficient into classical elastic-plastic constitutive frame, hybrid-hardening elastic-plastic constitutive model is established. A new stress compensation updating algorithm based on elasticity tensor is brought forward for constitutive solution, which promotes computational efficiency. Based on the model and algorithm, user material subroutine is developed, which is possible to realize simulations on Bauschinger effect in material deformation process successfully. So, it provides an effective means to investigate material anisotropic hardening in complex loading forming process.Based on the model proposed by Kalidindi, an implicit incremental model of ratedependent crystal plasticity is established in the intermediate configuration with the stress on Gauss point as the main unknowns. A two-level procedure is designed for the solution, which simplifies solution procedures and promotes computational efficiency. Further, in order to overcome the disadvantage of difficult convergence in two-level iterations, another implicit incremental model is established with shear strain increments of slip systems as the main unknowns. The homotopy auto-changing continuation method is employed for the solution of the two models. This algorithm enhances computational robustness. So, under the conditions of large strain, high strain rate and large time step, 3D simulations are performed successfully on the deformation process with complex loading and unloading on the basis of the implicit models.On the other hand, Taylor series expansion is utilized to linearize the nonlinear flow rule of slip systems. As a result, an explicit incremental model for rate-dependent crystal plasticity is proposed based on suitable simplification. The complete pivot Gaussian elimination method is adopted for the solution. This explicit model overcomes the difficulties of numerical calculations for rate-dependent crystal plasticity essentially, and improves computational efficiency greatly. This model makes it possible to carry out the calculations based on crystal plasticity on personal computer, which was possbile only on multi-CPU workstation or armada before.The corotational coordinate system for establishment of crystal plasticity model, simplifies the calculation of lattice orientation evolution. Based on this coordinate system, user material subroutines for rate-dependent crystal plasticity are developed on the basis of the above models. Simulation results of simple loading forming and cup drawing are verified by experiments, indicating that these rate-dependent crystal plasticity models and the implicit and explicit algorithms are reliable.Based on the developed subroutines for hybrid-hardening elastic-plastic model and rate-dependent crystal plasticity implicit model, 3D FE simulations on cold ring rolling process are performed on the platform of ABAQUS/Explicit, and influence rules of material macroscopic and microscopic parameters, plasticity anisotropy and rate dependency on this process are studied and defined.