Nguyen Ngoc Tam

Development of Dynamic Explicit Crystallographic Homogenization Finite Element Analysis Code to Assess Sheet Metal Formability

The crystallographic texture evolution induced by plastic deformation in the sheet metal forming process has a great influence on its formability. In the present study, a dynamic explicit finite element (FE) analysis code is newly developed by introducing a crystallographic homogenization method to estimate the polycrystalline sheet metal formability, such as the extreme thinning and “earing.” This code can predict the plastic deformation induced texture evolution at the micro scale and the plastic anisotropy at the macro scale, simultaneously. This multi‐scale analysis can couple the microscopic crystal plasticity inhomogeneous deformation with the macroscopic continuum deformation. In this homogenization process, the stress at the macro scale is defined by the volume average of those of the corresponding microscopic crystal aggregations in satisfying the equation of motion and compatibility condition in the micro scale “unit cell,” where the periodicity of deformation is satisfied. This homogenization a...

Development of Multi‐Scale Finite Element Analysis Codes for High Formability Sheet Metal Generation

In this study, the dynamic‐ and static‐explicit multi‐scale finite element (F.E.) codes are developed by employing the homogenization method, the crystalplasticity constitutive equation and SEM‐EBSD measurement based polycrystal model. These can predict the crystal morphological change and the hardening evolution at the micro level, and the macroscopic plastic anisotropy evolution. These codes are applied to analyze the asymmetrical rolling process, which is introduced to control the crystal texture of the sheet metal for generating a high formability sheet metal. These codes can predict the yield surface and the sheet formability by analyzing the strain path dependent yield, the simple sheet forming process, such as the limit dome height test and the cylindrical deep drawing problems. It shows that the shear dominant rolling process, such as the asymmetric rolling, generates “high formability” textures and eventually the high formability sheet. The texture evolution and the high formability of the newly ...

Parallel Computing of Multi‐scale Finite Element Sheet Forming Analyses Based on Crystallographic Homogenization Method

Since the multi-scale finite element analysis (FEA) requires large computation time, development of the parallel computing technique for the multi-scale analysis is inevitable. A parallel elastic/crystalline viscoplastic FEA code based on a crystallographic homogenization method has been developed using PC cluster. The homogenization scheme is introduced to compute macro-continuum plastic deformations and material properties by considering a poly- crystal texture. Since the dynamic explicit method is applied to this method, the analysis using micro crystal structures computes the homogenized stresses in parallel based on domain partitioning of macro-continuum without solving simultaneous linear equations. The micro-structure is defined by the Scanning Electron Microscope (SEM) and the Electron Back Scan Diffraction (EBSD) measurement based crystal orientations. In order to improve parallel performance of elastoplasticity analysis, which dynamically and partially increases computational costs during the analysis, a dynamic workload balancing technique is introduced to the parallel analysis. The technique, which is an automatic task distribution method, is realized by adaptation of subdomain size for macro-continuum to maintain the computational load balancing among cluster nodes. The analysis code is applied to estimate the polycrystalline sheet metal formability.

Asymmetric Rolling Process Simulations by Dynamic Explicit Crystallographic Homogenized Finite Element Method

Recently, the asymmetric rolling (ASR) has been applied to the material processing of aluminum alloy sheet to control micro‐crystal structure and texture in order to improve the mechanical properties. Previously, several studies aimed at high formability sheet generation have been carried out experimentally, but finite element simulations to predict the deformation induced texture evolution of the asymmetrically rolled sheet metals have not been investigated rigorously. In this study, crystallographic homogenized finite element (FE) codes are developed and applied to analyze the asymmetrical rolling processes. The textures of sheet metals were measured by electron back scattering diffraction (EBSD), and compared with FE simulations. The results from the dynamic explicit type Crystallographic homogenization FEM code shows that this type of simulation is a comprehensive tool to predict the plastic induced texture evolution.

SEM‐EBSD based Realistic Modeling and Crystallographic Homogenization FE Analyses of LDH Formability Tests

Homogenization algorithm is introduced to the elastic/crystalline viscoplastic finite element (FE) procedure to develop multi‐scale analysis code to predict the formability of sheet metal in macro scale, and simultaneously the crystal texture and hardening evolutions in micro scale. The isotropic and kinematical hardening lows are employed in the crystalline plasticity constitutive equation. For the multi‐scale structure, two scales are considered. One is a microscopic polycrystal structure and the other a macroscopic elastic plastic continuum. We measure crystal morphologies by using the scanning electron microscope (SEM) with electron back scattered diffraction (EBSD), and define a three dimensional representative volume element (RVE) of micro ploycrystal structure, which satisfy the periodicity condition of crystal orientation distribution. Since nonlinear multi‐scale FE analysis requires large computation time, development of parallel computing technique is needed. To realize the parallel analysis on ...

Multi‐scale Sheet Metal Forming Analyses by using Dynamic Explicit Homogenized Finite Element Method

Recently, the homogenization method has been proposed to predict the macroscopic material properties and characteristics of deformation by considering periodicity of poly crystal microstructure (Terada et al., 1996; Miehe, 1999,2002).We have developed the dynamic explicit finite element (FE) analysis code by using a crystallographic homogenization method. This multi‐scale analysis can couple the microscopic crystal plasticity inhomogeneous deformation with the macroscopic continuum deformation. In this homogenization process, the stress at the macro scale is defined by the volume average of those of the corresponding microscopic crystal aggregations in satisfying the equation of motion and compatibility condition in the micro scale “unit‐cell,” where the periodicity of deformation is satisfied. And this FEM has shown more reasonable prediction of plastic deformation for simulating the polycrystalline materials (Nakamachi et al. 2004).In this study, we try to determine the unit‐cell of AL6022‐T43 by using ...