An elasto-polycrystalline plastic finite element method is developed to simulate the deformation behavior and corresponding crystallographic textureevolution of sheet metals in stamping processes. A rate-independent crystalplasticity model and a degenerated shell element are introduced into the explicitfinite element formulation. A successive integration method by which the shear rates on the slip systems can be calculated without prior determination of active/non-active state of the slip systems, as generally done in rate-dependent models, is employed to calculate the plastic strain rate of a crystal during the de for mation.Represent ative crystal orientations are extracted from the orientation distribution function (ODF) data and assigned to the integration points of elements according to the distributional characteristic of crystal orientations. The macroscopic stress of a polycrystalline aggregate is evaluated by avolume-averaged response of the representative crystals. Two drawing processes are simulated, one with a cylindrical punch and the other with a square punch. Good agreements between the calculated results and experimental ones are obtained.

As an important sheet metal forming process, stretch flanging is widely applied in automobile industry. The formability of sheet metal during stretch flanging depends on appropriate process parameters. In this paper, an elastic-plastic large deformation FEM program is developed based on Mindlin shell element model. A quasi-flow corner theory of elastic-plastic finite deformation and a normally anisotropic yield criterion are introduced. Then the stretch flanging of a V-shaped sheet metal part is simulated and the effects of geometry and material on flanging are unveiled according to the calculated results. Meanwhile, a mathematical model for axisymmetric case (flanging tube) is developed based on the total strain theory and membrane assumption. Compared with material parameters, geometrical parameters exert greater effects on the formability and the flange angle is the most influential parameter affecting the free edge strain. The analytical model is easy to use, but it gives reasonable results only when the flange angle or initial flange length is small.

A rate independent crystal plasticity model is developed to analyze the plastic deformation of hexagonal close packed (HCP) materials by incorporating the crystallography of deformation twinning in plasticity model. The "successive integration method" is used to identify active slip/twinning systems and determine plastic strain. This model is implemented in the commercial finite element code ABAQUS/Explicit to simulate the deformation process of the magnesium alloy sheet. For the determination of model parameters, simulated stress-strain curves for uniaxial tension are adjusted to the measured curves. Then the stamping process of a cylindrical cup is simulated with the developed model, and the effect of initial crystal orientation on final cup earing is discussed.

Warm forming of magnesium alloy sheet has attracted more and more attention in recent years. The formability of magnesium alloy sheet at elevated temperature depends on appropriate processes, and the fabrication of high-performance sheet. In this research, an AZ31 magnesium alloy sheet with excellent performances is fabricated by the cross-rolling and the uniform annealing treatments. The uniaxial tensile tests are conducted using a Gleeble 3500 thermal-mechanical simulator, and the mechanical properties of AZ31 magnesium alloy sheet are analyzed. Finally, some limiting drawing ratio (LDR) experiments are performed. The experiments show that the LDR can reach 2.0 at the forming temperature of 150 1C and the drawing velocity of 15 mm/s. A warm deep drawing process is also simulated by the finite element method. The influences of drawing temperature and blank holder force on the formability are numerically investigated. The simulation demonstrated that variable blank holder force technology can improve the LDR from 3.0 to 3.5, and decrease the wall thinning ratio from 15.21% to 12.35%.

The superplastie forming potential of two fine-grained 5083 aluminum alloys were studied under biaxial tension using apneumatic bulge test. Experiments were performed at temperatures ranging from 475 to 525℃ with three different strain pathsranging from equi-biaxial to approaching plane strain. The shape of the forming limited diagram(FLD) is found to be significantlydifferent from FLDs commonly used in room temperature stamping. The effects of temperature on final thickness distribution, domeheight and cavitation were investigated for the case of equi-biaxial stretching. Increasing temperature in free bulge forming canimprove the thickness distribution of final parts but have no significant effect on dome height. The results indicate that determinationof forming limits in SPF cannot be represented with a simple FLD and additional metrics such as external thinning and internalcavitation needed to determine the SPF potential of a material.