| The focus of this research was the development of a computer model to simulate metal flow in axisymmetric and plane strain powder metallurgy processes and applicable to the manufacture of both powder metallurgy (P/M) and P/M-based isotropic metal matrix composite (MMC) parts.; Plastic flow of porous metals involves volume and density changes. Several authors have proposed yield criteria to account for these differences. The yield criterion of Shima and Oyane is the starting point for the current study. Based on this yield criterion, the required finite element equations were derived in an Eulerian reference frame, using a mixed formulation where the primary variables solved for are velocity and hydrostatic pressure. The equations are obtained by applying the rate of virtual work principle to a quasi-static variational formulation. The resultant non-linear equations are solved using the standard Newton-Raphson procedure. Density is calculated through the continuity equation. The equations were incorporated into the Eulerian finite element code, CFORM. The automatic and manual remeshing procedures associated with CFORM were modified to allow for interpolation of densities from the old mesh to the new mesh.; Several P/M processes were simulated during this research, including cylinder and ring compression and the closed-die forging of a flanged-hub shape. The simulation results are verified by comparisons with published numerical and experimental results. The results indicate that as relative density approaches unity, the velocity-pressure formulation is computationally more stable than the penalty constant approach proposed by other authors. The results also establish that the interpolation of densities from the old mesh to the new mesh (during remeshing) is satisfactory.; For isotropic MMCs (particulate- or randomly oriented whisker-reinforced), the current CFORM program may be used without further modification, by using appropriate material property data. For whisker reinforced MMCs, the fibers orient preferentially as the material flows. An approximate method of predicting fiber orientations based on the calculated velocity field is suggested. This will assist in studies of fiber alignment and in assessing the validity of the isotropy assumption. Simulations of the forming of metal matrix composites are presented but not verified. |
