In order to produce crack free metal powder compacts, the critical region of failure should be detected, so that the particular region can be strengthened during the compaction process. The finite element method, through the use of an appropriate constitutive model of the powder medium, has recently been used as an efficient design tool. The accuracy of this method highly depends on the faithfulness of the constitutive model and the quality of the material parameter set. Furthermore, in order for the simulation results to be reliable, they should be experimentally validated on real parts featuring density variations. Hence, the main concerns are the development of a standard calibration procedure for the cap material model as well as the development of a reliable technique for the experimental validation of the powder compaction simulation results. A FC-0208 automotive main bearing cap was compacted to investigate the microstructure changes at different locations within the parts. Measurements of the pore volume fraction, pore size, pore nearest neighbor, pore aspect ratio, and grain size were performed after compaction and sintering for the MBC. A finite element model for the compaction and monotonic performance of the bearing cap was developed to study the density distribution and the performance of the bearing cap during monotonic loading respectively. The image analysis methodology and monotonic load testing was created to measure density in the main bearing cap and to predict the critical location of failure respectively, and to validate the finite element model results. A comparison between the experiment and model for determining the performance of the bearing cap was carried out such that the model predicts the damage state during loading of the bearing cap.

The powder forming process is an extremely effective method of manufacturing structural metal components with high-dimensional accuracy on a mass production basis. The process is applicable to nearly all industry sectors. It offers competitive engineering solutions in terms of technical performance and manufacturing costs. For these reasons, powder metallurgy is developing faster than other metal forming technology. Computational Plasticity in Powder Forming Proceses takes a specific look at the application of computer-aided engineering in modern powder forming technologies, with particular attention given to the Finite Element Method (FEM). FEM analysis provides detailed information on conditions within the processed material, which is often more complete than can be obtained even from elaborate physical experiments, and the numerical simulation makes it possible to examine a range of designs, or operating conditions economically.* Describes the mechanical behavior of powder materials using classical and modern constitutive theories.* Devoted to the application of adaptive FEM strategy in the analysis of powder forming processes.* 2D and 3D numerical modeling of powder forming processes are presented, using advanced plasticity models.

In metal powder compaction, density non-uniformity due to friction can be a source of flaws. Currently in industry, uniform density distribution is achieved by the optimization of punch motions through trial and error. This method is both costly and time consuming. Over the last decade, the finite element (FE) method has received significant attention as an alternative to the trial and error method; however, there is still lack of an accurate and robust material model for the simulation of metal powder compaction. In this study, Cam-clay and Drucker-Prager cap (DPC) material models were implemented into the commercial FE software ABAQUS/Explicit using the user-subroutine VUMAT. The Cam-clay model was shown to be appropriate for simple geometries. The DPC model is a pressure-dependent, non-smooth, multi-yield surface material model with a high curvature in the cap yield surface. This high curvature tends to result in instability issues; a sub-increment technique was implemented to address this instability problem. The DPC model also shows instability problems at the intersection of the yield surfaces; this problem was solved using the corner region in DPC material models for soils. The computational efficiency of the DPC material model was improved using a novel technique to solve the constitutive equations. In a case study it was shown that the numerical technique leads to a 30% decrease in computational cost, while degrading the accuracy of the analysis by only 0.4%. The forward Euler method was shown to be accurate in the integration of the constitutive equations using an error control scheme. Experimental tests were conducted where cylindrical-shaped parts were compacted from Distaloy AE iron based powder to a final density of 7.0 g/cm3. To measure local density, metallography and image processing was used. The FE results were compared to experimental results and it was shown that the FE analysis predicted local relative density within 2% of the actual experimental density.

The development of finite element model for the simulation of a complete warm forming process of powder sintered component is presented here. The material constitutive laws were derived based on a continuum mechanics approach. The process of green compact generation was represented by a large displacement based finite element formulation. Three constitutive relations, i.e., Mohr-Coulomb, Elliptical Cap, and combination of these two yield models were used to describe the deformation behaviour of the powder mass during compaction. However, an Elliptical Cap model was shown to be the most appropriate. A plasticity theory of friction was employed in the treatment of the powder-tooling interface. The Roscoe-Burland criterion was used to describe the densification and dimensional change of the compact during the sintering. The staggered-incremental-iterative solution strategy was established to solve the non-linearity in the systems of equations. The numerical simulation results were validated through experimentation where a good agreement was observed.