A multi-particle finite element model (MPFEM) was used to explore the densification yield surfaces of a collection of monosize particles in 2-D. Individual particles discretized with a finite element mesh allow for a full description of the contact mechanics and the local and global particle kinematics. Compaction modes ranging from hydrostatic to that of high shear are studied for various levels of interparticle friction. Isodensity curves in stress-space during densification are shown to take the equivalent shape of a cap and cone model whose shear failure line has a slope that is a function of interparticle friction. The mechanical response predicted by this model is softer than the one predicted by the discrete element method (DEM) model of Redanz and Fleck (2001. Acta Mater. 49 (2001) 4325) suggesting that the stiffer response of DEM is the result of simplifications on interparticle contact behavior. Deviation from affine motion, rearrangement, and particle rotation are shown to be significant and to depend on interparticle friction and macroscopic stress triaxiality. Local deviatoric stresses and equivalent plastic strains are present during the formation of stress chains at low relative densities indicating that contact deformation can occur early in densification. The combined effect of particle movements with early contact indentation leads to a softer global response to externally applied strains than other analytical or computation models. This work illustrates that the MPFEM model is useful in describing and understanding the interparticle behavior and its effect on microscopic and macroscopic response for various strain histories.

Simulation of multi-axial compaction of granular media from loose to high relative densities

A complete database and constitutive laws are the key to successful computer simulations of powder compaction processes. However, the appropriate determination of material parameters that are used ...

Triaxial characterisation of iron powder behaviour

Research has been conducted into the effects of particle size on the core losses of soft magnetic materials. Various types of micro PM BLDC motors, produced with solid hog-out alloy steel, laminated alloy steel and Metal Injection Molding (MIM) alloy steel powders have been studied. The results show that the core loss of micro PM BLDC motors made by the MIM technique is in the acceptable level when compared with the laminated core motor.

Investigation of core loss in PM micro-motor made using MIM technology

A modified finite element method is proposed using a previously formulated version of porous body plasticity theory, which is intended for modelling compaction of powder materials. A number of compaction schemes are considered for articles with changes with respect to height. The effect of external friction and compaction scheme on the occurrence of compaction is analyzed. A compaction scheme whose use provides preparation of powder articles with uniform density distribution is studied separately. Theoretical results obtained are quite close to experimental data.

Numerical Modelling of the Compaction of Powder Articles of Complex Shape in Rigid Dies: Effect of Compaction Scheme on Density Distribution. Part 2. Modelling Procedure and Analysis of Forming Schemes

Finite Element Analysis of Friction-Assisted Powder Compaction Process

Data recorded during the compression of a part in five kinematic conditions are presented. Parts were made on a press instrumented to measure the forces acting on the tools and their displacements. After ejection, local densities were measured, and observation of the outer surfaces revealed defects. Results are analyzed in relation to the kinematics and forces acting during compression and during removal of the tools. A data base is established which, when combined with the characteristics of the powder, allows for a comparison with actual cases for numerical simulation.

G. Puente

Papers

Axisymmetric part compaction : Data base for numerical simulation