a b s t r a c tCold compaction of metal powders is now commonly studied at a microscopic scale, to further our understanding of contact mechanics between grains. The Discrete Element Method (DEM) is therefore, a good compromise between calculation time and precision. DEM simulations are in general limited to a relative density of about 0.8, because the existing contact laws do not reproduce all the physical phenomena involved in the densification of granular media. Local contact mechanics can be studied by finite element analyses on meshed distinct elements (MDEM, Meshed Distinct Element Method). However, this method is too time-consuming when in the presence of a large number of grains. In the following work, a new analytical contact law will be formulated with MDEM which will subsequently be used to validate the DEM model. Thus, it will be possible with DEM modeling to reproduce high-density compaction of random packings up to a relative density of about 0.95. By introducing a local relative density parameter in the force-displacement relationship, the incompressibility effects which rule high-density behaviors can be introduced in the modeling of powder compaction.

No abstract

stress that needs to be applied. The equipment that is closest to the industrial process is based on a cylindrical A complete database and constitutive laws are the key die but it is also the least homogeneous. Powder friction at to successful computer simulations of powder comthe die walls causes variation over the specimen height and paction processes. However, the appropriate detertherefore, stress and density are not homogeneous inside mination of material parameters that are used in the compact. To obtain the intrinsic characteristics of the mathematical models is difficult, and interpretation powder this mechanical behaviour must be taken into of scarce and often incomplete experimental data account, which leads to the well known slice method.1 depends on the modellers. It is therefore essential Gethin et al.2 showed that all the results obtained from die to have information on powder behaviour to define compaction are greatly dependent on the quantity of accuracy and identify the limits of the model predicpowder used. Mosbah et al.3 have proposed an analysis of tions. To make up for this lack of detailed informthe die pressing test in order to obtain relevant mechanical ation, this paper presents raw experimental data for a characteristics. Using lubricated and dry conditions for the typical iron powder and provides information on the die wall, it is shown that intrinsic parameters of the powder elastic-plastic behaviour. Useful analytical expresscan be determined from such equipment. ions of mechanical characteristics, used in most Few results concerning shear and tensile tests on powder constitutive laws, are then formulated. An equaare available in the literature4 since these stresses are tion for the hydrostatic compressibility is derived as always hard to induce and the results are not straightforwell as an equation on the critical state curve, which ward to analyse. Generally, only the shear stress and shear shows that under high pressure the plastic behaviour stress failure can be measured, the stress tensor itself of the compact is the same as that of the plastic behavremains unknown. Triaxial equipment is one of the ways iour of the constituent particle material. The elasticity available to characterise powder and is capable of inducing of compacts is also investigated showing non-linear both shear and compressive stress in the compact. This behaviour which depends on the density and not on method allows testing with different loading paths to the mean pressure.PM/0766 establish a more complete characterisation of the powder. Two types of experimental equipment exist. The first The authors are at the Laboratoire Sols, Solides, is a three dimensional apparatus, as used by Shima and Structures,

No abstract

No abstract

No abstract

In the powder shaping process, friction is often considered as one of the main limiting factors since it can be the cause of bad green density distributions as well as ejection defects. Therefore, knowledge of this is important for better controlling the compaction stage. This paper makes an attempt to bring out the different process parameters (density, normal stress, sliding velocity, temperature, and displacement) which influence the friction between a standard iron powder and a tool in tungsten carbide. With this view, a sliding piece device has been built and is described. Several tests have been performed; from the results emerge a decrease of the friction coefficient with increasing density or normal stress, conversely the velocity increases the friction while temperature has PM75554.10.1 no significant role. In this work, particular attention 1 Sliding piece device: 1=optical transducer, 2= is given to the amplitude of the displacement showing transducer, 3=disc, 4=parallelipipedic slab, 5=force that it can highly affect friction and wear of green transducer, 6=hydraulic press, 7=cylindrical die, 8= parts. An attempt is made at explaining the observed press phenomena and results are correlated with an analytical expression. PM/0952 the process parameters on friction. Using an iron powder, authors4,9 have observed that the friction coefficient Dr Doremus and Dr Toussaint are at Institut decreased when increasing normal stress while Mallender National Polytechnique de Grenoble, Laboratoire et al. are the only authors who have measured an increase Sols Solides Structures, Domaine Universitaire, of this coefficient with density. The second type of BP 53, 38041 Grenoble cedex 9, France and Dr Pavier equipment allows one to study the role of the different is with Ferroxdure, Aimants permanents, 41, rue parameters independently, such as the density of the Pierre Brossollette,

No abstract