Triaxial characterisation of iron powder behaviour

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,

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A modified Drucker-Prager Cap model for die compaction simulation of pharmaceutical powders

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