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A yield criterion for powdered metal compaction. (English) Zbl 0961.74015

The mechanism of densification during powder compaction involves bulk movement and plastic deformation of particles. Therefore, since the volume of the porous body does not remain constant in the process of compaction, the effect of hydrostatic pressure should be considered in the yield criterion. In the present paper the author proposes a yield criterion and the associated flow rule which can describe both the bulk movement and the consolidation of powder metal in a compaction process. The effect of volume change on the deformation during compaction is considered by including the first invariant of the stress tensor in the criterion formulation. Moreover, three material constants are introduced in the criterion. The yield locus is represented in the plane “normal stress-tangential stress” by an ellipse. The plastic flow determined by the left-hand part of the ellipse results in an increase in volume, while the right-hand part of the ellipse leads to a decrease in volume due to consolidation. The material constants can be determined by conducting shear and compression tests. A preliminary examination of the proposed yield criterion is made using the experimental results obtained from a three-dimensional compaction of electrolytic copper powder. Although this yield criterion agrees very good with test results, it should be noted that most of the experimental data are in the region of consolidation, i.e. correspond to the right-hand part of the yield locus. So, the experiments focused on the bulk movement of powder should be carried out to confirm the validity of the proposed criterion.

MSC:

74E20 Granularity
74C99 Plastic materials, materials of stress-rate and internal-variable type
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