Study on Compacting of Metal Powders (2nd Report)

(Investigation of compaction criterion by three dimensional compaction)

Abstract

Three dimensional compaction is carried out to determine a compaction criterion for metal powders. Compaction is attempted under various strain ratios or stress ratios. It is thereby confirmed that the compaction criterion is expressed by
F=√1/2{(σ1-σ2)²+(σ2-σ3)²+(σ3-σ1)²}+(σmlf)²,
where σ₁, σ₂ and σ₃ are three principal stresses, f and F are functions of density ratio. In case of copper powders tested
f=1/2√1-γ and F=46.7γ^2.5⋅
The compaction criterion appears to be a plastic potential which leads to a stress-strain relationship expressed by
dε_i=dλ{σ_i-(1-2/9f²)σ_m} (i=1, 2, 3).
The above equations are utilized to calculate a pressure versus density ratio in closed-die compaction, which shows a good agreement with the experimental results.