Present study is the first of its kind to measure the lateral stresses in a rigid die during both quasi-static and dynamic powder compaction and to relate these stresses to the specific powder particle characteristics (size, shape, specific surface area and particle size distribution) and their bulk properties. Standard techniques were employed to measure powder particle characteristics. The bulk properties of the powders were measured using the well established soil mechanics techniques.
For the first time in situ measurement of the shock velocity in the powder during dynamic compaction was possible using state-of-the art technology and also the powders were tested up to 5 MPa normal stress in an annular shear cell.
From the present study it has been shown that the free flow of powders co-relates with their shape (roundness) whereas the specific surface area of the powder particles was found to dominate the shear behaviour of powders.
The powder behaved according to the Mohr-Coloumb failure criterion both in quasi-static and dynamic compaction; die stress is a function of axial stress, coefficient of interparticle friction and cohesion. In quasi-static compaction fine powders, when compared with coarse powders, exhibited high initial coefficient of interparticle friction and the same fine powders, due to higher specific surface area of the particle, gained higher cohesion with a decrease in coefficient of interparticle friction which was found responsible for the exertion of higher die stress. The gain in cohesion was mutually supported by the change in compaction mechanism during quasi-static powder loading; from axial to iso-static compression due to the flow stresses that govern the powder stiffness. In dynamic compaction the high strain rate effect yielded higher coefficient of interparticle friction for all powders and the net die stress was lower than the quasi-static compaction for the corresponding axial stress. The Kawakita equation was valid for quasi-static compaction whereas the same equation was found sensitive to particle size effect in the dynamic compaction.