Abstract
The mechanical properties of powder beds were examined, with special attention paid to the movement of individual particles. The powder used was lactose, which was formed into a cylindrical green body, using compacting die. Direct and repeated compression tests were carried out using a triaxial compression apparatus.
Some interesting results have been obtained as follows.
(1) A concave type stress-strain curve to strain axis was obtained.
(2) The virgin curve having remarkably different style from non-virgin relations was observed in the repetitious compression tests.
(3) The deformation process could be divided into five typical stages depending on the movement of particles.
The results (1) and (2) mentioned above seem to have been caused by the difference of stress distribution between the compaction state in the compacting die and the compression state in the triaxial cell, which causes sliding by the breaking of bridge-like weak structures in powder bed.
These phenomena can not be explained fully by the common rheological model having spring, dashpot or slider elements. In order to describe these phenomena, a new mechanical model is presented by the authors based on the behavior of particles during these deformation process, which has new irrecoverable element as follows.
ε=ε0(1-e-ασ)
where α is experimental constant and σ, ε are stress and strain respectively.
