Shear and normal stresses in uniaxial compaction.

Abstract

Three- different groups of materials were chosen to investigate the uniaxial compaction of particulate solids. Dentritic and cubic sodium chloride were chosen as plastically deforming, dicalcium phosphcte and sugar as fragmentary and styrocell, homopolymer and copolyrinier as non-compactable materials. The uniaxial compaction of the materials was continuously followed by measurement. of 1-.h e applied force, the force transmitted radially to the die wall and the upper punch displacement. The data obtained was presented in the form of Mohr circles, stress pathways (shear-mean compaction stress planes) and a three dimensional representation in mean compaction stress, shear stress and volume change. The yield loci evaluated from Mohr circles and shear-mean compaction stress relationships of compactable and non-compactable materials were found to be similar in shape. The unloading stress profiles were however more informative. All unloading shear-mean compaction stres's curves of the compactable materials cross the mean compaction stress axis to give negative values of shear stress and reach a minimum value of T min' which was material and compaction p.,- essure dependent. The unloading curves of non-compactable materials gaye approximately zero shear. The parameters evaluated from the characteristic stress profiles were correlated to the tensile strength and hardness of compacts. Mathematical expressions have been proposed for the shear-mean compaction stress relationships of the materials investigated. TI he materials were characterised before and after compaction in terms of specific surface aroa, porosity and mechanical strength of compacts with ccrnpaction pressure.