Characterization of die-pressed green compacts

Die-pressed agglomerated alumina compacts, prepared as cylinders using single-ended nominally uniaxial compressive stresses, have been characterized by measuring their strength and density distributions. The strength of the alumina compacts, measured using the Brazilian configuration, increases up to an optimum compaction pressure; upon further increasing the compaction pressure, the strength of the green compacts decreases due to the formation of internal cracks. The density distributions in the alumina compacts have also been determined experimentally, using the coloured layer technique and also deduced indirectly from hardness measurements. The results obtained from these two experiments are shown to be in good agreement. The densest parts of the compacts, compressed uniaxially from the top planar surface adjacent to the compression source, are at the outer circumference at the top and the least dense parts are at the outer circumference at the bottom face. The density near the cylindrical surface of the compacts decreases with height from the top to the bottom of the compact. The density difference between the most dense and the least dense parts of the compacts increases with increasing aspect ratio; that is, the height-to-diameter ratio. The density distributions in the alumina compacts have also been estimated using a first-order predictive model. According to this model, the mean density variation along the height of the compact decreases linearly with height from the top to the bottom of the compact. These predictions are shown to be almost in accord with experiment.