Modelling pressure-assisted densification by power-law creep

Densification of ceramic powders by power-law creep during pressure-assisted compaction is analysed. The proposed densification model is based on two existing power-law creep densification models: one for a relative density up to 0.9 (stage I) and the other for densities above 0.9 (stage II). Using these two models independently in their respective density ranges for predicting hot pressing of homogeneous alumina powder results in a discontinuity in the densification rate time history curves as well as in the radial and hoop stress time histories in the compact. To eliminate these discontinuities a novel method of combining the two models into a single unified model is presented. Blending of the models is based on the assumption that porosity changes gradually from being completely open at the beginning of compaction to completely closed at full density. Experimental data generated by hot pressing homogeneous alumina cylindrical compacts at two different temperatures of 1400 and 1450 degrees C at different pressures were used to obtain the material creep constants that were employed in the unified model.