Compression curve analysis and compressive strength measurement of brittle granule beds in lieu of individual granule measurements

Abstract

Powders in granulated form are used in various processes to facilitate convenient usage. The durability of the formed granules is a crucial parameter, typically evaluated by the compressive strength of the granules. However, especially for granules with a diameter in the order of tens of microns, statistically relevant testing of individual granules is not a feasible alternative, and in such cases uniaxial bed compression is required.There has not been consensus on whether uniaxial compression of a granule bed can be used to study the fracture of micron size or brittle granules. In our case study of a bed of sintered kaolinite granules with diameters under 100μm, we show how the compressive strength of individual granules can be obtained from the compressive measurement of the entire bed by plotting the relative density versus the logarithmic pressure scale.We compressed the kaolinite powder with different loads; microscopy confirmed that below the analyzed strength the granules are intact, though the granules start to fracture in the curved region on the compression curve. We found that angle-fitting can be used to locate the average compressive strength on the compression curve and to follow the evolution of strength with sintering temperature. The experiments in unison demonstrate that compression curve analysis is applicable for strength analysis of brittle granules.