Failure mechanism determination for industrial granules using a repeated compression test

This work describes the development of a particle compression test that allows direct and repeated application of the stress. The test is designed to quickly reduce the load on a granule during its incipient failure. By so doing, the breakage can be arrested and thus the process can be studied in detail. Experimental tests have been made on samples of industrial enzyme granules, which have a complex layered structure, and reproducible results have been obtained. The contribution of the various layers to the strength of the granule has been investigated, showing that the use of coating materials results in improved granule strength. The microstructure of the granule determines the failure mode of the granule. It is concluded that the failure mechanisms can be defined from tests on only a few granules as can assessment of the relative contribution of the layers and of the granule core to its strength. A measurement of the distribution of strength requires a larger, statistically representative, sample.