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Abstract
The compression abilities of polycrystalline aggregates exhibiting well defined mosaic or radial structures are studied, taking also into account strength and size distribution of the aggregates.
Six samples of alumina trihydrate, having different origins, crystallization history and mechanical strength, were selected, as this material grows under the form of nearly spherical aggregates and can be considered as a model substance.
The samples with radial structures are weaker materials with respect to the samples with mosaic structures as shown by attrition tests. They have also a poorer compression ability, i.e. a smaller cohesion index, as shown by compression tests. On the other hand, inside the same type of structure, there is no direct correlation between cohesion index and attrition index.
The experiments also show that the smaller the aggregates are, the highest the cohesion index is, the improvement being more significant in the case of the mosaic structures.
By comparing the size distributions of the aggregates before and after compression it appears that the diameter of the particles is really affected only when the compression exceeds a critical value. These measurements, together with SEM observations, allow to understand the effect of compression on the different aggregate structures. In the case of a mosaic structure, compression induces the occurrence of one new population of particles, whereas in the case of a radial structure, compression induces the formation of two new populations of particles.