Effects of microstructure on the compressive yield stress

The effects of microstructure on the compressive properties of aggregated alumina suspensions are determined by intentionally introducing heterogeneities into the suspension. Suspensions are prepared at a high volume fraction and diluted with low hear hand mixing to a series of initial concentrations. As the initial concentration is increased, larger heterogeneities are introduced, and the suspension becomes more compressible relative to the compressive yield stress of the uniform suspension. A simple model is proposed in which the heterogeneous suspensions compress by rearrangement of the dense aggregates until a critical concentration (phi(c), which coincides with the volume fraction prior to dilution) is reached. Above phi(c), the suspensions consolidate identically to the uniform suspension. With a single fitting parameter (the size of the heterogeneities), the model shows semiquantitative agreement with the experimental data.