Executive Summary
The ball indentation method has been applied to a range of sizes of silanised glass beads, pea protein, maize starch, titania and alumina. The penetration depth range which provides a stable hardness measurement is determined for each material, which is identical for most materials. Ball indentation and shear cell measurements at moderate stresses allow the constraint factor to be determined. The value of constraint factor varies for different materials, but remains independent of consolidation stress in the range tested for all materials except pea protein, where a larger error is observed in the ball indentation measurements, and alumina. For silanised glass beads the constraint factor increases slightly as particle size is reduced. Comparison of the materials tested in this work and those by (Zafar, 2013) indicates that constraint factor varies between 1.7 – 4.8, and for most materials the value is below 3. All tested materials except titania, alumina and durcal 15 exhibit a notable deviation in flow behaviour at low stresses, with a rapid reduction in the yield stress inferred by ball indentation.
Future work will experimentally investigate the influences of size distribution, surface energy, density and shape on the constraint factor, with DEM also used to investigate the shape effect. DEM will investigate the variation of constraint factor in the low stress range that cannot be reached experimentally. Finally the reliable penetration depth range at higher strain rates will be determined using the freefall ball indentation method.