MICROSCALE FRACTURE MEASUREMENTS WITH APPLICATION TO COMMINUTION

Indentation fracture is widely used in the ceramics and hard-metals in dustries for the measurement of material fracture toughness, Particula r advantages unique to this technique are the relative ease of perform ing tests, the small quantity of material required, the low cost and r eady availability of equipment, and the simplicity of sample preparati on. We have applied this technique successfully to the measurement of fracture toughness of geological materials and measurements have been made on a number of samples, These measurements have been correlated w ith experimental results from particle breakage tests under impact con ditions. The very small volume of material involved in the indentation test makes the technique useful as a microstructural probe, It can be used to measure the relative fracture resistance of different portion s of a mineral composite, This is done by measuring the total extent o f the surface expression of cracking produced by a micro-indenter usin g image analysis procedures, Measurements in a number of mineralogical materials showed that the amount of fracturing in the vicinity of a g rain boundary is more extensive than in the bulk of the grain, and tha t in some materials, fracture along the grain boundary dominates over propagation into the adjacent grain. These effects could have signific ant implications for mineral liberation.