Microstructure Effect on Hard Rock Damage and Fracture During Indentation Process

This paper presents the results of simple and double indentation tests conducted on three hard rocks: granite, limestone and sandstone. The main objective is to analyze the rock behavior under indentation test in relation with the physical and microstructural properties. First, the experimental set-up used during the tests is described as well as the sample preparation. Then, an image analysis based technique is applied on thick sections made from the tested samples in order to evaluate the size of indentation-induced cracked zone and to assess the crack types (vertical or sub-horizontal) below the indenter. The interpretation of the results was made on two levels. First, several physical parameters (energies and displacements) have been derived from the so obtained experimental indentation curves. Very high correlations were found between the loading, indentation and specific energies versus the plastic displacement. Second, cracked zone radius was estimated showing a very high correlation to the specific energy and governed by the physical and mineralogical properties of the tested rocks. Finally, the analysis of double indentation tests proved that changing the distance between two adjacent inserts allows the determination of the optimal spacing producing overlay of cracked zones and causing rock damage and large chip departure.