Identification of fracture sequences during sharp indentation of polycrystalline Al2O3

Abstract

The effects of loading and unloading rate on fracture features formed during sharp indentation of polycrystalline Al2O3 have been studied. It was found that there is a transition between intergranular and transgranular fracture if the loading rate is increased by a factor of 104 during the whole indentation cycle. By varying the loading or unloading rate during indentation, and correlating the corresponding dependence of fracture features, the part of the indentation cycle can be identified in which specific segments of cracks are generated. Hence, the fracture sequence during indentation is established. The fracture sequence for polycrystalline Al2O3 is compared with those reported from direct observation in optically transparent materials such as soda-lime glass and various single crystal ceramics.