Determination of the Crack Initiation and Propagation Energies during Instrumented Indentation of Brittle Materials and Hardening Coatings

The well-known methods of determining the critical stress intensity factor K_Ic of the surface layers of materials by indentation of a pyramid for the formation of radial cracks propagating from the vertices of an indent are considered. It is noted that the existing methods for estimating the fracture toughness of a material by indentation do not allow one to determine the crack initiation energy. A technique is proposed to determine the specific crack initiation energy and the specific crack propagation energy using the critical points of a pyramid indentation diagram during instrumented indentation. Energy fracture toughness criterion G_Ic is found to be related to specific crack propagation energy ω_p, which is determined using an indentation diagram, for brittle materials and hardening coatings. This finding makes it possible to develop a technique for rapid estimation of critical stress intensity factor K_Ic using an indentation diagram recorded during instrumented indentation without measuring the geometric parameters of formed cracks and regardless of their type.