Determining fracture toughness by indentation hardness testing

2 Determining fracture toughness by indentation hardness testing 

Rough assessment of the brittleness of ceramic components is facilitated by obtaining fracture toughness data. Application of the Vickers and Knoop methods of inden- 

By relating residual stress intensity, indentation load P, and crack length C, Lawn et al. (1980) have developed the following formula for calculating fracture toughness  

The indentation load P and crack length C are obtained directly from testing. To determine the residual stress factor x, it is necessary to adopt certain models of plastic deformation as caused by the indentation. % can be determined by calibrating the fracture toughness in experiments with long cracks. According to Antis et al. (1981) the residual stress factor is determined by the following equation  

The modulus of elasticity E and hardness H are related to the elastic and plastic characteristics of the given material. A % value of 4.8 MPav was calculated by means of Eq. (4) for the Si3N4 material shown in Figs. 147 and 148. Various formulas for calculating fracture toughness have been pubUshed by Dinner and Stevens (1984), Evans and Charles (1976), Langier (1985), Evans (1979), Smith and Alavi (1985), and Munz and Fett (1989). All of these formulas maintain the fundamental dependence on c-  

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