A work approach to determine Vickers indentation fracture toughness

Autores: Yihui Feng|Taihua Zhang|Rong Yang
Fuente: J. Am. Ceram. Soc.
94 (2), 332-335
2011

The Vickers indentation fracture toughness test, or VIF, is addressed by considering its origins and the numerous equations that have been applied along with the technique to estimate the fracture resistance, or the KIc of ceramics. Initiation and propagation of cracks during the VIF test are described and contrasted with the pre-cracking and crack growth for internationally standardized fracture toughness tests. It is concluded that the VIF test technique is fundamentally different than standard fracture toughness tests. The VIF test has a complex three-dimensional crack system with substantial deformation residual stresses and damage around the cracks. The VIF test relates to an ill-defined crack arrest condition as opposed to the rapid crack propagation of the standardized fracture toughness tests.
According to the comparison of Vickers microindentation tests and Vickers macroindentation tests on several brittle materials, it is found that the ratio of hardness (H) to elastic modulus (E) is sensitive to well-developed radial cracks, but the ratio of unloading work (Wu) to total loading work (Wt) is not. Based on this finding together with the approximate linear relationship between the ratio of H to reduced modulus (Er) and Wu/Wt, a new approach taking Wu/Wt instead of H/E as the input parameter to determine Vickers indentation fracture toughness is proposed. For this proposed approach, all input parameters can be obtained in one single instrumented indentation test for fracture toughness, thus the test procedure can be simplified significantly. The formula of the newly proposed approach is calibrated by the macroindentation tests on several brittle materials. The validity of the new approach is investigated by comparing its estimation with the old one–s.