Using finite element analysis method for determining equivalent stress-strain relation of spherical pressure head indentation

Fracture toughness is a key parameter of brittle films, while stress-strain relation is important to metallic films. Especially, when test piece size is very small, such as micro structure, thin brittle films material, or some material that is difficult to process. The traditional method of uniaxial tension or compression test is difficult or unable to measure stress-strain relation, other feasible methods for measuring this type material should be sought. In this study, the definition of different representative strain is compared using real contact area and the method to estimate equivalent stress-strain (ESS) relation of metallic materials is improved, and validated by finite element analysis using different common metals. A method for experimentally estimating ESS curves from one indentation test is presented and extended to determine ESS relation of thin brittle films using nano indentation.