Assignment of strain and stress values for the beginning of plastic yielding in materials by instrumented indentation method

Abstract

The method of an instrumented automatic indentation method with use of new methodology of processing and the analysis of results on a plenty of various materials analytically also experimentally establishes of strain ε_IT and stress σ_IT values which correspond to the beginning of plastic yielding of a material at simple circuits of a loading (tension, compression, bend). It is shown that value of stress σ_IT is close to proportional limit value σ_pl of a material, i. e. σ_IT » σ_pl. Connection of values ε_IT and σ_IT with hardness Н_IT of a material, its modulus of elasticity E and the contact module of elasticity Еr of pair a material — an indentor is established: ε_IT = 0,307(Н_IT/Еr) and σ_IT = 0,307Н_IT?(Е/Еr) (for Berkovich"s indentor). It is established that the value of the relation of hardness to a stress of material Н_IT/σ_IT is determined by value of the relation of elastic moduluses Еr and Е as Н_IT/σ_IT = 3,257(Еr/Е) and depending on a concrete material can change in limits Н_IT/σ_IT = 1,78—3,257. It is shown that an instrumented automatic indentation method at room temperature it is possible to define concrete values of the beginning of plastic strain and a corresponding stress for brittle materials and superfirm coverings that is inaccessible to other known test methods. Full text download