An Estimation of Ramberg-Osgood Constants for Materials with and without Luder’s Strain Using Yield and Ultimate Strengths

Abstract

Tensile stress-strain curves for metallic materials typically show two different behaviors viz. with Luder’s strain and without Luder’s strain. Recently, Kamaya [1] proposed a method to estimate the true stress -true strain curve using a certain plastic strain together with yield and ultimate strengths. Kamaya’s method however, is not accurate enough for materials exhibiting Luder’s strain in their engineering stress-strain behavior. Hence, the aim of this paper is to propose a generalization of the Kamaya’s method for the materials with and without Luder’s strains. This new generalized approach uses plastic strain value corresponding to the Luder’s strain along with engineering yield strength and ultimate tensile strength to estimate the strain hardening exponent in the Ramberg-Osgood type of true stress - true strain relationship. The new approach was applied to 16 different materials with and without Luder’s strain to validate the proposed estimation procedure. In addition, an inverse method for assessing an apparent ultimate tensile stress (stress at “an apparent” point of zero slope in an engineering stress-strain curve) for materials with low ductility due to quenching or carburizing is also suggested.