Verificação da validade da regra de Neuber para um modelo elastoplástico, com relação tensão-deformação via equação de Ramberg-Osgood, mediante modelagem numérica

Abstract

Knowing the effects of geometric discontinuities is of great relevance in machine component designs since, generally, these geometric perturbations favor the nucleation of a fatigue crack in its vicinity. In this sense, the present study aims to verify the validity of Neuber’s rule for a elastoplastic constitutive model with stress-strains relationship via the Ramberg-Osgood equation. For this, the Finite Element Method was used, with the help of the ANSYS software. The Neuber’s rule is widespread as a procedure to incorporate the effect of loss of proportionality between stress and strain in the stress concentration analysis in fatigue, especially in the low cycle regime. Despite its daily application, such a rule is based on the premise of ideal elastoplasticity, which is a hypothesis quite distant from the real behavior of materials. Stress and strain fields were examined in plates containing elliptical notches with different sharpnesses, considering two-dimensional models with the plane stress state. It was sought to follow the plastic process zone evolution at the bottom of the notches by applying loads with sign reversal, until the closing of a cycle, with the consequent emergence of residual stresses. Specifically, the hypothesis of isotropic hardening was considered through a multilinear elastoplastic model. The model was adjusted to represent the Ramberg-Osgood equation, which is widely used to describe the stress-strain behavior of aluminum alloys, which are of special interest in the aeronautical industry. At the end of the analyzes, Neuber’s Rule was not validated for the certain parameters used.