Issue 38

M. A. Meggiolaro et alii, Frattura ed Integrità Strutturale, 38 (2016) 128-134; DOI: 10.3221/IGF-ESIS.38.17 128 Focussed on Multiaxial Fatigue and Fracture A unified rule to estimate multiaxial elastoplastic notch stresses and strains under in-phase proportional loadings Marco Antonio Meggiolaro, Jaime Tupiassú Pinho de Castro, Luiz Fernando Martha Pontifical Catholic University of Rio de Janeiro, PUC-Rio, R. Marquês de São Vicente 225, Rio de Janeiro, 22451-900, Brazil meggi@puc-rio.br, jtcastro@puc-rio.br, lfm@tecgraf.puc-rio.br Luiz Fernando Nazaré Marques Federal University of South and Southeast of Pará, UNIFESSPA, Av. dos Ipês S/N, Marabá, 68500-000, Brazil lfernando@unifesspa.edu.br A BSTRACT . Several methods can be used to estimate elastoplastic (EP) notch- tip stresses and strains from linear elastic calculations, providing EP stress and strain concentration factors. For uniaxial load histories, Neuber’s and Glinka’s rules are perhaps the most used. For non-proportional multiaxial histories, such corrections require incremental plasticity calculations to correlate stresses and strains at the notch root, a quite challenging task. However, for in-phase proportional multiaxial histories, where the principal directions do not change and the load path in a stress diagram follows a straight line, approximate methods can be used without requiring an incremental approach. Most of these methods are based on Neuber’s rule, so they usually result in conservative predictions, especially in plane strain-dominated cases associated with sharp notches. In this work, a Unified Notch Rule (UNR) is proposed for uniaxial and in-phase proportional multiaxial histories. The UNR can reproduce Neuber’s or Glinka’s rules, interpolate their notch-tip behaviors, or even extrapolate them for notches with increased constraint. Moreover, the UNR also allows a non-zero normal stress perpendicular to the free-surface. The proposed method predictions are compared with elastoplastic Finite Element calculations on notched shafts. K EYWORDS . Multiaxial fatigue; In-phase proportional loadings; Unified Notch Rule; Finite Element. Citation: Meggiolaro, M. A., Castro, J.T.P., Martha, L. F., Marques, L. F. N., A unified rule to estimate multiaxial elastoplastic notch stresses and strains under in-phase proportional loadings, Frattura ed Integrità Strutturale, 38 (2016) 128-134. Received: 18.05.2016 Accepted: 12.06.2016 Published: 01.10.2016 Copyright: © 2016 This is an open access article under the terms of the CC-BY 4.0, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited. I NTRODUCTION irection-sensitive materials like most metallic alloys tend to initiate a single dominant microcrack under fatigue loadings. Under multiaxial loading conditions this behavior tends to be well modeled by critical-plane fatigue- damage models, which search for the material plane at the critical point where the corresponding accumulated damage parameter is maximized. D