Issue 38

D. Marhabi et alii, Frattura ed Integrità Strutturale, 38 (2016) 36-46; DOI: 10.3221/IGF-ESIS.38.05 36 Focussed on Multiaxial Fatigue and Fracture Prediction of the critical stress to crack initiation associated to the investigation of fatigue small crack D. Marhabi H.E.I 13 Rue de TOUL 59046 Lille-cedex France driss.marhabi@hei.fr N. Benseddiq, G. Mesmacque University Lille 1 Villeneuve d’Ascq France noureddine.benseddiq@univ-lille1.fr gerard.mesmacque@univ-lille1.fr Z. Azari LaBPS, ENIM, 1 Route d’Ars Laquenexy, 57070 Metz, France azari@enim.fr J.M. Nianga H.E.I 13 Rue de TOUL 59046 Lille-cedex France Jean-Marie.NIANGA@hei.fr A BSTRACT . Fatigue design is of vital importance to avoid fatigue small crack growth in engineering structures. This study shows that the critical fatigue design stress can be defined below the usual endurance limit, considered in rules and codes. The material constitutive behaviour is using linear isotropic elasticity. Lassere and Pallin-Luc [1-2] use the elastic energy and over-energy under uniaxial load (tension and rotating bending). The authors deduce the influencing critical stress value corresponding to σ*. It’s a linear approach. We propose an over-energy under dissymmetrical rotating bending and expressed in the ellipse axes. An asymptotic approach is transformed the over-energy in polynomial function of critical stress. Unknown depend on experimental service conditions, endurance limit of tension and rotating bending of specimen. The fatigue database of 30NCD16 steel studied by Froustey and Dubar [3-13] is used. Critical stresses are evaluated (Fig. 2). The research done by Manning and all [4] has shown the small crack effect to be as large as 0.3 mm. Small crack and critical stress are illustrated here in as resulting from pure bending approach expressed by Bazant law [7]. It’s reproduces well the Kitagawa diagram [6] (Fig. 3). When the short cracks are hidden in the material, we shows that the number Citation: Marhabi, D., Benseddiq, N., Mesmacque, G., Azari, Z., Nianga, J.M., Prediction of the critical stress to crack initiation associated to the investigation of fatigue small crack, Frattura ed Integrità Strutturale, 38 (2016) 36-46. Received: 12.05.2016 Accepted: 20.06.2016 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.