Issue 38

H. Weil et alii, Frattura ed Integrità Strutturale, 38 (2016) 61-66; DOI: 10.3221/IGF-ESIS.38.08 61 Focussed on Multiaxial Fatigue and Fracture Fatigue modelling for gas nitriding H. Weil, S. Jégou, L. Barrallier MSMP Laboratory - Arts et Métiers hadrien.weil@ensam.fr, sebastien.jegou@ensam.eu, laurent.barrallier@ensam.fr A. Courleux, G. Beck Hispano-Suiza - Groupe SAFRAN alice.courleux@hispano-suiza-sa.com , guillaume.beck@hispano-suiza-sa.com A BSTRACT . The present study aims to develop an algorithm able to predict the fatigue lifetime of nitrided steels. Linear multi-axial fatigue criteria are used to take into account the gradients of mechanical properties provided by the nitriding process. Simulations on rotating bending fatigue specimens are made in order to test the nitrided surfaces. The fatigue model is applied to the cyclic loading of a gear from a simulation using the finite element software Ansys. Results show the positive contributions of nitriding on the fatigue strength. K EYWORDS . Nitriding; Fatigue; Lifetime. Citation: Weil, H., Jégou, S., Barrallier, L., Courleux, A., Beck, G., Fatigue modelling for gas nitriding, 38 (2016) 61-66. Received: 30.04.2016 Accepted: 08.06.2016 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 atigue resistance and mechanical capacity of aircraft engine components are of vital importance in aerospace industries. Thermochemical processing is exploited in order to improve superficial mechanical properties (residual stresses, hardness). Among surface treatments, the nitriding process is the most efficient despite its high cost. This study is specifically dedicated to gas nitriding of steels which is widely used by the aerospace industry. Due to the supply of nitrogen and its co-diffusion with carbon, precipitation of nanometric alloying elements nitrides and cementite at grain boundaries occurs leading to an increase of superficial hardness and providing compressive residual stresses in the surface layers [1-4]. The present work aims of creating a model for calculating fatigue lifetime of a nitrided layer whilst taking into account of mechanical improvements generated by nitriding. Based on previous works [5], the model takes into consideration the gradient of microstructure from the diffusion of carbon and nitrogen during nitriding and calculates the resulting gradient of compressive residual stresses from the volume change accompanying the precipitation. The fatigue model is built on multiaxial criterion like Crossland [6], and the fatigue life is calculated for each mechanical loading in a nitrided layer. F