Issue 33

F. Fremy et alii, Frattura ed Integrità Strutturale, 33 (2015) 397-403; DOI: 10.3221/IGF-ESIS.33.44 397 Focussed on multiaxial fatigue Crack tip fields in elastic-plastic and mixed mode I+II+III conditions, finite elements simulations and modeling F. Fremy, S. Pommier LMT (ENS Cachan / CNRS / Université Paris Saclay) Flavien.Fremy@ens-cachan.fr, Sylvie.Pommier@ens-cachan.fr E. Galenne EDF R&D Erwan.Galenne@edf.fr S. Courtin Areva NP Stephan.Courtin@areva.com A BSTRACT . This paper is devoted to the analysis of the load path effect on I+II+III mixed mode fatigue crack propagation in a 316L stainless steel. Experiments were conducted in mode I+II and in mode I+II+III. The same maximum, minimum and mean values of the stress intensity factors were used for each loading path in the experiments. The main result of this set of experiments is that very different crack growth rates and crack paths are observed for load paths that are however considered as equivalent in most fatigue criteria. The experiments conducted in mode I+II and in mode I+II+III, also allowed to show that the addition of mode III loading steps to a mode I+II loading sequence is increasing the fatigue crack growth rate, even when the crack path is not significantly modified. K EYWORDS . Fatigue crack growth; Mixed mode; Mode I; Mode II; Mode III. I NTRODUCTION ost cyclically loaded machines are subjected to multi-axial loadings. For example, power shafts are usually subjected to a combination of torsion and bending due to the transmission of the torque, the self-weight of the shaft and its rotation speed. For components loaded in proportional multi-axial conditions, the fracture mechanics concepts are normally used to determine the crack path for which the crack is loaded in mode I [1-7]. Then, the growth rate is usually predicted using the Paris’ law determined in mode I conditions. When non-proportional multiaxial loading conditions are encountered, various approaches have been derived from the Paris’ law, to predict the growth rate in mixed mode conditions [1-3]. Most of them are based on an equivalent stress intensity factor (Eq. 1), whose expression varies according to the authors, but is usually function of the stress intensity factor ranges (Eq. 2). da m eq CK dN  (1) M