Papers by Author: F. Galzy

Abstract: In this work, the effect of steel grade on the fatigue resistance of deep-rolled crankshafts is analysed. In the first part of this paper, the mechanisms leading to the increase of the fatigue resistance brought by the deep rolling treatment, is presented. This reinforcement is mainly linked to crack arrest due both to a decrease of the in-depth stress concentration factor and to remaining compressive residual stresses induced by the deep rolling. In a second part, an analytical model of residual stresses generation by deep-rolling and fatigue is presented. In this model the low cyclic fatigue behaviour of the steel is taken into account, and the residual stress stability with bending fatigue cycling can be predicted. After a presentation of the experimental validation on two different microstructures (baintic and ferrito- perlitic), this model is used for analysing the main parameters of the deep-rolling process and fatigue resistance.

Abstract: In the new types of diesel motors, the crankshaft loads increase dramatically. For that reason, to satisfy the requirements and needs of its motorist’s customers, ASCOMETAL has developed a special bending fatigue test applied to “Baldwin” specimens reinforced by deep rolling. Such test is representative of the main in-service loads existing in crankshaft crankpin fillets (one of the weakest point of the component). Thus, using this test, the mechanisms leading to the increase of the fatigue resistance brought by the deep rolling treatment, could be identified. This reinforcement is mainly linked to crack arrest due to both a decrease of the in-depth stress concentration factor and to remaining compressive residual stresses induced by the deep rolling. In this paper, the experimental methods (in particular X-rays diffraction) used to characterize the stress fields generated by the deep rolling treatment are described first. The equations of equilibrium and compatibility of the particular toric symmetry of the crankshaft crankpin fillets have been used then to analyze the surface and in-depth stress profiles of the tested sample. This allowed characterizing the shake down and stress relaxation induced by fatigue. The crack propagation behaviour and the associated fracture limits were also defined.