Fatigue life evaluation of 42CrMo4 nitrided steel by local approach: Equivalent strain-life-time

Experimental and analytical study of residual stresses relaxation in nitrided 42CrMo4 parts

“…The aim of this paper is to propose three empirical equations and to understand the residual stresses relaxation phenomenon. Experimental results obtained from other researchers confirm the calculated results based on the proposed models [5,7,15]. These results showed that the selected models are able to verify whether the residual stresses relaxation correlate with experimental data.…”

“…Fatigue life prediction of components is an important issue in engineering applications and could be extended by the near-surface macroscopic compressive residual stresses that retard fatigue crack initiation and crack growth. Major fatigue life prediction methods modify the fatigue limits to account for the presence of residual stresses [1][2][3][4][5][6][7][8][9][10]. The compressive residual stress resulting from the different surface treatments such as shot peening, carburizing, nitriding, have a favorable effect on the resistance of fatigue crack initiation [3,7,[10][11][12].…”

Low Cycle Fatigue Behaviour of Nitrided Layer of 42CrMo4 Steel

“…Thus, the resistance of the nitrided specimen remains controlled by the volume of basic material, whereas its ductility, slightly reduced, depends on the behaviour of the compound layer and the rate of superficial hardening. This ductility reduction is attributed to the nitrided heterogeneity and the introduction of a multi axial stresses state which rises from the difference of the Poisson's ratios when the basic material is plasticised, whereas the surface layers continue to have an elastic behaviour [11,13,16]. The helicoidally ruptures observed on the surface of the nitrided tensile specimens could justify the multi axial stresses state due to the difference in behaviour between core and layer of different elastic modulus.…”

“…These results obtained in the present study show a partial relaxation of these residual stresses on the surface of a specimen, broken under a cyclic loading and for an amplitude rather close to the ultimate stress fatigue gain caused by ion nitriding, (∆σ/ 2 = 850MPa). This relaxation under the effect of the cyclic loading (from -400MPato -300MPa), could increase as fast as the loading amplitude is raised, which consequently involves a fall of fatigue crack resistance of the nitrided layer [12,13,14,17,19,21].…”

“…This reveals that the in-depth penetration crack resistance of hardening elements (N 2 ), of the hardness of these layers [4,5,6,8] as well as the distribution of the residual stresses [7,9,10]. This beneficial effect of the treatment can be reduced or even reversed under the overload conditions, representative of the transient mode of transmission systems (gears, shafts, etc...) [10,11,13,16,19]. Thus the overload sensitivity of the nitrided parts became a significant parameter in the qualification in the treatment of superficial hardness.…”