Dalenda Jeddi - Academia.edu (original) (raw)
Papers by Dalenda Jeddi
Role of the martensitic microstructure in the stabilized residual stresses under cyclic loading and in the fatigue behavior of two steels
International Journal of Fatigue, Dec 31, 2023
Corrigendum to “Role of the martensitic microstructure in the stabilized residual stresses under cyclic loading and in the fatigue behavior of two steels”. [Int. J. Fatigue 182 (2024) 108168]
International journal of fatigue, Feb 1, 2024
Procedia Structural Integrity, 2018
During their operation, modern aircraft engine components are subjected to increasingly demanding... more During their operation, modern aircraft engine components are subjected to increasingly demanding operating conditions, especially the high pressure turbine (HPT) blades. Such conditions cause these parts to undergo different types of time-dependent degradation, one of which is creep. A model using the finite element method (FEM) was developed, in order to be able to predict the creep behaviour of HPT blades. Flight data records (FDR) for a specific aircraft, provided by a commercial aviation company, were used to obtain thermal and mechanical data for three different flight cycles. In order to create the 3D model needed for the FEM analysis, a HPT blade scrap was scanned, and its chemical composition and material properties were obtained. The data that was gathered was fed into the FEM model and different simulations were run, first with a simplified 3D rectangular block shape, in order to better establish the model, and then with the real 3D mesh obtained from the blade scrap. The overall expected behaviour in terms of displacement was observed, in particular at the trailing edge of the blade. Therefore such a model can be useful in the goal of predicting turbine blade life, given a set of FDR data.
Fatigue & Fracture of Engineering Materials & Structures, 2018
It is well-known that the high cycle fatigue (HCF) strength of steel components is influenced by ... more It is well-known that the high cycle fatigue (HCF) strength of steel components is influenced by a lot of factors depending on both material, loading (including environment), specimen or component geometry (design), and manufacturing process. Based on a literature review of a lot of experimental data, a synthesis is proposed in this paper to discuss the effect of the structural and operational factors on the very high cycle fatigue (VHCF) characteristics of steels. HCF and VHCF regimes are distinguished in terms of failure mechanisms and S-N curve shapes for high and low strength steels. Then, the effect of the microstructural and mechanical features on the VHCF resistance is debated as different parameters (microstructure, inclusion size type and depth, hydrogen, environment, maximum tensile strength, and residual stresses). Next, the influence of the loading conditions is addressed by taking into account both the frequency effect, the highly stressed volume, the loading type, and loading ratio. Finally, the influence of the testing techniques used in VHCF experiments is discussed.
Durcissement superficiel par laser CO2 continu : cas d’un acier à dispersoïdes de nuance 17MnCuNi7
Matériaux & Techniques, 2001
Le durcissement superficiel par faisceau laser CO 2 continu n'est generalement pas recommande... more Le durcissement superficiel par faisceau laser CO 2 continu n'est generalement pas recommande dans le cas des pieces metalliques de grandes surfaces par suite de l'important gradient de structure cree par les recouvrements de passes. En effet, les consequences de ce gradient sur l'heterogeneite du durcissement et la distribution des contraintes residuelles peuvent compromettre la tenue en service, et particulierement la resistance a la fatigue des pieces traitees. La solution industrielle reside dans la recherche et l'optimisation du couple acier/parametre de traitement laser, permettant de limiter voire d'eviter l'apparition de zones adoucies, sieges de contraintes residuelles de traction. Les modes d'interaction microstructure-traitement laser orientent les recherches vers les aciers a dispersoides susceptibles de compenser, par effet de durcissement structural, l'adoucissement resultant des recouvrements de passes. Dans ce cadre, nous avons etudie l'influence de deux types de traitements laser sur l'evolution des structures metallurgiques, des contraintes residuelles dans les zones de recouvrement de passes et leurs consequences sur la tenue en fatigue de l'acier a dispersoides de nuance 17MnCuNi7. Il en resulte une profondeur des couches affectees pouvant atteindre 2 mm, avec des modifications structurales etroitement liees aux gradients thermiques specifiques a chaque type de traitement. Le durcissement maximum est atteint en surface, avec des valeurs voisines de 700 HV 0.1 attribuees a une transformation martensitique. La distribution homogene des carbures mixtes de vanadium et de niobium, limite l'adoucissement dans les zones de recouvrement. Les contraintes residuelles sont de compression dans les zones durcies comme dans les zones adoucies. La tenue en fatigue de l'acier de nuance 17MnCuNi 7 durci par traitement laser depend en premier lieu du champ de contraintes residuelles dans les couches affectees par le traitement, en depit des pertes de durete provoquees par le recouvrement de passes. Les ameliorations apportees par ce traitement, en terme de limite d'endurance, varient de 10 a 20% par rapport a l'etat de reference, trempe revenu.
Matériaux & Techniques, 2007
-Les résultats des essais de fatigue flexion sur des éprouvettes entaillées en acier 14NiCr11, tr... more -Les résultats des essais de fatigue flexion sur des éprouvettes entaillées en acier 14NiCr11, traitées dans deux conditions de cémentation basse pression, ont montré des améliorations de la résistance à la fatigue des couches cémentées exprimées en terme de limite d'endurance à 10 6 cycles de l'ordre de 60 % et de 80 % par rapport à l'état non traité. Ces améliorations ont été interprétées sur la base des gradients de propriétés stabilisées des couches cémentées consécutifs à l'effet conjugué d'un phénomène de relaxation cyclique et d'un phénomène de transformation de l'austénite résiduelle en martensite au cours du chargement cyclique. Il s'établit une redistribution de durcissement et de contraintes résiduelles de compression stabilisées qui justifient les améliorations enregistrées. La prise en compte du durcissement superficiel et du champ de contraintes résiduelles, dans la martensite à l'état stabilisé, dans les différents critères de fatigue polycyclique considérés dans cette étude (critère de Crossland, de Dang Van et de Findley-Matake) a permis de bien rendre compte des résultats expérimentaux.
Role of Overlapping Passes on Fatigue Performance of Microalloyed 17MnCuNi7 Steel Treated by Continuous CO 2 Laser Beam
Surface Engineering, 2001
Abstract The widely used surface treatment by continuous CO2 laser beam requires superposition of... more Abstract The widely used surface treatment by continuous CO2 laser beam requires superposition of several laser passes, which can lead to a softened zone and to the creation of tensile residual stresses in overlapping passes. In this study, the effect of overlapping passes, microhardness, and metallurgical transformations on the fatigue performance of 17MnCuNi7 steel has been investigated by three series of bending fatigue tests corresponding to three types of continuous CO2 laser beam treatments. It has been concluded that suitable selection of material and control of the laser treatment parameters provides for the elimination of tensile residual stresses in softened zones, and can lead to homogeneous hardening of the surface. The fatigue limit of 17MnCuNi7 steel depends mainly on the residual stress in the layers affected by laser treatment, despite any hardness loss caused by overlapping passes. The improvement made by this treatment varies from 10 to 20% compared with the fatigue limit in the tempered state.
Procedia Engineering, 2010
Two vacuum carburizing treatments were applied to ductile steel 14NiCr11 to obtain equivalent har... more Two vacuum carburizing treatments were applied to ductile steel 14NiCr11 to obtain equivalent hardened layers with retained austenite contents of 25% and 41%. The properties of the carburized surfaces were examined and characterized before fatigue tests and during cyclic loading. Transformation of retained austenite into martensite during loading, was evaluated by dispersive X-ray diffraction method. The effects of this transformation on the residual stresses have been measured by X ray diffraction in martensite and in retained austenite structures. It was shown that the cyclic retained austenite transformation caused a redistribution of the compressive residual stresses and an increased surface hardness that stabilized after a small number of cycles. The dependence of fatigue behavior on surface properties was determined, and a relationship between the stabilized state and the fatigue limit is suggested. A phenomenological approach is proposed to correlate the influence of surface hardening and the stabilized residual stresses on fatigue limit of carburized specimens. The Crossland, Dang Van and Findley-Matake, multiaxial high cycle fatigue criteria were used in this approach and results have shown a good agreement with experimental data.
Journal of Materials Engineering and Performance, 2005
The role of retained austenite in the fatigue strength of carburized 14NiCr11 steel was studied b... more The role of retained austenite in the fatigue strength of carburized 14NiCr11 steel was studied by considering two gas-carburizing treatments leading to two maximum retained austenite fractions of 20 and 40%. These states led to endurance limit improvements evaluated at 40 and 10%, respectively, compared with the untreated state. These improvements were explained by the evolution of retained austenite during the cyclic loading using the dispersive x-ray diffraction technique. This reveals that the best fatigue strength is attributed to the homogeneous transformation of the retained austenite fraction in the treated layer during the cyclic loading.
Instabilite cyclique du gradient de microstructures et resistance a la fatigue de l'acier 14NiCr11 cemente
Rôle de l'austénite résiduelle dans la tenue en fatigue de l'acier 14NiCr11 cémenté
L'etude du role de l'austenite residuelle dans la resistance a la fatigue de l'acier ... more L'etude du role de l'austenite residuelle dans la resistance a la fatigue de l'acier 14 NiCr11 cemente a ete menee en considerant deux traitements de cementation gazeuse conduisant a deux taux d'austenite residuelle de 20 % et 40 %. Ces etats ont conduit a des ameliorations respectives en terme de limite d'endurance de 40 et de 10 %, par rapport a l'etat de reception. L'evolution de l'austenite residuelle au cours du chargement cyclique, evaluee par la technique de diffractometrie X en dispersion d'energie, a permis d'expliquer les resultats en s'appuyant sur l'analyse microfractographique au microscope electronique a balayage des mecanismes d'amorcage et de propagation des fissures de fatigue.
Fatigue strength of vacuum carburized layers: Experimental characterization and predictive approach
Role of the martensitic microstructure in the stabilized residual stresses under cyclic loading and in the fatigue behavior of two steels
International Journal of Fatigue, Dec 31, 2023
Corrigendum to “Role of the martensitic microstructure in the stabilized residual stresses under cyclic loading and in the fatigue behavior of two steels”. [Int. J. Fatigue 182 (2024) 108168]
International journal of fatigue, Feb 1, 2024
Procedia Structural Integrity, 2018
During their operation, modern aircraft engine components are subjected to increasingly demanding... more During their operation, modern aircraft engine components are subjected to increasingly demanding operating conditions, especially the high pressure turbine (HPT) blades. Such conditions cause these parts to undergo different types of time-dependent degradation, one of which is creep. A model using the finite element method (FEM) was developed, in order to be able to predict the creep behaviour of HPT blades. Flight data records (FDR) for a specific aircraft, provided by a commercial aviation company, were used to obtain thermal and mechanical data for three different flight cycles. In order to create the 3D model needed for the FEM analysis, a HPT blade scrap was scanned, and its chemical composition and material properties were obtained. The data that was gathered was fed into the FEM model and different simulations were run, first with a simplified 3D rectangular block shape, in order to better establish the model, and then with the real 3D mesh obtained from the blade scrap. The overall expected behaviour in terms of displacement was observed, in particular at the trailing edge of the blade. Therefore such a model can be useful in the goal of predicting turbine blade life, given a set of FDR data.
Fatigue & Fracture of Engineering Materials & Structures, 2018
It is well-known that the high cycle fatigue (HCF) strength of steel components is influenced by ... more It is well-known that the high cycle fatigue (HCF) strength of steel components is influenced by a lot of factors depending on both material, loading (including environment), specimen or component geometry (design), and manufacturing process. Based on a literature review of a lot of experimental data, a synthesis is proposed in this paper to discuss the effect of the structural and operational factors on the very high cycle fatigue (VHCF) characteristics of steels. HCF and VHCF regimes are distinguished in terms of failure mechanisms and S-N curve shapes for high and low strength steels. Then, the effect of the microstructural and mechanical features on the VHCF resistance is debated as different parameters (microstructure, inclusion size type and depth, hydrogen, environment, maximum tensile strength, and residual stresses). Next, the influence of the loading conditions is addressed by taking into account both the frequency effect, the highly stressed volume, the loading type, and loading ratio. Finally, the influence of the testing techniques used in VHCF experiments is discussed.
Durcissement superficiel par laser CO2 continu : cas d’un acier à dispersoïdes de nuance 17MnCuNi7
Matériaux & Techniques, 2001
Le durcissement superficiel par faisceau laser CO 2 continu n'est generalement pas recommande... more Le durcissement superficiel par faisceau laser CO 2 continu n'est generalement pas recommande dans le cas des pieces metalliques de grandes surfaces par suite de l'important gradient de structure cree par les recouvrements de passes. En effet, les consequences de ce gradient sur l'heterogeneite du durcissement et la distribution des contraintes residuelles peuvent compromettre la tenue en service, et particulierement la resistance a la fatigue des pieces traitees. La solution industrielle reside dans la recherche et l'optimisation du couple acier/parametre de traitement laser, permettant de limiter voire d'eviter l'apparition de zones adoucies, sieges de contraintes residuelles de traction. Les modes d'interaction microstructure-traitement laser orientent les recherches vers les aciers a dispersoides susceptibles de compenser, par effet de durcissement structural, l'adoucissement resultant des recouvrements de passes. Dans ce cadre, nous avons etudie l'influence de deux types de traitements laser sur l'evolution des structures metallurgiques, des contraintes residuelles dans les zones de recouvrement de passes et leurs consequences sur la tenue en fatigue de l'acier a dispersoides de nuance 17MnCuNi7. Il en resulte une profondeur des couches affectees pouvant atteindre 2 mm, avec des modifications structurales etroitement liees aux gradients thermiques specifiques a chaque type de traitement. Le durcissement maximum est atteint en surface, avec des valeurs voisines de 700 HV 0.1 attribuees a une transformation martensitique. La distribution homogene des carbures mixtes de vanadium et de niobium, limite l'adoucissement dans les zones de recouvrement. Les contraintes residuelles sont de compression dans les zones durcies comme dans les zones adoucies. La tenue en fatigue de l'acier de nuance 17MnCuNi 7 durci par traitement laser depend en premier lieu du champ de contraintes residuelles dans les couches affectees par le traitement, en depit des pertes de durete provoquees par le recouvrement de passes. Les ameliorations apportees par ce traitement, en terme de limite d'endurance, varient de 10 a 20% par rapport a l'etat de reference, trempe revenu.
Matériaux & Techniques, 2007
-Les résultats des essais de fatigue flexion sur des éprouvettes entaillées en acier 14NiCr11, tr... more -Les résultats des essais de fatigue flexion sur des éprouvettes entaillées en acier 14NiCr11, traitées dans deux conditions de cémentation basse pression, ont montré des améliorations de la résistance à la fatigue des couches cémentées exprimées en terme de limite d'endurance à 10 6 cycles de l'ordre de 60 % et de 80 % par rapport à l'état non traité. Ces améliorations ont été interprétées sur la base des gradients de propriétés stabilisées des couches cémentées consécutifs à l'effet conjugué d'un phénomène de relaxation cyclique et d'un phénomène de transformation de l'austénite résiduelle en martensite au cours du chargement cyclique. Il s'établit une redistribution de durcissement et de contraintes résiduelles de compression stabilisées qui justifient les améliorations enregistrées. La prise en compte du durcissement superficiel et du champ de contraintes résiduelles, dans la martensite à l'état stabilisé, dans les différents critères de fatigue polycyclique considérés dans cette étude (critère de Crossland, de Dang Van et de Findley-Matake) a permis de bien rendre compte des résultats expérimentaux.
Role of Overlapping Passes on Fatigue Performance of Microalloyed 17MnCuNi7 Steel Treated by Continuous CO 2 Laser Beam
Surface Engineering, 2001
Abstract The widely used surface treatment by continuous CO2 laser beam requires superposition of... more Abstract The widely used surface treatment by continuous CO2 laser beam requires superposition of several laser passes, which can lead to a softened zone and to the creation of tensile residual stresses in overlapping passes. In this study, the effect of overlapping passes, microhardness, and metallurgical transformations on the fatigue performance of 17MnCuNi7 steel has been investigated by three series of bending fatigue tests corresponding to three types of continuous CO2 laser beam treatments. It has been concluded that suitable selection of material and control of the laser treatment parameters provides for the elimination of tensile residual stresses in softened zones, and can lead to homogeneous hardening of the surface. The fatigue limit of 17MnCuNi7 steel depends mainly on the residual stress in the layers affected by laser treatment, despite any hardness loss caused by overlapping passes. The improvement made by this treatment varies from 10 to 20% compared with the fatigue limit in the tempered state.
Procedia Engineering, 2010
Two vacuum carburizing treatments were applied to ductile steel 14NiCr11 to obtain equivalent har... more Two vacuum carburizing treatments were applied to ductile steel 14NiCr11 to obtain equivalent hardened layers with retained austenite contents of 25% and 41%. The properties of the carburized surfaces were examined and characterized before fatigue tests and during cyclic loading. Transformation of retained austenite into martensite during loading, was evaluated by dispersive X-ray diffraction method. The effects of this transformation on the residual stresses have been measured by X ray diffraction in martensite and in retained austenite structures. It was shown that the cyclic retained austenite transformation caused a redistribution of the compressive residual stresses and an increased surface hardness that stabilized after a small number of cycles. The dependence of fatigue behavior on surface properties was determined, and a relationship between the stabilized state and the fatigue limit is suggested. A phenomenological approach is proposed to correlate the influence of surface hardening and the stabilized residual stresses on fatigue limit of carburized specimens. The Crossland, Dang Van and Findley-Matake, multiaxial high cycle fatigue criteria were used in this approach and results have shown a good agreement with experimental data.
Journal of Materials Engineering and Performance, 2005
The role of retained austenite in the fatigue strength of carburized 14NiCr11 steel was studied b... more The role of retained austenite in the fatigue strength of carburized 14NiCr11 steel was studied by considering two gas-carburizing treatments leading to two maximum retained austenite fractions of 20 and 40%. These states led to endurance limit improvements evaluated at 40 and 10%, respectively, compared with the untreated state. These improvements were explained by the evolution of retained austenite during the cyclic loading using the dispersive x-ray diffraction technique. This reveals that the best fatigue strength is attributed to the homogeneous transformation of the retained austenite fraction in the treated layer during the cyclic loading.
Instabilite cyclique du gradient de microstructures et resistance a la fatigue de l'acier 14NiCr11 cemente
Rôle de l'austénite résiduelle dans la tenue en fatigue de l'acier 14NiCr11 cémenté
L'etude du role de l'austenite residuelle dans la resistance a la fatigue de l'acier ... more L'etude du role de l'austenite residuelle dans la resistance a la fatigue de l'acier 14 NiCr11 cemente a ete menee en considerant deux traitements de cementation gazeuse conduisant a deux taux d'austenite residuelle de 20 % et 40 %. Ces etats ont conduit a des ameliorations respectives en terme de limite d'endurance de 40 et de 10 %, par rapport a l'etat de reception. L'evolution de l'austenite residuelle au cours du chargement cyclique, evaluee par la technique de diffractometrie X en dispersion d'energie, a permis d'expliquer les resultats en s'appuyant sur l'analyse microfractographique au microscope electronique a balayage des mecanismes d'amorcage et de propagation des fissures de fatigue.
Fatigue strength of vacuum carburized layers: Experimental characterization and predictive approach