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The DSpace digital repository system captures, stores, indexes, preserves, and distributes digital research material.Wed, 08 Apr 2020 05:54:28 GMT2020-04-08T05:54:28ZThe effect of quenching and defects size on the HCF behaviour of Boron steel
http://hdl.handle.net/10985/8460
The effect of quenching and defects size on the HCF behaviour of Boron steel
PESSARD, Etienne; ABRIVARD, Benjamin; MOREL, Franck; ABROUG, Foued; DELHAYE, Philippe
This work investigates the effect of natural and artificial surface defects and quenching on the fatigue strength of a Boron steel (22MnB5). A vast experimental campaign has been undertaken to study the high cycle fatigue behaviour and more specifically the fatigue damage mechanisms observed in quenched and untreated materials, under different loading conditions and with differents artificial defects sizes (from 25 μm to 370 μm radius). In order to test the sheet metal in shear an original test apparatus is used. The critical defect size is determined to be 100 ± 50 μm. This critical size does not appear to depend on the loading type or the microstructure of the material (i.e. ferritic–perlitic or martensitic). However, for large defects, the quenched material is more sensitive to the defect size than the untreated material. For a defect size range of 100–300 μm the slope of the Kitagawa–Takahashi diagram is approximately −1/3 and −1/6 for the quenched and untreated materials respectively. A probabilistic approach that leads naturally to a probabilistic Kitagawa type diagram is developed. This methodology can be used to explain the relationship between the influence of the heat treatment and the defect size on the fatigue behaviour of this steel.
Wed, 01 Jan 2014 00:00:00 GMThttp://hdl.handle.net/10985/84602014-01-01T00:00:00ZPESSARD, EtienneABRIVARD, BenjaminMOREL, FranckABROUG, FouedDELHAYE, PhilippeThis work investigates the effect of natural and artificial surface defects and quenching on the fatigue strength of a Boron steel (22MnB5). A vast experimental campaign has been undertaken to study the high cycle fatigue behaviour and more specifically the fatigue damage mechanisms observed in quenched and untreated materials, under different loading conditions and with differents artificial defects sizes (from 25 μm to 370 μm radius). In order to test the sheet metal in shear an original test apparatus is used. The critical defect size is determined to be 100 ± 50 μm. This critical size does not appear to depend on the loading type or the microstructure of the material (i.e. ferritic–perlitic or martensitic). However, for large defects, the quenched material is more sensitive to the defect size than the untreated material. For a defect size range of 100–300 μm the slope of the Kitagawa–Takahashi diagram is approximately −1/3 and −1/6 for the quenched and untreated materials respectively. A probabilistic approach that leads naturally to a probabilistic Kitagawa type diagram is developed. This methodology can be used to explain the relationship between the influence of the heat treatment and the defect size on the fatigue behaviour of this steel.Microstructural heterogeneities and fatigue anisotropy
http://hdl.handle.net/10985/6891
Microstructural heterogeneities and fatigue anisotropy
PESSARD, Etienne; MOREL, Franck; VERDU, Catherine; FLACELIERE, Laurent; BAUDRY, Gilles
In this study, various experimental methods are employed to determine the anisotropic fatigue behavior of a 25MnCrSiVB6 forged steel (Metasco MC). This material has a bainitic microstructure and contains many elongated non-metallic inclusions in the rolled direction, which are grouped into clusters. Specimens with different orientations relative to the rolling direction have been extracted from a hot rolled bar and the ability of certain experimental techniques to capture the fatigue anisotropy has been tested. Results obtained from monotonic tensile tests and Charpy impact tests show that the material has isotropic fracture strength and anisotropic ductility. The influence of the inclusion clusters is clearly demonstrated via observation of the fracture surfaces. Concerning the fatigue behavior, results from a classical staircase experimental procedure are compared to results from self-heating fatigue tests. For specimens orientated at 0° relative to the rolled direction, microcrack initiation is controlled by the material matrix and the prediction of the fatigue strength with the self-heating method has been observed to be correct. For specimens orientated at 45° and 90°, the elongated manganese sulfide inclusion clusters are the origin of crack initiation and the fatigue strength drops significantly. For this case, it appears that the self-heating method has difficulty predicting the fatigue behavior.
Sat, 01 Jan 2011 00:00:00 GMThttp://hdl.handle.net/10985/68912011-01-01T00:00:00ZPESSARD, EtienneMOREL, FranckVERDU, CatherineFLACELIERE, LaurentBAUDRY, GillesIn this study, various experimental methods are employed to determine the anisotropic fatigue behavior of a 25MnCrSiVB6 forged steel (Metasco MC). This material has a bainitic microstructure and contains many elongated non-metallic inclusions in the rolled direction, which are grouped into clusters. Specimens with different orientations relative to the rolling direction have been extracted from a hot rolled bar and the ability of certain experimental techniques to capture the fatigue anisotropy has been tested. Results obtained from monotonic tensile tests and Charpy impact tests show that the material has isotropic fracture strength and anisotropic ductility. The influence of the inclusion clusters is clearly demonstrated via observation of the fracture surfaces. Concerning the fatigue behavior, results from a classical staircase experimental procedure are compared to results from self-heating fatigue tests. For specimens orientated at 0° relative to the rolled direction, microcrack initiation is controlled by the material matrix and the prediction of the fatigue strength with the self-heating method has been observed to be correct. For specimens orientated at 45° and 90°, the elongated manganese sulfide inclusion clusters are the origin of crack initiation and the fatigue strength drops significantly. For this case, it appears that the self-heating method has difficulty predicting the fatigue behavior.Modelling the role of non metallic inclusions on the anisotropic fatigue behaviour of forged steel
http://hdl.handle.net/10985/6890
Modelling the role of non metallic inclusions on the anisotropic fatigue behaviour of forged steel
PESSARD, Etienne; MOREL, Franck; MOREL, Anne; BELLETT, Daniel
Forged components are known to show high cyclic and monotonic mechanical properties. This is mainly due to a better compactness and a finer microstructure introduced by the forming process. However, this good mechanical behaviour is sometimes a source of anisotropy especially when the microstructural heterogeneities are not randomly distributed and/or oriented. This study aims at describing the high cycle fatigue response of a forged bainitic steel. This material contains a lot of elongated manganese sulphide (MnS) inclusions, oriented as a function of the rolling or forging direction. Specimens with different orientations relative to the rolling direction are tested in fatigue under push-pull uniaxial and torsion loads. The influence of “inclusion clusters” is clearly demonstrated via the observation of the failure surfaces. Experiments show that the anisotropic fatigue behaviour is due to a change in the crack initiation mechanism. At 0°, when the inclusions are parallel to the applied stress, micro-crack initiation is controlled by the material matrix. At 45° and 90°, elongated manganese-sulfide inclusion clusters are the origin of crack initiation and the fatigue strength drops significantly. A statistical approach based on the competition between two different crack initiation mechanisms is proposed. One mechanism is modelled by local elastic shakedown concepts and the other by linear elastic fracture mechanics. This approach leads to a Kitagawa type diagram and explains the anisotropy in the material. The approach developed in this study demonstrates a framework using both the elastic shakedown concept and the weakest link theory to account for the loading mode, loading path and data scatter in High Cycle Fatigue.
Sat, 01 Jan 2011 00:00:00 GMThttp://hdl.handle.net/10985/68902011-01-01T00:00:00ZPESSARD, EtienneMOREL, FranckMOREL, AnneBELLETT, DanielForged components are known to show high cyclic and monotonic mechanical properties. This is mainly due to a better compactness and a finer microstructure introduced by the forming process. However, this good mechanical behaviour is sometimes a source of anisotropy especially when the microstructural heterogeneities are not randomly distributed and/or oriented. This study aims at describing the high cycle fatigue response of a forged bainitic steel. This material contains a lot of elongated manganese sulphide (MnS) inclusions, oriented as a function of the rolling or forging direction. Specimens with different orientations relative to the rolling direction are tested in fatigue under push-pull uniaxial and torsion loads. The influence of “inclusion clusters” is clearly demonstrated via the observation of the failure surfaces. Experiments show that the anisotropic fatigue behaviour is due to a change in the crack initiation mechanism. At 0°, when the inclusions are parallel to the applied stress, micro-crack initiation is controlled by the material matrix. At 45° and 90°, elongated manganese-sulfide inclusion clusters are the origin of crack initiation and the fatigue strength drops significantly. A statistical approach based on the competition between two different crack initiation mechanisms is proposed. One mechanism is modelled by local elastic shakedown concepts and the other by linear elastic fracture mechanics. This approach leads to a Kitagawa type diagram and explains the anisotropy in the material. The approach developed in this study demonstrates a framework using both the elastic shakedown concept and the weakest link theory to account for the loading mode, loading path and data scatter in High Cycle Fatigue.Comparative study and link between mesoscopic and energetic approaches in high cycle multiaxial fatigue
http://hdl.handle.net/10985/11221
Comparative study and link between mesoscopic and energetic approaches in high cycle multiaxial fatigue
MOREL, Franck; PALIN-LUC, Thierry; FROUSTEY, Catherine
Multiaxial fatigue analysis can be categorized into several viewpoints, i.e. empirical formulae, methods based on stress invariants, critical plane approaches, models using averages of stress quantities and energetic considerations. The aim of this paper is not to survey the current state of knowledge concerning multiaxial fatigue but to critically examine two endurance criteria so as to prove that a direct link can be established between them. The first of the two methods, proposed by Papadopoulos, has been built by exploring the fatigue of metals from the mesoscopic scale, that is from the scale of the metal grains of a metallic aggregate. The localized plastic strains developping in some less favourably oriented crystals is considered to be the main cause of fatigue crack nucleation. According to relationships between macroscopic and mesoscopic quantities, this model is finally expressed in terms of the usual macroscopic stresses relative to an elementary material volume. The second approach proposed by Froustey and Lasserre is an energetic based criterion. It has been deduced from experimental observations concerning multiaxial endurance limit and states that crack initiation occurs as soon as the total strain energy density exceeds a critical value. This paper shows that the critical value of the accumulated mesoscopic plastic strain used by Papadopoulos to characterize the endurance limit can be estimated with the global strain energy density at the macroscopic scale. Indeed, it is demonstrated that when dealing with in-phase or out-of-phase synchronous sinusoidal constant amplitude loadings, a single analytical formulation of these criteria can be written either with stress quantities or with energetic ones describing thus the same physical phenomenon. The mean stress influence is discussed; the predictions of the two approaches are similar when the material remains quasi elastic. Another important result concerns the phase difference of the stress tensor components. Very few approaches are able to predict the independence of the fatigue strength on the phase difference between normal and shear stresses. The two proposed criteria reflect this phenomenon which has been experimentally observed for many metals subjected to combined bending-torsion loading. Nevertheless, this independence with regard to the phase shift is no more effective when dealing with some biaxial stress systems with two normal stresses. In this case the two models are consistent with the experimental results since they show a marked influence of the phase difference.
Mon, 01 Jan 2001 00:00:00 GMThttp://hdl.handle.net/10985/112212001-01-01T00:00:00ZMOREL, FranckPALIN-LUC, ThierryFROUSTEY, CatherineMultiaxial fatigue analysis can be categorized into several viewpoints, i.e. empirical formulae, methods based on stress invariants, critical plane approaches, models using averages of stress quantities and energetic considerations. The aim of this paper is not to survey the current state of knowledge concerning multiaxial fatigue but to critically examine two endurance criteria so as to prove that a direct link can be established between them. The first of the two methods, proposed by Papadopoulos, has been built by exploring the fatigue of metals from the mesoscopic scale, that is from the scale of the metal grains of a metallic aggregate. The localized plastic strains developping in some less favourably oriented crystals is considered to be the main cause of fatigue crack nucleation. According to relationships between macroscopic and mesoscopic quantities, this model is finally expressed in terms of the usual macroscopic stresses relative to an elementary material volume. The second approach proposed by Froustey and Lasserre is an energetic based criterion. It has been deduced from experimental observations concerning multiaxial endurance limit and states that crack initiation occurs as soon as the total strain energy density exceeds a critical value. This paper shows that the critical value of the accumulated mesoscopic plastic strain used by Papadopoulos to characterize the endurance limit can be estimated with the global strain energy density at the macroscopic scale. Indeed, it is demonstrated that when dealing with in-phase or out-of-phase synchronous sinusoidal constant amplitude loadings, a single analytical formulation of these criteria can be written either with stress quantities or with energetic ones describing thus the same physical phenomenon. The mean stress influence is discussed; the predictions of the two approaches are similar when the material remains quasi elastic. Another important result concerns the phase difference of the stress tensor components. Very few approaches are able to predict the independence of the fatigue strength on the phase difference between normal and shear stresses. The two proposed criteria reflect this phenomenon which has been experimentally observed for many metals subjected to combined bending-torsion loading. Nevertheless, this independence with regard to the phase shift is no more effective when dealing with some biaxial stress systems with two normal stresses. In this case the two models are consistent with the experimental results since they show a marked influence of the phase difference.Competition between microstructure and defect in multiaxial high cycle fatigue
http://hdl.handle.net/10985/10058
Competition between microstructure and defect in multiaxial high cycle fatigue
MOREL, Franck; GUERCHAIS, Raphaël; SAINTIER, Nicolas
This study aims at providing a better understanding of the effects of both microstructure and defect on the high cycle fatigue behavior of metallic alloys using finite element simulations of polycrystalline aggregates. It is well known that the microstructure strongly affects the average fatigue strength and when the cyclic stress level is close to the fatigue limit, it is often seen as the main source of the huge scatter generally observed in this fatigue regime. The presence of geometrical defects in a material can also strongly alter the fatigue behavior. Nonetheless, when the defect size is small enough, i.e. under a critical value, the fatigue strength is no more affected by the defect. The so-called Kitagawa effect can be interpreted as a competition between the crack initiation mechanisms governed either by the microstructure or by the defect. Surprisingly, only few studies have been done to date to explain the Kitagawa effect from the point of view of this competition, even though this effect has been extensively investigated in the literature. The primary focus of this paper is hence on the use of both FE simulations and explicit descriptions of the microstructure to get insight into how the competition between defect and microstructure operates in HCF. In order to account for the variability of the microstructure in the predictions of the macroscopic fatigue limits, several configurations of crystalline orientations, crystal aggregates and defects are studied. The results of each individual FE simulation are used to assess the response at the macroscopic scale thanks to a probabilistic fatigue criterion proposed by the authors in previous works. The ability of this criterion to predict the influence of defects on the average and the scatter of macroscopic fatigue limits is evaluated. In this paper, particular emphasis is also placed on the effect of different loading modes (pure tension, pure torsion and combined tension and torsion) on the experimental and predicted fatigue strength of a 316 stainless steel containing artificial defect.
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Thu, 01 Jan 2015 00:00:00 GMThttp://hdl.handle.net/10985/100582015-01-01T00:00:00ZMOREL, FranckGUERCHAIS, RaphaëlSAINTIER, NicolasThis study aims at providing a better understanding of the effects of both microstructure and defect on the high cycle fatigue behavior of metallic alloys using finite element simulations of polycrystalline aggregates. It is well known that the microstructure strongly affects the average fatigue strength and when the cyclic stress level is close to the fatigue limit, it is often seen as the main source of the huge scatter generally observed in this fatigue regime. The presence of geometrical defects in a material can also strongly alter the fatigue behavior. Nonetheless, when the defect size is small enough, i.e. under a critical value, the fatigue strength is no more affected by the defect. The so-called Kitagawa effect can be interpreted as a competition between the crack initiation mechanisms governed either by the microstructure or by the defect. Surprisingly, only few studies have been done to date to explain the Kitagawa effect from the point of view of this competition, even though this effect has been extensively investigated in the literature. The primary focus of this paper is hence on the use of both FE simulations and explicit descriptions of the microstructure to get insight into how the competition between defect and microstructure operates in HCF. In order to account for the variability of the microstructure in the predictions of the macroscopic fatigue limits, several configurations of crystalline orientations, crystal aggregates and defects are studied. The results of each individual FE simulation are used to assess the response at the macroscopic scale thanks to a probabilistic fatigue criterion proposed by the authors in previous works. The ability of this criterion to predict the influence of defects on the average and the scatter of macroscopic fatigue limits is evaluated. In this paper, particular emphasis is also placed on the effect of different loading modes (pure tension, pure torsion and combined tension and torsion) on the experimental and predicted fatigue strength of a 316 stainless steel containing artificial defect.Machine d'essai en fatigue biaxiale disposant d'une éprouvette
http://hdl.handle.net/10985/9594
Machine d'essai en fatigue biaxiale disposant d'une éprouvette
DUPARQUE, Christian; AUGUSTINS, Louis; MOREL, Franck; BELLETT, Daniel
Machine d'essai en fatigue disposant d'une éprouvette (10), cette machine comportant un poinçon mobile appliquant une charge axiale cyclique sur une face de l'éprouvette (14) perpendiculaire à l'axe du poinçon, cette éprouvette étant en appui sur une base fixe par une face opposée (12) à la première face, caractérisée en ce que la machine d'essai comporte deux appuis annulaires de rayons différents centrés sur l'axe du poinçon, appliquant la charge du poinçon ou de la base fixe sur chacune des faces opposées (12, 14) de l'éprouvette (10), la partie centrale de cette éprouvette comprenant une zone de contrainte bi-axiale (22) comportant deux surfaces parallèles, et la face (12) comportant l'appui annulaire de plus grand rayon (A), recevant sur la zone de contrainte bi-axiale (22) des jauges de déformation (20).
Wed, 01 Jan 2014 00:00:00 GMThttp://hdl.handle.net/10985/95942014-01-01T00:00:00ZDUPARQUE, ChristianAUGUSTINS, LouisMOREL, FranckBELLETT, DanielMachine d'essai en fatigue disposant d'une éprouvette (10), cette machine comportant un poinçon mobile appliquant une charge axiale cyclique sur une face de l'éprouvette (14) perpendiculaire à l'axe du poinçon, cette éprouvette étant en appui sur une base fixe par une face opposée (12) à la première face, caractérisée en ce que la machine d'essai comporte deux appuis annulaires de rayons différents centrés sur l'axe du poinçon, appliquant la charge du poinçon ou de la base fixe sur chacune des faces opposées (12, 14) de l'éprouvette (10), la partie centrale de cette éprouvette comprenant une zone de contrainte bi-axiale (22) comportant deux surfaces parallèles, et la face (12) comportant l'appui annulaire de plus grand rayon (A), recevant sur la zone de contrainte bi-axiale (22) des jauges de déformation (20).A mechanistic approach to the Kitagawa-Takahashi diagram using a multiaxial probabilistic framework
http://hdl.handle.net/10985/7416
A mechanistic approach to the Kitagawa-Takahashi diagram using a multiaxial probabilistic framework
PESSARD, Etienne; BELLETT, Daniel; MOREL, Franck; KOUTIRI, Imade
The aim of this paper is to propose a flexible multiaxial modelling framework that is capable of combining two fatigue damage mechanisms so as to continuously describe the Kitagawa-Takahashi diagram. It is proposed that this diagram represents two distinct fatigue damage mechanisms: one associated with crack initiation (or microstructurally small cracks) and the other with crack propagation (or long cracks). It is further postulated that these damage mechanisms are more appropriately modelled using di erent fatigue criteria. A probabilistic modelling framework is proposed in which any two suitable fatigue criteria can be combined in order to simultaneously model both damage mechanisms and the transition between them. This framework is based on the weakest link hypothesis and results in a probabilistic Kitagawa-Takahashi type diagram.
Tue, 01 Jan 2013 00:00:00 GMThttp://hdl.handle.net/10985/74162013-01-01T00:00:00ZPESSARD, EtienneBELLETT, DanielMOREL, FranckKOUTIRI, ImadeThe aim of this paper is to propose a flexible multiaxial modelling framework that is capable of combining two fatigue damage mechanisms so as to continuously describe the Kitagawa-Takahashi diagram. It is proposed that this diagram represents two distinct fatigue damage mechanisms: one associated with crack initiation (or microstructurally small cracks) and the other with crack propagation (or long cracks). It is further postulated that these damage mechanisms are more appropriately modelled using di erent fatigue criteria. A probabilistic modelling framework is proposed in which any two suitable fatigue criteria can be combined in order to simultaneously model both damage mechanisms and the transition between them. This framework is based on the weakest link hypothesis and results in a probabilistic Kitagawa-Takahashi type diagram.High cycle fatigue damage mechanisms in cast aluminium subject to complex loads
http://hdl.handle.net/10985/6916
High cycle fatigue damage mechanisms in cast aluminium subject to complex loads
KOUTIRI, Imade; BELLETT, Daniel; MOREL, Franck; AUGUSTINS, Louis; ADRIEN, Jérôme
This article is dedicated to the high cycle fatigue behaviour of cast hypo-eutectic Al–Si alloys. In particular, the AlSi7Cu05Mg03 alloy is investigated. It presents the results of a vast experimental campaign undertaken to investigate the fatigue behaviour, and more specifically the fatigue damage mechanisms observed under complex loading conditions: plane bending with different load ratios, fully reversed torsion and equibiaxial bending with a load ratio of R = 0.1. A specific test set-up has been designed to create an equibiaxial stress state using disk shaped specimens. A tomographic analysis is also presented with the aim of characterising the micro-shrinkage pore population of the material. It is shown that two distinct and coexisting fatigue damage mechanisms occur in this material, depending on the presence of different microstructural heterogeneities (i.e. micro-shrinkage pores, Silicon particles in the eutectic zones, Fe-rich intermetallic phases, etc.). Furthermore, it is concluded that the effect of an equibiaxial tensile stress state is not detrimental in terms of high cycle fatigue. It is also shown that the Dang Van criterion is not able to simultaneously predict the multiaxial effect (i.e. torsion and equibiaxial tension) and the mean stress effect for this material.
Lien vers la version éditeur: http://www.sciencedirect.com/science/article/pii/S0142112312002356
Tue, 01 Jan 2013 00:00:00 GMThttp://hdl.handle.net/10985/69162013-01-01T00:00:00ZKOUTIRI, ImadeBELLETT, DanielMOREL, FranckAUGUSTINS, LouisADRIEN, JérômeThis article is dedicated to the high cycle fatigue behaviour of cast hypo-eutectic Al–Si alloys. In particular, the AlSi7Cu05Mg03 alloy is investigated. It presents the results of a vast experimental campaign undertaken to investigate the fatigue behaviour, and more specifically the fatigue damage mechanisms observed under complex loading conditions: plane bending with different load ratios, fully reversed torsion and equibiaxial bending with a load ratio of R = 0.1. A specific test set-up has been designed to create an equibiaxial stress state using disk shaped specimens. A tomographic analysis is also presented with the aim of characterising the micro-shrinkage pore population of the material. It is shown that two distinct and coexisting fatigue damage mechanisms occur in this material, depending on the presence of different microstructural heterogeneities (i.e. micro-shrinkage pores, Silicon particles in the eutectic zones, Fe-rich intermetallic phases, etc.). Furthermore, it is concluded that the effect of an equibiaxial tensile stress state is not detrimental in terms of high cycle fatigue. It is also shown that the Dang Van criterion is not able to simultaneously predict the multiaxial effect (i.e. torsion and equibiaxial tension) and the mean stress effect for this material.A probabilistic model for the high cycle fatigue behaviour of cast aluminium alloys subject to complex loads
http://hdl.handle.net/10985/7035
A probabilistic model for the high cycle fatigue behaviour of cast aluminium alloys subject to complex loads
KOUTIRI, Imade; BELLETT, Daniel; MOREL, Franck; PESSARD, Etienne
This article is dedicated to the high cycle fatigue behaviour of cast hypo-eutectic Al–Si alloys and in particular the AlSi7Cu05Mg03 alloy. In a vast experimental campaign undertaken to investigate the fatigue damage mechanisms operating in this alloy, subject to complex loading conditions, it was shown that two different coexisting fatigue damage mechanisms occur in this materials, depending on the presence of different microstructural heterogeneities (i.e. micro-shrinkage pores, Si particles, Fe-rich intermetallic phases, DAS of the Al-matrix, etc.). In order to take into account both of these damage mechanisms, a probabilistic approach using the weakest link concept is introduced to model the competition between the two mechanisms. This approach leads naturally to a probabilistic Kitagawa type diagram, which explains the relationship between the fatigue behaviour of the material and the different casting processes or post-treatments (e.g. gravity casting and HIP). It is shown that the sensitivity to the different loading modes (i.e. uniaxial with and without mean stress, torsion and equibiaxial tension) depends on the microstructural heterogeneities responsible for crack initiation. For a porosity-free alloy, the predictions are very good for combined tension–torsion loading modes. When pores are present and control the fatigue strength, the predictions are very satisfactory for the uniaxial loads with different R-ratios and slightly conservative for multiaxial loads (i.e. torsion and equibiaxial tension). Never-the-less, they are much better than the predictions of the Dang Van criterion [1].
Lien vers la version éditeur: http://www.sciencedirect.com/science/article/pii/S0142112312002472
Tue, 01 Jan 2013 00:00:00 GMThttp://hdl.handle.net/10985/70352013-01-01T00:00:00ZKOUTIRI, ImadeBELLETT, DanielMOREL, FranckPESSARD, EtienneThis article is dedicated to the high cycle fatigue behaviour of cast hypo-eutectic Al–Si alloys and in particular the AlSi7Cu05Mg03 alloy. In a vast experimental campaign undertaken to investigate the fatigue damage mechanisms operating in this alloy, subject to complex loading conditions, it was shown that two different coexisting fatigue damage mechanisms occur in this materials, depending on the presence of different microstructural heterogeneities (i.e. micro-shrinkage pores, Si particles, Fe-rich intermetallic phases, DAS of the Al-matrix, etc.). In order to take into account both of these damage mechanisms, a probabilistic approach using the weakest link concept is introduced to model the competition between the two mechanisms. This approach leads naturally to a probabilistic Kitagawa type diagram, which explains the relationship between the fatigue behaviour of the material and the different casting processes or post-treatments (e.g. gravity casting and HIP). It is shown that the sensitivity to the different loading modes (i.e. uniaxial with and without mean stress, torsion and equibiaxial tension) depends on the microstructural heterogeneities responsible for crack initiation. For a porosity-free alloy, the predictions are very good for combined tension–torsion loading modes. When pores are present and control the fatigue strength, the predictions are very satisfactory for the uniaxial loads with different R-ratios and slightly conservative for multiaxial loads (i.e. torsion and equibiaxial tension). Never-the-less, they are much better than the predictions of the Dang Van criterion [1].Prise en compte du rôle des inclusions non métalliques dans le comportement anisotrope en fatigue d’aciers forgés
http://hdl.handle.net/10985/6889
Prise en compte du rôle des inclusions non métalliques dans le comportement anisotrope en fatigue d’aciers forgés
PESSARD, Etienne; MOREL, Franck; MOREL, Anne
L’objectif de cette étude est de proposer un critère de fatigue anisotrope pour le dimensionnement en fatigue de pièces industrielles forgées. Des résultats de différentes campagnes d’essais obtenus sur 3 nuances d’acier laminés sont tout d’abord présentés. Une attention particulière est portée à l’observation et à l’analyse des mécanismes d’amorçage à l’origine du comportement anisotrope en fatigue. Un critère de fatigue probabiliste permettant de tenir compte de la compétition possible entre différents types de mécanismes d’amorçage est ensuite développé. Ce critère permet notamment de tracer un diagramme de type Kitagawa probabiliste.
Fri, 01 Jan 2010 00:00:00 GMThttp://hdl.handle.net/10985/68892010-01-01T00:00:00ZPESSARD, EtienneMOREL, FranckMOREL, AnneL’objectif de cette étude est de proposer un critère de fatigue anisotrope pour le dimensionnement en fatigue de pièces industrielles forgées. Des résultats de différentes campagnes d’essais obtenus sur 3 nuances d’acier laminés sont tout d’abord présentés. Une attention particulière est portée à l’observation et à l’analyse des mécanismes d’amorçage à l’origine du comportement anisotrope en fatigue. Un critère de fatigue probabiliste permettant de tenir compte de la compétition possible entre différents types de mécanismes d’amorçage est ensuite développé. Ce critère permet notamment de tracer un diagramme de type Kitagawa probabiliste.