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SAM captures, stores, indexes, preserves, and distributes digital research material.Thu, 20 Sep 2018 17:07:27 GMT2018-09-20T17:07:27ZOxidation induced changes in viscoelastic properties of a thermostable epoxy matrix
http://hdl.handle.net/10985/8226
TEREKHINA, Svetlana; MILLE, Marion; FAYOLLE, Bruno; COLIN, Xavier
Polymer Science - Series A
The thermal ageing of a neat epoxy matrix has been studied at 200°C in air by three complementary analytical techniques: optical microscopy, mechanical spectrometry and nano-indentation. Thermal oxidation is restricted in a superficial layer of about 195 µm of maximal thickness. It consists in a predominant chain scission process involving, in particular, chemical groups whose β motions have the highest degree of cooperativity and thus, are responsible for the high temperature side of β dissipation band. As a result, chain scissions decrease catastrophically the glass transition temperature, but also increase significantly the storage modulus at glassy plateau between Tβ and Tα. This phenomenon is called “internal antiplasticization”.
Starting from these observations, the Di Marzio and Gilbert’s theories have been used in order to establish relationships between the glass transition temperature and number of chain scissions, and between the storage modulus and β transition activity respectively. The challenge is now to establish a relationship between the transition activity and the concentration of the corresponding chemical groups
Thu, 07 Feb 2013 00:00:00 GMThttp://hdl.handle.net/10985/82262013-02-07T00:00:00ZTEREKHINA, SvetlanaMILLE, MarionFAYOLLE, BrunoCOLIN, XavierThe thermal ageing of a neat epoxy matrix has been studied at 200°C in air by three complementary analytical techniques: optical microscopy, mechanical spectrometry and nano-indentation. Thermal oxidation is restricted in a superficial layer of about 195 µm of maximal thickness. It consists in a predominant chain scission process involving, in particular, chemical groups whose β motions have the highest degree of cooperativity and thus, are responsible for the high temperature side of β dissipation band. As a result, chain scissions decrease catastrophically the glass transition temperature, but also increase significantly the storage modulus at glassy plateau between Tβ and Tα. This phenomenon is called “internal antiplasticization”.
Starting from these observations, the Di Marzio and Gilbert’s theories have been used in order to establish relationships between the glass transition temperature and number of chain scissions, and between the storage modulus and β transition activity respectively. The challenge is now to establish a relationship between the transition activity and the concentration of the corresponding chemical groupsÉtude numérique du comportement en fatigue à grand nombre de cycles d’agrégats polycristallins de cuivre
http://hdl.handle.net/10985/8269
ROBERT, Camille; SAINTIER, Nicolas; PALIN-LUC, Thierry; MOREL, Franck
Mécanique & Industries
Numerical study of high cycle fatigue behaviour of copper polycrystalline aggre-
gates. An analysis of high cycle fatigue behaviour is undertaken via the numerical simulation of polycrystalline aggregates. The metallic material chosen for investigation is Copper, which has a FCC crystalline structure. The REV, which is composed of 300 randomly orientated equiaxed grains, is loaded at the fatigue limit determined at 10/7 cycles. The aim is to calculate the mechanical quantities at the mesoscopic scale (average quantities in the grains) after cyclic stabilisation has been achieved. The results highlight the fact that the mechanical quantities at this scale have a large scatter. A statistical analysis of the response of the aggregate for different loading conditions (tensile, torsion, and in-phase tension-torsion) is done. Thanks to the sufficiently large number of different microstructures investigated, a critical analysis of the Dang Van and Crossland multiaxial fatigue criteria has been undertaken, using the local mechanical quantities.
Sat, 01 Jan 2011 00:00:00 GMThttp://hdl.handle.net/10985/82692011-01-01T00:00:00ZROBERT, CamilleSAINTIER, NicolasPALIN-LUC, ThierryMOREL, FranckNumerical study of high cycle fatigue behaviour of copper polycrystalline aggre-
gates. An analysis of high cycle fatigue behaviour is undertaken via the numerical simulation of polycrystalline aggregates. The metallic material chosen for investigation is Copper, which has a FCC crystalline structure. The REV, which is composed of 300 randomly orientated equiaxed grains, is loaded at the fatigue limit determined at 10/7 cycles. The aim is to calculate the mechanical quantities at the mesoscopic scale (average quantities in the grains) after cyclic stabilisation has been achieved. The results highlight the fact that the mechanical quantities at this scale have a large scatter. A statistical analysis of the response of the aggregate for different loading conditions (tensile, torsion, and in-phase tension-torsion) is done. Thanks to the sufficiently large number of different microstructures investigated, a critical analysis of the Dang Van and Crossland multiaxial fatigue criteria has been undertaken, using the local mechanical quantities.High cycle fatigue damage mechanisms in cast aluminium subject to complex loads
http://hdl.handle.net/10985/6916
KOUTIRI, Imade; BELLETT, Daniel; MOREL, Franck; AUGUSTINS, Louis; ADRIEN, Jérôme
International Journal of Fatigue
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
Fri, 01 Feb 2013 00:00:00 GMThttp://hdl.handle.net/10985/69162013-02-01T00:00:00ZKOUTIRI, 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
KOUTIRI, Imade; BELLETT, Daniel; MOREL, Franck; PESSARD, Etienne
International Journal of Fatigue
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
Fri, 01 Feb 2013 00:00:00 GMThttp://hdl.handle.net/10985/70352013-02-01T00:00:00ZKOUTIRI, 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
PESSARD, Etienne; MOREL, Franck; MOREL, Anne
Revue de métallurgie
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.Competition between microstructure and defect in multiaxial high cycle fatigue
http://hdl.handle.net/10985/10058
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.
Pas d'embargo connu sur Sherpa Romeo
Mon, 01 Jun 2015 00:00:00 GMThttp://hdl.handle.net/10985/100582015-06-01T00:00:00ZMOREL, 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.Constitutive Modelling of AZ31B-O Magnesium Alloy for Cryogenic Machining
http://hdl.handle.net/10985/7176
GIRAUD, Eliane; ROSSI, Frédéric; GERMAIN, Guénaël; OUTEIRO, José
The success of a FE model for metal cutting process is strongly dependent on the accurate characterization of the workpiece material, under similar conditions as those found in metal cutting. In this paper, dynamic shear tests using a Gleeble machine have been performed on 4 mm thickness disks of AZ31B-O magnesium alloy, using a special designed tool. In order to include the effects of the cryogenic cooling in the material behavior, the specimens have been submitted to temperatures ranging from -25ºC to 400ºC. A Johnson-Cook constitutive model has then been identified in order to describe the flow stress in machining.
Lien vers la version éditeur: http://www.sciencedirect.com/science/article/pii/S2212827113004216
Sat, 01 Jun 2013 00:00:00 GMThttp://hdl.handle.net/10985/71762013-06-01T00:00:00ZGIRAUD, ElianeROSSI, FrédéricGERMAIN, GuénaëlOUTEIRO, JoséThe success of a FE model for metal cutting process is strongly dependent on the accurate characterization of the workpiece material, under similar conditions as those found in metal cutting. In this paper, dynamic shear tests using a Gleeble machine have been performed on 4 mm thickness disks of AZ31B-O magnesium alloy, using a special designed tool. In order to include the effects of the cryogenic cooling in the material behavior, the specimens have been submitted to temperatures ranging from -25ºC to 400ºC. A Johnson-Cook constitutive model has then been identified in order to describe the flow stress in machining.A mechanistic approach to the Kitagawa-Takahashi diagram using a multiaxial probabilistic framework
http://hdl.handle.net/10985/7416
PESSARD, Etienne; BELLETT, Daniel; MOREL, Franck; KOUTIRI, Imade
Engineering Fracture Mechanics
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.
Sun, 15 Sep 2013 00:00:00 GMThttp://hdl.handle.net/10985/74162013-09-15T00:00:00ZPESSARD, 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.An experimental investigation of the behaviour of steels over large temperature and strain rate ranges
http://hdl.handle.net/10985/8604
HOR, Anis; MOREL, Franck; LEBRUN, Jean-Lou; GERMAIN, Guénaël
International Journal of Mechanical Sciences
During forging and machining manufacturing processes, the material is subject to large strains at high strain rates which provoke local heating and microstructural changes. Modelling of these phenomena requires precise knowledge of the stress–strain constitutive equations for a large range of strains, strain rates and temperatures. An experimental study of the rheology of both hyper- and hypo-eutectoid steels (with different microstructures) over a temperature range from 20°C to 1000°C and with strain rates from 0.01 to 100 000 s-1 has been undertaken. These tests were performed in compression on cylindrical specimens and in shear using hat-shaped specimens. Both a GLEEBLE 3500 thermomechanical testing machine and a Split-Hopkinson Pressure Bar apparatus were used. From these tests, three deformation domains have been identified as a function of the material behaviour and of the changes in the deformed microstructure. Each domain was characterized by its behaviour, including the competition between hardening and softening, strain rate sensitivity on the flow stress and the softening phenomenon (i.e. recrystallisation or recovery, etc.). Finally, based on thermodynamical considerations, the conditions of thermoplastic instability (i.e. shear bands, twinning, heterogeneities, etc.) and microstructural changes are highlighted using process maps of the dissipated power repartition.
Fri, 01 Feb 2013 00:00:00 GMThttp://hdl.handle.net/10985/86042013-02-01T00:00:00ZHOR, AnisMOREL, FranckLEBRUN, Jean-LouGERMAIN, GuénaëlDuring forging and machining manufacturing processes, the material is subject to large strains at high strain rates which provoke local heating and microstructural changes. Modelling of these phenomena requires precise knowledge of the stress–strain constitutive equations for a large range of strains, strain rates and temperatures. An experimental study of the rheology of both hyper- and hypo-eutectoid steels (with different microstructures) over a temperature range from 20°C to 1000°C and with strain rates from 0.01 to 100 000 s-1 has been undertaken. These tests were performed in compression on cylindrical specimens and in shear using hat-shaped specimens. Both a GLEEBLE 3500 thermomechanical testing machine and a Split-Hopkinson Pressure Bar apparatus were used. From these tests, three deformation domains have been identified as a function of the material behaviour and of the changes in the deformed microstructure. Each domain was characterized by its behaviour, including the competition between hardening and softening, strain rate sensitivity on the flow stress and the softening phenomenon (i.e. recrystallisation or recovery, etc.). Finally, based on thermodynamical considerations, the conditions of thermoplastic instability (i.e. shear bands, twinning, heterogeneities, etc.) and microstructural changes are highlighted using process maps of the dissipated power repartition.Reliability approach for safe designing on a locking system
http://hdl.handle.net/10985/8651
MEALIER, Nicolas; DAU, Frédéric; GUILLAUMAT, Laurent; ARNOUX, Philippe
Probabilistic engineering mechanics
The aim of this work is to predict the failure probability of a locking system. This failure probability is assessed using complementary methods: the First-Order Reliability Method (FORM) and Second-Order Reliability Method (SORM) as approximated methods, and Monte Carlo simulations as the reference method. Both types are implemented in a specific software [Phimeca software. Software for reliability analysis developed by Phimeca Engineering S.A.] used in this study. For the Monte Carlo simulations, a response surface, based on experimental design and finite element calculations [Abaqus/Standard User’s Manuel vol. I.], is elaborated so that the relation between the random input variables and structural responses could be established. Investigations of previous reliable methods on two configurations of the locking system show the large sturdiness of the first one and enable design improvements for the second one.
Fri, 01 Jan 2010 00:00:00 GMThttp://hdl.handle.net/10985/86512010-01-01T00:00:00ZMEALIER, NicolasDAU, FrédéricGUILLAUMAT, LaurentARNOUX, PhilippeThe aim of this work is to predict the failure probability of a locking system. This failure probability is assessed using complementary methods: the First-Order Reliability Method (FORM) and Second-Order Reliability Method (SORM) as approximated methods, and Monte Carlo simulations as the reference method. Both types are implemented in a specific software [Phimeca software. Software for reliability analysis developed by Phimeca Engineering S.A.] used in this study. For the Monte Carlo simulations, a response surface, based on experimental design and finite element calculations [Abaqus/Standard User’s Manuel vol. I.], is elaborated so that the relation between the random input variables and structural responses could be established. Investigations of previous reliable methods on two configurations of the locking system show the large sturdiness of the first one and enable design improvements for the second one.