A predictive fatigue life model for anodized 7050 aluminium alloy

The objective of this study is to predict fatigue life of anodized 7050 aluminum alloy specimens. In the case of anodized 7050-T7451 alloy, fractographic observations of fatigue tested specimens showed that pickling pits were the predominant sites for crack nucleation and subsequent failure. It has been shown that fatigue failure was favored by the presence of multiple cracks. From these experimental results, a fatigue life predictive model has been developed including multi-site crack consideration, coalescence between neighboring cracks, a short crack growth stage and a long crack propagation stage. In this model, all pickling pits are considered as potential initial flaws from which short cracks could nucleate if stress conditions allow. This model is built from experimental topography measurements of pickled surfaces which allowed to detect the pits and to characterize their sizes (depth, length, width). From depth crack propagation point of view, the pickling pits are considered as stress concentrator during the only short crack growth stage. From surface crack propagation point of view, machining roughness is equally considered as stress concentrator and its influence is taken into account during the all propagation stage. The predictive model results have been compared to experimental fatigue data obtained for anodized 7050-T7451 specimens. Predictions and experimental results are in good agreement

Surface characterization and influence of anodizing process on fatigue life of Al 7050 alloy

The present study investigates the influence of anodizing process on fatigue life of aluminium alloy 7050-T7451 by performing axial fatigue tests at stress ratio ‘R’ of 0.1. Effects of pre-treatments like degreasing and pickling employed prior to anodizing on fatigue life were studied. The post-exposure surface observations were made by scanning electron microscope (SEM) to characterize the effect of each treatment before fatigue testing. The surface observations have revealed that degreasing did not change the surface topography while pickling solution resulted in the formation of pits at the surface. Energy dispersive spectroscopy (EDS) was used to identify those constituent particles which were responsible for the pits formation. These pits are of primary concern with respect to accelerated fatigue crack initiation and subsequent anodic coating formation. The fatigue test results have shown that pickling process was detrimental in reducing the fatigue life significantly while less decrease has been observed for anodized specimens. Analyses of fracture surfaces of pickled specimens have revealed that the process completely changed the crack initiation mechanisms as compared to non-treated specimens and the crack initiation started at the pits. For most of the anodized specimens, fatigue cracks still initiated at the pits with very few cracks initiated from anodic coating. The decrease in fatigue life for pickled and anodized specimens as compared to bare condition has been attributed to decrease in initiation period and multi-site crack initiations. Multi-site crack initiation has resulted in rougher fractured surfaces for the pickled and anodized specimens as compare to bare specimens tested at same stress levels

Asynchronous Communications in MPI - the BIP/Myrinet Approach

In this paper, we present our experiments on asynchronous communications using the BIP and MPI interfaces on a cluster of PCs connected with a Myrinet network. We describe the implementation details of those communication- s and point the problems and solutions

Multiaxial fatigue behavior of 2618 aluminum alloy

The purpose of the present research project is to study multiaxial fatigue behavior of 2618 alloy. The influence of mean stress on the fatigue behavior under tension and torsion is particularly investigated. Fatigue tests under combined tensile-torsion, in or out of phase, as well as combined tensile-torsion-internal pressure tests have also been conducted. Multiaxial fatigue results are analyzed according to Fatemi-Socie criterion to predict the fatigue life

Programmation Haute Performance pour Architectures hybrides

National audienceProposer un modèle de distribution des calculs et des données et générer de façon semi-automatique un code parallèle efficace en consommation mémoire et en temps d'exécution

A Legislação Francesa de proteção à criança de 0 a 6 anos

Apresentar a legislação francesa deproteção à infancia (limitada à pequena infancia), implica em retomar rapidamente a evolução histórica de nossa legislação. Este retomar permite ao autor recuperar as grandes tendências que conformam a ossatura da política de proteç50 à infancia hoje, na França a permanência no domicilio, o direito dos usuários, aprevenção dos maus tratos. A organização administrativa e judiciária da proteção à infancia nas França, que permite colocar em prática esta política, em particular depois da descentralização, é descrita, ressaltando-se o papel desempenhado pelo setor comunitário (não governamental) nesta organização. No contexto de uma reflexão sobre a formação de alores no campo, junto à primeira infância, o autor se interroga sobre a legislação de proteção à infancia no Brasil e a importância de uma formação no referente a estes aspectos de legislação e de regulamentação.Présenter la législation française deprotection de l’enfance (limitée à la petite enfance), implique de faire un retour rapide sur l’évolution historique de notre législation. Ce retourperrnet à l’auteur de repérer les grandes tendances qui font l’ossature de la politique de protection de l’enfance aujourd’hui en France: le maintien à domicile, te droit des usagers,la prévention des mauvais traitements.L’organisation administrative et judiciaire de la protection de l’enfance en France, pem^lettant de mettre en oeuvre cette politique, en par~i^c^u^lier depuis la décentralisation; est décrite, soulignant le rôle joué par le secteur associatif (non gouvernemental) dans cette organisation.Dans le cadre d’une réflexion sur la formation d’acteurs de terrain auprès de la petite enfance, l’auteur s’interroge sur la législation de protectiOn de l’enfance au Brésil etl’importanced’uneformation surces aspects de législation et de règlementation

Influence of anodizing process on fatigue life of a machined aluminium alloy

In order to investigate the coupled effects of machining and anodizing processes on fatigue life of alloy 7010-T7451, a series of rotating bending fatigue tests were conducted at 60Hz. In the as machined condition, test results showed that fatigue life is surface roughness dependent and that fatigue life decreases with an increase in surface roughness and this effect is found to be more pronounced in high cycle fatigue where major portion of fatigue life is consumed in nucleating the cracks. Effects of pretreatments, like degreasing and pickling employed prior to anodizing, on fatigue life of the given alloy were also studied. Results demonstrated that degreasing showed no change in fatigue life while pickling had negative impact on fatigue life of specimens. The small decrease in fatigue life of anodized specimens as compare to pickled specimens is attributed to brittle and microcracking of the coating. Scanning electron microscopic (SEM) examination revealed multi-site crack initiation for the pickled and anodized specimens. SEM examination showed that pickling solution attacked the grain boundaries and intermetallic inclusions present on the surface resulting in pits formation. These pits are of primary concern with respect to accelerated fatigue crack nucleation and subsequent anodized coating formation

Influence du décapage sur la tenue en fatigue de l'alliage Al7010-T7451 traité par oxydation anodique chromique

L’oxydation anodique chromique (OAC) est un procédé de traitement des alliages d’aluminium pour améliorer leur tenue à la corrosion. L’influence de ce traitement sur la durée de vie de l’alliage 7010-T7451 est étudiée à partir d’essais de fatigue en flexion rotative. Une réduction de la durée de vie par rapport à l’état usiné est observée. Il est montré que cette diminution de la durée de vie est imputable en grande partie à la dégradation de la rugosité de la surface occasionnée par la phase de décapage. Il est également montré que la correction des résultats de fatigue par le coefficient de concentration de contrainte local, déterminé par la méthode des éléments finis à partir du relevé du profil de rugosité, permet de rationaliser les courbes de fatigue de cet alliage : l’ensemble des résultats d’essais obtenus sur des éprouvettes n’ayant rien subi après l’usinage ou n’ayant subi que les phases de dégraissage et de décapage s’alignent sur une même courbe de fatigue maîtresse. Il est également montré que, traités par cette méthode du Ktlocal, les résultats de la durée de vie obtenus sur des éprouvettes décapées puis anodisées s’alignent sur une deuxième courbe décalée par rapport à cette courbe maîtresse

Modélisation de la multi-fissuration d’un alliage d’aluminium 7010 traité par oxydation anodique chromique

L’oxydation anodique chromique (OAC) est un procédé de traitement des alliages d’aluminium pour améliorer leur tenue à la corrosion mais il entraîne une très forte réduction de la durée de vie par rapport à l’état usiné. Cette diminution de la durée de vie est largement imputable à la dégradation de la rugosité de la surface occasionnée par la phase de décapage. La présente étude est consacrée à la modélisation de la fissuration à partir des piqûres de décapage observées à la surface d’échantillon en alliage 7010 traités puis testés en flexion rotative. Ces piqûres de décapage sont caractérisées par mesures topographiques. Ces topographies servent à élaborer des modèles éléments finis qui permettent de déterminer la contrainte locale maximale au droit de ces piqûres. Dans le modèle de calcul en fatigue, ces piqûres sont considérées comme des microfissures qui, en se propageant aussi bien en surface qu’en profondeur, peuvent coalescer avant de poursuivre leur propagation. Le calcul en fatigue est stoppé à la fin du stade II de la propagation

Study and modelling of anodized 2618 aluminum behavior subjected to multiaxial fatigue

Anodized Aluminum alloys are widely used in aeronautic construction due to their specificmechanical properties. However, anodization process often leads to a decrease of the fatigue resistance of the alloys. In order to identify and characterize the different mechanisms involved in the detrimental effect of anodization of 2618-T851 alloy on its fatigue life and to determine the impact of loading nature, several tests have been performedon specimens with different surface states at various stress ratios. It was found that roughness of machining has no effect unlike the stress ratio or mean stress in tensiletests. Thetests on the pickled, anodized, impregnated and sealedspecimens showed it was the anodic oxidation step which was the more detrimental for fatigue resistance under tensile loading comparing to the other steps. It has been also observed that no suchdetrimental effect occurred under torsion loading. Concerning the prediction of fatigue life, two critical plane-based analysis approaches have been used (Morel and Fatemi-Socie criteria) to make fatigue life prediction for uniaxial and multiaxial fatigue test. Comparisons showed that both criteria gives overestimated fatigue life for uniaxial tensile loading under compression mean stress and underestimated fatigue life for tensile-torsion in phase loading