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

A fatigue multi-site cracks model using coalescence, short and long crack growth laws, for anodized aluminum alloys

It has been shown that decrease of the fatigue life of aluminium alloys treated with anodization can be explained by the degradation of surface condition due to pickling. In order to predict fatigue life of anodized aluminium alloys, a multi-site crack growth model is developed by considering the pickling pits sites as initial flaws from which fatigue cracks develop. A map of the pickled surface is built from topography measurement with a contact profilometer. Then the pits are detected and their sizes are defined (depth, length and width). At the beginning of the calculation, a short crack growth law is used for crack having depths less than grain size. Then Paris long crack growth law is used. The coalescence of cracks is considered when their lengths increased by its crack tip plastic zone are large enough to interact with other neighbouring short cracks. The fatigue life is calculated for Kmax achieving 70 % KIC

Fatigue analysis-based numerical design of stamping tools made of cast iron

This work concerns stress and fatigue analysis of stamping tools made of cast iron with an essentially pearlitic matrix and containing foundry defects. Our approach consists at first, in coupling the stamping numerical processing simulations and structure analysis in order to improve the tool stiffness geometry for minimizing the stress state and optimizing their fatigue lifetime. The method consists in simulating the stamping process by considering the tool as a perfect rigid body. The estimated contact pressure is then used as boundary condition for FEM structure loading analysis of the tool. The result of this analysis is compared with the critical stress limit depending on the automotive model. The acceptance of this test allows calculating the fatigue lifetime of the critical zone by using the S–N curve of corresponding load ratio. If the prescribed tool life requirements are not satisfied, then the critical region of the tool is redesigned and the whole simulation procedures are reactivated. This method is applied for a cast iron EN-GJS-600-3. The stress-failure (S–N) curves for this material is determined at room temperature under push pull loading with different load ratios R0σmin/σmax0−2, R0−1 and R00.1. The effects of the foundry defects are determined by SEM observations of crack initiation sites. Their presence in tested specimens is associated with a reduction of fatigue lifetime by a factor of 2. However, the effect of the load ratio is more important

Properties of the positive column of a glow discharge in flowing hydrogen

Results of a theoretical model for predicting the effects of gas flow on the properties of the positive column in a glow discharge are presented. A cylindrical discharge at low pressure (≤ 30 torr) in a hydrogen flow is considered. The two-dimensional model couples electric and molecular properties of the discharge through E/N, the ratio of electric field to neutral gas density. It predicts the electric field and the discharge voltage as a function of pressure, flow velocity, diameter and length of the discharge and current. Molar flow rates of vibrationally excited H2 molecules and H atoms produced by the discharge are calculated. Comparison with available experimental data is made.Les résultats d'un modèle théorique destiné à prévoir les effets de l'écoulement du gaz sur les propriétés de la colonne positive d'une décharge « glow » dans l'hydrogène sont présentés. On considère une décharge à basse pression (≤ 30 torrs) dans un écoulement d'hydrogène. Le modèle est à 2 dimensions et les propriétés électriques et moléculaires de la décharge sont couplées entre elles par l'intermédiaire de E/N, le rapport du champ électrique à la densité des neutres. Le modèle prédit le champ électrique et la tension de décharge en fonction de la pression, de la vitesse d'écoulement, du diamètre et de la longueur du tube et du courant. Les débits molaires de molécules H2(v = 1) et d'atomes H produits par la décharge sont calculés. Une comparaison avec les résultats expérimentaux disponibles est effectuée

A THEORETICAL AND EXPERIMENTAL STUDY OF A C.W.HC1 CHEMICAL LASER

Un modèle de calcul pour un laser chimique HCl continu à l'initiation électrique est présenté. Ce modèle utilise les divers processus chimiques et moléculaires nécessaires à une description complète des performances laser suivant la direction de 1'écoulement. Les valeurs approchées des degrés de dissociation et d'excitation vibrationnelle de H2 à la sortie des tubes à décharge sont obtenues à partir d'une analyse numérique bidimensionnelle de la décharge auto-entretenue. L'importance de la réaction Cl + H2(V = 1) → HCl (V = 1 ) + H sur le coefficient d'amplification de la bande 1-0 est soulignée. La distribution spectrale et la puissance laser totale ont été mésurées. Un accord satisfaisant entre les valeurs expérimentales et celles prédites par le calcul est observé.A computer model for an electrically initiated cw HCl chemical laser is presented. This model employs finite kinetics for the various pumping and molecular energy transfer processes required for a complete description of the laser performance along the flow direction. Reasonable estimates for the degrees of dissociation and vibrationnal excitation of H2 at the exit of the discharge tubes are obtained from a two-dimensional computer analysis of the self-sustained discharge. Emphasis is made on the influence of the reaction Cl + H2 (v = 1) → HCl (v = 1 ) + H on the gain coefficients for the 1-0 vibrational band. The output spectrum and the total output laser power was measured. Good agreement between experimental measurements and the computer simulation is observed

Paris law state-parameter identification based on the EKF

International audienc

Surfaces usinées: cas d'aillages d'aluminium aéronautiques

International audienceno abstrac

Machining parameters effects on surface and fatigue life of Aluminum alloy aeronautical parts

International audienceno abstrac

Machining parameters effects on surface and fatigue life of Aluminum alloy aeronautical parts

International audienceno abstrac