Experimental and numerical investigations into the behaviour of a 7175-T7351 aluminium alloy for aerospace gearbox housing applications at elevated temperatures

The 7175-T7351 aluminium alloy was studied to determine its suitability for the step-aside gearbox housing on the Rolls Royce Trent 1000 engine. The industrial motivation of this work was to reduce the weight of the gearbox housing using this lightweight material to ultimately improve the specific fuel consumption of the aircraft. This involved obtaining the mechanical properties of the aluminium alloy via a series of uniaxial mechanical tests with parameters based on the operating conditions of the gearbox housing during a typical flight cycle. Furthermore, a constitutive viscoplasticity model, with the inclusion of material ageing parameters, was developed to predict the material’s cyclic response under strain-controlled isothermal fatigue conditions at the gearbox housing’s operating temperatures. With this capability, a prediction for when the strength of the gearbox housing falls below the required design strength for safe use could be made. The room temperature hardness tests demonstrated the effect of time spent at elevated temperatures on the material’s hardness. It was found that the higher the soak temperature, the greater the initial rate of decrease in room temperature hardness and the lower the asymptotic value of hardness that was reached. For example, up to 24 hours of soaking at 200◦ C, the hardness decreased by 33%, and up to 1000 hours the hardness had decreased by 55%. For the same durations at 180◦ C, the hardness decrease was 17% and 47% respectively. Soaking at 120◦ C had an insignificant effect on the hardness of the material, indicating that the microstructure was thermally stable. Hardness testing could be used as a method to assess the strength of the gearbox housing for service monitoring during certifcation. Similar to the hardness tests, the elevated temperature tensile test results also revealed degradation in the mechanical strength of the alloy after prior soaking at elevated temperatures. The tests at 200◦ C on the as-received material decreased the yield stress by 31% and after soaking at test temperature for 20 hours prior to testing, the yield strength dropped by 52%. After a 2 hour temperature, the yield stress decreased from 220MPa to 165MPa which is alarming since the gearbox housing spends about 18 minutes at 200◦ C and 190MPa during climb. This suggests that in less than 6 flight cycles, the material’s strength will fall below the maximum operating stress of the gearbox housing and will be unsafe for continued use. Samples were soaked for up to 400 hours at 200◦ C and prepared for microstructural analysis. EBSD images showed that the grains were no significantly affected by the temperature exposure and showed no signs of coarsening. TEM and EDX analysis revealed that the majority of the particles within the grains were zinc-magnesium rich particles and were assumed to be MgZn 2 precipitates based on the TEM particle identification. The precipitate size and inter-particle spacing were found to increase with soak time. The change in monotonic yield strength was therefore attributed to the coarsening of these precipitates. The material characterisation suggested that, although the 7175-T7351 aluminium alloy initially appeared to have desirable mechanical properties, it is unsuitable for this or similar applications due to the rapid decrease in strength and thermally unstable microstructure. Furthermore, if an aluminium alloy is considered for this application, then it may be vital to account for material ageing behaviour. The unified, uniaxial viscoplasticity Chaboche model was implemented to predict the material response strain-controlled isothermal fatigue tests at 160◦ C and 200 ◦ C. A material ageing term was added to the model to account for the material ageing that decreased the yield strength with time. With this addition, two assumptions were made: 1) material ageing only affects isotropic hardening and 2) isotropic hardening can be de-coupled into material ageing (as a function of time at elevated temperature) and mechanical softening (a function of accumulated plastic strain). The tests at 160◦ C and 200◦ C showed that numerical and experimental results were in good agreement, providing accurate isothermal cyclic stress behaviour of the 7175-T7351 aluminium alloy. Furthermore, it was shown that the mechanical softening and material ageing components could be de-coupled. However, when the model was used to predict stress-controlled isothermal fatigue data and a cyclic stress relaxation tests, a number of deficiencies arose. The predicted ratcheting and ageing rate was greater than expected. The material ageing term may require an additional function to change the ageing rate depending on whether the material is elastically or plastically loaded. Norton’s creep power law could not predict term long stress relaxation behaviour but it was sufficient enough to describe to short- term viscous effects under the strain-controlled fatigue conditions. Despite these deficiencies, the model provided an initial point for a unified, viscoplasticity model for the 7175-T7351 alloy. Due to the rapid ageing of the material, the model could be used to predict if or when a material’s strength is unsuitable for safe operating use

Optical diamond turning of rapidly solidified aluminium alloy grade - 431

The high demand for ultraprecision machining systems is increasing day by day. The technology leads to increased productivity and quality manufactured products, with an excellent surface finish. Therefore, these products are in demand in many industrial fields such as space, national defence, the medical industry and other high-tech industries. Single point diamond turning (SPDT) is the core technology of ultraprecision machining, which makes use of single-point crystalline diamond as a cutting tool. This technique is used for machining an extensive selection of complex optical surfaces and other engineering products with a quality surface finish. SPDT can achieve dimensional tolerances in order of 0.01um and surface roughness in order of 1nm. SPDT is not restricted, but mostly applicable, to non-ferrous alloys; due to their reflective properties and microstructure that discourages tool wear. The focus of this study is the development of predictive optimisation models, used to analyse the influence of machining parameters (speed, feed, and depth of cut) on surface roughness. Moreover, the study aims to obtain the optimal machining parameters that would lead to minimum surface roughness during the diamond turning of Rapidly Solidified Aluminium (RSA) 431. In this study, Precitech Nanoform 250 Ultra grind machine was used to perform two experiments on RSA 431. The first machining process, experiment 1, was carried out using pressurized kerosene mist; while experiment 2 was carried out with water as the cutting fluid. In each experiment, machine parameters were varied at intervals and the surface roughness of the workpiece was measured at each variation. The measurements were taken through a contact method using Taylor Hobson PGI Dimension XL surface Profilometer. Acoustic emission (AE) was employed as a precision sensing technique – to optimize the machining quality process and provide indications of the expected surface roughness. The results obtained revealed that better surface roughness can be generated when RSA 431 is diamond-turned using water as a cutting fluid, rather than kerosene mist. Predictive models for surface roughness were developed for each experiment, using response surface methodology (RSM) and artificial neural networks (ANN). Moreover, RSM was used for optimisation. Time domain features acquired from AE signals, together with the three cutting parameters, were used as input parameters in the ANN design. The results of the predictive models show a close relationship between the predicted values and the experimental values for surface roughness. The developed models have been compared in terms of accuracy and cost of computation - using the mean absolute percentage error (MAPE)

Effect of homogenization and alloying elements on hot deformation behaviour of 1XXX series aluminum alloys = Effet des éléments d'alliage et d'homogénéisation sur le comportement à la déformation à chaud des alliages d'aluminium de la série 1XXX

The 1xxx series of aluminum alloys are widely used for applications in which excellent formability and thermal and electrical conductivity are required such as heatexchanger tubing and coaxial cable sheathing. The demand for high productivity during processing leads to the requirement for an increase in hot workability to provide low flow stress with desirable final mechanical properties. Commercially, D.C cast billets are typically homogenized prior to extrusion or rolling to improve hot workability and mechanical properties. However, there is very limited prior work on the effectiveness of the homogenization treatment in 1xxx alloy production. Furthermore, no systematic investigation of the influence of different alloying elements (Fe, Si, Mn and Cu) on the hot deformation behavior of dilute Al-Fe-Si alloys is available in the literature. In the present study, the effect of different alloying elements as well as the homogenization treatment on the hot workability and microstructure of dilute Al-Fe-Si alloys was investigated using hot compression tests, optical microscopy, SEM, electron EBSD, TEM, electrical conductivity measurements. The effect of the homogenization treatment on the microstructure and hot workability of two dilute Al-Fe-Si alloys was first investigated. Homogenization promoted the phase transformation from the metastable AlmFe or α-AlFeSi phase to the Al3Fe equilibrium phase and induced a significant change in solute levels in the solid solution. Homogenization at 550°C significantly reduced the solid solution levels due to the elimination of the supersaturation originating from the cast ingot and produced the lowest flow stress under all of the deformation conditions studied. An increase in the homogenization temperature from 550 to 630°C increased the flow stress by 10 to 23% and 15 to 45% for the Al-0.3Fe-0.1Si and Al-0.3Fe-0.25Si alloys, respectively, over the range of deformation conditions examined. The hot deformation behavior of dilute Al-Fe-Si alloys containing different amounts of Fe (0.1 to 0.7 wt%) and Si (0.1 to 0.25 wt%) was studied by uniaxial compression tests conducted at various temperatures (350-550 °C) and strain rates (0.01-10 s-1). The flow stress of the 1xxx alloys increased with increasing Fe and Si content. Increasing the Fe content from 0.1 to 0.7% raised the flow stress by 11-32% in Al-Fe-0.1Si alloys, whereas the flow stress increased 5-14% when the Si content increased from 0.1 to 0.25% in Al-0.1Fe-Si alloys. The experimental stress-strain data were employed to drive constitutive equations correlating flow stress, deformation temperature and strain rate considering the influence of the chemical composition. The microstructural analysis results revealed that dynamic recovery is the sole softening mechanism during hot deformation of dilute Al-Fe-Si alloys. Increasing the Fe and Si content retarded dynamic recovery and resulted in a decrease in the subgrain size and mean misorientation angle of the boundaries. Furthermore, the hot deformation behavior of dilute Al-Fe-Si alloys containing various Mn (0.1 and 0.2 wt%) and Cu (0.05, 0.18 and 0.31 wt%) contents was also investigated. It was found that both manganese and copper in solid solution have a significant influence on the hot workability of dilute Al-Fe-Si alloys. On a wt% basis, Mn exhibits a stronger strengthening effect compared to Cu. The activation energies for deformation were calculated from experimental data for all the alloys investigated. With a 0.2 wt% Mn addition, the activation energy increased from 161 and 176 kJ/mol for low-Fe (0.1wt%) and high-Fe (0.5wt%) base alloys to 181 and 192 kJ/mol, respectively. The addition of Cu up to 0.31 wt% only slightly increased the activation energy of low-Fe base alloy from 161 to 166 kJ/mol. Solute diffusion acted as the deformation rate controlling mechanism in these dilute alloys. Mn containing alloys have higher flow stress and higher activation energy due to the considerably lower diffusion rate of Mn in aluminum compared to Cu containing alloys. An addition of Mn and Cu also retarded the dynamic recovery and resulted in a decrease in the subgrain size and mean misorientation angle of the grain boundaries. In addition, based on hot compression tests, an artificial neural network model was developed to predict the high temperature flow behavior of Al-0.12Fe-0.1Si-Cu alloys as a function of chemical composition (with Cu contents of 0.002-0.31wt%) and process parameters. A three-layer feed-forward back-propagation artificial neural network with 20 neurons in a hidden layer was established in this study to predict the flow behavior of Al-0.12Fe-0.1Si alloy with various levels of Cu addition (0.002-0.31wt%) at different deformation conditions. The input parameters were Cu content, temperature, strain rate and strain, while the flow stress was the output. The performance of the proposed model was evaluated using various standard statistical parameters. An excellent agreement between experimental and predicted results was obtained. Sensitivity analysis indicated that the strain rate is the most important parameter, while the Cu content exhibited a modest but significant influence on the flow stress. The ANN model proposed in this study can accurately predict the hot deformation behavior of Al-0.12Fe-0.1Si alloys. Les séries 1xxx des alliages d'aluminium sont largement utilisées pour des applications où une excellente aptitude au formage et de la conductivité thermique et électrique sont nécessaires, tels que les tubes d'échangeur de chaleur et les câbles coaxiaux de revêtement. La demande pour une productivité élevée pendant le traitement conduit à une augmentation de l'aptitude au formage à chaud pour fournir une contrainte d'écoulement faible avec les propriétés mécaniques finales souhaitées. Commercialement, les billettes coulées sont généralement homogénéisés avant l'extrusion ou le laminage à chaud, afin d'améliorer leur fluidité et leurs propriétés mécaniques. Cependant, les travaux de recherche antérieurs restent limités au sujet de l'efficacité du traitement d'homogénéisation dans la production des alliages 1xxx. De plus, aucune étude systématique de l'influence des différents éléments d'alliage (Fe, Si, Mn et Cu) sur le comportement de déformation à chaud des alliages diluées Al-Fe-Si est disponible dans la littérature. Dans la présente étude, l'effet des différents éléments d'alliage ainsi que le traitement d'homogénéisation sur le formage à chaud et la microstructure des alliages dilués Al-Fe-Si ont été étudiés en utilisant des tests de compression à chaud, la microscopie optique, SEM, EBSD, TEM, ainsi que les mesures de conductivité électrique. L'effet du traitement d'homogénéisation sur la microstructure et le formage à chaud de deux alliages diluées Al-Fe-Si a été étudiée. L'homogénéisation a favorisé la transformation de phase à partir de la phase métastable AlmFe ou -AlFeSi vers la phase d'équilibre Al3Fe, et induit un changement significatif des concentrations de soluté dans la solution solide. L'homogénéisation à 550 ° C a significativement réduit les niveaux de solution solide en raison de l'élimination de la sursaturation en provenance du lingot coulé et a produit une contrainte d'écoulement plus basse sous toutes les conditions de déformation étudiées. Une augmentation de la température d'homogénéisation de 550 à 630 ° C augmente la contrainte d'écoulement de 10 à 23% et de 15 à 45% pour les alliages Al-0.3Fe-0.1Si et Al-0.3Fe-0.25Si, respectivement, dans la plage des conditions de déformation examinées. Le comportement à la déformation à chaud des alliages diluées Al-Fe-Si contenant diverses quantités de Fe (0,1 à 0,7% en poids) et Si (0,1 à 0,25% en poids) a été étudié par des tests de compression uniaxiale réalisés à différentes températures (350-550 °C) et des vitesses de déformation (de 0,01 à 10 s-1). La contrainte d'écoulement des alliages 1xxx augmente avec l'augmentation de la teneur en Fe et Si. L'augmentation de la teneur en Fe de 0,1 à 0,7% a augmenté la contrainte d'écoulement de 11 à 32% dans les alliages Al-Fe-0.1Si, tandis que la contrainte d'écoulement a augmenté de 5 à 14% lorsque la teneur en Si est portée de 0,1 à 0,25% dans les alliages Al-0,1 Fe-Si. Les données de contrainte-déformation expérimentales ont été utilisées pour dériver les équations constitutives en corrélation entre la contrainte d'écoulement, la température de déformation et la vitesse de déformation, compte tenu de l'influence de la composition chimique. Les résultats de l'analyse de la microstructure a révélé que le recouvrement dynamique est le seul mécanisme de ramollissement lors de la déformation à chaud des alliages diluées Al-Fe-Si. L'augmentation de la teneur en Fe et Si a retardé le recouvrement dynamique et a entraîné une diminution de la taille des sous-grains et de la désorientation des joints des grains. En outre, le comportement en déformation à chaud des alliages dilués Al-Fe-Si contenant diverses teneurs en Mn (0,1 et 0,2% en poids) et en Cu (0,05, 0,18 et 0,31% en poids) a également été étudié. Il a été constaté que le manganèse et le cuivre en solution solide ont une influence significative sur le formage à chaud des alliages dilués Al-Fe-Si. Sur une base de pourcentage massique, le Mn présente un effet de renforcement plus fort par rapport au Cu. Les énergies d'activation pour la déformation ont été calculés à partir de données expérimentales pour tous les alliages étudiés. Avec l’ajout de 0,2% en pourcentage massique de Mn, l'énergie d'activation augmente de 161 et 176 kJ / mol, à faible Fe (0,1% en pourcentage massique) et de haut Fe (0,5% en pourcentage massique) Les alliages à base de 181 et 192 kJ / mol, respectivement. L'addition de Cu jusqu'à 0,31% en pourcentage massique n'a que légèrement augmenté l'énergie d'activation de faible alliage à base de Fe de 161 à 166 kJ / mol. La diffusion du soluté a agi en tant que mécanisme de contrôle des taux de déformation dans ces alliages dilués. Les alliages contenant du Mn ont une contrainte d'écoulement plus élevée et une énergie d'activation plus élevée en raison de la vitesse de diffusion considérablement plus faible dans l’aluminium de Mn par rapport aux alliages contenant du cuivre. Une addition de Mn et Cu a aussi retardé le recouvrement dynamique et a généré une diminution de la taille des sous-grains et une désorientation des joints de grains. En outre, sur la base des données expérimentales des essais de compression à chaud, un modèle base sur les réseaux de neurones artificiels a été développé pour prédire le comportement en écoulement à haute température de l'alliages Al-0.12Fe-0.1Si-Cu en fonction de la composition chimique (avec différentes teneurs en Cu de 0.002-0.31 en pourcentage massique) et les paramètres de procédé. Un réseau de neurones de type backpropagation à trois couches avec 20 neurones dans la couche cachée a été établi dans cette étude pour prédire le comportement de l'écoulement de l'alliage Al-0.12Fe-0.1Si avec différents niveaux de Cu (0.002-0.31 en pourcentage massique) à différentes conditions de déformation. Les paramètres d'entrée étaient la teneur en Cu, la température, la vitesse de déformation et la contrainte, tandis que la contrainte d'écoulement constitue la sortie. La performance du modèle proposé a été évaluée à l'aide des différents paramètres statistiques classiques. Un excellent accord entre les résultats expérimentaux et prédits a été obtenu. L'analyse de sensibilité a indiqué que le taux de déformation est le paramètre le plus important, tandis que la teneur en Cu présentait une influence modeste mais significatif sur la contrainte d'écoulement. Le modèle ANN proposé dans cette étude peut prédire avec précision le comportement de déformation à chaud des alliages Al-0.12Fe-0.1Si

Numerical Simulation

Nowadays mathematical modeling and numerical simulations play an important role in life and natural science. Numerous researchers are working in developing different methods and techniques to help understand the behavior of very complex systems, from the brain activity with real importance in medicine to the turbulent flows with important applications in physics and engineering. This book presents an overview of some models, methods, and numerical computations that are useful for the applied research scientists and mathematicians, fluid tech engineers, and postgraduate students

Tribology of Machine Elements

Tribology is a branch of science that deals with machine elements and their friction, wear, and lubrication. Tribology of Machine Elements - Fundamentals and Applications presents the fundamentals of tribology, with chapters on its applications in engines, metal forming, seals, blasting, sintering, laser texture, biomaterials, and grinding

Analyse multi-échelles de la viscoplasticité à froid et de la rupture différée du titane en relation avec ses teneurs en hydrogène et oxygène.

Widely used for aircraft or rocket engine manufacturing titanium and its alloys are prone to the room-temperature creep that leads to the phenomenon of sustained load subcritical crack growth. One of the major cause of such unusual viscoplastic behavior of titanium is the phenomena of static and dynamic strain aging which represents an interaction between dislocations and interstitial atoms of oxygen and hydrogen. The aim of the present experimental and numerical multiscale study is to investigate the influence of the interstitial hydrogen and oxygen on the viscoplastic behavior and the resistance to sustained load cracking in commercially pure titanium of phase alpha.In a first step, a scenario of static and dynamic strain aging was proposed. The presence of the stress peak was attributed to the segregation of interstitial atoms of oxygen on the edge dislocations. In case of dynamic strain aging, the observed instabilities, typical for the Portevin-Le Chatelier effect, were associated with the non-planar core of screw -type dislocations. The crystal plasticity was introduced into the phenomenological model in order to capture the strain aging phenomena and the anisotropy of the mechanical properties. The modeling approach for strain aging suggested by Kubin-Estrin-McCormick is based on the internal variable called the aging time which corresponds to the waiting time of a dislocation in a pinned state. Finite element simulations were then performed on the polycrystalline aggregates for different number of grains. At the next step, fracture toughness and sustained load cracking tests were performed on the material with different levels of hydrogen. Finally, numerical simulations of toughness and sustained load cracking tests using the identified viscoplastic model were carried out for all experimental conditions. A cohesive zone model was then introduced ahead of the crack tip to simulate crack propagation.Le titane et ses alliages qui sont largement répandus dans l'industrie aéronautique, sont concernés par le fluage à température ambiante ce qui conduit à une réduction de la résistance et provoque le phénomène de rupture différée. Une partie des études montrent que ce comportement viscoplastique inhabituel à température ambiante est lié aux phénomènes d'interactions entre les dislocations et les atomes interstitiels comme l'hydrogène et l'oxygène, aussi appelés vieillissement statique et dynamique. Le but de cette étude à la fois expérimentale et numérique multi-échelle est de mieux comprendre les effets souvent antagonistes et en partie couplés de l'oxygène et de l'hydrogène en solution sur le comportement viscoplastique du titane non-allié de phase alpha. Dans un premier volet, un scénario du vieillissement statique et dynamique dans le titane non-allié de phase alpha est proposé. La présence du pic de traction est attribuée à la ségrégation des atomes interstitiels d'oxygène sur les dislocations coin de vecteur de Burgers . Dans le cas du vieillissement dynamique les instabilités observées, typiques de l'effet Portevin-Le Chatelier, sont associées à l'étalement du cœur non planaire des dislocations vis de vecteur de Burgers . Une loi de comportement prenant en compte les effets liés aux interactions entre dislocations et atomes en solution a été développée. Le modèle de Kubin-Estrin-McCormick qui permet de prendre en compte l'effet du vieillissement a été étendu au cas de la plasticité cristalline. Les simulations par éléments finis ont été réalisées sur des agrégats polycristallins avec différents nombres de grains. Ensuite, les essais de fissuration (ténacité et rupture différée) ont été réalisés sur les matériaux bruts, et chargés en hydrogène. Enfin, des simulations numériques de la rupture de ces éprouvettes ont été réalisées pour toutes les conditions expérimentales testées en utilisant le modèle de comportement mécanique macroscopique identifié. Un modèle de zone cohésive a été développé pour la simulation de la propagation des fissures