The phenomenal growth rate for the use of engineering ceramics is attributed to successful scientific responses to industrial demand. These materials are replacing metal and its alloys in diverse applications from cutting tools and heat engine components to integrated circuits. Joining technology plays a vital role in this changing and evolving technology as success and failure comes with breaking new barriers. It is important to improve existing techniques and to develop new techniques that reliably join simple shape components to form complex assemblies or join dissimilar materials such as metal to ceramic. Joining of ceramics is not simple due to their high chemical stability and low coefficient of thermal expansion (CTE). Joining between metal and ceramic is usually carried out at elevated temperatures and upon cooling thermal residual stresses are induced that lead to joint failure or poor strength. Most metal-ceramic joints cannot be used over 500°C primarily due to the low melting temperature of the interlayer. This investigation was concerned with the successful joining for higher temperature applications (above 500°C) of two dissimilar high temperature oxidation and corrosion resistant materials, Fecralloy and silicon nitride. The primary focus was on the effects of process conditions upon the microstructure and mechanical properties of the joint and to also study/identify the joining mechanism. Two novel techniques were employed to join successfully the metal to ceramic. The first was by use of a thin Cu foil that did not remain after joining. Joining occurs by a process that results in partial melting of the Fecralloy interface, where Fe, Cr, Al and Cu reactively infiltrate into the silicon nitride. This liquid mixture causes partial dissolution of the silicon nitride interface, where Si and N diffuse into the Fecralloy. A thin reaction product layer was formed at the silicon nitride interface and our results suggested that this was AIN. The free surface Si and porosity of the silicon nitride along with the eutectic temperatures above 1100°C are all vital for this joining process. The highest average shear strength of a Fecralloy-silicon nitride joint produced by the method was 67.5 MPa. The second route was that of a powder metallurgy one, where cold pressed Ni-Al (1:1 molar) compacts were used to join successfully the Fecralloy to silicon nitride. The formation of NiAl from its constituents is highly exothermic and this is initiated between 500-650°C. The high temperature reached causes partial melting of the Fecralloy interface and dissolution/reactive wetting at the silicon nitride interface. Mostly Fe infiltrates the NiAl improving room temperature ductility, fracture toughness and yield strength. Molten Al from the interlayer reacts and wets the silicon nitride interface with small amount of infiltration and no reaction product forming. The reaction synthesis of NiAl was studied using DTA and TGA, where the effects of Ni particle size and heating rate were investigated. This joining process is highly dependant upon process conditions, the most important of which are applied pressure, heating rate and Ni/A1 particle size. The highest average shear strength attained was 94.30 MPa and this is attributed to good interfacial bonding, high pressure, moderate process temperature and dwell time. The exothermic formation of the NiAl interlayer that is densified and monophase was paramount for this joining process. The Bansal-Doremus kinetic model for evaluating the kinetic parameters from non-isothermal DTA data was shown to be valid. The results obtained were identical to those by other authors who used a different model and approach.

No description available.

Cast iron, taking the advantages of the advanced castability forming components of complex geometries and favorable mechanical properties, is employed in engine components in truck industries. Compacted graphite iron (CGI) integrates both merits of lamellar graphite iron (LGI) and spheroidal graphite iron (SGI) such as good machinability and high thermal conductivity from LGI, high ultimate tensile strength (UTS), good fatigue resistance, high elastic modulus, and high ductility from SGI, thus is now becoming a competitive alternative of traditional LGI in cylinder blocks and heads. Due to the shape complexity of cast components, residual stresses arise accordingly. Normal methods for measuring stresses have various practical difficulties that affect accuracy. For example, in strain gauge measurements such as hole drilling and cutting, casting skins need to be polished as the attachment of strain gauge requires a smooth surface condition for precise detection, though any mechanical treatment would change the residual stress state. On the other hand, electropolishing applied in XRD measurement for extracting depth profile causes no release of stresses, nevertheless, there is no dissolution reaction on graphite particles. This would retard further polishing and form a rough surface instead of flat extraction. A visual strain detection system relies on a stable and clean surface condition, therefore, when it is combined with the drilling technique, the drilling chips could be a vital problem for repeatability when they block the view of drilling edges. Ultrasonic measurement, in theory, has lower precision by averaging the stresses within a certain volume beneath surfaces. A number of methods have been developed to measure residual stresses, ranging from destructive to non-destructive according to the removal amount of materials. In this thesis work, several measurement methods are implemented on cylinder heads and the results are compared with simulation to develop a suitable method of measuring residual stresses in cast engine components. It is found that longer shakeout time lowers the tensile stresses and develops more compressive stresses in the surface layer. Cutting is a suitable method compared with others. Incremental center-hole drilling technique is not suitable to measure cast components as the surface grinding before stain gauge mounting causes high deviation. Hole drilling with visual strain detection provided high errors within the first 0.1 mm as the strains were too weak to be visualized at the beginning of drilling. The electropolishing process was also found retarded by graphite particles, and the XRD results are more trustworthy with more tilt angles. Ultrasonic measurement is rather rough due to the influence of graphite on the traveling velocity of ultrasound. / Tack vare sin utmärkta gjutbarhet, som möjliggör gjutning av komplexa geometrier, samt goda mekaniska egenskaper är gjutjärn första valet i många motorkomponenter inom lastbilsindustrin. Kompaktgrafitjärn (CGI) kombinerar fördelarna med lamellärt grafitjärn (LGI) och sfäroidalt grafitjärn (SGI) såsom god bearbetbarhet och hög värmeledningsförmåga från LGI, hög draghållfasthet (UTS), hög utmattningshållfasthet, hög elastisk modul (E-modul) och hög duktilitet från SGI. Detta gör kompaktgrafitjärn till konkurrenskraftigt alternativ till traditionell LGI i cylinderblock och huvud. På grund av formkomplexiteten hos gjutkomponenter uppstår restspänningar. Normala metoder för att mäta spänningar har olika praktiska svårigheter som påverkar noggrannheten. Vid töjningsmätningar genom hålborrning och sågning måste t ex gjutskinn slipas bort eftersom fästning av töjningsmätare kräver en jämn yta för exakt detektion, även om prepareringen kan påverka spänningstillstånd. Å andra sidan orsakar elektropolering som appliceras i XRD-mätning för extrahering av djupprofil inte att spänningar frigörs, däremot finns det inget etsmedel för grafitpartiklar. Detta gör att poleringen skapar en ojämn yta istället för en platts yta. Systemet för visuell detektering av förlängning förlitar sig på en stabil och ren yta. Därför kan borrspånen, när visuell detektering kombineras med borrteknik, vara ett viktigt problem för repeterbarheten. Ultraljudsmätning har i teorin lägre precision genom att den endast mäter medelvärdet av spänningarna i en viss volym under ytan. Ett antal metoder har utvecklats för att mäta restspänningar, både förstörande och oförstörande. I denna examensarbetesrapport implementeras flera mätmetoder på motorcylinderhuvuden och resultaten jämförs med simulering för att utveckla en lämplig metod för att mäta restspänningar i gjutna motorkomponenter. Det visas i arbetet att längre urslagstid kan sänka dragspänningarna och utveckla mer tryckspänningar i ytskiktet. Sågning är en lämplig metod jämfört med de andra. Inkrementell hålborrningsteknik är inte lämplig för att mäta restspänningar på gjutkomponenter eftersom ytslipningen före montering av töjningsmätare orsakar hög avvikelse. Hålborrning med visuell töjningsdetektering gav höga fel inom den första 0,1 mm från ytan eftersom töjningen är för liten för att kunna visualiseras i början av borrningen. Det är hänt ofta att elektropoleringsprocessen före XRD-mätningen blir fördröjd av grafitpartiklar, och XRD-resultaten är mer pålitliga med fler lutningsvinklar. Ultraljudsmätning är grov på grund av grafitens påverkan på ultraljudets hastighet.

L'objectif de ce travail est de proposer une nouvelle démarche pour améliorer et accélérer les études de dimensionnement des pièces de turboréacteurs en avant-projets. Il s'agit de fournir une méthodologie complète pour la conception robuste sous contraintes. Cette méthodologie consiste en trois étapes : la réduction de la dimension et la méta-modélisation, la conception robuste sous contraintes puis la résolution de problèmes inverses sous contraintes. Ce sont les trois principaux sujets abordés dans cette thèse. La réduction de la dimension est un pré-traitement indispensable à toute étude. Son but est de ne conserver, pour une sortie choisie du système, que les entrées influentes. Ceci permet de réduire la taille du domaine d'étude afin de faciliter la compréhension du système et diminuer les temps de calculs des études. Les méthodes de méta-modélisations contribuent également à ces deux objectifs. L'idée est de remplacer le code de calculs coûteux par un modèle rapide à évaluer et qui représente bien la relation entre la sortie étudiée et les entrées du système. La conception robuste sous contraintes est une optimisation bi-objectifs où les différentes sources d'incertitudes du système sont prises en compte. Il s'agit, dans un premier temps, de recenser et modéliser les incertitudes puis de choisir une méthode de propagation de ces incertitudes dans le code de calculs. Ceci permet d'estimer les moments (moyenne et écart-type) de la loi de la sortie d'intérêt. L'optimisation de ces moments constitue les deux objectifs de la conception robuste. En dernier lieu, il s'agit de choisir la méthode d'optimisation multi-objectifs qui sera utilisée pour obtenir l'optimum robuste sous contraintes. La partie innovante de cette thèse porte sur le développement de méthodes pour la résolution de problèmes inverses mal posés. Ce sont des problèmes pour lesquels il peut y avoir une infinité de solutions constituant des ensembles non convexes et même disjoints. L'inversion a été considérée ici comme un complément à l'optimisation robuste dans laquelle l'optimum obtenu ne satisfaisait pas une des contraintes. Les méthodes d'inversion permettent alors de résoudre ce problème en trouvant plusieurs combinaisons des entrées qui satisfont la contrainte sous la condition de rester proche de l'optimum robuste. Le but est d'atteindre une valeur cible de la contrainte non satisfaite tout en respectant les autres contraintes du système auxquelles on ajoute la condition de proximité à l'optimum. Appliquée au dimensionnement d'un compresseur HP en avants-projets, cette méthodologie s'inscrit dans l'amélioration et l'accélération des études marquées par de nombreux rebouclages chronophages en termes de ressources informatiques et humaines. / The aim of this PhD dissertation is to propose a new approach to improve and accelerate preliminary design studies for turbofan engine components. This approach consists in a comprehensive methodology for robust design under constraints, following three stages : dimension reduction and metamodeling, robust design under constraints and finally inverse problem solving under constraints. These are the three main subjects of this PhD dissertation. Dimension reduction is an essential pre-processing for any study. Its aim is to keep only inputs with large effects on a selected output. This selection reduces the size of the domain on which is performed the study which reduces its computational cost and eases the (qualitative) understanding of the system of interest. Metamodeling also contributes to these two objectives by replacing the time-consuming computer code by a faster metamodel which approximates adequately the relationship between system inputs and the studied output. Robust design under constraints is a bi-objectives optimization where different uncertainty sources are included. First, uncertainties must be collected and modeled. Then a propagation method of uncertainties in the computation code must be chosen in order to estimate moments (mean and standard deviation) of output distribution. Optimization of these moments are the two robust design objectives. Finally, a multi-objectives optimization method has to be chosen to find a robust optimum under constraints. The development of methods to solve ill-posed inverse problems is the innovative part of this PhD dissertation. These problems can have infinitely many solutions constituting non convex or even disjoint sets. Inversion is considered here as a complement to robust design in the case where the obtained optimum doesn't satisfy one of the constraints. Inverse methods then enable to solve this problem by finding several input datasets which satisfy all the constraints and a condition of proximity to the optimum. The aim is to reach a target value of the unsatisfied constraint while respecting other system constraints and the optimum proximity condition. Applied to preliminary design of high pressure compressor, this methodology contributes to the improvement and acceleration of studies currently characterized by a numerous of loopbacks which are expensive in terms of cpu-time and human resources.