Shot peening is a surface enhancement process used to improve the fatigue strength of metals by introducing beneficial compressive residual stresses on the surface. Shot peening is widely used in a number of industrial applications, including gas turbine engines. However, the fatigue life improvement gained via shot peening is not explicitly accounted for in current engine components life prediction processes. Therefore, there is a significant potential for increasing the predicted damage tolerance capabilities of engine components if beneficial residual stress considerations are incorporated into the life prediction methodology. In this work, a finite element model was developed to apply residual stresses from shot peening as initial stresses to the finite element mesh. The proposed technique was validated using a simple numerical example and the sensitivity of the resulting stress distribution in the model was investigated. The capability of the proposed strategy was also demonstrated on a fatigue test specimen containing high stress concentration features, broadly used in gas turbine engine applications. With the proposed technique, the applied residual stress profile is not self-equilibrating. Therefore, a redistribution of stresses was found in the model after the application of the boundary conditions. The depth and magnitude of the tensile residual stresses had a significant influence on the resulting redistribution of stresses. / Le grenaillage est un traitement de surface visant à améliorer la résistance en fatigue des métaux en introduisant des contraintes résiduelles en compression sur la surface. Le grenaillage est largement utilisé dans de nombreuses applications industrielles particulièrement dans les moteurs à turbine à gaz. Cependant, l’effet des contraintes résiduelles de n’est pas explicitement inclus dans les analyses de la prédiction de la résistance en fatigue des composantes. Ceci entraîne des prédictions très conservatrices de la vie en fatigue des pièces. Dans ce travail, un modèle d'analyse par éléments finis a été développé en applicant les contraintes induites par le grenaillage comme contraintes initiales dans le modèle. La méthode d’analyse proposée a été validée par un exemple numérique unidimensionnel. L’effet de la distribution des contraintes initiales sur la répartition des contraintes finales à été étudié. Un exemple de calcul a été effectué pour un échantillon utilisé pour mesurer la vie en fatigue des matériaux utilisés dans les moteurs à turbine à gaz. Avec la technique proposée, la contrainte initiale appliquée n’est pas en équilibre et ceci provoque une redistribution des contraintes dans la pièce. Ainsi, la profondeur et l’amplitude des contraintes résiduelles ont un effet important sur la redistribution des contraintes initiales dans la pièce.

An experimental approach and an analytical procedure have been developed for the prediction of the force distribution in the grinding wheel and the workpiece contact zone. Additionally, a numerical analysis using finite element methods was carried out to verify the force distribution in the actual grinding cases. This work was motivated by the need to obtain the maximum force acting on individual active abrasive grains for establishing the probability of grain fracture and pullouts due to this force. In the experimental approach, forces were measured while grinding small segments of the full wheel-workpiece contact length. The measured forces were used to predict the forces corresponding to smaller segments of the full contact arc to obtain the force distribution. To illustrate the method, forces were measured for four different grinding conditions using a 60 grit CBN grinding wheel with a small segment of the nickel alloy (IN718) workpiece. The predicted force distributions were found to increase at a decreasing rate from the bottom to the top of the contact arc in all four cases. Further the force distributions were applied to predict the transient grinding power. The predicted power values were found to match very well with the measured values in all four cases. For the analytical prediction of the force distribution, a CBN grinding wheel and the workpiece were modeled using Solidworks, and the interaction between abrasive grains and the workpiece were simulated individually for a few revolutions of the wheel to predict the uncut chip geometries. The forces corresponding to the active grains in the contact arc were calculated from the uncut chip geometries, using which the force distributions were predicted. The predicted force distributions from the analytical and the experimental techniques were found to match very well. Furthermore, using DEFORM 3D, numerical analyses were carried out on single grain and multiple grains grinding cases to predict the for / Une approche expérimentale et une procédure analytique ont été développés pour la prédiction de la répartition de la force dans la meule et zone de contact de la pièce. En outre, un calcul numérique utilisant les méthodes des éléments finis a été réalisée pour vérifier la répartition de la force, dans le cas de broyage. Ce travail a été motivée par la nécessité d'obtenir la force maximale agissante sur les grains abrasifs actifs pour établir la probabilité de rupture du grain et pullouts en raison de cette force. Dans l'approche expérimentale, les forces ont été mesurées lors du meulage d’un petit segment de la roue longueur de contacte entre la meule et la pièce. Les forces mesurées ont été utilisées pour prédire les forces correspondantes à des segments plus petits que les coordonnées complètes de l'arc de contact pour obtenir la répartition. Pour illustrer la méthode, les forces ont été mesurées pour quatre conditions de broyage en utilisant du sable de 60 meules CBN avec un petit segment d’un pièce de l'alliage de nickel (IN718) pièce. Les prévisions de répartition de la force a été constaté à augmenter à un taux décroissant du bas vers le haut de l'arc de contact dans les quatre cas. En outre, les prévisions de répartition de la force a été appliquée pour prédire le pouvoir transitoire de broyage. La puissance prédit a éte trouvée qui corresponde très bien à la puissance mesurée dans les quatre cas. Pour la prévision analytique de la répartition de la force, typique meules CBN et la pièce ont été modelée en utilisant Solidworks, et l'interaction entre chaque grain abrasif sur la meule et la pièce a été simulée individuellement pour quelques révolutions de la meule pour prédire les géométries des coupeaux non coupés pour deux des quatre conditions expérimentales de broyage. Sur la base de ces géométries des coupaux non coupés la force correspondante à chaque grain dans l

This thesis develops improved stochastic models for the description of a large variety of fatigue crack growth phenomena that occur in structural and mechanical components of fundamental importance to the functionality and reliability of complex and modern engineering structures. In essence, the models are based upon the recently available McGill-Markov and the newly developed Closure-Lognormal stochastic processes. These models have not only the capability of predicting the statistical dispersion of the crack growth rate, which is dependent on the inherent crack resistance characteristics of the material being examined, but also, by incorporating the concept of crack closure into the Paris-Erdogan law through the use of the effective stress intensity range factor, have the capability of transferring the stochastic properties of crack growth rates measured under ideal laboratory conditions to situations of industrial significance, such as those occurring under adverse loading and/or environmental conditions. / The primary data required in order to be in a position to estimate the pertinent parameters of these stochastic models are obtained, as is fully discussed in this thesis, from a statistically significant number of replicate tests. The application of both the theory and the experimental technique are illustrated using a Ti-6Al-4V alloy of considerable importance to the aerospace industry. / The application of these models for the assessment of component reliability is detailed in the latter stages of the investigation reported in this thesis. Important reliability, availability and maintainability concepts are developed and thoroughly illustrated. In this way, fundamental models developed during the course of this investigation will in the future, have the capability of predicting reliability and maintenance parameters of considerable significance to the assessment of component reliability.

Mobility and kinematics of a folding cube are introduced. This cube is shown to be an array of 12 parallel, symmetric 1-dof 4-bar linkages. / The cube is composed of 8 corner tripods and 12 edge rods. There is a hinge at the end of each edge rod connected to an adjacent corner tripod leg. Motion is obtained by each tripod screwing inward about an axis along the cube space diagonal. Two different foldings are described by adjacent tripods screwing in the same, isorotation, or in the opposite, counter-rotation, hand. / Folding motion and direct and inverse kinematics are derived. Results are easily obtained in closed form not only for the folding cube but also for the underlying general four-bar kernel mechanism where crank and follower are of different radii and axes are skewed. Singularity and joint combinations analyses are presented along with other angular relationships among mechanism components. / The folding cube can be adapted as a robotic manipulator component which promises to be stiff, light and simple. This component mechanism appears to be a member of a family of similar, parallel mechanisms where the 4-bar kernel axes are coplanar. Family architecture appears to be based on the 5 platonic solids. The folding rectangle and the folding tetrahedron are introduced as two members of the family.

The aim of this research is to propose and experimentally investigate a pressure instrument for determining the skin friction on a flat surface over the entire range of roughness from smooth to fully rough. An instrument consisting of three pitot tubes and one static tube is found to be the simplest device satisfying these requirements. The principle of operation of the proposed "three tube" instrument depends on the existence of a logarithmic mean velocity profile in the wall region of the turbulent boundary layer. / The three tube instrument is tested on both smooth and rough surfaces in the boundary layer produced on the floor of the McGill University 914 mm x 610 mm wind tunnel, over the Reynolds number range from approximately $R sb{ theta} = 5 times10 sp3$ to $R sb{ theta} = 18 times10 sp3.$ The roughness is created using sandpaper of sizes #40 and #24 glued to the wind tunnel floor, and the experiments are performed over a range of non-dimensional roughness $k sbsp{s}{+} equiv k sb{s}u sb{r}/ nu$ from 0 to approximately 85.

No description available.

No description available.

<p> Water management in the porous media of proton exchange membrane (PEM) fuel cells, catalyst layer and porous transport layers (PTL) is confronted by two issues, flooding and dry out, both of which result in improper functioning of the fuel cell and lead to poor performance and degradation. The data that has been reported about water percolation and wettability within a fuel cell catalyst layer is limited to porosimetry. A new method and apparatus for measuring the percolation pressure in the catalyst layer has been developed. The experimental setup is similar to a Hele-Shaw experiment where samples are compressed and a fluid is injected into the sample. Pressure-Wetted Volume plots as well as Permeability plots for the catalyst layers were generated from the percolation testing. PTL samples were also characterizes using a Hele-Shaw method. Characterization for the PTLs was completed for the three states: new, conditioned and aged. This is represented in a Ce-t^* plots, which show a large offset between new and aged samples.</p>

<p> Cold-rolling mills reduce the thickness of an incoming metal strip to produce longer, thinner strip with desired mechanical, dimensional, and metallurgical properties. A primary factor in manufacturing high-quality cold-rolled sheet is accurately predicting the required rolling force. The rolling force directly influences roll-stack deflections, which correlate to the resulting rolled sheet flatness quality. Increasingly high demand for thin and ultra-thin cold-rolled sheet metal gauges, along with the correspondingly larger sensitivity of flatness defects, makes it more important to accurately and rapidly predict the rolling force before the rolling operation begins. Accurate rolling force predictions enable assignment of appropriate pass schedules and flatness mechanism set-points early in the rolling process, thereby improving quality and reducing time and scrap. Cold rolling force predictions have traditionally employed two-dimensional analytical models such as those proposed by Roberts and Bland &amp; Ford. These simplified methods are prone to inaccuracy, however, because of several uncertain, yet influential, model parameters that are difficult to establish deterministically for wide-ranging products. These parameters include, for example, the rolled strip average compressive yield strength, frictional characteristics relating to low and high mill speeds, and the yield strength strain rate dependency. Conventionally, these unknown parameters have been evaluated deterministically by comparing force predictions with industry force data and using a best-fit regression approach. </p><p> In this work, Bayesian updating using a probability function is applied to identify joint posterior probability distributions of the uncertain parameters in rolling force models. It is shown that the non-deterministic Bayesian updating approach is particularly useful as new rolling force data becomes available and the models can &ldquo;learn&rdquo; from this available production data. The goal is a model that can better predict necessary mill parameters based on accurate probability estimates of the actual rolling force. The rolling force data used in this work for applying Bayesian updating is actual production data of grades 301, 304L (low carbon), and 304 stainless steels, rolled on a 10-inch wide 4-high cold rolling mill. This force data was collected by observing and averaging load cell measurements at steady rolling speeds.</p>

Due to the wide range of variables involved and sophisticate d analysis techniques required, optimum structural design of laminated composite materials is known to be a challenge for designers. The complexity of the design problem is increased when manufacturing issues are also taken into account due to their strong connection with the structural performance. The major challenge involved in the coupled design problem is to handle multiple conflicting objectives. The problem, with its proper consideration through multi–objective optimization, is studied in this research. To solve the related multi–objective optimization problem, which for its intrinsic nature does not have a single solution, three strategies are proposed here. The first strategy requires reduced computational effort, while it yields only one solution. The second strategy requires more computational effort and returns a moderate number of optimum solutions. The third strategy, though involves high computational effort, provides a large number of optimum solutions and a clear image of the trade–off among objectives. For each strategy a hybrid algorithm consisting of a local search, a global search and a multi–objective optimization technique is proposed. The hybrid algorithms are developed particularly to provide a convergence rate higher than the one provided by available GA–based optimization methods. The extent of achieving this goal is evaluated by several test problems. The proposed hybrid algorithms are applied to two practical composite design problems, the results of which confirm the presence of a strong interconnection among structural and manufacturing objectives and demonstrate the effectiveness of the coupled design approach in providing alternative designs. Although dominated by the structural parameters, performance of a composite structure made by resin transfer moulding is shown to be strongly affected by the manu / Une méthodologie de conception pour incorporer les paramètres de fabrication dans le processus de conception structurale a été proposée. Son application pour la conception des matériaux composites stratifiés fabriqués par le procédé d'injection sur renfort est démontrée.Le défi principal dans l'optimisation simultanée des paramètres structuraux et de fabrication est le traitement de multiples objectifs contradictoires. Comme le problème d'optimisation à objectifs multiples n'a pas une solution unique, le problème de conception a été traité en utilisant trois stratégies différentes. La première stratégie, exigeant peu d'effort informatique, renvoie seulement une solution en fonction des préférences définies par l'utilisateur pour les objectifs. La deuxième stratégie, requérant un nombre modéré d'évaluations de fonction, fournit un nombre restreint de solutions optimales et présente un compromis approximatif des objectifs. La troisième stratégie fournit un grand nombre de solutions optimales donnant une image précise du compromis entre les objectifs et requiert un grand nombre d'évaluations de fonction.Pour chaque stratégie, un différent algorithme hybride consistant d'une recherche locale, d'une recherche globale, et d'une technique d'optimisation à objectifs multiples est proposé. Les algorithmes hybrides sont élaborés de manière à fournir un taux de convergence plus haut que le taux de convergence obtenu avec des méthodes d'optimisation d'algorithmes génétiques (GA) disponibles. Le degré d'achèvement de cet objectif est testé en utilisant les algorithmes hybrides proposés pour la résolution de plusieurs fonctions mathématiques.Les algorithmes hybrides proposés sont ensuite appliqués à deux problèmes pratiques de conception de matériaux composites. Les résultats confirment une forte interconnexion entre les paramètres structuraux et de fab