Master’s thesis deals with study of fatigue crack growth retardation models. This document presents description, evaluation, verification and finally application of retardation models demonstrated on the damage tolerant structure. Analysis was provided on the L 410 NG aircraft in the location of the rear spar lower flange joint. Output of this thesis is comparison of the damage tolerance analysis with the current method using in the Aircraft Industry a. s., i.e. linear model without using load interaction models. The comparisons are fatigue crack growth curves, threshold and intervals of inspection program. AFGROW software was used for verification and application of retardation models.

Teil 1 Karsten Berndt Die Festlegung von Toleranzen ist eine alltägliche Aufgabenstellung des Konstrukteurs. Dabei bedingt die Berechnung nichtlinearer Toleranzketten einen erheblichen Zeitaufwand, wodurch meist auf deren genaue Berechnung vezichtet wird und Toleranzen stattdessen auf Basis von Erfahrungswerten festgelegt werden. Die vorgestellte Methodik zeigt Wege, wie schnell und frühzeitig im Konstruktionsprozess belastbare Aussagen zu Toleranzen komplexer Mechanismen getroffen werden können. Dazu werden sogenannte Sensitivitätsanalysen in der CAD-Software "Creo Elements" durchgeführt und ausgewertet. Das Ergebnis sind erste konkrete Toleranzfelder für alle den Mechanismus beschreibenden, geometrischen Abmessungen, welche sich als Startwerte für den anschließenden Toleranzsynthese/-analyseprozess eignen. Teil 2 Marko Ebermann Dieser zweite Vortragsteil behandelt eine mögliche Vorgehensweise zur Tolerierung von Geometrieabweichungen in der frühen Entwurfsphase am Beispiel des Koppelgliedes einer Verpackungsmaschine. Ausgangspunkt für die frühe Tolerierung bildet die im ersten Vortragsteil behandelte Sensitivitätsanalyse des Koppelgetriebes, welche Informationen zur Empfindlichkeit der Funktionsmaße bezüglich der Einhaltung der Schließmaßtoleranz lieferte. Die daraus abgeleitete Form- und Lagetolerierung des Koppelgliedes soll durch anschließende Toleranzamalysen die Tolerierung im Baugruppenkontext bestätigen und auf möglich Fertigungsverfahren abzielen, ohne die genaue Gestalt der Komponenten zu kennen. So können teure und zeitintensive Iterationsschleifen im Konstruktionsprozess minimiert und die Funktionalität frühzeitig gesichert werden.

En conception de systèmes mécaniques, la phase de cotation fonctionnelle consiste à affecter des cotes, constituées d’une valeur nominale et d’un intervalle de tolérance, à des dimensions de pièces. En particulier, l’analyse des tolérances consiste à vérifier que les intervalles de tolérance choisis permettent le respect de la fonctionnalité du mécanisme. A l’inverse, la synthèse des tolérances vise à déterminer ces intervalles de tolérance, si possible de manière optimale, permettant le respect des exigences fonctionnelles. Les approches statistiques traditionnelles, bien que très utiles en phase de préconception, ne sont pas capables d’estimer avec précision le risque de non qualité. Cette thèse aborde ces problèmes selon un angle de vue différent, non plus pour garantir le respect d’exigences fonctionnelles, mais pour garantir le Taux de Non-Conformité (TNC) du mécanisme. Il s’agit de la probabilité que l’exigence fonctionnelle ne soit pas respectée. Les méthodes fiabilistes, s’appuyant sur la théorie des probabilités, permettent un calcul précis et efficace de cet indicateur. L’objectif de cette thèse est d’explorer le domaine de l’analyse et de la synthèse des tolérances afin d’identifier et d’exposer les apports des méthodes fiabilistes sur ces problématiques. Dans ces travaux de thèse, différents outils fiabilistes sont mis à disposition permettant l’analyse des tolérances de tous types de mécanismes avec ou sans jeu. La théorie probabiliste permet une modélisation très complète des dimensions des pièces. En particulier, l’approche APTA (Advanced Probability-based Tolerance Analysis of products) est développée afin de prendre en compte l’évolution aléatoire de certains paramètres de modélisation, notamment les décalages de moyenne, responsables de fortes variations du TNC. L’analyse des tolérances étant plus complexe pour les mécanismes avec jeux, une méthodologie spécifique a été développée basée sur une décomposition en situations de points de contacts et l’utilisation d’une méthode fiabiliste système. Différents indices de sensibilité sont aussi proposés afin d’aider à identifier les cotes ayant le plus d’influence sur le TNC d’un mécanisme. Enfin, l’optimisation du coût de production, sous contrainte de TNC, permet une synthèse des tolérances optimale. Les gains potentiels en termes de coût dépassent 50% par rapport aux conceptions initiales tout en maitrisant le niveau de qualité du produit. Les sociétés RADIALL SA et VALEO Système d’Essuyages, concepteurs et fabricants de produits pour l’automobile et l’aéronautique, ont proposé des cas d’études sur lesquels est démontrée la pertinence des travaux effectués. Sur la base de ces travaux, Phimeca Engineering, spécialisée dans l’ingénierie des incertitudes, développe et commercialise un outil informatique professionnel. / To design mechanical systems, functional dimensioning and tolerancing consists in allocating a target value and a tolerance to part dimensions. More precisely, tolerance analysis consists in checking that chosen tolerances allow the mechanism to be functional. In the opposite, the tolerance synthesis goal is to determine those tolerances, optimaly if possible, such as functional requirements are respected. Traditional statistical approaches are very useful in pre-design phases, but are incapable of estimating precisely non-quality risks. This PhD thesis adresses this problem from a different point of view. The objective is no longer to respect functional requirements but to guarantee the Non-Conformity Rate (NCR) of the mechanism. It is the probability that the functional requirement is not respected. Reliability methods, based on probabilistic theory, allow a precise and efficient calculation of the NCR. The main goal of this thesis is to explore tolerance analysis and synthesis domains in order to identify potential contributions of reliability methods to these issues. In this work, different reliability tools are provided enabling tolerance analysis of all kind of mechanisms with or without gaps. The probability theory allows a detailed modeling of parts dimensions. In particular, the APTA (Advanced Probability-based Tolerance Analysis of products) approach is designed to take into account random variations of some parameters such as mean shifts which influence highly the NCR. As tolerance analysis is more complex for mechanisms with gaps, a specific method is designed based on a decomposition of contact points situations and the use of a reliability system method. Several sensitivity indexes are also proposed to identify the leading dimensions on the NCR. The optimization of the production cost, under a NCR constraint, enables an optimal tolerance synthesis. The potential benefits in terms of costs exceed 50% compared to initial designs while keeping under control quality levels of products. Companies RADIALL SA and VALEO Wiping Systems, designers and manufacturers of products for the automotive and aeronautic industries, have provided case studies on which is demonstrated the relevance of the presented work. Based on this work, the company Phimeca Engineering, specialized in uncertainties, is developing and commercializing a professional computer tool.

This work deals with using modern active functional blocks in electronic circuits. These blocks have better features than classical operational amplifiers and are characterized especially by working in current mode. Therefore these blocks can be used in higher frequencies. Using those blocks it is possible to design e.g. electronically variable-frequency filters of types low-pass filter, high-pass filter, band-pass filter, etc. Then it is also possible to easily realize electronically variable-frequency oscillators. This work is focused on some of these blocks, their basic characteristics and principles. Also three oscillators with current conveyors of second generation are designed. Its made simulation, sensitivity and tolerance analysis and magnitude stabilization. Everything is performed in OrCAD PSpice program. These made oscillators are electronic tunable in the band frequency ones of MHz.

The diploma thesis deals with analysis, validation, measurement of parameters of the commercially available current multiplies (namely the EL2082 and EL4083) and their applications in practice. Control analysis are carried out in OrCAD PSpice program and compared with values from datasheets. Control analysis are focused on AC and DC characteristics of these active blocks. There are discusses the input impedance, the output impedance, the current gain and the possibility of electronic adjusting. The parameters of the elements were verified by measurements. Proposals for circuit applications (selective circuit, oscillator, frequency filter) with EL2082 and EL4083 are presented and analyzed in the program OrCAD. Three oscillator circuit designs are experimentally tested and the results are compared with the theoretical expectations and simulations in OrCAD. The possibility of electronic control for oscillators is examined. Also the sensitivity and the tolerance analysis are carried out. The constructional details of oscillators are presented at the end of this work.

Les lasers à cavité verticale émettant par la surface (VCSEL) à base d'antimoniures dans le moyen infrarouge permettent le développement et l'amélioration d'applications telles que la détection de gaz polluants. De nouveaux miroirs à réseaux à haut contraste d'indice (HCG) ont montré un pouvoir réflecteur comparable voire supérieur aux miroirs de Bragg conventionnels avec un gain d'épaisseur d'un facteur 10 tout en offrant un effet polarisant. L'insertion de ce nouveau type de miroir au sein d'une structure VCSEL présente ainsi des avantages prometteurs pour améliorer les propriétés de ces composants pour une émission dans le moyen infrarouge. Le travail présenté dans ce manuscrit de thèse concerne la conception de miroirs HCG qui répondent aux exigences d'une intégration VCSEL en prenant en compte les contraintes technologiques et la tolérance aux erreurs de fabrication. Pour cela, dans un premier temps, un algorithme d'optimisation global a été combiné à une méthode de simulation numérique de réseaux (RCWA) afin d'automatiser la conception de miroirs. L'étude précise des tolérances des paramètres géométriques du réseau a été menée pour pouvoir ensuite développer un algorithme d'optimisation robuste. Cet algorithme permet ainsi d'obtenir non seulement un miroir répondant aux exigences de réflectivités définies par l'utilisateur mais également de conserver ces performances pour de larges gammes de tolérances. Enfin, dans une dernière partie, l'intégration du miroir à réseau dans un VCSEL a été simulée par une méthode aux différences finies (FDTD) pour étudier le fonctionnement d'un composant complet. / In the mid infrared wavelength range, Vertical Cavity Surface Emitting Lasers (VCSEL) based on the antimony alloy is a promising solution to develop and enhance numerous applications such as polluting gas sensing. A new type of mirror based on High Contrast Grating (HCG) structures has shown similar reflectivities than the Bragg mirrors which are usually used in VCSELs. However, with a polarization selectivity and a reduction in thickness of a factor of 10, HCG mirrors can advantageously replace Bragg reflectors to enhance the properties of mid infrared VCSEL structures. The work presented in this manuscript is devoted to the design of high contrast grating mirrors for a VCSEL application and takes precisely into account the technological constraints and tolerance of fabrication. In a first part, a global optimization algorithm has been combined to a numerical analysis of grating structures (RCWA) to automatically design HCG mirrors for a VCSEL application. In a second part of this work, the tolerances of the grating dimensions have been precisely studied which has lead to the development of a robust optimization algorithm. This algorithm allows to design high contrast gratings which exhibit not only a high efficiency but also large tolerance values required by the manufacturing process. Finally, in a last part, a VCSEL structure using a high contrast grating as top mirror has been designed and simulated by FDTD to validate the use of HCG presented previously in a VCSEL structure.

The procedure of joining flexible or nonrigid parts using applied loads is called compliant assembly, and it is widely used in automotive, aerospace, electronics, and appliance manufacturing. Uncontrolled assembly processes may produce geometric errors that can exceed design tolerances and induce an increment of elastic energy in the structure due to the accumulation of internal stresses. This condition might create unexpected deformations and residual stress distributions across the structure that compromise product functionality. This thesis presents a method based on nonlinear Finite Element Analysis (FEA), metamodelling, and optimization techniques to provide accurate and on-time shimming strategies to support the definition of optimum assembly strategies. An example of the method on a typical aerospace wing box structure is demonstrated in the present study. The delivered outputs intend to support the production line by anticipating the response of the structure under a specific assembly condition and presenting alternative assembly strategies that can be applied to address eventual predicted issues on product requirements. / Graduate

<p>  </p> <p>There has been a growing interest within the aerospace industry for shifting towards a digital twin approach, for reliable assessment of individual components during the product lifecycle - across design, manufacturing, and in-service maintenance, repair & overhaul (MRO) stages. The transition towards digital twins relies on continuous updating of the product lifecycle datasets and interoperable exchange of data applicable to components, thereby permitting engineers to utilize current state information to make more-informed downstream decisions. In this thesis, we primarily develop a framework to store, track, update, and retrieve product lifecycle data applicable to a serialized component, its features, and individual locations. </p> <p>From a structural integrity standpoint, the fatigue performance of a component is inherently tied to the component geometry, its material state, and applied loading conditions. The manufacturing process controls the underlying material microstructure, which in turn governs the mechanical properties and ultimately the performance. The processing also controls the residual stress distributions within the component volume, which influences the durability and damage tolerance of the component. Hence, we have demonstrated multiple use cases for fatigue life assessment of critical aerospace components, by using the developed framework for efficiently tracking and retrieving (i) the current geometric state, (ii) the material microstructure state, and (iii) residual stress distributions.</p> <p>Model-based definitions (MBDs) present opportunities to capture both geometric and non-geometric data using 3D computer-aided design (CAD) models, with the overarching aim to disseminate product information across different stages of the lifecycle. MBDs can potentially eliminate error-prone information exchange associated with traditional paper-based drawings and improve the fidelity of component details, captured using 3D CAD models. However, current CAD capabilities limit associating the material information with the component’s shape definition. Furthermore, the material attributes of interest, viz., material microstructures and residual stress distributions, can vary across the component volume. To this end, in the first part of the thesis, we implement a CAD-based tool to store and retrieve metadata using point objects within a CAD model, thereby creating associations to spatial locations within the component. The tool is illustrated for storage and retrieval of bulk residual stresses developed during the manufacturing of a turbine disk component, acquired from process modeling and characterization. Further, variations in residual stress distribution owing to process model uncertainties have been captured as separate instances of the disk’s CAD models to represent part-to-part variability as an analogy to track individual serialized components for digital twins. The propagation of varying residual stresses from these CAD models within the damage tolerance analysis performed at critical locations in the disk has been demonstrated. The combination of geometric and non-geometric data inside the MBD, via storage of spatial and feature varying information, presents opportunities to create digital replica or digital twin(s) of actual component(s) with location-specific material state information.</p> <p>To fully realize a digital twin description of components, it is crucial to dynamically update information tied to a component as it evolves across the lifecycle, and subsequently track and retrieve current state information. Hence, in the second part of the thesis, we propose a dynamic data linking approach to include material information within the MBDs. As opposed to storing material datasets directly within the CAD model in the previous approach, we externally store and update the material datasets and create data linkages between material datasets and features within the CAD models. To this end, we develop a model-based feature information network (MFIN), a software agnostic framework for linking, updating, searching, and retrieving of relevant information across a product’s lifecycle. The use case of a damage tolerance analysis for a compressor bladed-disk (blisk) is demonstrated, wherein Ti-6Al-4V blade(s) are linear friction welded to the Ti-6Al-4V disk, comprising well-defined regions exhibiting grain refinement and high residuals stresses. By capturing the location-specific microstructural information and residual stress fields at the weld regions, this information was accessed within the MFIN and used for downstream damage tolerant analysis. The introduction of the MFIN framework facilitates access to dynamically evolving as well as location-specific data for use within physics-based models.</p> <p>In the third part of thesis, we extend the MFIN framework to enable a physics-based, microstructure sensitive and location-specific fatigue life analysis of a component. Traditionally, aerospace components are treated as monolithic structures during lifing, wherein microstructural information at individual locations are not necessarily considered. The resulting fatigue life estimates are conservative and associated with large uncertainty bounds, especially in components with gradient microstructures or distinct location-specific microstructures, thereby leading to under usage of the component’s capabilities. To improve precision in the fatigue estimates, a location-specific lifing framework is enabled via MFIN, for tracking and retrieval of microstructural information at distinct locations for subsequent use within a crystal plasticity-based fatigue life prediction model. A use case for lifing dual-microstructure heat treated LSHR turbine disk component is demonstrated at two locations, near the bore (fine grains) and near the rim (coarse grains) regions. We employ the framework to access (a) the grain size statistics and (b) the macroscopic strain fields to inform precise boundary conditions for the crystal plasticity finite-element analysis. The illustrated approach to conduct a location-specific predictive analysis of components presents opportunities for tailoring the manufacturing process and resulting microstructures to meet the component’s targeted requirements.</p> <p>For reliably conducting structural integrity analysis of a component, it is crucial to utilize their precise geometric description. The component geometries encounter variations from nominal design geometries, post manufacturing or after service. However, traditionally, stress analyses are based on nominal part geometries during assessment of these components. In the last part of the thesis, we expand the MFIN framework to dynamically capture deviations in the part geometry via physical measurements, to create a new instance of the CAD model and the associated structural analysis. This automated workflow enables engineers for improved decision-making by assessing (i) as-manufactured part geometries that fall outside of specification requirements during the materials review board or (ii) in-service damages in parts during the MRO stages of the lifecycle. We demonstrate a use case to assess the structural integrity of a turbofan blade that had experienced foreign object damage (FOD) during service. The as-designed geometry was updated based on coordinate measurements of the damaged blade surfaces, by applying a NURBS surface fit, and subsequently utilized for downstream finite-element stress analysis. The ramifications of the FOD on the local stresses within the part are illustrated, providing critical information to the engineers for their MRO decisions. The automated flow of information from geometric inspection within structural analysis, enabled by MFIN, presents opportunities for effectively assessing products by utilizing their current geometries and improving decision-making during the product lifecycle.</p>