Obtenção e caracterização de compósitos de benzoxazina/fibra de carbono

Pós-graduação em Engenharia Mecânica - FEG

Avaliação dos parâmetros tempo, corrente e pressão na soldagem por resistência elétrica de compósitos PEI/fibras contínuas: influência na resistência mecânica

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)

Sistema de gestão da qualidade numa organização pública de P&D: fatores que influenciam a certificação

Pós-graduação em Engenharia Mecânica - FEG

Neural models for predicting hole diameters in drilling processes

Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)

Neural models for predicting hole diameters in drilling processes

Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)

Estudo do efeito do transporte de massa nas curvas de polarização potenciodinâmica em ligas de alumínio da série 7XXX de aplicação aeronáutica

Aluminum Alloys are widely used as structural materials in the aerospace industry due to low weight, high mechanical strength and enduring corrosion resistance. Their resistance to corrosion is attributed to the rapidly formed stable oxide film (Al2O3) which spontaneously forms itself on the surface of the material. However, in the presence of aggressive ions, such as halide, Aluminum Alloys are subject to a localized process of corrosion. The electrochemical behavior of 7081-T73511 and 7050-T7451 Aluminum Alloys employed in the aerospace industry was investigated using a 0.6 M NaCl solution under the conditions of a controlled mass transport employing a rotating disk electrode. The theoretical limiting current density was determined by the Kouteki-Levich equation. The results confirmed that the inter-metallic Al7Cu2Fe acts as preferential cathode generating the galvanic coupling and the dissolution of the Aluminummatrix around it.

Influence of adhesive thickness on adhesively bonded joints under fatigue loading

Research on adhesive joints is arousing increasing interest in aerospace industry. Incomplete knowledge of fatigue in adhesively bonded joints is a major obstacle to their application. The prediction of the disbonding growth is yet an open question. This thesis researches the influence of the adhesive thickness on fatigue disbond growth. Experimental testing on specimens with different thickness has been performed. Both a conventional approach based on the strain energy release rate and an approach based on cyclic strain energy are provided. The inadequacy of the former approach is discussed. Outcomes from tests support the idea of correlating the crack growth rate to the cyclic strain energy. In order to push further the study, a 2D finite element model for the prediction of disbond growth under quasi-static loading has been developed and implemented in Abaqus. Numerical simulations have been conducted with different values of the adhesive thickness. The results from tests and simulations are in accordance with each other. According to them, no dependence of disbonding on the adhesive thickness has been evidenced.

Erfahrbares Programmieren durch den zielgerichten Einsatz von Flugdrohnen im Informatikunterricht

Informatik- und insbesondere Programmierunterricht sind heute ein wichtiger Bestandteil der schulischen Ausbildung. Vereinfachte Entwicklungsumgebungen, die auf die Abstraktion typischer Programmierkonzepte in Form von grafischen Bausteinen setzen, unterstützen diesen Trend. Zusätzliche Attraktivität wird durch die Verwendung exotischer Laufzeitumgebungen (z. B. Roboter) geschaffen. Die in diesem Paper vorgestellte Plattform “ScratchDrone” führt ergänzend zu diesen Angeboten eine moderne Flugdrohne als innovative Laufzeitumgebung für Scratch-Programme ein. Die Programmierung kann dabei dank modularer Systemarchitektur auf verschiedenen Abstraktionsebenen erfolgen, abhängig vom Lernfortschritt der Schüler. Kombiniert mit einem mehrstufigen didaktischen Modell, der Herausforderung der Bewegung im 3D-Raum sowie der natürlichen menschlichen Faszination für das Fliegen wird so eine hohe Lernmotivation bei jungen Programmieranfängern erreicht.

Aluminum slurry coatings to replace cadmium for aeronautic applications

Cadmium has been widely used as a coating to provide protection against galvanic corrosion for steels and for its natural lubricity on threaded applications. However, it is a toxic metal and a known carcinogenic agent, which is plated from an aqueous bath containing cyanide salts. For these reasons, the use of cadmium has been banned in Europe for most industrial applications. However, the aerospace industry is still exempt due to the stringent technical and safety requirements associated with aeronautical applications, as an acceptable replacement is yet to be found. Al slurry coatings have been developed as an alternative to replace cadmium coatings. The coatings were deposited on AISI 4340 steel and have been characterized by optical and electron microscopy. Testing included salt fog corrosion exposure, fluid corrosion exposure (immersion), humidity resistance, coating-substrate and paint-coating adhesion, electric conductivity, galvanic corrosion, embrittlement and fatigue. The results indicated that Al slurry coatings are an excellent alternative for Cd replacement.

High fidelity simulations of failure in fiber-reinforced composites

Los ensayos virtuales de materiales compuestos han aparecido como un nuevo concepto dentro de la industria aeroespacial, y disponen de un vasto potencial para reducir los enormes costes de certificación y desarrollo asociados con las tediosas campañas experimentales, que incluyen un gran número de paneles, subcomponentes y componentes. El objetivo de los ensayos virtuales es sustituir algunos ensayos por simulaciones computacionales con alta fidelidad. Esta tesis es una contribución a la aproximación multiescala desarrollada en el Instituto IMDEA Materiales para predecir el comportamiento mecánico de un laminado de material compuesto dadas las propiedades de la lámina y la intercara. La mecánica de daño continuo (CDM) formula el daño intralaminar a nivel constitutivo de material. El modelo de daño intralaminar se combina con elementos cohesivos para representar daño interlaminar. Se desarrolló e implementó un modelo de daño continuo, y se aplicó a configuraciones simples de ensayos en laminados: impactos de baja y alta velocidad, ensayos de tracción, tests a cortadura. El análisis del método y la correlación con experimentos sugiere que los métodos son razonablemente adecuados para los test de impacto, pero insuficientes para el resto de ensayos. Para superar estas limitaciones de CDM, se ha mejorado la aproximación discreta de elementos finitos enriqueciendo la cinemática para incluir discontinuidades embebidas: el método extendido de los elementos finitos (X-FEM). Se adaptó X-FEM para un esquema explícito de integración temporal. El método es capaz de representar cualitativamente los mecanismos de fallo detallados en laminados. Sin embargo, los resultados muestran inconsistencias en la formulación que producen resultados cuantitativos erróneos. Por último, se ha revisado el método tradicional de X-FEM, y se ha desarrollado un nuevo método para superar sus limitaciones: el método cohesivo X-FEM estable. Las propiedades del nuevo método se estudiaron en detalle, y se concluyó que el método es robusto para implementación en códigos explícitos dinámicos escalables, resultando una nueva herramienta útil para la simulación de daño en composites. Virtual testing of composite materials has emerged as a new concept within the aerospace industry. It presents a very large potential to reduce the large certification costs and the long development times associated with the experimental campaigns, involving the testing of a large number of panels, sub-components and components. The aim of virtual testing is to replace some experimental tests by high-fidelity numerical simulations. This work is a contribution to the multiscale approach developed in Institute IMDEA Materials to predict the mechanical behavior of a composite laminate from the properties of the ply and the interply. Continuum Damage Mechanics (CDM) formulates intraply damage at the the material constitutive level. Intraply CDM is combined with cohesive elements to model interply damage. A CDM model was developed, implemented, and applied to simple mechanical tests of laminates: low and high velocity impact, tension of coupons, and shear deformation. The analysis of the results and the comparison with experiments indicated that the performance was reasonably good for the impact tests, but insuficient in the other cases. To overcome the limitations of CDM, the kinematics of the discrete finite element approximation was enhanced to include mesh embedded discontinuities, the eXtended Finite Element Method (X-FEM). The X-FEM was adapted to an explicit time integration scheme and was able to reproduce qualitatively the physical failure mechanisms in a composite laminate. However, the results revealed an inconsistency in the formulation that leads to erroneous quantitative results. Finally, the traditional X-FEM was reviewed, and a new method was developed to overcome its limitations, the stable cohesive X-FEM. The properties of the new method were studied in detail, and it was demonstrated that the new method was robust and can be implemented in a explicit finite element formulation, providing a new tool for damage simulation in composite materials.

Smart aeronautical structures: development and experimental validation of a structural health monitoring system for damage detection

En muchas áreas de la ingeniería, la integridad y confiabilidad de las estructuras son aspectos de extrema importancia. Estos son controlados mediante el adecuado conocimiento de danos existentes. Típicamente, alcanzar el nivel de conocimiento necesario que permita caracterizar la integridad estructural implica el uso de técnicas de ensayos no destructivos. Estas técnicas son a menudo costosas y consumen mucho tiempo. En la actualidad, muchas industrias buscan incrementar la confiabilidad de las estructuras que emplean. Mediante el uso de técnicas de última tecnología es posible monitorizar las estructuras y en algunos casos, es factible detectar daños incipientes que pueden desencadenar en fallos catastróficos. Desafortunadamente, a medida que la complejidad de las estructuras, los componentes y sistemas incrementa, el riesgo de la aparición de daños y fallas también incrementa. Al mismo tiempo, la detección de dichas fallas y defectos se torna más compleja. En años recientes, la industria aeroespacial ha realizado grandes esfuerzos para integrar los sensores dentro de las estructuras, además de desarrollar algoritmos que permitan determinar la integridad estructural en tiempo real. Esta filosofía ha sido llamada “Structural Health Monitoring” (o “Monitorización de Salud Estructural” en español) y este tipo de estructuras han recibido el nombre de “Smart Structures” (o “Estructuras Inteligentes” en español). Este nuevo tipo de estructuras integran materiales, sensores, actuadores y algoritmos para detectar, cuantificar y localizar daños dentro de ellas mismas. Una novedosa metodología para detección de daños en estructuras se propone en este trabajo. La metodología está basada en mediciones de deformación y consiste en desarrollar técnicas de reconocimiento de patrones en el campo de deformaciones. Estas últimas, basadas en PCA (Análisis de Componentes Principales) y otras técnicas de reducción dimensional. Se propone el uso de Redes de difracción de Bragg y medidas distribuidas como sensores de deformación. La metodología se validó mediante pruebas a escala de laboratorio y pruebas a escala real con estructuras complejas. Los efectos de las condiciones de carga variables fueron estudiados y diversos experimentos fueron realizados para condiciones de carga estáticas y dinámicas, demostrando que la metodología es robusta ante condiciones de carga desconocidas. ABSTRACT In many engineering fields, the integrity and reliability of the structures are extremely important aspects. They are controlled by the adequate knowledge of existing damages. Typically, achieving the level of knowledge necessary to characterize the structural integrity involves the usage of nondestructive testing techniques. These are often expensive and time consuming. Nowadays, many industries look to increase the reliability of the structures used. By using leading edge techniques it is possible to monitoring these structures and in some cases, detect incipient damage that could trigger catastrophic failures. Unfortunately, as the complexity of the structures, components and systems increases, the risk of damages and failures also increases. At the same time, the detection of such failures and defects becomes more difficult. In recent years, the aerospace industry has done great efforts to integrate the sensors within the structures and, to develop algorithms for determining the structural integrity in real time. The ‘philosophy’ has being called “Structural Health Monitoring” and these structures have been called “smart structures”. These new types of structures integrate materials, sensors, actuators and algorithms to detect, quantify and locate damage within itself. A novel methodology for damage detection in structures is proposed. The methodology is based on strain measurements and consists in the development of strain field pattern recognition techniques. The aforementioned are based on PCA (Principal Component Analysis) and other dimensional reduction techniques. The use of fiber Bragg gratings and distributed sensing as strain sensors is proposed. The methodology have been validated by using laboratory scale tests and real scale tests with complex structures. The effects of the variable load conditions were studied and several experiments were performed for static and dynamic load conditions, demonstrating that the methodology is robust under unknown load conditions.

Machinability Study of an aluminum-copper alloy

Machinability of materials is one of the factors that make us wonder what tools to use and what material is best suited for a particular cutting tool and which process is more efficient in the production of a component. In the case of parts for the aerospace industry, manufacturing processes assume greater importance due to the extreme demands on reliability and quality.

An Empirical Comparison of Reuse in Embedded and Nonembedded Systems

High-quality software, delivered on time and budget, constitutes a critical part of most products and services in modern society. Our government has invested billions of dollars to develop software assets, often to redevelop the same capability many times. Recognizing the waste involved in redeveloping these assets, in 1992 the Department of Defense issued the Software Reuse Initiative. The vision of the Software Reuse Initiative was "To drive the DoD software community from its current "re-invent the software" cycle to a process-driven, domain-specific, architecture-centric, library-based way of constructing software.'' Twenty years after issuing this initiative, there is evidence of this vision beginning to be realized in nonembedded systems. However, virtually every large embedded system undertaken has incurred large cost and schedule overruns. Investigations into the root cause of these overruns implicates reuse. Why are we seeing improvements in the outcomes of these large scale nonembedded systems and worse outcomes in embedded systems? This question is the foundation for this research. The experiences of the Aerospace industry have led to a number of questions about reuse and how the industry is employing reuse in embedded systems. For example, does reuse in embedded systems yield the same outcomes as in nonembedded systems? Are the outcomes positive? If the outcomes are different, it may indicate that embedded systems should not use data from nonembedded systems for estimation. Are embedded systems using the same development approaches as nonembedded systems? Does the development approach make a difference? If embedded systems develop software differently from nonembedded systems, it may mean that the same processes do not apply to both types of systems. What about the reuse of different artifacts? Perhaps there are certain artifacts that, when reused, contribute more or are more difficult to use in embedded systems. Finally, what are the success factors and obstacles to reuse? Are they the same in embedded systems as in nonembedded systems? The research in this dissertation is comprised of a series of empirical studies using professionals in the aerospace and defense industry as its subjects. The main focus has been to investigate the reuse practices of embedded systems professionals and nonembedded systems professionals and compare the methods and artifacts used against the outcomes. The research has followed a combined qualitative and quantitative design approach. The qualitative data were collected by surveying software and systems engineers, interviewing senior developers, and reading numerous documents and other studies. Quantitative data were derived from converting survey and interview respondents' answers into coding that could be counted and measured. From the search of existing empirical literature, we learned that reuse in embedded systems are in fact significantly different from nonembedded systems, particularly in effort in model based development approach and quality where the development approach was not specified. The questionnaire showed differences in the development approach used in embedded projects from nonembedded projects, in particular, embedded systems were significantly more likely to use a heritage/legacy development approach. There was also a difference in the artifacts used, with embedded systems more likely to reuse hardware, test products, and test clusters. Nearly all the projects reported using code, but the questionnaire showed that the reuse of code brought mixed results. One of the differences expressed by the respondents to the questionnaire was the difficulty in reuse of code for embedded systems when the platform changed. The semistructured interviews were performed to tell us why the phenomena in the review of literature and the questionnaire were observed. We asked respected industry professionals, such as senior fellows, fellows and distinguished members of technical staff, about their experiences with reuse. We learned that many embedded systems used heritage/legacy development approaches because their systems had been around for many years, before models and modeling tools became available. We learned that reuse of code is beneficial primarily when the code does not require modification, but, especially in embedded systems, once it has to be changed, reuse of code yields few benefits. Finally, while platform independence is a goal for many in nonembedded systems, it is certainly not a goal for the embedded systems professionals and in many cases it is a detriment. However, both embedded and nonembedded systems professionals endorsed the idea of platform standardization. Finally, we conclude that while reuse in embedded systems and nonembedded systems is different today, they are converging. As heritage embedded systems are phased out, models become more robust and platforms are standardized, reuse in embedded systems will become more like nonembedded systems.

Layered silicate nanocomposites based on various high-functionality epoxy resins: The influence of an organoclay on resin cure

The influence of an organically modified clay on the curing behavior of three epoxy systems widely used in the aerospace industry and of different structures and functionalities, was studied. Diglycidyl ether of bisphenol A (DGEBA), triglycidyl p-amino phenol (TGAP) and tetraglycidyl diamino diphenylmethane (TGDDM) were mixed with an octadecyl ammonium ion modified organoclay and cured with diethyltoluene diamine (DETDA). The techniques of dynamic mechanical thermal analysis (DMTA), chemorheology and differential scanning calorimetry (DSC) were applied to investigate gelation and vitrification behavior, as well as catalytic effects of the clay on resin cure. While the formation of layered silicate nanocomposite based on the bifunctional DGEBA resin has been previously investigated to some extent, this paper represents the first detailed study of the cure behavior of different high performance, epoxy nanocomposite systems.

IT support for managing aircraft spares in a closed-loop supply chain

This paper reports on the development of elements of an e-supply chain management system for managing maintenance, repair and overhaul (MRO) relationships in the aerospace industry. A standard systems development methodology has been followed to produce a process model (i.e. the AMSCR model); an information model (i.e. business rules) and a computerised information management capability (i.e. automated optimisation). The proof of concept for this web-based MRO supply chain system has been established through the collaboration with a sample of the different types of supply chain members. The proven benefit is a reduction in the stock-holding costs for the whole supply chain whilst also minimising non-flying time of the aircraft that the supply chain supports. This type of system is now vital in an industry that has continuously decreasing profit margins, which in turn means pressure to reduce servicing times and increase the interval between maintenance actions.