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‣ Modelos de material para espumas poliméricas aplicadas a estruturas aeronáuticas em material compósito sanduíche; Material models for polymeric foams applied to aircraft structures in sandwich composite materials

Caliri Junior, Mauricio Francisco
Fonte: Biblioteca Digitais de Teses e Dissertações da USP Publicador: Biblioteca Digitais de Teses e Dissertações da USP
Tipo: Dissertação de Mestrado Formato: application/pdf
Publicado em 08/07/2010 Português
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Estruturas aeronáuticas são em sua grande parte fabricadas em material compósito para que sejam atendidas as especificações de projeto. Entre essas estruturas destaca-se a estrutura sanduíche. A utilização desse tipo de estrutura requer estudos extensos em novos materiais, bem como na aplicação dos mesmos. Uma atenção especial para o núcleo dessas estruturas é necessária, pois este material é na verdade uma estrutura celular, como as espumas poliméricas. Esta dissertação busca concatenar a literatura com a prática ao estudar a calibração de modelos de material para descrever o comportamento mecânico de espumas poliméricas, bem como avaliar suas potencialidades e limitações. Estas espumas são estruturas celulares cujos mecanismos de falha consistem em respostas micro e macroscópicas. A identificação e quantificação desses comportamentos podem ser feitas através da investigação de modelos de material micro-mêcanicos ou fenomenológicos (macro-mecânicos) associados a ensaios e análises experimentais tanto do material celular quanto da estrutura na qual este material é utilizado. Cada abordagem, micro ou macro-mecânica, possui vantagens e desvantagens que no presente trabalho são discutidas para o material estudado (espuma polimérica rígida de PVC...

‣ Estudo da corrosão e corrosão-fadiga em ligas de Al e Al - Li de alta resistência para aplicação aeronáutica; Study behaviour of corrosion and corrosion fatigue in high strength Al and Al - Li alloys for aeronautic application

Moreto, Jéferson Aparecido
Fonte: Biblioteca Digitais de Teses e Dissertações da USP Publicador: Biblioteca Digitais de Teses e Dissertações da USP
Tipo: Tese de Doutorado Formato: application/pdf
Publicado em 03/09/2012 Português
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A indústria aeronáutica está constantemente à procura de materiais que ofereçam benefícios em termos de redução de peso, desempenho e custo. Corrosão e fadiga em ligas de alumínio são questões importantes na avaliação da vida útil em estruturas de aeronaves e na gestão de frotas. O objetivo deste trabalho foi avaliar os processos de corrosão e corrosão-fadiga nas ligas 2198-T851 e 7081-T73511, que são promissoras substitutas das ligas 2524-T3 e 7050-T7451 normalmente utilizada pela indústria aeronáutica. As técnicas de potencial de circuito aberto (PCA), polarização potenciodinâmica, polarização potenciodinâmica em eletrodo cilíndrico rotatório, espectroscopia de impedância eletroquímica (EIE), eletrodo vibratório de alta resolução (SVET) e mapeamento de potencial (SKP) foram utilizadas para esclarecer e quantificar os mecanismos de corrosão destas ligas de alumínio. Os ensaios de fadiga e corrosão-fadiga foram realizados com uma razão de carga (R) de 0,1 e frequência de 15 Hz em ar e 0,1 Hz em meio de névoa salina. As amostras, antes e após os testes de corrosão e corrosão-fadiga foram analisadas usando microscopia eletrônica de varredura (MEV). As características localizadas das quatro ligas estão essencialmente relacionadas com a existência de compostos intermetálicos que...

‣ Damage and progressive failure analysis for aeronautic composite structures with curvature; Modelos de falha e dano para estruturas aeronáuticas com curvatura e fabricadas em material compósito

Ribeiro, Marcelo Leite
Fonte: Biblioteca Digitais de Teses e Dissertações da USP Publicador: Biblioteca Digitais de Teses e Dissertações da USP
Tipo: Tese de Doutorado Formato: application/pdf
Publicado em 03/04/2013 Português
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Recent improvements in manufacturing processes and materials properties associated with excellent mechanical characteristics and low weight have became composite materials very attractive for application on civil aircraft structures. However, even new designs are still very conservative, because the composite structure failure phenomena are very complex. Several failure criteria and theories have been developed to describe the damage process and how it evolves, but the solution of the problem is still open. Moreover, modern manufacturing processes, e.g. filament winding, have been used to produce a wide variety of structural shapes. Therefore, this work presents the development of a damage model and its application to simulate the progressive failure of flat composite laminates as well as for composite cylinders made by filament winding process. The proposed damage model has been implemented as a UMAT (User Material Subroutine) and VUMAT (User Material Subroutine for explicit simulations), which were linked to ABAQUSTM Finite Element (FE) commercial package. Progressive failure analyses have been carried out using FE Method in order to simulate the failure of filament wound composite structures under different quasi-static and impact loading conditions. In addition...

‣ Robust control to parametric uncertainties in smart structures using linear matrix inequalities

Da Suva, Samuel; Lopes, V.; Assunção, E.
Fonte: Universidade Estadual Paulista Publicador: Universidade Estadual Paulista
Tipo: Artigo de Revista Científica Formato: 430-437
Português
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The study of algorithms for active vibrations control in flexible structures became an area of enormous interest, mainly due to the countless demands of an optimal performance of mechanical systems as aircraft and aerospace structures. Smart structures, formed by a structure base, coupled with piezoelectric actuators and sensor are capable to guarantee the conditions demanded through the application of several types of controllers. This article shows some steps that should be followed in the design of a smart structure. It is discussed: the optimal placement of actuators, the model reduction and the controller design through techniques involving linear matrix inequalities (LMI). It is considered as constraints in LMI: the decay rate, voltage input limitation in the actuators and bounded output peak (output energy). Two controllers robust to parametric variation are designed: the first one considers the actuator in non-optimal location and the second one the actuator is put in an optimal placement. The performance are compared and discussed. The simulations to illustrate the methodology are made with a cantilever beam with bonded piezoelectric actuators.

‣ A review on the development and properties of continuous fiber/epoxy/aluminum hybrid composites for aircraft structures

Botelho, Edson Cocchieri; Silva, Rogério Almeida; Pardini, Luiz Cláudio; Rezende, Mirabel Cerqueira
Fonte: Universidade Estadual Paulista Publicador: Universidade Estadual Paulista
Tipo: Artigo de Revista Científica Formato: 247-256
Português
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Weight reduction and improved damage tolerance characteristics were the prime drivers to develop new family of materials for the aerospace/ aeronautical industry. Aiming this objective, a new lightweight Fiber/ Metal Laminate (FML) has been developed. The combination of metal and polymer composite laminates can create a synergistic effect on many properties. The mechanical properties of FML shows improvements over the properties of both aluminum alloys and composite materials individually. Due to their excellent properties, FML are being used as fuselage skin structures of the next generation commercial aircrafts. One of the advantages of FML when compared with conventional carbon fiber/epoxy composites is the low moisture absorption. The moisture absorption in FML composites is slower when compared with polymer composites, even under the relatively harsh conditions, due to the barrier of the aluminum outer layers. Due to this favorable atmosphere, recently big companies such as EMBRAER, Aerospatiale, Boing, Airbus, and so one, starting to work with this kind of materials as an alternative to save money and to guarantee the security of their aircrafts.

‣ Artificial Immune Systems with Negative Selection Applied to Health Monitoring of Aeronautical Structures

Anjos Lima, Fernando Parra dos; Chavarette, Fabio Roberto; Santos e Souza, Adriano dos; Frutuoso de Souza, Simone Silva; Martins Lopes, Mara Lucia; Tan, J.
Fonte: Trans Tech Publications Ltd Publicador: Trans Tech Publications Ltd
Tipo: Conferência ou Objeto de Conferência Formato: 283-289
Português
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In this paper we present a system for aircraft structural health monitoring based on artificial immune systems with negative selection. Inspired by a biological process, the principle of discrimination proper/non-proper, identifies and characterizes the signs of structural failure. The main application of this method is to assist in the inspection of aircraft structures, to detect and characterize flaws and decision making in order to avoid disasters. We proposed a model of an aluminum beam to perform the tests of the method. The results obtained by this method are excellent, showing robustness and accuracy.

‣ Análise de tensões e vida em fadiga de juntas coladas em estruturas aeronáuticas metálicas; Stress analysis and fatigue life of bonded joints in metallic aircraft structures

Carlos Alexandre Oliveira de Souza
Fonte: Biblioteca Digital da Unicamp Publicador: Biblioteca Digital da Unicamp
Tipo: Tese de Doutorado Formato: application/pdf
Publicado em 23/07/2013 Português
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Na indústria aeronáutica é de extrema importância o uso de juntas coladas, rebitadas e parafusadas na união de componentes ou partes estruturais. Com o desenvolvimento de novos materiais e novas técnicas de manufatura, as juntas coladas passaram a ser mais utilizadas devido a algumas vantagens sobre as tradicionais juntas rebitadas e parafusadas, tais como: melhor distribuição das tensões na região de colagem, melhor vedação, melhor acabamento, melhor resistência à fadiga, maior eficiência aerodinâmica e o mais importante em aplicações aeronáuticas, menor peso. O projeto de juntas coladas é baseado em análises para a determinação das tensões normais e cisalhantes no adesivo e do campo de deslocamentos ao longo da junta. E no caso de solicitação cíclica, ou seja, fadiga é necessário ainda desenvolver modelos para prever a vida em fadiga de trincas na camada de adesivo e nos aderentes. O objetivo deste trabalho é estudar o comportamento de juntas coladas em estruturas metálicas de aeronaves solicitadas em fadiga, através de modelos analíticos, numéricos e ensaios experimentais. No decorrer do trabalho foram realizados ensaios estáticos, de fadiga e tenacidade à fratura de corpos de prova com juntas coladas. Também foram projetados e testados subcomponentes que representam de forma aproximada...

‣ Elliptical and circular bonded composite repair under mechanical and thermal loading in aircraft structures

Benyahia,Faycal; Albedah,Abdulmohsen; Bouiadjra,Bel Abbes Bachir
Fonte: ABM, ABC, ABPol Publicador: ABM, ABC, ABPol
Tipo: Artigo de Revista Científica Formato: text/html
Publicado em 01/10/2014 Português
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In this study, the three-dimensional finite element method is used to achieve a comparison between the semi circular and semi elliptical patch repairs in aircraft structures. The comparison was done by the analysis of : the mechanical and thermal stress intensity factors (SIF and TSIF) at the tip of repaired crack and the distribution of the adhesive stresses for the two patch shapes. The obtained results show that the semi circular shape of the patch presents lower stress intensity factor at the crack tip, which is beneficial for the fatigue life and lower adhesives stresses, which is beneficial for the repair durability. In addition the circular patch is subjected to less significant thermal residual stresses compared to the elliptical shapes.

‣ Optical Fiber Sensors for Aircraft Structural Health Monitoring

García, Iker; Zubia, Joseba; Durana, Gaizka; Aldabaldetreku, Gotzon; Illarramendi, María Asunción; Villatoro, Joel
Fonte: MDPI Publicador: MDPI
Tipo: Artigo de Revista Científica
Publicado em 30/06/2015 Português
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Aircraft structures require periodic and scheduled inspection and maintenance operations due to their special operating conditions and the principles of design employed to develop them. Therefore, structural health monitoring has a great potential to reduce the costs related to these operations. Optical fiber sensors applied to the monitoring of aircraft structures provide some advantages over traditional sensors. Several practical applications for structures and engines we have been working on are reported in this article. Fiber Bragg gratings have been analyzed in detail, because they have proved to constitute the most promising technology in this field, and two different alternatives for strain measurements are also described. With regard to engine condition evaluation, we present some results obtained with a reflected intensity-modulated optical fiber sensor for tip clearance and tip timing measurements in a turbine assembled in a wind tunnel.

‣ Fibre Optic Sensors for Structural Health Monitoring of Aircraft Composite Structures: Recent Advances and Applications

Di Sante, Raffaella
Fonte: MDPI Publicador: MDPI
Tipo: Artigo de Revista Científica
Publicado em 30/07/2015 Português
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In-service structural health monitoring of composite aircraft structures plays a key role in the assessment of their performance and integrity. In recent years, Fibre Optic Sensors (FOS) have proved to be a potentially excellent technique for real-time in-situ monitoring of these structures due to their numerous advantages, such as immunity to electromagnetic interference, small size, light weight, durability, and high bandwidth, which allows a great number of sensors to operate in the same system, and the possibility to be integrated within the material. However, more effort is still needed to bring the technology to a fully mature readiness level. In this paper, recent research and applications in structural health monitoring of composite aircraft structures using FOS have been critically reviewed, considering both the multi-point and distributed sensing techniques.

‣ Técnicas de inteligência artificial aplicadas ao método de monitoramento de integridade estrutural baseado na impedância eletromecânica para monitoramento de danos em estruturas aeronáuticas; Artificial intelligence techniques applied to the impedance-based structural health monitoring technique for monitoring damage in aircraft structures

Palomino, Lizeth Vargas
Fonte: Universidade Federal de Uberlândia Publicador: Universidade Federal de Uberlândia
Tipo: Tese de Doutorado
Português
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O conceito básico da técnica de integridade estrutural baseada na impedância tem a ver com o monitoramento da variação da impedância eletromecânica da estrutura, causada pela presença alterações estruturais, através de pastilhas de material piezelétrico coladas na superfície da estrutura ou nela incorporadas. A impedância medida se relaciona com a impedância mecânica da estrutura. A partir da variação dos sinais de impedância pode-se concluir pela existência ou não de uma falha. Para quantificar esta falha, métricas de dano são especialmente definidas, permitindo atribuir-lhe um valor escalar característico. Este trabalho pretende inicialmente avaliar a influência de algumas condições ambientais, tais como os campos magnéticos e os meios iônicos na medição de impedância. Os resultados obtidos mostram que os campos magnéticos não tem influência na medição de impedância e que os meios iônicos influenciam os resultados; entretanto, ao blindar o sensor, este efeito se reduz consideravelmente. Também foi estudada a influencia da geometria, ou seja, do formato do PZT e da posição do sensor com respeito ao dano. Verificou-se que o formato do PZT não tem nenhuma influência na medição e que a posição do sensor é importante para detectar corretamente o dano. Neste trabalho se apresenta o desenvolvimento de um sistema de medição de impedância de baixo custo e portátil que tem a capacidade de medir e armazenar a medição de 16 PZTs sem a necessidade de intervenção humana. Um aspecto de fundamental importância no contexto deste trabalho é a caracterização do dano a partir dos sinais de impedância coletados. Neste sentido...

‣ Finite element modelling and high speed testing of countersunk composite aircraft joints

Egan, Brian
Fonte: University of Limerick Publicador: University of Limerick
Tipo: info:eu-repo/semantics/doctoralThesis; all_ul_research; ul_published_reviewed; ul_theses_dissertations
Português
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peer-reviewed; Bolted joints feature extensively in composite aircraft structures, facilitating disassembly for maintenance while offering a cost effective joining method. However, inadequate tools for predicting failure of composite bolted joints have led to extensive physical testing programs and conservative design solutions. As usage of composites in airframe design has increased, the optimisation of composite bolted joints has become a key priority for aircraft manufacturers. The phasing out of metal in large commercial aircraft has now reached the fuselage structure, with next-generation aircraft such as the Airbus A350 featuring all-composite designs. Bolted fuselage skin joints tend to be single-lap and incorporate countersunk fasteners for aerodynamic reasons. In order to investigate the mechanical behaviour of single-lap countersunk composite joints, detailed 3D FE models have been developed. Initially, this difficult contact problem was studied elastically using the implicit FE solver, Abaqus/Standard. The mechanical response and hole boundary stress distributions were studied for clearance levels both inside and outside typical aerospace tolerances. Increased clearance delayed load take-up, reduced stiffness and altered hole boundary stresses. Significant convergence issues in these elastic implicit analyses prompted the choice of an explicit solver for challenging simulations of bearing failure in single and multi-bolt joints. A composite damage model was developed for the simulaton of bearing failure in 3D Abaqus/Explicit joint models. Physically-based failure criteria and a crack band model ensured accurate and objective solutions. Predictions of bearing failure in quasistatically loaded...

‣ An investigation of stress determination for aircraft fatigue life estimation from in-flight strain data.

Horne, George Michael
Fonte: Monterey, California: Naval Postgraduate School Publicador: Monterey, California: Naval Postgraduate School
Tipo: Tese de Doutorado
Português
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A thorough knowledge of localized stresses due to geometric effects is necessary for accurate fatigue life estimation in aircraft structures. The Department of Aeronautics, Naval Postgraduate School, Monterey, California, has developed a strain monitoring system that provides data on nominal stresses experienced by aircraft structures, which can be applied to obtain local stresses at a stress concentration, provided a local stress vs. nominal strain relationship is available. A theory proposed by Neuber lends itself to development of a method by which local stress can be obtained with knowledge of nominal strain and material properties alone. Stress relaxation behavior was obtained for two cyclic loading histories of plate specimens in an effort to extend the monotonic local stress vs. nominal strain relationships into practical use for fatigue life estimation of aircraft structures

‣ Use of a novel fiber optical strain sensor for monitoring the vertical deflection of an aircraft flap

Durana, Gaizka; Kirchhof, Marlene; Luber, Michael; Sáez de Ocáriz, Idurre; Poisel, Hans; Zubía, Joseba; Vázquez, Carmen
Fonte: IEEE Publicador: IEEE
Tipo: Artigo de Revista Científica Formato: application/pdf
Publicado em /10/2009 Português
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The present paper reports the use of a plastic optical fiber-based sensor for elongation measurements in an aircraft flap subjected to different types of flexural loading conditions. The sensor, bonded to the surface of the aircraft structure, relies on measuring the phase shift that occurs between two sinusoidally modulated light signals when the aircraft structure is bent. The light signals are guided through two optical fibers, one of them fixed to the top surface of the flap, and the other one to the bottom surface. The sensor offers good signal stability and repeatability and represents a cost-effective alternative to other more sophisticated health-monitoring systems currently used.

‣ Aircraft fuel tank vulnerability to hydraulic ram : modification of the Northrop finite element, computer code BR-1 to include fluid-structure interaction ; theory and user's manual for BR-1HR

Ball, Robert E.
Fonte: Monterey, California. Naval Postgraduate School Publicador: Monterey, California. Naval Postgraduate School
Tipo: Relatório Formato: 35 p. : ill. ; 28 cm.
Português
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The finite element digital computer code BR-1, developed by the Northrop Corporation, for predicting the effects of internal air blast on combat aircraft structures is modified to include the effects of compressible fluid -structure interaction. The true interaction phenomenon is approximated by the piston theory. The modification enables the code to be used to predict the structural response of aircraft fuel tanks subjected to penetrating bullets and fragments. It can also be used in many other fluid-structure interaction problems. This report contains the theory, the modifications, and the additional instructions required to operate the modified code, called BR-1HR. The code is operational on the IBM 360/67 in FORTRAN IV, Level H.; Prepared for: Air Force Flight Dynamics Laboratory, Wright-Patterson AFB, OH 45433; http://archive.org/details/aircraftfueltank00ball; FY 1456-74-00001; NA

‣ Interface of materials and structures on airframes. Part 3, Design problems in aircraft structures including proceedings of Monterey Symposium / [by] Ulrich Haupt.

Haupt, Ulrich
Fonte: Monterey, California. Naval Postgraduate School Publicador: Monterey, California. Naval Postgraduate School
Tipo: Relatório
Português
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The proceedings of the Monterey Symposium on Design Problems in Aircraft Structures provide a basic survey of design problems from the engineer's viewpoint. Further analysis of the present situation draws attention to some essential aspects which are not yet generally recognized. This leads to the conclusion that recent design problems cannot be solved on a technological level alone. An organizational effort is needed to disseminate available information. Beyond this, the complexity of interactions must be understood more thoroughly and this requires an educational effort on a broad basis. A practical and systematic approach toward the solution of these problems is developed. (Author); Naval Air Systems Command Work Request No. WR- 2-6059; http://archive.org/details/interfaceofmater71111haup; NA

‣ Perturbation Analysis for Robust Damage Detection with Application to Multifunctional Aircraft Structures

HAJRYA, Rafik; MECHBAL, Nazih
Fonte: Techno-Press Publicador: Techno-Press
Português
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The most widely known form of multifunctional aircraft structure is smart structures for structural health monitoring (SHM). The aim is to provide automated systems whose purposes are to identify and to characterize possible damage within structures by using a network of actuators and sensors. Unfortunately, environmental and operational variability render many of the proposed damage detection methods difficult to successfully be applied. In this paper, an original robust damage detection approach using output-only vibration data is proposed. It is based on independent component analysis and matrix perturbation analysis, where an analytical threshold is proposed to get rid of statistical assumptions usually performed in damage detection approach. The effectiveness of the proposed SHM method is demonstrated numerically using finite element simulations and experimentally through a conformal load-bearing antenna structure and composite plates instrumented with piezoelectric ceramic materials.; FUI MSIE (Pole Astech)

‣ A study on driving interference-fit fastener using stress wave

Cao, Zhengqiang; Qin, Qing Hua
Fonte: Trans Tech Publications Publicador: Trans Tech Publications
Tipo: Artigo de Revista Científica
Português
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Interference-fit fasteners are used in large numbers throughout aircraft structures. Conventional installation methods are driving fasteners into aperture using pneumatic or hydraulic tooling, installation damage always occurs using these methods. This pa

‣ Aircraft Landing Problem: Efficient Algorithm for a Given Landing Sequence

Awasthi, Abhishek; Kramer, Oliver; Lässig, Jörg
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
Publicado em 26/10/2013 Português
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In this paper, we investigate a special case of the static aircraft landing problem (ALP) with the objective to optimize landing sequences and landing times for a set of air planes. The problem is to land the planes on one or multiple runways within a time window as close as possible to the preferable target landing time, maintaining a safety distance constraint. The objective of this well-known NP-hard optimization problem is to minimize the sum of the total penalty incurred by all the aircraft for arriving earlier or later than their preferred landing times. For a problem variant that optimizes a given feasible landing sequence for the single runway case, we present an exact polynomial algorithm and prove the run-time complexity to lie in $O(N^3)$, where $N$ is the number of aircraft. The proposed algorithm returns the optimal solution for the ALP for a given feasible landing sequence on a single runway for a common practical case of the ALP described in the paper. Furthermore, we propose a strategy for the ALP with multiple runways and present our results for all the benchmark instances with single and multiple runways, while comparing them to previous results in the literature.; Comment: 16th IEEE International Conference on Computational Science and Engineering (CSE 2013)

‣ Analytical and numerical modelling of plasticity-induced fatigue crack closure near cold-expanded holes in aircraft structures

Matos,Paulo F. P. de; Nowell,David
Fonte: Sociedade Portuguesa de Materiais Publicador: Sociedade Portuguesa de Materiais
Tipo: Artigo de Revista Científica Formato: text/html
Publicado em 01/01/2008 Português
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Over the last few years considerable effort has been put into the improvement of the fatigue life of aircraft structures. Aircraft experience complex loading conditions during flight and safe operation requires understanding of the underlying mechanics of fatigue crack growth. One of the outcomes of the research carried out over the last thirty years is that fatigue cracks in metals are partially closed over part of a load cycle. This phenomenon is thought by many researchers to be the key to understanding the effect of non-uniform loading. Understanding crack closure is particularly challenging when initial residual stress fields (e.g. due to manufacturing or mechanical treatment) need to be taken into account. For example, rivet holes are a critical area for fatigue and they are usually cold expanded to create a beneficial residual stress field and to improve the fatigue performance. This paper describes the development of a simple analytical model for plasticity-induced fatigue crack closure taking into account the residual stresses due to cold expansion of rivet holes. The model is compared to a more sophisticated finite element analysis of plasticity-induced crack closure. The results show that the residual stress field has a strong influence on the closure behaviour and therefore on fatigue crack propagation. The potential for the application of this model to real components is assessed by modelling some experiments taken from the literature. The model results agree with the experimental findings for the location of fatigue crack initiation. Residual stresses from FE analyses of cold expansion were used as an input to the analytical closure model...