1,721,560 research outputs found
Compressive response of notched, woven fabric, face sheet honeycomb sandwich panels
No full textCentre notched honeycomb sandwich panels with woven carbon-epoxy face sheets and Nomex™ cores, tested uniaxially in compression, have been analysed to estimate their strength and damage tolerance. A plain weave T-300 carbon fibre fabric was used for the face sheets in two stacking sequences:[45/0/90] and [0/90]. Observations of macroscopic damage behaviour were different in the two layups. Linear damage zones (LDZs), consisting of fibre microbuckles and extensive delamination, were typically observed in the [0/90] material. The [45/0/90] material exhibited a delamination/bulge zone (DBZ), which consisted of an out of plane curved deformation of the outer 45° ply accompanied by a delamination from the interior 0° plies. Modelling of these failure modes and comparison with experimental data showed that the only mode representative of damage tolerant behaviour is LDZ formation and propagation for both material systems, and that the delamination/bulge behaviour is a secondary phenomenon. A linear softening cohesive zone model predicts the notched compressive strength reasonably well
Aerospace engineering requirements in building with composites
No full textThe growing use of composite material has arisen from their high specific strength and stiffness when compared to the more conventional materials, and the ability to tailor their structure to produce aerodynamically more efficient structural configurations. In this introductory chapter, it is argued that fiber-reinforced polymers, especially carbon fiber-reinforced plastics can and will, in the near future, contribute more than 50% of the structural mass of an aircraft. Of course, affordability is the key to survival in aerospace, whether civil or military and therefore, effort should be devoted to low-cost manufacturing methods in addition to analysis and computational simulation of the manufacturing and assembly process. The simulation of the structural performance should not be neglected since they are intimately connected. Virtual reality models in engineering prior to manufacturing to identify potential problems will make Industry 4.0 and the smart factory for composites a reality. Industry 4.0 focuses on data-driven manufacturing, where in the future, billions of machines, systems, and sensors will communicate with each other and share information, physical systems connected to digital twins, the Industrial Internet of Things (IIoT). This will not only enable companies to make design and production significantly more efficient, but it will also give them greater flexibility when it comes to tailoring production to meet market requirements
Introduction
No full textThe growing use of composite material has arisen from their high specific strength and stiffness, when compared to the more conventional materials, and the ability to tailor their structure to produce more aerodynamically efficient structural configurations. In this introductory chapter, it is argued that fibre reinforced polymers, especially carbon fibre reinforced plastics (CFRP), can and will in the near future contribute more than 50% of the structural mass of an aircraft. Of course, affordability is the key to survival in aerospace, whether civil or military, and therefore effort should be devoted to low cost manufacturing methods in addition to analysis and computational simulation of the manufacturing and assembly process. The simulation of the structural performance should not be neglected, since they are intimately connected
Strength prediction of patch-repaired CFRP laminates loaded in compression
No full textThe repair of a composite structure with a composite patch may use mechanical fastening, which often introduces undesirable stress concentrations or adhesive bonding, external or flush patches. In this paper the compressive behaviour of bonded external patch repairs is examined; the compressive loading mode is more severe than the tensile mode owing to the instability of delaminated plies, instability of the patch and skin strength reductions occurring under elevated temperatures and absorbed moisture conditions. By using a non-linear shear-lag analysis [Soutis C, Hu FZ. Design and performance of bonded patch repairs of composite structures. Proc Instn Mech Engrs 1997;211(G):1–9], design guidelines are produced for the selection of patch size, shape and membrane stiffness. A three-dimensional finite-element analysis is then performed to determine the stress field in the optimum repaired configuration and is used with a recently developed cohesive zone model [Soutis C, Fleck NA. Static compression failure of carbon fibre T88/924C composite plate with a single hole. J Compos Mater 1991;24(5):536–58; Soutis C. Damage tolerance of open-hole CFRP laminates loaded in compression. Composites Engineering 1994;4(3):317–27] to estimate the compressive failure load of the repaired laminate. The predicted strength is within 10% of the experimental data
Modelling the compressive response behaviour of monolithic and sandwich composite structures
No full textFailure in compression of fiber composite laminates with an open hole is by the initiation and growth of a microbuckle from the edge of the hole. The geometric inhomogeneity induces fiber rotation under increasing applied load; deformation localizes within a band and a microbuckle is initiated. The microbuckle then propagates in a stable manner for 2–3 mm and the component fails at a higher load than the initiation load. This process in carbon-epoxy and carbon-PEEK laminates was compared to an equivalent crack containing cohesive stresses. It is a crack bridging analysis that predicts the size of the buckled region as a function of the applied load, with the local stress supported by the buckled fibers decreasing linearly with the closing displacement of the microbuckle. The model is able to predict successfully the effects of hole size and lay-up upon the compressive strength and has been incorporated into a user-friendly computer program. Tests had been performed to obtain both the laminate un-notched strength and the compressive energy release rate associated with fiber microbuckling, which are required as the model's input. From a design point of view, it is desirable to predict these laminate properties from the mechanical properties of the fibers and the matrix and from the lay-up geometry
Open hole compressive strength of composite laminates and sandwich panels: Comparison between Budiansky-Fleck-Soutis model and experiments
No full textIn this study, the compressive behaviour of carbon fibre reinforced plastic quasi-isotropic laminates and sandwich panels with carbon fibre reinforced plastic face sheets and syntactic foam core has been investigated. Experimentally determined open hole strengths have been compared with theoretical predictions obtained by applying a linear cohesive zone model. The unnotched compressive strength has been experimentally determined, and the in-plane fracture toughness has been analytically predicted as input parameters of the model. Buckling phenomena occurred on some specimens, and they have been taken into account. Evaluation of macroscopic failure modes in compression tests on unnotched specimens led to a better understanding on the advantages of the analytical model and on the possibility of applying the model to sandwich structures. The experimental results were in good agreement with the analytical prediction by the Budiansky-Soutis-Fleck cohesive zone model, and the difference between theoretical and experimental open hole strengths of Syncore sandwich panels was <9%
Damage Detection in Composites By Artificial Neural Networks Trained By Using in Situ Distributed Strains
No full textIn this paper, a passive structural health monitoring (SHM) method capable of detecting the presence of damage in carbon fibre/epoxy composite plates is developed. The method requires the measurement of strains from the considered structure, which are used to set up, train, and test artificial neural networks (ANNs). At the end of the training phase, the networks find correlations between the given strains, which represent the ‘fingerprint’ of the structure under investigation. Changes in the distribution of these strains is captured by assessing differences in the previously identified strain correlations. If any cause generates damage that alters the strain distribution, this is considered as a reason for further detailed structural inspection. The novelty of the strain algorithm comes from its independence from both the choice of material and the loading condition. It does not require the prior knowledge of material properties based on stress-strain relationships and, as the strain correlations represent the structure and its mechanical behaviour, they are valid for the full range of operating loads. An implementation of such approach is herein presented based on the usage of a distributed optical fibre sensor that allows to obtain strain measurement with an incredibly high resolution
Going Beyond Counting First Authors in Author Co-citation Analysis
Get PDFThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Variations on the Author
Get PDF“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
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