138 research outputs found
Flax fibre metal laminates (FLARE): A bio-based FML alternative combining impact resistance and vibration damping?
No full textFibre metal laminates (FML) were originally developed as a hybrid material, to create synergy between the impact resistance of metals and excellent fatigue and corrosion resistance of fibre reinforced polymers, and to overcome the shortcomings of monolithic materials. Yet, the scope of the FML concept is predominantly limited to GLAss REinforced laminates (GLARE) for aerospace structures [1]. However, with the rising concerns about climate change, and the issues of recycling glass fibre composites, a new generation of FMLs with a reduced carbon footprint should be envisaged. This can be achieved by using bio-based fibre reinforced composite layers, particularly flax fibre instead of glass fibre composite, rendering FMLs with lower embodied energy, in which aluminium layers can be easily recycled by incineration with energy recuperation of the flax composite. Flax fibres demonstrate promising specific mechanical properties compared to glass fibres, particularly regarding tensile stiffness and bending stiffness and strength. This means that flax fibres can outperform glass fibres in stiffness-based designs, and in applications in which the loading mode is predominantly in bending. This includes applications in the transportation and construction sectors as well as secondary structures for civil aircraft, such as automotive panels, flooring, and bridge decks. Additionally, flax fibre composites demonstrate high damping capabilities due to the unique hierarchical structure of these fibres. This makes them particularly suitable for applications where vibrational and acoustic damping is of interest which includes many of the above given examples. However, they also have disadvantages such as high moisture absorption that can restrict their use [2]. The FML concept would overcome these limitations and thus allow the introduction of these materials in primary structures. In this study, the combination of flax fibre reinforced epoxy with thin aluminium layers is realised as a partially biobased alternative to current FMLs, aiming to obtain primarily good vibration damping properties and improved impact resistance. The impact behaviour of the flax fibre reinforced aluminium (FLARE) will be evaluated by low velocity impact and quasi-static indentation tests to identify the role of each material constituent. The results will be compared with a predictive model based on the work of F. Morinière et al. [3]. For the damping properties, to cover a wide range of frequencies and to compare methods, the vibration absorption capacities will be measured by dynamic mechanical analysis and vibration beam tests. The results will be compared to the model predictions from the metal volume fraction method. Finally, this study will give a first overview of the properties of FLARE and will verify the validity of the predictive tools developed for conventional FMLs, which help in the design phase to optimise the structure according to specific requirementsStructural Integrity & CompositesBio-based Structures & Material
Development of a Methodology to Support Design of Complex Aircraft Wings
No full textThe design of complex systems in today’s aerospace domain requires a balance between the ever-increasing complexity of the supporting technology and the drive to develop those systems in a compressed timeframe. The performance knowledge of a preliminary design must shift backwards in the lifecycle in order to exploit that knowledge when there is still freedom in the design. Design of aerospace structures with fiber metal laminates (FML) represents one such area where the increased design freedom comes at a cost of increased design complexity. The potential benefits of FML technology, however, demand a solution to this design challenge. FMLs require a different approach to design and manufacturing that so far has been only moderately explored for possible automation. In order to support design of an FML wing, a tailored design methodology and prototyping tools are needed. The quantitative systems engineering field of knowledge based engineering (KBE) provides a solution. A KBE approach, leveraging parametric, geometry-based modeling and expert FML manufacturability knowledge, can work within a design framework to automate many of the non-creative activities of the FML designer, such as initial layup design and manufacturability rule application. This research seeks to frame the FML wing design process, develop critical KBE design modules tailored for FML knowledge, and illustrate their utility in the balance of aerospace structure weight and cost.Aerospace Materials and Manufacturing (AMM); Aerospace Structures & Design Methodologies (AS&DM)Aerospace Engineerin
Theoretical analysis of fatigue failure in mechanically fastened Fibre Metal Laminate joints containing multiple cracks
No full textMechanically fastened joints are susceptible to the presence of multiple-site damage (MSD) cracks in the critical fastener row. Different from the MSD growth in joints consisting of metallic substrates, the two coupled metal crack growth and interfacial delamination propagation failure mechanisms in Fibre Metal Laminates (FMLs) make the prediction of fatigue behaviour in FML joints with MSD scenario burdensome and impractical when considering all factors influencing the fatigue performance. This paper presents a theoretical study on the MSD crack growth behaviour in mechanically fastened FML joints with a focus of modelling the effects of bearing and bypass loads. The proposed model in this paper is built upon analytical models dealing with MSD growth in flat FML panels and single crack growth in FML panels subjected to a combined tension-pin loading case. This model would be particularly useful for symmetric FML joints where no secondary bending effects present. A deliberately designed symmetric FML joint was tested to validate the proposed model. The model captures the rapid crack growth in the vicinity of fastener holes due to bearing stresses and crack acceleration due to the interaction of cracks. It is identified that the load redistribution between intact fastener rows and the cracked fastener row accelerates crack growth with crack length. The effects of secondary bending stresses in FML joints on the crack growth behaviour is extensively discussed. The performance of the proposed model for single lap FML joints is also examined using test data from open literature. It is found that the proposed model provides a conservative prediction for the tested single shear lap FML joint from open literature.Structural Integrity & CompositesAerospace Structures & Material
The mechanical effects of kissing bonding defects in hybrid metal-composite laminates
No full textFibre metal laminates (FML) are hybrid materials perspective for wind-turbine, containers and marine objects, besides the aerospace industry. During the manufacturing process some faults can occur and can be hazardous for the reliability of FML structures. One of the most critical defects are kissing bonding due to their lack of detectability and strength compared to traditional delamination defect. The quantitative explanation were under consideration, such as loads effects; material properties; prediction of response; fracture analysis. The purpose of this work is the evaluation the impact of this type of defect on the part in-plane and the out-of-plane mechanical properties. It was presented that even responsive NDT methods are not able to detects the kissing bonding defect in FML components. Simultaneously, the kissing bonding impact on mechanical properties in FML is significant. In the case of FMLs with the orientation of the fibre perpendicular to the peel direction there is one failure pattern which is interlayer fracture. Whereas in the case of FMLs with the direction of the fibres longitudinal to the peel direction two failure patterns occur which is interlayer fracture and translaminar fibre crack. Depending on the kissing bonding area width the interlayer fracture in the composite can be observed until kissing bonding defect area and then transmission of the crack to the metal/composite interface through the fibres. In the case of low extension of poor adhesion area, the two parallel interlaminar cracking can be seen, one at the metal/composite interface in poor adhesion area, the second continuous in the composite layer.</p
POR QUE NÃO DESPREZAR O SACO HERNIÁRIO NAS HÉRNIAS INGUINAIS, UMBILICAIS E INCISIONAIS: UMA REVISÃO CRÍTICA
No full textThe contents of the hernial sac have always been a concern for the surgeon, although thestructure of its wall is still little studied and known. The objective of the work is to evaluate theinfluence of sex, color, age, region of the hernia sac, side of the hernia, width, length andperitoneal sample thickness in the presence of smooth muscle fibers (SMF) in the sac wallinguinal hernia. It is also intended to describe the histology of hernia sacs and presentsome theories about the origin of FML, in addition to highlighting the importance of knowing thesaccular structure in identifying covert pathological conditions and certifying the use of thebag as a reinforcement instrument in surgical corrections. Samples of 252 hernia sacs obtainedin the operative treatment of indirect, direct, recurrent and incarcerated inguinal hernias weresent for histopathological study, and were stained with Hematoxylin-Eosin (HE) andGomori trichrome for the identification of FML. These were present in 67.9% of the samples,and occurred significantly in indirect and recurrent hernias, when compared todirect and incarcerated. Regarding the variables studied, patients who presented FML did notdiffered significantly from those in which they were not observed. When present, theFML were often associated with thickened blood vessels, suggesting an origin frommiddle layer of the vessel and may represent tissue reinforcement in response to mechanical trauma orother factors in the pathogenesis of hernia. It was also observed that the hernial sac can host severalpathological processes that affect the parietal peritoneum, such as endometriosis, specific inflammationsand hyperplastic or even neoplastic processes, which may even constitute, in some cases, thefirst evidence of neoplasms.El contenido del saco herniario siempre ha sido una preocupación para el cirujano, aunque elLa estructura de su muralla es aún poco estudiada y conocida. El objetivo del trabajo es evaluar lainfluencia del sexo, color, edad, región del saco herniario, lado de la hernia, ancho, largo yGrosor de la muestra peritoneal en presencia de fibras musculares lisas (SMF) en la pared del saco.hernia inguinal. También se pretende describir la histología de los sacos herniarios y la actualidad.algunas teorías sobre el origen de la FML, además de resaltar la importancia de conocer laestructura sacular para identificar condiciones patológicas encubiertas y certificar el uso delBolsa como instrumento de refuerzo en correcciones quirúrgicas. Se obtienen muestras de 252 sacos herniarios.en el tratamiento operativo de las hernias inguinales indirectas, directas, recurrentes y encarceladas fueronenviados para estudio histopatológico, y fueron teñidos con Hematoxilina-Eosina (HE) yTricromo de Gomori para la identificación de FML. Estos estuvieron presentes en el 67,9% de las muestras,y ocurrió significativamente en hernias indirectas y recurrentes, en comparación condirecto y encarcelado. Respecto a las variables estudiadas, los pacientes que presentaron FML nodiferían significativamente de aquellos en los que no se observaron. Cuando está presente, elLas FML a menudo se asociaban con vasos sanguíneos engrosados, lo que sugiere un origen decapa media del vaso y puede representar un refuerzo del tejido en respuesta a un traumatismo mecánico ootros factores en la patogénesis de la hernia. También se observó que el saco herniario puede albergar variosProcesos patológicos que afectan el peritoneo parietal, como endometriosis, inflamaciones específicas.y procesos hiperplásicos o incluso neoplásicos, que pueden incluso constituir, en algunos casos, laPrimera evidencia de neoplasias.O conteúdo do saco herniário sempre foi motivo de preocupação por parte do cirurgião, embora a estrutura de sua parede seja ainda pouco estudada e conhecida. O objetivo do trabalho é avaliar a influência de sexo, cor, idade, região do saco herniário, lado da hérnia, largura, comprimento e espessura da amostra peritoneal na presença de fibras musculares lisas (FML) na parede do saco herniário inguinal. Pretende-se também descrever a histologia dos sacos herniários e apresentar algumas teorias sobre a origem das FML, além de destacar a importância do conhecimento da estrutura sacular na identificação de condições patológicas encobertas e certificar o uso do próprio saco como instrumento de reforço nas correções cirúrgicas. Amostras de 252 sacos herniários obtidos no tratamento operatório de hérnias inguinais indiretas, diretas, recidivadas e encarceradas foram encaminhadas para o estudo histopatológico, e foram coradas por Hematoxilina-Eosina (HE) e tricrômico de Gomori para a identificação de FML. Estas estiveram presentes em 67,9% das amostras, e ocorreram de modo significativo nas hérnias indiretas e recidivadas, quando comparadas com as diretas e encarceradas. Em relação às variáveis estudadas, os pacientes que apresentaram FML não diferiram significativamente daqueles em que as mesmas não foram observadas. Quando presentes, as FML muitas vezes estavam associadas com vasos sangüíneos espessos, sugerindo a origem a partir da camada média do vaso e podem representar um reforço tecidual em resposta ao trauma mecânico ou a outros fatores da patogênese da hérnia. Foi observado também que o saco herniário pode sediar vários processos patológicos que atingem o peritônio parietal, como a endometriose, inflamações específicas e processos hiperplásicos ou mesmo neoplásicos, inclusive podendo constituir, em alguns casos, a primeira evidência de neoplasias
Effect of prepreg gaps and overlaps on mechanical properties of fibre metal laminates
No full textDuring the automated manufacturing of fibre reinforced laminates, defects can be produced. Gaps and overlaps between adjacent prepreg layers can be produced in composites during the tape-layup process. However, the topic is not yet studied for hybrid materials, in which metal sheets and thin prepreg layers lead to different effects due to the defects than in full composites. Here, the effect of gaps and overlaps on the mechanical properties of the Fibre metal laminates (FML) is evaluated. Specimens are manufactured with a specified width of gaps/overlaps and the mechanical performance of the panels is evaluated by some selected mechanical tests. Gaps show to have a considerable effect on the mechanical performance of FML. Compression strength of samples with overlaps was rather increased. Discussions are presented on the influence on each mechanical property according to the severity of the defect (gaps/overlap) and the failure mode(s) under consideration.Structural Integrity & CompositesAerospace Manufacturing Technologie
Blunt Notch Behaviour of Stainless-Steel-CFRP Fiber Metal Laminates
No full textJoining of aerospace structures has been accomplished using mechanical fasteners since the advent of flight. With the growing application of lightweight composite structures in aircrafts, joining methods involving fasteners have been under scrutiny. The lack of material plasticity and high notch sensitivity of composites in the presence of structural discontinuities such as open holes for joints requires local laminate thickening, increased number of fasteners to comply with the strict fail-safe philosophy for certification of primary aerospace structures. However, this incurs a large cost and weight penalty that partially nullify the benefits of using composites. To circumvent this issue, popular solutions either do away with mechanical fasteners (adhesive bonds) or modify the substrates forming the joint (fiber metal laminates). Technical difficulties with respect to the maintenance and repair of adhesively bonded joints with current-day technology have prevented their certification for primary aerospace structures. On the other hand, fiber metal laminates (FML) have exhibited enhanced mechanical joint bearing strengths as high as 168% with titanium reinforcement and 232% with steel reinforcements with a metal content of 50% compared to traditional carbon fiber reinforced polymers (CFRP). Further, advancements in surface preparation of metals such as steel and titanium have improved the metal-CFRP bond durability thereby making them a lucrative solution to aerospace joints. This thesis evaluates the open hole tension (OHT) behaviour of the steel hybridized CFRP FML from an experimental, analytical and numerical standpoint. Experimental identification of the failure modes in the steel-CFRP FML failed by OHT testing is carried out with the help of non-destructive techniques such as digital image correlation and post-testing polished microscopy. Simple analytical models previously applied to the commercially successful Glare (glass laminate aluminium reinforced epoxy) are adopted to predict the blunt notch strength of the steel-CFRP FML with emphasis on the post-cure residual stresses. Within the scope of the experimental study, the analytical predictions of the blunt notch strength of steel-CFRP FML show a 2.5% deviation in accuracy. A high-fidelity numerical model incorporating interlaminar and intralaminar damage in the CFRP and steel layers is developed using Abaqus. Intralaminar damage initiation and progressive damage modelling is performed using a stress-strain formulation for CFRP while plasticity is defined for the steel layers. Interlaminar damage is addressed from a fracture mechanics perspective by the implementation of a cohesive zone model (CZM). Good correlation is observed between experimental results and the numerical model with respect to progression of damage in the CFRP/steel and failure load prediction.Aerospace Engineerin
Friction Stir Welding effects of defects in Glare
No full textSplicing technology is used to create fuselage panels due to the maximum width of the aluminium sheets of 60 inches as a result of the production process. A set of designing rules is required for the design of a spliced Glare fuselage resulting in a significant increase in complexity. Friction stir welding of the thin aluminium sheets in Glare results in larger Glare panels where the maximum dimensions are limited by the size of the autoclave. FSW Glare could result in reduced weight and production cost, and perhaps as well as having enhanced mechanical properties. But welding defects could occur which will compromise fatigue properties. Fatigue and damage tolerant properties of FSW Glare with welding defects are investigated, and recommendations are given in this thesis. Friction stir welding generally does not produce defects that are common to conventional welding technologies, such as warping and porosity. Instead unique defects can occur, such as the zig zag curve or lazy S defect, where the oxide particles of the aluminium are present in a concentrated form. Another typical form of defect is the tunnel defect, also know as the channel, cavity, or void defect. A physical channel is present in the cross section of the weld, which is not visible looking at the surface of the welded sheet. A similar defect is the groove defect where the absence of material is at the surface which makes it visible and tangible. Nevertheless, friction stir welding is a robust process where a wide range of welding parameters result in a defect free weld. Friction stir welding results in much more favourable fatigue properties compared to conventional welding methods, and S-N data lie well above the FAT40 design curve. Welding parameters, such as welding speed and tool pressure, as well as tool geometry play an important role in fatigue properties. Defects as a result of improper welding parameters have a large impact on fatigue properties. Surface properties of the weld also impact fatigue properties; post machining the rough surface results in improvements. Static properties are also favourable with friction stir welding. Two sets of FSW sheets with a welding defect are available for testing both in single sheet and FML form. Artificially damaged sheets are produced to model a welding defect and tested in both single sheet and FML form. This data is compared to standard 2024-T3 in single sheet form, and standard Glare in FML form. Both fatigue and static tests are performed. The Ccg and ncg coefficients derived from the single sheet 2024-T3 specimens deviate quite a lot from the Ccg and ncg coefficients derived from the Forman equation. Using the latter would have resulted in inaccurate comparisons of other single sheet FSW and Artificial Defect specimens. The single sheet FSW 0.3 – 0.4 mm specimens have a kissing bond defect, which resulted in degradation of fatigue performance. This defect was present, even though the welds on the sheets looked flawless. The single sheet FSW defect specimens show a significant drop in fatigue properties, but that is primarily due to the reduced cross section thickness of the weld. Correcting this data to the real thickness, or real stress, results in a substantial improvement, where some specimens even have the same fatigue properties as that of standard single sheet 2024-T3. The results are surprisingly favourable considering the visual state of the FSW sheets. The single sheet Artificial Defect groove specimens show the most reduction in fatigue properties. Standard Glare has a shorter crack initiation life than single sheet 2024-T3, but a much longer crack growth life resulting in an approximate doubled fatigue life. The worst case scenario is tested with the FML Artificial Defect severed weld specimens. Fatigue life is comparable to single sheet 2024-T3 at high stress amplitude, but fatigue properties are comparable to standard Glare at low stress amplitude. All other FML types perform between these two types of FMLs. The biggest degradation in fatigue occurs at high stress amplitude, whereas fatigue performance is comparable to standard Glare at low stress amplitude. The exception is FML 0.3 – 0.4 mm, which even performs slightly better than standard Glare. The reason is that the cross section of the centre FSW sheet was 0.35 millimetres, whereas it is considered as if it were only 0.3 mm. Fatigue properties of different types of material is much smaller in FML form than in single sheet form. The FMLgrow model predicts the fatigue life most accurately at low stress amplitude with a fatigue life that is 70% of the measured value. The least accurate prediction is at high stress amplitude with a fatigue life that is about 25% compared to the tested specimen. Crack initiation in the centre layer of the FML occurred only faster than in the outer aluminium layers with the Artificial Defect groove specimens, where the groove acts as a stress riser. The centre fatigue crack in this case is not longer than the fatigue crack in the outer aluminium layers when the latter reaches its final value of 2a = 50 millimetres. This is visible in the C-scan result where the delamination pattern doesn’t exceed the final crack length value in the outer layer. The outer crack, after initiation, catches up with the centre crack, and then all cracks continue to grow at the same rate. Crack growth rate in FML reduces after initiation to reach a minimum value before increasing again. Crack bridging is less efficient when cracks are small, and the discontinuity due to the notch are the reasons for this initial high crack growth rate before reducing to a minimum value. Exponential growth as a function of half crack length was observed in the FML specimens, resulting in the following expression: da/dN=C_exp·a Cexp is an intrinsic fatigue property of an FML as are the Ccg and ncg coefficients for single sheet. Different basic fatigue calculations can be performed. Modeling and understanding of crack growth in Glare can be facilitated knowing this relation, since exponential growth is an intrinsic fatigue property in an FML. Plotting the logarithmic Cexp as a function of linear Sa yields a relation similar to the S-N relation. Exploration of the FMLgrow model to account for the differences between its predictions and measured data resulted in the understanding that the Alderliesten model is flawed due to interdependency of the aluminium layer with the glass fibre in the (W-2a) region, resulting in an incorrect Kfarfield. Ktip?Kfarfield+Kbridging Glare is considered as a structure where the primary load is carried solely by the aluminium sheets. Hence the feasibility of FSW Glare is based on the fatigue properties of FSW single sheet. Single sheet FSW with a defect shows more degradation in fatigue performance than the FML variant. Therefore using single sheet performance to evaluate feasibility of FSW Glare result in a stricter selection of what defects can and cannot be tolerated. At the same time will the stricter selection not result in a heavier structure; only damage tolerance will benefit. 90% of the initiation and crack growth life of 2024-T3 is chosen as an arbitrary value for the requirements of the FSW sheets. This means that 90% of the fatigue life of 2024-T3 is required. None of the tested specimens fulfill this requirement. Zero defects are not feasible in reality; an example is the presence of air inclusions in Glare. Defects in FSW are continuous and occur only as a result of incorrect welding parameters. Therefore there is no validation in the discussion what type of FSW defect can or cannot be tolerated; FSW sheets should not have any welding defects at all for Glare application.Engineering DesignBiomechanical DesignMechanical, Maritime and Materials Engineerin
A review on the development and properties of continuous fiber/epoxy/aluminum hybrid composites for aircraft structures
No full textWeight 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
FML/QuilA-vaccinated dogs naturally infected with Leishmania infantum: serum cytokines, clinicopathological profile, and parasitological parameters
No full textDogs are the main reservoir of Leishmania infantum in endemic regions. Canine leishmaniasis, caused by L. infantum, can progress to a chronic disease resulting in death. Vaccines have been developed with a certain degree of success. The pathogenesis of this disease is not completely understood, especially in previously vaccinated dogs. We herein described clinical data, parasite load, serum levels of cytokines, and the reservoir potential in vdogs vaccinated with the fucose-mannose ligand (FML)/QuilA saponin vaccine (Leishmune™) naturally infected (Vi) and compared to vaccinated not infected dogs (Vn). Thirty-four dogs from private owners were divided into two groups: vaccinated/infected and vaccinated/uninfected. Clinical evaluation, hematological and biochemical parameters, and serum levels of cytokines were measured by conventional methods. The parasite burden in the bone marrow was measured by quantitative real-time PCR, and the transmissibility of parasites to sand flies was assessed by xenodiagnosis. Clinical, biochemical, and hematological parameters of vaccinated infected dogs were mostly normal. Vi dogs developed mild disease with low clinical scores. Serum levels of IL-10 were higher in Vi dogs, and a strong correlation was observed in IL-4 levels and the A/G ratio in Vi dogs. These results suggest a role of TH2 response in Vi dogs, although more data is needed to better understand the disease in vaccinated dogs.CNPq - Conselho Nacional de Desenvolvimento Científico e Tecnológic
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