Konstruieren mit Faser-Kunststoff-Verbunden
Abstract
Das Buch führt gründlich und umfassend in das Gebiet des Konstruierens mit Faserverbundwerkstoffen ein. Er behandelt die Werkstoffkunde, die Elastostatik und die Festigkeitslehre dieser Werkstoffklasse ebenso wie Entwurfsmethoden und Verbindungstechniken. Im Vordergrund stehen die mechanisch-mathematischen Verfahren zur Dimensionierung und Gestaltung hoch belastbarer Laminate. Die Herleitung grundlegender Zusammenhänge sowie eine Vielzahl detaillierter Abbildungen unterstützen die praktische Anwendbarkeit.
Die zweite Auflage wurde um Regeln zur leichtbaugerechten Gestaltung von Faserverbundstrukturen ergänzt. Ein neues Kapitel zeigt besondere konstruktive Möglichkeiten auf, die sich nur mit Faser-Kunststoff-Verbunden realisieren lassen.
Das Buch ist geschrieben für Ingenieure aus den Bereichen Luft- und Raumfahrttechnik, Automobilbau und Kunststofftechnik, ebenso für Studierende an Universitäten und Fachhochschulen, die sich mit dem konstruktiven Leichtbau beschäftigen.
Chapters (21)
... Alternative methodologies for predicting failure in unidirectional (UD) members are outlined in by several authors [4,[10][11][12]. Orifici et al. [10] presented failure (strength) theories for in-plane and interlaminar failure (damage onset), and employed classical fracture mechanics approaches to describe damage progression. ...
... Schürmann [11] has contributed more recent insights into pin-loaded FRP elements, particularly straps, loaded in tension-building upon Wörndle's earlier research [30]. Schürmann implemented a stress analysis based on force equilibrium principles, kinematic relations, and boundary conditions (the straps were assumed to be thick composite cylinders under internal pressure in their curved regions). ...
... It was experimentally observed that the failure region at the vertex area of the pin/strap contact interface was influenced by stress concentrations at that location. This was further verified by a simple three-dimensional one-eighth FE model of the pin/strap assembly (pin radius: 10 mm, strap thickness: 1 mm, strap width: 6 mm, friction coefficient: 0.5), where a local bending moment in the strap's curvature onset induced stress concentrations in the strap's vertex area (a phenomenon previously reported by Schürmann [11]). ...
Carbon fibre reinforced polymer (CFRP) pin-loaded looped straps are increasingly being used in a range of structural load-bearing applications, notably for bridge hanger cables in network arch rail and highway bridges. The static performance of such CFRP straps is investigated through experimental and numerical analyses. Finite
element (FE) models based on both one-eighth and half pin-strap assembly geometries were modelled. The resulting strains, stresses, and applied loads were compared against experimental data obtained using Digital Image Correlation, Distributed Fibre Optic Sensing (DFOS), and Fibre Bragg Grating (FBG) Sensing. The FE
models effectively captured local strain distributions around the vertex area, close to the pin ends of the straps, as well as in the mid-shaft region, and aligned reasonably with experimental observations. The half FE model accurately predicted the overall strain distribution when compared to DFOS data; however, higher strain magnitudes (by 0.45–10.2 %) and larger strain reductions were observed in some locations. Regarding failure loads, the FE models agreed well with Schürmann’s analytical solution and the maximum stress criterion, exhibiting less than 2.5 % deviations from the experimental data. Furthermore, the predicted onset of strap failure (by delamination) in the half model agreed with experimental values, with a maximum variance of 9.2 %.
... The strength of a short-fiber-reinforced material with a high degree of fiber alignment is expected to behave anisotropically, with a higher strength along the fiber orientation than in the transverse direction. The transverse material strength is expected to be below the neat matrix strength because the short fibers act as notches [9], reducing the transverse strength. ...
... For this study, the intermediate stiffness (E f 79.05 GPa) is selected. The Poisson's ratio (ν f 0.22) and CTE (α f 5.1 × 10 −6 K −1 ) for glass fibers are taken from the literature [9]. ...
... The lowest estimated strength is 4.7 MPa below the measured matrix strength. This confirms the facts described in [9] that short fibers in reinforced polymers do not have a strengthening effect when the material is loaded in its transverse direction. Here, the fibers act as notches, and, consequently, the transverse strength is expected to be below the polymer matrix strength. ...
Short-glass-fiber-reinforced adhesives are state-of-the-art materials used in the bond lines of wind turbine blades. Various alignments of the short fibers are emerging, which depend on the adhesive flow during the application and joining processes. This induces a spectrum of direction-dependent mechanical properties. The tensile strength, for instance, can vary by about 20% depending on the load direction. Therefore, the adhesive performance, which is normally determined under controlled laboratory conditions and implemented in bond line design routines, can deviate from the in situ application. This work investigates the effect of the short-fiber alignment on the tensile strength distribution of an industry-standard adhesive used in wind turbine rotor blades. The smeared short-fiber orientation of the tensile specimens tested is estimated locally near the damaged surface using a material model that is fed with thermomechanical measurements and calibrated via micro-computed-tomography analysis. A linear correlation between tensile strength and short-fiber alignment has been identified. This augments the identification of the material’s upper and lower strength limits for bond line design purposes.
... Continuous fiber reinforced thermoplastics (cFRTP) play a key role here, due to their excellent density-specific stiffness and strength properties, as well as their high specific energy absorption capacity. Further interesting advantages such as short cycle times, recyclability, and welding capability make them suitable for the large-scale production of safety-relevant structural components [1][2][3][4]. The virtual prediction of their mechanical behavior in the finite element analysis (FEA) is an efficient way of developing structural parts. ...
... The strain rate . ε is defined as a time derivative of the specimen's tensile strain ε according to Equation (1). To estimate the strain rate of rectangular specimens even before testing, the nominal strain rate . ...
... . ε = ∂ε ∂t (1) . ...
Continuous fiber reinforced thermoplastics (cFRTP) are one of the most promising lightweight materials. For their use in structural components, reproducible and comparable material values have to be evaluated, especially at high strain rates. Due to their high stiffness and outstanding strength properties, the evaluation of the material behavior at high strain rates is complex. In the presented work, a new tensile specimen geometry for strain rate testing is virtually optimized using a metamodel approach with an artificial neural network. The final specimen design is experimentally validated and compared with rectangular specimen results for a carbon fiber reinforced polycarbonate (CF-PC). The optimized specimen geometry leads to 100% valid test results in experimental validation of cross-ply laminates and reaches 9% higher tensile strength values than the rectangle geometry with applied end tabs at a strain rate of 40 s−1. Through the optimization, comparable material parameters can be efficiently generated for a successful cFRTP strain rate characterization.
... 2 feature approximate maximum fibre diameters of 24, 10 and 30 µm, respectively [10][11][12][13]. Hahn [14] summarises the different modes of FRP compressive failure as illustrated in Fig. 1. ...
... FRP consist of fibres from various source materials. These fibres serve to carry the load and are coated by a polymer matrix binding them together and protecting them against environmental impacts and stresses perpendicular to the fibre axis [10,11]. Regarding the mechanical properties of FRP, a significant difference between the compressive and tensile strength of FRP is known from the literature [1,10,11]. ...
... These fibres serve to carry the load and are coated by a polymer matrix binding them together and protecting them against environmental impacts and stresses perpendicular to the fibre axis [10,11]. Regarding the mechanical properties of FRP, a significant difference between the compressive and tensile strength of FRP is known from the literature [1,10,11]. Tensile failure results from rupture of single fibres. The polymer matrix, exhibiting a higher ultimate strain, redistributes stresses to the adjacent fibres resulting in a successive failure propagation across the FRP cross section. ...
Internationally leading standards currently do not permit to consider the contribution of reinforcement made of fibre reinforced polymers (FRP) to a concrete member’s compressive load-bearing capacity due to a lack of reliable knowledge regarding FRP’s material properties in compression. Thus, there is a very high demand for carefully specifying an optimised test setup for FRP bar reinforcement that accounts for both theoretical considerations and established standards from other industry branches. This paper presents an extensive literature review on mechanical approaches to describe FRP material properties in compression, existing test setups from various industry branches as well as experimental studies that have been conducted in order to research the compressive material properties of FRP reinforcement. Based on experimental results from literature a database was compiled. Following a reasonable choice of a test setup based on the literature study, an experimental campaign was setup, in order to investigate the influence of different fibre materials (carbon, glass, basalt), polymer matrices and bar diameters on the compressive material properties of FRP reinforcement bars. In addition to the experimental determination of the material properties, the joint evaluation of the total sample size of n = 95 own experimental test results and the results from the database generated from literature allows for
statistical investigations. Thus, the determination of material scatter and the estimation of the distribution type by means of a statistical analysis applying the Kolmogorov-Smirnov test provides the basis for further research towards the reliability of concrete structures reinforced with FRP bars in compression.
... Eine Möglichkeit Energieeffizienz zu steigern ist die Gewichtsreduktion von bewegten Verkleidungen oder Maschinenkomponenten. Kohlenstofffaserverstärkte Kunststoffe (CFK) ermöglichen eine solche Gewichtsreduktion ohne Einbußen der mechanischen Leistungsfähigkeit der Bauteile. [1] CFK ist ein Verbundwerkstoff, welcher aus Kohlenstofffasern und einer polymeren Matrix besteht. Die Fasern weisen eine hohe Festigkeit in Faserrichtung auf und dienen im Verbund der Kraftübertragung. ...
... Dadurch entstehen gestufte Oberflächen mit mehreren Mikrometer in das Material hineinreichenden Mikrorissen. [1,7] Hintze zeigte, dass die Rauheit bei definierter Schneide sowohl vom Fasertrennwinkel θ als auch vom räumlichen Fasertrennwinkel θ 0 abhängt. Der Fasertrennwinkel θ wird zwischen Schnittgeschwindigkeit und Faserrichtung in der Laminatebene aufgespannt, während der räumliche Fasertrennwinkel θ 0 räumlich zwischen den Richtungen aufgespannt wird. ...
The use of carbon fibre-reinforced polymers in high-performance electric motors enables higher levels of efficiency and system rigidity. The demands on the surface quality of the individual components are so high that they can only be achieved by grinding processes. This paper investigates the influence of fibre orientation and abrasive grain size on the surface roughness during side-face grinding of CFRP.
... For this reason, fibre-reinforced plastics are often preferred in material combinations in car bodies and combined with metals to achieve optimum material properties. Modern high-strength and ultra-high-strength steel materials are used alongside light metals such as aluminium and magnesium, which are particularly efficient due to their high weight-specific strength and stiffness [4]. In addition, the intelligent mixed construction method is supplemented by fibre-reinforced plastics, whereby the comparatively expensive lightweight construction material is only used in areas subject to high mechanical loads for local reinforcement and weight reduction. ...
... These materials often consist of stiff fibres embedded in a soft epoxy matrix, with the fibre generally oriented in the direction of the applied load. It should be noted that the interface is the main weak point of the FRP-metal hybrid joint, and the damage mechanisms present here are of particular interest [4]. It is important to emphasize that research into new lightweight design concepts is focused not only on hybrid concepts but also on other innovative approaches. ...
The use of hybrid materials as a combination of fibre-reinforced plastic (FRP) and metal is of great interest in order to meet the increasing demands for sustainability, efficiency, and emission reduction based on the principle of lightweight design. These two components can therefore be joined using the intrinsic joining technique, which is formed by curing the matrix of the FRP component. In this study, for the hybrid joint, unidirectionally pre-impregnated semi-finished products (prepregs) with duromer matrix resin and micro-alloyed HC340LA steel were used. In order to conduct a detailed investigation, the damage mechanisms of intrinsically produced fibre metal laminates (FMLs), a new clamping device, and a novel pressing tool were designed and put into operation. The prepregs were prestressed by applying a preloading force using a specially designed prestressing frame. Hybrid specimens were then produced and subjected to nanoindentation and a shear tensile test. In particular, the effect of the residual stress state by varying the defined prestressing force on the damage mechanisms was studied. The results showed that no fracture patterns occurred in the interface of the specimens without preloading as a result of curing at 120 °C, whereas specimens with preloading failed at the boundary layer in the tensile range. Nevertheless, all specimens cured at 160 °C failed at the boundary layer in the tensile range. Furthermore, it was proven that the force and displacement of the preloaded specimens were promisingly higher than those of the unpreloaded specimens.
... The layer parameter data was extracted from [Johnson et al., 1999]. For the failure parameters of the UD layer, the generally formulated data from [Schürmann, 2007] were used as a conservative estimate. The values were assumed to be slightly worse than in other more precise sources, such as [Moure et al., 2015]. ...
... The values were assumed to be slightly worse than in other more precise sources, such as [Moure et al., 2015]. The Puck parameters used were standard Ansys values similar to those specified in [Schürmann, 2007]. For the CZM model, data with experimental validation from [Robinson et al., 2005], referencing critical energy release rates from [Johnson et al., 1999], were utilized. ...
In the current effort towards sustainability, the aviation industry faces challenges in repurposing carbon fiber reinforced plastic (CFRP) components effectively. Traditional "downcycling" methods fail to maintain CFRP integrity, as they involve cutting load-bearing fibers and re-embedding them with new polymers, which leads to fragmentation and loss of properties. Innovative solutions like non-destructive disassembly or dismanteling offer precise separation without compromising fiber integrity. This method allows for the direct reuse of materials in similar or new applications and highlights the importance of advanced recycling technologies for fiber-reinforced plastics. Finite element method (FEM) analysis shows the basic separation mechanism functions without damaging the base material in simulated shell structures. Safety margins are within acceptable ranges, and additional damping forces enhance process safety. Thinner wedges are recommended as they generate lower loads, exhibit less dependency on plate stiffness, and require shorter crack lengths. Fracture risk is influenced by specific parameters. Critical parameters must be determined during structure development, as they cannot be varied in existing components without design considerations for recyclability. However, green inputs can be directly modified to improve the process. Targeted force applications, such as pressing at the crack tip and relieving force at the wedge contact point, reduce structural load. A cable force mechanism, supported by a lateral roller, effectively relieves wedge contact force. In summary, the wedge separation process is suitable for non-destructive disassembly of stiffeners, representing a promising approach for developing practical test stands.
... The modulus has to be substituted with an appropriate FRP specific equivalent. In this case, b G 12 (if 1-axis is in the direction of strip axis and 2 is in the direction of spring axis) was used 43 ...
... The combination of moduli b G 12 and b G 13 for the layered composite is also possible, which can be determined using the CLT for the specific material choice and layup. 43 Another important fact to consider is the space spiral, which possesses a variable radius, determining the midline of the rectangular cross-section. Each coil has a different radius and a different contribution to the spring rate. ...
Fiber-reinforced polymer (FRP) composites are particularly suitable for spring applications due to numerous advantages like lightweight design, intrinsic damping, or chemical resistance. Although there are many studies on the properties of FRPs and even some on springs made out of these materials, there is no holistic method for FRP spring design. Therefore, this article focuses on a new approach that combines all relevant design steps. This includes a spring-related overview of requirements and associated FRP properties, as well as recommendations regarding material and spring type selection with a specialization on polymer composite volute springs. Thereupon, a mountain bike rear suspension spring was designed and produced. These carbon fiber-reinforced polymer (CFRP) lightweight spring, which weighs only half of the metal spring, was examined in static and cyclic experiments. Important results of the tests are a lower spring rate than theoretically expected as well as a loss of stiffness of the spring of about 25% after 25,000 full deflections just before failure. Downhill riding tests were carried out and showed comparable driving characteristics as when using conventional steel springs. The research is a contribution to FRP spring design considerations as well as to extend the range of applications for composite springs, and especially volute springs, in the future.
... In the first step, the thermoset support part was designed based on the existing geometry of the steel part (C-profile). The basic design guidelines for thermoset components were taken into account [1]. In particular, a cross-section of the support part smaller than 1 mm, as is the case with standard radial shaft seals, is not feasible. ...
... Comparison of the lattice structure of thermoset, thermoplastic and elastomer[1] ...
... The stacking sequence of the carbon fiber reinforced layers and their thickness were determined from the investigated 6.8-liter cylinders. The material data of the unidirectional composite ply was calculated from the material data of the fibers and resin with the rules of mixture according to [41,42]. Here, a filament winding typical fiber volume ratio of 60 % was assumed, which was then proven by weighing the cylinders and X-ray microtomography. ...
... The properties of composite materials are mainly defined by the amount of fiber volume content available: the more fiber content the better the mechanical properties, although up to a limit. During the fabrication, using prefabricated pultruded rods with 65 % fiber content allows working with almost the maximum volume content that could be advantageously employed [24]. Conventional VI-based manufacturing methods for impregnating fibers or dry preforms can achieve fiber content values from 34 % up to 52 % or 55 % [10,27]. ...
... a. Automobile, Flugzeuge, Werkzeugmaschinenschlitten, Industrieroboter), führt die Substitution der Metallbauteile durch CFK-Bauteile zu einer Reduzierung der zu beschleunigenden Massen und damit wiederum zur Steigerung der Effizienz [3]. Weitere vorteilhafte Aspekte sind die gute Wärmeleitfähigkeit und der negative thermische Ausdehnungskoeffizient der Kohlenstofffasern [7]. Diese Eigenschaften können bei entsprechender Anordnung der Kohlenstofffasern genutzt werden, um beispielsweise in den Lagern entstehende Verluste gezielt von diesen wegzuleiten oder temperaturbedingte Verlagerungen, welche die Lager zusätzlich belasten würden, zu reduzieren [5]. ...
With increasing demands on the power density of electrical drive systems metal materials commonly used in mechanical engineering are reaching their performance limits. Further improvements can be achieved using carbon fiberreinforced polymers (CFRP). To enable their use in industrial practice, the SPOTLIGHT project focuses on the manufacturing and grinding of high-precision functional surfaces of CFRP components. The CFRP components are evaluated through drive technology demonstrators.
... For a linear material model, stresses ሼ ሽ and strains ሼ ሽ are assumed to be related by the wellknown Hooke's law [17], which is defined for a two-dimensional stress-state as follows: ...
A micromechanical, empirical quasi-static degradation model for glass-fiber reinforced epoxy laminates is presented, assuming that stiffness degradation begins with the first microcrack and is driven by the matrix damage behavior. A degradation factor is introduced, directly applying to the matrix' Young's modulus upon damage initiation. As input, the model requires fiber and matrix mechanical properties only. Based on micromechanical rules of mixture, ply stresses are transformed into stresses on the matrix level. The matrix stress exposure factor is calculated with a classical strain energy approach and is implemented in a damage onset criterion. Stiffness degradation curves are derived experimentally. As a result, two generic degradation functions for tensile/shear and for compressive loading as a function of the matrix stress exposure factor are proposed, that can be implemented in a layer-wise strength analysis.
... Here, due to the favourable fibre orientation for an inter-fibre failure, numerous cracks propagate into the laminate. Puck et al. identified a favourable fibre cutting angle for inter-fibre failure in the range θ 0 = 50 -60 • [15,16]. Furthermore, the minimum of the forces moves to lower θ 0 with decreasing κ r . ...
... For fiberreinforced components subject to high mechanical stresses, the next step is to design the load introduction into the component. Experimental verification of the design solution should always be performed, since the accuracy of computer-aided modeling is often insufficient [64]. The subsequent detail design of elements and element transitions should already be carried out with a view to a load-and function-appropriate fiber alignment and also to minimize the need for support structures. ...
Continuous fiber-reinforced material extrusion is an emerging additive manufacturing process that builds components layer by layer by extruding a continuous fiber-reinforced thermoplastic strand. This novel manufacturing process combines the benefits of additive manufacturing with the mechanical properties and lightweight potential of composite materials, making it a promising approach for creating high-strength end products. The field of design for additive manufacturing has developed to provide suitable methods and tools for such emerging processes. However, continuous fiber-reinforced material extrusion, as a relatively new technology, has not been extensively explored in this context. Designing components for this process requires considering both restrictive and opportunistic aspects, such as extreme anisotropy and opportunities for functional integration. Existing process models and methods do not adequately address these specific needs. To bridge this gap, a tailored methodology for designing continuous fiber-reinforced material extrusion is proposed, building on established process models. This includes developing process-specific methods and integrating them into the process model, such as a process selection analysis to assess the suitability of the method and a decision model for selecting the process for highly stressed components. Additionally, a detailed design process tailored to continuous fiber-reinforced material extrusion is presented. The application of the developed process model is demonstrated through a case study.
... according to Schürmann [265]. Being a polymer, the epoxy matrix of the CFRP material employed within this work, also shows viscoelastic behaviour. ...
Fibre-reinforced polymers (FRPs) are widely used as a lightweight material of choice due to their outstanding weight-specific mechanical properties such as stiffness and strength. The combination with sheets of metal, commonly referred to as fibre metal laminates (FMLs), additionally provides a high resistance and tolerance to damage. As with most lightweight materials, these advantages come at a cost. In particular, the high stiffness and low mass density of such materials or material systems make the resulting structures prone to vibrations as conventional lightweight materials usually offer only negligible material damping. The addition of highly compliant layers consisting of viscoelastic elastomer materials within the otherwise stiff laminate can significantly increases the achievable damping, following the principle of constrained-layer damping (CLD). Such a hybridisation then allows for highly damped lightweight laminates, which can be tailored to achieve specific damping capabilities. In particular, this work considers hybrid fibre metal elastomer laminates (FMELs), consisting of carbon fibre-reinforced polymer (CFRP), aluminium and different elastomer compounds in various laminate configurations.
These hybrid FMELs offer a tremendous design freedom with regard to material selection, layer thicknesses and general laminate lay-up. Since manufacturing and testing of new laminates can be cumbersome, predictive models are desirable in order to find optimal designs beforehand. The development of such a model based is subject of this work. In particular, an analytical model based on a unified plate theory for the rapid and precise prediction of the laminates’ static deformation behaviour, modal characteristics and steady-state response is presented. Subsequent studies applying this model investigate different FMELs with regard to their damping behaviour in order to uncover general correlations between laminate parameters and the achievable damping.
Furthermore, elastomer materials are known to exhibit progressive cyclic softening, called Mullins effect, when subjected to moderate or high strains. As there is no previous research on the role of the Mullins effect in CLD laminates, this work employs experimental and numerical methods in order to uncover an influence on the damping behaviour of hybrid CLD laminates.
FMLs and FMELs in particular are known for their tolerance to damage. The tolerance of the intrinsic CLD mechanism with regard to different types of damage, however, is so far entirely unexplored. The present work addresses this research gap by employing experimental methods for the determination of low-velocity impact damage in different FMELs. Subsequently, numerical models of those damaged laminates are used in order to identify the influence of the occurring types of damage on the damping capabilities of FMELs.
Overall, this work highlights the complexity and numerous dependencies of the CLD mechanism within FMELs. It presents experimental, analytical and numerical methods for predicting the damping capabilities of such laminates, in particular in order to optimise and assess its tolerance to damage.
... CCFRP parts are distinguished by their high strength-to-weight ratio and superior mechanical tensile properties along the fibre direction. Continuous fibre integration bolsters the mechanical properties of fibre-reinforced components along the load path [2]. ...
Incorporating continuous carbon fibre-reinforced polymer (CCFRP) parts within additive manufacturing processes presents a significant advancement in the fabrication of robust lightweight parts, particularly relevant to aerospace, engineering, and various industrial sectors. Nonetheless, prevailing additive manufacturing methodologies for CCFRP parts exhibit notable limitations. Techniques reliant on resin and extrusion entail extensive and costly post-processing procedures to eliminate support structures, constraining design versatility and complicating small-scale production endeavours. In contrast, laser sintering (LS) emerges as a promising avenue for industrial application. It facilitates the efficient and cost-effective manufacturing of resilient parts without needing support structures. However, the current state of research and technological capabilities has yet to yield an LS machine that integrates the benefits of continuous fibre reinforcement with the inherent advantages of the LS process. This paper describes the systematic development process according to VDI 2221 of a new type of LS machine with automated continuous fibre integration while keeping the advantages of the LS process. The resulting physical prototype of the machine is also presented. Furthermore, this study presents an approach to integrate the cost and Product Carbon Footprint of the process in the product design. For this purpose, a machine state model was developed, and the costs and Product Carbon footprint of a part were analysed based on the model. The promising potential for future lightweight products is demonstrated through the production of CCFRP parts.
... Consequently, the composite material often fails to perform over time according to expectations. Moreover, an increase in temperature reduces the stiffness for interfilamentous and interfacial load transfer, thus decreasing mechanical performance and increasing the deformability of the yarn [122][123][124]. This can be linked to the glass transition temperature (Tg) of the plastic-based impregnation, which for polymer-based impregnations is comparably low at around 100 °C. ...
Textile-reinforced concrete (TRC) has gained a lot of attraction in recent years. Adequate bond between the phases in this system allows to transfer high loadings, thus enabling high performance. The terminus textile reinforcement, however, comprises many different types of fabrics, which differ in their chemical composition, geometry, surface properties etc., and thus exhibit substantially different bond properties. In the course of RILEM’s Technical Committee 292 work on TRC it was found that a comprehensive understanding of the complex interactions between individual parameters is still lacking. This is amplified by the fact that different types of textile reinforcement are preferably used in different regions of the world. This paper therefore attempts to compile findings from literature on the bond in TRC. The database used was created in the course of the TC work. Additional papers of relevance were identified by scanning scientific web databases. The different influencing parameters are given in this paper in a hierarchical order, starting from the level of the individual constituents (filament and matrix) to impregnated fabrics and the influence of textile manufacturing and architecture on the bond. Finally, by mapping all the cited literature used in this paper based on grouped keywords the complex intercorrelations are visualised.
... 36,39,40 However, these studies did not contemplate the damage evolution in the matrix itself which contradicts basic composite mechanics. 41 On the other hand, considering crack initiation and crack growth in the composite, it becomes clear that the progressive damage evolution in the matrix and the matrix-fiber interface is at least in parts responsible for the nonlinear behavior of natural fiber composites. Similar deviations from linear elastic behavior were already observed in sheet molding compound, which, like the flax fiber composite, is also a long fiber reinforced polymer. ...
Natural fibers are a sustainable alternative to synthetic fibers due to their high weight‐specific Young's moduli and strengths. However, the mechanical properties of natural fibers are very sensitive to their moisture content. Therefore, chemical treatments are often applied to natural fibers to lower their water absorption and enhance fiber‐matrix interaction. The aim is to study the effects of fiber modifications with sodium hydroxide, silane, and siloxane on the water uptake and tensile properties of flax fiber composites produced via prepreg technology. In addition, the effect of moisture on the composites' tensile properties was investigated by conditioning one part of the tensile specimens according to DIN EN 2823 (at 70°C and 85% relative humidity). The NaOH treatment was the only modification that had positive effects on the Young's modulus and tensile strength in the unconditioned and conditioned state. The increase of the tensile modulus and strength are most likely due to changes in flax fiber composition, crystallinity of the cellulose and the rougher fiber surface of NaOH modified fibers. This shows that chemical treatment of natural fibers may improve the performance level of natural fiber composites and prevent a loss in their mechanical properties in humid environments.
Highlights
Flax fiber modifications with sodium hydroxide, silane, and siloxane.
Flax fiber composite production via prepreg technology.
Water uptake after conditioning at 70°C and 85% relative humidity.
Tensile tests before and after conditioning.
SEM images of modified flax fibers.
... Dadurch steigen vor allem im Prototypenbau und bei Kleinserien die Bauteilkosten enorm, da sich die gesamten Kosten des Formwerkzeugs auf eine geringe Bauteilanzahl verteilen. [1,2] Zur Reduktion der Werkzeugkosten gibt es schon Ansätze zur flexiblen Anpassungsfähigkeit von Formwerkzeugen an doppelt gekrümmte Geometrien. Ein vielversprechender Ansatz ist es, die Form aus einer Matrix mit höhenverstellbarer Pins aufzubauen. ...
Dieser Beitrag stellt die Entwicklung eines anpassbaren Formwerkzeugs vor. Es soll automatisiert an beliebige Geometrien angepasst werden können, um Faserverbundbauteile kostengünstig herzustellen. Im Rahmen des Vorhabens wird das Formwerkzeug durch einen Roboter angepasst. Dieser verstellt eine Matrix aus 80 Pins in der Höhe. Zur Validierung des Formwerkzeugs wird sowohl die Genauigkeit der Pinverstellung als auch der Werkzeug- form untersucht.
... However, due to the anisotropic properties of the high-performance fibers (very high tensile and low compressive stiffness/strength), slight deviations of the fiber orientation from the nominal orientation do cause a significant reduction in stiffness in the FRP component (10° deviation, approx. 30 % lower stiffness) [15][16][17]. In order to ensure the highest possible load-bearing capacity of the FRP with the lowest possible material input, the stretched orientation of the fibers shall be achieved in the 3D FRP component already during textile production as well as in the subsequent 3D shaping process. ...
Textile reinforcements have outstanding load-bearing capabilities due to the excellent tensile properties of high performance multifilament yarns (e.g. carbon fibers). However, in order to take full advantage of their high potential, it is necessary to ensure that the filaments run in a straight line. In order to guarantee this straight filament course, the highly efficient multiaxial warp knitting process is used for the production of 2D non-crimp fabrics (NCF) as textile preforms. In various industrial applications, most structures have complex 3D geometries. Therefore, the 2D textile needs to be shaped for reinforcement, which often results in a rearrangement of the filament orientation. Consequently, the 3D shaping process has to be taken into account during the textile production or in the shaping process itself in order to guarantee the highest mechanical properties. Using the example of lattice girders for concrete reinforcement, a new approach for the fabrication of 3D textile lattice girders in a continous shaping process is presented. The results of the production tests of the developed technology approach show no apparent filament damage and exact roving orientation with no inadvertent deflection, compression or bulging, indicating a precise and gentle shaping process. The developed technology contributes to the future reduction of the production costs of 3D textile reinforcements.
... (1) Creation of a local thin zone in the FRP by milling a groove and kinking up the hinge, possibly with detachment of the matrix system, which is preferably epoxy resin, using aramid fibers in the exposed hinge layer, which extend in a single layer over the entire component, plus glass or carbon fibers in the rigid body (Hanaor and Levy, 2001;Priegelmeir and Heilmeier, 2007;Kutscheid, 1998;Livingston-Peters and Gabriel, 2015) (2) Use of a low-modulus matrix system in the thinner hinge zone, if necessary with graded material transitions between the hinge and the rigid body (Masini et al., 2014;Brewer et al., 2012) (3) Use of elastomer or silicone in the hinge zone with constant thickness of the component (Chase and Scarpati, 1993;Malia et al., 2015;Schaube et al., 2012;Schaube and Plenk, 2013;Vielsack et al., 2013) With regard to the outdoor installation of a façade shading component, material approach (1) is not suitable due to the environment exposed aramid fiber and its low UV stability (Schürmann, 2007;Flemming and Roth, 2003). Furthermore, the bending angle is determined by the milled groove and in literature it is already stated that this approach is only suitable for a small number of load cycles (Priegelmeir and Heilmeier, 2007). ...
A continuously adjustable façade shading system functionalized with photovoltaics enables, besides adaptive shading, energy harvesting by solar tracking. This requires large bending motion in two directions. In this paper, the development of an appropriate façade module – FlectoSol – is presented. To achieve motion of ±80°, first time two pneumatic actuators are integrated into a GFRP-elastomer hybrid composite. To improve energy efficiency resp. air pressure consumption of actuation without impairing shading, a parametric study is performed. In detail the influencing criteria of the bending motion “overlap of the actuators” resp. “stiffness ratio of the actuator-surrounding GFRP” and their effect on the target parameters “bending angle”, “shadow width” resp. “air pressure consumption” are analyzed. It could be stated that the “stiffness ratio” only effects the air pressure consumption, but the “overlap” also effects the shadow width. The bending angle itself is, up to ±80°, only limited by the absolute laminate stiffness.
... The thermal conductivity of the unidirectional GFRP is orientation dependent. The parallel conductivity k c,k is calculated by the rule of mixture 59 : where k r is the resin's thermal conductivity. Different models exist to calculate the transverse thermal conductivity k c,' , while the rule of mixture for a series connection of fibers and resin is the easiest model 59 : ...
The pultrusion process is an efficient technology for the continuous production of fiber reinforced polymers. While the process is industrially established for decades, the interactions between process parameters and material quality of pultruded profiles are – despite various studies – not fully understood yet. Due to the complexity of the process and the variety of materials, it is difficult to identify generic and quality related process relationships. Based on a novel multidisciplinary approach, this paper investigates the correlation between simulation data and experimental based process- and quality data. Therefore, a pultrusion-specific epoxy resin is characterized and modelled and thermo-chemical process simulations are performed. A for pultrusion unique inline quality assurance and data acquisition system was developed, built-up and applied during the production of a rectangular, glass-fiber reinforced profile. The analyzed data involves cure variables, die pressure, temperature, pull-speed and -force, ultrasonic data, surface waviness and roughness and void content. As main result, the position of gelation at the profile’s centerline in respect to the die length was determined as important criteria to maintain a sufficient material quality. Furthermore, a correlation between the die pressure and an insufficient degree of cure was identified. No significant influences of the process parameters on the material quality could be observed as long as the process stayed in a stable process window. This indicates that no severe quality losses have to be expected at higher production rates. The methods and results developed in this work are applicable for the implementation in an automated process control in pultrusion.
... In [21] sind die thermischen Ausdehnungskoeffizienten zwischen 0 °C und 100 °C der Faser und Matrixmaterialien angegeben. Epoxidharze haben demnach einen Ausdehnungskoeffizienten von 50 bis 67 10 -6 /K, die HT-Kohlefasern in Längsrichtung einen Negativen von -0,5 10 -6 /K und in Querrichtung 12,5 10 -6 /K. ...
... The mass-specific strength or modulus of elasticity are significantly higher than most metallic alloys, allowing for unparalleled efficiency. The properties of FRPs are strongly influenced by the fibers, matrix material, and laminate structure, among other factors [1]. There are a variety of molding processes used to produce FRPs depending on part geometry and quantity. ...
During the production of fiber-reinforced plastics using resin transfer molding (RTM), various characteristic defects and flaws can occur, such as fiber displacement and fiber waviness. Particularly in high-pressure RTM (HP-RTM), fiber misalignments are generated during infiltration by local peaks in the flow rate, leading to a significant reduction in the mechanical properties. To minimize or avoid this effect, the manufacturing process must be well controlled. Simulative approaches allow for a basic design of the mold filling process; however, due to the high number of influencing variables, the real behavior cannot be exactly reproduced. The focus of this work is on flow front monitoring in an HP-RTM mold using phased array ultrasonic testing. By using an established non-destructive testing instrument, the effort required for integration into the manufacturing process can be significantly reduced. For this purpose, investigations were carried out during the production of test specimens composed of glass fiber-reinforced polyurethane resin. Specifically, a phased array ultrasonic probe was used to record individual line scans over the form filling time. Taking into account the specifications of the probe used in these experiments, an area of 48.45 mm was inspected with a spatial resolution of 0.85 mm derived from the pitch. Due to the aperture that had to be applied to improve the signal-to-noise ratio, an averaging of the measured values similar to a moving average over a window of 6.8 mm had to be considered. By varying the orientation of the phased array probe and therefore the orientation of the line scans, it is possible to determine the local flow velocities of the matrix system during mold filling. Furthermore, process simulation studies with locally varying fiber volume contents were carried out. Despite the locally limited measuring range of the monitoring method presented, conclusions about the global flow behavior in a large mold can be drawn by comparing the experimentally determined results with the process simulation studies. The agreement between the measurement and simulation was thus improved by around 70%.
Hole-drilling method is a standardized technique for obtaining residual stresses in isotropic structures. Previous studies provide a foundation that enables the use of this method to investigate orthotropic structures, such as fiber-reinforced composites. In this study, the incremental hole-drilling method was applied to investigate residual stresses in filament wound type 4 composite pressure vessels. The investigated composite cylinders were manufactured with different internal pressure functions during the winding process, to achieve distinct residual stress states. Additionally, the influence of the initial loading under sustained internal pressure and increased temperature on the stress distribution was investigated. It was shown that the residual stress state can be influenced by varying the internal pressure in the winding process. After testing at sustained load and increased temperature, a stress redistribution was observed, which took place due to creep phenomena. Finally, a discussion of the challenges for the application of the hole-drilling method to composite pressure vessels is provided.
A controlled laminate consolidation is one of the most essential approaches in the production of fiber-reinforced thermoplastics components. With the use of specific consolidation models, almost the entire strength potential of the material can be exploited. However, a controlled thermo-mechanical in situ consolidation (TMIC) strategy in the fused filament fabricated (FFF) process of continuous fiber-reinforced polymer composites (CFRPC) has not been considered so far and leads to deconsolidation defects in the 3D-printed material. These defects in terms of micro and macro volumetric flaws in the joining zone indicate a poor process parameter selection and inadequate thermo-mechanical consolidation. These imperfections lead to a reduction in the fiber volume content and a significant deterioration in the mechanical properties. In this work, a self-developed test rig is presented, which is able to influence and monitor the consolidation during the additive manufacturing (AM) process with a TMIC unit in a controlled manner. To evaluate the test rig, the mechanical construction and the implemented sensors were tested for full functionality. Subsequently, test specimens were fabricated for mechanical characterization using three-point bending (3PB) tests and microstructural analysis. Based on these results, the influence of TMIC, with its dependent process parameters (consolidation force, temperature, printing speed), is presented. A perspective on the future development of controlled consolidation in AM of CFRPC is shown.
Within this study, the impregnation behavior and resulting mechanical properties of unidirectional flax fiber-reinforced polyamide 11 biocomposites were investigated. Therefore, different grades of bio-based polyamide 11 have been evaluated regarding their eligibility as composite matrix material. The production of the unidirectional flax fiber-reinforced biocomposites was investigated using a continuous film-stacking method. It was found that the flow behavior of the polyamide 11 matrix polymer significantly affected the impregnation quality and the resulting mechanical properties as tested by tensile and bending tests. A lower shear viscosity and stronger shear thinning behavior led to better impregnation, a 15% higher stiffness, and 18% higher strength. This was also analyzed with morphological analysis by scanning electron microscopy. Additionally, the effect of the fiber volume content of the flax fibers on the mechanical properties was tested, showing a positive correlation between the fiber content and the resulting stiffness and strength, leading to an increase of 48% and 55%, respectively. In result, a maximum Young’s modulus of 16.9 GPa and tensile strength of 175 MPa at a fiber volume content of 33% was achieved. Thus, the unidirectional flax fiber-reinforced polyamide 11 biocomposites investigated can be a sustainable construction material for lightweight applications, e.g., in the automotive industry.
A methodology for establishing a structural digital twin is proposed to facilitate the lifetime prediction of fiber‐reinforced polymer (FRP) structures, in this case, a wind turbine rotor blade. The digital twin incorporates production peculiarities and imperfections occurring during the manufacturing process of the FRP component. The methodology involves the computation of process‐defined effective elastic properties and residual stresses through numerical simulation of the resin cure cycle. The results are then transferred to a structural finite‐element model. By applying local wind conditions to this model, a comprehensive state of stress is obtained. This serves as a basis for a practical evaluation of material fatigue within the composite, leading to the prediction of the component's lifetime. The entire workflow is implemented in a Jupyter‐based application that uses an ontology with an appertaining knowledge graph to facilitate the transfer of intermediate results between the observation scales and process steps of the digital twin. In line with the principles of open science, the methodology utilizes open‐source software.
For the development of efficient and economical car body structures, high-performance lightweight materials such as continuous fiber-reinforced plastics (C-FRP)—especially in combination with quasi-isotropic materials (f.e. metal) as multi-material components—have gained importance. However, the systematic design of such hybrid components is extremely challenging. In the following work, a newly developed method for the weight- and load-optimized design of hybrid components made of isotropic and anisotropic materials based on physical parameters is presented. With the principal stresses of a reference component a weight-optimized structure between isotropic "base material" and load-dependent reinforcement made of C-FRP is calculated for a new multi-material component. The user specifies the mechanical properties as well as min. and max. material thicknesses for the isotropic material and the C-FRP. With this information the lightest possible material combination of isotropic base material and anisotropic C-FRP is then determined. Using this method, a weight saving of 18–62% could be achieved with flat validation examples while maintaining the same stiffness. Application to the frame of a vehicle door also results in a significant weight saving without compromising stiffness. In summary, this method offers the possibility to identify suitable components for the application of weight- and load-dependent hybrid components and to design them in the early stage of the product development process.
A new approach to an automatable fiber impregnation and consolidation process for the manufacturing of fiber-reinforced composite parts is presented in this article. Therefore, a vacuum chamber sealing machine classically used in food packaging is modified for this approach—Vacuum Chamber Infusion (VCI). Dry fiber placement (DFP) preforms, made from 30 k carbon fiber tape, with different layer amounts and fiber orientations, are infused with the VCI and with the state-of-the-art process—Vacuum Assisted Process (VAP)—as the reference. VCI uses a closed system that is evacuated once, while VAP uses a permanently evacuated open system. Since process management greatly influences material properties, the mechanical properties, void content, and fiber volume fraction (FVF) are analyzed. In addition, the study aims to identify how the complexity of a resin infusion process can be reduced, the automation potential can be increased, and the number of consumables can be reduced. Comparable material characteristics and a reduction in consumables, setup complexity, and manufacturing time by a factor of four could be approved for VCI. A void content of less than 2% is measured for both processes and an FVF of 39% for VCI and 45% for VAP is achieved.
Machine vision is revolutionizing modern manufacturing, with new applications emerging regularly. The composites industry, relying on precision in aligning fibers, stands to benefit significantly from machine vision. Ensuring the exact fiber orientation is critical, as deviations can compromise product mechanical properties and lead to failure. Machine vision, particularly in wet fiber placement (WFP), offers a solution for monitoring and enhancing quality control in composite manufacturing. WFP involves pulling fiber bundles, impregnating them with resin, and precisely transporting them to mold tooling for layer-by-layer fabrication. The challenge lies in handling tacky, wet fiber bundles, making tactile sensors impractical. This makes WFP an ideal candidate for contactless process monitoring. The objective of this study is to employ a low budget machine vision in WFP, utilizing a webcam connected to a single-board computer. Artificial intelligence is trained using images of fiber bundles just before placement on the tooling mold. The module detects and measures the position and orientation of a roving in the starting position, enabling the initiation of the WFP process. The methods employed are thoroughly evaluated for reliability and feasibility. After completing only 50 training epochs, a roving detection accuracy of 91.3% could be achieved with almost no critical errors. With additional iterations per placement process, the system functions almost flawlessly at its current state.
Composites with continuous fiber reinforcement offer excellent fatigue properties but are tedious to characterize due to anisotropy and the interplay of fatigue properties, processing conditions, and the constituents. The global fiber volume content can affect both monotonic and fatigue strength. This dependence can increase the necessary testing effort even when processing conditions and constituents remain identical. This work presents an in situ edge observation method, enabling light microscopy during loading. As a result, digital image correlation can be employed to study local strains at cracking sites on the scale of fiber bundles. The geometric influence on fatigue damage is examined in non-crimp fabrics of glass and carbon fibers. Two epoxy resins (one modified by irradiation) are investigated to verify the geometric influence under changed polymer properties. The microscopy-based image correlation revealed that damage forms at very low global strains of only 0.2–0.3% in glass fiber-reinforced epoxy laminates. For carbon fiber-reinforced epoxy, laminate cracking was found to emanate mainly from regions containing stitching fibers. Across both reinforcements, irradiation treatment led to delayed cracks, emanating from interfaces. This detailed analysis of the damage formation is used as a basis for proposed applications of the in situ strain information.
The extensive use of carbon fiber-reinforced composites and aluminum alloys represents the highest level of automotive body-in-white lightweighting. The effective and secure joining of these heterogeneous materials remains a prominent and actively researched topic within the scientific community. Among various joining techniques, clinching has emerged as a particularly cost-effective solution, experiencing significant advancements. However, the application of clinching is severely limited by the properties of the joining materials. In this work, various clinching processes for the joining of composites and aluminum alloys reported in recent research are described in detail according to three broad categories based on the principle of technological improvement. By scrutinizing current clinching technologies, a forward-looking perspective is presented for the future evolution of clinching technology in terms of composite–aluminum joints, encompassing aspects of tool design, process analysis, and the enhancement of joint quality. This work provides an overview of current research on clinching of CFRP and aluminum and serves as a reference for the further development of clinching processes.
Reinforcement bars based on glass fibre reinforced polymers (GFRP) show good mechanical properties and advantageous durability properties compared to conventional steel reinforcement. The increasing use of GFRP reinforcement can, therefore, also be seen against the background of an advised resource-efficient adoption of materials in the construction industry. However, the mechanical properties of GFRP reinforcement are still not sufficiently researched, currently leading to regulatory restrictions. More specifically, regarding the compressive material properties of GFRP reinforcement bars under long-term loading, there is a significant lack of information. This paper introduces a novel model for predicting the stress redistribution in GFRP reinforced concrete members subjected to long-term compression. A comprehensive examination of the mechanical background and a brief summary of existing literature on relevant test results form the basis for the initial development of an extensive test program to be applied. In the first part of the experimental investigations, GFRP reinforcement bars are statically loaded for an experimental period of 1000 hours in order to determine creep rates. Subsequently, GFRP reinforced concrete specimens are subjected to compression for 190 days at three different load levels. The results show a significant stress increase in the GFRP reinforcement due to creep and shrinkage. The high ultimate loads of preloaded specimens demonstrate that the long-term loading did not lead to any damage. The proposed analytical model combines the two parts of the experimental program and provides a practical method for determining the load redistribution in GFRP reinforced concrete members under permanent compressive loading.
Carbon fiber-reinforced plastic (CFRP) components are known for their exceptional resilience and ultra-lightweight nature, making them the preferred choice for applications requiring high mechanical loads with minimal weight. However, the intricate and anisotropic structure of CFRP components poses challenges, resulting in expensive repairs and testing. This complexity also leads to increased waste generation. Yet, innovative recycling processes offer a solution by reintegrating carbon components into a closed material cycle, promoting sustainability and circular economy principles. This work focuses on recycled CFs (rCFs) obtained through a continuous recycling method for CFRP primary recyclate from composite pressure vessel. Furthermore, re-purposing of the separated matrix material for secondary energy sources makes the process, a 100% recycling route. This closed-loop approach addresses conventional pyrolysis challenges and contributes to more efficient utilization of CFRP waste components. rCF and recycled polyethylene terephthalate (rPET) polymers were compounded through an extrusion process. Test specimens were then fabricated according to standard test norms to evaluate the resulting tensile and bending properties. The tensile and flexural modulus of the rCF-rPET obtained are 6.80 and 4.99 GPa, respectively. The need for enhancing the quality of rCF is apparent. Suggestive and potential implications and the marketability of rCF-rPET compounds are also discussed.
Computed tomography images are of utmost importance when characterizing the heterogeneous and complex microstructure of discontinuously fiber reinforced polymers. However, the devices are expensive and the scans are time- and energy-intensive. Through recent advances in generative adversarial networks, the instantaneous generation of endless numbers of images that are representative of the input images and hold physical significance becomes possible. Hence, this work presents a deep convolutional generative adversarial network trained on approximately 30,000 input images from carbon fiber reinforced polyamide 6 computed tomography scans. The challenge lies in the low contrast between the two constituents caused by the close proximity of the density of polyamide 6 and carbon fibers as well as the small fiber diameter compared to the necessary resolution of the images. In addition, the stochastic, heterogeneous microstructure does not follow any logical or predictable rules exacerbating their generation. The quality of the images generated by the trained network of 256 pixel × 256 pixel was investigated through the Fréchet inception distance and nearest neighbor considerations based on Euclidean distance and structural similarity index measure. Additional visual qualitative assessment ensured the realistic depiction of the complex mixed single fiber and fiber bundle structure alongside flow-related physically feasible positioning of the fibers in the polymer. The authors foresee additionally huge potential in creating three-dimensional representative volume elements typically used in composites homogenization.
In the development of innovative and high-performance products, design expertise is a critical factor. Nevertheless, novel manufacturing processes often frequently lack an accessible comprehensive knowledge base for product developers. To tackle this deficiency in the context of emerging additive manufacturing processes, substantial design knowledge has already been established. However, novel additive manufacturing processes like continuous fiber-reinforced material extrusion have often been disregarded, complicating the process's wider dissemination. The importance of design knowledge availability is paramount, as well as the need for user-friendly design knowledge preparation, standardized structure, and methodological support for accessing the accumulated knowledge with precision. Hence, this paper presents an approach that furnishes formalized design knowledge. Opportunistic knowledge, presented as principle cards, is systematically derived, prepared, and made accessible. Moreover, an access system is developed to ensure the comprehensive utilization of process-specific potentials throughout the development process. Furthermore, we propose linking these principles through a synergy and conflict matrix, aiming to consider synergistic principles and identify potential conflicts at an early stage. Additionally, an approach to provide restrictive design knowledge in the form of a design rule catalog is proposed. The application of the knowledge system is demonstrated exemplarily using a weight-optimized component.
In the realm of bio‐based curing agents, recent investigations have focused on amino acids owing to their distinctive attributes. Nevertheless, the suitability of thermosets cured with aromatic amino acids as latent matrix materials for fiber‐reinforced composites remains to be empirically established. Consequently, this study is oriented toward assessing the mechanical properties of diglycidyl ether of bisphenol A when cured with either L‐tryptophan or L‐tyrosine, in the presence of a latent, urea‐based accelerator. The investigated properties include glass transition temperatures, tensile, flexural, compression, and fracture toughness properties. The predominant variations in the mechanical characteristics of these thermosets are confined to their Young's moduli and fracture toughness properties. This divergence is attributed to the greater presence of crystals in the L‐tyrosine‐cured thermoset, resulting in enhanced reinforcement and toughening effects compared to the L‐tryptophan‐cured thermoset.
Transient propeller noise generated by electric vertical takeoff and landing (eVTOL) aircraft is a critical contributor to urban air mobility annoyance. This paper analyses noise emissions in transient eVTOL maneuvers, concentrating on the hover, transition, and climb phases. The study employs aeroelastic simulation in the time domain, determining a two-bladed lifting propeller's unsteady aerodynamic forces and blade motion. Noise emissions are predicted with Farassat's formulation 1A. The designed lifting propeller has a predominant loading noise during hover, altered by elastic deformations. The climb and transition phases analysis reveals significant noise contributions from rotational speed variations and horizontal acceleration. Vertical acceleration has a lower impact on the noise emissions. Oblique inflow into the propeller plane leads to tonal peaks in a high-frequency band. Changes in the rotational speed lead to aperiodic beats.
With the green energy transition, the wind industry has grown rapidly in recent decades. Wind turbine blades (WTBs) are primarily manufactured from glass fibers and thermoset matrix composites. Considering their lifetime from 20 to 25 years, significant amounts of wind turbine components will eventually enter the global waste stream. Currently, recycling is not sufficiently optimized and commercially available. Other strategies, such as repurpose, are becoming relevant to divert components from waste streams. This research explores a pathway to sustainable repurposing of decommissioned WTBs. The concept of a tiny house constructed from the root section of a 5 MW/61.5 m WTB is presented (“5 MW house”). The deformations and stresses of the repurposed composite structures were investigated using a finite element analysis based on the three load cases, defined by (1) a combination of snow load and payload, (2) a combination of wind load and payload, and (3) a thermal stress analysis of a critical temperature distribution of the 5 MW house. Furthermore, a life cycle assessment (LCA) was conducted to evaluate the environmental impacts of the proposed concept. The numerical analysis results showed that the 5 MW house can withstand the applied loads, and that the deformations are within acceptable limits. A reduction of up to 97% in environmental impacts for most impact categories was calculated, compared to a wooden tiny house, whereas climate change, ozone depletion, and eutrophication potential were up to 3.7 times higher, mainly due to the weight and composition of the 5 MW house. The authors believe that the proposed concept may be a high-volume repurposed solution for large-scale WTB root sections.
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