Hydrogen is a promising candidate for achieving aviation sustainability, but storage aboard aircraft presents significant challenges. All-composite, double-walled, vacuum-insulated cryo-compressed storage vessels offer a potential solution by achieving high volumetric and gravimetric efficiencies. Load transfer connections between the tank's shells and the surrounding structure introduce concentrated loads in the composite shells. This work develops analytical models to characterize the stress state in composite shells under discrete in-plane loading, showing how stress concentrations decay and how laminate selection influences the decay rate. Discrepancies between the analytical and numerical models are noted, with suggestions for improving both. Additionally, the current model’s limitations due to the number of roots obtained from the governing equations are addressed by proposing additional boundary conditions. This research supports the structural and thermal analysis of composite hydrogen storage vessels, aiding the adoption of hydrogen as a sustainable aviation fuel.@en

Twist and crimp values are of paramount importance to the textile industry in understanding the properties and performance of a textile, and their quantification has been a subject of study since the early 20th century. Twist and crimp are the result of how the fibers have been modified from the original bundle to shape the textile, so the industrial methods used to measure them are based on mechanically reversing such deformations. The same information is needed to study the mechanics of historical fabrics such as canvas paintings supports and historical textiles, but they are more difficult to obtain because these are often brittle and impregnated with foreign materials, less homogeneous and very limited in availability for sampling. Therefore, such fundamental parameters are usually unavailable for conservation studies.

This paper examines the protocols used in the textile industry and proposes new methods, developed from previous research, for the reliable measurement of twist and crimp in historical textiles. The twist measurement method is non-destructive as it is based on observing the textile and the fibers on the surface of the yarn. Crimp is the undulation of the interlaced yarns and its measurement is an invasive examination of the internal structure of the textile, as it requires the observation of individual yarns. Both methods, applied here to a group of historical textiles, provide data in accordance with the current parameters of the textile industry, and their use is relatively simple and inexpensive.@en

During the early design stages of airframe components, many possible design architectures and production methods need to be traded to find the best configuration. Evaluating different production methods can be challenging as different production methods put different requirements on the product to be designed. This paper presents a new methodology that enables the inclusion of manufacturing and assembly in the design process. By extending the architectural design space model with components of the production system, the design choices regarding production are made explicit. Through the modeling of product and production requirements and assigning them a verification method, a dynamic MDAO workflow is formulated. Within a dynamic workflow, the design variables, analysis tools, and constraints change depending on the current design vector. The methodology has been applied to the design and manufacturing of a wing rib in which two manufacturing options were traded: metal machining and composite stamp forming. The dynamic MDAO workflow successfully found the Pareto front for both manufacturing methods. The main benefit is that only one workflow needed to be formulated and executed, whereas previously a separate MDAO workflow needed to be created for each combination of product design and production method. Overall, the newly presented methodology enables the optimization and trade-off between different production methods while ensuring the design complies with the production-specific requirements.@en

Twin matrix composites (TMC) are novel composite architectures where reinforcing composite elements are embedded in a secondary resin to address various mechanical functions suited for diverse engineering applications such as morphing wings. Here, for the first time, a recyclable twin matrix composite using micro-pultruded rods as reinforcements will be manufactured. Within the scope of the work, the design of the TMC mould which allows 0°/90°/0° reinforced layup will be discussed and created through additive manufacturing. Recycling and remanufacturing TMC will be conducted up to 4 times, and surface characteristics of the rods will be examined to monitor the effect of recycling. Interlaminar shear strength of TMC made from fresh and recycled rods will be investigated comparatively.

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Hydrogen is being investigated as aviation fuel, with the objective to achieve an energy transition for the aviation sector. Effective storage solutions are crucial to mitigate the aerodynamic penalty caused by its low volumetric energy density. The focus of this study is the integration of a cryo-compressed vacuum-insulated storage vessel into the primary structure of aircraft, aiming to enhance structural efficiency. This is achieved by implementing analytical methods to analyse the thermo-mechanical loading of the inner and outer walls of the fuel tank. It is envisioned that the inner wall rather than the outer wall is more suitable to sustain additional loads. However, it is unclear how the cryogenic environment affects the stress state of the composite material.

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Vacuum-insulated, all-composite hydrogen storage vessels are promising for achieving viable gravimetric and volumetric efficiencies in aviation applications. However, stress concentrations arise due to the connections between the composite shells and to the surrounding structure. This study develops analytical models which capture the stress state of composite cylinders subjected to pressure loading and discrete in-plane edge loads. The models allow for easy adjustments in tank geometry, lamination, and load introduction parameters, including the number and width of connection points. This aids in the preliminary structural and thermal analysis of composite hydrogen storage vessels, pushing the implementation of hydrogen as a sustainable fuel for aviation. @en

Hydrogen is deemed a viable contender to make the aviation industry more sustainable. However, while its mass-energy density of 120 MJ/kg with a density of 70 kg/m³ is an improvement with respect to the energy density of 43 MJ/kg of conventional aviation fuels, it's volumetric energy density of only 8 MJ/m³ is four times larger, which inevitably has a detrimental effect on the aircraft's aerodynamics. Accordingly, the fuel shall be stored under pressure and at low temperatures to achieve the assumed density values. The actual values for the storage pressure and temperature are topics of discussion. This research aims at studying the effects of storing liquid or gas hydrogen on the mission of an aircraft, by investigating the temperature and pressure profile during such a mission. During this study, multiple tank configurations and aircraft missions are investigated. Using a two-phase hydrogen approach an increase in the gravimetric efficiency by a factor of two can be achieved, compared to gas hydrogen. Moreover, trends have been found in the definition of the topology of hydrogen tanks for different aircraft missions. Increasing design freedom by allowing multiple tanks shows that the loss in gravimetric efficiency is limited to 10%.

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For pick-and-place processes to become widely implemented in industry a consistent and acceptable product quality needs to be achieved. One important quality criterion is the fiber angle deviations in the reinforcement. Handling a reinforcement will subject it to forces due to e.g. gravity and accelerations. These forces can result in in-plane shear and subsequently in fiber angle deviations. The current work looks at predicting and preventing in-plane shear induced fiber angle deviations by studying the positioning of pick-up points. In the state of the art the positioning of individual pick-up points is typically either not discussed or is based on the mould where the fabric is to be draped on – not on the effect of the handling on the fabric. The relationship between the positioning of the pick-up points and the behavior of the fabric should however also be considered. Finite element simulations validated through experimental work will be used to study the influence of pick-up point location on the in-plane shear strain for a bi-axial Non Crimp Fabric [NCF]. In [1] tolerances have been set for the fiber angle deviations, additionally the relationship between in-plane shear strain and fiber angle deviations has been demonstrated for the specific NCF. These results are used in the present work to evaluate the results from the simulations. The current work will demonstrate that it is possible to control the in-plane shear induced fiber angle deviations by varying the position and number of the pick-up points. Additionally, It will show whether simulations for the positioning of pick-up points on large reinforcements can be simplified by looking at one instance of a repeating pattern. The paper will provide a framework for the determination of positioning of pick-up points while predicting and preventing in-plane shear induced fiber angle deviations. @en

The automated handling of non-crimp fabrics using pick-and-place processes will subject the fabrics to forces due to e.g. gravity and movement. These forces can result in undesired fiber angle deviations. The current work looks at predicting and preventing in-plane shear induced fiber angle deviations by studying the positioning of pick-up points. Experimental work shows that the layers of non-crimp fabrics should be expected to deform as individual layers unless they are fixed using an external mechanism. This is to be taken into account when choosing the gripping mechanism for the pick-up points to avoid unexpected behavior. The experimental work is also used for the preliminary validation of a numerical model based on deflections. Results from the current work are a basis for further research on the influence of pick-up point location on the fibre angle deviations in non-crimp fabrics.

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For pick-and-place processes to become widely implemented in industry a consistent and acceptable product quality needs to be achieved. In the state of the art it is assumed that reinforcements will be in perfect condition at the start of forming or draping. In reality the handling process can already result in undesired deformations. The current work will look at fiber angle deviations that occur during this process due to in-plane shear. It is shown that bounds can be set for these fiber angle deviations based on experimental work. Periodic representative volume element homogenization is used to obtain homogenized material properties for a bi-axial non-crimp fabric with a specific construction. With these material properties the in-plane shear strain, and thus the fiber angle deviations, can be predicted. The presented methodology and results obtained using it can be a basis in the design process for automated handling of reinforcements and for in-situ quality control of the pick-and-place process.

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A realistic wear test was developed for porous thermal insulation systems exposed to high temperature turbulent gas flow, because it is essential for the development of existing and new concepts of such insulation and therefore also for the performance of processes that depend on such insulation. Wear is crucial and often dominant for the long-term performance of thermal insulation and, because of the complex nature of insulation wear under exposure of high-temperature turbulent flow, realistic testing capability is a necessary tool for improvement. A test rig was developed to subject fibrous ceramic insulation, the most encountered type of thermal insulation, to conditions representative for in-service use and to enable investigation of the occurring phenomena and behaviour. This rig can accommodate a range of different insulation configurations and is compatible with many turbulent flow sources. This test rig, its components, the experimental procedure, its accuracy and representative results are presented.

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The purpose of this work is to experimentally establish the combined influence on the flow and thermal resistance of an exhaust pipe wall formed by a porous, compliant layer with overlying discrete roughness elements exposed to the pulsating exhaust gas flow of a combustion engine. Through measuring the streamwise pressure drop over and radial temperature differences in different pipe samples for a range of flow states with different Reynolds numbers and non-dimensional pulsation frequencies, the effects were discerned. The configurations of the sample walls covered a range of mesh pitches, compliant-layer densities, and compliant-layer compression ratios. The (non-sinusoidally) pulsating exhaust gas flow spanned the following range: Re_b (= u_bD/ν_b) = 1⋅ 10⁴ - 3⋅ 10⁴, T_b = 500 - 800 ^∘C, ω⁺(= ωνb/uτ2) = 0.003 - 0.040. The friction factors were found to be effectively constant with Reynolds number and non-dimensional pulsation frequency while the variation with insulation density/compression was not significant. Additionally, for both mesh pitches, the measured friction factors were in line with those reported in literature for similar geometries with steady flow and solid walls. Together this indicates that neither compliance nor the pulsations in the exhaust gas flow significantly affect the friction for this configuration. Comparison of the samples based on the derived thermal resistance showed a similar influence of the fluid-wall interface as for the friction. Additionally a distinct influence of compression, independent of the insulation density, was observed that increases with increasing temperature. It was concluded that the increased resistance was due to additional radiation resistance because of fibre reorientation due to compression.

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Tubular adhesive joints, used in truss structures to join pultruded carbon fibre-reinforced polymer members to aluminium nodes, are modelled with varying dimensions. The numerical model uses a Cohesive Zone Modelling formulation with a trapezoidal traction-separation law for the adhesive layer, and experimental tests are carried to validate it. The results showed that the joint strength increases significantly with the bonding area, with a limit on the overlap length above which it stops increasing. This upper limit is affected by the thickness and tapering angle of the adherends, due to their influence on the shear stress distribution along the overlap. On the other hand, the adhesive thickness has only a marginal influence on the joint strength.

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For the application of composite materials to become more widespread and replace traditional materials their manufacturing processes and final products will need to be competitive and be e.g. lighter, stronger or stiffer and quicker, easier or more cost-efficient to produce than traditional materials. The state of the art for pick-and-place operations for the manufacturing of composite parts focuses on handling single lab-sized layers at undisclosed speeds. The process could however be more competitive by being able to handle more and larger layers in a faster manner than currently presented in research. The aim of the paper is to evaluate the existing pick-and-place strategies on their suitability for the swift automated handling of multiple large-sized layers of reinforcement. The review shows that many of the existing techniques could be suitable for different scenario’s and discusses which factors are to be taken into account when dealing with large layers, more than one layer or rapid handling. (Figure presented.).

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Understanding of the thermal and mechanical behaviour of conformal tanks when utilized in cryogenic fuel storage is considered crucial in the hypersonic aircraft sector. This behaviour is strongly dependent on the way the tank itself is designed. This study focuses on the effect of design on the performance of an innovative Type IV multi-spherical composite-overwrapped pressure vessel at both ambient and cryogenic conditions. A method to evaluate the required number of reinforcement rings at the intersections and thus avoid damage in those regions under pressurization is outlined. A thermo-mechanical FE-based model coupled with a progressive failure analysis (PFA) algorithm enables to evaluate the pressure window of the multi-sphere at ambient conditions. Additionally, a transient analysis -included in this study-is used to determine the different heat transfer mechanisms, temperature and strain evolution at the tank wall throughout cryogenic operation (chill-down, pressure cycling and purging). The temperature dependency of the tank wall materials is obtained by coupon testing and fitting functions and is hereby incorporated in the analysis. The most important outcome here is the absence of damage in the composite overwrap at cryogenic environments; this may be considered as a positive indication about the suitability of the Type IV multi-spherical COPVs for cryogenic storage.@en

Two-matrix composites combine fibers with two distinct matrices. This is achieved by impregnating fiber bundles with a high-stiffness matrix and embedding the cured bundles in a flexible matrix. Two-matrix composites have been shown to offer unprecedented combinations of transverse flexibility and longitudinal tensile strength, and could offer improved fiber alignment and manufacturability. Here, we explore this concept further by embedding carbon fiber micropultrusions in flexibilized epoxy matrices and examining the longitudinal compression behavior. Our results on thin-walled rings reveal that the failure mode depends on micropultrusion diameter, with small diameters resulting in micropultrusion kinking and larger diameters in splitting and crushing. Additionally, we find that two-matrix composites can offer higher compression strength than conventional composites with the same flexible matrix, despite a lower fiber volume fraction. The inherent manufacturing advantages and high anisotropy could make two-matrix composites interesting candidates for specific applications, such as morphing wings or additively manufactured composites.@en

Laser assisted automated tape or fiber placement (LATP/LAFP) with in-situ consolidation is a promising technique for manufacturing large structures, eliminating the limitations of autoclave curing. Currently, 2-D models are mostly preferred for the thermal analysis of the process. A 3-D, transient thermal finite element model is developed to analyze the effect of the alignment of the heat source with the tape laying direction and is compared with a model imitating a 2-D analysis space. This aspect of the process has not been considered in the literature so far. Effects of this aspect on temperature history and intimate contact evolution are presented.@en

In the context of lightweight structure design for the transportation and robotics industries, new types of composite structures are being developed, in the form of trusses made of fiber-reinforced polymer composite members of small diameter. The main objective of this work is to study adhesive joints, bonding pultruded composite tubes inside aluminum pieces, numerically and experimentally. More specifically, the objective is to determine which numerical model is able to predict the joint strength the most accurately, and to examine the influence of several design parameters on the strength and weight of the joints. With this purpose, samples are manufactured with varying dimensions, and tested in tension until failure. Next to the manufacturing numerical models using either a continuum mechanics or a damage mechanics (CZM) approach are built. The comparison of the numerical results with the experimental results show that the damage mechanics approach results in the most accurate joint strength predictions. It is also found that increasing the adhesive overlap length has the highest impact on increasing the joint strength, and that reducing the adherend thickness has the highest impact on reducing the structural weight, while preserving the joint strength.@en

In the context of lightweight structure design for the transportation and robotics industries, new types of composite structures are being developed, in the form of trusses made of fiber-reinforced polymer composite members of small diameter (a few millimeters thick at most). Some concepts of wound trusses can be found in the literature, but in more general cases, for which a predefined wound truss shape is not usable, individual truss members must be joined together. The axial strength of the composite members allow them to carry a high load, and the joints between those members should be strong enough to carry this load as well. With the objective of developing an efficient joint design for an application in thin composite trusses (member thickness ranging from 0.5 to 5 mm), finite element models of several adhesive joint designs were built, and their strengths were compared. The comparison was made using the same joint configuration (number of members, member cross-sectional area, joint dimensions) and loading conditions. Adhesive failure was considered in this study, and the strength of each design was determined from the value of the peak maximum principal strain in the adhesive layer, as this failure criterion is suitable for the toughened adhesive material used in the models. A trade-off between the strength, weight and manufacturability of each joint design was made in order to conclude on their overall performance. Results suggested that, among the joint designs modelled, round-based composite rods inserted in a tubular metallic piece are the most efficient in terms of strength-to-weight ratio.@en

What started out as an exercise in exploring the weight reduction potential of those allegedly “heavy recip crossheads”, turned out to be a fast leap towards implementation of a new hybrid material concept for very lightweight pistons. This was enabled by a next phase in the EFRC R&D group research project which has been subject of this conference before.The 2014 paper was technical in nature, addressing the context and requirements and defining the solid polymer concept (SPP) as an exciting solution, as well as the characterization of polymer composite materials in fatigue. Building on these foundations, the current paper focuses on the challenge of turning the obvious good idea into a readily available technology under the restrictions of pre-competitive research. Therefore it identifies the things that should be done, how to do it and also which things are best left until later. Bypassing the extensive volume of technical work that had to be done to demonstrate feasibility and develop key materials and testing technology, the results of the full scale validation experiments are presented as well. Following an earlier 1:10 scale piston fatigue test, a full scale test demonstrated a residual strength – after accelerated fatigue – of 400 kN. Comparing against commonly encountered designs based on steel and aluminium, a 30 – 70% mass reduction is found for typical larger size pistons. Enabled by the full scale validation of the concept, the technology readiness is enhanced to a level that by 2016, the technology seems ready for validation in an actual compressor. As a matter of fact, the results of the R&D project are industrially applied, witnessed by the emergence of a spin-off company and plans by major compressor manufacturers to design and/or launch new and significantly improved machines. The authors argue that the EFRC R&D project may be seen as a model case in efficacious creative innovation, where the time between idea generation and industrial application is less than 3 years. A brief discussion of why we believe this was possible is included. It explains what is required to achieve success – in spite of a rather odd idea introducing an unknown ‘plastic’ material into a self-declared conservative industry – to get a disruptive innovation like the solid polymer piston accepted so quickly. @en