This study focuses on the understanding of the thermal and structural behavior of an innovative Type IV multi-spherical composite-overwrapped pressure vessel through an experimental assessment that consists of hydrostatic testing at ambient conditions and pressure cycling with a cryogenic medium (LN2). During hydro-burst testing at a high displacement rate, the strain and damage progression is monitored with Digital-Image-Correlation (DIC) and Acoustic Emission (AE) techniques respectively. The effect of filling with LN2, pressure cycling and draining on the composite overwrap temperature gradient and strain evolution is additionally obtained with Fiber Bragg Gratings (FBGs) and thermocouples. Utilization of AE helped to reveal the different damage mechanisms occurring and enabled the evaluation of the pressure window of the multi-sphere. The experimental measurements in the cryogenic regime verified the suitability of the involved stiffness and coefficient of thermal expansion (CTE) fitting functions developed in [32] that enable to establish of a relationship between strain and temperature during cryogenic chill-down and pressure cycling. This study provides a framework about the suitability of conformal Type IV multi-spherical COPVs for cryogenic storage.@en

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

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

The simulation of long life behavior and environmental aging effects on composite materials are subjects of investigation for future aerospace applications (i.e. supersonic commercial aircrafts). Temperature variation in addition to matrix oxidation involves material degradation and loss of mechanical properties. Crack initiation and growth is the main damage mechanism. In this paper, an extended finite element analysis is proposed to simulate damage on carbon fiber reinforced polymer as a consequence of thermal fatigue between −50℃ and 150℃ under atmospheres with different oxygen content. The interphase effect on the degradation process is analyzed at a microscale level. Finally, results are correlated with the experimental data in terms of material stiffness and, hence, the most suitable model parameters are selected.@en

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.@en

This paper outlines the structural performance of a conformable pressurizable tank consisting of intersecting spherical shells (multi-cell tank). Multi-cell tanks outrival conventional multiple cylindrical tanks in volumetric efficiency when required to fit in a rectangular envelope in the automotive industry. When pressurized, the multi-cell (or multi-bubble) tank experiences high stress concentrations at the vicinity of the junctions, and thus the concept of effectively reinforcing those regions without adding significant excess weight becomes crucial. Furthermore, when applied for cryogenic medium storage, the heat transfer between different bodies and the generation of respective thermal stresses in such vessels makes the solution more complicated. In this paper the effect of the i) fiber-reinforced materials at the membrane and ii) unidimensional carbon tows at the intersections on the structural integrity of the tank is analysed for different loading scenarios. An operating window for the proposed tank configuration under the given loading scenario is established indicating the safe zone where the tank can operate.@en

Heating the thermoset tape to a higher temperature than is used in the conventional automated tape laying process can affect the cure cycle, void content, interlaminar shear strength and residual stresses of the final product. In this study, the effects of different heating strategies on the degree of cure in thermoset tapes were modelled. This was done for two tape laying speeds and by heating different combinations of the incoming tape, the previously laid tape and the mould. The model predicts the thermochemical profile of two different materials and is validated by experimental data from thermocouples and a pyrometer. @en

Heating the thermoset tape to a higher temperature than is used in the conventional automated tape laying process can affect the cure cycle, void content, interlaminar shear strength and residual stresses of the final product. In this study, the effects of different heating strategies on the degree of cure in thermoset tapes were modelled. This was done for two tape laying speeds and by heating different combinations of the incoming tape, the previously laid tape and the mould. The model predicts the thermochemical profile of two different materials and is validated by experimental data from thermocouples and a pyrometer. @en

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: Reb (= ubD/νb) = 1⋅ 104 - 3⋅ 104, Tb = 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.@en

In the field of cryogenic storage, the medium inside the pressure vessel is in a liquid state and thus is incompressible. Therefore the storage tank should be designed in a way, that makes the best possible use of the available space within an aircraft. A composite-overwrapped pressure vessel (COPV) based on intersecting spheres (multi-sphere) provides a volumetrically efficient solution and leads to weight savings, due to reduced hoop stresses and less required thermal insulation. The latter is the result of the minimization of passive heat in the cryogenic liquid, associated with the fact that spheres have the minimum surface area for a given volume. In the present work, a numerical and experimental study of a novel multi-spherical COPV with a plastic liner was performed. A thermo-mechanical model based on Finite Element Analysis (FEA) was developed to assess the effect of cryogenic operation at the structure. The model incorporated the dependency of engineering properties and coefficient of thermal expansion of the composite overwrap and liner materials to temperature, in order to describe the structural response to cryogenic temperatures more accurately. This dependency was determined through using approximation functions based on results from material coupon testing. The temperature profile and strain response of the tank were assessed through thermocouples and Fiber Bragg Gratings (FBGs) respectively throughout the cryogenic chill-down and pressure cycling test. The experimental results verified the accuracy of the involved stiffness and CTE functions and the FE analysis with average offset of 10 [%]. The most important outcome from the study is the absence of damage in the composite overwrap after cryonic chill-down and pressure cycling, which can be regarded as positive indication of the suitability of Type IV multi-spherical COPVs for cryogenic storage applications.@en