| Liquid hydrogen storage and transportation utilizes the double-wall vaccum-jacketed storage tanks to reduce the evaporation loss due to external heat leakage.The support structures of the liquid hydrogen tank are used to connect the inner vessel and outer jacket,with large temperature difference between the both ends,as well as need to bear the static load from the inner vessel and impact load for the mobile vessels,requiring high strength and low thermal conductivity to ensure the safety and low heat leakage.Fibre-reinforced composites with high strength and low thermal conductivity at cryogenic temperature,are commonly used as the support structures for cryogenic container,whose thermo-mechanical properties depend on numerous factors with no accurate mathematical models to predict physical parameters.The properties of fibre-reinforced composites vary with fibre orientation and temperatures.It is necessary to investigate the anisotropic and cryogenic effects of the properties.In order to investigate the effect of cryogenic temperature and fibre orientation on the properties of fibre-reinforced composites to support the design of liquid hydrogen container,the paper provides a comparasion of the thermo-mechanical properties of various epoxy resin composites.Epoxy/glass fibre(EP/GF)composites with the optimal thermo-mechanical properties at liquid hydrogen temperature,was sampled along the fibre direction(parallel direction)and perpendicular(vertical direction)to it,as well as mechanical and thermal conductivities testings were carried out to calculate the thermo-mechanical coefficient integrating the type of load and heat flow direction.The major researches are as following:(1)Compare the properties-temperature curves of different fibre composites and calculate the thermo-mechanical coefficient.The thermo-mechanical coefficient of fibrereinforced composites increases with decreasing temperature.EP/GF exhibits the best thermomechanical properties from room temperature to the liquid nitrogen temperature.Carbon fibre reinforced composite has the best thermo-mechanical coefficient at liquid helium temperature.EP/GF is the optimal option for supporting structures in liquid hydrogen containers.(2)Thermal conductivity testing: the thermal conductivity was firstly determined for the isotropic model by using the transient plane source(TPS)method and the transient hot wire method to demonstrate the effect of sampling method and location,and the differences between the results of the two approaches are also analysed.Then,the relationship between fibre direction and thermal conductivity was investigated using the TPS method for the anisotropic model,and the results were verified using a series-parallel model.Meanwhile,the coefficient of thermal conductivity at varying temperature was fitted to predict the thermal conductivity of EP/GF at the liquid hydrogen temperature.The results show that: the thermal conductivity of EP/GF is related to the sampling method and unrelated to the location of the sampling.The difference in transfer of internal yarns during testing contributes to the difference in the determination of the two measurement methods.The thermal conductivity along the fibres is greater than the thermal conductivity vertical to the fibres.The resin matrix softens and decomposes after sanding,as well as the glass fibres become bared and the number of micro convex at the contact interfaces increase,which result an increase in the EP/GF thermal conductivity with ageing wearing.(3)Mechanical performance testing: the EP/GF tensile,flexural and shear testing were carried out with cryogenic testing equipment to investigate the effects of the cryogenic temperature on the microstructure and macromechanical properties.Meanwhile,the mechanical properities at varying temperature was fitted to predict the shear and tensile strength in the liquid hydrogen temperature.Compression and shear testing were carried out on two types of fibre direction(parallel and vertical)specimens to investigate the relationship between fibre direction and mechanical properties.The results show that: the tensile,shear and flexural strengths of EP/GF are enhanced with the decreasing temperature;the compressive and shear strength perpendicular to the fibre direction is superior than parallel to the fibre direction.(4)Calculation of thermo-mechancial coefficient: thermo-mechancial coefficient is calculated by room-cryogenic and different fibre direction thermo-mechanical properties parameters,integrating the loading type and heat flow direction.The results show that:decreasing thermal conductivity and increasing mechanical properties at cryogenic temperature of EP/GF lead to a significant increase of the thermo-mechanical coefficient.Depending on the type of loading imposed on the specimens in the parallel and vertical directions,a relation exists for the thermo-mechancial coefficient as following: vertical compression load > vertical flexural load > parallel tension load > parallel compression load >vertical shear load > parallel shear load.The fiber direction of the support structures should be integrated in accordance with the type of thermo-mechancial coefficient.The paper investigates the thermo-mechanical properties of EP/GF in terms of both temperature and fibre direction.It provides a theoretical basis and data support for the design and selection of support structures of liquid hydrogen tank as well as thermal leakage analysis. |
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