Determination of key parameters responsible for polymeric liner collapse in hyperbaric type IV hydrogen storage vessels

Depressurization tests at a laboratory scale, coupled with numerical modelling, are used to determine the key parameters responsible for the polymeric liner collapse in hyperbaric type IV hydrogen storage vessels. X-ray tomography allows to determine the damages suffered by the sample during the depressurization step. Results show that the differential pressure induced during the depressurization step between the liner/composite interface and the free surface of the liner is the main factor responsible for the collapse of the liner. For a given temperature, this pressure gradient can be modified by changing the maximum H₂ pressure, the emptying rate or by adding a residual pressure plateau. Temperature is also of prime importance by influencing the yield point of the liner, the interface resistance and the amount of gas dissolved into the vessel. Thus, increasing temperature also increases the risk of liner collapse for the same gas exposure conditions.     

Effects of surface preparation on bond behavior CFRP-to-PA6 bonded joints using different adhesives

This paper focuses on an experimental study of the explosive decompression on representative samples of the hyperbaric type IV hydrogen storage vessels. The adhesion of the composite to the liner is achieved by different adhesives. The bond behavior of liner-to-composite bonded joint considerably depends on the properties of adhesives, as well as the assembly process. X-ray tomography allows determining the damages before and after explosive decompression tests. Tomographic observations have revealed a certain level of porosity due to the assembly process with plasma treatment. This porosity influences the damage mechanisms induced by explosive decompression. Results show that 1) the increasing of the maximum hydrogen pressure (differential pressure induced during the depressurization step between the liner/adhesive interface or the adhesive/composite) increases the risk of liner collapse for the same gas exposure conditions, 2) Compared with soft adhesive, the stiff adhesive has proven better adhesion between the composite and the liner, 3) the flame treatment improved the surface energy of the PA6 and subsequently increased the collapse limit pressure, 4) adhesive RCA-20 with plasma preparation can be defined as a kind of low strength to collapse adhesive with a collapse limit pressure less than 2 MPa, 5)adhesive RCA-2000 with flame treatment can be defined as a kind of high strength to collapse adhesive in the present report with a collapse limit pressure between 15 MPa and 17.5 MPa.     

Sample scale testing method to prevent collapse of plastic liners in composite pressure vessels

Type IV pressure vessels are commonly used for hydrogen on-board, stationary or bulk storages. When pressurised, hydrogen permeates through the materials and solves into them. Emptying then leads to a difference of pressure at the interface between composite and liner, possibly leading to a permanent deformation of the plastic liner called “collapse” or “buckling”. This phenomenon has been studied through French funded project Colline, allowing to better understand its initiation and long-term effects. This paper presents the methodology followed, using permeation tests, hydrogen decompression tests on samples, and gas diffusion calculation in order to determine safe operating conditions, such as maximum flow rate or residual pressure level.     

A literature review of failure prediction and analysis methods for composite high-pressure hydrogen storage tanks

With the development of hydrogen fuel cell vehicles, the on-board hydrogen storage technology with safety, efficiency and economy has become a fundamental part. Low cost, light weight and good safety performance are required for the on-board hydrogen storage tanks. The composite high-pressure hydrogen storage tank has been recognized as an efficient solution that could address these problems. However, the complex working environment of hydrogen-thermo-mechanism presents challenge to the failure analysis and predictive model establishment of the composite hydrogen storage tanks. The crucial parameters or indicators for tank's failure analysis include burst pressure, damage state and fatigue lifetime, etc. So this paper gives a comprehensive review on the failure behavior analysis methods and prediction models of composite high-pressure hydrogen storage tanks from the literature. First, the failure analysis methods of composite high-pressure hydrogen storage tanks are summarized. Second, the latest literature regarding failure mode predictive methods and models of type III and type IV tanks are reviewed. The different failure criteria are compared and summarized, including some new failure criteria. These criteria enable failure analysis methods to obtain the interaction information on the interaction between the microscopic and macroscopic aspects of the composite. Damage evolution model and constitutive model are summarized. The post-initial failure behavior of the composite laminates structure is simulated by the material property degradation method (MPDM), especially the continuum damage mechanics (CDM) in conjunction with commercial finite element (FE) analysis method. The process of progressive failure analysis of composite tank is summarized as a reference for subsequent failure analysis. The future work of progressive failure analysis should focus on the initial failure of the composite material and microscopic failure mechanisms. The burst, fiber damage and fatigue life are the mainly investigated failure modes for type III composite hydrogen storage tank. For Type IV, the mainly researched failure modes are the collapse and blistering of the liner, burst and damage. The different finite element analysis methods and failure predictive models were classified and summarized. Further improvements were required for the simulation models of full-scale structure of the tank in the working environment or under the complex fiber winding modes. The liner of the type IV cylinder is completely distinct from that of the type III, therefore the behavior of collapse and blistering of the liner needs to be further investigated. The factors that affect collapse and blistering should be explored. The future research need focus on controlling these factors and monitoring the effects of these factors towards structural strength.     

Application of PET as a non-metallic liner for the 6.8 L type-4 cylinder based on the hydrogen cycling test

This study aims to find the evidence that polyethylene terephthalate (PET) is pertinent, with respect to the risk of thermal degradation during fueling, as a liner material of a type-4 composite cylinder for storing 6.8 L of compressed hydrogen. In particular, one type-4 cylinder with the PET liner of thickness 0.6 mm and one type-3 cylinder for comparison have simultaneously undergone 6 cycles of fast fueling (0.15 MPa/s) and fast defueling (0.55 MPa/s) with hydrogen gas in the range of 2 to 45 MPa. The hydrogen temperatures in cylinders, which were measured by a specially-devised thermocouple inserted in each cylinder, change within the range of ?30.0 to 70.0 ^°C. Although the temperature in the type-4 cylinder rises higher than that in the type-3 cylinder due to the lower heat conductivity of PET, it does not exceed 85 ^°C, which is the limit set by the international standards, EC No. 79. Furthermore, from the measurements of the deformation by the laser displacement sensors, the type-4 cylinder swells less than the type-3 cylinder. The pressure-displacement analysis shows that the deformation of type-4 cylinders occurs reversibly, i.e., defueling makes the cylinder regain its previous shape. In essence, PET is safe against thermal degradation when applied as a liner of a 6.8 L type-4 cylinder for hydrogen storage.     

Analysis of multi-layered thick-walled filament-wound hydrogen storage vessels

In this paper a three-dimensional elasticity analysis on multi-layered thick-walled filament-wound hydrogen storage vessels is outlined. An exact solution to stresses of the metal liner and each anisotropic layer is presented, based on Lekhnitskii's theory and the generalized plane strain assumption. The governing equation for determining the radial displacement of the hydrogen vessel is derived and the stresses in the cylindrical coordinates are then obtained. The matrix equation that determines the integration coefficients of the governing equation is formulated by considering the boundary and interface conditions. The normal and in-plane shear stresses and the twisting rate of the vessel are calculated for various thicknesses of the aluminum liner; the results are then compared to those presented by Xia et al. It is shown that the addition of the liner significantly reduces the stress magnitude of the hydrogen vessel; this stress magnitude decreases as the liner thickness increases. The results also revealed that the twisting effect is reduced by increasing the liner thickness. The ratio of hoop-to-axial stress is no longer a constant through the vessel wall and varies within the wall thickness. In addition, various combinations of anisotropic composites and isotropic liner materials are here examined to pinpoint preferable material combinations that lead to a lower equivalent stress level of the liner and higher strength reserve of the composite laminate.     

Advances on materials design and manufacture technology of plastic liner of type Ⅳ hydrogen storage vessel

The growing demand for type IV hydrogen tanks with long life, lightweight, high hydrogen storage density characteristics has posed new issues for liners. The paper discusses the causes of liner failure in terms of hydrogen permeation, thermal instability, and mechanical damage, as well as a focused analysis of alternative material optimization strategies. Through a detailed investigation of aggregate state structures, formulations and processes, the principles of material modification, primarily inorganic functional filler/polymer filler filling composite and laminated orientation, and their enhancing effects are sorted out. Besides, the benefits and drawbacks of blow molding, injection and welding, and the rotating technique, which were employed by some manufacturers are contrasted in the article, for overcome the problematic molding of hollow plastic liners with metal BOSS structures. This text will be a valuable resource for material exploitation as well as efficient and reliable molding of various liners.     

Methodology to improve the lifetime of type III HP tank with a steel liner

The present paper aims at studying a high-pressure hydrogen storage vessel, combining a steel liner and a wrapped composite reinforcement. Nowadays, this means of storage is notably used in transport. However, limits appear insofar as fatigue problem happens when the operating pressure is 700 bar. This matter has to be solved. This study tries to arrange a method to build a 700 bar vessel which could resist to cyclic pressure loading, and particularly focuses on the behaviour of the liner which seems to be the critical element to control. In addition, as a large part of this gaseous storage is bound to be on board, the composite optimization and thus weight optimization is considered.     

Performance of hydrogen storage tank with TPRD in an engulfing fire

The performance of a composite hydrogen storage tank with TPRD in an engulfing fire is studied. The non-adiabatic tank blowdown model, including in fire conditions, using the under-expanded jet theory is described. The model input includes thermal parameters of hydrogen and tank materials, heat flux from a fire to the tank, TPRD diameter and TPRD initiation delay time. The unsteady heat transfer from surroundings through the tank wall and liner to hydrogen accounts for the degradation of the composite overwrap resin and melting of the liner. The model is validated against the blowdown experiment and the destructive fire test with a tank without TPRD. The model accurately reproduces experimentally measured hydrogen pressure and temperature dynamics, blowdown time, and tank's fire-resistance rating, i.e. time to tank rupture in a fire without TPRD. The lower limit for TPRD orifice diameter sufficient to prevent the tank rupture in a fire and, at the same time, to reduce the flame length and mitigate the pressure peaking phenomenon in a garage to exclude its destruction, is assessed for different tanks, e.g. it is 0.75 mm for largest studied 244 L, 70 MPa tank. The phenomenon of Type IV tank liner melting for TPRD with lower diameter is revealed and its influence on hydrogen blowdown is assessed. This phenomenon facilitates the blowdown yet requires further detailed experimental validation.     

MATLAB和APDL在气缸套变形量可视化的应用

内燃机气缸套工作过程中会产生变形,变形量如果过大,会影响内燃机整机性能,因此要对气缸套变形量进行分析研究.现多采用有限元方法计算其变形量,但ANSYS软件后处理的结果不能清晰展示变形量的具体情况.为解决此问题,应用APDL采集气缸套内壁所要考察横截面的有限元计算数据,在此基础上,用MATLAB程序批量绘制气缸套内壁横截面变形的极坐标图形.结果显示,气缸套内壁某截面变形量在这种图形中比ANSYS软件后处理的结果更加便于观测,该方法也可用于柱类有限元模型变形量可视化研究.     

Research on hydrogen permeability of polyamide 6 as the liner material for type Ⅳ hydrogen storage tank

As the liner material of type IV hydrogen storage tank, polymer is restricted in commercial application due to its high hydrogen permeability. In this paper, for the first time, the suitability of polyamide 6 (PA6) filled with lamellar inorganic components (LIC) as the hydrogen storage tank liner is comprehensively investigated, including thermal and mechanical properties, morphology and structure, rheology, and the hydrogen permeability under various temperature (−10 °C, 25 °C, 85 °C) and pressure (25 MPa, 35 MPa, 50 MPa) conditions. The results show that comparing with PA6, the thermal and processing properties of LIC/PA6 have been improved, the tensile strength, bending strength and bending modulus of LIC/PA6 are increased by 36%, 17% and 12%, respectively. Especially, the hydrogen permeability of LIC/PA6 is decreased by 3–5 times which meets the requirements specified by the hydrogen tank standard. The research work provides a theoretical basis and reference for the preparation and selection of high barrier liner materials in the future.     

D系列柴油机气缸套变形和气缸垫密封可靠性的有限元分析

本文对发动机缸套-机体-垫片系统在缸盖螺栓压紧力作用下的受力进行了分析,采用轴对称模形,对D系列柴油机气缸套变形和气缸垫密封可靠性进行有限元分析。结果表明,D系列柴油机气缸套的变形不同于传统的柴油机气缸套,在各种影响因素中,温度的影响起主要作用;D系列柴油机缸盖螺栓压紧力在缸套和机体之间的分配是合理的,缸套凸出机体顶面的量对气缸垫密封压力有一定影响。     

Numerical modelling of transient heat transfer of hydrogen composite cylinders subjected to fire impingement

To improve the current design standards of the hydrogen composite cylinders, it is essential to understand the thermal response of the hydrogen composite cylinders subjected to fire impingement. In the present study, a fully coupled conjugate heat transfer model based on a multi-region and multi-physics approach is proposed for modelling the transient heat transfer behaviour of composite cylinders subjected to fire impingement. The fire scenario is modelled using the in-house version of FireFOAM, the large eddy simulation (LES) based fire solver within the frame of OpenFOAM. Three dimensional governing equations based on the finite volume method are written to model the heat transfer through the regions of composite laminate, liner and pressurized hydrogen, respectively. The governing equations are solved sequentially with temperature-dependent material properties and coupled interface boundary conditions. The proposed conjugate heat transfer model is validated against a bonfire test of a commercial Type-4 cylinder and its transient heat transfer behaviour is also studied.     

Optimal design of a Type 3 hydrogen vessel: Part I—Analytic modelling of the cylindrical section

The present paper aims to study the cylindrical section of a Type 3 high-pressure hydrogen storage vessel, combining an aluminium liner which prevents gas diffusion and an overwrapped composite devoted to reinforce the structure. Today, this technique is widely used but still requires consistent time investments whenever a competitive solution, involving to definitely increase weight efficiency, is needed. The laminate composite is assumed to be an elasto-damage material whereas the liner behaves as an elasto-plastic material. Based on the classical laminate theory and on Hill's criterion to take into account the anisotropic plastic flow of the liner, the model provides an exact solution for stresses and strains on the cylindrical section of the vessel under thermomechanical static loading. Part I focuses on the theoretical background. The effect of the stacking sequence on the gap occurrence, on the residual stress magnitude and on the structure stiffness may then be investigated. This will be done and be compared with results of experiments which are carried out on prototypes in the second part of this paper before an optimization is performed.     

Experimental and analytical investigation of the cylindrical part of a metallic vessel reinforced by filament winding while submitted to internal pressure

In this work, we present an experimental and analytical investigation of a hydrogen storage vessel. This vessel is made of a carbon/epoxy envelope coated on a metal liner. In the theoretical part, an analytical model is proposed in which the laminate composite is assumed to be an anisotropic purely elastic material, whereas the liner is considered as an elasto-plastic material. The suggested analytical model provides an exact solution for stresses and strains on the cylindrical section of the vessel solution submitted to mechanical static loading. The aim of the experimental part is to validate the results of the theoretical model by manufacturing and testing some prototype vessels. Some analytical results are compared with the finite element solutions, a good correlation is observed.     

A coupled elastoplastic-transient hydrogen diffusion analysis to simulate the onset of necking in tension by using the finite element method

Hydrogen-enhanced localized plasticity (HELP) is an acceptable mechanism for hydrogen embrittlement which is based on the experimental observations and the theoretical computations. The underlying principle in the HELP theory is that the presence of hydrogen causes the localization of the slip bands which results in the decrease of the fracture strength. In a sample under plane-strain tensile stress, plastic instability can lead to either the concentration of plastic flow in a narrow neck or bifurcation from homogeneous deformation into a mode of an exclusively localized narrow band of intense shear. Recently, it has been demonstrated that the presence of hydrogen can indeed induce shear banding bifurcation at macroscopic strains. By using a steady-state equilibrium equation for hydrogen diffusion analysis, the effect of hydrogen on the bifurcation of a homogeneous deformation in a plane-strain tension specimen into a necking or a shear localization mode of deformation has already been studied. In the present research, using a transient hydrogen diffusion analysis and introducing a new constitutive equation accompanied by considering the reduction in the local flow stress upon hydrogen dissolution into the lattice, the effect of hydrogen on shear localization is investigated. In addition, progress has been made in that, the changes in the distribution of the total and trapping hydrogen concentrations through the loading time and particularly during the development of the necking event have been determined.     

Numerical investigation on temperature-rise of on-bus gaseous hydrogen storage cylinder with different thickness of liner and wrapping material

Gaseous hydrogen stored in high-pressure cylinder is a proper solution for the application of hydrogen fuel cell buses (HFCB). As far as the on-bus hydrogen storage system (OBHSS) is concerned, the filling of hydrogen gas needs to be finished in an acceptable time, which unavoidably brings the increase of temperature of hydrogen gas in OBHSS. And excessive temperature of hydrogen gas is unfavorable to mechanical properties of wrapping material and even the service life of the storage cylinder, so it is urgent to work out effective strategies on the temperature-rise in the storage cylinder. It is noticed that the studies on the relationship between the temperature-rise and the geometrical parameters of on-bus gaseous hydrogen storage cylinder (OBGHSC), e.g. thickness of liner and fiber/epoxy composite laminate, are still not deep enough. Motivated by this fact, this research is therefore devoted to studying the relationship between the temperature-rises of both hydrogen gas and solid materials in OBGHSC and the geometrical parameters of wrapping material and liner of OBGHSC, and to developing several temperature-rise correlations. To do so, a 2-dimensional (2D) axisymmetric computational fluid dynamics (CFD) model is applied for the simulation of fast filling process and holding process of 70 MPa OBGHSC. The simulation results show that the temperature distribution during the filling is different for different type III storage cylinders, while the highest temperature is always in the head dome junction region for type IV storage cylinders. For the carbon fiber/epoxy composite laminate (CFEC), the temperature varying tendencies are not the same for different type III storage cylinders, while the temperature in type IV storage cylinder decreases with the increase of thickness of CFEC. At last, based on the obtained numerical data, the correlations for highest value of mass-averaged temperature-rise of hydrogen gas and the correlations for maximum temperature-rise of CFEC that account for the effects of dimensionless parameters are proposed. The correlations reveal the relationship between the temperature-rise and the structure of hydrogen storage cylinder and can be used to direct the fast filling process for OBHSS in this research.     

A composite of borohydride and super absorbent polymer for hydrogen generation

To develop a hydrogen source for underwater applications, a composite of sodium borohydride and super absorbent polymer (SAP) is prepared by ball milling sodium borohydride powder with SAP powder, and by dehydrating an alkaline borohydride gel. When sodium polyacrylate (NaPAA) is used as the SAP, the resulting composite exhibits a high rate of borohydride hydrolysis for hydrogen generation. A mechanism of hydrogen evolution from the NaBH₄-NaPAA composite is suggested based on structure analysis by X-ray diffraction and scanning electron microscopy. The effects of water and NiCl₂ content in the precursor solution on the hydrogen evolution behavior are investigated and discussed.     

Damage evolution in polymer due to exposure to high-pressure hydrogen gas

The use of hydrogen as a fuel is increasing exponentially, and the most economical way to store and transport hydrogen for fuel use is as a high-pressure gas. Polymers are widely used for hydrogen distribution and storage systems because they are chemically inert towards hydrogen. However, when exposed to high-pressure hydrogen, some hydrogen diffuses through polymers and occupies the preexisting cavities inside the material. Upon depressurization, the hydrogen trapped inside polymer cavities can cause blistering or cracking by expanding these cavities. A continuum mechanics–based deformation model was deployed to predict the stress distribution and damage propagation while the polymer undergoes depressurization after high-pressure hydrogen exposure. The effects of cavity size, cavity location, and pressure inside the cavity on damage initiation and evolution inside the polymer were studied. The stress and damage evolution in the presence of multiple cavities was also studied, because interaction among cavities alters the damage and stress field. It was found that all these factors significantly change the stress state in the polymer, resulting in different paths for damage propagation. The effect of adding carbon black filler particles and plasticizer on the damage was also studied. It was found that damage tolerance of the polymer increases drastically with the addition of carbon black fillers, but decreases with the addition of the plasticizer.