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Modeling and simulation of a composite high-pressure vessel made of sustainable and renewable alternative fibers
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Modeling and simulation of a composite highpressure vessel made of sustainable and renewable alternative fibers Mathilde Bouvier, Vincent Guiheneuf*, Alan Jean-marie Altran Technologies, Departement Recherche, 2 Rue Paul Dautier, CS 90599, 78454 Velizy-Villacoublay, France
article info
abstract
Article history:
To substitute the standard carbon fiber reinforced epoxy composite, sustainable and
Received 13 November 2018
renewable alternative fibers are investigated for the use of high-pressure vessel through a
Received in revised form
finite element model. The standard T700S carbon fiber pressure vessel exhibits a minimum
11 March 2019
burst pressure of 1483 bar on the first layer oriented at 90 . The burst occurs in the central
Accepted 13 March 2019
part showing a safe burst and the radial deformation reaches 1.12 mm. Several alternative
Available online 5 April 2019
fibers (basalt, E-glass, flax and recycled T700S carbon) are compared to the T700S carbon fiber. It results of lower burst pressures and none of the alternative composites caters for
Keywords:
the minimum pressure threshold of 1400 bar. According to the storage pressure and in
Fiber reinforced composite
respect of the mechanical requirements, hybrid vessels integrating alternative and T700S
High-pressure vessel
carbon fibers are proposed to improve physical, environmental and economic perfor-
Finite element simulation
mances. From an economic point of view, the optimal vessels are the E-glass/T700S carbon
Alternative fibers
hybrid vessel and E-glass vessel for 700 and 350 bar, respectively. Regarding the environmental impact, the most suitable fibers are basalt/T700S carbon for a 700-bar storage and Eglass for 350 bar. Concerning the vessel mass, T700S carbon composite stays obviously the best candidate for a 700-bar storage but at 350 bar T700S carbon/flax fibers composite appears to be more efficient. © 2019 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved.
Introduction The combined effects of increased energy needs, the depletion of fossil fuel resources and the emergency to reduce greenhouse gas (GHG) emissions promote a diversity of energy carriers. Transport and electricity production industries are particularly concerned by these issues [1,2]. Among the various alternative energies, hydrogen could be a key energy carrier due to its flexibility and its adaptability. With
electricity and biofuels, hydrogen is one of only three potentially net zero-emission energy carriers promoting decarbonization strategies. It is an energy carrier that can be used as a fuel for transportation, renewable energy storage or chemical feedstock. Coupled with electrolysis, hydrogen can be an interface between the power sector and other end-consumer technologies by offering flexible operation and the option for storing energy in chemical form. Indeed, hydrogen can be a significant element to support the integration of renewable electricity by offering controllable consumption and storage.
* Corresponding author. E-mail addresses: [email protected] (M. Bouvier), [email protected] (V. Guiheneuf), alan.jean-marie@altran. com (A. Jean-marie). https://doi.org/10.1016/j.ijhydene.2019.03.088 0360-3199/© 2019 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved.
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Nowadays, hydrogen is usually stored in gaseous form. This storage technology is simple and well controlled with proven industrial equipment. Gaseous hydrogen storage may answer to two applications: stationary storage for large quantities of immobilized hydrogen and mobile storage. Each application corresponds to different storage tanks in terms of volume, design, materials and requirements. In the case of mobile storage, there are four types of tanks. Type I highpressure vessel is characterized by a metallic tank (steel or aluminum) with a maximum operating pressure of 300 bar, a high mass and therefore a low storage density. For type II, the tank consists of a thick metal shell tank wrapped with a fiberresin composite on the cylindrical part while, in the type III, the vessel is composed of metallic inner coating (liner) wrapped in a fiber-resin composite with a maximum operating pressure of 700 bar. Finally, the type IV high-pressure vessel is the most efficient vessel with polymer inner shell container fully wrapped with a fiber-resin composite. The specificity of type IV vessel is based on the use of a polymeric inner layer involving the vessel weight reduction, the resistance to internal pressure being provided by the composite. The polymer liner is generally made of high-density polyethylene (HDPE) but polyamide 6 (PA-6) or polyurethane liners may also be used [3,4]. The boss is metallic and integrated into the vessel structure. The maximal pressure varies between 350 and 900 bar depending on the nature of the composite material. Type IV vessel manufacturing shall take into account the service pressures, the external stresses (temperature, vibrations, weight of connectors, aggressive environment), the lifetime (cycling) and the safety requirements. The internal polymeric liner can be made with two different ways. The first method called roto-molding process consists in introducing the polymer or the powder monomer into a mold of the shell form. The whole is heated in a furnace beyond the polymerization temperature and then cooled. The metal additions like boss are integrated during the rotational molding process or assembled to the liner before filament winding step. Another method consists in welding the sections of spheres and cylinders equipped with metal tips. Cylinders are created by extrusion blow molding (EBM) process. During the process, the polymer is melted and extruded into a hollow tube which is formed in a cooled metal mold. Air is then injected into the cylinder giving its shape to the hollow part and, after polymer cooling, the piece is obtained. Concerning the fiber/resin composite, the most used manufacturing process is the filament winding enabling continuous manufacturing [5]. It is
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also well adapted to develop cylindrical parts subjected to internal pressures. To offer a homogeneous composite, a guidance system deposits resin-impregnated filaments under tension over a rotating mandrel which maintains the liner. It is possible to use pre-impregnated materials or an in-line impregnation system (resin bath). The winding angle can be modulated by the guidance system. There are three types of filament winding for cylindrical tanks: circumferential, polar or helical. For type IV high-pressure vessel, a combination of polar and circumferential windings is generally used. The thickness and the orientation of the layers are determined by the operating pressure, the winding speed and the criteria of the bursting or cycling. The winding is followed by a step of resin crosslinking by heat treatment. During the filling of high-pressure vessel, two kinds of bursting phenomenon can occur [6]. Fig. 1 shows failures of the high-pressure vessel by the maximum stress criterion. This criterion corresponds to the ratio of the applied stress on the uniaxial tensile strength for the first layer of the carbon fiber-reinforced epoxy composite. A safe burst is characterized by a burst along the axis of the tank generally induced by a rupture of the circumferential folds in the center of the cylindrical part of the tank, a matrix cracking or a delamination (Fig. 1a). This type of burst is to be favored from a safety point of view. On the contrary, a burst is said to be unsafe if the dome of the vessel is impacted by mechanical stress (Fig. 1b). In this case, the boss could be ejected and involves a serious safety issue. Fiber break failure in helical plies is the main damage mode participating to the unsafe structural failure. This work focuses on comparing various sustainable and renewable alternative fibers applied to a fiber reinforced polymer composite on a type IV high-pressure vessel. The aim of this study is to propose a relevant and efficient alternative material design of the standard type IV vessel made of carbon reinforced polymer composite. Mineral, vegetable and synthetic fibers are investigated and compared according to the physical, economic and environmental points of view. After modeling a high-pressure vessel by finite elements, its mechanical performances are evaluated using vessel's burst pressure and composite's radial deformation.
Numerical modeling A 3D CAD model of the fiber reinforced composite highpressure vessel has been created using 3D software CATIA V5® and implemented in ANSYS® finite element software for
Fig. 1 e Two types of bursting mechanism: (a) safe mode and (b) unsafe mode.
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Fig. 2 e Images of fiber reinforced composite pressure vessel: (a) 3D-view with dimensions and (b) one-eighth meshed view. calculation. The dimensions specifications are given in the following Fig. 2 and are identical to a high-pressure vessel geometry from the literature to facilitate model checking [7e9]. However, the actual shape of the dome is not exactly known due to lack of information about the layer thicknesses and the fiber orientations. No specific reinforcement of the dome has been modeled. The composite layer thickness is the same as the central part of the vessel which leads probably to stress over-estimation. The high-pressure vessel has a volume of 2.08 L, an internal diameter of 106 mm, a length of 289.5 mm with the boss and 259 mm without boss. In order to reduce calculation time, modeling is carried out on one-eighth of tank. Indeed, the problem being symmetrical to each of the planes (xy, yz and zx), it is sufficient to work only on oneeighth of tank and to deduce the results on the rest of the tank by symmetry. The high-pressure vessel includes a metallic boss, an inner polymer layer called liner and 25 outer composite layers. The inner polymer layer prevents the gas leakage and provides a rigid structure for filament winding process. The liner consists of a high-density polyethylene (HDPE) layer with a thickness of 4 mm. Its mechanical properties are: a Young's modulus of 1500 MPa, a Poisson's ratio of 0.3 and a density of 0.95 g/cm3 [10]. The liner layer is built on an ellipse and the back of the boss is covered with a layer of 1 mm thickness in polymer liner. On the opposite, the composite layers provide mechanical strength. According to Thomas and Gentilleau [7,8], the whole composite layer is composed of 25 layers for a total thickness of 11.1 mm. The thickness and the orientation of each layer are provided in Table 1. The orientations of the different layers are defined with respect to the cylinder axis and are valid only on the cylindrical part.
Table 1 e Properties of each layer of the fiber reinforced composite. Thickness Layer Orientation along Fiber material for [mm] number the cylinder axis [ ] hybrid structure 0.56 0.55 0.23 0.55 0.23 0.55 0.23 0.54 0.53 0.23 0.52 0.23
1 to 2 3 to 4 5 6 to 8 9 10 to 12 13 14 15 to 17 18 19 to 21 22 to 25
±10 ±10 90 ±20 90 ±30 90 40 ±50 90 ±60 90
Carbon Alternative Carbon Alternative Carbon Alternative Carbon Alternative Alternative Carbon Carbon Carbon
fiber fiber fiber fiber fiber
Table 2 provides mechanical properties of each composite made of the selected fibers namely T700S carbon, basalt, Eglass, flax and recycled T700S carbon. Young's modulus, Poisson's ratio, shear modulus and tensile strength are defined and used for modeling and simulation of the fiber reinforced composite vessel. For the finite elements modeling of mechanical behavior of composite hydrogen storage vessel, the composite tank has a laminated structure. The classical composite laminate theory induces basic assumptions: a perfect bonding is considered at the layers interface, the mechanical properties of composite laminates are substituted by those of a middle plane and the normal stress is neglected at the section parallel to the middle plane [16]. A mechanical behavior of materials called isotropic linear elastic is chosen in which the density, the Young's modulus and the Poisson's ratio have to be provided. In this case, the material is simply described by Hooke's law linking linearly the stress tensor to that of the deformations. The parameters E, n, sij and εij are respectively the Young's modulus, the Poisson's ratio, the coefficients of the matrices of stresses and deformations. This description is used for the 316 L stainless steel boss and the HDPE liner. Concerning the composite materials, an orthotropic linear elastic behavior is chosen. In fact, the fiber reinforced polymer composites have an orthotropic behavior which is defined by different macroscopic properties according to the orientation on the vector space. Such materials need to be described by 9 independent variables used in Hooke's law to link deformations and constraints. The Young's modulus in the corresponding directions are given by Ex, Ey and Ez. The Poisson's ratios nxy, nyz and nzx represent the ratios between the transverse deformations and the deformations applied in uniaxial extension according to the direction. For example, nxy is a contraction in the y direction when an extension is applied in the x direction. Gxy, Gyz and Gzx are the shear modulus in the corresponding planes. Hexahedral elements are used to mesh the liner and composite layers having cylindrical shape. The mesh is refined at the edges and under the boss where the liner thickness is thin because of the high mechanical constraints. For each layer, only one mesh thickness is considered because the deposit is supposed homogeneous. Due to a more complex geometry, the boss is meshed with tetrahedrons elements. The imposed boundary conditions use the ANSYS® option called frictionless support. Translational displacement is allowed in all directions except into and out of the supported plane so it prevents the selected face from moving in translation/rotation or deforming in its normal direction. In the case of flat surfaces, this type of boundary condition is
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Table 2 e Mechanical properties of selected fiber reinforced polymer composites. Volume fraction Young's Modulus [GPa] Poisson's ratio Shear modulus [GPa] Tensile strength [MPa]
T700S carbon/Epoxy [8] E-glass/Epoxy [11] Flax/Epoxy [12] Basalt/Epoxy [13] T700S recycled carbon/Epoxy [14,15]
[%]
EX
EY
EZ
60 60 45 60 45
134.4 53.3 32 50 70
8.2 17.7 20 21 25
8.2 17.7 20 21 25
nXY nYZ nXZ 0.36 0.278 0.16 0.25 0.3
0.38 0.4 0.18 0.39 0.42
0.36 0.278 0.16 0.25 0.3
GXY
GYZ
GXZ
sX
sY
sZ
4.7 5.83 2.02 1.0 7.0
2.96 5.83 2.02 1.0 7.0
4.7 5.83 2.02 1.0 7.0
2830 1140 345 1600 422
69 35 8.25 50 180
69 35 8.25 50 180
This section investigates the mechanical behavior of a type IV high-pressure vessel with a T700S carbon fiber reinforced epoxy resin composite. To simulate the filling process, the vessel is subjected to an internal pressure up to 1500 bar to withstand at least two times higher pressure than the maximum operating pressure of 700 bar. To characterize its behavior, the burst pressure of each composite layer is shown in Fig. 3. For the T700S carbon fiber pressure vessel, the minimum burst pressure translating a maximum stress is reached in the layer n 5, i.e. the first fiber reinforced composite layer oriented at 90 . The burst occurs in the central part of the tank showing a safe bursting. With a value of 1483 bar, the minimum burst pressure is higher than the minimum pressure requirement of 1400 bar. Moreover, the critical layers are characterized by a 90 fibers orientation (layers 5, 9, 13, 18, 22 to 25) and the 10 -oriented layer, layer number 1. Radial deformation is also calculated in order to evaluate the vessel expansion during its filling (Fig. 4). Results are
compared to the radial deformation of a simulated carbon fiber pressure vessel by Gentilleau [8]. In both studies, the high-pressure vessels present same features regarding to the geometry and the composite characteristics (number of layers, orientation and thickness). Nonetheless, the exact layup of the carbon fiber pressure vessel is not known but the information in the literature provides a good approximation [7e9]. For both simulations, the radial deformations show a linear trend with increasing pressure. The slopes of the two radial deformation curves are similar and the radial deformations at 1400 bar are 1.12 and 1.05 mm for simulated and Gentilleau's deformation data, respectively. To describe the T700S carbon/epoxy composite, different mechanical properties are used. In our simulation, the Young's modulus and the Poisson's ratio are 134.4 GPa and 0.36 whereas, in the Gentilleau's work, theses parameters are equal to 113.4 GPa and 0.35, respectively. In theory, higher Young's modulus involves higher stiffness and so lower deformation. In the same way, higher Poisson's ratio renders higher stiffness. So, it appears that the higher slope of simulated curve is probably linked to other model parameters (mesh, boundary conditions). Fig. 5 exhibits schematic views of the stress at 1500 bar for T700S carbon fiber reinforced composite. It should be noted that vessel model presents some differences against the real composite vessel. The composite layers at the head of the vessel do not have a well structured and homogeneously distributed due to the boss. The winding geometry at the boss/ liner interface is not perfectly taken into account and does not show specific distribution of mechanical stress (Fig. 5a). At
Fig. 3 e Variation of the burst pressure for a vessel with carbon fiber reinforced composite.
Fig. 4 e Comparison of the radial deformation for the standard carbon fiber reinforced composite vessels: simulated and from Gentilleau [8].
equivalent to a symmetry condition. This boundary condition enforces normal constraint on an entire surface of liner, composite and boss. The extremity of the boss is also fixed using the same boundary condition. The final model is composed of 366709 nodes and 123346 elements with three linked pieces (boss, liner and composite).
Results and discussion Carbon fiber reinforced polymer composite
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Fig. 5 e Schematic view of the maximum stress in the fiber direction at 1500 bar for the standard carbon fiber reinforced composite vessels: (a) whole composite and (b) layer 5. 700 bar, the maximal stress of the layer n 5 reaches 1504 MPa against 1047 MPa for Gentilleau's results. The gap is less important at 1500 bar with maximal stress of 3007 and 2437 MPa.
Alternative fiber reinforced polymer composites In this section, the substitution of T700S carbon fiber is studied for various mineral (basalt and E-glass), vegetable (flax) and synthetic (recycled T700S carbon) fibers. Table 3 shows the weaker layer, the type of burst, the burst pressure and the radial deformation at 1400 bar for several alternative composite fibers: basalt, E-glass, flax and recycled T700S carbon. Compared to the standard T700S carbon fiber reinforced polymer composite vessel, the burst pressures are lower and none of the alternative composites caters for the minimum pressure threshold of 1400 bar. Except for basalt composite where the first layer bursts first in an unsafe mode, all the alternative composites fail in the 5th layer in a safe mode. E-glass and basalt composites burst respectively at 1039 bar and 873 bar. Due to the unsafe burst of basalt composite vessel, only the E-glass composite could be used for 350 bar high-pressure vessel. Conversely, with burst pressures of 422 and 415 bar, flax and recycled T700S carbon composites cannot be viable solutions for type IV high-pressure vessel. Values of radial deformation at 1400 bar confirm a good stiffness of synthetic fibers (recycled and standard T700S carbon) and an insufficient rigidity of natural fibers involving a high expansion of the high-pressure vessel. In Fig. 6, a comparison of the burst pressure distribution for the four alternative fibers composite vessels is provided. First of all, none of alternative fibers satisfies the minimum burst pressure requirement. In fact, these alternative fibers cannot completely substitute the T700S carbon fiber for a 700-bar vessel. For the two mineral fibers (basalt and E-glass), the burst pressure profiles are similar to those of T700S carbon fiber. The critical layers are the first layer oriented at 10 and
those oriented at 90 . For the flax fiber composite, the burst pressures of the different layers vary with small fluctuations. This result can be explained by similar value of directional Young's modulus (Ex, Ey and Ez) involving lower fiber orientation dependence. Thus, flax's Young's modulus Ex is 1.6 times higher than Ey and Ez whereas it is about 2.5 times for Eglass or basalt composites and 16.4 for T700S carbon composite. The recycled T700S carbon fiber composite has a comparable burst pressure distribution than flax composite characterized by low burst values and a flat profile. Fig. 7 presents the radial deformation of the previous alternative fiber reinforced polymer composites. As expected, similarities can be noted according to the kind of fiber investigated. The synthetic fibers induce a similar low radial deformation with values of 1.30 and 1.10 mm at 1400 bar for recycled and non-recycled T700S carbon, respectively. The recycled carbon fiber behavior is similar to that of virgin carbon fiber because of their similar composition. However when recycled carbon fibers are integrated in laminated composites, their performances are being deteriorated for various reasons such as a diminution of the fiber/matrix adhesion or inhomogeneous fibers repartition in the laminated composite [17]. Moreover, recycling processes of carbon fiber often involve fiber degradation or even grinding decreasing the strength of the composite [14,15]. Finally, the recycled carbon fibers may have different mechanical properties depending on the recycling process. When they are reformed as a composite, a large number of adhesives can be used to improve adhesion especially with the matrix. With intermediate deformations of 2.04 and 1.97 mm at 1400 bar, the basalt and E-glass fibers could constitute relevant alternatives for the use of mineral fibers in 350 bar high-pressure vessels [18,19]. Regarding the radial deformations of studied alternative fibers, the worst fiber is the flax vegetable fiber. The flax fiber composite is characterized by a large radial deformation of 2.44 mm due to poor dimensional stability (swelling) which are specific of natural fibers [12].
Hybrid reinforced polymer composites Table 3 e Main characteristics of the bursting mechanism for alternative high-pressure vessel as a function of fiber material. T700S Basalt E-glass Flax Recycled carbon T700S carbon Weaker layer Type of burst Burst pressure [bar] Radial deformation at 1400 bar [mm]
5 Safe 1483 1.10
1 Unsafe 873 2.04
5 Safe 1039 1.97
5 Safe 422 2.44
5 Safe 415 1.30
To improve high-pressure vessel performances, hybrid reinforced polymer composites which are defined by an alternation of two different fibers (carbon and alternative fiber) are proposed. Following the results of the alternative fiber reinforced polymer composites, basalt, E-glass, flax fibers and recycled T700S carbon are selected as alternative fibers of the hybrid vessel. The hybrid vessel composites keep the same geometry (fiber orientation, thickness), the same epoxy matrix and only the fiber materials (Young's modulus, Poisson's ratio,
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Fig. 6 e Comparison of the burst pressure distribution in the alternative composite layers: (a) basalt fiber, (b) E-glass fiber, (c) flax fiber and (d) recycled T700S carbon fiber.
Fig. 7 e Comparison of the radial deformation for alternative fiber reinforced composite vessels.
density) are modified. From the burst pressure profile of the alternative fiber composites, T700S carbon composite is used for the critical layers characterized by a low burst pressure which have to support high mechanical stresses. For each hybrid composite, there are 13 layers of carbon fiber and 12 layers of alternative fibers such as basalt, E-glass, flax and recycled T700S carbon, as shown in Table 1. Table 4 provides the weaker layer, the type of bursting, the burst pressure values and the radial deformation at 1400 bar according to the hybrid composite. First, it should be noted that safe bursting occurs on the central part of all hybrid composites. Unlike standard T700S carbon fiber pressure vessel, the hybrid composites exhibit a weaker layer in the external layers, in the 16th or 22nd layers depending on the hybrid vessels. Mineral hybrid composites using basalt and E-
glass fibers appear to be suitable for gaseous storage at 700 bar. Indeed, burst pressure of the weaker layer (layer 22) is greater than 1400 bar but always lesser than the 1483 bar obtained for the standard T700S carbon vessel. With a burst pressure of 1080 bar, vegetable flax hybrid composite does not exhibit sufficient mechanical strength for 700-bar vessel. However, regarding these mechanical performances, a gaseous storage at 350 bar is absolutely feasible. For recycled T700S carbon hybrid composite, results are close to those of vegetable hybrid composite. Defined by a safe burst, the burst pressure does not exceed 770 bar with a failure of the 16th layer. This could also be used in 350-bar hybrid tanks. The analysis of the radial deformations establishes that the hybrid composites undergo a reasonable expansion phenomenon during filling. But the alternation of the alternative fibers with T700S carbon fiber impacts fundamentally the radial deformation compared to alternative composites without T700S carbon. Although they are higher, the radial deformations of all the hybrid composites are acceptable compared to the standard carbon composite. The E-glass/T700S carbon composite provides the lower radial deformation at 1400 bar with a value of 1.14. In the same way, the recycled T700S carbon/ T700S carbon composite shows good performances inducing a radial deformation of 1.21 mm. Flax/T700S carbon and basalt/ T700S carbon composites achieve same results, namely radial deformations of 1.27 (þ15.1%) and 1.28 mm (þ15.6%) respectively. Burst pressure profile of each hybrid composite is provided in Fig. 8. It should be underlined that the critical layers for basalt and E-glass hybrid composites remain approximately the same than for the T700S carbon composite. The first 10 oriented layer and all of the 90 -oriented layers exhibit lower mechanical strength with low burst pressures. Nevertheless
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Table 4 e Main characteristics of the bursting mechanism for hybrid high-pressure vessel as a function of fiber material.
Weaker layer Type of bursting Burst pressure [bar] Radial deformation at 1400 bar [mm]
T700S carbon
Basalt/T700S carbon
E-glass/T700S carbon
Flax/T700S carbon
Recycled T700S carbon/T700S carbon
5 Safe 1483 1.10
22 Safe 1409 1.28
22 Safe 1432 1.14
16 Safe 1080 1.27
16 Safe 771 1.21
Fig. 8 e Comparison of the burst pressure distribution in the hybrid composite layers: (a) basalt/T700S carbon, (b) E-glass/ T700S carbon, (c) flax/T700S carbon and (d) recycled T700S carbon/T700S carbon.
the two mineral hybrid composites (basalt and E-glass) fulfill the minimum pressure condition needed for a gaseous storage at 700 bar. The burst pressures of the flax composite show a different profile from other hybrid or carbon composites. The burst pressure profile is flatter than the one of T700S carbon composite with burst pressure values ranging between 1080 and 2000 bar except the 2nd layer. In the flax hybrid composite, T700S carbon layers show the higher burst pressures, between 1423 and 2887 bar, whereas the flax layers break off between 1080 and 1400 bar. The hybrid vessel with recycled T700S carbon fiber presents a similar burst pressure profile but it has lower mechanical performances than the flax/carbon hybrid vessel. Only the T700S carbon layers obtain burst pressures higher than 1400 bar, the recycled T700S carbon layers burst pressures are between 771 and 1321 bar.
Environmental and economic comparison An environmental and economic comparison is carried out to evaluate gains that could be made using hybrid high-pressure vessel. The analysis considers raw materials (fibers, matrix, liner and boss) and does not take into account the cost nor the
energy consumption for the manufacturing processes. Four parameters are used to compare each hybrid vessel to the reference vessel: vessel and composite masses, vessel cost and environmental impact (GHG emissions). For the 700-bar vessels comparison, the reference pressure vessel is a T700S carbon fiber reinforced composite vessel whereas it is the Eglass fiber reinforced composite vessel under 350 bar. In this aims, it is necessary to determine the high-pressure vessel mass. Volume of each component of the pressure vessel (liner, boss and composite) is calculated from ANSYS®. The vessel has a storage capacity of 1.7.106 mm3. The T700S carbon vessel has metallic boss made of 316L stainless steel which weights 1.30 kg, a HDPE liner mass of 0.33 kg and a T700S carbon/epoxy composite mass of 1.29 kg for a total vessel mass of 3.52 kg. These values are consistent with those of Ramirez with the same high-pressure vessel except for the polyamide 6 (PA6) liner [6]. The masses are 1.29 kg for the boss, 0.513 kg for PA6 liner and 1.82 for the T700S carbon composite; the total mass is equal to 3.62 kg. Knowing the mass of each component (fibers, matrix, boss, liner), their cost and their environmental impact defined as greenhouse gas (GHG) emissions per kg can be calculated for a whole vessel (Table 5).
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Table 5 e Main properties of selected fibers for environmental and economic comparison for a whole pressure vessel. Volume fraction [%]
Density [g/cm3]
Cost [USD/kgfiber]
GHG emissions [kgCO2/kgfiber]
60 [20] 60 [13] 60 [11] 45 [24] 45 [15]
1.8 [20] 2.66 [18] 2.55 [20] 1.45 [12] 1.8 [25]
28 [21] 6 [21] 3.5 [20] 1 [12] 16 [22]
22.4 [20] 0.98 [23] 2.05 [20] 0.798 [20] 3.5 [26]
T700S carbon Basalt E-glass Flax Recycled T700S carbon
Table 6 e Main properties of selected hybrid type IV vessels for storage pressures of 700 and 350 bar. Storage pressure [bar] T700S carbon E-glass/T700S carbon Basalt/T700S carbon E-glass Flax/Carbon Recycled T700S carbon/T700S carbon
700 700 700 350 350 350
Vessel mass
Composite mass
Vessel cost
Environmental impact
Value [kg] RSD [%] Value [kg] RSD [%] Value [USD] RSD [%] Value [kgCO2] RSD [%] 3.52 3.82 3.86 4.08 3.34 3.45
e þ8.5 þ9.7 e 18.1 15.4
Table 6 compares the vessel and the composite masses, the cost and the GHG emissions for the more efficient composite structures. At 700 bar, pressure vessels designed with three types of fibers are investigated: T700S carbon, E-glass/carbon and basalt/carbon. These three pressure vessels satisfy the mechanical requirements, i.e. a burst pressure higher than 1400 bar. Concerning the mass, E-glass and basalt hybrid vessels induce an increase of the composite mass with relative standard deviations (RSD) of þ16.5 and þ 18.6% respectively. Thus, this negative result can limit the use of such hybrid high-pressure vessels for mobile applications. However, the use of hybrid high-pressure vessels has a significant effect on both the cost and the environmental impacts. The raw materials cost drops by more than 30% by integrating mineral fibers instead of the T700S carbon fiber. Otherwise, by replacing half of the carbon composite layers with mineral layers, the environmental impact is highly reduced by about 40% in RSD. These results have to be put into perspective according to the features of the high-pressure vessel. Indeed, the choice was made to study a prototype vessel with a low capacity. So the mass distribution of the vessel components is not representative and proportional to that of a high-pressure vessel having a storage capacity of 60 or 120 L. In this study, the boss mass is quite close to that of the composite layer while the composite layer represents the largest part of the total mass in a larger capacity vessel. This increase in mass penalizes even more the use of E-glass or basalt fibers. At 350 bar, the comparison of hybrid composites with alternative fibers (flax and recycled T700S carbon) is carried out with respect to an E-glass fiber reinforced polymer composite vessel. Although the hybrid flax/T700S carbon composite has a higher burst pressure than the E-glass composite, it is not economically or environmentally attractive. Indeed, the flax composite contains a large amount of T700S carbon fiber involving a cost increase of þ52.2% and a GHG emission rise of þ41.1%. However, the substantial gains in terms of mass allow to consider the deployment of this type of high-
1.88 2.19 2.23 2.45 1.71 1.82
e þ16.5 þ18.6 e 30.2 25.7
48.0 30.7 33.6 18.4 28.0 36.5
e 36.0 30.0 e þ52.2 þ98.4
36.3 21.6 20.6 14.6 20.6 22.2
e 40,5 43.3 e þ41.1 þ52,1
pressure vessel for mobile applications. The recycled T700S carbon/T700S carbon vessel exhibits the same characteristics but in lower proportions. The vessel mass gain (25.7%) is less important than for the flax hybrid vessel (30.2%) and unfortunately the cost doubles over that of the E-glass vessel (36.5 versus 18.4 USD). Moreover, the environmental impact evaluated by GHG emissions highlights the harmful effect of the use of T700S carbon fibers. The GHG emissions range from 14.6 to 22.2 kgCO2 by substituting E-glass fiber for recycled T700S carbon/T700S carbon fibers.
Conclusion Although it is not possible to provide an exhaustive answer to the concern of the carbon fiber substitution by sustainable and renewable alternative fibers, this work gives some keys to selected suitable fiber for design optimization according different indicators. These different indicators that may be antagonist are the mechanical performances, the vessel mass, the vessel cost and the greenhouse gas emissions. Results put into evidence the best fiber reinforced polymer composite according to the key indicator and for two storage pressures: 700 and 350 bar. The mechanical performances are only taken into account through the storage pressure definition of the selected high-pressure vessel. In other words, the alternative vessels are chosen for 700-bar storage if their burst pressures are higher than 1400 bar whereas the burst pressures have to be higher than 700 bar for 350-bar storage. If the key indicator is the composite cost, the optimal vessels are identified as being the E-glass/T700S carbon hybrid vessel and E-glass vessel for 700 and 350-bar vessels respectively. Regarding the environmental impact and the GHG emissions, the more adaptable fibers in a composite high-pressure vessel are basalt/T700S carbon for 700-bar storage and E-glass for 350-bar storage. Concerning the indicator of vessel mass, the standard T700S carbon composite is obviously the preferred candidate for 700bar storage. But at 350 bar, a hybrid composite integrated flax
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and T700S carbon fibers appears to be the more efficient highpressure vessel to reduce the weight of the hydrogen storage system. Other parameters that mechanical performances should be taken into account like component aging, corrosion or fire resistance in the choice of materials.
Acknowledgment The authors acknowledge Mr Kristian Bozhkov and Dr Ali Sikandar for providing helps on the ANSYS® modeling of highpressure vessel. They also wish to thank Dr Youssef Alilou and Dr Yao Avevor for their assistance in finite element simulation and mechanical analysis.
references
[1] Hua TQ, Ahluwalia RK, Peng J-K, et al. Technical assessment of compressed hydrogen storage tank systems for automotive applications. Int J Hydrogen Energy 2011;36:3037e49. [2] Posdziech O, Schwarze K, Brabandt J. Efficient hydrogen production for industry and electricity storage via hightemperature electrolysis. Int J Hydrogen Energy 2018. https:// doi.org/10.1016/j.ijhydene.2018.05.169. [3] Villalonga S, Nony F, Magnier C, et al. Composite 700 barvessel for on-board compressed gaseous hydrogen storage. In: Proceedings of the 17th international conference on composite materials (ICCM); 2007. Edinburgh, UK. [4] Zheng J, Liu X, Xu P, et al. Development of high pressure gaseous hydrogen storage technologies. Int J Hydrogen Energy 2012;37:1048e57. [5] Barthelemy H. Hydrogen storage - industrial prospectives. Int J Hydrogen Energy 2012;37:17364e72. [6] Ramirez JPB, Halm D, Grandidier JC, et al. 700 bar type IV high pressure hydrogen storage vessel burst e simulation and experimental validation. Int J Hydrogen Energy 2015;40:13183e92. canismes d'endommagement des [7] Thomas C. Etude des me composites fibres carbone/matrice polyamide : application a alisation de re servoirs de stockage de gaz sous haute la re pression de type IV. Thesis. France: Ecole Nationale rieure des Mines de Paris; 2011. Supe lisation et validation expe rimentale du [8] Gentilleau B. Mode canique de multicouches comportement thermome re-composite bobine. Application au stockage polyme ne hyperbare. Thesis. France: Ecole d'hydroge Nationale rieure de Me canique et d’Ae rotechnique; 2012. Supe [9] Magneville B, Gentilleau B, Villalonga S, et al. Modeling, parameters identification and experimental validation of composite materials behavior law used in 700 bar type IV hydrogen high pressure storage vessel. Int J Hydrogen Energy 2015;40:13193e205.
[10] Farhood NH, Karuppanan S, Ya HH, et al. Burst pressure investigation of filament wound type IV composite pressure vessel. American Institute of Physics Conference Proceedings 1901; 2017. p. 030017. [11] Shanmugavel M, Velmurugan T. Finite element analysis of burst pressure of composite storage vessels. J Mech Civ Eng 2014:73e7. [12] Yan L, Chouw N, Jayaraman K. Flax fibre and its composites e a review. Composites Part B 2014;56:296e317. [13] Lapena MH, Marinucci G, de Carvalho O. Mechanical characterization of unidirectional basalt fiber epoxy composite. Seville, Spain: 16th European Conference on Composite Materials (ECCM15); 2014. [14] Turner TA, Warrior NA, Pickering SJ. Development of high value moulding compounds from recycled carbon fibres. Plast, Rubber Compos 2010;39:151e6. [15] Pimenta S. Toughness and strength of recycled composites and their virgin precursors. Thesis. United Kingdom: Imperial College London; 2013. [16] Liu PF, Chu JK, Hou SJ, et al. Numerical simulation and optimal design for composite high-pressure hydrogen storage vessel: a review. Renew Sustain Energy Rev 2012;16:1817e27. [17] Maxey A, Kline S, Schrader J. Fabrication of a recycled tow carbon fiber overwrapped pressure vessel. USA: SPE Automotive Composites Conference, MI; 2017. [18] Pavlovski D, Mislavsky B, Antonov A. CNG cylinder manufacturers test basalt fiber. Reinforc Plast 2007;51:36e7. [19] Weisberg AH, Aceves SM, Espinosa-Loza F, et al. Cold hydrogen delivery in glass fiber composite pressure vessels : analysis, manufacture and testing. Int J Hydrogen Energy 2013;38:9271e84. [20] Bachmann J, Hidalgo C, Bricout S. Environmental analysis of innovative sustainable composites with potential use in aviation sector - a life cycle assessment review. Sci China Technol Sci 2017;60:1301e17. [21] Leavitt M. High pressure hydrogen tank manufacturing. Department of Energy Workshop; 2011. [22] Dong PAV, Azzaro-Pantel C, Cadene AL. Economic and environmental assessment of recovery and disposal pathways for CRFP waste management, Resources. Conserv Recycl 2018;133:63e75. [23] Azrague K, Wiik MK, Alnæs LI, et al. Life cycle assessment as a tool for resource optimisation of continuous basalt fibre production in Iceland. In: Conference: life cycle assessment and other assessment tools for waste management and resource optimization. ECI Symposium Series; 2016. [24] Pickering KL, Aruan Efendy MG, Le TM. A review of recent developments in natural fibre composites and their mechanical performance. Composites Part A 2016;83:98e112. [25] Oliveux G, Dandy LO, Leeke GA. Current status of recycling of fibre reinforced polymers: review of technologies, reuse and resulting properties. Prog Mater Sci 2015;72:61e99. [26] ELG Carbon Fibre Ltd. Recycled carbon fibre as an enabler for cost effective lightweight structures. Detroit: Global Automotive Lightweight Materials; 2016.
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Modeling and simulation of a composite highpressure vessel made of sustainable and renewable alternative fibers Mathilde Bouvier, Vincent Guiheneuf*, Alan Jean-marie Altran Technologies, Departement Recherche, 2 Rue Paul Dautier, CS 90599, 78454 Velizy-Villacoublay, France
article info
abstract
Article history:
To substitute the standard carbon fiber reinforced epoxy composite, sustainable and
Received 13 November 2018
renewable alternative fibers are investigated for the use of high-pressure vessel through a
Received in revised form
finite element model. The standard T700S carbon fiber pressure vessel exhibits a minimum
11 March 2019
burst pressure of 1483 bar on the first layer oriented at 90 . The burst occurs in the central
Accepted 13 March 2019
part showing a safe burst and the radial deformation reaches 1.12 mm. Several alternative
Available online 5 April 2019
fibers (basalt, E-glass, flax and recycled T700S carbon) are compared to the T700S carbon fiber. It results of lower burst pressures and none of the alternative composites caters for
Keywords:
the minimum pressure threshold of 1400 bar. According to the storage pressure and in
Fiber reinforced composite
respect of the mechanical requirements, hybrid vessels integrating alternative and T700S
High-pressure vessel
carbon fibers are proposed to improve physical, environmental and economic perfor-
Finite element simulation
mances. From an economic point of view, the optimal vessels are the E-glass/T700S carbon
Alternative fibers
hybrid vessel and E-glass vessel for 700 and 350 bar, respectively. Regarding the environmental impact, the most suitable fibers are basalt/T700S carbon for a 700-bar storage and Eglass for 350 bar. Concerning the vessel mass, T700S carbon composite stays obviously the best candidate for a 700-bar storage but at 350 bar T700S carbon/flax fibers composite appears to be more efficient. © 2019 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved.
Introduction The combined effects of increased energy needs, the depletion of fossil fuel resources and the emergency to reduce greenhouse gas (GHG) emissions promote a diversity of energy carriers. Transport and electricity production industries are particularly concerned by these issues [1,2]. Among the various alternative energies, hydrogen could be a key energy carrier due to its flexibility and its adaptability. With
electricity and biofuels, hydrogen is one of only three potentially net zero-emission energy carriers promoting decarbonization strategies. It is an energy carrier that can be used as a fuel for transportation, renewable energy storage or chemical feedstock. Coupled with electrolysis, hydrogen can be an interface between the power sector and other end-consumer technologies by offering flexible operation and the option for storing energy in chemical form. Indeed, hydrogen can be a significant element to support the integration of renewable electricity by offering controllable consumption and storage.
* Corresponding author. E-mail addresses: [email protected] (M. Bouvier), [email protected] (V. Guiheneuf), alan.jean-marie@altran. com (A. Jean-marie). https://doi.org/10.1016/j.ijhydene.2019.03.088 0360-3199/© 2019 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved.
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Nowadays, hydrogen is usually stored in gaseous form. This storage technology is simple and well controlled with proven industrial equipment. Gaseous hydrogen storage may answer to two applications: stationary storage for large quantities of immobilized hydrogen and mobile storage. Each application corresponds to different storage tanks in terms of volume, design, materials and requirements. In the case of mobile storage, there are four types of tanks. Type I highpressure vessel is characterized by a metallic tank (steel or aluminum) with a maximum operating pressure of 300 bar, a high mass and therefore a low storage density. For type II, the tank consists of a thick metal shell tank wrapped with a fiberresin composite on the cylindrical part while, in the type III, the vessel is composed of metallic inner coating (liner) wrapped in a fiber-resin composite with a maximum operating pressure of 700 bar. Finally, the type IV high-pressure vessel is the most efficient vessel with polymer inner shell container fully wrapped with a fiber-resin composite. The specificity of type IV vessel is based on the use of a polymeric inner layer involving the vessel weight reduction, the resistance to internal pressure being provided by the composite. The polymer liner is generally made of high-density polyethylene (HDPE) but polyamide 6 (PA-6) or polyurethane liners may also be used [3,4]. The boss is metallic and integrated into the vessel structure. The maximal pressure varies between 350 and 900 bar depending on the nature of the composite material. Type IV vessel manufacturing shall take into account the service pressures, the external stresses (temperature, vibrations, weight of connectors, aggressive environment), the lifetime (cycling) and the safety requirements. The internal polymeric liner can be made with two different ways. The first method called roto-molding process consists in introducing the polymer or the powder monomer into a mold of the shell form. The whole is heated in a furnace beyond the polymerization temperature and then cooled. The metal additions like boss are integrated during the rotational molding process or assembled to the liner before filament winding step. Another method consists in welding the sections of spheres and cylinders equipped with metal tips. Cylinders are created by extrusion blow molding (EBM) process. During the process, the polymer is melted and extruded into a hollow tube which is formed in a cooled metal mold. Air is then injected into the cylinder giving its shape to the hollow part and, after polymer cooling, the piece is obtained. Concerning the fiber/resin composite, the most used manufacturing process is the filament winding enabling continuous manufacturing [5]. It is
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also well adapted to develop cylindrical parts subjected to internal pressures. To offer a homogeneous composite, a guidance system deposits resin-impregnated filaments under tension over a rotating mandrel which maintains the liner. It is possible to use pre-impregnated materials or an in-line impregnation system (resin bath). The winding angle can be modulated by the guidance system. There are three types of filament winding for cylindrical tanks: circumferential, polar or helical. For type IV high-pressure vessel, a combination of polar and circumferential windings is generally used. The thickness and the orientation of the layers are determined by the operating pressure, the winding speed and the criteria of the bursting or cycling. The winding is followed by a step of resin crosslinking by heat treatment. During the filling of high-pressure vessel, two kinds of bursting phenomenon can occur [6]. Fig. 1 shows failures of the high-pressure vessel by the maximum stress criterion. This criterion corresponds to the ratio of the applied stress on the uniaxial tensile strength for the first layer of the carbon fiber-reinforced epoxy composite. A safe burst is characterized by a burst along the axis of the tank generally induced by a rupture of the circumferential folds in the center of the cylindrical part of the tank, a matrix cracking or a delamination (Fig. 1a). This type of burst is to be favored from a safety point of view. On the contrary, a burst is said to be unsafe if the dome of the vessel is impacted by mechanical stress (Fig. 1b). In this case, the boss could be ejected and involves a serious safety issue. Fiber break failure in helical plies is the main damage mode participating to the unsafe structural failure. This work focuses on comparing various sustainable and renewable alternative fibers applied to a fiber reinforced polymer composite on a type IV high-pressure vessel. The aim of this study is to propose a relevant and efficient alternative material design of the standard type IV vessel made of carbon reinforced polymer composite. Mineral, vegetable and synthetic fibers are investigated and compared according to the physical, economic and environmental points of view. After modeling a high-pressure vessel by finite elements, its mechanical performances are evaluated using vessel's burst pressure and composite's radial deformation.
Numerical modeling A 3D CAD model of the fiber reinforced composite highpressure vessel has been created using 3D software CATIA V5® and implemented in ANSYS® finite element software for
Fig. 1 e Two types of bursting mechanism: (a) safe mode and (b) unsafe mode.
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Fig. 2 e Images of fiber reinforced composite pressure vessel: (a) 3D-view with dimensions and (b) one-eighth meshed view. calculation. The dimensions specifications are given in the following Fig. 2 and are identical to a high-pressure vessel geometry from the literature to facilitate model checking [7e9]. However, the actual shape of the dome is not exactly known due to lack of information about the layer thicknesses and the fiber orientations. No specific reinforcement of the dome has been modeled. The composite layer thickness is the same as the central part of the vessel which leads probably to stress over-estimation. The high-pressure vessel has a volume of 2.08 L, an internal diameter of 106 mm, a length of 289.5 mm with the boss and 259 mm without boss. In order to reduce calculation time, modeling is carried out on one-eighth of tank. Indeed, the problem being symmetrical to each of the planes (xy, yz and zx), it is sufficient to work only on oneeighth of tank and to deduce the results on the rest of the tank by symmetry. The high-pressure vessel includes a metallic boss, an inner polymer layer called liner and 25 outer composite layers. The inner polymer layer prevents the gas leakage and provides a rigid structure for filament winding process. The liner consists of a high-density polyethylene (HDPE) layer with a thickness of 4 mm. Its mechanical properties are: a Young's modulus of 1500 MPa, a Poisson's ratio of 0.3 and a density of 0.95 g/cm3 [10]. The liner layer is built on an ellipse and the back of the boss is covered with a layer of 1 mm thickness in polymer liner. On the opposite, the composite layers provide mechanical strength. According to Thomas and Gentilleau [7,8], the whole composite layer is composed of 25 layers for a total thickness of 11.1 mm. The thickness and the orientation of each layer are provided in Table 1. The orientations of the different layers are defined with respect to the cylinder axis and are valid only on the cylindrical part.
Table 1 e Properties of each layer of the fiber reinforced composite. Thickness Layer Orientation along Fiber material for [mm] number the cylinder axis [ ] hybrid structure 0.56 0.55 0.23 0.55 0.23 0.55 0.23 0.54 0.53 0.23 0.52 0.23
1 to 2 3 to 4 5 6 to 8 9 10 to 12 13 14 15 to 17 18 19 to 21 22 to 25
±10 ±10 90 ±20 90 ±30 90 40 ±50 90 ±60 90
Carbon Alternative Carbon Alternative Carbon Alternative Carbon Alternative Alternative Carbon Carbon Carbon
fiber fiber fiber fiber fiber
Table 2 provides mechanical properties of each composite made of the selected fibers namely T700S carbon, basalt, Eglass, flax and recycled T700S carbon. Young's modulus, Poisson's ratio, shear modulus and tensile strength are defined and used for modeling and simulation of the fiber reinforced composite vessel. For the finite elements modeling of mechanical behavior of composite hydrogen storage vessel, the composite tank has a laminated structure. The classical composite laminate theory induces basic assumptions: a perfect bonding is considered at the layers interface, the mechanical properties of composite laminates are substituted by those of a middle plane and the normal stress is neglected at the section parallel to the middle plane [16]. A mechanical behavior of materials called isotropic linear elastic is chosen in which the density, the Young's modulus and the Poisson's ratio have to be provided. In this case, the material is simply described by Hooke's law linking linearly the stress tensor to that of the deformations. The parameters E, n, sij and εij are respectively the Young's modulus, the Poisson's ratio, the coefficients of the matrices of stresses and deformations. This description is used for the 316 L stainless steel boss and the HDPE liner. Concerning the composite materials, an orthotropic linear elastic behavior is chosen. In fact, the fiber reinforced polymer composites have an orthotropic behavior which is defined by different macroscopic properties according to the orientation on the vector space. Such materials need to be described by 9 independent variables used in Hooke's law to link deformations and constraints. The Young's modulus in the corresponding directions are given by Ex, Ey and Ez. The Poisson's ratios nxy, nyz and nzx represent the ratios between the transverse deformations and the deformations applied in uniaxial extension according to the direction. For example, nxy is a contraction in the y direction when an extension is applied in the x direction. Gxy, Gyz and Gzx are the shear modulus in the corresponding planes. Hexahedral elements are used to mesh the liner and composite layers having cylindrical shape. The mesh is refined at the edges and under the boss where the liner thickness is thin because of the high mechanical constraints. For each layer, only one mesh thickness is considered because the deposit is supposed homogeneous. Due to a more complex geometry, the boss is meshed with tetrahedrons elements. The imposed boundary conditions use the ANSYS® option called frictionless support. Translational displacement is allowed in all directions except into and out of the supported plane so it prevents the selected face from moving in translation/rotation or deforming in its normal direction. In the case of flat surfaces, this type of boundary condition is
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Table 2 e Mechanical properties of selected fiber reinforced polymer composites. Volume fraction Young's Modulus [GPa] Poisson's ratio Shear modulus [GPa] Tensile strength [MPa]
T700S carbon/Epoxy [8] E-glass/Epoxy [11] Flax/Epoxy [12] Basalt/Epoxy [13] T700S recycled carbon/Epoxy [14,15]
[%]
EX
EY
EZ
60 60 45 60 45
134.4 53.3 32 50 70
8.2 17.7 20 21 25
8.2 17.7 20 21 25
nXY nYZ nXZ 0.36 0.278 0.16 0.25 0.3
0.38 0.4 0.18 0.39 0.42
0.36 0.278 0.16 0.25 0.3
GXY
GYZ
GXZ
sX
sY
sZ
4.7 5.83 2.02 1.0 7.0
2.96 5.83 2.02 1.0 7.0
4.7 5.83 2.02 1.0 7.0
2830 1140 345 1600 422
69 35 8.25 50 180
69 35 8.25 50 180
This section investigates the mechanical behavior of a type IV high-pressure vessel with a T700S carbon fiber reinforced epoxy resin composite. To simulate the filling process, the vessel is subjected to an internal pressure up to 1500 bar to withstand at least two times higher pressure than the maximum operating pressure of 700 bar. To characterize its behavior, the burst pressure of each composite layer is shown in Fig. 3. For the T700S carbon fiber pressure vessel, the minimum burst pressure translating a maximum stress is reached in the layer n 5, i.e. the first fiber reinforced composite layer oriented at 90 . The burst occurs in the central part of the tank showing a safe bursting. With a value of 1483 bar, the minimum burst pressure is higher than the minimum pressure requirement of 1400 bar. Moreover, the critical layers are characterized by a 90 fibers orientation (layers 5, 9, 13, 18, 22 to 25) and the 10 -oriented layer, layer number 1. Radial deformation is also calculated in order to evaluate the vessel expansion during its filling (Fig. 4). Results are
compared to the radial deformation of a simulated carbon fiber pressure vessel by Gentilleau [8]. In both studies, the high-pressure vessels present same features regarding to the geometry and the composite characteristics (number of layers, orientation and thickness). Nonetheless, the exact layup of the carbon fiber pressure vessel is not known but the information in the literature provides a good approximation [7e9]. For both simulations, the radial deformations show a linear trend with increasing pressure. The slopes of the two radial deformation curves are similar and the radial deformations at 1400 bar are 1.12 and 1.05 mm for simulated and Gentilleau's deformation data, respectively. To describe the T700S carbon/epoxy composite, different mechanical properties are used. In our simulation, the Young's modulus and the Poisson's ratio are 134.4 GPa and 0.36 whereas, in the Gentilleau's work, theses parameters are equal to 113.4 GPa and 0.35, respectively. In theory, higher Young's modulus involves higher stiffness and so lower deformation. In the same way, higher Poisson's ratio renders higher stiffness. So, it appears that the higher slope of simulated curve is probably linked to other model parameters (mesh, boundary conditions). Fig. 5 exhibits schematic views of the stress at 1500 bar for T700S carbon fiber reinforced composite. It should be noted that vessel model presents some differences against the real composite vessel. The composite layers at the head of the vessel do not have a well structured and homogeneously distributed due to the boss. The winding geometry at the boss/ liner interface is not perfectly taken into account and does not show specific distribution of mechanical stress (Fig. 5a). At
Fig. 3 e Variation of the burst pressure for a vessel with carbon fiber reinforced composite.
Fig. 4 e Comparison of the radial deformation for the standard carbon fiber reinforced composite vessels: simulated and from Gentilleau [8].
equivalent to a symmetry condition. This boundary condition enforces normal constraint on an entire surface of liner, composite and boss. The extremity of the boss is also fixed using the same boundary condition. The final model is composed of 366709 nodes and 123346 elements with three linked pieces (boss, liner and composite).
Results and discussion Carbon fiber reinforced polymer composite
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Fig. 5 e Schematic view of the maximum stress in the fiber direction at 1500 bar for the standard carbon fiber reinforced composite vessels: (a) whole composite and (b) layer 5. 700 bar, the maximal stress of the layer n 5 reaches 1504 MPa against 1047 MPa for Gentilleau's results. The gap is less important at 1500 bar with maximal stress of 3007 and 2437 MPa.
Alternative fiber reinforced polymer composites In this section, the substitution of T700S carbon fiber is studied for various mineral (basalt and E-glass), vegetable (flax) and synthetic (recycled T700S carbon) fibers. Table 3 shows the weaker layer, the type of burst, the burst pressure and the radial deformation at 1400 bar for several alternative composite fibers: basalt, E-glass, flax and recycled T700S carbon. Compared to the standard T700S carbon fiber reinforced polymer composite vessel, the burst pressures are lower and none of the alternative composites caters for the minimum pressure threshold of 1400 bar. Except for basalt composite where the first layer bursts first in an unsafe mode, all the alternative composites fail in the 5th layer in a safe mode. E-glass and basalt composites burst respectively at 1039 bar and 873 bar. Due to the unsafe burst of basalt composite vessel, only the E-glass composite could be used for 350 bar high-pressure vessel. Conversely, with burst pressures of 422 and 415 bar, flax and recycled T700S carbon composites cannot be viable solutions for type IV high-pressure vessel. Values of radial deformation at 1400 bar confirm a good stiffness of synthetic fibers (recycled and standard T700S carbon) and an insufficient rigidity of natural fibers involving a high expansion of the high-pressure vessel. In Fig. 6, a comparison of the burst pressure distribution for the four alternative fibers composite vessels is provided. First of all, none of alternative fibers satisfies the minimum burst pressure requirement. In fact, these alternative fibers cannot completely substitute the T700S carbon fiber for a 700-bar vessel. For the two mineral fibers (basalt and E-glass), the burst pressure profiles are similar to those of T700S carbon fiber. The critical layers are the first layer oriented at 10 and
those oriented at 90 . For the flax fiber composite, the burst pressures of the different layers vary with small fluctuations. This result can be explained by similar value of directional Young's modulus (Ex, Ey and Ez) involving lower fiber orientation dependence. Thus, flax's Young's modulus Ex is 1.6 times higher than Ey and Ez whereas it is about 2.5 times for Eglass or basalt composites and 16.4 for T700S carbon composite. The recycled T700S carbon fiber composite has a comparable burst pressure distribution than flax composite characterized by low burst values and a flat profile. Fig. 7 presents the radial deformation of the previous alternative fiber reinforced polymer composites. As expected, similarities can be noted according to the kind of fiber investigated. The synthetic fibers induce a similar low radial deformation with values of 1.30 and 1.10 mm at 1400 bar for recycled and non-recycled T700S carbon, respectively. The recycled carbon fiber behavior is similar to that of virgin carbon fiber because of their similar composition. However when recycled carbon fibers are integrated in laminated composites, their performances are being deteriorated for various reasons such as a diminution of the fiber/matrix adhesion or inhomogeneous fibers repartition in the laminated composite [17]. Moreover, recycling processes of carbon fiber often involve fiber degradation or even grinding decreasing the strength of the composite [14,15]. Finally, the recycled carbon fibers may have different mechanical properties depending on the recycling process. When they are reformed as a composite, a large number of adhesives can be used to improve adhesion especially with the matrix. With intermediate deformations of 2.04 and 1.97 mm at 1400 bar, the basalt and E-glass fibers could constitute relevant alternatives for the use of mineral fibers in 350 bar high-pressure vessels [18,19]. Regarding the radial deformations of studied alternative fibers, the worst fiber is the flax vegetable fiber. The flax fiber composite is characterized by a large radial deformation of 2.44 mm due to poor dimensional stability (swelling) which are specific of natural fibers [12].
Hybrid reinforced polymer composites Table 3 e Main characteristics of the bursting mechanism for alternative high-pressure vessel as a function of fiber material. T700S Basalt E-glass Flax Recycled carbon T700S carbon Weaker layer Type of burst Burst pressure [bar] Radial deformation at 1400 bar [mm]
5 Safe 1483 1.10
1 Unsafe 873 2.04
5 Safe 1039 1.97
5 Safe 422 2.44
5 Safe 415 1.30
To improve high-pressure vessel performances, hybrid reinforced polymer composites which are defined by an alternation of two different fibers (carbon and alternative fiber) are proposed. Following the results of the alternative fiber reinforced polymer composites, basalt, E-glass, flax fibers and recycled T700S carbon are selected as alternative fibers of the hybrid vessel. The hybrid vessel composites keep the same geometry (fiber orientation, thickness), the same epoxy matrix and only the fiber materials (Young's modulus, Poisson's ratio,
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Fig. 6 e Comparison of the burst pressure distribution in the alternative composite layers: (a) basalt fiber, (b) E-glass fiber, (c) flax fiber and (d) recycled T700S carbon fiber.
Fig. 7 e Comparison of the radial deformation for alternative fiber reinforced composite vessels.
density) are modified. From the burst pressure profile of the alternative fiber composites, T700S carbon composite is used for the critical layers characterized by a low burst pressure which have to support high mechanical stresses. For each hybrid composite, there are 13 layers of carbon fiber and 12 layers of alternative fibers such as basalt, E-glass, flax and recycled T700S carbon, as shown in Table 1. Table 4 provides the weaker layer, the type of bursting, the burst pressure values and the radial deformation at 1400 bar according to the hybrid composite. First, it should be noted that safe bursting occurs on the central part of all hybrid composites. Unlike standard T700S carbon fiber pressure vessel, the hybrid composites exhibit a weaker layer in the external layers, in the 16th or 22nd layers depending on the hybrid vessels. Mineral hybrid composites using basalt and E-
glass fibers appear to be suitable for gaseous storage at 700 bar. Indeed, burst pressure of the weaker layer (layer 22) is greater than 1400 bar but always lesser than the 1483 bar obtained for the standard T700S carbon vessel. With a burst pressure of 1080 bar, vegetable flax hybrid composite does not exhibit sufficient mechanical strength for 700-bar vessel. However, regarding these mechanical performances, a gaseous storage at 350 bar is absolutely feasible. For recycled T700S carbon hybrid composite, results are close to those of vegetable hybrid composite. Defined by a safe burst, the burst pressure does not exceed 770 bar with a failure of the 16th layer. This could also be used in 350-bar hybrid tanks. The analysis of the radial deformations establishes that the hybrid composites undergo a reasonable expansion phenomenon during filling. But the alternation of the alternative fibers with T700S carbon fiber impacts fundamentally the radial deformation compared to alternative composites without T700S carbon. Although they are higher, the radial deformations of all the hybrid composites are acceptable compared to the standard carbon composite. The E-glass/T700S carbon composite provides the lower radial deformation at 1400 bar with a value of 1.14. In the same way, the recycled T700S carbon/ T700S carbon composite shows good performances inducing a radial deformation of 1.21 mm. Flax/T700S carbon and basalt/ T700S carbon composites achieve same results, namely radial deformations of 1.27 (þ15.1%) and 1.28 mm (þ15.6%) respectively. Burst pressure profile of each hybrid composite is provided in Fig. 8. It should be underlined that the critical layers for basalt and E-glass hybrid composites remain approximately the same than for the T700S carbon composite. The first 10 oriented layer and all of the 90 -oriented layers exhibit lower mechanical strength with low burst pressures. Nevertheless
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Table 4 e Main characteristics of the bursting mechanism for hybrid high-pressure vessel as a function of fiber material.
Weaker layer Type of bursting Burst pressure [bar] Radial deformation at 1400 bar [mm]
T700S carbon
Basalt/T700S carbon
E-glass/T700S carbon
Flax/T700S carbon
Recycled T700S carbon/T700S carbon
5 Safe 1483 1.10
22 Safe 1409 1.28
22 Safe 1432 1.14
16 Safe 1080 1.27
16 Safe 771 1.21
Fig. 8 e Comparison of the burst pressure distribution in the hybrid composite layers: (a) basalt/T700S carbon, (b) E-glass/ T700S carbon, (c) flax/T700S carbon and (d) recycled T700S carbon/T700S carbon.
the two mineral hybrid composites (basalt and E-glass) fulfill the minimum pressure condition needed for a gaseous storage at 700 bar. The burst pressures of the flax composite show a different profile from other hybrid or carbon composites. The burst pressure profile is flatter than the one of T700S carbon composite with burst pressure values ranging between 1080 and 2000 bar except the 2nd layer. In the flax hybrid composite, T700S carbon layers show the higher burst pressures, between 1423 and 2887 bar, whereas the flax layers break off between 1080 and 1400 bar. The hybrid vessel with recycled T700S carbon fiber presents a similar burst pressure profile but it has lower mechanical performances than the flax/carbon hybrid vessel. Only the T700S carbon layers obtain burst pressures higher than 1400 bar, the recycled T700S carbon layers burst pressures are between 771 and 1321 bar.
Environmental and economic comparison An environmental and economic comparison is carried out to evaluate gains that could be made using hybrid high-pressure vessel. The analysis considers raw materials (fibers, matrix, liner and boss) and does not take into account the cost nor the
energy consumption for the manufacturing processes. Four parameters are used to compare each hybrid vessel to the reference vessel: vessel and composite masses, vessel cost and environmental impact (GHG emissions). For the 700-bar vessels comparison, the reference pressure vessel is a T700S carbon fiber reinforced composite vessel whereas it is the Eglass fiber reinforced composite vessel under 350 bar. In this aims, it is necessary to determine the high-pressure vessel mass. Volume of each component of the pressure vessel (liner, boss and composite) is calculated from ANSYS®. The vessel has a storage capacity of 1.7.106 mm3. The T700S carbon vessel has metallic boss made of 316L stainless steel which weights 1.30 kg, a HDPE liner mass of 0.33 kg and a T700S carbon/epoxy composite mass of 1.29 kg for a total vessel mass of 3.52 kg. These values are consistent with those of Ramirez with the same high-pressure vessel except for the polyamide 6 (PA6) liner [6]. The masses are 1.29 kg for the boss, 0.513 kg for PA6 liner and 1.82 for the T700S carbon composite; the total mass is equal to 3.62 kg. Knowing the mass of each component (fibers, matrix, boss, liner), their cost and their environmental impact defined as greenhouse gas (GHG) emissions per kg can be calculated for a whole vessel (Table 5).
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Table 5 e Main properties of selected fibers for environmental and economic comparison for a whole pressure vessel. Volume fraction [%]
Density [g/cm3]
Cost [USD/kgfiber]
GHG emissions [kgCO2/kgfiber]
60 [20] 60 [13] 60 [11] 45 [24] 45 [15]
1.8 [20] 2.66 [18] 2.55 [20] 1.45 [12] 1.8 [25]
28 [21] 6 [21] 3.5 [20] 1 [12] 16 [22]
22.4 [20] 0.98 [23] 2.05 [20] 0.798 [20] 3.5 [26]
T700S carbon Basalt E-glass Flax Recycled T700S carbon
Table 6 e Main properties of selected hybrid type IV vessels for storage pressures of 700 and 350 bar. Storage pressure [bar] T700S carbon E-glass/T700S carbon Basalt/T700S carbon E-glass Flax/Carbon Recycled T700S carbon/T700S carbon
700 700 700 350 350 350
Vessel mass
Composite mass
Vessel cost
Environmental impact
Value [kg] RSD [%] Value [kg] RSD [%] Value [USD] RSD [%] Value [kgCO2] RSD [%] 3.52 3.82 3.86 4.08 3.34 3.45
e þ8.5 þ9.7 e 18.1 15.4
Table 6 compares the vessel and the composite masses, the cost and the GHG emissions for the more efficient composite structures. At 700 bar, pressure vessels designed with three types of fibers are investigated: T700S carbon, E-glass/carbon and basalt/carbon. These three pressure vessels satisfy the mechanical requirements, i.e. a burst pressure higher than 1400 bar. Concerning the mass, E-glass and basalt hybrid vessels induce an increase of the composite mass with relative standard deviations (RSD) of þ16.5 and þ 18.6% respectively. Thus, this negative result can limit the use of such hybrid high-pressure vessels for mobile applications. However, the use of hybrid high-pressure vessels has a significant effect on both the cost and the environmental impacts. The raw materials cost drops by more than 30% by integrating mineral fibers instead of the T700S carbon fiber. Otherwise, by replacing half of the carbon composite layers with mineral layers, the environmental impact is highly reduced by about 40% in RSD. These results have to be put into perspective according to the features of the high-pressure vessel. Indeed, the choice was made to study a prototype vessel with a low capacity. So the mass distribution of the vessel components is not representative and proportional to that of a high-pressure vessel having a storage capacity of 60 or 120 L. In this study, the boss mass is quite close to that of the composite layer while the composite layer represents the largest part of the total mass in a larger capacity vessel. This increase in mass penalizes even more the use of E-glass or basalt fibers. At 350 bar, the comparison of hybrid composites with alternative fibers (flax and recycled T700S carbon) is carried out with respect to an E-glass fiber reinforced polymer composite vessel. Although the hybrid flax/T700S carbon composite has a higher burst pressure than the E-glass composite, it is not economically or environmentally attractive. Indeed, the flax composite contains a large amount of T700S carbon fiber involving a cost increase of þ52.2% and a GHG emission rise of þ41.1%. However, the substantial gains in terms of mass allow to consider the deployment of this type of high-
1.88 2.19 2.23 2.45 1.71 1.82
e þ16.5 þ18.6 e 30.2 25.7
48.0 30.7 33.6 18.4 28.0 36.5
e 36.0 30.0 e þ52.2 þ98.4
36.3 21.6 20.6 14.6 20.6 22.2
e 40,5 43.3 e þ41.1 þ52,1
pressure vessel for mobile applications. The recycled T700S carbon/T700S carbon vessel exhibits the same characteristics but in lower proportions. The vessel mass gain (25.7%) is less important than for the flax hybrid vessel (30.2%) and unfortunately the cost doubles over that of the E-glass vessel (36.5 versus 18.4 USD). Moreover, the environmental impact evaluated by GHG emissions highlights the harmful effect of the use of T700S carbon fibers. The GHG emissions range from 14.6 to 22.2 kgCO2 by substituting E-glass fiber for recycled T700S carbon/T700S carbon fibers.
Conclusion Although it is not possible to provide an exhaustive answer to the concern of the carbon fiber substitution by sustainable and renewable alternative fibers, this work gives some keys to selected suitable fiber for design optimization according different indicators. These different indicators that may be antagonist are the mechanical performances, the vessel mass, the vessel cost and the greenhouse gas emissions. Results put into evidence the best fiber reinforced polymer composite according to the key indicator and for two storage pressures: 700 and 350 bar. The mechanical performances are only taken into account through the storage pressure definition of the selected high-pressure vessel. In other words, the alternative vessels are chosen for 700-bar storage if their burst pressures are higher than 1400 bar whereas the burst pressures have to be higher than 700 bar for 350-bar storage. If the key indicator is the composite cost, the optimal vessels are identified as being the E-glass/T700S carbon hybrid vessel and E-glass vessel for 700 and 350-bar vessels respectively. Regarding the environmental impact and the GHG emissions, the more adaptable fibers in a composite high-pressure vessel are basalt/T700S carbon for 700-bar storage and E-glass for 350-bar storage. Concerning the indicator of vessel mass, the standard T700S carbon composite is obviously the preferred candidate for 700bar storage. But at 350 bar, a hybrid composite integrated flax
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and T700S carbon fibers appears to be the more efficient highpressure vessel to reduce the weight of the hydrogen storage system. Other parameters that mechanical performances should be taken into account like component aging, corrosion or fire resistance in the choice of materials.
Acknowledgment The authors acknowledge Mr Kristian Bozhkov and Dr Ali Sikandar for providing helps on the ANSYS® modeling of highpressure vessel. They also wish to thank Dr Youssef Alilou and Dr Yao Avevor for their assistance in finite element simulation and mechanical analysis.
references
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