Combined pressure vessel formed by gradient fiber reinforced cylinder body and metal end socket

Abstract

The invention relates to the technical field of pressure vessels, in particular to a combined pressure vessel composed of a gradient fiber reinforced cylinder body and a metal end socket, which comprises a combined pressure vessel main body, the combined pressure vessel main body comprises a cylinder body area, and the two ends of the cylinder body area are provided with connecting areas. The two connecting areas are connected with two metal end socket components respectively, and the barrel body area is made of composite materials and formed by stacking a plurality of single layers in the radial direction to form a gradient elastic modulus tubular structure with the specific thickness. The combined type pressure vessel has the beneficial effects that the barrel body area is arranged, firstly, the elasticity modulus is gradually reduced layer by layer in the thickness direction of the barrel body, the rigidity difference of the connecting area of the composite barrel body and the metal end socket is weakened, non-coordinated deformation of the inner wall area after pressure bearing is reduced, and the bonding strength of the combined type pressure vessel in the connecting area is improved; secondly, the material is layered in the thickness direction, a single layer is equivalent to a uniform material, and the material attributes of different layers change in a step mode;

Description

Technical Field

[0001] This invention relates to the field of pressure vessel technology, and in particular to a combined pressure vessel consisting of a gradient fiber reinforced cylinder and a metal head. Background Technology

[0002] Fiber-reinforced composite materials are widely used in pressure vessel manufacturing due to their high strength, high modulus, and high toughness, such as high-pressure hydrogen storage cylinders. In the fabrication of pressure vessels, composite material cylinders are often used in conjunction with other components; for example, a pressure vessel is formed by bonding a composite material cylinder to metal end caps at both ends.

[0003] A pressure vessel with a reinforced head is disclosed in Chinese Patent Publication No. CN107850259A. This pressure vessel with a reinforced head achieves reduced manufacturing costs and weight of the pressure vessel while maintaining the same strength, reduces the amount of fiber material used, improves the strength of the head area, and reduces the overall weight of the vessel. However, based on the combined pressure vessels provided in related fields and existing technologies, it has the following drawbacks:

[0004] I. The risk of structural failure has increased significantly.

[0005] Local stress exceeding the limit: The difference in stiffness between metal and composite materials leads to uneven stress distribution at the joint. Local stress may exceed the material strength limit (such as the interlaminar shear strength of carbon fiber, which is usually only 50-100MPa), causing delamination or fiber breakage.

[0006] Fatigue failure: Under cyclic loading (such as pressure fluctuations and temperature changes), microcracks are prone to form and propagate in stress concentration areas.

[0007] Sudden rupture: Under high pressure conditions (such as 70MPa hydrogen storage pressure), the edge effect may directly lead to brittle fracture at the interface between the cylinder and the head, causing a catastrophic accident.

[0008] II. Decreased sealing performance

[0009] Interface deformation leakage: Stress concentration causes non-uniform deformation at the interface between the metal head and the composite material cylinder, damaging the sealing structure.

[0010] Microcrack leakage: Cracks between composite material layers form microchannels, and for hydrogen storage containers, the hydrogen leakage rate can exceed the safety threshold.

[0011] III. Accelerated degradation of material properties

[0012] Damage to composite materials: Interlaminar shear stress leads to debonding of the resin matrix from the fibers;

[0013] Fiber fracture: T700 grade carbon fiber begins to fracture when the local strain exceeds 0.8%;

[0014] Matrix cracking: Microcracks develop in the epoxy resin matrix under continuous stress.

[0015] Metal fatigue / corrosion: Electrochemical corrosion is prone to occur at the edge of the end cap. Summary of the Invention

[0016] The purpose of this invention is to overcome the shortcomings of the prior art, solve the problems mentioned in the background art, and provide a combined pressure vessel composed of a gradient fiber reinforced cylinder and a metal head.

[0017] The objective of this invention is achieved through the following technical solution: a combined pressure vessel consisting of a gradient fiber reinforced cylindrical body and metal end caps, comprising a combined pressure vessel body, wherein the combined pressure vessel body includes a cylindrical body region, wherein the two ends of the cylindrical body region are provided with connecting regions, and the two connecting regions are respectively connected to two metal end cap components, wherein the cylindrical body region is a composite material and is composed of multiple single layers stacked radially to form a tubular structure with a gradient elastic modulus of a specific thickness.

[0018] Furthermore, the fibers in the cylindrical body region are distributed within an annular cross-section and do not penetrate the thickness direction. There are obvious interfaces between the layers, so the mechanical properties can be effectively designed using the layered homogenization method.

[0019] Furthermore, the material in the cylindrical body region is layered along the thickness direction, with each layer being equivalent to a uniform material, and the material properties of different layers undergoing a step change.

[0020] Furthermore, the cylindrical body area is woven with interlaced warp and weft yarns.

[0021] Furthermore, the cylindrical body area employs a two-dimensional circular weaving device, which weaves and layers the previous layer of fabric multiple times to ultimately form a layered tubular preform.

[0022] Furthermore, when the braiding array, the axial traction rate of the preform, and the thickness of the yarn remain constant in the cylinder region, each layer of woven circular tube fabric forms a structure with relatively stable geometric parameters.

[0023] Furthermore, in the cylinder area, as the weaving radius increases, parameters such as weaving angle, circular tube fabric thickness, and mandrel coverage will continuously change radially, thus forming a tubular geometric structure with properties that change along the radial direction as the number of layers and wall thickness increase.

[0024] Furthermore, the warp and weft yarns follow a wavy spiral trajectory along the surface of the mandrel.

[0025] Furthermore, during the weaving process, the two sets of yarns in the bobbin area move in opposite directions and intertwine with each other under the drive of the circumferentially arranged yarn carriers, thus moving in clockwise and counterclockwise directions respectively on the weaving track.

[0026] Furthermore, the cylinder body region is woven in layers according to the weaving process to form a gradient structure with varying radial geometric parameters, thereby reducing the modulus difference of the components in the connection area, reducing the strain difference in the pipe wall under non-uniform stress, thus alleviating the edge effect and improving the performance of the composite fiber reinforced composite pressure vessel.

[0027] The beneficial effects of the present invention are as follows: by setting the cylindrical body area, firstly, by utilizing the elastic modulus to decrease layer by layer along the thickness direction of the cylindrical body, the stiffness difference between the composite material cylindrical body and the metal head connection area is weakened, the non-coordinated deformation of the inner wall area after pressure is reduced, and the bonding strength of the combined pressure vessel in the connection area is improved; secondly, by layering the material along the thickness direction, a single layer is equivalent to a uniform material, and the material properties of different layers change stepwise. Attached Figure Description

[0028] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0029] Figure 1 This is a schematic diagram of the pressure vessel of the present invention;

[0030] Figure 2 This is a cross-sectional view of the pressure vessel of the present invention;

[0031] Figure 3 This is a schematic diagram of the layered woven tubular preform of the present invention;

[0032] Figure 4 This is a schematic diagram of the woven tubular preform and the yarn spiral trajectory of the present invention;

[0033] Figure 5 This is a schematic diagram of the sub-layer model and local coordinate system of the present invention;

[0034] Figure 6 This is a schematic diagram of the off-axis strain and normal-axis strain of the present invention;

[0035] Figure 7 The axial stress at the cylinder body of this invention is distributed radially;

[0036] Figure 8 The axial strain at the cylinder body of this invention is distributed radially.

[0037] In the diagram: 1. Cylinder body area; 2. Connection area; 3. Metal end cap component. Detailed Implementation

[0038] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0039] Additional aspects and advantages of the invention will be further set forth in the description which follows in conjunction with the accompanying drawings, and in part will be obvious from the description or may be learned by practice of the invention.

[0040] An embodiment of the present invention, comprising a gradient fiber reinforced cylindrical body and a metal end cap, is shown below. Figure 1 As shown, the system includes a combined pressure vessel body, which includes a cylindrical body region 1. The cylindrical body region 1 has connection regions 2 at both ends. The two connection regions 2 are respectively connected to two metal end cap components 3. The cylindrical body region 1 is made of composite material and is composed of multiple single layers stacked radially to form a tubular structure with a gradient elastic modulus of a specific thickness.

[0041] The fibers in the cylinder region 1 are distributed within the annular cross section and do not penetrate the thickness direction. There are obvious interfaces between the layers. Therefore, the mechanical properties can be effectively designed using the layered homogenization method. The material of the cylinder region 1 is layered along the thickness direction, and a single layer is equivalent to a homogeneous material. The material properties of different layers change abruptly.

[0042] like Figure 5 As shown in the figure, axes 1 and 2 correspond to the fiber direction and tangential direction, respectively. The braided layer can be further subdivided into two sets of unidirectional sublayer structures that are symmetrical about the z-axis and form ±α angles with the z-axis.

[0043] like Figure 6 As shown in the figure, the left side represents the off-axis strain, and the right side represents the normal-axis strain. The off-axis and normal-axis strains and stresses of a uniaxial sublayer also exhibit similar relationships. The elastic modulus of the sublayer along the material coordinate system directions (i.e., axes 1 and 2) is called the normal-axis elastic modulus. The elastic modulus along the global coordinate system directions (i.e., axes z and θ) is called the off-axis elastic modulus. The normal-axis modulus can be measured experimentally, and the off-axis modulus can be obtained through transformation relationships.

[0044] In summary, the quantitative relationship between the elastic modulus of each layer and the weaving angle can be obtained through the derivation of the above relationships, thereby obtaining a gradient fiber reinforced cylinder through the gradual change of the weaving angle.

[0045] like Figures 2 to 4 As shown, the bobbin region 1 is woven with interlaced warp and weft yarns. The warp and weft yarns follow a wavy spiral trajectory along the surface of the mandrel. The bobbin region 1 is woven using a two-dimensional circular weaving device (the weaving device consists of a rotating weaving platform, mandrel, extraction mechanism, guide ring, and weaving yarn). It is woven multiple times and layered on the basis of the previous layer of fabric to finally form a layered tubular preform. When the weaving array, the axial traction rate of the preform, and the thickness of the yarn remain constant, the circular tube fabric of each layer of the bobbin region 1 forms a structure with relatively stable geometric parameters. As the weaving radius of the bobbin region 1 increases, the parameters such as the weaving angle, the thickness of the circular tube fabric, and the mandrel coverage will continuously change radially. Thus, as the number of layers increases and the wall thickness increases, a tubular geometric structure with properties that change along the radial direction is formed. During the weaving process of the bobbin region 1, the two sets of yarns move in opposite directions and intertwine with each other under the drive of the circumferentially arranged yarn carriers, thus moving in clockwise and counterclockwise directions on the weaving track, respectively.

[0046] like Figures 2 to 4 As shown, the cylindrical body region 1 is woven in layers using a braiding process to create a gradient structure with varying radial geometric parameters. This reduces the modulus difference of the components in the connection region 2, decreases the strain difference in the pipe wall under non-uniform stress, thereby mitigating edge effects and improving the performance of the composite fiber-reinforced composite pressure vessel. The degree of local non-coordinated deformation in the structural connection region 2 of the cylindrical body region 1 with a gradient elastic modulus is less than that of the uniform modulus cylindrical body. Under the same load, the stress concentration at the end nodes of the gradient modulus cylindrical body is lower than that of the uniform modulus cylindrical body (wherein, the maximum stress of the gradient modulus cylindrical body is 71.61% of that of the uniform modulus tube). The comparative analysis results show that the gradient change of the modulus has a certain effect on improving stress concentration; the strain distribution shows a large non-uniformity, decreasing in layers from the inside to the outside. The maximum strain occurs near the connection area 2 with the metal head component 3. Under axial load, the strain value at the end node of the cylinder with the elastic modulus gradient distribution is smaller than that of the uniform modulus tube, and the maximum value is reduced by 58.71% (due to the discontinuity of the structure at the connection of the combined pressure vessel, it is impossible to completely avoid the sudden change of stress and strain when subjected to internal pressure. However, the effect of the edge effect on the connection strength can be weakened by the gradient structure optimization design of the fiber cylinder).

[0047] like Figure 4 As shown, the yarn follows a wavy helical trajectory along the mandrel surface. The projection of this wavy helical trajectory onto the bottom is a sinusoidal arc. In the figure, dS represents a micro-arc in the actual helical trajectory of the yarn, and dθ is the arc corresponding to the projection of this micro-element onto the bottom. The wavy helical trajectory of the yarn can be represented in a three-dimensional Cartesian coordinate system as follows:

[0048]

[0049] In the formula, R is the equivalent mandrel radius, rs is the radius of the yarn undulation trajectory, α is the helix angle, defined as the acute angle formed by the tangent of the helix on the cylindrical surface and the straight generatrix of the cylindrical surface passing through the point of tangency. β is the weaving angle, defined as the acute angle formed by the tangent on the actual trajectory of the weaving yarn and the straight generatrix of the cylindrical surface. θ is the base angle, defined as the angle between the projection of a point on the yarn trajectory at the bottom and the coordinate axis, with a value range of (0, 2π).

[0050] The radial distribution of axial stress and strain at the fiber-reinforced cylinder is obtained by substituting the values ​​into the numerical calculations. Figure 7 , Figure 8 As shown. By Figure 7 It can be seen that when the inner side of the cylinder is subjected to an axial load, the stress is not uniformly distributed from the inside to the outside along the wall thickness, with the stress value being the largest on the inner wall, decreasing to 0 along the radial direction, and then slightly increasing in the reverse direction. As the material gradient parameter β increases, the stress peak at the inner wall rises. The gradient parameter has an influence on the critical position of the strain peak, such as... Figure 8 As shown, when β≥5, the maximum strain occurs on the inner wall, while when β<5, the maximum strain occurs on the outer wall. With the increase of the gradient parameter, the difference between the maximum and minimum strain in the cylinder wall decreases. This is reflected in the figure as the strain curve becoming flatter. The reduction in strain difference helps to avoid excessive local deformation leading to interface failure.

[0051] The gradient fiber reinforced bobbin is manufactured by controlling the braiding angle layer by layer. The braiding angle α has the following relationship with the angular velocity ω of the yarn carrier and the mandrel extraction speed v:

[0052]

[0053] In the formula, R is the knitting radius, ω is the equivalent rotational speed of the yarn carrier, v is the mandrel extraction speed, and C is the mandrel circumference.

[0054] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A combined pressure vessel consisting of a gradient fiber reinforced cylindrical body and a metal end cap, characterized in that: The system includes a combined pressure vessel body, which includes a cylindrical body region (1). The cylindrical body region (1) has connecting regions (2) at both ends. The two connecting regions (2) are respectively connected to two metal end caps (3). The cylindrical body region (1) is made of composite material and is formed by multiple single layers stacked radially to form a tubular structure with a gradient elastic modulus of a specific thickness.

2. The combined pressure vessel consisting of a gradient fiber reinforced cylindrical body and a metal head according to claim 1, characterized in that: The fibers in the cylindrical body region (1) are distributed within the annular cross section and do not penetrate the thickness direction. There are obvious interfaces between the layers, so the mechanical properties can be effectively designed using the layered homogenization method.

3. The combined pressure vessel consisting of a gradient fiber reinforced cylindrical body and a metal head according to claim 2, characterized in that: The material of the cylinder body region (1) is layered along the thickness direction, and a single layer is equivalent to a uniform material, with the material properties of different layers changing abruptly.

4. The combined pressure vessel consisting of a gradient fiber reinforced cylindrical body and a metal end cap as described in claim 2, characterized in that: The cylindrical body area (1) is woven with interlaced warp and weft yarns.

5. The combined pressure vessel consisting of a gradient fiber reinforced cylindrical body and a metal end cap as described in claim 4, characterized in that: The cylindrical body area (1) adopts a two-dimensional circular weaving device, which weaves and covers multiple layers on the basis of the previous layer of fabric, and finally forms a layered tubular preform.

6. The combined pressure vessel consisting of a gradient fiber reinforced cylindrical body and a metal end cap as described in claim 5, characterized in that: When the braiding array, the axial traction rate of the preform, and the thickness of the yarn remain constant, each layer of the woven circular tube fabric in the tube body region (1) forms a structure with relatively stable geometric parameters.

7. The combined pressure vessel consisting of a gradient fiber reinforced cylindrical body and a metal head according to claim 6, characterized in that: In the cylindrical area (1), as the weaving radius increases, parameters such as weaving angle, thickness of circular tube fabric and core coverage will continuously change radially, thus forming a tubular geometric structure with performance changes along the radial direction as the number of layers increases and the wall thickness increases.

8. The combined pressure vessel consisting of a gradient fiber reinforced cylindrical body and a metal head according to claim 7, characterized in that: The warp and weft yarns follow a wavy spiral trajectory along the surface of the mandrel.

9. A combined pressure vessel consisting of a gradient fiber reinforced cylindrical body and a metal head according to claim 8, characterized in that: During the weaving process, the two sets of yarns in the bobbin area (1) move in opposite directions and intertwine with each other under the drive of the circumferentially arranged yarn carriers, so that they move in clockwise and counterclockwise directions respectively on the weaving track.

10. A combined pressure vessel consisting of a gradient fiber reinforced cylindrical body and a metal head according to claim 9, characterized in that: The cylindrical body region (1) is woven in layers according to the weaving process to form a gradient structure with varying radial geometric parameters, thereby reducing the modulus difference of the components in the connection region (2), reducing the strain difference of the components in the pipe wall under non-uniform stress, thereby alleviating the edge effect and improving the performance of the composite fiber reinforced composite pressure vessel.

Images