阅读说明：本技术 一种耐高温高压碳纤维聚酰亚胺复合材料气瓶设计方法 (Design method of high-temperature-resistant high-pressure-resistant carbon fiber polyimide composite gas cylinder ) 是由 王冲 廉彬 胡森 王维东 张著 徐铁峰 于 2020-12-18 设计创作，主要内容包括：本发明公开了一种耐高温高压碳纤维聚酰亚胺复合材料气瓶设计方法,第一步,聚酰亚胺作为碳纤维浸渍树脂,并测试其各种性能,用于有限元分析；第二步,设定金属内衬尺寸,气瓶瓶包括薄壁筒身段和前后封头段,封头采用内、外型面双椭圆设计,计算碳纤维聚酰亚胺复合材料层和聚酰亚胺高温应变补偿层；第三步：利用有限元仿真计算；第四步：优化调整；第五步：进行试验件爆破和分析对比。本申请可以设计出可以实现环境温度在250℃-400℃,和高压情况下,最接近气瓶实际应力结构的设计方案,适用于高温条件下复合材料层受理分析设计方案的制定,不仅限于聚酰亚胺碳纤维复合材料,也适应于其它高强度纤维连接材料。(The invention discloses a design method of a high-temperature and high-pressure resistant carbon fiber polyimide composite gas cylinder, which comprises the following steps of firstly, taking polyimide as carbon fiber impregnating resin, testing various performances of the carbon fiber impregnating resin and using the polyimide for finite element analysis; secondly, setting the size of a metal lining, wherein the gas cylinder comprises a thin-wall cylinder body section and front and rear head sealing sections, the head sealing adopts a double-ellipse design of inner and outer profile, and a carbon fiber polyimide composite material layer and a polyimide high-temperature strain compensation layer are calculated; the third step: utilizing finite element simulation calculation; the fourth step: optimizing and adjusting; the fifth step: test piece blasting and analytical comparison were performed. The design scheme can be designed to realize that the environmental temperature is 250-400 ℃ and the actual stress structure of the gas cylinder is closest to the high-pressure condition, is suitable for making the composite material layer acceptance analysis design scheme under the high-temperature condition, is not limited to polyimide carbon fiber composite materials, and is also suitable for other high-strength fiber connecting materials.)

1. A design method of a high-temperature and high-pressure resistant carbon fiber polyimide composite gas cylinder comprises the following steps:

step one, polyimide is used as carbon fiber impregnating resin, and the following performances, namely glass transition temperature, density, specific heat capacity and heat conductivity in a temperature range of 550 ℃, transverse average linear expansion coefficient of a unidirectional plate at RT-500 ℃, longitudinal average linear expansion coefficient of the unidirectional plate at RT-500 ℃, 5% thermal weight loss temperature and 1800s thermal weight loss in air at 500 ℃ are tested, and records are made for finite element analysis;

secondly, setting the size of the metal lining, and calculating the carbon fiber polyimide composite material layer and the polyimide high-temperature strain compensation layer; the gas cylinder comprises a thin-wall cylinder body section and front and back sealing head sections, the sealing head adopts a double-ellipse design with an inner surface and an outer surface, an outer ellipse section curve C1 and an inner ellipse section curve C2,

the formula for curve C1 is:

wherein:

a_ithe abscissa value of any point on the curve C1;

b_iis the ordinate value of any point on the curve C1;

X₁is the length value of the minor axis of the outer ellipse;

Y₁is the length value of the major axis of the outer ellipse.

The elliptic equation for curve 2 is the formula:

wherein:

c_ithe abscissa value of any point on the curve C2;

d_iis the ordinate value of any point on the curve C2;

X₂is the length value of the minor axis of the inner ellipse;

Y₂is the length value of the major axis of the inner ellipse.

Wherein X₁/Y₁The value range is 0.73-0.76, 0.75, X₂/Y₂The value range is 0.61-0.63, 0.625,

the third step: by utilizing a finite element simulation calculation method,

the metal lining is connected with the high-temperature strain compensation layer, the high-temperature strain compensation layer is connected with the carbon fiber polyimide composite material layer, a small slip mode is set in a surface-surface contact mode, and parameters of the metal lining, the high-temperature strain compensation layer and the carbon fiber polyimide composite material layer are set;

the fourth step: and when the model strain result in the last step does not meet the size matching level or the stress result exceeds the allowable stress level of the material, the method for re-matching the wall thickness of the polyimide high-temperature strain supplement layer is adopted, and the radius and the wall thickness of the arc transition section of the straight line section and the ellipse of the metal lining are optimized.

The fifth step: and carrying out test piece blasting, and comparing with the blasting result of the test piece of the design scheme.

2. The design method of the high-temperature and high-pressure resistant carbon fiber polyimide composite gas cylinder as claimed in claim 1, is characterized in that: in the second step, the ellipse of the end socket and the straight cylinder are in arc transition, and the radius of the arc transition is 40mm-50 mm.

3. The design method of the high-temperature and high-pressure resistant carbon fiber polyimide composite gas cylinder as claimed in claim 1, is characterized in that: in the second step, X₁/Y₁Values of 0.75, X₂/Y₂Taking the value of 0.625.

4. The design method of the high-temperature and high-pressure resistant carbon fiber polyimide composite gas cylinder as claimed in claim 1, is characterized in that: and in the third step, setting relevant thermophysical properties such as the heat conductivity coefficients of the metal lining, the high-temperature strain compensation layer, the carbon fiber polyimide composite material layer and the like for simulating temperature and stress transfer. Setting surface heat exchange conditions and physical properties such as heat conductivity coefficient and the like for simulating temperature and stress transfer, then applying fixed constraint on the inner surface of the liner, and setting a 400 ℃ temperature environment outside the simulated gas cylinder by setting the temperature in the boundary conditions.

Technical Field

The invention relates to the technical field of a high-temperature and high-pressure resistant carbon fiber polyimide composite gas cylinder.

Background

At present, composite material gas cylinders are widely applied to military rockets, missiles, airplanes, civil automobiles, natural gas storage pressure vessels and the like at home and abroad, with the continuous development of military high-structure efficiency and high-flying Mach missiles and aircrafts, the use environment conditions of the composite material gas cylinders are improved, and the high-temperature-resistant and high-bearing composite material gas cylinders become a trend for the development of gas cylinders in the aerospace field.

At present, the scheme that the composite material gas cylinder structure widely adopted at home and abroad is a metal lining and composite material winding layer is adopted, the composite material gas cylinder winding layer mainly adopts an epoxy resin system, the maximum service temperature of the composite material gas cylinder is limited by the indoor heat resistance of the epoxy resin system, and generally can not exceed 250 ℃, so that the epoxy resin system composite material gas cylinder can not meet the requirement of higher environmental service temperature.

The heat-resistant temperature of the polyimide can reach more than 600 ℃, the long-term use temperature range is 200-500 ℃, and the polyimide is a main material of a high-temperature-resistant and high-bearing structure which is universal internationally. Under the current development situation, carbon fiber polyimide composite materials are increasingly used for high-pressure gas cylinders, for example, in a bottle body structure disclosed in patent application 2017105985041, the bottle body comprises a metal lining and a composite material shell wound outside the metal lining, wherein the composite material shell is formed by winding a carbon fiber material adhesive polyimide glue solution on the metal lining and curing the glue solution at a high temperature. However, the properties of the polyimide, such as glass transition temperature, transverse and longitudinal average linear expansion coefficients, thermal conductivity and the like, are completely different from those of the conventional polyimide, so that the polyimide cannot be applied mechanically, and the thickness distribution of the winding layer can also cause different mechanical properties according to the shape of the gas cylinder. In order to meet the requirements of high-temperature and high-pressure working environments and light-weight design requirements, and reasonable winding shape and thickness distribution, a brand new design scheme is needed.

Disclosure of Invention

The invention aims to solve the technical problem of providing a design method of a high-temperature and high-pressure resistant carbon fiber polyimide composite gas cylinder, solving the problem of reduction of the actual pressure-bearing capacity of the composite gas cylinder caused by large difference of thermal expansion strains of a metal lining and a composite material layer, and realizing the application of the composite gas cylinder when the environmental temperature is 250-400 ℃.

The invention adopts the technical scheme that a method for designing a high-temperature and high-pressure resistant carbon fiber polyimide composite gas cylinder comprises the following steps:

step one, polyimide is used as carbon fiber impregnating resin, and the following performances, namely glass transition temperature, density, specific heat capacity and heat conductivity in a temperature range of 550 ℃, transverse average linear expansion coefficient of a unidirectional plate at RT-500 ℃, longitudinal average linear expansion coefficient of the unidirectional plate at RT-500 ℃, 5% thermal weight loss temperature and 1800s thermal weight loss in air at 500 ℃ are tested, and records are made for finite element analysis;

secondly, setting the size of the metal lining, and calculating the carbon fiber polyimide composite material layer and the polyimide high-temperature strain compensation layer; the gas cylinder comprises a thin-wall cylinder body section and front and back sealing head sections, the sealing head adopts a double-ellipse design with an inner surface and an outer surface, an outer ellipse section curve C1 and an inner ellipse section curve C2,

the formula for curve C1 is:

wherein:

a_ithe abscissa value of any point on the curve C1;

b_iis the ordinate value of any point on the curve C1;

X₁is the length value of the minor axis of the outer ellipse;

Y₁is the length value of the major axis of the outer ellipse.

The elliptic equation for curve 2 is the formula:

wherein:

c_ithe abscissa value of any point on the curve C2;

d_iis the ordinate value of any point on the curve C2;

X₂is the length value of the minor axis of the inner ellipse;

Y₂is the length value of the major axis of the inner ellipse.

Wherein X₁/Y₁The value range is 0.73-0.76, 0.75, X₂/Y₂The value range is 0.61-0.63, 0.625,

the third step: by utilizing a finite element simulation calculation method,

the metal lining is connected with the high-temperature strain compensation layer, the high-temperature strain compensation layer is connected with the carbon fiber polyimide composite material layer, a small slip mode is set in a surface-surface contact mode, and parameters of the metal lining, the high-temperature strain compensation layer and the carbon fiber polyimide composite material layer are set;

the fourth step: and when the model strain result in the last step does not meet the size matching level or the stress result exceeds the allowable stress level of the material, the method for re-matching the wall thickness of the polyimide high-temperature strain supplement layer is adopted, and the radius and the wall thickness of the arc transition section of the straight line section and the ellipse of the metal lining are optimized.

The fifth step: and carrying out test piece blasting, and comparing with the blasting result of the test piece of the design scheme.

The composite material gas cylinder has the advantages that the lightweight requirement and the gas cylinder thickness requirement are met, the composite material gas cylinder capable of achieving the environment temperature of 250-400 ℃ and under the high-pressure condition is designed, the design scheme which is closest to the actual stress structure of the gas cylinder is provided, the composite material layer accepting analysis design scheme is suitable for making under the high-temperature condition, and the composite material layer accepting analysis design scheme is not only limited to polyimide carbon fiber composite materials, but also suitable for other high-strength fiber connecting materials.

Drawings

Fig. 1 is a schematic structural diagram of a carbon fiber polyimide composite gas cylinder of the invention.

Fig. 2 is a schematic structural diagram of the end socket.

Fig. 3 is an enlarged view of a portion of a region a in fig. 2.

Fig. 4 is a schematic diagram of the thickness change of the high-temperature strain compensation layer at the end socket.

Labeled as: 1-polyimide composite material layer, 2-high temperature strain compensation layer and 3-metal lining.

Detailed Description

The following is a description of specific embodiments.

The method comprises the following specific steps:

firstly, according to the use temperature of the composite material gas cylinder with the maximum temperature of 400 ℃ and the working pressure index of 3MPa (under the condition of normal temperature of 20 ℃), polyimide is used as carbon fiber impregnating resin, and the physical properties of the carbon fiber impregnating resin are tested and determined, wherein the specific data are shown in Table 1.

Thermophysical properties	Parameter(s)	Remarks for note
			Glass transition temperature (. degree. C.)	482
Density (g/cm)3)	1.6
			Specific heat capacity in the temperature range of 450-	1.67～1.75
Thermal conductivity (W/(m.K))	0.86～0.95
			The average linear expansion coefficient of the unidirectional plate at RT-500 ℃ in the transverse direction	8.5×10-6/K
Mean linear expansion coefficient of unidirectional plate at RT-500 deg.C	0.19×10-6/K
			5% Heat weight loss temperature (. degree.C.)	600
Thermal weight loss of 1800s in 500 deg.C air (Quartz lamp)	0.1％

The second step is that: according to the volume, the shape envelope size and the allowable highest working pressure index in the design requirement of the composite material gas cylinder, the metal lining structure is designed: the metal lining configuration selects a long cylindrical shape with the length-diameter ratio larger than 2, the wall thickness of the liner cylinder body is 1mm according to engineering experience, the end socket adopts an elliptical shape, as shown in figure 2,

the end socket adopts a double-ellipse design with an inner ellipse surface and an outer ellipse surface, an outer ellipse section curve C1 and an inner ellipse section curve C2, the transition position of the ellipse and the straight cylinder is shown in figure 3, and the transition is realized through an arc section with the radius of R.

The formula of the curve C1 is to establish the coordinate system as shown in fig. 1:

wherein:

a_ithe abscissa value of any point on the curve C1;

b_iis the ordinate value of any point on the curve C1;

X₁is the length value of the minor axis of the outer ellipse;

Y₁is the length value of the major axis of the outer ellipse.

The elliptic equation for curve 2 is the formula:

wherein:

c_ithe abscissa value of any point on the curve C2;

d_iis the ordinate value of any point on the curve C2;

X₂is the length value of the minor axis of the inner ellipse;

Y₂is the length value of the major axis of the inner ellipse.

Wherein X₁/Y₁The optimum value is 0.75, X₂/Y₂The optimum value is 0.625 and,

the best embodiment of the application is

Curve C1 is an equation

Curve C2 is an equation

The above values are in units of millimeters. At the moment, R is 40mm-50mm, and according to the verification of a bursting test, the gas cylinder adopting the embodiment has the most excellent pressure bearing capacity under the condition of meeting the size requirement.

Given the initial model, by this point, the liner size assignment is complete.

And (3) calculating and distributing a carbon fiber polyimide composite material layer and a high-temperature strain compensation layer:

because the gas cylinder is divided into a thin-wall cylinder body section and front and rear sealing head sections, and the difference of thermal expansion is brought by the difference of the geometric dimensions, the invention provides a structural form of a non-uniform wall thickness compensation layer, as shown in figure 1.

Considering that the comprehensive influence of axial expansion and radial expansion exists at the end socket, the axial thermal expansion variation is more obvious, so that the straight cylinder section adopts a uniform high-temperature strain compensation layer, and the end socket adopts a high-temperature strain compensation layer design with an axially thickened layer, so that the high-temperature strain compensation layer design from thin to thick appears at the end socket, as shown in fig. 4, the thickness value range can be 2-3 times of the thickness of the high-temperature strain compensation layer of the bottle body, and in the embodiment, the value is 0.3mm-1.0 mm.

The design method of the compensation layer comprises the following steps:

selecting the average linear thermal expansion coefficient as a calculation, selecting the average linear thermal expansion coefficient in a temperature range as a thermal expansion coefficient, and then according to a formula:

Δ L ═ L × Δ T × β … … … … … … … … … … formula 5

Wherein: delta L- -amount of thermal expansion change

L- -thermal expansion calculating initial length

Delta T- -temperature variation

Beta-average linear expansion coefficient

For the design of the thermal expansion of the gas cylinder, the change of the internal pressure load caused by the rise of the temperature is also involved, so that an inner container generated by gas expansion is added and a conforming material is wound to be expanded, so that new design variables also need to be added in the design of the high-temperature strain compensation layer of the gas cylinder, and the checking and the finishing are carried out through finite elements on the basis of the preliminary result obtained in the formula 5.

Winding layer linear design:

the winding layer design method has previously applied patents, and is recorded in the book of fiber winding material forming and process, but the winding design method variable does not contain resin matrix material, mainly comprises reinforced matrix, namely the performance parameters of the carbon fiber, such as tensile strength, but the strength result after winding is influenced by the composite material formed by combining the resin and the reinforced matrix, the resin matrix material has influence on the tensile strength exertion rate of the carbon fiber, the evaluation on the design is not good, the test piece blasting test is required to verify, and no experience value about polyimide and carbon fiber systems is used for the winding exertion rate at present. Therefore, the fiber strength exertion rate of the system of carbon fiber reinforced polyimide under the winding method needs to be corrected through a bursting test. Fiber strength development rate is the average strength of the actual strength/fiber tensile test, and the actual strength is related to the burst value. However, depending on the winding method, for example, the winding angle is adjusted, the final burst value is also affected, i.e., the fiber utilization rate is also different in the carbon fiber polyimide.

The carbon fiber polyimide winding layer can be designed by selecting carbon fibers with different tensile strength indexes, the purpose of controlling the thickness of the carbon fiber polyimide composite material layer is achieved, and the overall mechanism scheme is distributed to meet the requirement of overall dimension. The schematic structural diagram of the carbon fiber polyimide composite gas cylinder is shown in figure 1.

The third step: and (3) performing finite element simulation calculation, selecting an ABAQUS/Standard module, adopting a structural shell unit, establishing a model according to the initial carbon fiber polyimide composite material gas cylinder structure designed in the second step, and performing meshing by using a CAX4R unit. The metal lining is connected with the high-temperature strain compensation layer, the high-temperature strain compensation layer is connected with the carbon fiber polyimide composite material layer, a small sliding mode is set in a surface-surface contact mode, and related thermophysical properties such as heat conductivity coefficients of the metal lining, the high-temperature strain compensation layer and the carbon fiber polyimide composite material layer are set for simulating temperature and stress transfer. Setting surface heat exchange conditions and physical properties such as heat conductivity coefficient and the like for simulating temperature and stress transfer, then applying fixed constraint on the inner surface of the liner, and setting a 400 ℃ temperature environment outside the simulated gas cylinder by setting the temperature in the boundary conditions.

In the prior art, the epoxy resin meets the condition that the material has low use temperature and unobvious thermal expansion, the liner can be directly connected with the epoxy resin composite material layer in the finite element analysis process, the difference between the design analysis result and the actual strain result of the design scheme is not great, so the formed design habits are all directly connected, the concept of a compensation layer is completely absent, and the point in the technical scheme of the application cannot be ignored.

And then applying 35MPa internal pressure load on the surface of the metal lining of the model, setting boundary conditions for applying fixed constraint on the carbon fiber polyimide composite gas cylinder, simultaneously setting a predefined field to control the external temperature of the model, and calculating by a solver to obtain the stress and strain results of the model at the temperature of 400 ℃.

The fourth step: and when the model strain result in the third step does not meet the size matching level or the stress result exceeds the allowable stress level of the material, performing the third step again by optimizing the fillets and the wall thickness of the straight-line section and the arc transition section of the metal lining and re-matching the wall thickness of the polyimide high-temperature strain supplement layer to obtain a final design scheme.

The fifth step: and carrying out comparison of the blasting results of the test piece of the initial design scheme and the blasting results of the test piece of the final design scheme.

The first explosion test can obtain the fiber strength exertion rate of the carbon fiber reinforced polyimide system in the winding method, and subsequent tests can verify and compare the design results.

The design scheme of this application solves the great problem of difference of metal inside lining and combined material layer thermal energy strain, and the actual bearing capacity of material gas cylinder is constantly improved through the optimal design link to the reaction combined material gas cylinder that can be real.