Method for obtaining biaxial compression strength forecast curve of composite material deep sea pressure-resistant cabin cylinder section

Abstract

The invention relates to the technical field of composite material pressure-resistant cabins, in particular to a method for obtaining a biaxial compression strength forecasting curve of a composite material deep sea pressure-resistant cabin cylinder section. Comprising the following steps: (1) externally pressing an existing composite material deep sea pressure-resistant cabin cylinder section until the cylinder section is damaged, and drawing an axial stress and circumferential stress curve of each position in the axial direction of the composite material deep sea pressure-resistant cabin cylinder section; 2) drawing a ratio distribution curve of axial stress and circumferential stress; (3) selecting a plurality of point values from the abscissa of the distribution curve of the ratio of the axial stress to the circumferential stress, and multiplying each point value by 2 to prepare a corresponding cylinder section; (4) preparing biaxial compression test pieces, pressurizing the test barrel until each test piece is damaged, and obtaining a plurality of groups of axial breaking stress and circumferential breaking stress, and (5) fitting each group of axial breaking stress and circumferential breaking stress by using a curve fitting method to form an envelope curve, and obtaining a biaxial compression strength forecasting curve of the composite material deep sea pressure-resistant cabin cylinder section.

Description

Technical Field

[0001] The invention relates to the technical field of composite pressure cabins, and in particular to a method for obtaining a biaxial compression strength prediction curve of a cylinder section of a composite deep-sea pressure cabin. Background Art

[0002] There are rich biological and mineral resources in the deep sea, which provide important sources of minerals, food, etc. for human beings. The ocean connects many countries and is an important channel for international trade. It is related to the national security of various countries and is an important asset for human development. In marine science research, the research on the ocean hadal area is a weak link. At present, many countries have launched deep-sea scientific research plans, which is a frontier field of marine science research. In the field of deep-sea exploration, deep-sea submersibles are the most important means for human beings to explore, develop and utilize the ocean. Submersibles can be divided into manned submersibles and unmanned submersibles. Unmanned submersibles can be divided into cabled submersibles, cable-free submersibles and underwater gliders.

[0003] Underwater submersibles work in the deep sea, and there are high requirements for the pressure resistance of their structures. The external structure of deep-sea submersibles is composed of a light outer shell and a pressure hull structure. The pressure hull bears the hydrostatic pressure conditions of the deep sea, isolates the internal equipment of the hull from seawater, and avoids damage to the equipment by the pressure force and corrosion of seawater. The mass of the pressure hull accounts for a high proportion of the total mass of the underwater submersible, providing most of the displacement volume, while the heavier pressure hull will limit the battery carrying capacity of the underwater submersible. Therefore, under the condition that the pressure hull guarantees its strength performance, stability performance and internal volume, optimizing the geometric parameters and layup design of the pressure hull, reducing the structural mass, thereby increasing its payload, and reducing the power consumption of the power unit are of great significance to improving the performance of deep-sea unmanned submersibles, and are an important factor in determining the maximum depth and performance of the submersible.

[0004] There is still no standardized design and test method for the cylinder section structure of lightweight composite deep-sea pressure tank structure, which cannot provide support for the design of lightweight deep-sea pressure tank structure; the cylinder section structure of the deep-sea pressure tank structure is subjected to stress including radial pressure of seawater, axial pressure of end cover and contact constraint of end cover boundary. Specifically, the stress mode of the local structure of the cylinder section is biaxial compression stress state, and the axial and hoop stress magnitudes and stress ratios of the local structure at different axial positions of the cylinder are different; for traditional metal structure deep-sea pressure tank, the strength prediction method of its cylinder section structure at different positions is consistent, and mises stress is used to judge the structural strength, and it is verified by experiments, but the strength of composite structure deep-sea pressure tank is different under different axial and hoop load ratios. For the cylinder section structure with a long length, strength failure usually occurs near the ends of the cylinder section. Due to the effect of the boundary, there is an obvious additional bending moment at this position, which leads to uneven axial stress distribution and premature strength failure.

[0005] The current common composite material strength prediction model usually uses the classical layer theory to determine the external load shared by each layer, and then analyzes the response of the single layer until it is destroyed, and finally obtains the overall performance of the laminate; however, under the action of biaxial combined loads, the laminate failure occurs layer by layer, and the first failure is called the initial failure, and the corresponding load is called the initial failure strength of the laminate. It is predicted that the strength of the laminate under biaxial compression load is not significantly lower than the uniaxial strength, and even the strength of the laminate under biaxial compression load is higher than the uniaxial compression strength. This type of strength theory is quite different from the results of the external pressure cylinder test and cannot predict the strength failure under biaxial compression stress state.

[0006] For the Max-stress strength theory shown below, the theory is for a single prepreg layer in a composite laminate, where σ 11 is the stress in the fiber direction of a single layer of material, σ 22 is the stress in the single-layer material perpendicular to the fiber direction, τ 12 is the shear stress of a single layer of prepreg, and X t is the tensile strength of a single layer of material in the fiber direction, the X c is the compressive strength of a single layer of material in the fiber direction, the Y t is the tensile strength of a single-layer material perpendicular to the fiber direction, the Y c is the compressive strength of a single-layer material perpendicular to the fiber direction, the S 12 is the shear strength of a single layer of material, the σ 11 , σ 22 It is a positive value in the tensile state and a negative value in the compressive state. According to the test results, the strength theory represented by the Max-stress strength theory with a formula index of "1" cannot predict the biaxial compression strength. The exponent of the ratio of stress to allowable value is "1", which cannot reflect the coupling effect of the strength of composite materials in biaxial compression.

[0007]

[0008] For the Tsai-Hill strength theory shown below, which is for a single layer of prepreg in a composite laminate, the σ 11 is the stress in the fiber direction of a single layer of material, σ 22 is the stress in the single-layer material perpendicular to the fiber direction, τ 12 is the shear stress of a single-layer prepreg, X is the fiber direction strength of a single-layer material, Y is the vertical fiber direction strength of a single-layer material, and S 12It is the shear strength of a single layer of material. According to the test results, the strength theory represented by the Tsai-Hill strength theory with a formula index of "2" cannot predict the biaxial compression strength. The exponent of the ratio of stress to allowable value is "2", which cannot reflect the effect of reduced unidirectional strength caused by biaxial compression of composite materials in biaxial compression.

[0009]

[0010] Therefore, in view of the above problems, the present invention urgently needs to provide a method for obtaining a biaxial compression strength prediction curve of a composite material deep-sea pressure tank column section. Summary of the invention

[0011] The technical problem solved by the present invention is to provide a method for obtaining a prediction curve of the biaxial compression strength of a composite material deep-sea pressure tank cylinder section, so that the biaxial compression strength of the composite material cylinder section structure under different load ratios can be measured, thereby promoting the application of composite materials in deep-sea pressure tank structures.

[0012] The present invention provides a method for obtaining a biaxial compression strength prediction curve of a composite material deep-sea pressure tank column section, comprising the following steps: 1) Seal both ends of the existing composite material deep-sea pressure tank cylinder section, apply external pressure to it until it is destroyed, calculate the axial stress and hoop stress of the existing composite material deep-sea pressure tank cylinder section at various axial positions according to the axial strain and hoop strain at various axial positions at the time of destruction, and draw the axial stress curve and hoop stress curve at various axial positions; 2) Perform a ratio operation on the point value on the axial stress curve and the corresponding point value on the hoop stress curve to obtain the ratio of the axial stress to the hoop stress at various axial positions of the existing composite material deep-sea pressure tank column section, and draw a distribution curve of the ratio of the axial stress to the hoop stress at various axial positions; 3) Select multiple point values ​​from the horizontal coordinate of the distribution curve of the ratio of axial stress to hoop stress, multiply each point value by 2, and obtain the effective compressive length of multiple cylinder sections. 筒 =L 有效 +L 安装 *2 Prepare the corresponding column section, where L 筒 is the length of the cylinder section, L 有效 is the effective compression length of the column section, L 安装 is the installation length of the cylinder section; the diameter and material of each cylinder section are the same as those of the existing composite material deep-sea pressure-resistant tank cylinder section; 4) Prepare multiple heads matching each cylinder section, insert and fix each head at the two ends of each cylinder section respectively and completely cover the installation length of the cylinder section, obtain biaxial compression test pieces, load each test piece into a test barrel respectively, pressurize the test barrel until each test piece is destroyed, and obtain the axial failure stress and annular failure stress of multiple groups of failure positions; 5) The axial failure stress and the circumferential failure stress of each group of failure positions are fitted using the curve fitting method to form an envelope curve, and the biaxial compression strength prediction curve of the cylinder section of the composite material deep-sea pressure tank is obtained.

[0013] Preferably, the axial stress and the hoop stress of the existing composite material deep-sea pressure-resistant tank column section at each axial position are calculated according to the following formula: , ;in, The axial stress of the existing composite material deep-sea pressure tank column section is The hoop stress of the existing composite material deep-sea pressure tank column section is The axial strain at each position along the axial direction when the existing composite material deep-sea pressure tank column section is destroyed. It is the hoop strain at various positions along the axial direction when the existing composite material deep-sea pressure tank column section is destroyed. is the axial equivalent elastic modulus of the composite laminate, is the hoop equivalent elastic modulus of the composite laminate, is the Poisson’s ratio of the composite laminate under axial compression of the corresponding cylindrical section, is the Poisson’s ratio of the composite laminate under axial compression of the corresponding cylindrical section.

[0014] Preferably, each end cap and each column section are sealed by sealant, and the installation length of the column section is 38 mm.

[0015] Preferably, the wall thickness of the portion of each head used for plugging with the column section is 5 times the wall thickness of the column section.

[0016] Preferably, the length of each cylindrical segment is smaller than the radius of the cylindrical segment.

[0017] Preferably, in step 4), the failure position is the middle position of the side wall of the cylinder section along the axial direction, and the axial failure stress and the annular failure stress are measured by strain gauges attached to the side wall of the cylinder section.

[0018] Preferably, each head is made of stainless steel, and the test barrel is made of steel.

[0019] Preferably, in step 4), each test piece is pressurized with hydraulic oil or water.

[0020] Preferably, the x-axis of the distribution curve of the ratio of axial stress to hoop stress at various axial positions of the existing composite material deep-sea pressure tank cylinder section is the axial length of the existing composite material deep-sea pressure tank cylinder section, and the y-axis is the ratio of axial stress to hoop stress at various positions; the x-axis of the biaxial compression strength prediction curve is the axial failure stress, and the y-axis is the hoop failure stress.

[0021] Preferably, the material of the column section is a composite material obtained by wet winding.

[0022] Compared with the prior art, the present invention has the following beneficial effects: The present invention provides a method for obtaining a prediction curve of biaxial compression strength of a composite material deep-sea pressure-resistant tank cylinder section. Firstly, an external pressure destruction test is performed on an existing composite material deep-sea pressure-resistant tank cylinder section to obtain a distribution curve of the ratio of axial stress to hoop stress at various axial positions, thereby making the cylinder section length correspond to the ratio of axial stress to hoop stress; by preparing cylinder sections of different lengths and performing external pressure destruction tests on each of them, multiple groups of axial failure stresses and hoop stresses, that is, the biaxial compression strength of the composite material cylinder section under different axial to hoop stress ratios are obtained; each group of axial failure stresses and hoop stresses are fitted to form an envelope curve, and the bearing capacity of the composite material pressure-resistant tank shell under different axial to hoop stress ratios can be predicted through the curve; through the above operations, the present invention enables the biaxial compression strength of the composite material cylinder section structure under different load ratios to be measured, thereby realizing the prediction of the bearing capacity of the composite material pressure-resistant tank at different positions. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 It is a flow chart of a method for obtaining a biaxial compression strength prediction curve of a composite material deep-sea pressure-resistant tank column section according to an embodiment of the present invention. DETAILED DESCRIPTION

[0024] The following will be combined with the embodiments of the present invention to clearly and completely describe the technical solution of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0025] like Figure 1 As shown, this embodiment provides a method for obtaining a biaxial compression strength prediction curve of a composite material deep-sea pressure tank column section, comprising the following steps: 1) Seal both ends of the existing composite material deep-sea pressure tank cylinder section, apply external pressure to it until it is destroyed, calculate the axial stress and hoop stress of the existing composite material deep-sea pressure tank cylinder section at various axial positions according to the axial strain and hoop strain at various axial positions at the time of destruction, and draw the axial stress curve and hoop stress curve at various axial positions; 2) Perform a ratio operation on the point value on the axial stress curve and the corresponding point value on the hoop stress curve to obtain the ratio of the axial stress to the hoop stress at various axial positions of the existing composite material deep-sea pressure tank column section, and draw a distribution curve of the ratio of the axial stress to the hoop stress at various axial positions; 3) Select multiple point values ​​from the horizontal coordinate of the distribution curve of the ratio of axial stress to hoop stress, multiply each point value by 2, and obtain the effective compressive length of multiple cylinder sections. 筒 =L 有效 +L 安装 *2 Prepare the corresponding column section, where L 筒 is the length of the cylinder section, L 有效 is the effective compression length of the column section, L 安装 is the installation length of the cylinder section; the diameter and material of each cylinder section are the same as those of the existing composite material deep-sea pressure-resistant tank cylinder section; 4) Prepare multiple heads matching each cylinder section, insert and fix each head at the two ends of each cylinder section respectively and completely cover the installation length of the cylinder section, obtain biaxial compression test pieces, load each test piece into a test barrel respectively, pressurize the test barrel until each test piece is destroyed, and obtain the axial failure stress and annular failure stress of multiple groups of failure positions; 5) The axial failure stress and the circumferential failure stress of each group of failure positions are fitted using the curve fitting method to form an envelope curve, and the biaxial compression strength prediction curve of the cylinder section of the composite material deep-sea pressure tank is obtained.

[0026] The method for obtaining the biaxial compression strength prediction curve of the cylinder section of a composite material deep-sea pressure tank described in the present invention can be applied to the thickness design of the composite material deep-sea pressure tank shell. After obtaining the biaxial compression strength prediction curve, the axial stress and the hoop stress at each position of the shell are adjusted and marked in the coordinate system so that they all fall on the biaxial compression strength prediction curve. Then, the size of the pressure tank shell with higher structural efficiency can be obtained, and the pressure tank shell with higher strength can be obtained, thereby realizing the prediction of the bearing capacity of different positions of the composite material pressure tank.

[0027] The present invention provides a method for obtaining a prediction curve of biaxial compression strength of a composite material deep-sea pressure-resistant tank cylinder section. Firstly, an external pressure destruction test is performed on an existing composite material deep-sea pressure-resistant tank cylinder section to obtain a distribution curve of the ratio of axial stress to hoop stress at various axial positions, thereby making the cylinder section length correspond to the ratio of axial stress to hoop stress; by preparing cylinder sections of different lengths and performing external pressure destruction tests on each of them, multiple groups of axial failure stresses and hoop stresses, that is, the biaxial compression strength of the composite material cylinder section under different axial to hoop stress ratios are obtained; each group of axial failure stresses and hoop stresses are fitted to form an envelope curve, and the bearing capacity of the composite material pressure-resistant tank shell under different axial to hoop stress ratios can be predicted through the curve; through the above operations, the present invention enables the biaxial compression strength of the composite material cylinder section structure under different load ratios to be measured, thereby realizing the prediction of the bearing capacity of the composite material pressure-resistant tank at different positions.

[0028] In this embodiment, the axial stress and the hoop stress of the existing composite material deep-sea pressure tank column section at each axial position are calculated according to the following formula: , ;in, The axial stress of the existing composite material deep-sea pressure tank column section is The hoop stress of the existing composite material deep-sea pressure tank column section is The axial strain at each position along the axial direction when the existing composite material deep-sea pressure tank column section is destroyed. It is the hoop strain at various positions along the axial direction when the existing composite material deep-sea pressure tank column section is destroyed. is the axial equivalent elastic modulus of the composite laminate, is the hoop equivalent elastic modulus of the composite laminate, is the Poisson’s ratio of the composite laminate under axial compression of the corresponding cylindrical section, is the Poisson’s ratio of the composite laminate under axial compression of the corresponding cylindrical section.

[0029] In this embodiment, each end cap and each column section are sealed by sealant, and the installation length of the column section is 38 mm.

[0030] In this embodiment, the wall thickness of the portion of each head used for plugging with the column section is 5 times the wall thickness of the column section.

[0031] In this embodiment, the length of each cylindrical segment is smaller than the radius of the cylindrical segment.

[0032] In this embodiment, in step 4), the failure position is the middle position of the side wall of the cylinder segment along the axial direction, and the axial failure stress and the annular failure stress are measured by strain gauges attached to the side wall of the cylinder segment.

[0033] In this embodiment, the material of each head is stainless steel, and the material of the test barrel is steel.

[0034] In this embodiment, in step 4), hydraulic oil or water is used to pressurize each test piece.

[0035] In this embodiment, the x-axis of the distribution curve of the ratio of axial stress to hoop stress at various axial positions of the existing composite material deep-sea pressure tank cylinder section is the axial length of the existing composite material deep-sea pressure tank cylinder section, and the y-axis is the ratio of axial stress to hoop stress at various positions; the x-axis of the biaxial compression strength prediction curve is the axial failure stress, and the y-axis is the hoop failure stress.

[0036] In this embodiment, the material of the cylindrical section is a composite material obtained by wet winding.

[0037] The biaxial compression strength prediction curve of the composite material deep-sea pressure-resistant tank column section obtained by the present invention is applicable to the thickness design method of the composite material deep-sea pressure-resistant tank shell, and the design method comprises the following steps: 1) Determine the layup scheme, adjust the ratio of the axial equivalent modulus and the hoop equivalent modulus of the shell skin to 1:2 based on the classical laminate theory, and calculate the axial equivalent elastic modulus and the hoop equivalent elastic modulus of the shell; 2) Prepare a flat plate specimen with the same material as the shell, and perform uniaxial compression tests on the flat plate specimen in the axial direction and circumferential direction of the shell to obtain the strength and Poisson's ratio under uniaxial compression in the axial and circumferential directions; 3) Prepare a cylindrical specimen made of the same material as the shell, seal both ends of the cylindrical specimen, and conduct an external pressure failure test on the cylindrical specimen to obtain the axial strain and hoop strain corresponding to the failure. According to the axial strain and hoop strain at various axial positions at the time of failure, calculate the axial stress and hoop stress at various axial positions of the existing composite material deep-sea pressure tank column section, and draw the axial stress curve and hoop stress curve at various axial positions; 4) Perform a ratio operation on the point value on the axial stress curve and the corresponding point value on the hoop stress curve to obtain the ratio of the axial stress to the hoop stress at various axial positions of the existing composite material deep-sea pressure tank column section, and draw a distribution curve of the ratio of the axial stress to the hoop stress at various axial positions; 5) Select multiple point values ​​from the horizontal coordinate of the distribution curve of the ratio of axial stress to hoop stress, multiply each point value by 2, and obtain the effective compressive length of multiple cylinder sections. 筒 =L 有效 +L 安装 *2 Prepare the corresponding column section, where L 筒 is the length of the cylinder section, L 有效 is the effective compression length of the column section, L 安装is the installation length of the cylinder section; the diameter and material of each cylinder section are the same as those of the existing composite material deep-sea pressure-resistant tank cylinder section; 6) Prepare multiple heads matching each cylinder section, insert and fix each head at the two ends of each cylinder section respectively and completely cover the installation length of the cylinder section, obtain biaxial compression test pieces, load each test piece into a test barrel respectively, pressurize the test barrel until each test piece is destroyed, and obtain the axial failure stress and annular failure stress of multiple groups of failure positions; 7) The axial failure stress and the circumferential failure stress of each group of failure positions are fitted using a curve fitting method to form an envelope curve, and the biaxial compression strength prediction curve of the cylinder section of the composite material deep-sea pressure tank is obtained; the thickness of the shell at each position is adjusted so that the axial stress and the circumferential stress at each position fall on the biaxial compression strength prediction curve, and the shell size of the pressure tank with the highest structural efficiency is obtained, and the design of the shell of the composite material deep-sea pressure tank is completed; The biaxial compression formula is: ,in, is the axial stress of the cylindrical specimen, is the hoop stress of the cylindrical specimen, is the strength of the flat specimen under axial compression, is the strength of the flat specimen under hoop compression, m is the axial compression parameter, and n is the hoop compression parameter.

[0038] Obviously, the above embodiments are merely examples for the purpose of clear explanation, and are not intended to limit the implementation methods. For those skilled in the art, other different forms of changes or modifications can be made based on the above description. It is not necessary and impossible to list all the implementation methods here. The obvious changes or modifications derived therefrom are still within the scope of protection of the invention.

Claims

1. A method for obtaining a biaxial compression strength prediction curve of a composite material deep-sea pressure tank column section, characterized in that: The steps include: 1) Seal both ends of the existing composite material deep-sea pressure tank cylinder section, apply external pressure to it until it is destroyed, calculate the axial stress and hoop stress of the existing composite material deep-sea pressure tank cylinder section at various axial positions according to the axial strain and hoop strain at various axial positions at the time of destruction, and draw the axial stress curve and hoop stress curve at various axial positions; 2) Perform a ratio operation on the point value on the axial stress curve and the corresponding point value on the hoop stress curve to obtain the ratio of the axial stress to the hoop stress at various axial positions of the existing composite material deep-sea pressure tank column section, and draw a distribution curve of the ratio of the axial stress to the hoop stress at various axial positions; 3) Select multiple point values ​​from the horizontal coordinate of the distribution curve of the ratio of axial stress to hoop stress, multiply each point value by 2, and obtain the effective compressive length of multiple cylinder sections. 筒 =L 有效 +L 安装 *2 Prepare the corresponding column section, where L 筒 is the length of the cylinder section, L 有效 is the effective compression length of the column section, L 安装 is the installation length of the cylinder section; the diameter and material of each cylinder section are the same as those of the existing composite material deep-sea pressure-resistant tank cylinder section; 4) Prepare multiple heads matching each cylinder section, insert and fix each head at the two ends of each cylinder section respectively and completely cover the installation length of the cylinder section, obtain biaxial compression test pieces, load each test piece into a test barrel respectively, pressurize the test barrel until each test piece is destroyed, and obtain the axial failure stress and annular failure stress of multiple groups of failure positions; 5) The axial failure stress and the circumferential failure stress of each group of failure positions are fitted using the curve fitting method to form an envelope curve, and the biaxial compression strength prediction curve of the cylinder section of the composite material deep-sea pressure tank is obtained.

2. The method for obtaining the biaxial compression strength prediction curve of the composite material deep-sea pressure tank column section according to claim 1 is characterized in that: The axial stress and hoop stress of the existing composite material deep-sea pressure tank column section at various positions along the axial direction are calculated according to the following formula: , ;in, The axial stress of the existing composite material deep-sea pressure tank column section is The hoop stress of the existing composite material deep-sea pressure tank column section is The axial strain at each position along the axial direction when the existing composite material deep-sea pressure tank column section is destroyed. It is the hoop strain at various positions along the axial direction when the existing composite material deep-sea pressure tank column section is destroyed. is the axial equivalent elastic modulus of the composite laminate, is the hoop equivalent elastic modulus of the composite laminate, is the Poisson’s ratio of the composite laminate under axial compression of the corresponding cylindrical section, is the Poisson’s ratio of the composite laminate under axial compression of the corresponding cylindrical section.

3. The method for obtaining the biaxial compression strength prediction curve of the composite material deep-sea pressure tank column section according to claim 2 is characterized in that: Each head and each column section is sealed by sealant, and the installation length of the column section is 38mm.

4. The method for obtaining the biaxial compression strength prediction curve of the composite material deep-sea pressure tank column section according to claim 3 is characterized in that: The wall thickness of the plug-in portion of each head for connection with the cylinder section is 5 times the wall thickness of the cylinder section.

5. The method for obtaining the biaxial compression strength prediction curve of the composite material deep-sea pressure tank column section according to claim 4, characterized in that: The length of each cylindrical section is less than the radius of the cylindrical section.

6. The method for obtaining the biaxial compression strength prediction curve of the composite material deep-sea pressure tank column section according to claim 5, characterized in that: In step 4), the failure position is the middle position of the side wall of the cylinder section along the axial direction, and the axial failure stress and the annular failure stress are measured by strain gauges attached to the side wall of the cylinder section.

7. The method for obtaining the biaxial compression strength prediction curve of the composite material deep-sea pressure tank column section according to claim 6, characterized in that: The material of each head is stainless steel and the material of the test barrel is steel.

8. The method for obtaining the biaxial compression strength prediction curve of the composite material deep-sea pressure tank column section according to claim 7, characterized in that: In step 4), each test piece is pressurized using hydraulic oil or water.

9. The method for obtaining the biaxial compression strength prediction curve of the composite material deep-sea pressure tank column section according to claim 8, characterized in that: The x-axis of the distribution curve of the ratio of axial stress to hoop stress at various positions along the axial direction of the existing composite material deep-sea pressure tank cylinder section is the axial length of the existing composite material deep-sea pressure tank cylinder section, and the y-axis is the ratio of axial stress to hoop stress at various positions; the x-axis of the biaxial compression strength prediction curve is the axial failure stress, and the y-axis is the hoop failure stress.

10. The method for obtaining the biaxial compression strength prediction curve of the composite material deep-sea pressure tank column section according to claim 9, characterized in that: The material of the cylinder section is a composite material obtained by wet winding.

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