A method for obtaining the biaxial compression strength prediction curve of the cylindrical section of a deep-sea pressure-resistant cabin made of composite materials

Abstract

The present invention relates to the technical field of composite material pressure-resistant cabins, and in particular to a method for obtaining a biaxial compression strength prediction curve of a cylindrical section of a composite material deep-sea pressure-resistant cabin, comprising the following steps: 1) subjecting an existing cylindrical section of a composite material deep-sea pressure-resistant cabin to external pressure until failure, and plotting the axial stress and circumferential stress curves at each axial position thereof; 2) plotting the distribution curve of the ratio of the axial stress to the circumferential stress; 3) selecting multiple point values from the abscissa of the distribution curve of the ratio of the axial stress to the circumferential stress, multiplying each point value by 2, and preparing corresponding cylindrical sections; 4) preparing biaxial compression test pieces, pressurizing the test barrel to the failure of each test piece, and obtaining multiple groups of axial failure stresses and circumferential failure stresses; 5) fitting each group of axial failure stresses and circumferential failure stresses using a curve fitting method to form an envelope curve, and obtaining the biaxial compression strength prediction curve of the cylindrical section of the composite material deep-sea pressure-resistant cabin.

Description

Technical Field

[0001] The present invention relates to the technical field of composite material pressure-resistant cabins, and particularly relates to a method for obtaining a biaxial compression strength prediction curve of a cylindrical section of a deep-sea pressure-resistant cabin made of composite materials. Background Art

[0002] There are rich biological and mineral resources in the deep sea, which provide important sources of minerals, food, etc. for humans. The ocean connects many countries and is an important channel for international trade, which is related to the national security of each country and is an important wealth for human development. In marine scientific research, the research on the deep-sea abyssal region is a weak link. At present, many countries have launched deep-sea scientific research plans, which is the forefront field of marine scientific research. In the field of deep-sea exploration, deep-sea submersibles are one of the most important means for humans to explore, develop and utilize the ocean. Submersibles can be divided into manned submersibles and unmanned submersibles according to their types. Unmanned submersibles can be divided into cable-connected submersibles, cable-free submersibles and underwater gliders.

[0003] Underwater submersibles operate in the deep sea and have high requirements for the pressure-resistant performance of their structures. The external structure of a deep-sea submersible consists of a light outer shell and a pressure-resistant shell structure. The pressure-resistant shell bears the hydrostatic pressure conditions in the deep sea, isolates seawater from the internal equipment of the shell, and avoids damage to the equipment caused by seawater pressure and corrosion. The mass of the pressure-resistant shell accounts for a very high proportion of the total mass of the underwater submersible, providing most of the displacement volume. However, the heavier pressure-resistant shell will limit the battery-carrying capacity of the underwater submersible. Therefore, under the condition of ensuring its strength performance, stability performance and internal volume, optimizing the geometric parameters and ply design of the pressure-resistant shell, reducing the structural mass, thereby increasing its payload and reducing the power consumption of the power device, is of great significance for improving the performance of deep-sea unmanned submersibles and is an important factor determining the ultimate depth and performance of the submersible.

[0004] For the cylindrical section structure of the lightweight composite material deep-sea pressure-resistant cabin structure, there is still no standardized design and test method at present, which cannot provide support for the design of the lightweight deep-sea pressure-resistant cabin structure. The forces on the cylindrical section structure of the deep-sea pressure-resistant cabin structure include the radial pressure of seawater, the axial pressure of the end caps, and the contact constraints at the end cap boundaries. Specifically, the force mode of the local structure of the cylindrical section is a biaxial compression stress state, and the magnitudes and stress ratios of the axial and circumferential stresses of the local structures at different axial positions of the cylinder are different. For the traditional metal structure deep-sea pressure-resistant cabin, the strength prediction methods for its cylindrical section structure at different positions are the same. The mises stress is used to judge the structural strength and is verified by experiments. However, the strength of the composite material structure deep-sea pressure-resistant cabin is different under different axial and circumferential load ratios. For the cylindrical section structure with a longer length, strength failure usually occurs at the positions near the end heads of the cylindrical section. Due to the effect of the boundary at this position, there is an obvious additional bending moment, resulting in uneven distribution of the axial stress and premature strength failure.

[0005] Currently, the commonly used composite material strength prediction models usually use the classical laminate theory to determine the external load borne by each layer, then analyze the response of the single ply until failure, and finally obtain the overall performance of the laminated plate. However, under the action of biaxial combined loads, the failure of the laminated plate occurs layer by layer. The first failure is called the initial failure, and the corresponding load is called the initial failure strength of the laminated plate. It is predicted that the strength of the laminated plate under biaxial compressive loads does not decrease significantly compared with the unidirectional strength, and even the strength of the laminated plate under biaxial compressive loads is higher than the uniaxial compressive strength. There is a large difference between this kind of strength theory and the results of the external pressure cylinder test, and it cannot predict the strength failure under the biaxial compressive stress state.

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

[0007]

[0008] For the Tsai-Hill strength theory shown below, this theory is for the single ply prepreg in the composite material laminated plate, where, the σ 11 is the stress in the fiber direction of the single ply material, σ 22 is the stress perpendicular to the fiber direction of the single ply material, τ 12 is the shear stress of the single ply prepreg, the X is the strength in the fiber direction of the single ply material, the Y is the strength perpendicular to the fiber direction of the single ply material, and the S 12is the shear strength of the single-layer material; according to the test results, the strength theory with a formula exponent of "2" represented by the Tsai-Hill strength theory cannot predict the biaxial compressive strength, and the exponent of the ratio of stress to allowable value is "2", which cannot reflect the effect of the reduction of the unidirectional strength caused by biaxial compression of the composite material in biaxial compression.

[0009]

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

[0011] The technical problem solved by the present invention is to provide a method for obtaining the biaxial compressive strength prediction curve of the composite material deep-sea pressure-resistant cabin cylinder section, so as to measure the biaxial compressive strength of the composite material cylinder section structure under different load ratios, and promote the application of the composite material in the deep-sea pressure-resistant cabin structure.

[0012] The present invention provides a method for obtaining the biaxial compressive strength prediction curve of the composite material deep-sea pressure-resistant cabin cylinder section, including the following steps:

[0013] 1) Seal both ends of the existing composite material deep-sea pressure-resistant cabin cylinder section, apply external pressure to it until it fails, and calculate the axial stress and circumferential stress at each axial position along the axial direction according to the axial strain and circumferential strain at each axial position at the time of failure, and draw the axial stress curve and circumferential stress curve at each axial position along the axial direction;

[0014] 2) Perform a ratio operation on the point values on the axial stress curve and the corresponding point values on the circumferential stress curve to obtain the ratio of the axial stress to the circumferential stress at each axial position along the axial direction of the existing composite material deep-sea pressure-resistant cabin cylinder section, and draw the distribution curve of the ratio of the axial stress to the circumferential stress at each axial position along the axial direction;

[0015] 3) Select multiple point values from the abscissa of the distribution curve of the ratio of axial stress to circumferential stress, multiply each point value by 2 to obtain multiple effective compression lengths of the cylinder section, and prepare the corresponding cylinder section according to L 筒 =L 有效 +L 安装 *2, where L 筒 is the length of the cylinder section, L 有效 is the effective compression length of the cylinder section, and 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 cabin cylinder section;

[0016] 4) Prepare a plurality of end caps that match each cylinder column section, respectively insert and fix each end cap at both ends of each cylinder column section and completely cover the installation length of the cylinder column section to obtain a biaxial compression test piece. Install each test piece into a test barrel respectively, pressurize the test barrel until each test piece fails, and obtain the axial failure stress and circumferential failure stress at multiple failure positions;

[0017] 5) Fit the axial failure stress and circumferential failure stress at each group of failure positions using the curve fitting method to form an envelope curve, and obtain the biaxial compression strength prediction curve of the composite material deep-sea pressure-resistant cabin cylinder column section.

[0018] Preferably, the axial stress and circumferential stress at each position along the axis of the existing composite material deep-sea pressure-resistant cabin cylinder column section are calculated according to the following formula: σ X = ε X *E X + μ XY *ε Y *E X , σ Y = ε Y *E Y + μ YX *ε X *E Y ; where, σ X is the axial stress of the existing composite material deep-sea pressure-resistant cabin cylinder column section, σ Y is the circumferential stress of the existing composite material deep-sea pressure-resistant cabin cylinder column section, ε X is the axial strain at each position along the axis when the existing composite material deep-sea pressure-resistant cabin cylinder column section fails, ε Y is the circumferential strain at each position along the axis when the existing composite material deep-sea pressure-resistant cabin cylinder column section fails, E X is the axial equivalent elastic modulus of the composite material laminate, E Y is the circumferential equivalent elastic modulus of the composite material laminate, μ XY is the Poisson's ratio of the composite material laminate under compression in the axial direction of the corresponding cylinder column section, μ YX is the Poisson's ratio of the composite material laminate under compression in the circumferential direction of the corresponding cylinder column section.

[0019] Preferably, each end cap and each cylinder column section are sealed with sealant, and the installation length of the cylinder column section is 38 mm.

[0020] Preferably, the wall thickness of the insertion part of each end cap for the cylinder column section is 5 times the wall thickness of the cylinder column section.

[0021] Preferably, the length of each cylinder column section is less than the radius of the cylinder column section.

[0022] Preferably, in step 4), the failure position is the middle position of the side wall of the cylindrical column section along the axial direction, and the axial failure stress and the circumferential failure stress are obtained by measuring the strain gauges pasted on the side wall of the cylindrical column section.

[0023] Preferably, the material of each head is stainless steel, and the material of the test barrel is steel.

[0024] Preferably, in step 4), hydraulic oil or water is used to pressurize each test piece.

[0025] Preferably, for the distribution curve of the ratio of the axial stress to the circumferential stress at each axial position of the existing composite deep-sea pressure-resistant cabin cylindrical column section, the x-axis is the axial length of the existing composite deep-sea pressure-resistant cabin cylindrical column section, and the y-axis is the ratio of the axial stress to the circumferential stress at each position; for the biaxial compression strength prediction curve, the x-axis is the axial failure stress, and the y-axis is the circumferential failure stress.

[0026] Preferably, the material of the cylindrical column section is a composite material obtained by wet winding.

[0027] Compared with the prior art, the present invention has the following beneficial effects:

[0028] The present invention provides a method for obtaining the biaxial compression strength prediction curve of the cylindrical column section of a composite deep-sea pressure-resistant cabin. First, through the external pressure failure test of the existing cylindrical column section of the composite deep-sea pressure-resistant cabin, the distribution curve of the ratio of the axial stress to the circumferential stress at each axial position is obtained, so as to correspond the length of the cylindrical column section to the ratio of the axial stress to the circumferential stress; by preparing cylindrical column sections of different lengths and conducting external pressure failure tests on each of them, multiple groups of axial failure stresses and circumferential failure stresses are obtained, that is, the biaxial compression strengths of the composite cylindrical column sections under different axial and circumferential stress ratios; the envelope curve is formed by fitting the axial failure stresses and circumferential failure stresses of each group, and the bearing capacity of the composite pressure-resistant cabin shell under different axial and circumferential stress ratios can be predicted through the curve; through the above operations, the present invention enables the biaxial compression strengths of the composite cylindrical column section structures under different load ratios to be measured, so as to realize the prediction of the bearing capacity of different positions of the composite pressure-resistant cabin. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] Figure 1 is a flowchart of the method for obtaining the biaxial compression strength prediction curve of the cylindrical column section of a composite deep-sea pressure-resistant cabin according to an embodiment of the present invention. DETAILED DESCRIPTION

[0030] Next, in combination with the embodiments of the present invention, the technical solutions of the present invention will be clearly and completely described. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all of the embodiments. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts belong to the scope of protection of the present invention.

[0031] As Figure 1 shown, this embodiment provides a method for obtaining the biaxial compression strength prediction curve of the cylindrical section of a composite material deep-sea pressure-resistant cabin, including the following steps:

[0032] 1) Seal both ends of the existing cylindrical section of the composite material deep-sea pressure-resistant cabin, apply external pressure to it until it fails, and calculate the axial stress and circumferential stress at each axial position along the existing cylindrical section of the composite material deep-sea pressure-resistant cabin according to the axial strain and circumferential strain at each axial position at the time of failure, and draw the axial stress curve and circumferential stress curve at each axial position along it;

[0033] 2) Perform a ratio operation on the point values on the axial stress curve and the corresponding point values on the circumferential stress curve to obtain the ratio of the axial stress to the circumferential stress at each axial position along the existing cylindrical section of the composite material deep-sea pressure-resistant cabin, and draw the distribution curve of the ratio of the axial stress to the circumferential stress at each axial position along it;

[0034] 3) Select multiple point values from the abscissa of the distribution curve of the ratio of the axial stress to the circumferential stress, multiply each point value by 2 to obtain the effective compression lengths of multiple cylindrical sections, and prepare corresponding cylindrical sections according to L 筒 = L 有效 + L 安装 *2, where L 筒 is the length of the cylindrical section, L 有效 is the effective compression length of the cylindrical section, and L 安装 is the installation length of the cylindrical section; the diameters and materials of each cylindrical section are the same as those of the existing cylindrical section of the composite material deep-sea pressure-resistant cabin;

[0035] 4) Prepare multiple heads matching each cylindrical section, respectively insert and fix each head at both ends of each cylindrical section and completely cover the installation length of the cylindrical section to obtain biaxial compression test pieces, respectively install each test piece into the test barrel, pressurize the test barrel until each test piece fails, and obtain multiple groups of axial failure stresses and circumferential failure stresses at the failure positions;

[0036] 5) Use the curve fitting method to fit the axial failure stress and circumferential failure stress at each group of failure positions to form an envelope curve, and obtain the biaxial compression strength prediction curve of the cylindrical section of the composite material deep-sea pressure-resistant cabin.

[0037] The method for obtaining the biaxial compression strength prediction curve of the cylindrical section of a composite deep-sea pressure-resistant cabin of the present invention can be applied to the thickness design of the shell of a composite deep-sea pressure-resistant cabin. After obtaining the biaxial compression strength prediction curve, adjust the axial stress and circumferential stress at each position of the shell and mark them in the coordinate system so that they all fall on the biaxial compression strength prediction curve, then the size of the pressure-resistant cabin shell with higher structural efficiency can be obtained, and the pressure-resistant cabin shell with higher strength can be obtained, thereby realizing the prediction of the bearing capacity of different positions of the composite pressure-resistant cabin.

[0038] The present invention provides a method for obtaining the biaxial compression strength prediction curve of the cylindrical section of a composite deep-sea pressure-resistant cabin. First, through the external pressure failure test of the existing cylindrical section of the composite deep-sea pressure-resistant cabin, obtain the distribution curve of the ratio of the axial stress to the circumferential stress at each position along the axis, so as to correspond the length of the cylindrical section to the ratio of the axial stress to the circumferential stress; by preparing cylindrical sections of different lengths and conducting external pressure failure tests on each of them, obtain multiple groups of axial failure stresses and circumferential failure stresses, that is, the biaxial compression strengths of the composite cylindrical sections under different axial and circumferential stress ratios; fit the axial failure stresses and circumferential failure stresses of each group to form an envelope curve, and through the curve, the bearing capacity of the composite pressure-resistant cabin shell under different axial and circumferential stress ratios can be predicted; through the above operations of the present invention, the biaxial compression strengths of the composite cylindrical section structures under different load ratios are determined, thereby realizing the prediction of the bearing capacity of different positions of the composite pressure-resistant cabin.

[0039] In this embodiment, the axial stress and circumferential stress at each position along the axis of the existing cylindrical section of the composite deep-sea pressure-resistant cabin are calculated according to the following formula: σ X = ε X *E X + μ XY *ε Y *E X , σ Y = ε Y *E Y + μ YX *ε X *E Y ; where, σ X is the axial stress of the existing cylindrical section of the composite deep-sea pressure-resistant cabin, σ Y is the circumferential stress of the existing cylindrical section of the composite deep-sea pressure-resistant cabin, ε X is the axial strain at each position along the axis when the existing cylindrical section of the composite deep-sea pressure-resistant cabin fails, ε Y is the circumferential strain at each position along the axis when the existing cylindrical section of the composite deep-sea pressure-resistant cabin fails, E X is the axial equivalent elastic modulus of the composite laminate, E Y is the circumferential equivalent elastic modulus of the composite laminate, μXY is the Poisson's ratio of the composite laminate under axial compression in the corresponding cylinder section, μ YX is the Poisson's ratio of the composite laminate under circumferential compression in the corresponding cylinder section.

[0040] In this embodiment, each head and each cylinder section are sealed with sealant, and the installation length of the cylinder section is 38 mm.

[0041] In this embodiment, the wall thickness of the insertion part of each head for the cylinder section is 5 times that of the cylinder section.

[0042] In this embodiment, the length of each cylinder section is less than the radius of the cylinder section.

[0043] In this embodiment, 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 circumferential failure stress are obtained by measuring the strain gauges pasted on the side wall of the cylinder section.

[0044] In this embodiment, the material of each head is stainless steel, and the material of the test barrel is steel.

[0045] In this embodiment, in step 4), hydraulic oil or water is used to pressurize each test piece.

[0046] In this embodiment, for the existing distribution curve of the ratio of axial stress to circumferential stress at each axial position of the cylinder section of the composite deep-sea pressure-resistant cabin, the x-axis is the axial length of the cylinder section of the existing composite deep-sea pressure-resistant cabin, and the y-axis is the ratio of the axial stress to the circumferential stress at each position; for the biaxial compression strength prediction curve, the x-axis is the axial failure stress and the y-axis is the circumferential failure stress.

[0047] In this embodiment, the material of the cylinder section is a composite material obtained by wet winding.

[0048] The biaxial compression strength prediction curve of the cylinder section of the composite deep-sea pressure-resistant cabin obtained by the present invention is applicable to the design method of the shell thickness of the composite deep-sea pressure-resistant cabin. The design method includes the following steps:

[0049] 1) Determine the ply stacking sequence. Based on the classical laminate theory, adjust the ratio of the axial equivalent modulus to the circumferential equivalent modulus of the shell skin to 1:2, and calculate the axial equivalent elastic modulus and circumferential equivalent elastic modulus of the shell;

[0050] 2) Prepare flat specimens with the same material as the shell, and conduct uniaxial compression tests on the flat specimens in the axial direction and circumferential direction corresponding to the shell respectively to obtain the strength and Poisson's ratio under axial and circumferential uniaxial compression;

[0051] 3) Prepare a cylindrical specimen made of the same material as the housing. Seal both ends of the cylindrical specimen and conduct an external pressure failure test on the cylindrical specimen to obtain the axial strain and circumferential strain corresponding to the failure. Based on the axial strain and circumferential strain at each position along the axis at the time of failure, calculate the axial stress and circumferential stress at each position along the axis of the existing composite deep-sea pressure-resistant cabin cylinder section, and draw the axial stress curve and circumferential stress curve at each position along the axis;

[0052] 4) Perform a ratio operation on the point values on the axial stress curve and the corresponding point values on the circumferential stress curve to obtain the ratio of the axial stress to the circumferential stress at each position along the axis of the existing composite deep-sea pressure-resistant cabin cylinder section, and draw the distribution curve of the ratio of the axial stress to the circumferential stress at each position along the axis;

[0053] 5) Select multiple point values from the abscissa of the distribution curve of the ratio of the axial stress to the circumferential stress, multiply each point value by 2 to obtain the effective compression lengths of multiple cylinder sections, and prepare the corresponding cylinder sections according to L_cylinder = L_effective + 2 * L_installation, where L_cylinder is the length of the cylinder section, L_effective is the effective compression length of the cylinder section, and L_installation is the installation length of the cylinder section; the diameters and materials of each cylinder section are the same as those of the existing composite deep-sea pressure-resistant cabin cylinder section;

[0054] 6) Prepare multiple heads matching each cylinder section, respectively insert and fix each head at both ends of each cylinder section and completely cover the installation length of the cylinder section to obtain a biaxial compression test piece. Put each test piece into the test barrel respectively, pressurize the test barrel until each test piece fails, and obtain the axial failure stress and circumferential failure stress at multiple failure positions;

[0055] 7) Fit the axial failure stress and circumferential failure stress at each group of failure positions using the curve fitting method to form an envelope curve, and obtain the biaxial compression strength prediction curve of the composite deep-sea pressure-resistant cabin cylinder section; adjust the thickness dimensions at each position of the housing so that the axial stress and circumferential stress at each position fall on the biaxial compression strength prediction curve, and obtain the pressure-resistant cabin housing dimensions with the highest structural efficiency to complete the design of the composite deep-sea pressure-resistant cabin housing;

[0056] Among them, the biaxial compression formula is Among them, σ X is the axial stress of the cylindrical specimen, σ Y is the circumferential stress of the cylindrical specimen, X C is the strength of the flat specimen under axial compression, Y C is the strength of the flat specimen under circumferential compression, m is the axial compression parameter, and n is the circumferential compression parameter.

[0057] Obviously, the above embodiments are merely examples given for clear illustration and not limitations on the implementation manners. For those of ordinary skill 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 exhaustively list all implementation manners here. And the obvious changes or modifications derived therefrom still fall within the protection scope of the present invention.

Claims

1. A method for obtaining the biaxial compression strength prediction curve of the cylindrical section of a deep-sea pressure-resistant cabin of a composite material, characterized in that: It includes the following steps: 1) Seal both ends of the existing composite material deep-sea pressure-resistant cylinder section, apply external pressure to it until it fails, and calculate the axial stress and circumferential stress at each axial position along the axial direction when it fails according to the axial strain and circumferential strain at each axial position. Draw the axial stress curve and circumferential stress curve at each axial position along it; 2) Perform a ratio operation on the point values on the axial stress curve and the corresponding point values on the circumferential stress curve to obtain the ratio of the axial stress to the circumferential stress at each axial position along the existing composite material deep-sea pressure-resistant cylinder section, and draw the distribution curve of the ratio of the axial stress to the circumferential stress at each axial position along it; 3) Select multiple point values from the abscissa of the distribution curve of the ratio of axial stress to circumferential stress, multiply each point value by 2 to obtain the effective compression lengths of multiple cylindrical column segments. According to L 筒 = L 有效 + L 安装 * 2 to prepare the corresponding cylindrical column segments, where L cylinder is the length of the cylindrical column segment, L effective is the effective compression length of the cylindrical column segment, and L installation is the installation length of the cylindrical column segment; the diameters and materials of each cylindrical column segment are the same as those of the existing composite material deep-sea pressure-resistant cabin cylindrical column segments; 4) Prepare a plurality of heads matching each cylinder section, respectively insert and fix each head at both ends of each cylinder section and completely cover the installation length of the cylinder section to obtain a biaxial compression test piece. Install each test piece into the test barrel respectively, pressurize the test barrel until each test piece fails, and obtain the axial failure stress and circumferential failure stress at multiple failure positions; 5) Fit the axial failure stress and circumferential failure stress at each group of failure positions using the curve fitting method to form an envelope curve, and obtain the biaxial compression strength prediction curve of the composite material deep-sea pressure-resistant cylinder section.

2. The method for obtaining the biaxial compression strength prediction curve of the deep-sea pressure-resistant cylinder section of the composite material according to claim 1, wherein: The axial stress and circumferential stress at each axial position of the existing composite material deep-sea pressure-resistant cylinder section are calculated according to the following formula: , ; where, is the axial stress of the existing composite material deep-sea pressure-resistant cylinder section, is the circumferential stress of the existing composite material deep-sea pressure-resistant cylinder section, is the axial strain at each axial position of the existing composite material deep-sea pressure-resistant cylinder section at the time of failure, is the circumferential strain at each axial position of the existing composite material deep-sea pressure-resistant cylinder section at the time of failure, is the axial equivalent elastic modulus of the composite laminate, is the circumferential equivalent elastic modulus of the composite laminate, is the Poisson's ratio of the composite laminate under compression in the axial direction of the corresponding cylinder section, is the Poisson's ratio of the composite laminate under compression in the circumferential direction of the corresponding cylinder section.

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

4. The method for obtaining the biaxial compression strength prediction curve of the deep-sea pressure-resistant cylindrical section of the composite material according to claim 3, wherein: The wall thickness of the plugging part of each head for 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 deep-sea pressure-resistant cylinder column section according to claim 4, wherein: The length of each cylinder section is less than the radius of the cylinder section.

6. The method for obtaining the biaxial compression strength prediction curve of the composite material deep-sea pressure-resistant cabin cylinder section according to claim 5, wherein: In step 4), the failure position is the middle position along the axial direction of the side wall of the cylinder section, and the axial failure stress and circumferential failure stress are obtained by measuring with strain gauges pasted on 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-resistant cabin cylinder section according to claim 6, wherein: 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 deep-sea pressure-resistant cabin cylinder section according to claim 7, characterized in that: In step 4), each test piece is pressurized with hydraulic oil or water.

9. The method for obtaining the biaxial compression strength prediction curve of the composite deep-sea pressure-resistant cylinder column section according to claim 8, wherein: The x-axis of the distribution curve of the ratio of the axial stress to the circumferential stress at each axial position along the existing composite material deep-sea pressure-resistant cylinder section is the axial length along the existing composite material deep-sea pressure-resistant cylinder section, and the y-axis is the ratio of the axial stress to the circumferential stress at each position; the x-axis of the biaxial compression strength prediction curve is the axial failure stress, and the y-axis is the circumferential failure stress.

10. The method for obtaining the biaxial compression strength prediction curve of the composite deep-sea pressure-resistant cylinder 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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