A design method for a deep-sea pressure-resistant device composite material shell and application thereof

Abstract

This invention discloses a design method for composite material shells of deep-sea pressure-resistant devices and its application. The design method selects four key parameters: initial out-of-roundness amplitude, wall thickness deviation coefficient, hybrid fiber ratio, and difference in elastic modulus between inner and outer fibers. Combining nonlinear finite element analysis and response surface regression techniques, a quantitative prediction model of nonlinear buckling load with respect to the above parameters is established. Based on this, the buckling resistance advantages and performance-cost marginal benefit relationship of hybrid ply configuration are systematically explained from the two dimensions of structural mechanics mechanism and engineering economy.

Description

Technical Field

[0001] This invention relates to the field of pressure-resistant structure design and evaluation technology for deep-sea submersibles, and in particular to a design method for composite material shells of deep-sea pressure-resistant devices and its application. Background Technology

[0002] Fiber-reinforced composites have broad application prospects in deep-sea pressure-resistant structures (such as pressure hulls for submersibles and underwater observation chambers) due to their advantages such as high specific strength, high specific modulus, and strong designability. Carbon fiber composites have excellent mechanical properties, but are expensive; basalt fiber composites are less expensive and have advantages such as corrosion resistance, thermal insulation, and electrical insulation, but their stiffness and strength are generally lower than those of carbon fiber.

[0003] To balance performance and cost, hybrid fiber composites are considered an effective technological approach. However, the research and engineering application of introducing hybrid fiber layups into deep-sea pressure-resistant cylindrical shell structures is still in its early stages. For cylindrical shell structures where buckling is the primary failure mode under hydrostatic pressure, simple fiber mixing often fails to achieve the desired results. Deep-sea pressure-resistant shells bear loads dominated by external pressure, and their failure modes, defect sensitivities, and damage evolution patterns differ fundamentally from those in the aforementioned application areas. Especially for the specific hybrid configuration of "high-modulus fibers (such as carbon fiber) on the inner and outer surfaces and low-modulus fibers (such as basalt fiber) in the middle core layer," existing technologies have the following gaps and shortcomings:

[0004] 1. There is a lack of quantitative prediction models that comprehensively consider the coupled effects of initial geometric defects and mixed ply characteristics on external nonlinear buckling loads. Traditional linear formulas cannot accurately reflect the load-bearing capacity reduction under the combined effects of manufacturing deviations and material mixing.

[0005] 2. There is a lack of systematic explanation of the structural mechanical advantages of this type of hybrid plywood configuration under hydrostatic external pressure, such as the distribution of bending stiffness, interlayer stress relief mechanism, and defect sensitivity reduction effect.

[0006] 3. There is a lack of marginal benefit assessment methods that quantify the correlation between external pressure bearing capacity and fiber material cost, making it difficult to flexibly select the optimal hybridization ratio for different depth levels and cost constraints during the design phase. Summary of the Invention

[0007] Purpose of the invention: To address the above-mentioned problems, the purpose of this invention is to provide a design method for composite material shells of deep-sea pressure-resistant devices and its application. This method can comprehensively reflect the influence of process geometric defects and hybrid layup characteristics, and form a systematic structural advantage demonstration and cost-benefit analysis system, enabling the shell to maintain a high buckling load capacity while reducing material costs.

[0008] Technical solution: A design method for a composite material shell of a deep-sea pressure-resistant device, comprising the following steps:

[0009] Step 1: Calculate the theoretical linear buckling load for a defect-free, ideally ply composite cylindrical shell. The load is calculated using analytical formulas based on Flügge shell theory and classical laminate theory, taking into account the effects of layup sequence, fiber angle and stiffness matrix.

[0010] Step 2: Select the initial out-of-roundness amplitude Wall thickness deviation coefficient , proportion of mixed fibers and the ratio of elastic modulus of inner and outer fibers As a key parameter affecting the attenuation coefficient, it is defined and calculated;

[0011] Step 3: For each parameter combination, establish a nonlinear buckling analysis model that includes geometric defects, non-uniform wall thickness, mixed ply layup, and material property corrections. Extract the nonlinear ultimate bearing load using the Riks arc length method. And calculate the attenuation coefficient of the corresponding sample, that is, the sample with specific parameters. ;

[0012] Step 4: Calculate the attenuation coefficient for each group of samples. As the response variable, a quadratic polynomial response surface regression was performed to establish... about The prediction formula was derived, and the significance and accuracy of the regression model were verified.

[0013] Step 5: Based on the classical laminate theory, the contribution of shell layup to bending stiffness is proportional to the distance from its center plane. Design an actual hybrid fiber-wound cylindrical shell, concentrating high-modulus fibers on the inner and outer surface areas so that they bear the main stress when the shell bends, and using a low-modulus core layer between the inner and outer surfaces; define three evaluation indicators: relative buckling load RP, relative fiber cost RC, and marginal performance-cost ratio MPR, and quantitatively analyze the relationship between the improvement of load-bearing capacity and the increase in cost under different hybridization ratios to obtain the final actual hybrid fiber-wound cylindrical shell;

[0014] Step 6: For the actual hybrid fiber-wound cylindrical shell to be evaluated, obtain its true value through physical measurement methods. The parameter values ​​are substituted into the regression formula obtained in step four to calculate the attenuation coefficient corresponding to the shell. And then from Predict its nonlinear ultimate bearing capacity.

[0015] Furthermore, in step 1, the stiffness matrix includes the in-plane stiffness matrix, the coupled stiffness matrix, and the bending stiffness matrix; the critical buckling pressure of the shell... Represented as:

[0016] ;

[0017] Wherein, the coefficient matrix The elements include the in-plane stiffness matrix. Coupling stiffness matrix and bending stiffness matrix ;

[0018] The stiffness matrix is ​​calculated using classical laminate theory:

[0019] ;

[0020] in, For the first The distance between layers from the neutral plane of the laminate. Let be the off-axis stiffness coefficient of the k-th layer, determined by the winding angle. The engineering constants of the material are determined, and the expression is:

[0021] ;

[0022] in, , , , , , , Let i be the elastic modulus of the material in the principal direction, i = 1, 2. It is Poisson's ratio.

[0023] Furthermore, in step 2, the initial out-of-roundness amplitude Defined as the difference between the maximum and minimum radial distances on the shell surface. With nominal total wall thickness The ratio is expressed as:

[0024] ;

[0025] This parameter reflects the degree of non-circularity of the shell cross-section caused by mold deformation, tension fluctuations, and residual stress release during the winding and curing process;

[0026] The wall thickness deviation coefficient B is defined as the difference between the maximum and minimum wall thickness within the same circumferential section. With average wall thickness The ratio is expressed as:

[0027] ;

[0028] The maximum value of multiple axial test sections is taken as the shell wall thickness deviation coefficient to conservatively characterize the influence of circumferential wall thickness non-uniformity on local stiffness.

[0029] Blended fiber ratio Defined as the total thickness of the high-modulus fiber layer Total thickness of the shell The percentage is expressed as:

[0030] ;

[0031] This parameter controls the ratio of shell bending stiffness to tensile stiffness.

[0032] ratio of inner and outer fiber elastic modulus Defined as the longitudinal tensile modulus of high modulus fiber monolayer. Longitudinal tensile modulus of low modulus fiber monolayer The ratio is expressed as:

[0033] ;

[0034] This parameter characterizes the degree of stiffness matching between the materials on both sides of the hybrid interface and has a significant impact on interlaminar stress distribution and progressive damage evolution. The larger the value, the more significant the difference in stiffness between the two fibers.

[0035] Furthermore, in step 4, the prediction formula is expressed as:

[0036] ;

[0037] in , Each term represents a regression coefficient. The significance of each term is tested using analysis of variance. The accuracy of the model's predictions is evaluated using a reserved validation sample to ensure the coefficient of determination. And the prediction error is less than .

[0038] Ideally, in step 5, the relative buckling load RP is expressed as:

[0039] ;

[0040] in For hybrid shell buckling loads, For buckling loads of all low-modulus fiber shells;

[0041] The relative fiber cost RC is expressed as:

[0042] ;

[0043] in This refers to the percentage of fiber layers. This represents the fiber volume fraction. Fiber density, Price per unit; subscript and These represent high-modulus and low-modulus fibers, respectively.

[0044] The marginal performance-cost ratio (MPR) is expressed as:

[0045] ;

[0046] This indicator quantifies the increase in relative carrying capacity obtained for each additional unit of relative cost.

[0047] A pressure-resistant shell using the aforementioned deep-sea pressure-resistant device composite material shell design method is provided. The shell is a hollow cylinder, and its core load-bearing component is a composite material shell. The composite material shell comprises three layers from the inside out, wherein the inner and outer layers are composite material layer one made of high-performance carbon fiber, and the middle layer is composite material layer two made of basalt fiber.

[0048] Ideally, the thickness of the first composite layer of the inner and outer layers is 0.4–0.6 mm, and the thickness of the second composite layer of the middle layer is 1.0–1.2 mm.

[0049] Furthermore, the outer periphery of the mandrel is covered with a composite material shell. The mandrel is a polytetrafluoroethylene tube. The composite material shell is wound around the outer periphery of the mandrel to form an integral structure. Both ends of the composite material shell are sealed with epoxy resin and end caps are installed. A sealing ring is provided at the joint between the end caps and the composite material shell.

[0050] A method for processing the composite material pressure-resistant shell of the aforementioned deep-sea pressure-resistant device includes the following steps:

[0051] Step 1: Select a polytetrafluoroethylene tube with an outer diameter that meets the design requirements as the winding mandrel and the inner lining of the shell. Inspect its outer surface to ensure it is smooth and free of defects, and clean it with solvent to remove contaminants.

[0052] Step 2: Based on the performance requirements and economic constraints of the target pressure shell, determine the final layup structure, including the number of inner and outer carbon fiber layers, the number of intermediate basalt fiber layers, and the fiber winding angle of each layer; then, based on the selected material and layup structure, determine the winding process parameters, including the fiber bundle winding tension, winding speed, impregnation tank temperature, doctor blade gap, and the length of the transition and effective sections and the number of nodes in the winding process.

[0053] Step 3: Install the prepared mandrel on the four-axis CNC winding machine and import the winding program determined in Step 2;

[0054] Step 4: After the winding is completed, the mandrel assembly with composite layup is transferred to the rotary curing oven. The curing program is started, and the temperature is increased from room temperature to 80°C at a rate of 2°C / min. The temperature is then maintained at this temperature for 2-3 hours to allow the resin to initially gel. The temperature is then increased to 110°C and maintained for 3-4 hours to ensure that the resin system is completely cured. The entire curing process is carried out while the mandrel is continuously rotating to prevent the resin from flowing under gravity and causing uneven distribution. After the curing program is completed, the sample is allowed to cool naturally to room temperature with the oven.

[0055] Step 5: Use cutting equipment to remove the transition sections at both ends of the cylindrical shell caused by the winding process, retaining the middle effective section with uniform structure. Clean the outer surface of the effective section shell to remove processing residues, and then place it at room temperature to dry thoroughly.

[0056] Step Six: According to application requirements, use high-performance epoxy resin to seal and install the upper and lower end caps to both ends of the shell to form a complete pressure-resistant compartment.

[0057] Ideally, in step two, the single-bundle winding tension of carbon fiber is 20-25 N, the double-bundle winding tension of basalt fiber is 40-50 N, and the temperature of the impregnation tank is 40℃-50℃.

[0058] In step three, the inner carbon fiber layer is first laid. Using carbon fiber bundles, the inner carbon fiber composite material layer is wound and laid on the mandrel to the set thickness according to the preset parameters. After the inner carbon layer is completed, it is replaced with basalt fiber bundles, and the parameters are adjusted to the corresponding set values. One or more layers of basalt fiber composite material are continuously wound and laid on the wound inner carbon layer to form the middle main body layer of the shell to the set thickness. After the middle basalt layer is completed, it is replaced with carbon fiber bundles again, the corresponding parameters are restored, and one or more layers of carbon fiber composite material are wound and laid on the outer layer to form the outer protective layer.

[0059] Beneficial effects: Compared with the prior art, the advantages of the present invention are:

[0060] The attenuation coefficient is quantified by transforming abstract process deviations and layup characteristics into four measurable and modelable dimensionless or dimensionless parameters. By establishing an attenuation coefficient prediction formula through response surface regression, the accurate correction of linear theoretical buckling load is achieved, thereby improving the reliability of bearing capacity assessment.

[0061] Hybrid layup offers significant mechanical advantages. By concentrating high-modulus fibers on the inner and outer surfaces, it fully utilizes the cubic relationship between bending stiffness and distance from the mid-surface, reducing the amount of high-modulus fibers while maintaining essentially the equivalent bending stiffness. The stiffness gradient formed by the low-modulus core layer alleviates interlaminar shear stress concentration, reduces the shell's sensitivity to initial geometric defects, and provides a certain impact toughening effect.

[0062] Cost-effectiveness can be quantified and controlled. By introducing RP, RC, and MPR indicators, the marginal relationship between performance gain and cost increment under different hybridization ratios can be intuitively reflected, providing designers with a quantitative decision-making tool to flexibly select the optimal hybrid scheme based on cost constraints and load requirements.

[0063] By laying high-cost, high-performance carbon fiber in the inner and outer layers, which bear the greatest bending moment and are most sensitive to buckling stability, and laying low-cost, high-toughness basalt fiber in the middle layer, this invention significantly reduces raw material costs while minimizing the loss of ultimate buckling capacity. The basalt fiber in the middle layer also effectively inhibits crack propagation and improves damage tolerance.

[0064] Symmetrical layered structures avoid coupling effects caused by asymmetry, making the shell more uniformly stressed under hydrostatic pressure, reducing stress concentration, and thus improving the stability and reliability of the structure. Attached Figure Description

[0065] Figure 1 This is a flowchart of the design method of the present invention;

[0066] Figure 2 This is a schematic diagram of the pressure-resistant shell structure;

[0067] Figure 3 for Figure 2 Enlarged schematic diagram A;

[0068] Figure 4 This is a diagram showing the structural relationship between the composite material shell and the mandrel;

[0069] Figure 5 This is a schematic diagram of the initial out-of-roundness amplitude;

[0070] Figure 6 This is a schematic diagram of the wall thickness deviation coefficient;

[0071] Figure 7 The graph shows the relative buckling load (RP), relative fiber cost (RC), and marginal performance-cost ratio (MPR) as a function of high-modulus fiber content.

[0072] Figure 8 This is a flowchart of the pressure-resistant housing processing method. Detailed Implementation

[0073] The present invention will be further illustrated below with reference to the accompanying drawings and specific embodiments. It should be understood that these embodiments are for illustrative purposes only and are not intended to limit the scope of the invention.

[0074] A design method for composite material shells of deep-sea pressure-resistant devices, such as Figure 1 As shown, it includes the following steps:

[0075] Step 1: Calculation of theoretical linear buckling load;

[0076] The critical buckling load of a composite cylindrical pressure shell is influenced by material and geometric parameters, including elastic modulus, Poisson's ratio, thickness, length, and radius. This invention uses analytical formulas based on Flügge shell theory and classical laminated plate theory to calculate the linear buckling load of a defect-free ideal shell. This formula comprehensively considers the combined effects of composite material layup sequence, fiber angle, and stiffness matrix.

[0077] Critical buckling pressure of the shell Determined by the following formula:

[0078] ;

[0079] Wherein, the coefficient matrix The elements include in-plane stiffness Coupling stiffness and bending stiffness The specific expression is as follows:

[0080] ;

[0081] ;

[0082] ;

[0083] ;

[0084] ;

[0085] ;

[0086] ;

[0087] ;

[0088] In the formula, The length of the cylindrical shell. The average radius, , , and These are the axial half-wave number and the circumferential wave number, respectively.

[0089] The stiffness matrix is ​​calculated using classical laminate theory:

[0090] ;

[0091] in, For the first The distance between layers from the neutral plane of the laminate. Let be the off-axis stiffness coefficient of the k-th layer, determined by the winding angle. The engineering constants of the material are determined, and the expression is as follows:

[0092] ;

[0093] in, , , , , , , (i=1,2) represents the elastic modulus of the material in the principal direction. It is Poisson's ratio.

[0094] Step 2: Derivation of the attenuation coefficient and method for obtaining parameters;

[0095] 1. Definition of attenuation coefficient;

[0096] Nonlinear ultimate bearing capacity of composite cylindrical shells under hydrostatic pressure Compared with theoretical linear buckling loads based on ideal geometry and linear elastic assumptions There are significant differences between them. Define the attenuation coefficient. for:

[0097] ;

[0098] The value is usually less than Its specific value is jointly controlled by factors such as shell geometric defects, manufacturing tolerances, and material dispersion.

[0099] 2. Selection and definition of key influencing parameters;

[0100] Parameter 1: Initial out-of-roundness amplitude ;

[0101] like Figure 5 As shown, the initial out-of-roundness amplitude A is defined as the difference between the maximum and minimum radial distances on the shell surface. With nominal total wall thickness The ratio:

[0102] ;

[0103] This parameter reflects the degree of non-circularity of the shell cross-section caused by mold deformation, tension fluctuations, and residual stress release during the winding and curing process.

[0104] Parameter 2: Wall thickness deviation coefficient ;

[0105] like Figure 6 As shown, the wall thickness deviation coefficient Defined as the maximum wall thickness within the same circumferential cross section With minimum wall thickness The ratio of the difference to the average wall thickness:

[0106] ;

[0107] The maximum value of multiple axial test sections is taken as the shell wall thickness deviation coefficient to conservatively characterize the influence of circumferential non-uniformity of wall thickness on local stiffness.

[0108] Parameter 3: Blended fiber ratio ;

[0109] Defined as the total thickness of high-modulus fiber layers (such as carbon fiber layers). Total thickness of the shell Percentage:

[0110] ;

[0111] This parameter directly controls the ratio of shell bending stiffness to tensile stiffness, and is a core variable in hybrid layup design.

[0112] Parameter 4: Ratio of elastic modulus between inner and outer fibers ;

[0113] Defined as the longitudinal tensile modulus of high modulus fiber monolayer. Longitudinal tensile modulus of low modulus fiber monolayer The ratio:

[0114] ;

[0115] This parameter characterizes the degree of stiffness matching between the materials on both sides of the hybrid interface and has a significant impact on interlayer stress distribution and progressive damage evolution. The larger the value, the more significant the difference in stiffness between the two fibers.

[0116] 3. Establishment of formulas for response surface regression and attenuation coefficient

[0117] A Box-Behnken experimental design method was used to generate a simulation sample matrix containing four factors and three levels. For each parameter combination, a nonlinear buckling analysis model was established in Abaqus: an initial out-of-roundness defect (scaling factor) was introduced via *IMPERFECTION. ); The non-uniform wall thickness varying with the circumferential angle is defined by the analytical field (and (related); in the composite material layup module according to Allocate inner and outer high-modulus layers and intermediate low-modulus layers; according to Adjust the material engineering constants. Run Riks analysis to extract... ,calculate .

[0118] Each group Using the value as the response variable, a quadratic polynomial response surface regression was performed in Design-Expert software to obtain the formula for predicting the attenuation coefficient:

[0119]

[0120] in , Each term represents a regression coefficient. The significance of each term is tested using analysis of variance, and the predictive accuracy of the model is evaluated using a reserved validation sample to ensure the coefficient of determination. And the prediction error is less than .

[0121] Step 3: The structural buckling resistance mechanism of hybrid fiber cylindrical shells;

[0122] 1. The cubic distribution effect of bending stiffness;

[0123] According to classical laminate theory, the bending stiffness coefficient of a laminate is... The results are obtained by weighted cubic integrals of the stiffness of each individual layer and its distance from the mid-surface:

[0124] ;

[0125] The further the layup is from the mid-surface, the more significant its contribution to flexural stiffness. This invention concentrates high-modulus fibers on the inner and outer surface regions, allowing them to bear the main stress during shell bending and maximizing stiffness advantages; while the low-modulus core layer near the mid-surface has a very limited effect on reducing flexural stiffness. Therefore, with the same total thickness, hybrid layups can achieve flexural stiffness similar to a fully high-modulus shell, while significantly reducing the amount of high-modulus fibers used.

[0126] 2. The effect of stiffness gradient on mitigating interlayer stress;

[0127] High-modulus shells exhibit uniform or abrupt stiffness along their thickness, leading to a concentration of interlaminar shear stress at the interfaces during bending, which can induce delamination. This invention introduces a low-modulus core layer between the inner and outer high-modulus layers and the mid-surface, creating a gradual stiffness gradient from the outside in. This results in a smoother distribution of interlaminar shear stress, reducing its peak value and thus delaying delamination initiation and propagation, thereby improving damage tolerance.

[0128] 3. The toughening and impact resistance aiding role of the low-modulus core layer;

[0129] Low-modulus fibers (such as basalt fibers) have high elongation at break and good interfacial bonding with the resin matrix. When subjected to impact, the core fibers can absorb energy through stretching, pull-out, and progressive fracture, inhibiting delamination propagation and mitigating the impact damage on residual load-bearing capacity.

[0130] Step 4: Performance and cost marginal benefit analysis;

[0131] 1. Definition of evaluation indicators;

[0132] Relative buckling load :

[0133] ;

[0134] in For hybrid shell buckling loads, For the buckling load of the all-low modulus fiber shell.

[0135] relative fiber cost :

[0136] ;

[0137] in This refers to the percentage of fiber layers. This represents the fiber volume fraction. Fiber density, Price per unit; subscript and These represent high-modulus and low-modulus fibers, respectively.

[0138] Marginal performance-cost ratio :

[0139] ;

[0140] This indicator quantifies the increase in relative carrying capacity obtained for each additional unit of relative cost.

[0141] 2. The impact of hybridization ratio on the performance-cost relationship;

[0142] Figure 7 This demonstrates the effect of high modulus fiber content The trends of RP, RC, and MPR as the fiber content increases from 0% to 100% show that in the low-to-high modulus fiber content range, increasing the number of high-modulus layers on both the inner and outer surfaces significantly improves the buckling load, while the fiber cost increases approximately linearly. The value is relatively high. When the content of high-modulus fibers is maintained at a certain threshold (e.g., When the following conditions are met, This indicates that the performance improvement outweighs the cost increase, demonstrating the significant cost-effectiveness of hybrid design. As the high-modulus fiber content further increases, the rate of increase in buckling load slows down. Down to The marginal benefits diminish as a result. Therefore, for shallow water applications that are cost-sensitive and have moderate load-bearing requirements, a hybrid scheme with a low to medium modulus fiber content is preferable; for deep water applications with extremely high load-bearing requirements and less stringent cost constraints, a high-content scheme can be selected.

[0143] The pressure-resistant hull involved in the above-mentioned deep-sea pressure-resistant device composite material hull design method, such as... Figures 2-4 As shown, the shell is a hollow cylinder, and its core load-bearing component is a composite material shell 3. The composite material shell 3 comprises three layers from the inside out. The inner and outer layers are both composite material layers 301 made of high-performance carbon fiber, and the middle layer is composite material layer 302 made of basalt fiber. The layered configuration of the composite material shell 3 is strictly symmetrically distributed along the wall thickness direction. Specifically, the outermost layer (directly in contact with the external high-pressure environment) and the innermost layer (forming the internal space interface) are both composite material layers 301 made of high-performance carbon fiber. Located between the inner and outer carbon layers is a composite material layer 302 made of basalt fiber, forming a symmetrical carbon-basalt-carbon sandwich structure.

[0144] The shell also includes a core mold 4, which is a polytetrafluoroethylene tube. The outer peripheral surface of the core mold 4 is covered with a composite material shell 3. The composite material shell 3 is wound around the outer peripheral surface of the core mold 4 to form an integral structure. The two ends of the composite material shell 3 are respectively sealed with epoxy resin glue 5 to install end caps 1. A sealing ring 2 is provided at the joint between the end cap 1 and the composite material shell 3.

[0145] The above-mentioned processing method for pressure-resistant housings, such as Figure 8 As shown, it includes the following steps:

[0146] Step 1: Select a polytetrafluoroethylene (PTFE) tube with an outer diameter that meets the design requirements as the inner liner for the winding mandrel and the final shell. Strictly screen its outer surface to ensure it is smooth and free of defects, and thoroughly clean it with solvent to remove oil and other contaminants.

[0147] Step Two: Based on the performance requirements of the target pressure shell (such as the target buckling load) and economic constraints, determine the final layup structure, including the number of inner and outer carbon fiber layers, the number of intermediate basalt fiber layers, and the fiber winding angle of each layer. Subsequently, based on the selected materials and layup structure, determine the winding process parameters, including but not limited to: fiber bundle winding tension (e.g., 20-25 N for a single carbon fiber bundle, 40-50 N for a double basalt fiber bundle), winding speed, impregnation bath temperature (e.g., 40℃ to control resin viscosity), doctor blade gap, and the length of transition and effective sections in the winding process, as well as the number of nodes.

[0148] Step 3: Install the prepared PTFE mandrel on the four-axis CNC winding machine and import the winding program determined according to step S2.

[0149] a. Laying the inner carbon fiber layer: Using carbon fiber bundles, according to preset parameters such as tension, speed and winding angle, the innermost carbon fiber composite material layer is wound and laid on the mandrel to the set thickness.

[0150] b. Laying the intermediate basalt layer: After completing the inner carbon layer, replace it with basalt fiber bundles and adjust parameters such as tension to the corresponding set values. On top of the already wound inner carbon layer, continuously wound and lay one or more layers of basalt fiber composite material to form the intermediate main layer of the shell.

[0151] c. Laying the outer carbon fiber layer: After completing the intermediate basalt layer, replace it with carbon fiber bundles again, restoring the corresponding parameters. One or more layers of carbon fiber composite material are then wound and laid on the outermost layer to form the outermost protective layer. This sequence achieves a symmetrical or quasi-symmetrical layup configuration of "inner carbon-basalt-outer carbon".

[0152] Step 4: After winding, transfer the entire mandrel assembly with composite layups to a rotary curing oven. Initiate the curing program: increase the temperature from room temperature to 80°C at a rate of approximately 2°C / min, and hold at this temperature for 2 hours to allow the resin to initially gel; then continue heating to 110°C and hold for 3 hours to ensure complete curing of the resin system. The entire curing process is carried out while the mandrel is continuously rotating to prevent the resin from flowing under gravity and causing uneven distribution. After the curing program is completed, allow the sample to cool naturally to room temperature with the oven.

[0153] Step 5: Due to the use of a PTFE liner, no additional demolding method is usually required; it will detach on its own. Use cutting equipment to remove the transition sections at both ends of the cylindrical shell caused by the winding process, retaining the structurally uniform middle effective section. Clean the outer surface of the effective section shell to remove processing residues, and then allow it to dry thoroughly at room temperature.

[0154] Step Six: According to application requirements, use high-performance epoxy resin adhesive (such as Araldite 2015) to seal and install the upper and lower end caps to both ends of the shell to form a complete pressure-resistant compartment.

Claims

1. A method of designing a composite shell for a deep-sea pressure- resistant device, characterized in that Includes the following steps: Step 1: Calculate the theoretical linear buckling load of a perfect, ideal-ply composite cylindrical shell This load is calculated using an analytical formula based on the Flügge shell theory and the classical laminate theory, taking into account the effects of ply sequence, fiber angle, and stiffness matrix. Step 2: Select initial amplitude of out-of-roundness , wall thickness deviation coefficient , hybrid fiber ratio , and inner and outer fiber elastic modulus ratio as key parameters affecting the attenuation coefficient, and define and calculate them; Step 3: For each set of parameter combination, a nonlinear buckling analysis model including geometric imperfection, non-uniform wall thickness, hybrid layup and material property modification is established, and the nonlinear ultimate bearing load is extracted by Riks arc-length method and calculate the attenuation coefficient of the corresponding sample ; Step 4: Attenuation coefficients of each group of samples were calculated As the response variable, the quadratic polynomial response surface regression was carried out to establish The prediction formula of , and the significance test and precision verification of the regression model were carried out; Step 5: Based on the classical laminate theory, the contribution of shell layup to bending stiffness is proportional to the distance from its center plane. Design an actual hybrid fiber-wound cylindrical shell, concentrating high-modulus fibers on the inner and outer surface areas so that they bear the main stress when the shell bends, and using a low-modulus core layer between the inner and outer surfaces; define three evaluation indicators: relative buckling load RP, relative fiber cost RC, and marginal performance-cost ratio MPR, and quantitatively analyze the relationship between the improvement of load-bearing capacity and the increase in cost under different hybridization ratios to obtain the final actual hybrid fiber-wound cylindrical shell; Step 6: For the actual hybrid fiber-wound cylindrical shell to be evaluated, its real parameter values are obtained by physical measurement means, and the attenuation coefficient of the shell is obtained by substituting the regression formula obtained in step four, and then the nonlinear ultimate bearing capacity of the shell is predicted. ​​ 2. The method of designing a composite shell for a deep-sea pressure- resistant device according to claim 1, wherein In step 1, the stiffness matrix includes an in-plane stiffness matrix, a coupling stiffness matrix, and a bending stiffness matrix; the critical buckling pressure of the shell is represented as: ； wherein the elements of the coefficient matrix contain an in-plane stiffness matrix , a coupling stiffness matrix , and a bending stiffness matrix ; The stiffness matrix is ​​calculated using classical laminate theory: ； wherein, is the first is the distance from the layer to the neutral plane of the laminate, is the off-axis stiffness coefficient of the kth layer, determined from the winding angle and the engineering constants of the material, expressed as: ； wherein , , , , , , is the modulus of elasticity of the material in the main direction, i = 1, 2, is the Poisson's ratio.

3. The method of designing a deep-sea pressure-resistant device composite shell according to claim 1, wherein, In step 2, the initial out-of-roundness amplitude defined as the difference between the maximum and minimum radial directions of the housing surface to the nominal total wall thickness is expressed as: ； This parameter reflects the degree of non-circularity of the shell cross-section caused by mold deformation, tension fluctuations, and residual stress release during the winding and curing process; The wall thickness deviation coefficient B is defined as the difference between the maximum wall thickness and the minimum wall thickness in the same circumferential section to the average wall thickness is expressed as: ； The maximum value of multiple axial test sections is taken as the shell wall thickness deviation coefficient to conservatively characterize the influence of circumferential wall thickness non-uniformity on local stiffness. Hybrid fiber ratio defined as the total thickness of the high modulus fiber layer as a percentage of the total shell thickness is expressed as: ； This parameter controls the ratio of shell bending stiffness to tensile stiffness. Ratio of the modulus of elasticity of the inner fiber to the modulus of elasticity of the outer fiber Defined as the ratio of the longitudinal tensile modulus of a single ply of high modulus fiber to the longitudinal tensile modulus of a single ply of low modulus fiber and is expressed as: ； The parameter represents the stiffness matching degree of the materials on both sides of the hybrid interface, which has a significant influence on the interlaminar stress distribution and progressive damage evolution, The larger the value is, the more significant the stiffness difference between the two kinds of fibers is.

4. The method of claim 1, wherein, In step 4, the prediction formula is expressed as: ； wherein , Each item is the regression coefficient, and the significance of each item is tested by analysis of variance. The prediction accuracy of the model is evaluated by using the reserved validation samples to ensure that the determination coefficient and the prediction error is less than .

5. The method of designing a deep-sea pressure-resistant device composite shell according to claim 1, wherein, In step 5, the relative buckling load RP is expressed as: ； wherein Bcfor hybrid shell buckling load, Bcfor full low modulus fiber shell buckling load; The relative fiber cost RC is expressed as: ； wherein is the fiber volume fraction, is the fiber volume fraction, is the fiber density, is the unit price; subscript and represent high modulus and low modulus fibers, respectively; The marginal performance-cost ratio (MPR) is expressed as: ； This indicator quantifies the increase in relative carrying capacity obtained for each additional unit of relative cost.

6. A pressure hull designed by the method of any one of claims 1 to 5, wherein: The shell is a hollow cylinder, and its core load-bearing component is a composite material shell (3). The composite material shell (3) includes a three-layer structure from the inside to the outside, wherein the inner and outer layers are composite material layer one (301) made of high-performance carbon fiber, and the middle layer is composite material layer two (302) made of basalt fiber.

7. The deep-sea pressure-resisting apparatus composite pressure hull according to claim 6, characterized by: The thickness of the inner and outer composite material layer 1 (301) is 0.5-0.6 mm, and the thickness of the middle composite material layer 2 (302) is 1.1-1.2 mm.

8. The deep-sea pressure-resisting device composite pressure hull according to claim 6, characterized in that: The outer periphery of the core mold (4) is covered with a composite material shell (3). The core mold (4) is a polytetrafluoroethylene tube. The composite material shell (3) is wound around the outer periphery of the core mold (4) to form an integral structure. The two ends of the composite material shell (3) are sealed with epoxy resin glue (5) and a sealing ring (2) is provided at the joint between the sealing head (1) and the composite material shell (3).

9. The method of claim 8, wherein the method further comprises the step of: Includes the following steps: ​ Step 1: Select a polytetrafluoroethylene tube with an outer diameter that meets the design requirements as the winding mandrel (4) as the inner lining of the shell, inspect its outer surface to ensure it is smooth and free of defects, and clean it with solvent to remove contaminants; Step 2: Based on the performance requirements and economic constraints of the target pressure hull, determine the final layup structure, including the number of inner and outer carbon fiber layers, the number of intermediate basalt fiber layers, and the fiber winding angle of each layer. Subsequently, based on the selected material and layup structure, the winding process parameters are determined, including the winding tension of the fiber bundle, winding speed, impregnation tank temperature, doctor blade gap, and the length of the transition and effective sections and the number of nodes in the winding process. Step 3: Install the prepared mandrel (4) on the four-axis CNC winding machine and import the winding program determined in Step 2; Step 4: After the winding is completed, the entire mandrel assembly with composite layup is transferred to a rotary curing oven. The curing program is started, and the temperature is increased from room temperature to 80°C at a rate of 2°C / min. The temperature is then maintained at this temperature for 2-3 hours to allow the resin to initially gel. Subsequently, the temperature is increased to 110°C and maintained for 3-4 hours to ensure that the resin system is completely cured. The entire curing process is carried out while the mandrel is continuously rotating to prevent the resin from flowing under gravity and causing uneven distribution. After the curing program is completed, the sample is allowed to cool naturally to room temperature with the oven. Step 5: Use cutting equipment to remove the transition sections at both ends of the cylindrical shell caused by the winding process, retaining the effective middle section with uniform structure. Clean the outer surface of the effective section shell to remove processing residues, and then place it at room temperature to dry thoroughly. Step 6: According to the application requirements, use high-performance epoxy resin adhesive (5) to seal and install the upper and lower end caps (1) to both ends of the shell to form a complete pressure-resistant compartment.

10. The method of claim 9, wherein the method further comprises: In step two, the single-bundle winding tension of carbon fiber is 20-25 N, the double-bundle winding tension of basalt fiber is 40-50 N, and the temperature of the impregnation tank is 40℃-50℃. ​ In step three, the inner carbon fiber layer is first laid. Using carbon fiber bundles, the inner carbon fiber composite material layer is wound and laid on the mandrel to the set thickness according to the preset parameters. After the inner carbon layer is completed, it is replaced with basalt fiber bundles, and the parameters are adjusted to the corresponding set values. One or more layers of basalt fiber composite material are continuously wound and laid on the wound inner carbon layer to form the middle main body layer of the shell to the set thickness. After the middle basalt layer is completed, it is replaced with carbon fiber bundles again, the corresponding parameters are restored, and one or more layers of carbon fiber composite material are wound and laid on the outer layer to form the outer protective layer.

Images