Method for determining performance index of light alloy material of large cylindrical shell structure in deep sea

Abstract

The application discloses a method for determining performance indexes of lightweight alloy materials of large deep-sea cylindrical shell structures, and comprises the following steps: 1) researching the deformation field evolution law of the cylindrical shell structure to obtain a strain expression of the cylindrical shell structure in a deformation-instability process; 2) researching the fracture failure mode of the cylindrical shell structure to obtain an expression of a local instability mode of the cylindrical shell structure; 3) confirming that the maximum relative deformation amount of the main shell-rib between adjacent ribs is a structural failure deformation characteristic parameter; 4) deducing the corresponding relationship between the maximum relative deformation amount of the main shell-rib between adjacent ribs and the plastic performance of the material; and 5) combining a structure fracture factor, and obtaining a material plastic performance index determination model according to the criterion that the structure does not fracture before instability collision occurs, so that the material plastic performance index determination model is used to quickly determine the performance indexes of the lightweight alloy materials.

Description

Technical Field

[0001] This invention relates to the field of deep-sea pressure-resistant structure technology, specifically to a method for determining the performance indicators of lightweight alloy materials for large deep-sea cylindrical shell structures. Background Technology

[0002] With the increasing demand for deep-sea resource development, the diving depth of large-scale deep-sea equipment is getting greater and greater. Deep-sea pressure-resistant structures are key structures to ensure the safety of personnel and maintain the normal operation of core equipment. Among them, the materials used in deep-sea pressure-resistant structures are the key factors to improve the pressure resistance of deep-sea pressure-resistant structures.

[0003] With the development of materials technology, lightweight alloys, which have advantages such as low density, high strength, good creep resistance and corrosion resistance, have a better structural buoyancy ratio than high-strength steel structures. In recent years, they have been widely used in the design and construction of pressure-bearing structures for deep-sea manned submersibles and large unmanned underwater vehicles.

[0004] Compared to high-strength steel, lightweight alloy structures are more prone to fracture or fragmentation due to differences in alloy crystal structure and microstructure. Since the load-bearing capacity and failure modes of lightweight alloy structures are closely related to material performance parameters, and currently lacking reasonable methods for determining material performance indicators in the design and evaluation of large lightweight pressure-resistant structures, it is impossible to predict and verify the pressure resistance of the designed large lightweight pressure-resistant structures. Summary of the Invention

[0005] The purpose of this invention is to provide a method for determining the performance indicators of lightweight alloy materials for large deep-sea cylindrical shell structures. By establishing a model for determining the plasticity performance indicators of materials, the performance indicators of lightweight alloy materials can be determined, thereby solving the technical problems existing in the prior art.

[0006] To solve the above-mentioned technical problems, the present invention specifically provides the following technical solution:

[0007] A method for determining the performance indicators of lightweight alloy materials for deep-sea large cylindrical shell structures is proposed, which involves establishing a model for determining the plasticity performance indicators of the materials to determine the performance indicators of the lightweight alloy materials.

[0008] The steps for establishing a model to determine the plasticity property index of materials are as follows:

[0009] Step 1) Study the evolution law of the deformation field of the cylindrical shell structure to obtain the strain expression of the cylindrical shell structure during the deformation-instability process;

[0010] Step 2) Based on the strain of the cylindrical shell structure, study the fracture failure mode of the cylindrical shell structure to obtain the number of local instability modes of the cylindrical shell structure;

[0011] Step 3) Confirm that the maximum relative deformation between the main shell and the ribs between adjacent ribs is the structural failure deformation characterization parameter;

[0012] Step 4) Derive the correspondence between the maximum relative deformation of the main shell and ribs between adjacent ribs and the plasticity of the material;

[0013] Step 5) Combining the geometric characteristics of structural fracture and the structural fracture factor, and taking the absence of fracture before structural instability collision as the criterion, a model for determining the material plasticity performance index is obtained.

[0014] Step 6) Perform numerical simulation based on the given structural and material parameters to obtain the material plasticity performance index, and verify the model based on the obtained material plasticity performance index.

[0015] Furthermore, in step 1), by studying the evolution law of the deformation field of the cylindrical shell structure, the expression for the strain on the non-mid-surface of the cylindrical shell structure is obtained:

[0016] (1);

[0017] (2);

[0018] (3);

[0019] in, , and These represent the axial strain, circumferential strain, and shear strain on the non-mid-surface of the cylindrical shell structure, respectively. , and θ represents the axial strain, circumferential strain, and shear strain of the mid-surface of the cylindrical shell structure, respectively, where x is the generatrix direction and θ is the circumferential direction.

[0020] Furthermore, in step 1), during the deformation of the cylindrical shell structure, the cylindrical shell structure will become unstable. The expression for the radial deflection after the cylindrical shell structure becomes unstable is:

[0021] (4);

[0022] in, This represents the radial deflection after the cylindrical shell structure becomes unstable. The longitudinal length of the cylindrical shell. Let be the displacements at both ends of the cylindrical shell corresponding to the modal number m. For the deflection corresponding to the modal number m, The amplitude of the relative displacement curve corresponding to the modal number m is the maximum deformation of the main shell relative to the rib between adjacent ribs.

[0023] Furthermore, in step 2), because the plastic strain is much greater than the elastic strain during the nonlinear large deformation of the cylindrical shell structure, the equivalent plastic strain expression for the cylindrical shell structure is:

[0024] (5);

[0025] Using the material's plastic strain as the criterion for fracture failure, at this time Where h is the shell thickness; therefore, the expression for the local instability fracture of a cylindrical shell structure is:

[0026] (6).

[0027] Furthermore, in step 4), we obtain from formulas (1) to (6):

[0028] (7);

[0029] in, Let be the material fracture strain, h be the principal shell thickness, L be the distance between adjacent ribs, and n be the number of circumferential instability deformation modes. Pi The amplitude of the relative displacement curve corresponding to the modal number m is the maximum deformation of the main shell relative to the rib between adjacent ribs.

[0030] Furthermore, in step 5), the structural fracture factor is:

[0031] (8);

[0032] in, This refers to the thickness of the ribs;

[0033] make The model for determining the plasticity properties of materials is obtained as follows:

[0034] (9).

[0035] Compared with the prior art, the present invention has the following advantages:

[0036] The present invention provides a method for determining the performance indicators of lightweight alloy materials for large deep-sea cylindrical shell structures. By studying the correspondence between strain and material plasticity during the deformation process of lightweight cylindrical shell structures, a model for determining the plasticity indicators of materials is established. This model is then used to quickly determine the performance indicators of lightweight alloy materials. Attached Figure Description

[0037] To more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are merely exemplary, and those skilled in the art can derive other embodiments based on the provided drawings without creative effort.

[0038] Figure 1 A schematic diagram showing the relationship between the load-bearing capacity and material strength of a ring-ribbed reinforced structure;

[0039] Figure 2 This is a geometric schematic diagram of the main shell-rib structure in a cylindrical shell structure;

[0040] Figure 3 This is a schematic diagram of the relative deformation between the main shell and the ribs in a cylindrical shell structure.

[0041] Figure 4 This is a schematic diagram showing the circumferential mode number and relative displacement under structural failure modes;

[0042] Figure 5 A graph showing the relationship between structural fracture characterization parameters and material plasticity properties;

[0043] Figure 6 This is a graph showing the relationship between the structural fracture factor and the material's plastic properties. Detailed Implementation

[0044] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0045] This invention provides a method for determining the performance indicators of lightweight alloy materials for large deep-sea cylindrical shell structures. It mainly involves studying the evolution law of the deformation field of cylindrical shell structures, which reveals that cylindrical shell structures undergo three stages during pressure resistance: deformation, instability, and failure. By studying the correspondence between strain and material plasticity during the deformation process of lightweight cylindrical shell structures, a model for determining the plasticity indicators of materials is established to determine the performance indicators of lightweight alloy materials.

[0046] like Figure 1 As shown, the load-bearing capacity increases proportionally with the increase of the material's yield strength. However, when the yield strength reaches a certain critical value, the structural load-bearing capacity no longer increases, but is controlled by the structural stiffness. The corresponding critical value of the material's yield strength is determined by the specific structural parameters.

[0047] This invention provides a specific implementation method for establishing a model to determine the plasticity performance index of materials. The derivation process of the formulas involved is mainly based on theoretical analysis. The specific steps are as follows:

[0048] Step 1) Study the evolution law of the deformation field of the cylindrical shell structure to obtain the strain expression of the cylindrical shell structure in the deformation-instability process.

[0049] When a cylindrical shell is subjected to external loads (such as axial pressure, torque, lateral pressure, etc.), it will deform; at this stage, its deformation is analyzed based on the basic assumptions and theories of elasticity.

[0050] Obtain the expression for the strain on the non-mid-surface of a cylindrical shell structure:

[0051] (1);

[0052] (2);

[0053] (3);

[0054] in, , and These represent the axial strain, circumferential strain, and shear strain on the non-mid-surface of the cylindrical shell structure, respectively. , and θ represents the axial strain, circumferential strain, and shear strain of the mid-surface of the cylindrical shell structure, respectively, where x is the generatrix direction and θ is the circumferential direction.

[0055] As the external load increases, when a certain critical value is reached, the equilibrium state of the cylindrical shell will change from stable to unstable. This phenomenon is called instability. When instability occurs, the deformation of the cylindrical shell will suddenly increase and no longer follow the laws of the elastic deformation stage.

[0056] Specifically, the instability modes can be analyzed using linear stability theory. For example, in the case of axial compressive instability, the instability modes may manifest as multiple wavy deformations in the circumferential direction of the cylindrical shell, and the complete wave number is the circumferential mode number. This deformation mode leads to a significant change in the stress distribution of the cylindrical shell.

[0057] In this embodiment, the radial deflection expression of the cylindrical shell structure after instability during deformation is as follows:

[0058] (4);

[0059] in, This represents the radial deflection after the cylindrical shell structure becomes unstable. The longitudinal length of the cylindrical shell. Let represent the displacement at both ends of the cylindrical shell. For the deflection corresponding to the modal number m, The amplitude of the relative displacement curve corresponding to the modal number m is the maximum deformation of the main shell relative to the rib between adjacent ribs.

[0060] Furthermore, the instability phenomenon can be verified by gradually increasing the external pressure and observing the deformation of the cylindrical shell; when the pressure approaches the critical value, the cylindrical shell may exhibit slight radial contraction deformation, and once the critical pressure is exceeded, the radial deformation will increase rapidly.

[0061] Failure of cylindrical shell structures mainly includes material failure and structural failure.

[0062] Material failure typically occurs when a material reaches its ultimate strength or fracture strain. For example, when stress exceeds the material's yield strength, plastic deformation begins, and further stress increases until the ultimate strength is reached, leading to fracture. Structural failure, on the other hand, may be due to excessive deformation exceeding the structure's design limits, or buckling instability causing the structure to malfunction.

[0063] Step 2) Based on the strain of the cylindrical shell structure, study the fracture failure mode of the cylindrical shell structure to obtain the expression of the local instability mode of the cylindrical shell structure.

[0064] During the nonlinear large deformation of a cylindrical shell structure, the plastic strain is much greater than the elastic strain; therefore, the equivalent plastic strain expression for a cylindrical shell structure is:

[0065] (5);

[0066] Using the material's plastic strain as the criterion for fracture failure, at this time Where h is the shell thickness; therefore, the expression for the local instability failure of the cylindrical shell structure is:

[0067] (6).

[0068] Step 3) The structural failure of the cylindrical shell structure is studied, and the maximum relative deformation between the main shell and the ribs between adjacent ribs is confirmed as the deformation characterization parameter for structural failure.

[0069] like Figure 2 and Figure 3 As shown, in a cylindrical shell structure, the ribs are components that enhance structural stability and are closely connected to the main shell. The main shell bears external loads and transmits the force to the ribs. When subjected to external loads, there is a difference in the degree of deformation between the ribs and the middle of the span. This difference is the relative deformation between the main shell and the ribs.

[0070] The coordinated work of the main shell and ribs is crucial for the stability of a cylindrical shell structure, and the relative deformation directly reflects their synergy. If the relative deformation is within a reasonable range, it indicates that the main shell and ribs can effectively resist external loads together, and the structure is in good working condition.

[0071] Overall deformation parameters (such as axial shortening and radial shrinkage in cylindrical shell structures) primarily reflect the overall deformation of the structure. However, in many cases, even if the overall deformation is within acceptable limits, problems may have already occurred at the local shell-rib connection points.

[0072] The relative deformation focuses more on local coordinated deformation and can reflect the adverse effects of insufficient local stiffness of the structure. Therefore, the maximum relative deformation between the main shell and the rib between adjacent ribs is used as a parameter to characterize the structural failure deformation.

[0073] Step 4), derive the correspondence between the maximum relative deformation of the main shell and ribs between adjacent ribs and the plasticity of the material.

[0074] In cylindrical shell structures, the circumferential modes of the main shell and ribs during deformation represent different displacement patterns. For example, the main shell undergoes periodic wavy deformation (circumferential modes) in the circumferential direction, while the ribs, due to their higher stiffness, deform relatively less. This difference causes the relative deformation between the main shell and ribs to change within a complete modal cycle. Therefore, the greatest difference between the main shell and rib deformation occurs at the trough of the mode, meaning the relative deformation between the main shell and ribs reaches its maximum value.

[0075] From formulas (1) to (6), we get:

[0076] (7);

[0077] in, Let be the material fracture strain, h be the principal shell thickness, L be the distance between adjacent ribs, and n be the number of circumferential instability deformation modes. Pi The amplitude of the relative displacement curve corresponding to the modal number m (the maximum deformation of the main shell relative to the rib between adjacent ribs).

[0078] Step 5) Combining the geometric characteristics and fracture factor of structural fracture, and taking the absence of fracture before structural instability collision as the criterion, a model for determining the plastic performance index of materials is obtained.

[0079] The geometric characteristics of structural fracture can include the length, width, and depth of the crack, as well as the shape of the crack (such as straight, bifurcated, etc.); the fracture factor is a parameter that comprehensively considers multiple factors to measure the probability of structural fracture.

[0080] In this embodiment, the structural fracture factor is:

[0081] (8);

[0082] in, This refers to the thickness of the ribs.

[0083] Based on the criterion that the structure does not fracture before the collision causes instability, a method for determining the material plasticity performance index that meets the structural safety requirement is proposed: the structural fracture factor must be 0.

[0084] Therefore, let The model for determining the plasticity properties of materials is obtained as follows:

[0085] (9).

[0086] Step 6) Perform numerical simulation based on the given structural and material parameters to obtain the material plasticity performance index, and verify the model based on the obtained material plasticity performance index.

[0087] For the specific structural parameters that indicate local instability and failure, L=160mm, R=650mm, h=18.85mm, and t can be selected here. w =13mm.

[0088] According to the relationship between formula (9) and the circumferential mode number n, as follows Figure 4 As shown, there is an extreme value when the modal number n=12, and the corresponding material performance parameters are as follows: 0.30.

[0089] The simulation results show that the error is within an acceptable range, indicating that the established model for determining the plasticity properties of materials has high accuracy and reliability.

[0090] For detailed simulation results, please see [link / details]. Figure 5 and Figure 6 As shown in the figure:

[0091] The theoretically predicted material plasticity (fracture strain) is approximately 0.30; Figure 6 It can be seen that the material's plasticity property index (fracture strain) obtained from the numerical simulation is approximately 0.32. The error between the two is less than 7%, and the theoretical prediction is slightly smaller than the numerical simulation, which is consistent with the conclusion that theoretical predictions tend to be conservative.

[0092] It is worth noting that this prediction corresponds to the material properties during the dynamic process of structural instability and fracture, specifically at a strain rate of 200 s⁻¹. -1 The fracture strain of the material can be further inverted to the fracture strain under quasi-static conditions based on the material strain rate effect.

[0093] The above embodiments are merely exemplary embodiments of this application and are not intended to limit this application. The scope of protection of this application is defined by the claims. Those skilled in the art can make various modifications or equivalent substitutions to this application within its substance and scope of protection, and such modifications or equivalent substitutions should also be considered to fall within the scope of protection of this application.

Claims

1. A method for determining the performance index of a lightweight alloy material for a deep-sea large cylindrical shell structure, characterized in that, The performance indicators of lightweight alloy materials are determined by establishing a model to determine the plasticity performance indicators of the materials. The steps for establishing a model to determine the plasticity property index of materials are as follows: Step 1) Study the evolution law of the deformation field of the cylindrical shell structure to obtain the strain expression of the cylindrical shell structure during the deformation-instability process; Step 2) Based on the strain of the cylindrical shell structure, study the fracture failure mode of the cylindrical shell structure to obtain the mode number when the cylindrical shell structure is locally unstable; Step 3) Confirm that the maximum relative deformation between the main shell and the ribs between adjacent ribs is the structural failure deformation characterization parameter; Step 4) Derive the correspondence between the maximum relative deformation of the main shell and ribs between adjacent ribs and the plasticity of the material; Step 5) Combining the geometric characteristics of structural fracture and the structural fracture factor, and taking the absence of fracture before structural instability collision as the criterion, a model for determining the material plasticity performance index is obtained. Step 6) Perform numerical simulation based on the given structural and material parameters to obtain the material plasticity performance index, and verify the model based on the obtained material plasticity performance index.

2. The method of claim 1, wherein the method is characterized by: In step 1), by studying the evolution law of the deformation field of the cylindrical shell structure, the expression for the strain on the non-mid-surface of the cylindrical shell structure is obtained: （1）； （2）； （3）； wherein, , and are the axial strain, the hoop strain and the shear strain of the non-mid-surface of the cylindrical shell structure, respectively; , and are the axial strain, the hoop strain and the shear strain of the mid-surface of the cylindrical shell structure, respectively, x is the generatrix direction, θ is the hoop direction, is the radial deflection of the cylindrical shell structure after instability.

3. The method of claim 1, wherein the method is characterized by: In step 1), during the deformation of the cylindrical shell structure, the structure will become unstable. The expression for the radial deflection after the cylindrical shell structure becomes unstable is: （4）； wherein, is the radial deflection of the cylindrical shell after instability, is the longitudinal length of the cylindrical shell, is the displacement of the cylindrical shell at both ends for the corresponding modal number m, is the deflection for the corresponding modal number m, is the relative displacement curve amplitude for the corresponding modal number m, i.e. the maximum deformation of the main shell between adjacent ribs, x is the generatrix direction, Θ is the hoop direction, and n is the hoop instability deformation modal number.

4. The method of claim 1, wherein the method is characterized by: In step 2), because the cylindrical shell structure undergoes large nonlinear deformation, the plastic strain is much greater than the elastic strain; therefore, the equivalent plastic strain expression for the cylindrical shell structure is: （5）； With the plastic strain of the material as the fracture failure criterion, at this time h is the shell thickness; , and are the axial strain, hoop strain and shear strain, respectively, of the non-mid-plane of the cylindrical shell structure; Therefore, the expression for the local instability criterion of a cylindrical shell structure is: （6）； Strain at which the material breaks.

5. The method of claim 1, wherein the method is characterized by: In step 4), we obtain the following from formulas (1) to (6): （7）； wherein, is the material fracture strain, h is the main shell thickness, L is the adjacent frame spacing, n is the number of circumferential buckling modes, is the circle constant, is the relative displacement curve amplitude for the corresponding mode number m, i.e. the maximum deformation of the main shell between adjacent frames.

6. The method of claim 1, wherein the method is characterized by: In step 5), the structural fracture factor is: （8）； wherein is the rib thickness; make The model for determining the plasticity properties of materials is obtained as follows: （9）； This represents the amplitude of the relative displacement curve corresponding to the modal number m, i.e., the maximum deformation of the main shell relative to the ribs between adjacent ribs. Where L is the shell thickness and L is the distance between adjacent ribs. Let π be the mathematical constant, and n be the number of circumferential modes. This represents the fracture strain of the material.

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