An optimization method and system for improving the connection performance of a continuous fiber reinforced metal matrix composite thin-walled pipe

Abstract

The present application belongs to the technical field of composite material connection, and specifically relates to an optimization method and system for improving the connection performance of continuous fiber reinforced metal matrix composite thin-walled tube, comprising the following steps: constructing an asymptotic damage constitutive relation based on Hashin failure criterion, traction-separation law and continuous stiffness degradation; establishing a finite element analysis model of the thin-walled tube connection structure under uniaxial tensile load; taking the connection strength, connection length and tube diameter as design variables, obtaining the influence law of each variable on the bearing capacity; extracting stress, strain and damage cloud pictures, analyzing the asymptotic failure process and damage mode, and optimizing the matching relationship of connection strength, connection length and inner diameter. The present application establishes the correlation between connection performance and failure mode, solves the problems of insufficient connection strength, poor stability and poor bearing capacity of the thin-walled tube truss structure, significantly shortens the research and development cycle, reduces the test cost, and provides theoretical guidance for the design of composite material thin-walled tube connection structure.

Description

Technical Field

[0001] This invention belongs to the field of composite material joining technology, specifically an optimized method and system for improving the joining performance of thin-walled tubes made of continuous fiber reinforced metal matrix composites. Background Technology

[0002] With the rapid development of aerospace technology, lightweight design of spacecraft, communication satellites, solar sails, and other space vehicles has become one of the key technologies to meet the requirements. Truss structures are widely used in this field due to their simple structural form, reasonable load distribution, and high material utilization rate; their main stress characteristic is bearing axial forces. Continuous fiber reinforced metal matrix composites, due to their high specific strength, high specific modulus, low density, and excellent unidirectional mechanical properties, are an ideal alternative to commonly used materials such as aluminum alloys and titanium alloys in truss structures, significantly reducing structural weight and saving costs.

[0003] Compared to traditional materials, the theoretical research and engineering applications of composite trusses remain relatively limited, particularly in terms of systematic analysis of their connection performance. However, the connection design in composite trusses is a crucial factor affecting the overall structural performance, directly determining the structure's stability and load-bearing capacity. In practical engineering applications, trusses are often formed by welding, bolting, or adhesive bonding of numerous thin-walled tubes. These connections often face challenges such as insufficient shear resistance, susceptibility to failure, and difficulty in guaranteeing reliability. Therefore, the widespread application of composite trusses in aerospace and other fields remains significantly constrained.

[0004] Publication No. CN118744568A proposes a SiC fiber-reinforced metal matrix composite pipe structure and its preparation method, focusing on improving the load-bearing capacity and reducing the weight of the structural components through the preparation process, without addressing the optimization design of the SiC fiber-reinforced metal matrix composite pipe structure. Publication No. CN108115944A proposes a connection method between composite material pipes and metal pipes, addressing the connection problem of dissimilar components, without addressing the connection problem between composite material pipes. Publication No. CN112983949A proposes a carbon fiber composite pipe connection structure and connection method, mainly solving the stress concentration problem of bolted connections to improve the reliability of the connection, without addressing the optimization design of the connection performance of composite material pipes.

[0005] Existing technologies mainly focus on the research of preparation and connection methods for thin-walled tubes made of composite materials. However, systematic enhancement schemes for the performance of connection structures are still lacking, and a clear correlation between connection performance and failure modes has not yet been established, making it difficult to form a complete design and optimization system. Summary of the Invention

[0006] The purpose of this invention is to provide an optimized method and system for improving the connection performance of thin-walled tubes in continuous fiber reinforced metal matrix composites. This method improves the stress state of the thin-walled tube connection joints, enhances the load-bearing capacity and stability of the thin-walled tube connection structure, and increases the overall failure limit strength of the connection components.

[0007] The technical solution adopted by the present invention to achieve the above objectives is: an optimized method for improving the connection performance of thin-walled tubes of continuous fiber-reinforced metal matrix composites, comprising the following steps:

[0008] Step S1: Determine the damage initiation of the fiber and matrix based on the failure criteria, use a bilinear cohesive force model based on the traction-separation law to describe the constitutive relationship of the cohesive element, and introduce a continuous stiffness degradation rule to simulate damage evolution, thereby jointly constructing the asymptotic damage constitutive relationship of the continuous fiber reinforced metal matrix composite.

[0009] Step S2: Use finite element software to establish a finite element analysis model of the continuous fiber-reinforced metal matrix composite thin-walled tube connection structure under uniaxial tensile load;

[0010] Step S3: Using connection strength, connection length, and thin-walled tube inner diameter as design variables, obtain the influence law of each variable on the load-bearing capacity of the connection structure through parametric simulation calculation, and determine the critical parameter value that makes the load-bearing capacity of the structure tend to saturate.

[0011] Step S4: Extract stress cloud diagrams, strain cloud diagrams, and damage cloud diagrams under different design variables, analyze the asymptotic failure process and damage mode of the connection structure, and optimize the matching relationship between connection strength, connection length, and inner diameter based on the analysis results until the structural bearing capacity meets the preset strength design requirements.

[0012] Before performing step S1, the process also includes: establishing the linear elastic stress-strain constitutive relationship of the undamaged state of the continuous fiber reinforced metal matrix composite material;

[0013] The linear elastic stress-strain constitutive relation of the continuous fiber reinforced metal matrix composite in the undamaged state is as follows:

[0014]

[0015] in, These are stress components in different directions. Indicates the stiffness coefficient. These represent strain components in different directions.

[0016] In step S1, the determination of the damage initiation between the fiber and the matrix based on failure criteria specifically involves:

[0017] The failure criteria include four damage initiation criteria, namely:

[0018] when At this time, it is the fiber tensile damage mode, that is:

[0019]

[0020] when At this time, it is the fiber compression damage mode, that is:

[0021]

[0022] when At this time, the matrix tensile damage mode is adopted, that is:

[0023]

[0024] when At that time, the matrix compression damage mode is as follows:

[0025]

[0026] in, These are stress components in different directions; , , and These represent longitudinal tensile strength, longitudinal compressive strength, transverse tensile strength, and transverse compressive strength, respectively. , and Expressed as shear strength; , , and This represents the damage initiation parameter under the corresponding mode, with the initial damage value being 0; when At that time, the damage began to appear.

[0027] In step S1, the constitutive relation of the cohesive unit is described using a bilinear cohesive force model based on the traction-separation law, namely:

[0028]

[0029] in, Normal traction force; and It is the tangential traction force; This is the normal displacement; and Represents tangential displacement; For elastic stiffness in different directions;

[0030] The damage initiation criterion for cohesive elements is as follows:

[0031]

[0032] in , and These are the stress components in three directions.

[0033] The introduced continuous stiffness degradation rule is specifically as follows:

[0034] A damage variable D is introduced to quantitatively characterize the nonlinear degradation process of cohesive elements from damage initiation to complete failure. The damage variable D is expressed as:

[0035]

[0036] in, Indicates the equivalent displacement. Represented as the maximum equivalent displacement, This represents the equivalent displacement when the system completely fails.

[0037] In step S2, the finite element analysis model of the continuous fiber reinforced metal matrix composite thin-walled tube connection structure includes: an outer thin-walled tube, an inner thin-walled tube, and a zero-thickness cohesive interface between the two, and an end face surface force load is applied.

[0038] A finite element analysis model of the thin-walled tube connection structure was established using finite element software, specifically as follows:

[0039] Step S2-1: Construct a geometric model of the connection structure formed by the outer thin-walled tube and the inner thin-walled tube; wherein, the composite material thin-walled tube is composed of an outer sheath, a composite material core and an inner sheath;

[0040] Step S2-2: Use zero-thickness cohesive elements to simulate the connection interface between the outer thin-walled tube and the inner thin-walled tube;

[0041] Step S2-3: Assign solid element meshes to the sheath and composite core, and cohesive element meshes to the cohesive elements;

[0042] Step S2-4: Set the analysis step to a dynamic analysis step to simulate a quasi-static tensile process;

[0043] Step S2-5: Fix the end face of the outer thin-walled tube and apply a displacement load to the end face of the inner thin-walled tube.

[0044] Step S3 includes the following steps:

[0045] Step S3-1: Select multiple different connection strength values, multiple different connection length values, and multiple different thin-walled tube inner diameter values ​​as design variables;

[0046] Step S3-2: Extract the load-displacement curves under each parameter combination through parametric simulation calculation;

[0047] Step S3-3: Based on the load-displacement curve, obtain the law that the bearing capacity first increases and then stabilizes with the increase of connection strength, increases and then tends to saturate with the increase of connection length, and increases monotonically with the increase of inner diameter. Take the fact that the structural bearing capacity no longer increases significantly with the increase of parameters as the critical criterion, determine the critical parameter value that makes the structural bearing capacity tend to saturate, and then determine the optimization parameter range.

[0048] Step S4 includes the following steps:

[0049] Step S4-1: Extract the axial stress cloud map and damage cloud map of the inner and outer thin-walled tubes under different connection strengths, read the maximum axial stress value of the inner and outer thin-walled tubes respectively, and compare the damage distribution area and damage variable size of the cohesive unit and the composite core in the damage cloud map; determine whether the failure mode is caused by insufficient strength of the cohesive unit or insufficient transverse strength of the composite material.

[0050] Step S4-2: Extract stress distribution cloud maps of thin-walled tube connection structures under different connection lengths, identify stress concentration areas at the ends of the connection interfaces, and determine whether the effective force transmission area is sufficient based on the ratio of peak stress to average stress in the stress concentration areas.

[0051] Step S4-3: Extract load-displacement curves for different inner diameters, calculate the slope of each curve in the elastic and plastic segments, and compare the magnitude of the load values ​​under the same displacement to analyze the contribution of cross-sectional area to bearing capacity.

[0052] Step S4-4: Based on the analysis results of steps S4-1 to S4-3, optimize the thin-walled tube connection structure to fully utilize the load-bearing capacity of the composite material.

[0053] In step S4-4, based on the analysis results of steps S4-1 to S4-3, the following steps are performed:

[0054] a) When the failure is determined to be mainly due to insufficient strength of the cohesive unit, increase the connection strength to above the critical value that makes the load-bearing capacity tend to saturate;

[0055] b) When the failure is determined to be mainly due to insufficient transverse strength of the composite material, increase the connection length to above the critical value that makes the load-bearing capacity tend to saturate;

[0056] c) When the cross-sectional area does not meet the set requirements for load-bearing capacity, increase the inner diameter of the thin-walled tube within the allowable range of structural space.

[0057] An optimization system for improving the connection performance of thin-walled tubes made of continuous fiber-reinforced metal matrix composites, for performing the optimization method, comprising:

[0058] The constitutive relation construction module is used to establish the linear elastic stress-strain constitutive relation of continuous fiber reinforced metal matrix composites in the undamaged state; and to determine the damage initiation of the fiber and matrix based on the failure criterion. It adopts a bilinear cohesive force model based on the traction-separation law to describe the constitutive relation of the cohesive element, and introduces a continuous stiffness degradation rule to simulate damage evolution, thereby constructing the asymptotic damage constitutive relation of the composite material.

[0059] The finite element modeling module is used to establish a finite element analysis model of a continuous fiber-reinforced metal matrix composite thin-walled tube connection structure under uniaxial tensile load. The finite element analysis model includes an outer thin-walled tube, an inner thin-walled tube, and a zero-thickness cohesive element between them, and applies end face surface force load.

[0060] The parametric analysis module is used to obtain the influence of each variable on the load-bearing capacity of the thin-walled tube connection structure through parametric simulation calculation, using connection strength, connection length and thin-walled tube inner diameter as design variables, and to determine the critical parameter value that makes the load-bearing capacity of the structure tend to saturate.

[0061] The optimization decision module is used to extract stress cloud maps, strain cloud maps, and damage cloud maps under different design variables, analyze the asymptotic failure process and damage mode of thin-walled tube connection structures, and optimize the matching relationship between connection strength, connection length, and inner diameter based on the analysis results until the structural bearing capacity meets the preset strength design requirements.

[0062] The present invention has the following beneficial effects and advantages:

[0063] 1. This invention provides an optimization method for improving the connection performance of thin-walled tubes made of continuous fiber reinforced metal matrix composites. By establishing a finite element analysis model of the connection structure of thin-walled tubes made of continuous fiber reinforced metal matrix composites under uniaxial tensile load, the connection strength, connection length and tube diameter are accurately predicted to affect the connection performance of the thin-walled tube structure. Based on a multi-objective optimization method, the connection performance of thin-walled tubes made of continuous fiber reinforced metal matrix composites is significantly improved.

[0064] 2. This invention can effectively solve the problems of high cost and long cycle in the preparation and experimental research of thin-walled tubes of continuous fiber reinforced metal matrix composites, and also optimizes the problem of overall component failure caused by insufficient connection strength of thin-walled tubes of continuous fiber reinforced metal matrix composites. Attached Figure Description

[0065] Figure 1 This is a schematic flowchart of an optimized method for improving the connection performance of thin-walled tubes made of continuous fiber-reinforced metal matrix composites according to the present invention.

[0066] Figure 2 Finite element analysis model of a thin-walled tube connection structure of continuous fiber reinforced metal matrix composite material;

[0067] Figure 3 Load-displacement curves of thin-walled tube connection structures of continuous fiber-reinforced metal matrix composites with an interfacial strength of 50 MPa are shown.

[0068] Figure 4 The stress distribution cloud map of S11 before the fracture of the thin-walled tube connection structure;

[0069] Figure 5 This is a cloud map showing the damage distribution of a thin-walled tube connection structure with an interface strength of 50 MPa before fracture. Detailed Implementation

[0070] 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.

[0071] like Figure 1 As shown in the figure, an optimization method for improving the connection performance of thin-walled tubes of continuous fiber reinforced metal matrix composites provided by an embodiment of the present invention includes the following steps:

[0072] Step 1: Determine the damage initiation of the fiber and matrix based on the Hashin failure criterion, use a bilinear cohesive force model based on the traction-separation law to describe the constitutive relationship of the cohesive element, and introduce a continuous stiffness degradation rule to simulate damage evolution, thereby jointly constructing the asymptotic damage constitutive relationship of continuous fiber reinforced metal matrix composites.

[0073] Step 2: Establish a finite element analysis model of the continuous fiber-reinforced metal matrix composite thin-walled tube connection structure under uniaxial tensile load using finite element software;

[0074] Step 3: Using connection strength, connection length, and thin-walled tube inner diameter as design variables, obtain the influence law of each variable on the load-bearing capacity of the connection structure through parametric simulation calculation, and determine the critical parameter value that makes the load-bearing capacity of the structure tend to saturate.

[0075] Step 4: Extract stress cloud diagrams, strain cloud diagrams, and damage cloud diagrams under different design variables, analyze the asymptotic failure process and damage mode of the connection structure, and optimize the matching relationship between connection strength, connection length, and inner diameter based on the analysis results until the structural bearing capacity meets the preset strength design requirements.

[0076] Example 1:

[0077] This embodiment provides an optimized method for improving the connection performance of thin-walled tubes made of continuous fiber-reinforced metal matrix composites, specifically including the following steps:

[0078] 1. Establishment of material parameters and undamaged constitutive models

[0079] First, quasi-static uniaxial tensile tests, quasi-static uniaxial compression tests, and shear tests were designed to obtain their stress-strain curves. Then, based on literature and experience, the material property parameters of each component of the continuous fiber reinforced metal matrix composite were obtained.

[0080] 2. Establishment of the finite element analysis model

[0081] A finite element model of a continuous fiber-reinforced metal matrix composite thin-walled tube connection is established using finite element software. In this embodiment, the specific steps for establishing the finite element analysis model in step two are as follows:

[0082] Step S2-1: Construct a geometric model of the connection structure consisting of an outer thin-walled tube and an inner thin-walled tube; wherein, the composite material thin-walled tube is composed of an outer sheath, a composite material core, and an inner sheath.

[0083] Step S2-2: Use zero-thickness cohesive elements to simulate the connection interface between the outer thin-walled tube and the inner thin-walled tube.

[0084] Step S2-3: Assign solid element mesh (C3D8R) to the cladding and composite core, and cohesive element mesh (COH3D8) to the cohesive elements.

[0085] Step S2-4: Set the analysis step to a dynamic analysis step to simulate a quasi-static tensile process.

[0086] like Figure 2 As shown. Regarding step two, the thin-walled tube connection structure in this embodiment consists of an outer composite material thin-walled tube and an inner composite material thin-walled tube, wherein the dimensions of the composite material thin-walled tubes are all 10mm*50mm (diameter*length). Zero-thickness cohesive elements are used to simulate the interface of the composite material thin-walled tube connection. The composite material thin-walled tube consists of an outer sheath, a composite material core, and an inner sheath, with thicknesses of 0.2 mm, 0.36 mm, and 0.2 mm, respectively. For the mesh type, the sheath, interface, and composite material core use C3D8R, COH3D8, and C3D8R, respectively. The analysis step type is selected as dynamic analysis to simulate the quasi-static process of uniaxial tension in the continuous fiber-reinforced metal matrix composite thin-walled tube connection component. The post-processing module is then used to extract the load and displacement curves of the reference points and fit them into a load-displacement curve using a function.

[0087] The progressive damage model for continuous fiber reinforced metal matrix composites is described using the three-dimensional Hashin criterion. Continuous fiber reinforced metal matrix composites are orthotropic materials. Before damage initiation, the undamaged state can be represented by a linear stress-strain relationship, as follows:

[0088]

[0089] in, These are stress components in different directions. Indicates the stiffness coefficient. These represent strain components in different directions.

[0090] The three-dimensional Hashin criterion was used to characterize the modes of fiber tensile failure, fiber compressive failure, matrix tensile failure, and matrix compressive failure in continuous fiber-reinforced metal matrix composites, which are as follows:

[0091] when At this time, it is the fiber tensile damage mode, that is:

[0092]

[0093] when At this time, it is the fiber compression damage mode, that is:

[0094]

[0095] when At this time, the matrix tensile damage mode is adopted, that is:

[0096]

[0097] when At that time, the matrix compression damage mode is as follows:

[0098]

[0099] in, These are stress components in different directions; , , and These represent longitudinal tensile strength, longitudinal compressive strength, transverse tensile strength, and transverse compressive strength, respectively. , and Expressed as shear strength; , , and This represents the damage initiation parameter under the corresponding mode, with the initial damage value being 0; when At that time, the damage began to appear.

[0100] Once the damage initiation criterion is met, the stiffness of the element is reduced according to the material degradation model to achieve material performance degradation. After the element reaches the failure criterion, its stiffness component is multiplied by the corresponding degradation coefficient to achieve performance degradation, as shown in Table 1.

[0101] Table 1. Stiffness degradation coefficients under different damage modes

[0102]

[0103] In step one, since the failure modes of the connection interface are complex and diverse, the cohesive zone modelling is used to accurately describe the dynamic evolution process of crack initiation, propagation and failure of the connection interface by defining the constitutive behavior of the interface.

[0104] The constitutive relation of the cohesive element is described by a bilinear cohesive force model based on the traction-separation law, namely:

[0105]

[0106] in, Normal traction force; and It is the tangential traction force; This is the normal displacement; and Represents tangential displacement; For elastic stiffness in different directions;

[0107] The damage initiation of cohesive elements is defined using the secondary stress criterion:

[0108]

[0109] in , and These are the stress components in three directions.

[0110] To quantitatively characterize the nonlinear process from damage initiation to complete failure, a damage variable D is introduced: The damage variable D is used to quantitatively characterize the nonlinear degradation process of the cohesive unit from damage initiation to complete failure. The damage variable D is expressed as:

[0111]

[0112] in, Indicates the equivalent displacement. Represented as the maximum equivalent displacement, This represents the equivalent displacement when the system completely fails.

[0113] The strain at each component reference point is substituted into the corresponding failure criterion to determine the failure status of the reference point. Based on the failure status, the macroscopic elastic constants of the composite material are reduced by combining the fiber-dominated failure model, the matrix-dominated failure model, and the stiffness reduction matrix, and the initial macroscopic elastic constants of stiffness are replaced. The above failure analysis process is written into a UMAT subroutine for macroscopic asymptotic failure analysis of composite materials using the Fortran language.

[0114] 3. Research on the influence of parameterization

[0115] In thin-walled tube connection structures, the connection interface plays a crucial role in the stress transmission process. Therefore, finite element software was used to construct continuous fiber-reinforced metal matrix composite thin-walled tube connection models with different connection strengths, connection lengths, and tube diameters, and the mechanical response law of the structure under external loads was determined.

[0116] In this embodiment, the research described in step three specifically includes the following sub-steps:

[0117] Step S3-1: Select a finite element model with a connection strength of 50MPa, an interface connection length of 10mm, and a pipe diameter of 10mm.

[0118] Step S3-2: Extract the load-displacement curve of the model through simulation calculation.

[0119] Step S3-3: Design models with different connection strengths, connection lengths and inner diameters, and use the fact that the structural bearing capacity no longer increases significantly with the increase of parameters as the critical judgment criterion to determine the critical parameter values ​​that make the structural bearing capacity tend to stabilize.

[0120] 4. Damage Mode Analysis and Structural Optimization

[0121] In this embodiment, the damage analysis and optimization described in step four specifically includes the following sub-steps:

[0122] Step S4-1: To further investigate the influence of connection strength on the failure mechanism of thin-walled tubes, stress distribution cloud maps and damage distribution cloud maps with interfacial strengths of 50 MPa were extracted, as shown below. Figure 4 As shown in the figure. The results show that when the connection strength is 50 MPa, the maximum S11 of the inner tube is 1254.9 MPa and the maximum S11 of the outer tube is 1082.7 MPa. This value is lower than the strength of the continuous fiber reinforced metal matrix composite, indicating that the composite core of the thin-walled tube with a connection strength of 50 MPa fails to perform its expected load-bearing capacity.

[0123] like Figure 5 The image shown is a damage contour plot for a connection strength of 50 MPa. Figure 5It can be seen that when the connection strength is 50 MPa, both the inner and outer thin-walled tubes show different degrees of damage but neither fails. Moreover, the interface has failed, indicating that the failure of the connection structure of the thin-walled tube is caused by the low strength of the connection interface.

[0124] Step S4-2: Design finite element models with different combinations of connection strength, connection length, and pipe diameter, and study the relationship between their structural characteristics and load-bearing capacity. Taking load-bearing capacity stability and the ability of the composite core to fully utilize its load-bearing capacity as references, determine the optimal structural dimensions of the continuous fiber-reinforced metal matrix composite thin-walled tube.

[0125] Example 2:

[0126] This embodiment provides an optimization system for improving the connection performance of thin-walled tubes made of continuous fiber-reinforced metal matrix composites. This system can automatically execute the aforementioned optimization method, significantly shortening the research and development cycle and reducing testing costs. The system includes:

[0127] Constitutive relation construction module: used to establish linear elastic stress-strain constitutive relations in the undamaged state, determine damage initiation based on the Hashin criterion, use a bilinear cohesive model to describe the interface constitutive relation, and introduce a continuous stiffness degradation rule to construct asymptotic damage constitutive relations.

[0128] Finite Element Modeling Module: Used to establish finite element analysis models of thin-walled tube connection structures under uniaxial tensile loads, including geometric modeling, mesh generation, and boundary condition application.

[0129] Parametric analysis module: Used to obtain the influence of connection strength, connection length and pipe diameter on load-bearing capacity through parametric simulation, and to determine the critical parameter values.

[0130] Optimization Decision Module: Used to extract stress, strain and damage cloud maps, analyze the failure process and damage mode, and optimize parameter matching relationship based on the dominant failure factors until the strength design requirements are met.

[0131] In summary, the core of this invention lies in the organic integration of asymptotic damage constitutive relations, finite element modeling, parametric analysis, and damage mode recognition, forming a complete design optimization system. This system not only accurately predicts the structural load-bearing performance under different connection parameters but also infers the failure mechanism from damage contour maps, thereby allowing for targeted adjustments to the matching relationship between connection strength, connection length, and pipe diameter. Experimental results show that the continuous fiber-reinforced metal matrix composite thin-walled tube connection structure optimized using the method of this invention exhibits significantly improved ultimate load-bearing capacity and stability, while effectively shortening the development cycle and reducing testing costs. This provides a reliable theoretical basis and engineering guidance for the design of high-performance composite truss structures in aerospace and other fields.

[0132] Those skilled in the art will understand that the above description is merely a preferred embodiment of the present invention, and the features described in the various embodiments of this disclosure can be combined or combined in various ways, even if such combinations or combinations are not explicitly described in this disclosure. This is not intended to limit the present invention. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art can still modify the technical solutions described in the foregoing embodiments or make equivalent substitutions for some of the technical features. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. An optimized method for improving the connection performance of thin-walled tubes made of continuous fiber-reinforced metal matrix composites, characterized in that, Includes the following steps: Step S1: Determine the damage initiation of the fiber and matrix based on the failure criteria, use a bilinear cohesive force model based on the traction-separation law to describe the constitutive relationship of the cohesive element, and introduce a continuous stiffness degradation rule to simulate damage evolution, thereby jointly constructing the asymptotic damage constitutive relationship of the continuous fiber reinforced composite material. Step S2: Use finite element software to establish a finite element analysis model of the continuous fiber-reinforced metal matrix composite thin-walled tube connection structure under uniaxial tensile load; Step S3: Using connection strength, connection length, and thin-walled tube inner diameter as design variables, obtain the influence law of each variable on the load-bearing capacity of the connection structure through parametric simulation calculation, and determine the critical parameter value that makes the load-bearing capacity of the structure tend to saturate. Step S4: Extract stress cloud diagrams, strain cloud diagrams, and damage cloud diagrams under different design variables, analyze the asymptotic failure process and damage mode of the connection structure, and optimize the matching relationship between connection strength, connection length, and inner diameter based on the analysis results until the structural bearing capacity meets the preset strength design requirements.

2. The optimization method for improving the connection performance of thin-walled tubes of continuous fiber-reinforced metal matrix composites according to claim 1, characterized in that, Before performing step S1, the process also includes: establishing the linear elastic stress-strain constitutive relationship of the undamaged state of the continuous fiber reinforced metal matrix composite material; The linear elastic stress-strain constitutive relation of the continuous fiber reinforced metal matrix composite in the undamaged state is as follows: ； in, These are stress components in different directions. Indicates the stiffness coefficient. These represent strain components in different directions.

3. The optimized method for improving the connection performance of thin-walled tubes of continuous fiber-reinforced metal matrix composites according to claim 1, characterized in that, In step S1, the determination of the damage initiation between the fiber and the matrix based on failure criteria specifically involves: The failure criteria include four damage initiation criteria, namely: when At this time, it is the fiber tensile damage mode, that is: ； when At this time, it is the fiber compression damage mode, that is: ； when At this time, the matrix tensile damage mode is adopted, that is: ； when At that time, the matrix compression damage mode is as follows: ； in, These are stress components in different directions; , , and These represent longitudinal tensile strength, longitudinal compressive strength, transverse tensile strength, and transverse compressive strength, respectively. , and Expressed as shear strength; , , and This represents the damage initiation parameter under the corresponding mode, with the initial damage value being 0; when At that time, the damage began to appear.

4. The optimization method for improving the connection performance of thin-walled tubes of continuous fiber-reinforced metal matrix composites according to claim 1, characterized in that, In step S1, the constitutive relation of the cohesive unit is described using a bilinear cohesive force model based on the traction-separation law, namely: ； in, Normal traction force; and It is the tangential traction force; This is the normal displacement; and Represents tangential displacement; For elastic stiffness in different directions; The damage initiation criterion for cohesive elements is as follows: ； in , and These are the stress components in three directions.

5. The optimized method for improving the connection performance of thin-walled tubes of continuous fiber-reinforced metal matrix composites according to claim 1, characterized in that, The introduced continuous stiffness degradation rule is specifically as follows: A damage variable D is introduced to quantitatively characterize the nonlinear degradation process of cohesive elements from damage initiation to complete failure. The damage variable D is expressed as: ； in, Indicates the equivalent displacement. Represented as the maximum equivalent displacement, This represents the equivalent displacement when the system completely fails.

6. The optimized method for improving the connection performance of thin-walled tubes of continuous fiber-reinforced metal matrix composites according to claim 1, characterized in that, In step S2, the finite element analysis model of the continuous fiber reinforced metal matrix composite thin-walled tube connection structure includes: an outer thin-walled tube, an inner thin-walled tube, and a zero-thickness cohesive interface between the two, and an end face surface force load is applied. A finite element analysis model of the thin-walled tube connection structure was established using finite element software, specifically as follows: Step S2-1: Construct a geometric model of the connection structure formed by the outer thin-walled tube and the inner thin-walled tube; wherein, the composite material thin-walled tube is composed of an outer sheath, a composite material core and an inner sheath; Step S2-2: Use zero-thickness cohesive elements to simulate the connection interface between the outer thin-walled tube and the inner thin-walled tube; Step S2-3: Assign solid element meshes to the sheath and composite core, and cohesive element meshes to the cohesive elements; Step S2-4: Set the analysis step to a dynamic analysis step to simulate a quasi-static tensile process; Step S2-5: Fix the end face of the outer thin-walled tube and apply a displacement load to the end face of the inner thin-walled tube.

7. The optimized method for improving the connection performance of thin-walled tubes of continuous fiber-reinforced metal matrix composites according to claim 1, characterized in that, Step S3 includes the following steps: Step S3-1: Select multiple different connection strength values, multiple different connection length values, and multiple different thin-walled tube inner diameter values ​​as design variables; Step S3-2: Extract the load-displacement curves under each parameter combination through parametric simulation calculation; Step S3-3: Based on the load-displacement curve, obtain the law that the bearing capacity first increases and then stabilizes with the increase of connection strength, increases and then tends to saturate with the increase of connection length, and increases monotonically with the increase of inner diameter. Take the fact that the structural bearing capacity no longer increases significantly with the increase of parameters as the critical criterion, determine the critical parameter value that makes the structural bearing capacity tend to saturate, and then determine the optimization parameter range.

8. The optimized method for improving the connection performance of thin-walled tubes of continuous fiber-reinforced metal matrix composites according to claim 1, characterized in that, Step S4 includes the following steps: Step S4-1: Extract the axial stress cloud map and damage cloud map of the inner and outer thin-walled tubes under different connection strengths, read the maximum axial stress value of the inner and outer thin-walled tubes respectively, and compare the damage distribution area and damage variable size of the cohesive unit and the composite core in the damage cloud map; determine whether the failure mode is caused by insufficient strength of the cohesive unit or insufficient transverse strength of the composite material. Step S4-2: Extract stress distribution cloud maps of thin-walled tube connection structures under different connection lengths, identify stress concentration areas at the ends of the connection interfaces, and determine whether the effective force transmission area is sufficient based on the ratio of peak stress to average stress in the stress concentration areas. Step S4-3: Extract load-displacement curves for different inner diameters, calculate the slope of each curve in the elastic and plastic segments, and compare the magnitude of the load values ​​under the same displacement to analyze the contribution of cross-sectional area to bearing capacity. Step S4-4: Based on the analysis results of steps S4-1 to S4-3, optimize the thin-walled tube connection structure to fully utilize the load-bearing capacity of the composite material.

9. An optimized method for improving the connection performance of thin-walled tubes of continuous fiber-reinforced metal matrix composites according to claim 8, characterized in that, In step S4-4, based on the analysis results of steps S4-1 to S4-3, the following steps are performed: a) When the failure is determined to be mainly due to insufficient strength of the cohesive unit, increase the connection strength to above the critical value that makes the load-bearing capacity tend to saturate; b) When the failure is determined to be mainly due to insufficient transverse strength of the composite material, increase the connection length to above the critical value that makes the load-bearing capacity tend to saturate; c) When the cross-sectional area does not meet the set requirements for load-bearing capacity, increase the inner diameter of the thin-walled tube within the allowable range of structural space.

10. An optimization system for improving the connection performance of thin-walled tubes made of continuous fiber-reinforced metal matrix composites, used to perform the optimization method as described in any one of claims 1-9, characterized in that, include: The constitutive relation construction module is used to establish the linear elastic stress-strain constitutive relation of continuous fiber reinforced metal matrix composites in the undamaged state; and to determine the damage initiation of the fiber and matrix based on the failure criterion, to describe the constitutive relation of the cohesive unit using a bilinear cohesive force model based on the traction-separation law, and to introduce a continuous stiffness degradation rule to simulate damage evolution, thereby constructing the asymptotic damage constitutive relation of the composite material. The finite element modeling module is used to establish a finite element analysis model of a continuous fiber-reinforced metal matrix composite thin-walled tube connection structure under uniaxial tensile load. The finite element analysis model includes an outer thin-walled tube, an inner thin-walled tube, and a zero-thickness cohesive element between them, and applies end face surface force load. The parametric analysis module is used to obtain the influence of each variable on the load-bearing capacity of the thin-walled tube connection structure through parametric simulation calculation, using connection strength, connection length and thin-walled tube inner diameter as design variables, and to determine the critical parameter value that makes the load-bearing capacity of the structure tend to saturate. The optimization decision module is used to extract stress cloud maps, strain cloud maps, and damage cloud maps under different design variables, analyze the asymptotic failure process and damage mode of thin-walled tube connection structures, and optimize the matching relationship between connection strength, connection length, and inner diameter based on the analysis results until the structural bearing capacity meets the preset strength design requirements.

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