Multi-level simulation method for impact damage residual performance of thin-wall carbon fiber tube

Abstract

The invention provides a multilayer simulation method for impact damage residual performance of a thin-wall carbon fiber tube, and belongs to the technical field of finite element simulation and nondestructive testing of composite materials. Finite element analysis is carried out based on the material attribute parameters of the thin-wall carbon fiber tube, the geometric dimension of the thin-wall carbon fiber tube and the layering angle to construct a solid model of the thin-wall carbon fiber tube; a thin-wall carbon fiber tube solid model is utilized, a failure criterion based on energy fracture is introduced by setting contact conditions, a clamp and an impactor, and a thin-wall carbon fiber tube model with impact damage is obtained; and changing the contact condition, the clamp and the constraint condition of the thin-wall carbon fiber tube model with the impact damage to obtain a compression model containing the damaged thin-wall carbon fiber tube, and outputting a damage representation variable. The problems that the modeling process of the thin-wall carbon fiber pipe is complex, and the time cost for rebuilding pipe fittings with parameters such as different geometric sizes and laying angles is high are solved.

Description

Technical Field

[0001] The invention relates to the technical field of finite element simulation and nondestructive testing of composite materials, and in particular to a multi-level simulation method for residual performance of impact damage of a thin-walled carbon fiber tube. Background Art

[0002] Thin-walled structural composite materials are widely used in aerospace, automotive engineering, shipbuilding, civil engineering, sports equipment and other fields due to their advantages such as high specific strength, specific modulus, small linear expansion coefficient, good fatigue resistance and damping performance. Among them, thin-walled carbon fiber tubes are widely used in the truss structure of satellite antennas as representative products. However, since thin-walled carbon fiber tubes are very sensitive to lateral impact damage, a series of damages such as delamination may occur at a lower impact energy level. This impact damage will seriously affect the structural integrity of the tube, causing the residual performance of the tube to decline, and there is a fatal risk of failure during use. At the same time, the manufacturing cost of thin-walled carbon fiber tubes in antenna structures is high, and the size is large, the experimental cost is high and it is not easy to carry out. Therefore, it is of great significance to establish a model that can accurately and efficiently reflect the low-energy impact response of thin-walled carbon fiber tubes, and analyze the residual performance based on this model. Through the impact energy that may be generated in actual work and the load conditions of the working state, the simulation results of thin-walled carbon fiber tubes with different parameters are obtained, so as to provide a reference for the production and performance optimization of pipe fittings.

[0003] Accurate modeling simulation analysis results are the premise for analyzing the impact damage response and residual performance of thin-walled carbon fiber tubes. The current simulation analysis methods are to analyze the residual performance by establishing a model of a composite thin-walled structure with viscous layer damage. However, whether it is to define the material parameters of the viscous layer to make it lose its constraint ability, or to directly cut the viscous layer to achieve the modeling method of simulating delamination damage, it is impossible to fully show the damage form of the thin-walled composite structure after low-energy lateral impact. Moreover, the damage defined by this modeling method cannot be mapped to the specific impact energy, and the subsequent simulation results obtained will be significantly different from the experimental results. In addition, the existing Hashin failure criterion is used to determine the fiber damage, and on this basis, the first-order shear deformation theory or Linde failure criterion is used to determine the damage between layers and the matrix. In the actual model analysis process, it takes a lot of time. The existing multi-level simulation, by establishing a model to predict impact damage, the subsequent residual compression performance analysis is re-modeled based on numerical results or experimental results, ignoring many failure modes other than delamination damage. In addition, the existing finite element simulation prediction model of delamination damage has an irregular geometric structure due to the division of the viscous layer, making the meshing difficult and the calculation time long.

[0004] Therefore, a multi-level simulation method for the residual performance of thin-walled carbon fiber tubes with impact damage is needed, which can accurately reflect the impact damage of thin-walled carbon fiber tubes and quickly model them. Summary of the invention

[0005] In view of this, the present invention provides a multi-level simulation method for the residual performance of thin-walled carbon fiber tubes with impact damage, which solves the problem of incomplete modeling of damaged thin-walled carbon fiber tubes and low accuracy of subsequent residual performance analysis and prediction.

[0006] To this end, the present invention provides the following technical solutions:

[0007] Multi-level simulation method for impact damage residual performance of thin-walled carbon fiber tubes, including:

[0008] Finite element analysis is performed based on the material property parameters, geometric dimensions and ply angles of the thin-walled carbon fiber tube to construct a solid model of the thin-walled carbon fiber tube;

[0009] Using the solid model of thin-walled carbon fiber tube, by setting contact conditions, fixtures and impactors, and introducing failure criteria based on energy fracture, a thin-walled carbon fiber tube model with impact damage is obtained.

[0010] The contact conditions, fixtures and constraints of the thin-walled carbon fiber tube model with impact damage are changed to obtain the compression model of the thin-walled carbon fiber tube with damage, and the damage representation variable is output.

[0011] Furthermore, the energy-fracture-based failure criterion utilizes a stiffness degradation matrix containing damage variables to describe the reduction in material stiffness.

[0012] Furthermore, the stiffness degradation matrix:

[0013]

[0014] d f =(1-d ft )(1-d fc )

[0015] d m =(1-S mt d mt )(1-S mc d mc )

[0016] Δ=1-d f d m ν 12 ν 21 -d m ν 23 ν 32 -d f ν 13 ν31 -2d f d m ν 21 ν 32 v 13

[0017] Among them, d I Denotes damage variable; the subscripts “ft”, “fc”, “mt”, and “mc” denote fiber tension, fiber compression, matrix tension, and matrix compression, respectively.

[0018] Furthermore, the damage variables include fiber stretching, fiber compression, matrix stretching and matrix compression:

[0019] Fiber stretching

[0020] Fiber compression

[0021] Matrix stretching

[0022] Matrix compression

[0023]

[0024] in, and E ij (ij=1, 2, 3) represents the elastic strain tensor and Young's modulus; and represents the initial failure elastic strain of the corresponding failure mode; X T and X C Respectively represent the tensile strength and compressive strength in the fiber direction; Y T and Y C Respectively represent the transverse tensile strength and compressive strength; S 12 , S 13 and S 23 represents the shear modulus.

[0025] Furthermore, after reaching the damage initiation criterion, the damage evolves as follows:

[0026]

[0027] Among them, d I ∈(0,1), I=ft,fc,mt,mc; is the elastic strain in the corresponding direction; the final failure elastic strain when the corresponding damage variable reaches 1 is expressed as:

[0028]

[0029]

[0030] Among them, G I (I = ft, fc, mt, mc) is the fracture energy of the corresponding failure mode, and I is the characteristic length of the element, which is calculated from the cube root of the volume of the corresponding element.

[0031] Furthermore, the material property parameters of the thin-walled carbon fiber tube include: length, outer diameter, inner diameter, density, elastic modulus, shear modulus, Poisson's ratio, longitudinal tensile strength, longitudinal compressive strength, transverse tensile strength, transverse compressive strength, longitudinal shear strength and transverse shear strength.

[0032] Furthermore, the damage representation variable describes the damage condition of the pipe;

[0033] The damage representation variables include: tensile and compressive damage, shear damage, and depth cross-sections of tensile and compressive damage locations.

[0034] Advantages and positive effects of the present invention:

[0035] The present invention inputs the geometric dimensions, ply angles and material property parameters of the thin-walled carbon fiber tube, and can achieve rapid modeling; by using the energy-based damage criterion as the failure criterion, the Raya damage and shear damage of the thin-walled carbon fiber tube are used for judgment. Compared with the traditional criterion that requires judgment of material-level anisotropy, the accuracy is guaranteed and the time cost is shortened during the simulation calculation. The material property parameters are set according to the energy-based damage criterion. The model can directly complete tedious tasks such as assembly, analysis step setting and meshing. The problem of complex modeling process of thin-walled carbon fiber tubes and high time cost of re-establishing pipes with different geometric dimensions, ply angles and other parameters is solved. The present invention can establish a thin-walled carbon fiber tube that is closer to the actual damage after impact and conduct subsequent analysis through a multi-level modeling and analysis method, which ensures the mapping relationship between impact damage and impact energy, and at the same time ensures the accuracy of the residual performance simulation results. Therefore, the method has the advantages of high prediction accuracy, convenient modeling and efficient calculation. BRIEF DESCRIPTION OF THE DRAWINGS

[0036] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative labor.

[0037] Figure 1 The impact damage model of the thin-walled carbon fiber tube established in the analysis step 1 in the embodiment of the present invention;

[0038] Figure 2 The compression model of the damaged thin-walled carbon fiber tube established in the analysis step 2 in the embodiment of the present invention;

[0039] Figure 3 The simulation results of impact damage at different ply angles in the embodiment of the present invention;

[0040] Figure 4 The impact result and the damage expansion result during compression in the embodiment of the present invention;

[0041] Figure 5 The simulation result of residual compression performance in the embodiment of the present invention;

[0042] Figure 6 The simulation result of residual bending performance in the embodiment of the present invention;

[0043] Figure 7 A geometric dimension setting module in an embodiment of the present invention;

[0044] Figure 8 It is a ply angle setting module in an embodiment of the present invention;

[0045] Fig. 9 It is an impactor setting module in the embodiment of the present invention;

[0046] Fig.10 The load-time curve of the pipe under different impact energies in the embodiment of the present invention;

[0047] Fig.11 It is a flow chart in an embodiment of the present invention. DETAILED DESCRIPTION

[0048] In order to enable those skilled in the art to better understand the scheme of the present invention, the technical scheme in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work should fall within the scope of protection of the present invention.

[0049] It should be noted that the terms "first", "second", etc. in the specification and claims of the present invention and the above-mentioned drawings are used to distinguish similar objects, and are not necessarily used to describe a specific order or sequence. It should be understood that the data used in this way can be interchanged where appropriate, so that the embodiments of the present invention described herein can be implemented in an order other than those illustrated or described herein. In addition, the terms "including" and "having" and any variations thereof are intended to cover non-exclusive inclusions, for example, a process, method, system, product or device that includes a series of steps or units is not necessarily limited to those steps or units that are clearly listed, but may include other steps or units that are not clearly listed or inherent to these processes, methods, products or devices.

[0050] The present invention provides a multi-level simulation method for the residual performance of impact damage of thin-walled carbon fiber tubes. The concept is as follows: for the thin-walled carbon fiber tubes in the satellite antenna structure, a finite element model of a thin-walled carbon fiber tube is established by a multi-analysis step method to simulate and analyze the impact damage and residual performance thereof; based on the demand for rapid modeling of thin-walled carbon fiber tubes and considering the sensitivity of the factors affecting the damage of thin-walled carbon fiber tubes, by calling a GUI program, the rapid modeling of changing the structural size and the laying method is focused, and the rapid modeling of thin-walled carbon fiber tubes with different sizes and laying parameters can be performed. And using the damage criterion based on fracture energy as the failure criterion, the impact damage of the tube and the subsequent residual performance simulation analysis results can be well reflected, while ensuring the accuracy of the prediction, the simulation time is also shortened, and the time cost is saved. The material attribute parameters of the input model are designed according to the damage criterion based on fracture energy. The problem of inaccurate and complex structure of the residual performance characterization model for impact damage of thin-walled carbon fiber tubes in the prior art is solved, resulting in incomplete modeling of damaged thin-walled carbon fiber tubes and low prediction accuracy of subsequent residual performance analysis.

[0051] Combination Fig.11 The process of the present invention is further described as follows:

[0052] S1. Based on the energy criterion, define the material property parameters of key pipe parts; use the geometric dimensions, ply angle parameters and material property parameters to construct a thin-walled carbon fiber tube model through finite element software;

[0053] In actual production, the layup angle and the geometric dimensions of the pipe are the parameters that are most easily changed, and these parameters have a greater impact on the impact damage performance of the pipe and the residual performance after impact. Therefore, in this embodiment, rapid modeling is achieved by utilizing thin-walled carbon fiber tubes with different geometric dimensions and layup angle parameters.

[0054] S2, the thin-walled carbon fiber tube model is subjected to simulated impact through the failure criterion based on energy fracture to obtain the impact damage model;

[0055] Specifically, considering the energy release rate required when the crack of the thin-walled carbon fiber tube begins to expand under the action of external force and the influence of the internal crack expansion on the structural integrity, the failure criterion based on energy fracture is adopted in this embodiment; when the thin-walled carbon fiber tube is subjected to external force and damaged, its stiffness will decrease accordingly. Therefore, the stiffness degradation matrix containing the damage variable is used to describe the reduction of the material stiffness, so as to more realistically reflect the mechanical behavior of the material during the damage process.

[0056] The damage criterion based on energy fracture is judged by the Laya damage and shear damage of thin-walled carbon fiber tubes. Compared with the traditional criterion that needs to judge the material-level anisotropy, it reduces the calculation variables and ensures accuracy while shortening the time cost during the simulation calculation.

[0057] The stiffness degradation matrix containing the damage variables is:

[0058]

[0059]

[0060] d f =(1-d ft )(1-d fc )

[0061] d m =(1-S mt d mt )(1-S mc d mc )

[0062] Δ=1-d f d m v 12 v 21 -d m v 23 v 32 -d f v 13 v 31 -2d f d m v 21 v 32 v 13

[0063] Among them, d I Denotes damage variable; the subscripts “ft”, “fc”, “mt”, and “mc” denote fiber tension, fiber compression, matrix tension, and matrix compression, respectively.

[0064] Fiber stretching:

[0065]

[0066] Fiber Compression:

[0067]

[0068] Matrix stretching:

[0069]

[0070] Matrix Compression:

[0071]

[0072] in, and E ij (ij=1, 2, 3) represents the elastic strain tensor and Young's modulus; and represents the initial failure elastic strain of the corresponding failure mode; X T and X C Respectively represent the tensile strength and compressive strength in the fiber direction; Y T and Y C Respectively represent the transverse tensile strength and compressive strength; S 12 , S 13 and S 23 represents the shear modulus.

[0073] After reaching the damage initiation criterion, the damage evolves as follows:

[0074]

[0075] Among them, d I ∈(0,1), I=ft,fc,mt,mc; is the elastic strain in the corresponding direction; is the final failure elastic strain when the corresponding damage variable reaches 1. It is calculated as follows:

[0076]

[0077] Among them, G I (I = ft, fc, mt, mc) is the fracture energy of the corresponding failure mode, and I is the characteristic length of the element, which is calculated from the cube root of the volume of the corresponding element.

[0078] In this embodiment, as a preferred embodiment, a multi-analysis step modeling analysis method is adopted, including:

[0079] First, in step 1, the material parameters are shown in Table 1. The ply method of the thin-walled carbon fiber tube is [±15 / 0 / ±30 / 02 / ±30 / 0 / ±15]. The impact damage model of the thin-walled carbon fiber tube is established as follows: Figure 1As shown in the figure; the time length of the analysis step is 0.2s. The interaction between the pipe and the fixture is surface contact, and the penalty coefficient is set to 0.3. The interaction between the pipe and the impactor is surface contact, the tangential constraint is smooth, and the normal constraint is "hard" contact. In the "Load" module, the impactor is given an initial velocity, and the impact energy is changed by changing the velocity.

[0080] Table 1

[0081]

[0082]

[0083] S3, axial compression damage analysis based on impact damage model;

[0084] Specifically, analysis step 2 is established after analysis step 1. In this analysis step, the contact conditions, fixtures and impactors in analysis step 1 are deleted, and new fixtures and constraints are reset.

[0085] In this embodiment, the model established in the analysis step 2 is as follows Figure 2 As shown in the figure, the plate and the end faces of the tube are in surface contact, the penalty coefficient is set to 0.3, and the time of this analysis step is set to 2s. At the same time, in the "Load" module, a displacement function that varies with time is applied to the plate to achieve the purpose of axial compression of the tube during the analysis process. Since analysis step 2 is set after analysis step 1, the two analysis steps are in a progressive relationship. The damaged pipe obtained by simulation in analysis step 1 will be directly used for analysis in analysis step 2 in a damaged state.

[0086] In this embodiment, the output variables include: the tensile and compressive damage (TCD) and shear damage (SD) of the tube after impact, and the depth section (DC) of the tensile and compressive damage positions, which represent the damage condition of the thin-walled carbon fiber tube.

[0087] In this modeling method, the two independent analysis steps are sequential in time: first, the impact simulation is performed, in which the impact energy can be controlled to obtain damaged pipes under different impact energies; then, the residual compression performance simulation analysis is directly performed based on the damaged pipes obtained in the previous simulation. Through the damage criterion of the subroutine, all damage modes of the pipes after impact can be saved and used for subsequent analysis. At the same time, both simulation analyses can set their own independent constraints and time lengths, which well ensures the accuracy of the simulation results.

[0088] Figure 3The results of the impact simulation of thin-walled carbon fiber tubes with different ply angles changed by GUI plug-in modeling are shown. It can be clearly observed in the simulation results that the tube after impact can be seen that the fracture energy damage criterion proposed by this method can well characterize the damage state of the tube under different impact energies, which is very beneficial to the subsequent residual performance analysis compared to the existing modeling method of viscous layer division.

[0089] In the subsequent analysis step, by setting the axial compression loading condition, the damage evolution of the impact-damaged pipe in the subsequent compression process is as follows: Figure 4 As shown. Among them, (a) impact damage result diagram; (b) compression displacement 6mm result diagram; (c) compression displacement 9mm result diagram (d) compression displacement 30mm result diagram; From the results shown, it can be seen that the established finite element model can well reflect the damage expansion of the pipe with impact damage during the compression process. The multi-analysis step analysis method proposed in this method can well reflect the damage state of the pipe at each time node in the residual compression performance simulation.

[0090] Figure 5 , 6 The stress-time of the damaged area and the defined failure index-time curve are output. The simulation result curve obtained by the model established by this method can clearly reflect the impact and the stress change of any part of the pipe during the subsequent residual performance analysis. At the same time, the definition of the failure index can show the time of the start of damage failure (the damage index is not 0) and the state of damage (complete failure if the value no longer changes). The amplitude function assigned by this method can calculate the load or compression (bending) displacement of the pipe at the corresponding moment. The determination of this threshold value has important practical significance for the production of thin-walled carbon fiber tubes with better performance.

[0091] In this embodiment, the GUI calling process includes:

[0092] All the parameters required for the analysis step, such as ply angle, constraint conditions, assembly relationship, analysis step settings, etc., are written into the code through defined variables to complete the writing of the GUI plug-in script language. The completed Python script is imported into the default working directory of the finite element software plug-in, and the mapping between the input parameters and the script variables, as well as the layout and beautification adjustments of the plug-in are performed through the built-in "plugs in" compiler.

[0093] The pipe geometry setting module is as follows: Figure 7As shown in the figure, the "Overall parameters" option represents the overall geometric dimensions of the pipe fitting. The three parameters shown in the figure represent the length, outer diameter and inner diameter of the pipe fitting. The "Sectional parameters" option represents the area division of the pipe fitting. By setting the radius length dn, the purpose of layer thickness division of the pipe fitting can be achieved. The figure shows that the key is evenly divided into twelve layers, and the thickness of each layer is 0.1mm.

[0094] Layer angle setting and impactor setting modules such as Figure 8 Fig. 9 As shown in the figure, the angle of each layer can be changed by assigning a value to the angle parameter An, and the definition of the angle of each layer is explained in the diagram in the construction. The setting of the impactor module can change the size of the impactor radius, so as to achieve the purpose of changing the mass of the impactor. At the same time, the speed of the impactor can be set, and the mass and speed jointly control the size of the impact energy.

[0095] In this embodiment, in order to verify the correctness of the simulation method, the two sides of the thin-walled carbon fiber tube are constrained according to the boundary conditions set in the simulation, the experimental results of the thin-walled carbon fiber tube under different impact energies are compared with the results obtained by the finite element method, and the accuracy of the error evaluation method is calculated.

[0096] The simulation output load-time curve obtained by this method is compared with the experimental curve. Fig.10 As shown in the figure, both the experiment and the numerical calculation have impacted the pipe fittings with 2J, 4J, 6J, 8J and 10J respectively. As can be seen from the figure, the simulation results well show the three stages of the contact load change between the impactor and the pipe fitting surface during the impact process: first, the load rises sharply, which is due to the impact, and in this change process, it can be considered that the key thing that occurs is elastic deformation until the load reaches the peak value; after reaching the peak value, the load will drop sharply and maintain a certain range of fluctuations and slowly drop. This stage is called the plateau period. The appearance of this stage indicates that the pipe fittings have irreversible damage; the last is the unloading stage, and the load drops rapidly, indicating the end of the impact process; among them, because no irreversible impact damage is produced when the impact energy is 2J, the changes in the above three stages do not occur.

[0097] Fig.10 Load-time curves of pipe fittings under different impact energies: (a) 2J; (b) 4J; (c) 6J; (d) 8J; (e) 10J.

[0098] The experimental and simulation curves correspond well in the plateau period of the peak load and impact damage curve. The maximum error of the peak load is 7.8% at 6 J. Compared with the impact simulation model with the same mesh division and material parameter definition modeled by the traditional method, the simulation time of this method is about 2.5 hours, which saves time cost while ensuring the simulation accuracy.

[0099] Aiming at the problem of inaccurate residual performance characterization model and complex structure of impact damage of thin-walled carbon fiber tube, the present invention adopts a damage criterion of fracture energy as a standard based on the existing theory. Compared with the experimental results, the damage criterion adopted is a relatively classic damage criterion, which can shorten the simulation time while ensuring its accuracy, and ensure the accuracy and speed of analysis.

[0100] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or replace some or all of the technical features therein with equivalents. However, these modifications or replacements do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A multi-level simulation method for residual performance of impact damage of thin-walled carbon fiber tubes, characterized in that: include: Finite element analysis is performed based on the material property parameters, geometric dimensions and ply angles of the thin-walled carbon fiber tube to construct a solid model of the thin-walled carbon fiber tube; Using the solid model of thin-walled carbon fiber tube, by setting contact conditions, fixtures and impactors, and introducing failure criteria based on energy fracture, a thin-walled carbon fiber tube model with impact damage is obtained. The contact conditions, fixtures and constraints of the thin-walled carbon fiber tube model with impact damage are changed to obtain the compression model of the thin-walled carbon fiber tube with damage, and the damage representation variable is output.

2. The multi-level simulation method for residual performance of impact damage of thin-walled carbon fiber tube according to claim 1 is characterized in that: The energy-fracture-based failure criterion uses a stiffness degradation matrix containing damage variables to describe the reduction in material stiffness.

3. The multi-level simulation method for residual performance of impact damage of thin-walled carbon fiber tube according to claim 1, characterized in that: The stiffness degradation matrix: d f =(1-d ft )(1-d fc ) d m =(1-S mt d mt )(1-S mc d mc ) Δ=1-d f d m v 12 v 21 -d m v 23 v 32 -d f v 13 v 31 -2d f d m v 21 v 32 v 13 Among them, d I represents the damage variable; the subscripts “ft”, “fc”, “mt”, and “mc” represent fiber tension, fiber compression, matrix tension, and matrix compression, respectively.

4. The multi-level simulation method for residual performance of impact damage of thin-walled carbon fiber tubes according to claim 2 is characterized in that: The damage variables include fiber tension, fiber compression, matrix tension, and matrix compression: in, and E ij (ij=1, 2, 3) represents the elastic strain tensor and Young's modulus; and represents the initial failure elastic strain of the corresponding failure mode; X T and X C Respectively represent the tensile strength and compressive strength in the fiber direction; Y T and Y C Respectively represent the transverse tensile strength and compressive strength; S 12 , S 13 and S 23 represents the shear modulus.

5. The multi-level simulation method for residual performance of impact damage of thin-walled carbon fiber tube according to claim 2, characterized in that: After reaching the damage initiation criterion, the damage evolves as follows: Among them, d I ∈ (0, 1), I=ft, ​​fc, mt, mc; is the elastic strain in the corresponding direction; the final failure elastic strain when the corresponding damage variable reaches 1 is expressed as: Among them, G I (I = ft, fc, mt, mc) is the fracture energy of the corresponding failure mode, and I is the characteristic length of the element, which is calculated from the cube root of the volume of the corresponding element.

6. The multi-level simulation method for residual performance of impact damage of thin-walled carbon fiber tube according to claim 1, characterized in that: The material property parameters of the thin-walled carbon fiber tube include: length, outer diameter, inner diameter, density, elastic modulus, shear modulus, Poisson's ratio, longitudinal tensile strength, longitudinal compressive strength, transverse tensile strength, transverse compressive strength, longitudinal shear strength and transverse shear strength.

7. The multi-level simulation method for residual performance of impact damage of thin-walled carbon fiber tube according to claim 1, characterized in that: The damage representation variable describes the damage condition of the pipe fitting; The damage representation variables include: tensile and compressive damage, shear damage, and depth cross-sections of tensile and compressive damage locations.

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