A fabric preform initial shape optimization cutting method based on finite element simulation

Abstract

The application belongs to the field of composite manufacturing process simulation and optimization design, and particularly relates to a kind of initial shape optimization cutting method of fabric preform based on finite element simulation, parameterized simulation and evaluation model of fabric shape control loading, and the maximum value of the absolute value of the fiber main direction compression strain is output;The polar coordinates of the control points in the simulation and evaluation model are initialized, and the value range of the polar coordinates is determined;Then, based on the design target, set the optimization target, constraint condition of the simulation and evaluation model in Isight software, and select the optimization algorithm to run calculation until the optimal solution is obtained. The optimal solution of the fabric shape corresponding to the minimum fabric forming defect characterization quantity can be obtained through numerical simulation calculation, which avoids repeated trial and error based on a large number of fabric forming physical tests, and can effectively save the process design time and cost;With the fabric shape as the optimization design variable, the material usage can be saved by setting the maximum area constraint of the fabric.

Description

Technical Field

[0001] This application belongs to the field of simulation and optimization design of composite material manufacturing processes, and specifically relates to a method for optimizing the initial shape of fabric preforms based on finite element simulation. Background Technology

[0002] Liquid molding technology based on dry fiber preforms impregnated with liquid resin is an important approach for the rapid and low-cost preparation of composite materials. As a crucial step in the liquid molding process, two-dimensional dry fiber fabrics need to be extruded and shaped using a die to obtain a flexible preform adapted to the three-dimensional geometry of the component. This preform is then impregnated and cured with liquid resin to obtain the final composite component. Therefore, the uniformity of fiber orientation within the preform is critical to the mechanical properties of the finished composite material. However, the dry fiber fabric forming process suffers from problems such as large fabric deformation, difficulty in controlling boundary constraints, and friction between the die and fabric, which can easily induce manufacturing defects such as fabric wrinkles, fiber buckling, and fiber breakage, thereby reducing the mechanical properties and quality consistency of the finished composite material. Therefore, suppressing manufacturing defects during the fabric forming stage is a significant challenge in ensuring the performance of composite materials.

[0003] Researchers have conducted extensive work on suppressing defects in the forming of composite preforms.

[0004] The literature "Inter-ply stitching optimization of highly drapeable multi-ply preforms" first proposed the quantitative evaluation index of preform defects based on the axial compressive strain of fabric fibers, which is used in this patent, and optimized the design for the position of interlayer stitches in multi-layer fabrics. The literature "Formability optimization of fabric preforms by controlling material draw-in through in-plane constraints" proposed an optimization method for the position and stiffness of fabric boundary clamping, aiming to minimize fabric shear strain. The literature "Optimisation of intra-ply stitch removal for improved formability of biaxial non-crimp fabrics" proposed an optimization design method for selective removal of intralayer stitches in non-crimp fabrics, aiming to minimize fabric shear strain and the area of ​​intralayer stitches, thus realizing the occurrence of wrinkle defects in the preform. However, the design variables used in the above three optimization design methods are different from the fabric boundary shape used in this patent.

[0005] Therefore, how to more effectively suppress manufacturing defects is a problem that needs to be solved. Summary of the Invention

[0006] The purpose of this application is to provide a method for optimizing the initial shape of fabric preforms based on finite element simulation, so as to solve the problem that it is difficult to effectively suppress manufacturing defects in the prior art.

[0007] The technical solution of this application is: a method for optimizing the initial shape of a fabric preform based on finite element simulation, comprising:

[0008] The initial configuration data of the two-dimensional fiber fabric is obtained and input into the Abaqus platform. The unit direction vector in the initial configuration data is obtained, and then an orthogonal coordinate system is constructed using the unit direction vector. The transformation matrix of the GN coordinate system is calculated based on the orthogonal coordinate system. The increment of the stress components of the initial configuration data in a single orthogonal coordinate system is calculated. Then, the stress in the fiber coordinate system in the current increment step is calculated. Then, the stress in the orthogonal coordinate system is transformed to the GN coordinate system by combining the transformation matrix. The total stress in the GN coordinate system is superimposed to form a finite element calculation model.

[0009] To obtain the initial dimensions of a two-dimensional fiber fabric, polar coordinates [θ] are used. k r k Define the coordinates of the control points on the fabric boundary, based on the k-th control point P on the fabric boundary. k Set control point P k Radial distance from the minimum boundary of the fabric |RP k |Restriction conditions r k ; Obtain each control point P k angular coordinates θ k The angular coordinates θ of the control points generated by the optimization algorithm k Sort; then sort by diagonal coordinates θ k The sorted fabric mesh with initial size is parametrically "trimmed" to obtain the "trimmed" fabric mesh; the deformation of the fabric material is simulated and calculated based on the finite element model to obtain the fabric strain distribution; then the severity of forming defects is evaluated based on the fabric strain distribution to obtain a parametric simulation and evaluation model for controlling the shape of the loaded fabric.

[0010] A parameterized simulation and evaluation model for fabric shape control is loaded, and the maximum absolute value of the compressive strain in the principal fiber directions is output. The polar coordinates [θ] of the control points in the simulation and evaluation model k r kInitialize and determine the range of polar coordinate values; then, based on the design objectives, set the optimization objectives and constraints of the simulation and evaluation model in the Isight software, and select the optimization algorithm to run the calculation until the optimal solution is obtained, thus completing the design of the fabric shape parameters.

[0011] Preferably, the orthogonal coordinate system is [e f1 ,e f2 ,e f3 ] and [e f1 ,e f2 ,e f3 ], where vector e fi For e fi The contravariant vector, vector e fi The formula for calculation is:

[0012]

[0013] e f3 e is a unit vector perpendicular to the fabric plane. f3 The formula for calculation is:

[0014]

[0015] Preferably, the formula for calculating the increment of the stress component in the single orthogonal coordinate system is:

[0016] Where E f1 and E f2 These are the moduli in the two principal directions of the fiber, G. 12 Shear modulus of the fabric; and For the increments in the directions of different stress components; and These represent stress components in different directions.

[0017] Preferably, the formula for calculating the transformation matrix is:

[0018]

[0019] Among them, Q f1 and Q f2 Both are transformation matrices, Q f1→GN and Q f2→GN g1, g2, and g3 are the two principal fiber directions in the orthogonal coordinate system, respectively, and g1, g2, and g3 are the three orthogonal directions in the orthogonal coordinate system.

[0020] Preferably, the stress in the fiber coordinate system of the current increment step is determined by the increment dσ of the stress components in the fiber coordinate system within the current increment step. fi Stress compared to the previous increment step The result is obtained by superposition, and the calculation formula is:

[0021]

[0022] The formula for calculating stress transformation from the orthogonal coordinate system to the GN coordinate system is as follows:

[0023]

[0024] Preferably, the set point P k The radial coordinates are measured starting from the minimum boundary of the fabric, and point P is... k Radial distance from the minimum boundary of the fabric |RP k |Regularization, forming limiting conditions r k Constraints r k for: r k ∈[0,1].

[0025] Preferably, the specific steps for parametric "trimming" the fabric mesh are as follows: retaining the cells inside the polygon obtained by connecting the control points and deleting the cells outside it, thereby obtaining the "trimmed" fabric mesh; using the maximum absolute value of the compressive strain in the principal direction of the fabric fibers in the fabric strain distribution. To evaluate the severity of forming defects.

[0026] Preferably, the polar coordinates [θ] of the control points in the model are obtained through the Variables option of the Optimisation component. k r k Parameter initialization; set the optimization objective of the optimization model through the Objectives option of the Optimization component; set the constraints of the optimization model through the Constraints option of the Optimization component; select the optimization algorithm through the General option of the Optimization component; select RunComponent to run the calculation.

[0027] The fabric preform initial shape optimization and cutting method based on finite element simulation proposed in this application has the following advantages:

[0028] It can obtain the optimal solution of fabric shape corresponding to the minimum of fabric forming defect characterization quantity through numerical simulation calculation, avoiding repeated trial and error based on a large number of fabric forming physical tests, and can effectively save process design time and cost; using fabric shape as optimization design variable, it can achieve material consumption savings by setting the maximum area constraint of fabric. Attached Figure Description

[0029] To more clearly illustrate the technical solutions provided in this application, the accompanying drawings will be briefly described below. Obviously, the drawings described below are merely some embodiments of this application.

[0030] Figure 1 The overall design flowchart for this application is optimized.

[0031] Figure 2 This is a schematic diagram of the main fiber direction before and after the deformation of the two-dimensional fabric fibers in this application.

[0032] Figure 3 This is a schematic diagram of fabric boundary parameterization based on boundary control points in this application.

[0033] Figure 4 This is a schematic diagram of the fabric mesh construction method based on boundary polyline cutting in this application;

[0034] Figure 5 This is a microstructure diagram of the biaxial non-curled structure of this application;

[0035] Figure 6 This is a schematic diagram of the finite element model of the hemispherical die stamping process in this application;

[0036] Figure 7 This is a schematic diagram of the finite element model of the hemispherical die stamping process in this application;

[0037] Figure 8 This is a schematic diagram of the optimized fabric shape boundary in this application;

[0038] Figure 9 This is a schematic diagram of the compressive strain distribution in the main fiber direction before and after the fabric shape optimization in this application. Detailed Implementation

[0039] 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.

[0040] A method for optimizing the initial shape of fabric preforms based on finite element simulation is proposed. By designing the initial shape of the two-dimensional fabric, the strain distribution of the fabric after forming and deformation is adjusted to minimize manufacturing defects, thereby improving the quality of the preform.

[0041] like Figure 1 As shown, it includes the following steps:

[0042] Step S100: Finite element calculation model for fabric forming based on non-orthogonal constitutive relations.

[0043] The initial configuration data of the two-dimensional fiber fabric is obtained and input into the Abaqus platform. The unit direction vector in the initial configuration data is obtained, and then an orthogonal coordinate system is constructed using the unit direction vector. The transformation matrix of the GN coordinate system is calculated based on the orthogonal coordinate system. The increment of the stress components of the initial configuration data in a single orthogonal coordinate system is calculated based on the GN coordinate system. The stress in the fiber coordinate system of the current increment step is calculated based on the increment of the stress components in a single orthogonal coordinate system. Then, the stress in the orthogonal coordinate system is transformed to the GN coordinate system by combining the transformation matrix, and then the total stress in the GN coordinate system is superimposed to form a finite element calculation model.

[0044] By embedding the subelastic nonorthogonal constitutive relation describing the in-plane deformation of two-dimensional fabrics into the finite element model, effective simulation of the forming deformation of two-dimensional fabrics can be achieved. The definition of the principal fiber directions is as follows: Figure 2 ,in, 0 g α (α=1,2,3) is the material coordinate system of the finite element integration points in Abaqus, also known as the Green-Naghdi coordinate system, hereinafter referred to as the GN coordinate system.

[0045] Preferably, the unit direction vector e of the fiber under the current configuration is obtained using the deformation gradient tensor F. fi The calculation formula is:

[0046]

[0047] In equation (1), Let i be the unit direction vector of the fiber in the initial configuration, with subscripts i = 1 and 2 representing the two principal directions of the fiber in the fabric.

[0048] Preferably, such as Figure 2 The orthogonal coordinate system is [e f1 ,e f2 ,e f3 ] and [e f1 ,e f2 ,e f3 ], where vector e fi For e fi The contravariant vector, vector e fi The formula for calculation is:

[0049]

[0050] e f3 e is a unit vector perpendicular to the fabric plane. f3 The formula for calculation is:

[0051]

[0052] Preferably, the formula for calculating the transformation matrix is:

[0053]

[0054] Among them, Q f1 and Q f2 Both are transformation matrices, Q f1→GN and Q f2→GN g1, g2, and g3 are the two principal fiber directions in the orthogonal coordinate system, respectively, and g1, g2, and g3 are the three orthogonal directions in the orthogonal coordinate system.

[0055] Preferably, the formula for calculating the increment of stress components in a single orthogonal coordinate system is:

[0056]

[0057] Where E f1 and E f2 These are the moduli in the two principal directions of the fiber, G. 12 Shear modulus of the fabric; and For the increments of different stress components; and All are stress components.

[0058] Preferably, the stress in the fiber coordinate system at the current increment step is determined by the increment dσ of the stress components in the fiber coordinate system within the current increment step. fi Stress compared to the previous increment step The result is obtained by superposition, and the calculation formula is:

[0059]

[0060] The formula for calculating stress transformation from the orthogonal coordinate system to the GN coordinate system is as follows:

[0061]

[0062] Step S200: Parametric forming simulation and evaluation model based on fabric shape control

[0063] To ensure the fabric completely covers the hemispherical mold after forming and deformation, a minimum fabric boundary R needs to be set; simultaneously, the size of the cut fabric should not exceed its initial size. Based on this, this application defines the fabric's boundary after cutting by sequentially connecting discrete control points using multiple straight lines. Therefore, control point P... k The feasible region is the area enclosed between the initial boundary of the fabric and the minimum boundary of the fabric, such as... Figure 3 .

[0064] Specifically, the initial dimensions of the two-dimensional fiber fabric are obtained using polar coordinates [θ]. k r kDefine the coordinates of the control points on the fabric boundary, based on the k-th control point P on the fabric boundary. k Set control point P k Radial distance from the minimum boundary of the fabric |RP k |Restriction conditions r k So that point P k Always within the feasible region; obtain each control point P k angular coordinates θ k Then diagonal coordinates θ k The sorted fabric mesh with initial dimensions is parametrically "trimmed" to avoid self-intersection of control point sequential lines. Then, the fabric mesh with initial dimensions is parametrically "trimmed" using the Abaqus / Python platform to obtain the "trimmed" fabric mesh. The deformation of the fabric material is simulated based on the finite element model and submitted to the Abaqus platform for calculation to obtain the fabric strain distribution. Then, the severity of forming defects is evaluated based on the fabric strain distribution to obtain a parametric simulation and evaluation model for loading and controlling the shape of the fabric.

[0065] Constraints r k for: r k ∈[0,1].

[0066] To ensure point P k Always within the feasible region, set point P k The radial coordinates are measured starting from the minimum boundary of the fabric, and point P is... k Radial distance from the minimum boundary of the fabric |RP k |Regularization, forming limiting conditions r k Angular coordinates θ k For connecting to OP k The angle between the x-axis and the x-axis.

[0067] Preferably, the specific steps for parametric "trimming" the fabric mesh are as follows: retain the cells inside the polygon obtained by connecting the control points, delete the cells outside it, and thus obtain the "trimmed" fabric mesh. In this application, cells whose three nodes are all located within the boundary are considered as cells to be retained, and the rest are cells to be deleted, such as... Figure 4 As shown.

[0068] Preferably, the maximum absolute value of the compressive strain in the principal direction of the fabric fibers in the fabric strain distribution is used. To evaluate the severity of forming defects; that is... The higher the probability of forming defects, the worse the forming quality of the preform; conversely, the lower the probability of forming defects, the better the forming quality.

[0069] Step S300: Optimize fabric shape design process based on Isight software to suppress surface forming defects.

[0070] Specifically, this involves loading a parametric simulation and evaluation model for fabric shape control into the Isight software and outputting the maximum absolute value of the compressive strain in the principal fiber directions. The polar coordinates [θ] of the control points in the simulation and evaluation model k r k Initialize and determine the range of polar coordinate values; then, based on the design objectives, set the optimization objectives and constraints of the simulation and evaluation model in the Isight software, and select the optimization algorithm to run the calculation until the optimal solution is obtained, thus completing the design of the fabric shape parameters.

[0071] Preferably, the polar coordinates [θ] of the control points in the model are set using the Variables option of the Optimisation component. k r k Parameter initialization; set the optimization objective of the optimization model through the Objectives option of the Optimization component; set the constraints of the optimization model through the Constraints option of the Optimization component; select the optimization algorithm through the General option of the Optimization component; select RunComponent to run the calculation.

[0072] As a specific implementation method, the following description uses biaxial non-curled fabric hemispherical mold compression molding as an example.

[0073] like Figure 5 As shown, the biaxial non-crimped fabric consists of two layers of straight fibers bound together by interlaced stitches along the thickness direction, with the stitches forming a 45° angle with the principal fiber direction. The material properties in the finite element model are: nominal modulus of the principal fiber direction is 10 GPa, surface weight is 440 g / m², and nominal thickness is 0.4 mm; the in-plane shear force F... NCF With shear strain γ 12 The relationship is non-linear, and the specific relationship is shown in equation (10):

[0074]

[0075] Among them, F yarn rotation F represents the contribution of in-plane rotation of the fiber bundle to the in-plane shear force of the fabric. stitch This represents the contribution of seam deformation to the in-plane shear force of the fabric.

[0076] See compression molding configuration Figure 6The inner boundary of the edge-pressing fixture is square, with an inner dimension of 300mm × 300mm. Its center contains a circular through-hole with a radius of 52mm, and the hole's edge has a 6mm chamfer to accommodate the stamping die and fabric material. The hemispherical stamping die has a radius of 50mm and a stamping stroke of 50mm. The initial shape of the non-curled fabric is a 300mm × 300mm square, clamped between the upper and lower edge-pressing fixtures. The main direction of the fabric fibers forms a 45° angle with the straight edge of the edge-pressing fixture.

[0077] The implementation process is as follows:

[0078] 1) Based on the above fabric material performance parameters, write the material user subroutine VUMAT according to the method in step S100;

[0079] 2) Establish a finite element model of fabric stamping based on a hemispherical mold: The single-layer fabric is constructed using membrane element M3D4R; the fabric model contains a total of 3600 elements, with an element size of 5mm×5mm; the components in the model adopt the GeneralContact contact relationship, the friction coefficient between fabrics is 0.36, and the friction coefficient between fabric and mold is 0.2.

[0080] 3) Set load boundary conditions: The pressure force on the lower edge is a uniformly distributed pressure, acting on the bottom surface of the lower edge, with a magnitude of 12500Pa and a resultant force of approximately 1000N.

[0081] 4) Set displacement boundary conditions: Apply a 50mm stamping displacement to the hemispherical mold.

[0082] 5) Using the Isight software, following the steps in section S300, integrate the Optimisation and Simcode components to create a system as follows: Figure 7 The analysis framework shown enables the connection of computational programs.

[0083] 6) In the Simcode component, load the Abaqus / Python parametric modeling script file using the Input option, initialize the coordinates of the boundary control points as design variables; load the Abaqus executable file using the Command option; load the output file using the Output option, and read the calculation results data.

[0084] 7) In the Isight software, through the Variables option of the Optimisation component, select the variables corresponding to the control point coordinates to initialize the design variables and set their value range, i.e., θ. k ∈[0,2π],r k ∈[0,1].

[0085] 8) Fiber compressive strain is strongly correlated with the severity of fabric forming defects. Therefore, in this example, in the Objective option of the Optimisation component of the Isight software, the maximum absolute value of the compressive strain in the principal fiber direction of the fabric is selected. The objective function is to minimize... To minimize fabric forming defects.

[0086] 9) In the General option of the Optimisation component of the Isight software, select Multi-island Genetic Algorithm as the optimization algorithm.

[0087] 10) In the Isight software, select RunComponent to run the optimization process, obtain the optimal solution, and complete the fabric shape design for suppressing forming defects.

[0088] Figure 8 The optimized fabric boundary shape and control point distribution are shown. Figure 9 The compressive strain distribution of the main fiber direction of the fabric before and after optimization was compared. The magnitude and distribution area of ​​the compressive strain were significantly reduced, and the maximum value of the compressive strain decreased by 12%, which verifies the feasibility of the method.

[0089] In summary, this application has the following advantages:

[0090] It can obtain the optimal solution of fabric shape corresponding to the minimum of fabric forming defect characterization quantity through numerical simulation calculation, avoiding repeated trial and error based on a large number of fabric forming physical tests, and can effectively save process design time and cost; using fabric shape as optimization design variable, it can achieve material consumption savings by setting the maximum area constraint of fabric.

[0091] Finally, it should be noted that the accompanying drawings of the embodiments disclosed in this invention only involve the structures involved in the embodiments disclosed in this invention. Other structures can refer to the general design. In the absence of conflict, the same embodiment and different embodiments of this invention can be combined with each other.

[0092] In conclusion, the above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. 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. A method for optimizing the initial shape of a fabric preform based on finite element simulation, characterized in that, include: Obtain the initial configuration data of the two-dimensional fiber fabric and input the values ​​into the Abaqus platform; Obtain the unit direction vector from the initial configuration data, then construct an orthogonal coordinate system using the unit direction vector, calculate the transformation matrix of the GN coordinate system based on the orthogonal coordinate system, and calculate the increment of the stress components of the initial configuration data in a single orthogonal coordinate system. Then, the stress in the fiber coordinate system at the current incremental step is calculated, and then the stress in the orthogonal coordinate system is transformed to the GN coordinate system by combining the transformation matrix. The total stress in the GN coordinate system is then superimposed to form a finite element calculation model. To obtain the initial dimensions of a two-dimensional fiber fabric, polar coordinates [θ] are used. k r k Define the coordinates of the control points on the fabric boundary, based on the k-th control point P on the fabric boundary. k Set control point P k Radial distance from the minimum boundary of the fabric |RP k |Restriction conditions r k ; Obtain each control point P k angular coordinates θ k The angular coordinates θ of the control points generated by the optimization algorithm k Sort; then sort by diagonal coordinates θ k The sorted fabric mesh with initial dimensions is parametrically "trimmed" to obtain the "trimmed" fabric mesh; The deformation of the fabric material was simulated and calculated based on the finite element model, and the strain distribution of the fabric was obtained. Then, based on the fabric strain distribution, the severity of forming defects is evaluated, and a parameterized simulation and evaluation model for controlling the shape of the loaded fabric is obtained. A parameterized simulation and evaluation model for fabric shape control is loaded, and the maximum absolute value of the compressive strain in the principal fiber directions is output. The polar coordinates [θ] of the control points in the simulation and evaluation model k r k Initialize and determine the range of polar coordinate values; then, based on the design objectives, set the optimization objectives and constraints of the simulation and evaluation model in the Isight software, and select the optimization algorithm to run the calculation until the optimal solution is obtained, thus completing the design of the fabric shape parameters.

2. The method for optimizing the initial shape of fabric preforms based on finite element simulation as described in claim 1, characterized in that: The orthogonal coordinate system is [e f1 ,e f2 ,e f3 ] and [e f1 ,e f2 ,e f3 ], where vector e fi For e fi The contravariant vector, vector e fi The formula for calculation is: e f3 e is a unit vector perpendicular to the fabric plane. f3 The formula for calculation is:

3. The method for optimizing the initial shape of fabric preforms based on finite element simulation as described in claim 2, characterized in that: The formula for calculating the increment of the stress component in the single orthogonal coordinate system is: Where E f1 and E f2 These are the moduli in the two principal directions of the fiber, G. 12 Shear modulus of the fabric; and For the increments in the directions of different stress components; and These represent stress components in different directions.

4. The method for optimizing the initial shape of fabric preforms based on finite element simulation as described in claim 2, characterized in that: The formula for calculating the transformation matrix is: Among them, Q f1 and Q f2 Both are transformation matrices, Q f1→GN and Q f2→GN g1, g2, and g3 are the two principal fiber directions in the orthogonal coordinate system, respectively, and g1, g2, and g3 are the three orthogonal directions in the orthogonal coordinate system.

5. The method for optimizing the initial shape of fabric preforms based on finite element simulation as described in claim 4, characterized in that: The stress in the fiber coordinate system at the current increment step is determined by the increment dσ of the stress components in the fiber coordinate system within the current increment step. fi Stress compared to the previous increment step The result is obtained by superposition, and the calculation formula is: The formula for calculating stress transformation from the orthogonal coordinate system to the GN coordinate system is as follows:

6. The method for optimizing the initial shape of a fabric preform based on finite element simulation as described in claim 1, characterized in that: The set point P k The radial coordinates are measured starting from the minimum boundary of the fabric, and point P is... k Radial distance from the minimum boundary of the fabric |RP k |Regularization, forming limiting conditions r k Constraints r k for: r k ∈[0,1].

7. The method for optimizing the initial shape of fabric preforms based on finite element simulation as described in claim 1, characterized in that: The specific steps for parametric "trimming" the fabric mesh are as follows: Retain the cells inside the polygon obtained by connecting the control points, and delete the cells outside, thus obtaining the "trimmed" fabric mesh; Use the maximum absolute value of the compressive strain in the principal direction of the fabric fibers in the fabric strain distribution. To evaluate the severity of forming defects.

8. The method for optimizing the initial shape of fabric preforms based on finite element simulation as described in claim 1, characterized in that: Using the Variables option of the Optimisation component, the polar coordinates [θ] of the control points in the model are... k r k Parameter initialization; set the optimization objective of the optimization model through the Objectives option of the Optimization component; set the constraints of the optimization model through the Constraints option of the Optimization component; select the optimization algorithm through the General option of the Optimization component; select RunComponent to run the calculation.

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