Method for predicting mechanical property of composite material prepared from non-woven structure carbon fiber / thermoplastic fiber felt

Abstract

The invention provides a method for predicting the mechanical property of a composite material prepared from a non-woven structure carbon fiber / thermoplastic fibrofelt, the method is a comprehensive prediction method based on a representative volume element (RVE), a bridging model and a real stress theory, and compared with the prior art, the method has the advantages that: 1, the prediction precision is obviously improved; the method has the advantages of simple operation, accurate description of the anisotropy of the composite material, enhancement of the prediction capability of the damage behavior, and wide applicability and popularization value. The method provided by the invention is not only suitable for recovering the carbon fiber / polypropylene needled felt reinforced composite material, but also can be popularized and applied to mechanical property prediction of other types of fiber reinforced composite materials. The method provides a new and more effective technical means for the field of composite material mechanical property prediction through the prediction thought of accurate description and comprehensive consideration of microstructure characteristics, and has wide application prospects and important academic values.

Description

Technical Field

[0001] This invention belongs to the field of carbon fiber composite material technology, and particularly relates to a method for predicting the mechanical properties of composite materials prepared from non-woven carbon fiber / thermoplastic fiber felt. Background Technology

[0002] Composite materials are widely used in many fields due to their excellent properties, and accurate prediction of their mechanical properties is crucial for product design, optimization, and reliability assessment. For recycled carbon fiber / polypropylene needle-punched felt reinforced composites, with the continuous expansion of their applications, establishing effective methods for predicting the mechanical properties, especially the elastic modulus of the composite, is particularly urgent.

[0003] Currently, the prediction of mechanical properties of recycled carbon fiber / polypropylene needle-punched felt reinforced composites is not accurate enough, making it difficult to meet the performance evaluation needs of practical engineering applications. Existing prediction methods are mostly based on theoretical models of traditional continuous fiber reinforced composites or short fiber reinforced composites. However, the carbon fiber length in recycled carbon fiber / polypropylene needle-punched felt reinforced composites falls between these two categories and exhibits significant anisotropy. These characteristics make it impossible for traditional models to accurately describe its mechanical behavior, resulting in a large deviation between the predicted results and actual experimental values. Summary of the Invention

[0004] The purpose of this invention is to provide a method for predicting the mechanical properties of composite materials made from nonwoven carbon fiber / thermoplastic fiber felt. The prediction method in this invention can accurately describe the anisotropy of composite materials, improve the prediction accuracy of mechanical properties, and enhance the ability to predict the failure behavior of composite materials.

[0005] This invention provides a method for predicting the mechanical properties of composite materials prepared from nonwoven carbon fiber / thermoplastic fiber mat, comprising the following steps:

[0006] A) Measure and analyze the length of carbon fibers in the composite material prepared by non-woven carbon fiber / thermoplastic fiber felt to obtain the probability density function and cumulative distribution function of carbon fiber length;

[0007] The carbon fiber orientation angle inside the composite material prepared by non-woven carbon fiber / thermoplastic fiber felt was measured to obtain the probability density function and cumulative distribution function of the carbon fiber orientation angle.

[0008] B) Based on the probability density function of carbon fiber length, the cumulative distribution function of carbon fiber length, the probability density function of carbon fiber orientation angle, and the cumulative distribution function of carbon fiber orientation angle, a representative volume element RVE is constructed using a random generation algorithm.

[0009] C) By analyzing the stress transmission path and stress distribution law of carbon fiber and thermoplastic matrix in representative volume element RVE under different load conditions, the stress bridging relationship between carbon fiber and thermoplastic matrix is ​​constructed by applying bridging model theory, and the bridging parameters are calculated.

[0010] D) After obtaining the bridging parameters, apply the real stress theory to perform stress analysis on the carbon fiber and thermoplastic matrix in the representative volume element RVE model, and calculate their real stress state under different load conditions.

[0011] Preferably, the method of constructing the representative volume unit (RVE) using a random generation algorithm specifically includes the following steps:

[0012] The length of each carbon fiber is determined based on the probability density function and cumulative distribution function of the carbon fiber length. The spatial orientation of each carbon fiber is determined based on the probability density function and cumulative distribution function of the carbon fiber orientation angle. Carbon fibers are randomly generated within the representative volume unit RVE space. Then, thermoplastic matrix material is filled around the generated carbon fibers to ensure full contact between the carbon fibers and the thermoplastic matrix, thus obtaining the representative volume unit RVE.

[0013] Preferably, the bridging parameters include bridging stiffness, bridging flexibility, stress concentration factor, and bridging matrix.

[0014] Preferably, the formula for the bridging matrix is ​​shown in Equation I:

[0015] Formula I;

[0016]

[0017]

[0018]

[0019]

[0020] in, and For bridging parameters, , and These are the transverse elastic modulus and axial shear modulus of carbon fiber, respectively. and These are the elastic modulus and shear modulus of the thermoplastic matrix, respectively; , , and are the coefficients in the flexibility matrices of carbon fiber and thermoplastic matrix, respectively.

[0021] Preferably, after constructing the representative volumetric unit (RVE), the RVE model is optimized. The optimization process includes: slicing the representative volumetric unit (RVE) and introducing a correction coefficient to correct the carbon fiber volume content in the slice to the carbon fiber volume content data of the representative volumetric unit (RVE).

[0022] Preferably, the bridging parameters of multiple slices are calculated and then superimposed to obtain the bridging parameters of the entire representative volume element RVE.

[0023] Preferably, step D) specifically includes:

[0024] Different strain fields were applied in the representative volume element RVE, and the true stress components in each direction of the carbon fiber and thermoplastic matrix were calculated according to the bridging model and the true stress theory. The macroscopic stress-strain relationship curve of the composite material prepared by non-woven carbon fiber / thermoplastic fiber felt was further calculated, and the elastic modulus data were obtained from the macroscopic stress-strain relationship curve.

[0025] Preferably, in step C), bridging parameters are calculated based on the microstructure characteristics and mechanical performance requirements of the composite material prepared from nonwoven carbon fiber / thermoplastic fiber felt;

[0026] The microstructure characteristics of the composite material prepared by the nonwoven carbon fiber / thermoplastic fiber felt include the carbon fiber volume fraction, carbon fiber orientation angle, or interface properties; the mechanical performance requirements include strength, modulus, or toughness.

[0027] Preferably, in the representative volume unit RVE, the carbon fibers do not overlap.

[0028] Preferably, after optimizing the representative volumetric unit RVE, the results are verified by comparing it with the microstructure observation results of the actual composite material.

[0029] The microstructure observation results include the distribution density of carbon fibers, the orientation distribution of carbon fibers, and the contact between carbon fibers and the thermoplastic matrix.

[0030] This invention provides a method for predicting the mechanical properties of composite materials prepared from nonwoven carbon fiber / thermoplastic fiber felt, comprising the following steps: A) Measuring and analyzing the length of carbon fibers in the composite material prepared from nonwoven carbon fiber / thermoplastic fiber felt to obtain the probability density function and cumulative distribution function of carbon fiber length; measuring the orientation angle of carbon fibers inside the composite material prepared from nonwoven carbon fiber / thermoplastic fiber felt to obtain the probability density function and cumulative distribution function of carbon fiber orientation angle; B) Constructing a representative volume element (RVE) using a random generation algorithm based on the probability density function, cumulative distribution function, probability density function, and cumulative distribution function of carbon fiber orientation angle; C) Analyzing the stress transmission path and stress distribution law of carbon fibers and thermoplastic matrix in the representative volume element RVE under different load conditions, applying bridging model theory to construct the stress bridging relationship between carbon fibers and thermoplastic matrix, and calculating the bridging parameters; D) After obtaining the bridging parameters, applying true stress theory to perform stress analysis on carbon fibers and thermoplastic matrix in the representative volume element RVE model to calculate their true stress state under different load conditions.

[0031] This invention proposes a comprehensive prediction method based on representative volume element (RVE), bridging model, and true stress theory. Compared with existing technologies, this invention has the following significant advantages:

[0032] 1. Significantly Improved Prediction Accuracy: By constructing an RVE model that accurately reflects the microstructural characteristics of composite materials and combining it with bridging models and true stress theory for mechanical property prediction, this invention can fully consider the influence of factors such as carbon fiber length variation, orientation angle distribution, and stress concentration on mechanical properties. Compared with traditional mixture-based regular models, semi-empirical models, and theoretical models based on mean stress, the deviation between the predicted elastic modulus of composite materials and actual experimental values ​​is significantly reduced, and the prediction accuracy is significantly improved, providing a more reliable theoretical basis for the design and application of composite materials.

[0033] 2. Accurate Description of Composite Material Anisotropy: Recycled carbon fiber / polypropylene needle-punched felt reinforced composite materials exhibit significant anisotropy, and the RVE construction method and mechanical property prediction model of this invention can accurately reflect this anisotropy. Through precise description of the carbon fiber orientation angle distribution and its reasonable application in the prediction process, this invention can accurately characterize the differences in mechanical properties of composite materials in different directions, providing strong support for the structural optimization and performance control of composite materials, and helping to fully leverage the performance advantages of composite materials.

[0034] 3. Enhanced ability to predict failure behavior: Based on the theory of true stress, this invention can accurately describe the true stress state of carbon fibers and thermoplastic matrix in the plastic stage of composite materials, thereby effectively capturing stress concentration phenomena. This makes the invention more accurate and reliable in predicting the failure behavior and material modulus of composite materials, enabling better assessment of the safety and reliability of composite materials under actual working conditions, and providing important protection for the safe application of composite materials.

[0035] 4. Wide applicability and promotional value: The method proposed in this invention is not only applicable to recycled carbon fiber / polypropylene needle-punched felt reinforced composites, but can also be extended to the prediction of mechanical properties of other types of carbon fiber reinforced composites. Its precise description of microstructural characteristics and comprehensive prediction approach provide a new and more effective technical means for the field of composite material mechanical property prediction, possessing broad application prospects and significant academic value. Attached Figure Description

[0036] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on the provided drawings without creative effort.

[0037] Figure 1 The probability density function (PDF) for carbon fiber length in this embodiment of the invention.

[0038] Figure 2 This refers to the cumulative distribution function (CDF) of carbon fiber length in this embodiment of the invention.

[0039] Figure 3 Here is the probability density function (PDF) for carbon fiber orientation in this embodiment of the invention, where a) is the orientation angle and b) is the elevation angle;

[0040] Figure 4 Here is the cumulative distribution function (CDF) of carbon fiber orientation in this embodiment of the invention, where a) is the orientation angle and b) is the elevation angle;

[0041] Figure 5 This is a schematic diagram (side view) of the RVE carbon fiber model constructed in an embodiment of the present invention.

[0042] Figure 6 This is a schematic diagram (cross-sectional view) of the RVE carbon fiber model constructed in an embodiment of the present invention.

[0043] Figure 7 This is a schematic diagram of the applied load of the RVE model constructed in this embodiment of the invention;

[0044] Figure 8 These are the predicted and actual values ​​of the elastic modulus of the RVE model in this embodiment of the invention. Detailed Implementation

[0045] This invention provides a method for predicting the mechanical properties of composite materials prepared from nonwoven carbon fiber / thermoplastic fiber mat, comprising the following steps:

[0046] A) Measure and analyze the length of carbon fibers in the composite material prepared by non-woven carbon fiber / thermoplastic fiber felt to obtain the probability density function and cumulative distribution function of carbon fiber length;

[0047] The carbon fiber orientation angle inside the composite material prepared by non-woven carbon fiber / thermoplastic fiber felt was measured to obtain the probability density function and cumulative distribution function of the carbon fiber orientation angle.

[0048] B) Based on the probability density function of carbon fiber length, the cumulative distribution function of carbon fiber length, the probability density function of carbon fiber orientation angle, and the cumulative distribution function of carbon fiber orientation angle, a representative volume element RVE is constructed using a random generation algorithm.

[0049] C) By analyzing the stress transmission path and stress distribution law of carbon fiber and thermoplastic matrix in representative volume element RVE under different load conditions, the stress bridging relationship between carbon fiber and thermoplastic matrix is ​​constructed by applying bridging model theory, and the bridging parameters are calculated.

[0050] D) After obtaining the bridging parameters, apply the real stress theory to perform stress analysis on the carbon fiber and thermoplastic matrix in the representative volume element RVE model, and calculate their real stress state under different load conditions.

[0051] The method for predicting the mechanical properties of composite materials prepared from spun carbon fiber / thermoplastic fiber felt in this invention mainly includes three steps: establishing representative volume element (RVE), applying the bridging model, and applying the real stress theory.

[0052] ① Establishment of Representative Volumetric Element (RVE)

[0053] Determine the size and shape of the RVE: Select an appropriate RVE size and shape based on the actual size of the composite material and research requirements. Typically, the RVE should be large enough to contain more than 300 carbon fibers to represent the microstructural characteristics of the composite material; simultaneously, the structure of the RVE should closely approximate the overall structure of the composite material to ensure the model's rationality and accuracy.

[0054] Obtain the distribution patterns of carbon fiber length and orientation angle:

[0055] Carbon fiber length measurement: A certain number of carbon fibers were randomly selected from the composite material prepared from nonwoven carbon fiber / thermoplastic fiber mat, and the length of each carbon fiber was measured using a high-precision measuring instrument, and the data was recorded. Statistical analysis was performed on the measured carbon fiber length data to obtain the probability density function (PDF) and cumulative distribution function (CDF) of the carbon fiber length.

[0056] Carbon fiber orientation angle measurement: Advanced image processing and Micro-CT scanning technologies were employed to observe the internal structure of composite materials made from nonwoven carbon fiber / thermoplastic fiber mat. By analyzing the obtained three-dimensional images, the angles between the carbon fibers and specific directions (such as the principal axis of the material) were measured to obtain the distribution of carbon fiber orientation angles. Similarly, statistical methods were used to obtain the PDF and CDF of the carbon fiber orientation angles, providing accurate parameter data for subsequent RVE establishment.

[0057] In this invention, the carbon fiber orientation angle is characterized by an orientation angle and an elevation angle. The carbon fiber orientation angle refers to the orientation angle of the carbon fiber on the horizontal projection plane. It is usually based on a fixed reference direction (such as due east or due north) within the horizontal projection plane and is used to describe the orientation of the carbon fiber in the horizontal direction. The elevation angle, on the other hand, refers to the angle between the carbon fiber and the horizontal plane. It is used to describe the degree of inclination of the carbon fiber in the vertical direction.

[0058] Random carbon fiber generation: Within a defined RVE space, carbon fibers are randomly generated according to their length and orientation angle distributions. First, the length of each carbon fiber is randomly determined based on its length PDF; then, the spatial orientation of each carbon fiber is randomly determined based on its orientation angle PDF. During the generation process, it is ensured that the carbon fibers do not overlap and that their distribution conforms to the actual carbon fiber distribution patterns in composite materials.

[0059] Adding thermoplastic matrix material: A thermoplastic matrix material is filled around the generated carbon fibers to ensure full contact between the carbon fibers and the thermoplastic matrix, forming a complete RVE structure. The addition of the thermoplastic matrix material should ensure a clear interface between it and the carbon fibers, and the volume fraction of the thermoplastic matrix should conform to the composition ratio of the actual composite material.

[0060] Model Optimization and Validation: The constructed RVE model is optimized by establishing representative volumetric elements of the composite material through slicing, and by introducing correction coefficients to adjust the carbon fiber volume content of the slices to match the data in the RVE model, eliminating potential defects and inconsistencies. For example, the contact between the carbon fiber and the thermoplastic matrix is ​​checked, and the carbon fiber distribution density is adjusted. Simultaneously, the model is validated by comparing it with the microstructure observation results of actual composite materials to ensure that the RVE model accurately reflects the microstructural characteristics of the composite material.

[0061] ② Application of the bridging model

[0062] Establishing the stress bridging relationship between carbon fiber and thermoplastic matrix: Based on the RVE model, the stress bridging relationship between carbon fiber and thermoplastic matrix is ​​established using bridging model theory. Specifically, by analyzing the interaction between carbon fiber and thermoplastic matrix, the stress transmission path and stress distribution law of carbon fiber and thermoplastic matrix under different load conditions are determined. A certain transformation relationship exists between stress and strain in the material, which can be summarized into a coefficient matrix, as shown in Equation I. This matrix can be used to calculate the relationship between the stress of carbon fiber and thermoplastic matrix in the composite material, thereby linking the stress of the thermoplastic matrix with the stress of the carbon fiber to form a complete stress transmission network.

[0063] Formula I;

[0064]

[0065]

[0066]

[0067]

[0068] in, and For bridging parameters, , and These are the transverse elastic modulus and axial shear modulus of carbon fiber, respectively. and These are the elastic modulus and shear modulus of the thermoplastic matrix, respectively; , , and are the coefficients in the flexibility matrices of carbon fiber and thermoplastic matrix, respectively.

[0069] Calculating bridging parameters: Based on the microstructural characteristics of the composite material, such as carbon fiber volume fraction, carbon fiber orientation, and interface properties, and the required mechanical properties, such as strength, modulus, and toughness, the bridging model can be used to calculate key parameters in the bridging relationship, such as bridging stiffness and bridging flexibility. These parameters reflect the interaction strength and stress transfer efficiency between the carbon fiber and the thermoplastic matrix, and are crucial for accurately predicting the elastic modulus of the composite material.

[0070] The bridging model can link the stress in the thermoplastic matrix with the stress in the carbon fiber, and calculate the increment of the mechanical properties of the carbon fiber and the thermoplastic matrix through the bridging matrix.

[0071] By combining theoretical derivation and numerical simulation, the relationship between these parameters and factors such as carbon fiber length, orientation angle, and thermoplastic matrix properties is determined, providing a foundation for subsequent mechanical property prediction.

[0072] ③ Application of the theory of true stress

[0073] The real stress theory mentioned is the real stress theory proposed by Professor Huang Zhengming of Tongji University. For details, please refer to Huang Zhengming. Real stress theory of matrix [J]. Acta Mechanica Sinica, 2022, 43(3): 243-256.

[0074] Calculating the True Stress of Carbon Fibers and Thermoplastic Matrix: After obtaining the bridging parameters, stress analysis is performed on the carbon fiber and thermoplastic matrix in the RVE model based on true stress theory to calculate their true stress state under different loading conditions. Unlike traditional mean stress theory, true stress theory can consider the geometric changes and nonlinear behavior of the composite material, as well as the inhomogeneity of the microstructure, such as the interface effect between carbon fiber and thermoplastic matrix, and stress concentration phenomena, thus more accurately reflecting the actual stress situation of carbon fiber and thermoplastic matrix.

[0075] By establishing corresponding mathematical models and numerical calculation methods, the true stress components of carbon fibers and thermoplastic matrices in various directions are solved, providing more accurate stress information for predicting the mechanical properties of composite materials. Stress concentration is considered: based on the theory of true stress, the potential stress concentration phenomena within the composite material are further considered. Stress concentration typically occurs near the interface between the carbon fiber and the thermoplastic matrix, at the tips or defects of the carbon fibers, and can significantly affect the strength and failure behavior of the composite material. By introducing concepts such as the stress concentration factor (SCF), these stress concentration regions are analyzed and quantified in detail, and incorporated into the mechanical property prediction model, improving the accuracy of predicting the failure behavior and ultimate strength of composite materials.

[0076] The specific steps for predicting mechanical properties are as follows:

[0077] Elastic modulus prediction: Different strain fields are applied in the RVE model. Based on the true stress components in each direction of the carbon fiber and thermoplastic matrix calculated using the bridging model and true stress theory, the macroscopic stress-strain relationship of the composite material is calculated using methods such as numerical integration. Elastic property parameters such as the elastic modulus of the composite material are extracted from the macroscopic stress-strain curve, thereby achieving accurate prediction of the elastic modulus of composite materials prepared from nonwoven carbon fiber / thermoplastic fiber felt.

[0078] To further illustrate the present invention, the following detailed description of the method for predicting the mechanical properties of a composite material prepared from a nonwoven carbon fiber / thermoplastic fiber felt provided by the present invention is provided in conjunction with embodiments, but it should not be construed as limiting the scope of protection of the present invention.

[0079] Example

[0080] The material is composed of recycled carbon fiber and polypropylene fiber. Specifically, it is a needle-punched felt reinforced composite material, in the form of a sheet with a certain thickness.

[0081] A certain number of carbon fibers were randomly selected from recycled carbon fiber / polypropylene needle-punched felt. The length of each carbon fiber was measured using a high-precision measuring instrument, and the data was recorded. Statistical analysis was performed on the measured carbon fiber length data to obtain the probability density function (PDF) and cumulative distribution function (CDF) of the carbon fiber length, such as... Figures 1-2 As shown.

[0082] Advanced image processing and Micro-CT scanning technologies were employed to observe the internal structure of recycled carbon fiber / polypropylene needle-punched felt reinforced composites. By analyzing the obtained three-dimensional images, the angles between the carbon fibers and specific directions (such as the principal axis of the material) were measured to obtain the distribution of carbon fiber orientation angles. Similarly, statistical methods were used to obtain the PDF and CDF of the carbon fiber orientation angles, such as... Figures 3-4 As shown.

[0083] Based on the carbon fiber length distribution and carbon fiber orientation angle distribution, carbon fibers are randomly generated within the representative volume element RVE space, ensuring that the carbon fibers do not overlap. Then, a polypropylene matrix material is filled around the generated carbon fibers to ensure sufficient contact between the carbon fibers and the matrix. Figures 5-6 As shown, the RVE model is constructed.

[0084] During the analysis, the RVE model can be divided into 8 slices, each containing 300 carbon fibers. The unit cell model used for RVE modeling is a unit cell model of continuous carbon fiber reinforced composite material, with an average carbon fiber length of 30.50 mm and an average carbon fiber diameter of 7.05 μm.

[0085] The calculated parameters include carbon fiber length distribution, carbon fiber orientation angle distribution, and carbon fiber volume content. The axial modulus of elasticity of the composite material composed of recycled carbon fiber and polypropylene fiber can be predicted. To predict the axial modulus of elasticity, the compliance matrix transformation relation and stress correction relation are required. The former calculates the compliance matrix of the composite material using a bridging model and compliance matrix. This is then converted to a compliance matrix in a global coordinate system, and the compliance matrix of the entire RVE is obtained by superimposing the compliance matrices of each slice. During the plastic stage, the actual internal stress of the carbon fiber and thermoplastic matrix deviates from the defined value and needs to be multiplied by a stress concentration factor (SCF). In the carbon fiber-thermoplastic matrix unit cell composite model involved, the point stress in the carbon fiber portion is uniform, and the actual stress value and the mean stress value are equal. Therefore, only the stress in the thermoplastic matrix portion needs to be corrected using SCF.

[0086] The axial modulus of elasticity of the composite material is calculated using the compliance matrix of the entire RVE. The relationship between the compliance matrix and strain is shown in Equation II:

[0087] Formula II;

[0088] In formula II, —The compliance matrix of the material.

[0089] The compliance matrix of polypropylene in composite materials is defined as shown in Equation III:

[0090] Formula III;

[0091] The compliance matrix of carbon fibers in composite materials is defined as shown in Equation IV:

[0092] Formula IV;

[0093] In the formula: dε i --strain;

[0094] dσ i --stress;

[0095] E 11 —Axial elastic modulus;

[0096] E 22 —Normal elastic modulus;

[0097] v 12 —Axial Poisson's ratio;

[0098] The superscript f stands for fiber, meaning carbon fiber.

[0099] The superscript m stands for matrix, which refers to the polypropylene matrix.

[0100] v 23 —Normal Poisson's ratio;

[0101] G 12 —In-plane shear modulus;

[0102] G 23 — Normal shear modulus.

[0103] The predicted value obtained after calculation was 18.60 GPa, while the actual experimental value was 18.81 GPa, a difference of only 1.11%.

[0104] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the principle of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A method for predicting the mechanical properties of composite materials prepared from nonwoven carbon fiber / thermoplastic fiber mat, characterized in that, Includes the following steps: A) Measure and analyze the fiber length in the composite material prepared by non-woven carbon fiber / thermoplastic fiber felt to obtain the probability density function and cumulative distribution function of carbon fiber length; The carbon fiber orientation angle inside the composite material prepared by non-woven carbon fiber / thermoplastic fiber felt was measured to obtain the probability density function and cumulative distribution function of the carbon fiber orientation angle. B) Based on the probability density function of carbon fiber length, the cumulative distribution function of carbon fiber length, the probability density function of carbon fiber orientation angle, and the cumulative distribution function of carbon fiber orientation angle, a representative volume element RVE is constructed using a random generation algorithm. C) By analyzing the stress transmission path and stress distribution law of carbon fiber and thermoplastic matrix in representative volume element RVE under different load conditions, the stress bridging relationship between carbon fiber and thermoplastic matrix is ​​constructed by applying bridging model theory, and the bridging parameters are calculated. D) After obtaining the bridging parameters, apply the real stress theory to perform stress analysis on the carbon fiber and thermoplastic matrix in the representative volume element RVE model, and calculate their real stress state under different load conditions.

2. The method for predicting the mechanical properties of composite materials prepared from nonwoven carbon fiber / thermoplastic fiber mat according to claim 1, characterized in that, The method of constructing the representative volume unit (RVE) using a random generation algorithm specifically includes the following steps: The length of each carbon fiber is determined based on the probability density function and cumulative distribution function of the carbon fiber length. The spatial orientation of each carbon fiber is determined based on the probability density function and cumulative distribution function of the carbon fiber orientation angle. Carbon fibers are randomly generated within the representative volume unit RVE space. Then, thermoplastic matrix material is filled around the generated carbon fibers to ensure full contact between the carbon fibers and the thermoplastic matrix, thus obtaining the representative volume unit RVE.

3. The method for predicting the mechanical properties of composite materials prepared from nonwoven carbon fiber / thermoplastic fiber mat according to claim 1, characterized in that, The bridging parameters include bridging stiffness, bridging flexibility, stress concentration factor, and bridging matrix.

4. The method for predicting the mechanical properties of composite materials prepared from nonwoven carbon fiber / thermoplastic fiber mat according to claim 3, characterized in that, The formula for the bridging matrix is ​​shown in Equation I: Formula I; in, and For bridging parameters, , and These are the transverse elastic modulus and axial shear modulus of carbon fiber, respectively. and These are the elastic modulus and shear modulus of the thermoplastic matrix, respectively; , , and are the coefficients in the flexibility matrices of carbon fiber and thermoplastic matrix, respectively.

5. The method for predicting the mechanical properties of composite materials prepared from nonwoven carbon fiber / thermoplastic fiber mat according to claim 1, characterized in that, After constructing the representative volume element (RVE), the RVE model is optimized. The optimization process includes: slicing the representative volume element (RVE) and introducing a correction coefficient to correct the carbon fiber volume content in the slice to the carbon fiber volume content data of the representative volume element (RVE).

6. The method for predicting the mechanical properties of composite materials prepared from nonwoven carbon fiber / thermoplastic fiber mat according to claim 5, characterized in that, The bridging parameters of multiple slices are calculated and then superimposed to obtain the bridging parameters of the entire representative volume element RVE.

7. The method for predicting the mechanical properties of composite materials prepared from nonwoven carbon fiber / thermoplastic fiber mat according to claim 1, characterized in that, Step D) specifically includes: Different strain fields were applied in the representative volume element RVE, and the true stress components in each direction of the carbon fiber and thermoplastic matrix were calculated according to the bridging model and the true stress theory. The macroscopic stress-strain relationship curve of the composite material prepared by non-woven carbon fiber / thermoplastic fiber felt was further calculated, and the elastic modulus data were obtained from the macroscopic stress-strain relationship curve.

8. The method for predicting the mechanical properties of composite materials prepared from nonwoven carbon fiber / thermoplastic fiber mat according to claim 1, characterized in that, In step C), bridging parameters are calculated based on the microstructure characteristics and mechanical performance requirements of the composite material prepared from nonwoven carbon fiber / thermoplastic fiber felt. The microstructure characteristics of the composite material prepared by the nonwoven carbon fiber / thermoplastic fiber felt include the carbon fiber volume fraction, carbon fiber orientation angle, or interface properties; the mechanical performance requirements include strength, modulus, or toughness.

9. The method for predicting the mechanical properties of composite materials prepared from nonwoven carbon fiber / thermoplastic fiber mat according to claim 1, characterized in that, In the representative volume unit RVE, the carbon fibers do not overlap.

10. The method for predicting the mechanical properties of composite materials prepared from nonwoven carbon fiber / thermoplastic fiber mat according to claim 5, characterized in that, After optimizing the representative volume element RVE, the results were verified by comparing it with the microstructure observation results of the actual composite material. The microstructure observation results include the distribution density of carbon fibers, the orientation distribution of carbon fibers, and the contact between carbon fibers and the thermoplastic matrix.

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