Method for evaluating the mechanical properties of a plain weave composite material at multiple scales

Abstract

The application discloses a kind of plain weave composite cross-scale mechanical property evaluation method, for carbon fiber pultrusion plate material using plain weave composite bonding structure, the intrinsic mechanical behavior of fiber and matrix is considered at mesoscale scale, the influence of weaving structure is reflected at mesoscale scale and multiple failure mechanisms are integrated, and through cross-scale parameter transmission between mesoscale scale, mesoscale scale and macro scale, the cross-scale failure method based on mesoscale failure mechanism is used to predict its structural stiffness and strength, the failure mechanism and strength limit of woven composite under different loading modes can be predicted, the problem that macro / mesoscale single-scale prediction method does not consider the distribution of fiber matrix inside woven composite is solved, and the corresponding detailed design simulation model can be formulated for the wind power beam structure of woven composite bonded carbon fiber pultrusion plate material, which can improve efficiency and reduce cost in material selection and structure matching.

Description

Technical Field

[0001] This invention belongs to the field of composite material mechanical property evaluation technology, and relates to a method for evaluating the cross-scale mechanical properties of plain weave composite material structures, and more specifically to a method for evaluating the mechanical properties of fabric-bonded carbon fiber pultruded plates for wind turbine blades. Background Technology

[0002] With the booming development of renewable energy, wind power generation, as a clean energy technology, has received widespread attention. The development of ultra-long and flexible wind turbine blades helps to improve power generation efficiency, reduce costs, and increase power output. Especially in low-wind-speed areas and offshore applications, it can make fuller use of wind resources. As wind turbine blades develop towards ultra-long and flexible designs, carbon fiber pultruded structures, with their high strength and lightweight characteristics, are showing great application advantages.

[0003] Carbon fiber pultrusion (CFPD) materials are produced by impregnating continuous carbon fiber bundles in resin and then pultruding them through a die to obtain structural components with excellent mechanical properties. These components, used in wind turbine blades, not only provide sufficient strength and stiffness but also significantly reduce blade weight, thereby improving the power generation efficiency of wind turbines. However, to improve the reliability of CFPD structures in wind turbine blades, predictive structural design is necessary. Despite the many advantages of CFPD structures, due to their relatively uniform fiber distribution, they are prone to failure at the splicing and overlapping interfaces under stress. Therefore, the performance of the bonding interface between CFPD sheets and glass fiber braided composites at multiple scales has a significant impact on the overall performance and reliability of the blades.

[0004] Plain-weave composite materials are made by interlacing warp and weft fiber bundles. Their most prominent characteristic is the high number of interlacing nodes between the warp and weft threads, resulting in high flexural and tensile strength, as well as high structural balance. Due to their unique weave structure, plain-weave composite materials exhibit naturally multi-scale characteristics under stress. Individual macroscopic or microscopic composite mechanics methods are insufficient to comprehensively predict the mechanical behavior of woven composite materials. Macroscopic mechanics methods, primarily based on experimental data, study their mechanical properties using empirical theories. However, by neglecting details such as the internal structure and defects of the material, they cannot accurately describe the complex damage processes and failure mechanisms within the composite material, leading to limitations in predictive accuracy. While microscopic mechanics methods can effectively describe the microscopic damage processes within the material, they cannot be directly applied to the mechanical analysis of macroscopic structures, thus limiting their practical engineering applications.

[0005] Given the above, for plain-weave composite materials, which naturally possess multi-scale structural characteristics, there is an urgent need to develop a cross-scale mechanical property evaluation method that integrates the advantages of macroscopic and microscopic mechanical methods. This method would comprehensively and accurately predict the mechanical behavior of plain-weave composite materials, thereby revealing not only the damage and failure mechanisms of materials at different scales but also providing a scientific basis for material design and engineering applications. In short, how to fully consider the structural characteristics and multi-scale mechanical behavior of woven composite materials in cross-scale mechanical property evaluation is a pressing technical problem that needs to be solved. Summary of the Invention

[0006] (I) Purpose of the Invention

[0007] To address the problems encountered in existing macro / micro single-scale analyses of woven composite materials, such as the inability to comprehensively predict the mechanical behavior of plain-weave woven composite materials and the neglect of internal structural details and their impact on overall performance, this invention proposes a cross-scale mechanical property evaluation method for plain-weave woven composite materials. Specifically, for structures using plain-weave woven composite materials bonded to carbon fiber pultruded sheets, this method predicts structural stiffness and strength through cross-scale parameter transfer between micro, meso, and macro scales, employing a cross-scale failure method based on micro-failure mechanisms. The micro-scale involves both fiber and matrix components, the meso-scale is represented by plain-weave units composed of fiber bundles and bulk resin, and the macro-scale is the structure of woven composite materials bonded to carbon fiber pultruded sheets. This method enables refined design and simulation modeling of wind turbine beam structures using woven composite materials bonded to carbon fiber pultruded sheets, improving the efficiency of material selection and structural matching, reducing costs, and ultimately achieving comprehensive prediction of the mechanical properties of woven composite materials.

[0008] (II) Technical Solution

[0009] To achieve the objective of this invention and solve its technical problems, the present invention adopts the following technical solution:

[0010] The first objective of this invention is to provide a method for evaluating the cross-scale mechanical properties of plain-weave composite materials, encompassing three scales: mesoscopic, mesoscopic, and macroscopic. This method includes steps such as microscopic observation of the fabric sheet cross-section, establishment of a mesoscopic unit cell model, establishment of a mesoscopic micro-element model, extraction of mesoscopic-mesoscopic stress transformation parameters, transfer of mesoscopic-mesoscopic cross-scale failure prediction parameters, and cross-scale failure prediction using the mesoscopic micro-element model.

[0011] SS1. Microscopic observation of the cross-section of fabric-based panels

[0012] Cross-sectional microscopic observations were performed on plain weave composite fabric sheets to obtain the geometric dimensions and distribution parameters of fiber bundles, including the major axis width, minor axis width, fiber diameter, fiber spacing, total area of ​​fiber bundles, and number of fibers within fiber bundles.

[0013] SS2. Establishment of Microscopic Unit Cell Model

[0014] A microscopic fiber / matrix unit cell model was established based on fiber bundle microscopic observation data. The initial material properties of the fiber and matrix were preset according to their material types. By applying boundary conditions and loading mesoscopic stresses in different directions to the microscopic unit cell model, the stress distribution of the fiber and matrix under different loading conditions was obtained. Then, the overall stiffness of the unit cell model was calculated, and the stress distribution parameters after stiffness decay due to fiber / matrix failure were extracted.

[0015] SS3. Establishment of Mesoscopic Micro-element Model

[0016] Based on the microscopic observation data of fiber bundles, a mesoscopic micro-element model was established, which includes a plain weave pattern and consists of warp fiber bundles, weft fiber bundles, and resin between fiber bundles. The stiffness of the fiber bundles in the unit cell model calculated in step SS2 under different stress states was substituted into the mesoscopic micro-element model to calculate the structural stiffness of the mesoscopic micro-element model. The structural stiffness of the mesoscopic micro-element model was compared and verified with the experimental data of the fabric layer. The microscopic elastic constant of the fiber matrix was corrected by the back-reasoning method.

[0017] SS4. Extraction of Mesoscopic-Mesoscopic Stress Transformation Parameters

[0018] Based on the modified microscopic elastic constants of the fiber and matrix, the microscopic-mesoscopic stress conversion parameters are extracted from the microscopic unit cell model. These parameters include the mechanical stress amplification matrix due to the difference in mechanical properties between the fiber and the matrix, and the thermal stress amplification matrix due to the difference in thermal expansion coefficients between the fiber and the matrix. The mechanical stress amplification matrix and the thermal stress amplification matrix are calculated by applying mechanical stress and thermal stress to the unit cell model respectively. When the properties of the fiber or matrix degrade, the mechanical stress amplification matrix and the thermal stress amplification matrix are recalculated. Finally, the microscopic-mesoscopic stress conversion parameters are extracted under three states: fiber and matrix undamaged state, fiber damaged state, and matrix damaged state.

[0019] SS5. Parameter Transfer for Micro-Mesoscale Cross-Scale Failure Prediction

[0020] Based on three sets of mechanical stress amplification factor matrices (for non-destructive fiber matrix, fiber damage, and matrix damage) and thermal stress amplification factor matrices, the damage parameters of the fiber and matrix are transferred to the fiber cross-scale failure criterion. The mesoscopic failure intensity of the fiber matrix is ​​applied to the mesoscopic unit cell model to calculate the mesoscopic fiber bundle stress. Failure prediction is performed on the fiber bundle braiding micro-element model. The maximum longitudinal stress failure criterion is used for the fibers within the fiber bundle, the modified Von Mises failure criterion is used for the matrix within the fiber bundle, and the shear-based Von Mises failure criterion is used for the bulk resin outside the fiber bundle.

[0021] SS6. Mesoscopic Micro-element Model for Cross-Scale Failure Prediction

[0022] The cross-scale failure criterion in the SS5 step was used to perform failure analysis on the fiber bundles and resin in the mesoscopic micro-element model. The failure analysis of the mesoscopic micro-element model, i.e. the representative unit of plain weave, was transformed into the prediction results of the macroscopic fabric sheet scale, including the warp / weft tensile strength, in-plane shear strength, out-of-plane shear strength, and out-of-plane tensile strength of the laminate. The mechanical property prediction results of the fabric sheet were compared and verified with the experimental results to determine the stiffness attenuation scheme and the failure criterion correction, and to obtain an effective simulation model of the mechanical properties of plain weave composite materials.

[0023] The second objective of this invention is to provide a method for predicting the tensile shear strength of a plain weave composite material woven fabric bonded with carbon fiber pultruded sheet. This method, based on the cross-scale evaluation method for woven composite materials provided in the first objective, predicts the tensile shear strength of the woven composite material bonded with carbon fiber pultruded sheet. It applies the Hashin failure criterion to the carbon fiber pultruded sheet to predict the failure of both the carbon fiber and resin within the sheet, ultimately obtaining the failure strength and failure mode of the woven fabric bonded carbon fiber pultruded sheet. This data can provide design guidance for the application of carbon fiber pultruded sheets in wind turbine blades.

[0024] (III) Technical Effects

[0025] Compared with the prior art, the cross-scale mechanical property evaluation method for plain weave composite materials of the present invention has the following beneficial and significant technical effects:

[0026] (1) The mechanical property evaluation method of plain weave composite material of the present invention predicts the structural stiffness and strength by transferring cross-scale parameters between the micro-scale, meso-scale and macro-scale and adopting a cross-scale failure method based on the micro-failure mechanism. This solves the problem that the macro / micro single-scale prediction method does not consider the distribution of the internal fiber matrix of the woven composite material. It can formulate a corresponding refined design simulation model for the wind power beam structure of woven composite material bonded to carbon fiber pultruded plate, which can improve efficiency and reduce cost in terms of material selection and structural matching.

[0027] (2) The mechanical property evaluation method for plain weave composite materials of the present invention adopts an analysis framework of three scales: mesoscopic, mesoscopic, and macroscopic. This framework can comprehensively consider the microstructural characteristics of the woven composite material and its influence on macroscopic mechanical behavior, overcoming the limitations of existing single-scale analysis methods. Simultaneously, this method establishes a fiber / matrix unit cell model at the mesoscopic scale, which can fully describe the intrinsic mechanical behavior of the fiber and matrix; and establishes a micro-element model containing the weaving arrangement pattern at the mesoscopic scale, which can accurately reflect the influence of the weaving structure on material properties. Through mesoscopic-mesoscopic stress transformation and cross-scale failure criteria, seamless connection between scales is achieved, ensuring the accuracy of the prediction results. Furthermore, this method integrates various failure mechanisms, including fiber tensile / compression failure and matrix shear / tensile failure, which can predict the failure mechanism and strength limit of woven composite materials under different loading modes, providing an important basis for structural design. Attached Figure Description

[0028] To more clearly illustrate the technical solutions of the embodiments of the present invention, the drawings used in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0029] Figure 1 This is a flowchart of the cross-scale mechanical property evaluation method for plain weave composite materials of the present invention;

[0030] Figure 2 This is a schematic diagram of the boundary conditions and stress state of the microscopic unit cell model in an embodiment of the present invention, wherein (A) is a square unit cell and (B) is a rectangular unit cell;

[0031] Figure 3 This is a schematic diagram of the weaving method and resin distribution of the warp and weft fiber bundles in the micro-element model of the present invention. (A) shows the micro-element model, (B) shows the warp fiber bundle, (C) shows the weft fiber bundle, and (D) shows the resin outside the fiber bundle. Detailed Implementation

[0032] To better understand the present invention, the following embodiments further illustrate the content of the present invention. In the accompanying drawings, the same or similar reference numerals denote the same or similar elements or elements having the same or similar functions throughout. The described embodiments are some, but not all, embodiments of the present invention. The embodiments described below with reference to the accompanying drawings are exemplary and intended to explain the present invention, and should not be construed as limiting the present invention. 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. The structure and technical solution of the present invention are further described in detail below with reference to the accompanying drawings, and one embodiment of the present invention is given. The plain weave composite material described in the present invention refers to a square-grid glass fiber cloth used for bonding carbon pultruded sheets. The present invention predicts the stiffness and strength of fiber bundles based on a micro-cell model, incorporates the fiber bundle properties into the fabric micro-element model to calculate the stiffness and strength of the fabric sheet, verifies it through experiments, and repeatedly calculates to finally obtain effective cross-scale analysis parameters for predicting the tensile shear strength of the carbon pultruded sheet tensile-shear joint bonded with the fabric.

[0033] Example 1

[0034] As a specific example, the mechanical property evaluation method for plain weave composite materials based on cross-scale technology of the present invention is used to analyze plain weave composite materials bonded to carbon fiber pultruded sheets, and to determine the influence of the fabric sheet properties on the bonding properties. The flowchart of the method during implementation is as follows: Figure 1 As shown, the main steps include: microscopic observation of the cross-section of the fabric sheet, establishment of the mesoscopic unit cell model, establishment of the mesoscopic micro-element model, extraction of mesoscopic-mesoscopic stress transformation parameters, transfer of mesoscopic-mesoscopic cross-scale failure prediction parameters, and cross-scale failure prediction using the mesoscopic micro-element model.

[0035] SS1. Microscopic observation of the cross-section of fabric-based panels

[0036] Cross-sectional microscopic observation was performed on the cured plain-weave composite fabric to obtain parameters such as the major axis width of the fiber bundle, the minor axis width of the fiber bundle, the fiber diameter, the fiber spacing, the total area of ​​the fiber bundle, and the number of fibers within the fiber bundle. The volume content of the fibers within the fiber bundle can be estimated from the fiber bundle diameter, the total area of ​​the fiber bundle, and the number of fibers within the fiber bundle. The length and width of the micro-element model and the fiber bundle area can be determined from the major axis width and the minor axis width of the fiber bundle.

[0037] SS2. Establishment of Microscopic Unit Cell Model

[0038] A microscopic unit cell model containing fibers and matrix was established based on fiber bundle microscopic observation data (e.g., Figure 2As shown, the initial material properties of the fiber and the matrix are preset according to their material types. By applying boundary conditions and loading mesoscopic stresses in different directions to the micro-unit cell model, the micro-stress distribution of the fiber and the matrix under different loading conditions is obtained. Then, the overall stiffness of the micro-unit cell model, i.e. the stiffness parameters of the fiber bundle, is calculated. At the same time, the stress distribution after stiffness decay due to fiber failure and matrix failure is extracted.

[0039] In some preferred embodiments, the microscopic unit cell model is based on the volume content of fibers within the fiber bundle, with the same proportion of fibers and matrix to reflect the intrinsic composition characteristics of the fiber bundle. The volume content of fibers within the fiber bundle is estimated based on the fiber diameter, total area of ​​the fiber bundle, and number of fibers within the fiber bundle determined by microscopic observation of the fabric sheet in step SS1.

[0040] In some preferred examples, the microscale analysis uses a unit cell model composed of fibers and matrix as the analysis object. Considering the randomness of the spacing between fibers and matrix, two unit cell models are set according to the fiber volume content: square unit cell and rectangular unit cell (e.g., Figure 2 As shown in (A) and (B), two geometric forms of unit cell models, square unit cell and rectangular unit cell, are constructed simultaneously to represent different spacing distributions. The influence of spacing randomness on mechanical properties is considered by comprehensively analyzing the two types of unit cell models.

[0041] In some preferred embodiments, the method for selecting the material properties of the fibers and matrix at the microscale is to pre-determine the initial modulus of the fibers and matrix according to the material type, and then calculate the three principal stresses (σ) by applying appropriate boundary conditions and stress loading methods in different directions. 11 ,σ 22 ,σ 33 ) and 3 shear stresses (τ) 12 ,τ 13 ,τ 23 The micro-stress distribution at characteristic points of the unit cell model under stress was analyzed. Based on the stress-strain relationship, nine independent engineering constants were calculated and extracted, including three Young's moduli, three shear moduli, and three Poisson's ratios. Subsequently, the overall stiffness of the unit cell model, i.e. the stiffness parameters of the fiber bundle, was calculated.

[0042] SS3. Establishment of Mesoscopic Micro-element Model

[0043] In the representative unit of plain weave, besides the warp and weft fiber bundles, a large portion of the resin area is interspersed, and the fiber bundles and resin together constitute the representative unit of plain weave. By homogenizing the design of the warp and weft fiber bundle orientation and resin distribution in the micro-element model, and based on microscopic observations, a mesoscopic micro-element model (e.g., [missing information]) is established according to the fiber bundle major axis width, fiber bundle minor axis width, and total fiber bundle area, containing the plain weave pattern and composed of warp fiber bundles, weft fiber bundles, and resin between fiber bundles. Figure 3 (As shown). The fiber bundle stiffness parameters (9 engineering constants) of the unit cell model obtained in step SS2 under different stress states are substituted into the mesoscopic micro-element model along with the material properties of the bulk resin to calculate the structural stiffness of the fabric board. The overall structural stiffness of the woven micro-element model is compared and verified by the fabric board test. The microscopic elastic constants of the fiber matrix are calculated by the back-calculation method.

[0044] In some preferred embodiments, the micro-element model of fiber bundles and resin is woven using screening units. The basic structure of the micro-element model includes one complete warp fiber bundle, with two half-bundles of warp fibers distributed on each side; similarly, it includes one complete weft fiber bundle, with two half-bundles of warp fibers distributed on each side. The warp and weft directions follow the same pattern but in different directions, interlacing in an up-and-down weaving pattern. A small portion of the fibers is exposed on the surface of the micro-element model; the area of ​​exposed fibers can be adjusted based on actual electron microscopy scans. A small number of resin units are present between the warp and weft fibers; the resin thickness can be adjusted based on actual electron microscopy scans.

[0045] In some preferred examples, when the structural stiffness of the fabric board calculated based on the mesoscopic micro-element model is compared and verified with experimental data, if the deviation between the two is greater than a set threshold, it is necessary to feed back and correct the initial material property parameters of the fiber and matrix in the mesoscopic unit cell model, and repeat the iteration until the deviation between the structural stiffness calculated by the micro-element model and the experimental data is limited to within the set threshold.

[0046] SS4. Extraction of Mesoscopic-Mesoscopic Stress Transformation Parameters

[0047] Based on the modified microscopic elastic constants of the fiber and matrix, the microscopic-mesoscopic stress conversion parameters are extracted from the microscopic unit cell model. These parameters include the mechanical stress amplification matrix due to the difference in mechanical properties between the fiber and the matrix, and the thermal stress amplification matrix due to the difference in thermal expansion coefficients between the fiber and the matrix. By applying mesoscopic mechanical stress and thermal stress to the unit cell model respectively, the mechanical stress amplification matrix and the thermal stress amplification matrix are calculated separately. Furthermore, when the properties of the fiber or matrix degrade, the mechanical stress amplification matrix and the thermal stress amplification matrix are recalculated. Finally, the microscopic-mesoscopic stress conversion parameters are extracted under three states: fiber-matrix undamaged state, fiber damaged state, and matrix damaged state.

[0048] In some preferred embodiments, the conversion of mesoscopic stress in the fiber bundle to mesoscopic stress in the fiber matrix is ​​achieved through a stress amplification factor:

[0049]

[0050] σ 6×6 For the mesoscopic stress vector of the nodes within the unit cell, The mesoscopic stress vector of a unit cell; It is the mechanical stress amplification factor matrix caused by the difference in mechanical properties between the fiber and the matrix; This is the thermal stress amplification factor matrix due to the difference in thermal expansion coefficients between the fiber and the matrix. It is also related to the longitudinal and transverse stresses (σ) at the mesoscopic and mesoscopic levels of the fiber bundle and the fiber matrix. 11 , σ 22 , σ 33 and transverse shear stress (σ) 23 There is a coupling relationship between the two longitudinal shear stresses (σ). 12 , σ 13 There is a coupling relationship between them, therefore The matrix can be expanded as follows:

[0051]

[0052] Equation (3) can be expanded as follows when the unit cell is subjected to different macroscopic stresses:

[0053]

[0054] For example, when applying at the boundary of a unit cell When the macroscopic stress components are calculated, the other macroscopic stress components are zero. In this case, the six mesoscopic stress components at each reference point in the unit cell can be calculated, and the mechanical stress amplification factor matrix can then be obtained. The first column; similarly, we can obtain... Other components of the matrix. Select appropriate reference points to calculate its mechanical stress amplification factor matrix and thermal stress amplification factor matrix. When the fiber or matrix properties degrade, recalculate the mechanical / thermal stress amplification factor matrix.

[0055] To simplify the calculation, the six macroscopic stresses corresponding to the mechanical stress of the mesoscopic unit cell are all set to 1 MPa, and the temperature change corresponding to the thermal stress of the mesoscopic unit cell is set to 1 °C. Based on this, a unit cell model is established. No stress is applied to the unit cell model, only a temperature field is applied, and a thermal stress model is established to calculate the A matrix. Next, without applying a temperature field, a unit cell model with stress in six directions is established, with the stress set to 1 MPa. Appropriate displacement values ​​are obtained through iterative programming, and these displacement values ​​are then input into the mesoscopic unit cell model containing the temperature field. The stress at the characteristic reference point under the combined action of mechanical and thermal stress is calculated, and the M matrix is ​​calculated.

[0056] SS5. Parameter Transfer for Micro-Mesoscale Cross-Scale Failure Prediction

[0057] By using three sets of mechanical stress amplification factor matrices (mesoscopic fiber matrix non-destructive, fiber damaged, and matrix damaged) and thermal stress amplification factor matrices, the damage parameters of the fiber and matrix are transferred to the fiber cross-scale failure criterion. Through mesoscopic-mesoscopic cross-scale stress transfer and failure prediction, a cross-scale failure criterion for the fiber bundle is formed. Among them, the failure prediction of the fiber within the fiber bundle adopts the maximum longitudinal stress failure criterion, the failure prediction of the matrix within the fiber bundle adopts the modified Von Mises failure criterion, and the failure prediction of the bulk resin outside the fiber bundle adopts the shear-based Von Mises failure criterion.

[0058] In some preferred embodiments, based on the mesoscopic-mesoscopic stress transformation parameters under three states—undamaged fiber matrix, damaged fiber matrix, and damaged matrix matrix—the tensile failure strength and compressive failure strength of the mesoscopic fibers, and the mesoscopic shear failure strength and tensile failure strength of the matrix are preset and substituted into the failure criterion. The corresponding mesoscopic unit failure stress is calculated using the mesoscopic / mesoscopic stress transformation method and the pre-calculated M and A matrices. This method is used to predict the failure of fiber bundles in the micro-element model. At the same time, the Von Mises failure criterion based on shear is used to predict the failure of bulk resin.

[0059] In some preferred embodiments, for fibers within a fiber bundle, preset mesoscopic fiber tensile and compressive failure strengths are used as criteria for failure prediction, and the maximum longitudinal stress failure criterion is used for failure prediction.

[0060] Fiber tensile failure: Fiber compression failure:

[0061] In the formula, K fT and K fC T represents the tensile failure index and compressive failure index of the fiber. f and C f σ represents the tensile strength and compressive strength of the fiber, respectively. f11The micro-stress in the fiber direction;

[0062] For the matrix within the fiber bundle, the preset microscopic shear failure strength and tensile failure strength of the matrix are used as the criteria for failure prediction, and the modified Von Mises failure criterion is adopted for failure prediction:

[0063]

[0064] I1=σ m1 +σ m2 +σ m3

[0065]

[0066] Matrix distortion failure: Matrix expansion failure:

[0067] In the formula, σ VM The Von Mises criterion equivalent stress for micro-stress within the matrix, where I1 is the first stress invariant, I2 is the second stress invariant, and σ m1 σ m2 σ m3 σ m12 σ m13 σ m23 K represents the six independent stress components of the matrix. mS and K mT S represents the matrix shear and compression failure index. m and T m denoted as the shear failure strength and tensile failure strength of the matrix, and μ is the influence coefficient of Von Mises stress on the expansion failure of the matrix.

[0068] For the resin outside the fiber bundle, the preset shear strength is used as the criterion for failure prediction, and the Von Mises failure criterion based on shear failure is used for failure prediction:

[0069]

[0070] In the formula, σ wVM For the Von Mises criterion equivalent stress of the resin outside the fiber bundle, K wS S is the failure index of the resin outside the fiber bundle. wm This represents the shear strength of the resin outside the fiber bundle.

[0071] SS6. Mesoscopic Micro-element Model for Cross-Scale Failure Prediction

[0072] Based on the mesoscopic-mesoscopic cross-scale failure criterion determined in step SS5, and on the basis of failure analysis of fiber bundles and resin in the mesoscopic micro-element model, the mechanical properties of the macroscopic fabric sheet are predicted by the cross-scale failure of the mesoscopic micro-element model. The predicted mechanical properties of the fabric sheet are compared and verified with the experimental results, so as to back-derive and correct the stiffness attenuation scheme and failure criterion of the mesoscopic micro-element model, and finally form an effective simulation model of the mechanical properties of plain weave composite materials.

[0073] In some preferred examples, when performing failure analysis on fiber bundles and resin in a mesoscopic micro-element model based on the mesoscopic-mesoscopic cross-scale failure criterion, the analysis results include tensile and compressive failures of fibers within the fiber bundles, torsional and expansion failures of the matrix within the fiber bundles, and shear failures of bulk resin outside the fiber bundles. Furthermore, when predicting the mechanical properties of macroscopic fabric sheets using the mesoscopic micro-element model's cross-scale failure, it is necessary to transform the stress distribution and analysis results of the mesoscopic micro-element model into macroscopic fabric sheet mechanical property prediction results through homogenization and scale transformation methods. This includes the warp and weft tensile strengths, in-plane shear strengths, out-of-plane shear strengths, and out-of-plane tensile strengths of the fabric layers, thereby achieving prediction from the mesoscopic to the macroscopic scale.

[0074] In some preferred examples, the failure criteria in step SS5 are used to predict the failure of the two materials in the micro-element model. Under the premise of preset mesoscopic failure strength, the stiffness reduction scheme is finally determined as follows: the fiber breaks when the longitudinal stress reaches the tensile strength according to the maximum longitudinal stress criterion, and the stiffness is reduced by 0.01. The failure of the matrix is ​​a gradual process and there is an elastoplastic phenomenon. Therefore, according to the modified Von Mises failure criterion, failure begins when the failure index reaches 1, and a stiffness reduction of 0.05 occurs when the failure index reaches 1.5.

[0075] Example 1 demonstrates the mechanical property evaluation method for plain weave composite materials based on cross-scale technology provided by this invention. This method can systematically analyze and predict the mechanical properties and failure behavior of plain weave composite materials at the mesoscopic, mesoscopic, and macroscopic scales. Through steps such as cross-sectional microscopic observation, establishment of mesoscopic unit cell models, establishment of mesoscopic micro-element models, extraction of mesoscopic-mesoscopic stress conversion parameters, and cross-scale failure prediction, accurate transmission and prediction of stress and failure behavior from the microscopic to the macroscopic scale are achieved. This method systematically considers the microstructural characteristics and macroscopic mechanical behavior of woven composite materials, and can accurately predict the damage evolution process of fibers and the matrix within the fiber bundle and its impact on macroscopic mechanical properties, providing strong support for the structural design and performance optimization of woven composite materials.

[0076] Example 2

[0077] Based on Example 1, Example 2 mainly introduces a method for predicting the tensile shear strength of carbon fiber pultruded sheets using the cross-scale mechanical property evaluation method of plain weave composite materials of the present invention. Considering that different materials have different matching conditions, failure may occur at the fabric interface or inside the carbon pultruded sheet. The Hashin failure criterion is applied to the carbon fiber pultruded sheet to predict the failure of carbon fibers and resin inside the carbon fiber pultruded sheet. The failure criterion is as follows:

[0078] Fiber failure prediction is based on:

[0079] Matrix failure is assessed using:

[0080] In the formula, σ ii τ represents the normal stress in three directions within the layer. ij X represents the shear stress in three directions within the layer. T X C Y represents the tensile and compressive strengths along the fiber direction, respectively. T Y C Z represents the tensile and compressive strengths perpendicular to the fiber direction, respectively. T Z C These represent the tensile and compressive strengths, respectively, in the thickness direction perpendicular to the fiber direction; F T1 F T2 This represents the state value used in failure criteria to determine whether a structure has failed. When this value is greater than 1, it is considered that the pultruded composite sheet has been damaged in the corresponding fiber or matrix. When the damage occurs in either the fiber or the matrix, the material properties are reduced according to the expression of the corresponding type. If both are damaged, the properties need to be reduced in both types simultaneously.

[0081] For example, by establishing a carbon fiber pultruded sheet model with a single-layer fabric bond, and the failure modes being single-layer fabric interface failure and carbon pultruded sheet matrix failure, the failure criteria in step SS5 can be supplemented with the Hashin failure criterion of the carbon pultruded sheet for failure prediction, thus enabling failure prediction of the tensile shear strength of the carbon fiber pultruded sheet model.

[0082] The objectives of this invention have been fully and effectively achieved through the above embodiments. Those skilled in the art will understand that this invention includes, but is not limited to, the contents described in the accompanying drawings and the specific embodiments described above. Although the invention has been described with reference to what is currently considered the most practical and preferred embodiments, it should be understood that the invention is not limited to the disclosed embodiments, and any modifications that do not depart from the functional and structural principles of the invention will be included within the scope of the claims.

Claims

1. A method for evaluating the cross-scale mechanical properties of plain-weave composite materials, characterized in that, The cross-scale mechanical performance evaluation method includes at least the following steps: SS1. Microscopic observation of the cross-section of fabric-based panels By performing microscopic observation of the fiber bundles in the cross section of the plain weave composite material fabric, the geometric dimensions and distribution parameters of the fiber bundles are obtained, including the width of the major axis of the fiber bundle, the width of the minor axis of the fiber bundle, the fiber diameter, the fiber bundle spacing, the total area of ​​the fiber bundle, and the number of fibers in the fiber bundle. SS2. Establishment of a microscopic unit cell model A mesoscopic unit cell model containing fibers and a matrix was established based on fiber bundle microscopic observation data. The initial material properties of the fibers and the matrix were preset according to their material types. By applying boundary conditions and loading mesoscopic stresses in different directions to the mesoscopic unit cell model, the micro-stress distribution of the fibers and the matrix under different loading conditions was obtained. Then, the overall stiffness of the mesoscopic unit cell model, i.e. the stiffness parameters of the fiber bundle, was calculated. At the same time, the stress distribution after stiffness decay due to fiber failure and matrix failure was extracted. SS3. Establishment of Mesoscopic Micro-element Model Based on the microscopic observation data of fiber bundles, a mesoscopic micro-element model consisting of warp fiber bundles, weft fiber bundles and resin between fiber bundles with plain weave pattern is established. The fiber bundle stiffness parameters calculated in step SS2 are substituted into the mesoscopic micro-element model along with the material properties of bulk resin to calculate the structural stiffness of the fabric board. The calculation results are compared and verified with the experimental data of the fabric layer. Based on the comparison and verification results, the mesoscopic elastic constants of fibers and matrix in the mesoscopic unit cell model are back-derived and corrected. SS4. Extraction of Mesoscopic-Mesoscopic Stress Transformation Parameters Based on the modified microscopic elastic constants of the fiber and matrix, the microscopic-mesoscopic stress conversion parameters are extracted from the microscopic unit cell model. These parameters include the mechanical stress amplification factor matrix caused by the difference in mechanical properties between the fiber and the matrix, and the thermal stress amplification factor matrix caused by the difference in thermal expansion coefficients between the fiber and the matrix. The mechanical stress amplification factor matrix and the thermal stress amplification factor matrix are calculated by applying mesoscopic mechanical stress and thermal stress to the unit cell model respectively. At the same time, when the properties of the fiber or matrix degrade, the mechanical stress amplification factor matrix and the thermal stress amplification factor matrix are recalculated. Finally, the microscopic-mesoscopic stress conversion parameters are extracted under three states: fiber and matrix undamaged state, fiber damaged state, and matrix damaged state. SS5. Parameter Transfer for Micro-Mesoscale Cross-Scale Failure Prediction Based on the meso-mesoscopic stress transformation parameters under three states—no fiber matrix, damaged fiber, and damaged matrix—the damage parameters of the fiber and matrix at the mesoscopic scale are transferred to the mesoscopic scale. Through the stress transfer and failure prediction across the meso-mesoscopic scales, a cross-scale failure criterion for fiber bundles is formed. Among them, the failure prediction of fibers within the fiber bundle adopts the maximum longitudinal stress failure criterion, the failure prediction of the matrix within the fiber bundle adopts the modified Von Mises failure criterion, and the failure prediction of bulk resin outside the fiber bundle adopts the shear-based Von Mises failure criterion. SS6. Cross-scale failure prediction using mesoscopic micro-element models Based on the mesoscopic-mesoscopic cross-scale failure criterion determined in step SS5, and on the basis of failure analysis of fiber bundles and resin in the mesoscopic micro-element model, the mechanical properties of the macroscopic fabric sheet are predicted by the cross-scale failure of the mesoscopic micro-element model. The predicted mechanical properties of the fabric sheet are compared and verified with the experimental results, so as to back-derive and correct the stiffness attenuation scheme and failure criterion of the mesoscopic micro-element model, and finally form an effective simulation model of the mechanical properties of plain weave composite materials.

2. The method for evaluating the cross-scale mechanical properties of plain-weave composite materials according to claim 1, characterized in that, In step SS2 above, the microscopic unit cell model is set with the same proportion of fibers and matrix based on the volume content of fibers in the fiber bundle to reflect the intrinsic component characteristics of the fiber bundle. The volume content of fibers in the fiber bundle is estimated based on the fiber diameter, total area of ​​the fiber bundle, and number of fibers in the fiber bundle determined by microscopic observation of the fabric sheet in step SS1.

3. The method for evaluating the cross-scale mechanical properties of plain-weave composite materials according to claim 1, characterized in that, In step SS2 above, the microscale analysis takes the unit cell model composed of fibers and matrix as the analysis object. Considering the randomness of the spacing between fibers and matrix, two geometric forms of unit cell models, square unit cell and rectangular unit cell, are constructed simultaneously to represent different spacing distributions. The influence of spacing randomness on mechanical properties is considered by comprehensively analyzing the two types of unit cell models.

4. The method for evaluating the cross-scale mechanical properties of plain-weave composite materials according to claim 1, characterized in that, In step SS2 above, by applying periodic boundary conditions and stress loading methods in different directions, the unit cell model is made to withstand principal stresses (σ) in three directions. 11 ,σ 22 ,σ 33 ) and shear stress in three directions (τ) 12 ,τ 13 ,τ 23 The micro-stress distribution of characteristic points in the unit cell model under each mesoscopic stress state is calculated. At the same time, based on the stress-strain relationship, nine independent engineering constants are calculated and extracted, including three Young's moduli, three shear moduli, and three Poisson's ratios. Then, the overall stiffness of the unit cell model, i.e. the stiffness parameters of the fiber bundle, is calculated.

5. The method for evaluating the cross-scale mechanical properties of plain-weave composite materials according to claim 1, characterized in that, In step SS3 above, based on the fiber bundle major axis width, fiber bundle minor axis width, fiber bundle spacing and total fiber bundle area obtained by microscopic observation in step SS1, and based on the plain weave representative unit, the orientation of the warp and weft fiber bundles and the resin distribution in the mesoscopic unit cell model are homogenized to establish a mesoscopic micro-element model consisting of warp fiber bundles, weft fiber bundles and a large middle resin block arranged in a plain weave pattern.

6. The method for evaluating the cross-scale mechanical properties of plain-weave composite materials according to claim 1, characterized in that, In step SS3 above, when comparing and verifying the structural stiffness of the fabric board calculated based on the mesoscopic micro-element model with the experimental data, if the deviation between the two is greater than the set threshold, it is necessary to feed back and correct the initial material property parameters of the fiber and matrix in the mesoscopic unit cell model, and repeat the iteration until the deviation between the structural stiffness calculated by the micro-element model and the experimental data is limited to within the set threshold.

7. The method for evaluating the cross-scale mechanical properties of plain-weave composite materials according to claim 1, characterized in that, In step SS4 above, the transfer and transformation of mesoscopic stress in the fiber bundle to mesoscopic stress in the fiber matrix is ​​achieved through a stress amplification factor matrix: In the formula, σ is the mesoscopic stress vector of the nodes within the unit cell model. M is the mesoscopic stress vector of the unit cell model. σ Let A be the mechanical stress amplification factor matrix. σ This is the thermal stress amplification factor matrix; In a non-destructive state, by applying mesoscopic stresses (σ) in six different directions individually to the unit cell model without applying a temperature field. 11 σ 22 σ 33 τ 12 τ 13 τ 23 Calculate the micro-stress distribution of the fiber and matrix at the characteristic reference points respectively, and calculate the corresponding value of each column in the mechanical stress amplification factor matrix one by one, thus completing the mechanical stress amplification factor matrix M. σ The extraction and construction of thermal stress amplification factor matrix A involves calculating the mesoscopic stress distribution at a feature reference point by applying only temperature variation conditions without applying mesoscopic stress, and then extracting and constructing the thermal stress amplification factor matrix A. σ ; Under the damaged state of the fiber or matrix, by updating the corresponding material property parameters, and using the same method as under the undamaged state, the mechanical stress amplification factor matrix M is calculated respectively after the performance degradation due to fiber damage and the performance degradation due to matrix damage. σ and thermal stress amplification factor matrix A σ .

8. The method for evaluating the cross-scale mechanical properties of plain-weave composite materials according to claim 1, characterized in that, In step SS5 above, based on the mesoscopic-mesoscopic stress conversion parameters under three states—undamaged fiber matrix, damaged fiber matrix, and damaged matrix matrix—the corresponding mesoscopic stress is calculated by applying the mesoscopic failure intensity of the fiber matrix to the mesoscopic unit cell model. This allows the failure behavior at the mesoscopic level to be reflected at the mesoscopic level, forming a mesoscopic-mesoscopic cross-scale failure criterion, which is ultimately applied to the failure prediction and judgment of fiber bundles.

9. The method for evaluating the cross-scale mechanical properties of plain-weave composite materials according to claim 1, characterized in that, In step SS5 above, for fibers within a fiber bundle, the preset mesoscopic fiber tensile failure strength and compressive failure strength are used as the criteria for failure prediction, and the maximum longitudinal stress failure criterion is used for failure prediction: Fiber tensile failure: Fiber compression failure: In the formula, K fT and K fC T represents the tensile failure index and compressive failure index of the fiber. f and C f σ represents the tensile strength and compressive strength of the fiber, respectively. f11 The micro-stress in the fiber direction; For the matrix within the fiber bundle, the preset microscopic shear failure strength and tensile failure strength of the matrix are used as the criteria for failure prediction, and the modified Von Mises failure criterion is adopted for failure prediction: Matrix distortion failure: Matrix expansion failure: In the formula, σ VM The Von Mises criterion equivalent stress for micro-stress within the matrix, where I1 is the first stress invariant, I2 is the second stress invariant, and σ m1 σ m2 σ m3 σ m12 σ m13 σ m23 K represents the six independent stress components of the matrix. mS and K mT S represents the matrix shear and compression failure index. m and T m denoted as the shear failure strength and tensile failure strength of the matrix, and μ is the influence coefficient of Von Mises stress on the expansion failure of the matrix. For the resin outside the fiber bundle, the preset shear strength is used as the criterion for failure prediction, and the Von Mises failure criterion based on shear failure is used for failure prediction: In the formula, σ wVM For the Von Mises criterion equivalent stress of the resin outside the fiber bundle, K wS S is the failure index of the resin outside the fiber bundle. wm This represents the shear strength of the resin outside the fiber bundle.

10. The method for evaluating the cross-scale mechanical properties of plain-weave composite materials according to claim 1, characterized in that, In step SS6 above, when performing failure analysis on fiber bundles and resin in the mesoscopic micro-element model based on the mesoscopic-mesoscopic cross-scale failure criterion, the analysis results include tensile and compressive failures of fibers within the fiber bundles, torsional and expansion failures of the matrix within the fiber bundles, and shear failures of bulk resin outside the fiber bundles.

11. The method for evaluating the cross-scale mechanical properties of plain-weave composite materials according to claim 1, characterized in that, In step SS6 above, when predicting the mechanical properties of macroscale fabric panels through cross-scale failure using a mesoscopic micro-element model, the stress distribution and analysis results of the mesoscopic micro-element model need to be transformed into macroscale mechanical property prediction results for the fabric panels through homogenization and scale conversion methods. These results include the warp and weft tensile strength, in-plane shear strength, out-of-plane shear strength, and out-of-plane tensile strength of the fabric panels, thereby achieving prediction from the mesoscopic to the macroscopic scale.

12. A method for predicting the tensile shear strength of a plain-weave composite material fabric bonded to a carbon fiber pultruded sheet structure, characterized in that, Based on the cross-scale mechanical property evaluation method of plain weave composite material according to any one of claims 1 to 11, the tensile shear strength of the woven composite material bonded carbon fiber pultruded sheet structure is predicted, the Hashin failure criterion is applied to the carbon fiber pultruded sheet to realize the failure prediction of carbon fiber and resin in the carbon fiber pultruded sheet, and finally the failure strength and failure mode of carbon fiber pultruded sheet bonded with fabric are obtained.

13. The method for predicting the tensile shear strength of a plain-weave composite material fabric bonded to a carbon fiber pultruded sheet structure according to claim 12, characterized in that, When applying the Hashin failure criterion to carbon fiber pultruded sheets to predict the failure of carbon fibers and resin within the sheets: Fiber failure prediction is based on: Matrix failure is assessed using: In the formula, σ ii τ represents the normal stress in three directions within the layer. ij X represents the shear stress in three directions within the layer. T X C Y represents the tensile and compressive strengths along the fiber direction, respectively. T Y C Z represents the tensile and compressive strengths perpendicular to the fiber direction, respectively. T Z C These represent the tensile and compressive strengths, respectively, in the thickness direction perpendicular to the fiber direction; F T1 F T2 This represents the state value used in failure criteria to determine whether a structure has failed. When this value is greater than 1, it is considered that the pultruded composite sheet has been damaged in the corresponding fiber or matrix. When the damage occurs in either the fiber or the matrix, the material properties are reduced according to the expression of the corresponding type. If both are damaged, the properties need to be reduced in both types simultaneously.

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