Digital representation method, system, device and storage medium for complex structure preform of woven composite material

Abstract

The present invention discloses a method, system, equipment and storage medium for digitally characterizing the morphology of a complex structure preform of a woven composite material, and relates to the technical field of material analysis. The method establishes a macroscopic anisotropic hyperelastic constitutive model of a three-dimensional woven fabric and a microscopic refined unit cell geometric model of a three-dimensional woven fabric, and proposes a macroscopic and microscopic combined numerical simulation method for digitally characterizing the geometric morphology of a complex structure fiber preform of a three-dimensional woven composite material, effectively predicts the direction of the microscopic yarns and the cross-sectional morphology changes of the preform after the complex molding process, and provides a refined microscopic geometric model for the subsequent mechanical property analysis of the complex structure of the woven composite material.

Description

Technical Field

[0001] The present invention relates to the technical field of material analysis, and in particular to a digital characterization method, system, equipment and storage medium for the morphology of a complex structure preform of a woven composite material. Background Art

[0002] Three-dimensional woven composite materials use weaving technology to interweave different yarns in three-dimensional space to form a spatial structure in which the yarn layers are interconnected, which significantly improves the shortcomings of poor interlayer performance and easy delamination of traditional laminated composite materials, and has excellent comprehensive mechanical properties and near-net forming capabilities of complex structures. In addition, in order to meet the multifunctional requirements of drag reduction and noise reduction, wave absorption and stealth, pressure resistance and explosion resistance, and thermal insulation integration, more and more complex structures of three-dimensional woven composite materials are emerging, such as large torsion and variable thickness aircraft engine fan blades, and casings with alternating positive and negative curvatures. For these complex structures of woven composite materials, the preform needs to undergo a complex draping molding process during the preparation process in order to have a geometric shape consistent with the final complex structure of the composite material. In order to adapt to this process, the fabric will undergo very complex micro-structural changes in space, such as yarn slip buckling, changes in yarn orientation and curling, and preform wrinkle defects caused by changes in yarn micro-structure. The above situation has two difficulties in predicting the deformation process of the preform and digitally representing the geometric morphology. First, the preform after molding has complex structural features such as distortion, and the unit cell geometry at different positions is different. Therefore, it is impossible to use local unit cell morphology to characterize the overall structure. Second, the characterization method based on the macro scale can only obtain the mechanical response of the fabric during the molding process and the macroscopic geometry after molding, and cannot characterize the microscopic geometry that affects the mechanical properties of the composite material structure; although the full-size mesoscale characterization method can effectively obtain the microscopic morphology of the composite material structure, there is a problem of large computational complexity. In response to the above problems, it is urgent to take the complex structure of three-dimensional woven composite preforms as the research object, and develop efficient numerical analysis methods for the deformation process and geometric morphology characterization of fiber preforms, so as to provide a theoretical basis and technical support for the optimization design of the preforming process and the prediction of the mechanical properties of the composite material structure.

[0003] In the prior art, there are experimental methods, phenomenological constitutive preform structure macroscopic simulation methods and full-size microscopic structure simulation methods for performing corresponding analyses.

[0004] Experimental method: The reconstruction technology of CT scan images can establish the microscopic structure of the composite material preform and truly reflect the morphology of the yarn inside the composite material structure. However, the quality of CT scan imaging is directly affected by the size of the scanned specimen, and it is impossible to perform high-resolution observation of the microscopic morphology of the yarn inside the entire complex structure. In addition, there are problems such as long detection cycle, high cost, large amount of data, and direct impact of component material density differences on image resolution.

[0005] Phenomenological constitutive method for macroscopic simulation of preform structure: Luycker et al. simulated the torsional deformation of three-dimensional woven fabrics based on the torsional deformation of the blade preform using the subelastic constitutive theory. Barbagallo et al. simulated the eccentric stretching and hemispherical stamping forming process of three-dimensional woven fabrics using the divalent gradient theory. Charmetant et al. proposed a hyperelastic constitutive model suitable for large deformation analysis of thick 3D angle-linked fabrics based on six deformation modes of fabrics. Aridhi et al. developed an orthotropic elastic model and considered the update of fiber direction caused by the forming process. Mathieu et al. proposed an improved modeling method, which introduced the bending stiffness of the fiber on the basis of the orthotropic hyperelastic constitutive model, that is, adding additional curvature-related internal loads to the 3D solid unit, and calculating the curvature of the fiber according to the node position of the adjacent units of the hexahedron, so as to consider the influence of the bending stiffness of the fiber on the deformation behavior of the woven composite preform. The phenomenological constitutive method for macroscopic simulation of preform structure has the advantages of high computational efficiency and can be combined with the finite element method, but it cannot characterize the changes in the orientation and morphology of the yarns inside the complex structure and ignores the microstructure of the preform.

[0006] Full-scale microstructure simulation method: Chen Zhiming established a full-scale microstructure model of three-dimensional woven fabrics, simulated the torsional deformation process of the fabric, and explored the changes in the yarn microstructure. However, due to the oversimplification of the yarn microstructure model, the simulation results of the fabric shear modulus and the experimental results have a large deviation. Said et al. proposed a semi-refined geometric model of three-dimensional woven fabrics based on the digital unit modeling method. First, a refined micro-refined geometric model was established using digital units, and then a mesoscopic yarn model with a shell unit surface was established using spatial geometric reconstruction technology. The yarn was distinguished from the hollow tube unit by establishing a local support unit inside the yarn and the cross-sectional shape could change. The model was used to simulate the complex forming process of the fabric and compared with the scanning results. However, when facing a forming process with severe local wrinkles and out-of-plane buckling, this method will lead to a too small critical shear angle due to ignoring the real lateral deformation of the yarn. The full-scale microstructure simulation method is too large in model, the computer conditions are limited, and there are too many contacts between the yarns in the model, resulting in a particularly large amount of simulation calculations, which makes it difficult to apply to the numerical simulation of the forming process of complex structure preforms. Moreover, since the microscopic constitutive model of the yarn is too simple, there is a large deviation between the simulated fabric model and the test results, and the accuracy is too low.

[0007] In summary, the existing numerical simulation methods for characterizing the geometric morphology of complex structure preforms of three-dimensional woven composites have disadvantages such as high computational cost and low accuracy. Summary of the invention

[0008] In view of the above-mentioned deficiencies in the prior art, the present invention provides a method, system, device and storage medium for digitally characterizing the morphology of complex structure preforms of woven composite materials, which solves the problems of excessive computational cost and low accuracy in existing numerical simulation methods for characterizing the geometric morphology of complex structure preforms of three-dimensional woven composite materials.

[0009] In order to achieve the above-mentioned object of the invention, the technical solution adopted by the present invention is:

[0010] A method for digitally characterizing the morphology of a complex structure preform of a woven composite material is provided, which comprises the following steps:

[0011] S1. Establish a macroscopic finite element model of the flat fabric before forming, simulate the draping molding process of the woven fabric by establishing a macroscopic anisotropic hyperelastic constitutive model of the three-dimensional woven fabric, and extract the displacement size generated by each macroscopic unit node;

[0012] S2. Establish a three-dimensional woven fabric micro-refined unit cell geometry model based on the digital unit method and spatial geometry reconstruction modeling algorithm;

[0013] S3, embedding the boundary elements of the three-dimensional woven fabric mesoscopic refined unit cell geometric model into the macroscopic finite element model of the flat fabric before molding to obtain the embedded model;

[0014] S4, taking the displacement of the macro unit node obtained in step S1 as the deformation condition of the embedded model, deforming the meso boundary unit and the macro unit simultaneously based on the embedded unit method, taking the deformation of the meso boundary unit as the displacement condition of the unit cell deformation, and simulating all the deformed unit cell geometric models;

[0015] S5. Assemble all deformed unit cell geometric models to generate a three-dimensional special-shaped structure preform micro-geometry model, and complete the digital representation of the complex structure preform morphology of the woven composite material.

[0016] Furthermore, the specific method for extracting the displacement magnitude generated by each macro unit node in step S1 is:

[0017] The macroscopic finite element model of the flat fabric before forming is divided into macroscopic units according to the unit cell size. For each macroscopic unit, the corresponding material directions are assigned to the warp, weft yarn directions and thickness directions according to the position of its centroid. The friction coefficient between the steel plate and the flat fabric is set, and the macroscopic finite element model of the flat fabric before forming is placed between two twisted steel plates with the same geometric shape. The steel plate below the flat fabric is fixed and the steel plate above the flat fabric is moved until the relative distance between the two steel plates reaches the specified thickness of the preform, and the displacement generated by each macroscopic unit node is obtained.

[0018] Furthermore, the friction coefficient between the steel plate and the flat fabric is set by the Abaqus / Explicit module.

[0019] Furthermore, the specific method of step S2 includes the following sub-steps:

[0020] S2-1. By using the digital unit method, the fiber is assumed to be a digital unit flexible chain composed of one-dimensional rod and / or beam units, a number of digital unit flexible chains are gathered into digital unit yarns, and the digital unit yarns are arranged into a loose initial ideal topological three-dimensional woven fabric structure according to the fabric interlacing rule, and a three-dimensional woven fabric digital unit finite element unit cell model is obtained when the yarns do not interact with each other;

[0021] S2-2, based on the three-dimensional woven fabric digital unit finite element unit cell model when the yarns do not interact with each other, the fabric forming process is simulated by applying yarn tension and interaction between yarns to obtain a three-dimensional woven fabric digital unit finite element unit cell model when the simulated thickness reaches the real fabric thickness;

[0022] S2-3, dividing all digital chain nodes in the woven fabric into node sets by considering the one-dimensional rod and / or beam unit nodes located within the same cross-section set distance as a node set;

[0023] S2-4, calculating the coordinates of the geometric center point of each node set, treating it as the center point of the corresponding cross section, and sequentially connecting all the center points in the same yarn through a periodic spline curve to form the center line direction of the yarn;

[0024] S2-5, extracting the polygonal outer contour of each node set by using the Alpha-shapes algorithm;

[0025] S2-6. Sequentially number the unit nodes forming the node set and their corresponding yarn centerline directions and polygonal outer contours and store them in an inp text file, and call the inp text file through Abaqus software to generate a three-dimensional woven fabric micro-refined unit cell geometry model.

[0026] Furthermore, the specific method of step S3 is:

[0027] The yarn cross-section unit on the periodic boundary of the mesoscopic refined unit cell geometric model of the three-dimensional woven fabric is extracted, and the yarn cross-section unit is moved to each unit boundary position of the macroscopic finite element model of the flat fabric before molding according to the unit cell size, so as to generate the boundary unit of all the mesoscopic unit cells in the flat fabric, that is, to obtain the mesoscopic boundary unit and the embedded model.

[0028] Furthermore, the specific method of step S4 includes the following sub-steps:

[0029] S4-1, obtaining the deformation displacement of the macro unit node in step S1, and applying it to the embedded model in the form of boundary conditions, so that the micro boundary unit and the macro unit are deformed simultaneously, and the position of the micro boundary unit node in the reference coordinate system of the macro unit is maintained unchanged;

[0030] S4-2. The deformation of the meso boundary unit is used as the displacement condition of the meso unit cell deformation. The meso deformation of all unit cells is calculated through the meso refined unit cell geometric model of the three-dimensional woven fabric to obtain the geometric model of all deformed unit cells.

[0031] Furthermore, the specific method of step S5 is:

[0032] The cross-section nodes and unit information of all deformed unit-cell geometric models are assembled in sequence to generate a microscopic geometric model of a three-dimensional special-shaped structure preform, thus completing the digital representation of the morphology of the complex structure preform of the woven composite material.

[0033] A system based on a digital characterization method for the morphology of a complex structure preform of a woven composite material is provided, comprising:

[0034] The macro unit node displacement extraction module is used to establish a macro finite element model of the flat fabric before forming. By establishing a macro anisotropic hyperelastic constitutive model of a three-dimensional woven fabric, the draping molding process of the woven fabric is simulated, and the displacement generated by each macro unit node is extracted;

[0035] The module for constructing a mesoscopic and refined unit cell geometric model of three-dimensional woven fabrics is used to establish a mesoscopic and refined unit cell geometric model of three-dimensional woven fabrics based on the digital unit method and the spatial geometric reconstruction modeling algorithm;

[0036] An embedding module is used to embed the boundary elements of the three-dimensional woven fabric micro-refined unit cell geometric model into the macroscopic finite element model of the flat fabric before molding to obtain the embedded model;

[0037] The module for simulating the geometric model of the deformed unit cell is used to use the displacement of the macro unit node obtained in the macro unit node displacement extraction module as the deformation condition of the embedded model, and to make the micro boundary unit and the macro unit deform simultaneously based on the embedded unit method, and to use the deformation of the micro boundary unit as the displacement condition of the unit cell deformation, so as to simulate and obtain all the geometric models of the deformed unit cells;

[0038] The assembly module is used to assemble all deformed unit cell geometric models, generate a three-dimensional special-shaped structure preform micro-geometry model, and complete the digital representation of the complex structure preform morphology of the woven composite material.

[0039] An electronic device is provided, comprising: a processor, and a memory communicatively connected to the processor;

[0040] Memory stores computer-executable instructions;

[0041] The processor executes the computer execution instructions stored in the memory to realize a digital representation method for the morphology of a complex structure preform of a woven composite material.

[0042] Provided is a computer-readable storage medium, in which computer-executable instructions are stored. When the computer-executable instructions are executed by a processor, they are used to implement a digital characterization method for the morphology of a complex structure preform of a woven composite material.

[0043] The beneficial effects of the present invention are as follows: the present invention establishes a macroscopic anisotropic hyperelastic constitutive model of three-dimensional woven fabrics and a microscopic refined unit cell geometry model of three-dimensional woven fabrics, and proposes a macroscopic and microscopic combined numerical simulation method for digitally characterizing the geometric morphology of complex structural fiber preforms of three-dimensional woven composite materials, effectively predicting the direction and cross-sectional morphology changes of the microscopic yarns of the preform after the complex molding process, and providing a refined microscopic geometry model for the subsequent mechanical properties analysis of the complex structure of the woven composite material. BRIEF DESCRIPTION OF THE DRAWINGS

[0044] Figure 1 is a schematic diagram of the process of this method;

[0045] Figure 2 is a schematic diagram of a woven composite material under the present method;

[0046] Figure 3 are the six deformation modes of woven fabrics;

[0047] Figure 4 Schematic diagram of macroscopic finite element simulation of woven fabric forming process;

[0048] Figure 5 It is a schematic diagram of the simulation of the three-dimensional woven fabric forming process;

[0049] Figure 6 It is the physical transformation process of the simulation results of the three-dimensional woven fabric digital unit;

[0050] Figure 7 Extracting schematic diagrams for digital chain unit node sets;

[0051] Figure 8 There are four deformation modes for yarn;

[0052] Fig. 9 Schematic diagram of deformation conditions of embedded unit model;

[0053] Fig.10 It is a schematic diagram of the spatial coordinate transformation principle of micro- and macro-unit nodes;

[0054] Fig.11 It is a microscopic geometric model of a three-dimensional special-shaped structure preform;

[0055] Fig.12 1 and 2 are the unit cell deformation results at different positions in the embodiment. DETAILED DESCRIPTION

[0056] The specific implementation modes of the present invention are described below so that those skilled in the art can understand the present invention. However, it should be clear that the present invention is not limited to the scope of the specific implementation modes. For those of ordinary skill in the art, as long as various changes are within the spirit and scope of the present invention as defined and determined by the attached claims, these changes are obvious, and all inventions and creations utilizing the concept of the present invention are protected.

[0057] like Figure 1 and Figure 2 As shown, the digital characterization method of the complex structure preform of the woven composite material includes the following steps:

[0058] S1. Establish a macroscopic finite element model of the flat fabric before forming, simulate the draping molding process of the woven fabric by establishing a macroscopic anisotropic hyperelastic constitutive model of the three-dimensional woven fabric, and extract the displacement size generated by each macroscopic unit node;

[0059] S2. Establish a three-dimensional woven fabric micro-refined unit cell geometry model based on the digital unit method and spatial geometry reconstruction modeling algorithm;

[0060] S3, embedding the boundary elements of the three-dimensional woven fabric mesoscopic refined unit cell geometric model into the macroscopic finite element model of the flat fabric before molding to obtain the embedded model;

[0061] S4, taking the displacement of the macro unit node obtained in step S1 as the deformation condition of the embedded model, deforming the meso boundary unit and the macro unit simultaneously based on the embedded unit method, taking the deformation of the meso boundary unit as the displacement condition of the unit cell deformation, and simulating all the deformed unit cell geometric models;

[0062] S5. Assemble all deformed unit cell geometric models to generate a three-dimensional special-shaped structure preform micro-geometry model, and complete the digital representation of the complex structure preform morphology of the woven composite material.

[0063] In the specific implementation process, this embodiment also provides a system based on a digital characterization method of the morphology of a complex structure preform of a woven composite material, which includes:

[0064] The macro unit node displacement extraction module is used to establish a macro finite element model of the flat fabric before forming. By establishing a macro anisotropic hyperelastic constitutive model of a three-dimensional woven fabric, the draping molding process of the woven fabric is simulated, and the displacement generated by each macro unit node is extracted;

[0065] The module for constructing a mesoscopic and refined unit cell geometric model of three-dimensional woven fabrics is used to establish a mesoscopic and refined unit cell geometric model of three-dimensional woven fabrics based on the digital unit method and the spatial geometric reconstruction modeling algorithm;

[0066] An embedding module is used to embed the boundary elements of the three-dimensional woven fabric micro-refined unit cell geometric model into the macroscopic finite element model of the flat fabric before molding to obtain the embedded model;

[0067] The module for simulating the geometric model of the deformed unit cell is used to use the displacement of the macro unit node obtained in the macro unit node displacement extraction module as the deformation condition of the embedded model, and to make the micro boundary unit and the macro unit deform simultaneously based on the embedded unit method, and to use the deformation of the micro boundary unit as the displacement condition of the unit cell deformation, so as to simulate and obtain all the geometric models of the deformed unit cells;

[0068] The assembly module is used to assemble all deformed unit cell geometric models, generate a three-dimensional special-shaped structure preform micro-geometry model, and complete the digital representation of the complex structure preform morphology of the woven composite material.

[0069] An electronic device is provided, comprising: a processor, and a memory communicatively connected to the processor;

[0070] Memory stores computer-executable instructions;

[0071] The processor executes the computer execution instructions stored in the memory to realize a digital representation method for the morphology of a complex structure preform of a woven composite material.

[0072] Provided is a computer-readable storage medium, in which computer-executable instructions are stored. When the computer-executable instructions are executed by a processor, they are used to implement a digital characterization method for the morphology of a complex structure preform of a woven composite material.

[0073] In the specific implementation process, the unit node is a part of the unit. Taking the hexahedral unit as an example, the vertex of the hexahedron is the unit node of the hexahedral unit. The macroscopic anisotropic hyperelastic constitutive model of three-dimensional woven fabrics comes from "Charmetant A, Orliac JG, Vidal-Sallé E, et al. Hyperelastic model for large deformation analyses of 3D interlock composite preforms[J]. CompositesScience and Technology". In the hyperelastic constitutive theory, the stress-strain relationship is expressed by the relationship between the strain energy density function and the invariant. The macroscopic deformation of the fabric material is simulated by designing the strain energy density function. The material directions of three-dimensional woven fabrics include the warp and weft directions that are perpendicular to each other and the thickness direction perpendicular to the plane where the warp and weft yarns are located. The characteristics of this symmetrical material can be expressed by three structural tensors respectively. express, The macroscopic mechanical properties of fabrics can be expressed by the following strain energy function: W Characterization:

[0074] (1)

[0075] in , , , , and is the Cauchy-Green deformation tensor C = FT F The invariant of is the deformation gradient tensor, and the superscript T is the transpose of the matrix; , , ; The remaining invariants can be expressed using the structure tensor as follows:

[0076]

[0077]

[0078]

[0079] For three-dimensional woven fabrics, the deformation is mainly divided into six independent basic deformation modes, such as Figure 3 As shown, they are respectively the longitudinal stretching ( elong 1) Weft stretching ( elong 2) Out-of-plane compression of warp and weft yarns ( Comp )、Warp and weft yarn in-plane shear( Cp ), interlayer shear in the warp direction ( Ct 1) and interlaminar shear in the weft direction ( Ct 2). Each deformation mode can be defined by a corresponding invariant based on the description of material characteristics. By combining the eleven invariants in formula (1), the invariants corresponding to the six deformation modes of three-dimensional woven fabrics can be obtained, which are:

[0080]

[0081]

[0082]

[0083]

[0084]

[0085]

[0086] It is assumed that the contribution of each deformation mode is independent of the other modes. Strain energy density function W It can be expressed as the sum of the strain energy functions of these six independent deformations:

[0087]

[0088] According to the six deformation modes of fabrics mentioned above, the relevant strain energy can be determined through simple warp and weft tensile tests, out-of-plane compression tests, in-plane shear tests and interlaminar shear tests in two directions.

[0089] Second-order Piola-Kirchhoff stress tensor S It can be expressed by the following formula:

[0090]

[0091] The Cauchy stress tensor can be derived from the deformation gradient tensor and the second-order Piola-Kirchhoff tensor:

[0092]

[0093] in J is the Jacobian matrix used to describe the local volume change during deformation.

[0094] The above-mentioned fabric macro-anisotropic hyperelastic constitutive analysis process can be realized by writing the ABAQUS user subroutine VUMAT.

[0095] In the specific implementation process, Figure 4 The macroscopic finite element model of the flat fabric (where (a) is the calculation model and (b) is the deformation result) simplifies the experimental fixture into two twisted steel plates with the same geometric shape, and places the rectangular flat fabric between the two steel plates. The Abaqus / Explicit module is used for simulation analysis, and the friction coefficient between the steel plate and the fabric is set. The macroscopic fabric model is divided into unit cell size units, and each unit is assigned corresponding material directions in the warp and weft yarn directions and thickness directions according to the position of its centroid. Fix steel plate 2 and move steel plate 1 until the relative distance between the steel plates reaches the specified thickness of the preform.

[0096] The weaving process of three-dimensional woven fabrics is a dynamic process of gradual interaction between fibers, which can be achieved through the digital unit method. In this embodiment, the fibers are assumed to be digital unit flexible chains composed of one-dimensional tiny rods and / or beam units, and several digital unit chains are gathered into digital unit yarns. The digital unit yarns are arranged into a loose initial ideal topological three-dimensional woven fabric structure according to the fabric interweaving rules. The fabric forming process is simulated by applying yarn tension and the interaction between yarns, and finally a more realistic three-dimensional woven fabric digital unit model is obtained. Figure 5 The finite element models of the three stages in the three-dimensional woven fabric forming process obtained by the digital unit method are the digital unit finite element models of the three-dimensional woven fabric when the yarns do not interact before simulation ( Figure 5 In part (a), the three-dimensional woven fabric digital unit finite element model when the yarns come into contact with each other during the simulation process ( Figure 5 (b)), and the three-dimensional woven fabric digital unit finite element model when the simulated thickness reaches the real fabric thickness ( Figure 5(c) in the figure.

[0097] In this embodiment, a three-dimensional woven fabric with a layer-layer three-twill angle interlocking structure is taken as an example. This type of fabric is composed of two yarn components, namely warp yarn (x direction) and weft yarn (y direction). The specific implementation process of the digital unit method is as follows:

[0098] (1) First, you need to establish ( Figure 5 The initial fabric topology finite element model shown in (a) of Figure 1. To ensure that the fiber units do not penetrate each other and the yarns do not contact and interact with each other before numerical calculation, a certain gap needs to be set between the yarns. In addition, in theory, it is more accurate to use each digital unit chain to represent each real fiber in the yarn, but this will incur a huge computational cost, and a yarn composed of 19 to 61 digital unit chains can also effectively represent the cross-sectional morphology;

[0099] (2) The finite element ABAQUS software is used to simulate the simulation forming process of woven fabrics. The main driving force of the three-dimensional woven fabric weaving process is the yarn tension. By reducing the temperature of the digital unit chain of the warp yarn, a yarn-like tension can be generated, thereby generating a lateral force on the inner weft yarn. At the same time, increasing the temperature of the digital unit chain of the weft yarn increases the length of the straight weft yarn, and then a process occurs in which the weft yarn waviness gradually approaches that of the real fabric. This process is a quasi-static evolution process, in which the yarns gradually interact with each other and the whole changes from one equilibrium state to another.

[0100] The physical transformation process of the simulation results of the three-dimensional woven fabric digital unit is as follows: Figure 6 As shown in the figure, the process uses spatial geometric reconstruction modeling technology, the core of which is the extraction of microscopic yarn contours and the calculation of the yarn centerline direction, which are mutually iterative processes. Figure 7 As shown in Figure 2, the specific implementation process of spatial geometry reconstruction is as follows:

[0101] (1) The one-dimensional rod or beam unit nodes with close to the same cross-section are regarded as a node set, and all digital chain nodes in the fabric are divided into a large number of node sets (Sets);

[0102] (2) Calculate the coordinates of the geometric center point of each node set, regard it as the center point of the corresponding section, and use periodic spline curves to connect all the center points in the same yarn in sequence to form the direction of the yarn centerline;

[0103] (3) Extract the polygonal outer contour of each node set by using the Alpha-shapes algorithm;

[0104] (4) Write a Python script to sequentially number all the unit nodes that have undergone the above processing and store them in an inp text file. By calling the Python file in the Abaqus software, a complete fabric micro-refined unit cell finite element model can be generated.

[0105] In order to subsequently simulate the deformation of the mesoscopic unit cells of fabrics with complex structures, a hyperelastic constitutive model is also needed to describe the deformation of the yarn. Unlike the macroscopic anisotropic hyperelastic constitutive model, the mesoscopic yarn is a transversely isotropic material, and a transversely isotropic hyperelastic model needs to be established to study the mesoscopic deformation of the fabric. Since the essence of the hyperelastic constitutive model is the same, only the differences from the macroscopic anisotropic hyperelastic constitutive model are introduced here. For the symmetry group of transversely isotropic materials, the yarn can be divided into four basic deformation modes, namely, tensile deformation along the yarn fiber direction, compression deformation in the transverse direction of the yarn, transverse shear deformation of the yarn, and shear deformation of the yarn along the fiber direction, such as Figure 8 As shown (where (a) is elongation in the fiber direction, (b) is transverse compression, (c) is transverse shear, and (d) is shear in the fiber direction). The invariance of the deformation gradient tensor corresponding to the four deformation modes I elong , I comp , I shear and I dist They can be obtained through the following formulas:

[0106]

[0107] Where ln is the logarithm with the natural constant e as the base.

[0108] These invariants are used to define the strain energy function corresponding to each deformation mode W It can be expressed as the sum of the strain energy functions of four independent deformations:

[0109]

[0110] The constitutive equation can be implemented in Abaqus / Explicit software using a user-defined subroutine VUMAT written in Fortran. Similarly, according to the four deformation modes mentioned above, the material parameters of the relevant deformation modes can be determined by yarn tensile test, yarn transverse compression test, fabric uniaxial tensile test and fabric biaxial tensile test.

[0111] In the specific implementation process, Fig. 9As shown in the figure (where (a) is the three-dimensional woven fabric micro-refined unit cell geometry model, (b) is the boundary unit embedded in the macroscopic finite element model of the flat fabric before molding, and (c) is the unit cell geometry model after deformation), by extracting the yarn cross-section unit on the periodic boundary of the three-dimensional woven fabric micro-refined unit cell geometry model, and moving the yarn cross-section unit to each unit boundary position of the macroscopic finite element model of the flat fabric before molding according to the unit cell size, the boundary units of all the mesoscopic unit cells in the flat fabric are generated, that is, the mesoscopic boundary units and the embedded model are obtained.

[0112] The deformation displacement of the macro unit node in step S1 is obtained, and it is applied to the embedded model in the form of boundary conditions, so that the meso boundary unit and the macro unit are deformed simultaneously, and the position of the meso boundary unit node in the reference coordinate system of the macro unit is maintained unchanged; the deformation of the meso boundary unit is used as the displacement condition of the meso unit cell deformation, and the meso deformation of all unit cells is calculated through the meso refined unit cell geometry model of the three-dimensional woven fabric, so as to obtain the geometry model of all deformed unit cells.

[0113] like Fig.10 As shown in the figure, the node relationship between the macro unit node and the micro unit node is:

[0114]

[0115] in is the reference coordinate system of the macro unit, and are the spatial coordinates of the meso- and macro-nodes; Expressed as shape functions between coordinate systems; in the initial state and deformed state, the natural coordinates of the microscopic boundary nodes in the macro unit are The position of the mesoscopic unit cell embedded in the macroscopic unit cell remains unchanged. Therefore, the deformation obtained by macroscopic simulation can provide the geometric deformation of the mesoscopic unit cell boundary at the mesoscopic scale, which is called the embedded mesoscopic model.

[0116] In the specific implementation process, all deformed microscopic unit cells can be parametrically assembled by writing a Python program (assembled through cross-section nodes and unit information). Fig.11 The micro-geometric model of the three-dimensional special-shaped preform is shown. Due to the large overall size, the micro-structure is not very clear. Two local areas are extracted for result display. It can be seen that the established micro-geometric model of the three-dimensional special-shaped preform can fully display the geometric morphology of the yarn at different positions.

[0117] In one embodiment of the present invention, in order to evaluate and verify the effectiveness of the microscopic geometric model of the three-dimensional special-shaped structure preform established by the present method, this embodiment is tested based on the German Diondo D5 high-power dual-source dual-detection industrial Micro-CT system to scan and reconstruct the overall geometric structure of the preform after molding, such as Fig.12 As shown in the figure (where (a) is the overall geometric structure of the preform reconstructed by scanning, and (b) is the microscopic geometric model of the three-dimensional special-shaped structure preform obtained by this method). The slice information and finite element simulation results of the red and blue dotted areas are extracted to verify the geometric model. It can be seen that the microscopic geometric model of the three-dimensional special-shaped structure preform established by this method is basically consistent with the Micro-CT scanning results, including the cross-sectional shape and yarn path.

[0118] In summary, the present invention effectively predicts the direction of the microscopic yarns and the changes in the cross-sectional morphology of the preform after the complex molding process, which can be achieved digitally without the need to model by scanning the sample.

Claims

1. A digital characterization method for the morphology of complex structure preforms of woven composite materials, It is characterized in that The following steps are involved: S1. Establish a macroscopic finite element model of the flat fabric before forming, simulate the draping molding process of the woven fabric by establishing a macroscopic anisotropic hyperelastic constitutive model of the three-dimensional woven fabric, and extract the displacement size generated by each macroscopic unit node; S2. Establish a three-dimensional woven fabric micro-refined unit cell geometry model based on the digital unit method and spatial geometry reconstruction modeling algorithm; S3, embedding the boundary elements of the three-dimensional woven fabric mesoscopic refined unit cell geometric model into the macroscopic finite element model of the flat fabric before molding to obtain the embedded model; S4, taking the displacement of the macro unit node obtained in step S1 as the deformation condition of the embedded model, deforming the meso boundary unit and the macro unit simultaneously based on the embedded unit method, taking the deformation of the meso boundary unit as the displacement condition of the unit cell deformation, and simulating all the deformed unit cell geometric models; S5. Assemble all deformed unit cell geometric models to generate a three-dimensional special-shaped structure preform micro-geometry model, and complete the digital representation of the complex structure preform of the woven composite material; The specific method for extracting the displacement size generated by each macro unit node in step S1 is: The macroscopic finite element model of the flat fabric before forming is divided into macroscopic units according to the unit cell size. For each macroscopic unit, the corresponding material direction is assigned to the warp and weft yarn directions and the thickness direction according to the position of its centroid; the friction coefficient between the steel plate and the flat fabric is set, and the macroscopic finite element model of the flat fabric before forming is placed between two twisted steel plates with the same geometric shape, the steel plate below the flat fabric is fixed and the steel plate above the flat fabric is moved until the relative distance between the two steel plates reaches the specified thickness of the preform, and the displacement generated by each macroscopic unit node is obtained; The specific method of step S2 includes the following sub-steps: S2-1. By using the digital unit method, the fiber is assumed to be a digital unit flexible chain composed of one-dimensional rod and / or beam units, a number of digital unit flexible chains are gathered into digital unit yarns, and the digital unit yarns are arranged into a loose initial ideal topological three-dimensional woven fabric structure according to the fabric interlacing rule, and a three-dimensional woven fabric digital unit finite element unit cell model is obtained when the yarns do not interact with each other; S2-2, based on the three-dimensional woven fabric digital unit finite element unit cell model when the yarns do not interact with each other, the fabric forming process is simulated by applying yarn tension and interaction between yarns to obtain a three-dimensional woven fabric digital unit finite element unit cell model when the simulated thickness reaches the real fabric thickness; S2-3, dividing all digital chain nodes in the woven fabric into node sets by considering the one-dimensional rod and / or beam unit nodes located within the same cross-section set distance as a node set; S2-4, calculating the coordinates of the geometric center point of each node set, treating it as the center point of the corresponding cross section, and sequentially connecting all the center points in the same yarn through a periodic spline curve to form the center line direction of the yarn; S2-5, extracting the polygonal outer contour of each node set by using the Alpha-shapes algorithm; S2-6, sequentially numbering the unit nodes forming the node set and their corresponding yarn centerline directions and polygonal outer contours and storing them in an inp text file, and calling the inp text file through Abaqus software to generate a three-dimensional woven fabric micro-refined unit cell geometry model; The specific method of step S3 is: The yarn cross-section unit on the periodic boundary of the mesoscopic refined unit cell geometric model of the three-dimensional woven fabric is extracted, and the yarn cross-section unit is moved to each unit boundary position of the macroscopic finite element model of the flat fabric before molding according to the unit cell size, so as to generate the boundary unit of all the mesoscopic unit cells in the flat fabric, that is, to obtain the mesoscopic boundary unit and the embedded model.

2. The digital characterization method for the morphology of a complex structure preform of a woven composite material according to claim 1, It is characterized in that The friction coefficient between the steel plate and the flat fabric is set using the Abaqus / Explicit module.

3. The digital characterization method for the complex structure preform of a woven composite material according to claim 1, It is characterized in that The specific method of step S4 includes the following sub-steps: S4-1, obtaining the deformation displacement of the macro unit node in step S1, and applying it to the embedded model in the form of boundary conditions, so that the micro boundary unit and the macro unit are deformed simultaneously, and the position of the micro boundary unit node in the reference coordinate system of the macro unit is maintained unchanged; S4-2. The deformation of the meso boundary unit is used as the displacement condition of the meso unit cell deformation. The meso deformation of all unit cells is calculated through the meso refined unit cell geometric model of the three-dimensional woven fabric to obtain the geometric model of all deformed unit cells.

4. The digital characterization method for the complex structure preform of a woven composite material according to claim 3, It is characterized in that The specific method of step S5 is: The cross-section nodes and unit information of all deformed unit-cell geometric models are assembled in sequence to generate a microscopic geometric model of a three-dimensional special-shaped structure preform, thus completing the digital representation of the morphology of the complex structure preform of the woven composite material.

5. A system based on the digital characterization method of the morphology of a complex structure preform of a woven composite material according to any one of claims 1 to 4, It is characterized in that include: The macro unit node displacement extraction module is used to establish a macro finite element model of the flat fabric before forming. By establishing a macro anisotropic hyperelastic constitutive model of a three-dimensional woven fabric, the draping molding process of the woven fabric is simulated, and the displacement generated by each macro unit node is extracted; The module for constructing a mesoscopic and refined unit cell geometric model of three-dimensional woven fabrics is used to establish a mesoscopic and refined unit cell geometric model of three-dimensional woven fabrics based on the digital unit method and the spatial geometric reconstruction modeling algorithm; An embedding module is used to embed the boundary elements of the three-dimensional woven fabric micro-refined unit cell geometric model into the macroscopic finite element model of the flat fabric before molding to obtain the embedded model; The module for simulating the geometric model of the deformed unit cell is used to use the displacement of the macro unit node obtained in the macro unit node displacement extraction module as the deformation condition of the embedded model, and to make the micro boundary unit and the macro unit deform simultaneously based on the embedded unit method, and to use the deformation of the micro boundary unit as the displacement condition of the unit cell deformation, so as to simulate and obtain all the geometric models of the deformed unit cells; The assembly module is used to assemble all deformed unit cell geometric models, generate a three-dimensional special-shaped structure preform micro-geometry model, and complete the digital representation of the complex structure preform morphology of the woven composite material.

6. An electronic device, It is characterized in that include: A processor, and a memory communicatively connected to the processor; Memory stores computer-executable instructions; The processor executes the computer-executable instructions stored in the memory to implement the method according to any one of claims 1 to 4.

7. A computer-readable storage medium, It is characterized in that The computer-readable storage medium stores computer-executable instructions, which are used to implement the method according to any one of claims 1 to 4 when executed by a processor.

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