Method for predicting high and low temperature mechanical properties of flax fiber composite material

Abstract

The application aims to provide a flax fiber composite material high-low temperature mechanical property prediction method, solves the problem that an existing prediction method cannot reveal the influence of different components in a service temperature interval on the macroscopic performance of the composite material through cross-scale cooperation, cannot realize performance prediction of plant fiber composites at different temperatures, mainly researches the mechanical response and damage evolution of the composite material at three scales of micro, meso and macro, constructs a correction function of the mechanical property changing with temperature, realizes mechanical property prediction of continuous flax fiber / epoxy resin composites in a service temperature interval, and provides a new method for performance prediction of the composite material.

Description

Technical Field

[0001] This invention belongs to the field of composite material performance prediction technology, and particularly relates to a method for predicting the high and low temperature mechanical properties of flax fiber composite materials. Background Technology

[0002] Composite materials refer to multiphase solid materials made by combining two or more component materials through various composite processes. As an emerging multifunctional material, they possess many excellent properties, such as high specific strength and specific modulus, excellent thermal insulation performance, good damping and shock absorption performance, and excellent chemical corrosion resistance. Natural plant fibers are readily available, inexpensive, have high specific strength, are renewable, and biodegradable, meeting the requirements of energy conservation and environmental protection. More and more automakers are beginning to use plant fiber-reinforced composite materials in functional components such as bumpers, hoods, and sound-absorbing panels, as well as interior and exterior trim components such as dashboards, headliners, and trunk liners.

[0003] Fiber-reinforced composite materials used in vehicle structures are inevitably subjected to the temperature field of the automotive industry during actual service. Continuous plant fiber reinforced composite materials are mainly composed of two components: fiber and resin. Their thermophysical properties are more complex than those of single-component materials. The reinforcing phase and the matrix phase generally have different thermodynamic properties, possessing different thermophysical parameters such as elastic modulus, Poisson's ratio, thermal conductivity, and coefficient of thermal expansion. These differences lead to different thermophysical property changes in each component under the influence of the external temperature field. Furthermore, the constraints of the overall structure and its components can increase internal stress or strain, causing the composite material to exhibit heterogeneity and anisotropy, ultimately affecting its performance. Therefore, studying the mechanical properties of composite materials at different service temperatures and establishing effective methods for predicting mechanical properties are of great significance for further promoting the widespread use of composite materials in the automotive industry.

[0004] Research methods for fiber-reinforced composites can be divided into two categories: macroscopic mechanics and microscopic mechanics. Macroscopic mechanics methods for composites are based on the homogenization assumption, treating the composite material as a macroscopic homogeneous medium, considering the reinforcing phase and matrix as a single entity, and disregarding the mutual influence of the component phases, focusing only on the average performance of the composite material. Microscopic mechanics can obtain the complete stress and strain fields at the microscale to reflect the macroscopic response characteristics of the composite material, thus enabling quantitative analysis of the dependence of the macroscopic properties of the composite material on the microstructure. The multi-scale method based on micromechanics has become a hot topic in the study of plain weave composites in recent years. This method can analyze the mechanical properties of materials at three scales: micro, meso, and macro. It can capture multiple complex failure modes of materials, accelerate the modeling process, and reduce computational workload, which is of great significance for composite material research.

[0005] Existing research methods on continuous fiber / resin composites mainly focus on the establishment and improvement of mechanical models at room temperature. They lack failure simulation methods for plant fiber reinforced composites that consider the influence of temperature effects, cannot reveal the influence of cross-scale interaction of different components on the macroscopic properties of composites within the service temperature range, and cannot predict the performance of plant fiber composites at different temperatures. Summary of the Invention

[0006] To address the aforementioned problems, the present invention aims to propose a method for predicting the mechanical properties of flax fiber composite materials within the service temperature range of vehicles. This method solves the problem that existing prediction methods cannot reveal the influence of cross-scale interactions of different components on the macroscopic properties of composite materials within the service temperature range, and cannot predict the performance of plant fiber composite materials at different temperatures.

[0007] The technical solution for predicting the mechanical properties of fiber-reinforced composite materials is as follows:

[0008] A microscopic Reduction and Variation (RVE) model for the matrix-fiber composite material was determined. A hexagonal fiber bundle unit cell model was established, with the microfiber bundle unit cell mesh discretized using tetrahedral elements. Shared nodes were used between the fibers and the matrix to ensure displacement continuity. The maximum stress criterion was selected to characterize the damage initiation of both the fibers and the matrix, and a damage degradation criterion based on fracture toughness was used to describe the damage evolution of both the fibers and the matrix. Simulation calculations were performed on the fiber bundle unit cell model, and the mechanical property parameters of the matrix and fibers at various temperatures were substituted to obtain the mechanical property parameters of the fiber bundle at different temperatures. A function of the fiber bundle mechanical property parameters based on temperature variation was constructed. Finally, a microscopic RVE model for the composite material was determined, simplifying the fiber bundle path to a straight line and a sine curve. By combining and simplifying the cross-section of the fiber bundles to an ellipse, a mesoscopic model of flax fiber / epoxy resin composite material is established. Mesh generation and property definition of each component are performed, and appropriate periodic boundary conditions are added. The maximum principal stress criterion and stiffness degradation based on fracture energy are used to describe the damage initiation and evolution of the matrix. The three-dimensional Hashin failure criterion is used to determine the initial damage of the fiber bundles, and a progressive degradation method is employed to characterize the damage evolution. Simulation calculations are performed on the mesoscopic RVE model, applying a typical service temperature field. Substituting the mechanical property parameters of the fiber bundles and resin materials, a function of the macroscopic composite material's mechanical property parameters based on temperature changes is constructed, resulting in a predictive model for the mechanical properties of fiber-reinforced composite materials.

[0009] In the above or some embodiments, the function of the mechanical property parameters of the matrix material with temperature includes functions of tensile modulus and shear modulus, tensile strength, compressive strength and shear strength, and the coefficient of thermal expansion of epoxy resin.

[0010] In the above or some embodiments, the function between the mechanical property parameters of the fiber material and temperature includes the function of the longitudinal tensile modulus, the transverse / normal tensile modulus, the functions of the two in-plane shear modulus and the out-of-plane shear modulus, the function of tensile strength and compressive strength, and the function of the longitudinal thermal expansion coefficient and the transverse thermal expansion coefficient.

[0011] In the above or some embodiments, a macroscopic finite element model is established, and failure criteria and degradation criteria are defined to describe the damage initiation and stiffness degradation of the macroscopic model. The composite material mechanical property parameters are substituted into a function based on temperature change, and finite element analysis is performed on the finite element model to obtain the prediction results.

[0012] In the above or some embodiments, a macroscopic finite element model of tension and three-point bending is established, and the three-dimensional Hashin failure criterion and the progressive degradation criterion based on fracture energy are used to describe the damage initiation and stiffness degradation of macroscopic composite materials.

[0013] The method for predicting the mechanical properties of fiber-reinforced composite materials is used to predict the mechanical properties of macroscopic components, which are characterized by tensile and three-point bending.

[0014] This invention establishes a method for predicting the high and low temperature mechanical properties of flax fiber composites, providing a fundamental prediction for the further application of flax fiber / epoxy resin green composites in the automotive parts field. This invention adopts a multi-scale method to study the mechanical response and damage evolution of composites at three scales: micro, meso, and macro. It constructs a correction function for the change of mechanical properties with temperature, realizing the prediction of mechanical properties of continuous flax fiber / epoxy resin composites within the service temperature range, providing a new approach to the performance prediction of composite materials.

[0015] Instruction manual illustrations

[0016] Figure 1 This is a flowchart of the steps of the present invention.

[0017] Figure 2 This is a diagram of a single-cell model of a fiber bundle in this invention.

[0018] Figure 3 This is a diagram showing the microstructure of the fiber bundle mesh in this invention.

[0019] Figure 4 This is the front view of the microscopic unit cell model in this invention.

[0020] Figure 5 This is a side view of the microscopic unit cell model in this invention.

[0021] Figure 6 This is a schematic diagram of a macroscopic model in one embodiment of the present invention. Detailed Implementation

[0022] Embodiments of the present invention will be described in detail below. Examples of the embodiments are shown in the accompanying drawings, where the same or similar reference numerals denote the same or similar elements or elements having the same or similar functions throughout. The embodiments described below by referring to the accompanying drawings are exemplary and are intended to explain the present invention and should not be construed as limiting the present invention.

[0023] In the description of the present invention, the meaning of "plurality" is two or more, unless otherwise specifically defined.

[0024] In this technical solution, the fiber material can be selected from natural fiber materials, including but not limited to linen fiber, and its matrix material can be selected from resin materials, including but not limited to epoxy resin materials. Taking linen fiber and epoxy resin materials as an example, linen fiber specimens, epoxy resin specimens and composite material specimens are prepared before the experiment, and high and low temperature experiments are carried out. Referring to the relevant standards of high and low temperature experiments in the automotive industry, a universal testing machine is used to conduct tensile tests, compression tests and shear tests at temperatures of -40°C, -10°C, 20°C, 50°C and 80°C. The environmental temperature required for testing is provided by a high and low temperature environmental chamber supporting the testing machine. The high temperature is provided by heating the electric heating wire in the environmental chamber, and the low temperature is achieved by injecting liquid nitrogen into the environmental chamber. With an intelligent control unit, the temperature can be controlled within the range of the predetermined temperature value ±1°C. Finally, the thermal expansion coefficient of the experiment is measured by an inductive dilatometer. One end of the specimen is fixed to the end of the support, and the other end is in contact with the ejector rod. The specimen, the support and the ejector rod are heated simultaneously, and the thermal expansion difference between the specimen and these components is transmitted by the ejector rod and measured.

[0025] Through the experimental process, the mechanical parameters of linen fiber and epoxy resin at different temperature points are obtained respectively. The experimental data are integrated to obtain the laws of linen fiber and epoxy resin changing with temperature, that is, step one. According to the mechanical property parameter data of the matrix material and the fiber material changing with temperature, the function of the material changing with temperature is defined. Among them, the functions of the mechanical property parameters of the matrix material and temperature (T), the tensile modulus and the shear modulus and temperature (T) are E m (T), G m (T), the functions of the tensile strength, the compressive strength and the shear strength and temperature (T) are M T (T), M C (T), M S (T), and the function of the thermal expansion coefficient (α) of the epoxy resin and temperature (T) is α m (T); the functions of the mechanical property parameters of the fiber material and temperature are defined. The functions of the longitudinal tensile modulus and the transverse / normal tensile modulus of the fiber material and temperature (T) are E f11 (T), Ef22 (T) / E f33 (T), the in-plane shear modulus and out-of-plane shear modulus of the fiber as a function of temperature (T) are G, ... f12 (T) / G f13 (T), G f23 The tensile strength and compressive strength of the fiber as a function of temperature (T) are FT and FC, respectively. T (T), F c (T), the longitudinal and transverse thermal expansion coefficients of the fiber as a function of temperature (T) are α and α, respectively. f1 (T), α f2 (T);

[0026] A microscopic RVE model for matrix-fiber composite materials is defined. A fiber bundle unit cell model is established using a hexagonal distribution. The microscopic fiber bundle unit cell mesh is discretized using tetrahedral elements. The fiber and matrix are connected by common nodes to ensure the continuity of displacement. The maximum stress criterion is selected to characterize the damage initiation of the fiber and matrix. The damage degradation criterion based on fracture toughness is used to describe the damage evolution of the fiber and matrix.

[0027] Adding periodic boundaries to the fiber bundles of composite materials, since they are considered transversely isotropic unidirectional composite materials with uniform fiber distribution in the matrix, their structure exhibits significant periodicity. The macroscopic fiber bundle structure can be considered as an array of microscopic fiber bundle unit cells. Therefore, it is essential to ensure that each unit cell in the fiber bundle exhibits the same deformation mode under external load and that they do not separate or nest with each other. Furthermore, since the fiber filaments can be considered transversely isotropic materials and the epoxy resin matrix can be considered homogeneous isotropic materials, the maximum stress criterion is used to characterize the damage initiation of the fibers. The specific expression is as follows:

[0028]

[0029] Where F it F ic and F ijs These represent the tensile, compressive, and shear strengths of the fiber in its three main directions.

[0030] For the matrix, the maximum principal stress criterion is used to characterize the initial damage, and the specific expression is as follows:

[0031]

[0032] Where σ1 and σ3 are the first and third principal stresses, respectively.

[0033] When a material is damaged, its various mechanical properties are weakened. Therefore, a damage degradation criterion based on fracture toughness is used to describe the damage evolution of the fiber and the matrix. The corresponding expressions for the damage variables are as follows:

[0034]

[0035] Among them, З f This represents the strain component along the longitudinal direction of the fiber.

[0036] The expression for the damage variable of the matrix is ​​as follows:

[0037]

[0038] In summary, the stiffness matrix expressions after fiber and matrix damage are as follows:

[0039]

[0040] Where C f(m) This is the stiffness matrix when the fiber or matrix is ​​undamaged.

[0041] Finally, simulation calculations were performed on the fiber bundle unit cell model, and the fiber and resin material parameters at various temperatures were substituted to obtain the fiber bundle performance parameters at different temperatures.

[0042] Simulation calculations were performed on the above fiber bundle unit cell model. By substituting the mechanical property parameters of the matrix and fiber materials at various temperatures, the mechanical property parameters of the fiber bundle at different temperatures were obtained, and a function of the fiber bundle mechanical property parameters based on temperature change was constructed. To facilitate model establishment and subsequent calculations, the fiber bundle path was simplified to a combination of straight lines and sine curves, and the cross-section of the fiber bundle was simplified to an ellipse. The fiber bundle volume accounts for 62.5% of the unit cell volume.

[0043] The longitudinal and transverse / normal tensile moduli of the fiber bundle as functions of temperature are E, respectively. f11 ’ (T), E f22 ’ (T) / E f33 (T), the functions of the in-plane shear modulus and the out-of-plane shear modulus with temperature, are G and G respectively. f12 ’ (T) / G f13 ’ (T), G f23 ’ (T); the longitudinal tensile strength and longitudinal compressive strength of the fiber bundle as functions of temperature, respectively X T (T), X C (T); the functions of transverse tensile strength, transverse compressive strength and temperature, respectively, are Y T (T), Y C (T); functions relating in-plane and out-of-plane shear strength to temperature, denoted as Si. 12 (T) / S 13(T), S 23 (T); The longitudinal and transverse thermal expansion coefficients of the fiber bundle are functions of temperature, α and β, respectively. X (T), α Y (T);

[0044] A microscopic RVE model for composite materials is defined, simplifying fiber bundle paths to combinations of straight lines and sine curves, and fiber bundle cross-sections to ellipses. A microscopic model of flax fiber / epoxy resin composite material is established, meshed, and the properties of each component are defined. Appropriate periodic boundary conditions are added. The matrix uses the maximum principal stress criterion and stiffness degradation based on fracture energy to describe the damage initiation and evolution of the material. The fiber bundles are assessed using the three-dimensional Hashin failure criterion to determine the initial damage, and a progressive degradation method is used to characterize the damage evolution. Due to the complex internal structure of the microscopic model unit cell, tetrahedral elements are used to discretize the unit cell model, with a mesh size of 0.1 mm. Fiber bundle elements and matrix elements are connected by common nodes to ensure displacement continuity. In the high-fidelity microscopic unit cell of the composite material, the matrix still uses the maximum principal stress criterion and stiffness degradation based on fracture energy to describe the damage initiation and evolution of the material. The Hashin failure criterion is used to determine the initial damage of the material, which considers four typical damage forms: fiber tensile damage, fiber compressive damage, matrix tensile damage, and matrix compressive damage. The specific expressions corresponding to the four types of damage are as follows:

[0045] (1) Fiber tensile damage ( )

[0046]

[0047] (2) Fiber compression damage )

[0048]

[0049] (3) Matrix tensile damage ( )

[0050]

[0051] (4) Matrix compression damage )

[0052]

[0053] Where X t X c These represent the longitudinal tensile and longitudinal compressive strengths of the fiber bundle, respectively; Y t Y c These represent the transverse tensile and transverse compressive strengths of the fiber bundle, respectively; S12 S 13 and S 23 These represent the in-plane shear strength and out-of-plane shear strength of the fiber bundle, respectively.

[0054] Finally, a progressive degradation method was used to characterize the damage evolution of the fiber bundles. The microscopic model was simulated and calculated, and the parameters of the fiber bundles at various temperatures were substituted to complete the model establishment.

[0055] A function of the macroscopic mechanical properties of composite materials as a function of temperature was constructed. Simulations were performed on a microscopic RVE model, applying a typical automotive service temperature field. Substituting fiber bundle and resin material parameters, functions of the macroscopic mechanical properties of the composite materials based on temperature were constructed: functions relating the longitudinal tensile modulus, longitudinal compressive modulus, transverse tensile modulus, and transverse compressive modulus to temperature, denoted as E... t1 (T) / E c1 (T) / E t2 (T) / E c2 (T), the in-plane and out-of-plane shear moduli of the material as functions of temperature, are G and G, respectively. 12 (T) / G 13 (T), G 23 (T), the relationship between longitudinal tensile strength / transverse tensile strength and longitudinal compressive strength / transverse compressive strength as a function of temperature, respectively X T ’ (T) / Y T ’ (T), X C ’ (T) / Y C ’ (T), the in-plane and out-of-plane shear strengths of the material as a function of temperature, are S XY (T), S YZ (T);

[0056] A macroscopic finite element model of flax fiber / epoxy resin composite material under tensile and three-point bending was established. The three-dimensional Hashin failure criterion and the progressive degradation criterion based on fracture energy were used to describe the damage initiation and stiffness degradation of the macroscopic composite material. The macroscopic elastic property function and failure strength function of flax fiber / epoxy resin composite material as a function of temperature were substituted into the macroscopic model. Finite element analysis was carried out under different temperature fields to predict the mechanical properties of flax fiber composite material at different temperatures.

[0057] Example

[0058] The tensile / compression modulus data obtained from quasi-static tensile / compression experiments were statistically analyzed. A quadratic polynomial function was used to fit the experimental data, and the fitting accuracy was compared. The experimental data conformed to the function. The functions relating the longitudinal tensile modulus, longitudinal compressive modulus, transverse tensile modulus, and transverse compressive modulus (GPa) to temperature are as follows:

[0059]

[0060]

[0061]

[0062]

[0063] The shear modulus data obtained from shear experiments were statistically analyzed. A quadratic polynomial function was used to fit the experimental data, and the fitting accuracy was compared. The experimental data conformed to the function, which is a function of the in-plane shear modulus and out-of-plane shear modulus (GPa) of the material with temperature.

[0064]

[0065]

[0066]

[0067] The tensile / compression modulus data obtained from tensile / compression experiments were statistically analyzed. A quadratic polynomial function was used to fit the experimental data, and the fitting accuracy was compared. The experimental data conformity functions, representing the relationship between longitudinal tensile strength / transverse tensile strength and longitudinal compressive strength / transverse compressive strength (MPa) and temperature, are respectively...

[0068]

[0069]

[0070]

[0071]

[0072] The shear modulus data obtained from shear experiments were statistically analyzed. A quadratic polynomial function was used to fit the experimental data, and the fitting accuracy was compared. The experimental data conforms to the function, which is a function of the in-plane and out-of-plane shear strength (MPa) of the material with temperature, respectively.

[0073]

[0074]

[0075] The mechanical properties of flax fiber / epoxy resin composites under the service temperature range were predicted, and the results showed that the tensile test error was 7.86%.

Claims

1. A method for predicting the mechanical properties of fiber-reinforced composites: A microscopic Reduction-Effect (RVE) model of the matrix-fiber composite is determined. A fiber bundle unit cell model is established using a hexagonal distribution. In this model, the microscopic fiber bundle unit cell mesh is discretized using tetrahedral elements. The fibers and matrix are connected by common nodes to ensure displacement continuity. The maximum stress criterion is used to characterize the damage initiation of the fibers and matrix, and a damage degradation criterion based on fracture toughness is used to describe the damage evolution of the fibers and matrix. Simulation calculations are performed on the fiber bundle unit cell model. The mechanical property parameters of the matrix and fiber materials at various temperatures are substituted to obtain the fiber bundle mechanical property parameters at different temperatures. A function of the fiber bundle mechanical property parameters based on temperature change is constructed. A microscopic RVE model of the composite material is determined, and the fiber bundle is... The fiber bundle path is simplified to a combination of straight lines and sine curves, and the cross-section of the fiber bundle is simplified to an ellipse. A mesoscopic model of flax fiber / epoxy resin composite material is established, meshing is performed, and the properties of each component are defined. Periodic boundary conditions are added. The maximum principal stress criterion and stiffness degradation based on fracture energy are used to describe the damage initiation and evolution of the matrix. The three-dimensional Hashin failure criterion is used to determine the initial damage of the fiber bundle, and a progressive degradation method is used to characterize the damage evolution. The mesoscopic RVE model is simulated and calculated. A typical service temperature field is applied, and the mechanical property parameters of the fiber bundle and resin material are substituted to construct a function of the mechanical property parameters of the macroscopic composite material based on temperature change, thus obtaining a predictive model of the mechanical properties of fiber-reinforced composite materials.

2. The method for predicting the mechanical properties of fiber-reinforced composite materials according to claim 1, characterized in that, The functions relating the mechanical properties of the matrix material to temperature include functions of tensile modulus and shear modulus, tensile strength, compressive strength, and shear strength, and the coefficient of thermal expansion of epoxy resin.

3. The method for predicting the mechanical properties of fiber-reinforced composite materials according to claim 2, wherein the functions of the mechanical property parameters of the fiber material with temperature include functions of the longitudinal tensile and transverse / normal tensile moduli of the fiber material, functions of the in-plane shear moduli and out-of-plane shear moduli, functions of tensile strength and compressive strength, and functions of the longitudinal thermal expansion coefficient and the transverse thermal expansion coefficient.

4. The method for predicting the mechanical properties of fiber-reinforced composite materials according to any one of claims 1-3, characterized in that, A macroscopic finite element model is established, and failure criteria and degradation criteria are defined to describe the damage initiation and stiffness degradation of the macroscopic model. The mechanical property parameters of the composite material are substituted into a function based on temperature change, and finite element analysis is performed on the finite element model to obtain the prediction results.

5. The method for predicting the mechanical properties of fiber-reinforced composite materials according to claim 4, characterized in that, Macroscale finite element models for tensile and three-point bending were established, and the three-dimensional Hashin failure criterion and the progressive degradation criterion based on fracture energy were used to describe the damage initiation of macroscopic composite materials. Initial stiffness degradation.

6. The application of the method for predicting the mechanical properties of fiber-reinforced composite materials according to any one of claims 1-5, wherein the method for predicting the mechanical properties of fiber-reinforced composite materials is used to predict components with macroscopic dimensions.

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