A multi-scale analysis method and system for ultra-low temperature mechanical properties of composite materials

Abstract

The present invention relates to the field of material science and technology, and specifically to a multi-scale analysis method and system for ultra-low temperature mechanical properties of composite materials. The method of the present invention comprises the following steps: establishing a constitutive model according to the matrix of the composite material; introducing temperature parameters into the constitutive model to obtain a low-temperature constitutive model; using the low-temperature constitutive model as a new matrix of the composite material, and constructing a representative volume element model of the composite material based on the fiber of the composite material; solving the representative volume element model of the composite material to obtain ultra-low temperature multi-scale mechanical performance indicators of the composite material. The present invention introduces the ultra-low temperature influence effect to establish a temperature-dependent elastic-plastic constitutive model, accurately characterizes the mechanical properties and failure behavior of composite materials under low temperature environments, and solves the problems of poor prediction accuracy and poor applicability of ultra-low temperature mechanical performance analysis models for composite materials.

Description

Technical Field

[0001] The present invention relates to the field of material science and technology, and in particular to a multi-scale analysis method and system for ultra-low temperature mechanical properties of composite materials. Background Art

[0002] Fiber-reinforced resin-based composites have been widely used in the aerospace field. Some structures of spacecraft face prominent ultra-low temperature (below 112 K) application environments during service, such as liquid hydrogen (20 K) and liquid oxygen (90 K) cryogenic propellant tanks of launch vehicles, and cryogenic optical modules of infrared remote sensing satellites using liquid helium (4.2 K) as a cooling source. In ultra-low temperature environments, the stiffness and strength of fiber-reinforced composites will change significantly. A large number of experimental studies have observed a significant increase in the lateral modulus of unidirectional plates and a sharp decrease in failure strain. This low-temperature effect poses a challenge to the safety of its application in the low-temperature field, and it is urgent to develop a method to predict the ultra-low temperature mechanical properties of composite materials.

[0003] However, the low-temperature effect of composite materials involves a complex coupling mechanism of its components: on the one hand, the mechanical properties of the resin matrix have a strong temperature correlation, and the temperature effect must be considered for the prediction of macroscopic properties; on the other hand, the large difference in thermal expansion coefficients between the fiber and the matrix and the anisotropic characteristics of fiber thermal expansion lead to complex thermal stresses between the fiber-matrix layers, which aggravates the difficulty of predicting the low-temperature strength of composite materials.

[0004] Multiscale analysis methods provide an effective method for studying the interaction principles and failure mechanisms of composite components. Existing methods often use representative volume elements to study the macroscopic effects of the mesoscopic mechanical behavior of composite materials, and have subsequently been applied to the evaluation of low-temperature thermal stress and thermal cycle effects of composite materials. However, since the evolution law of the low-temperature performance of the resin matrix is ​​not clear, it is still quite difficult to carry out multi-scale computational research on the low-temperature mechanical properties of materials. At the same time, existing methods focus more on the performance of resin materials at liquid nitrogen and liquid helium temperatures. In actual service environments, the temperature of composite structures is often affected by cold sources and is distributed in a gradient. In addition, the low-temperature evolution law of the mechanical properties of the resin matrix is ​​complex. It is difficult to reasonably evaluate the low-temperature strength of the structure only by the material properties at liquid nitrogen and liquid helium temperature points. In existing studies, the strength of resin materials has been widely studied, and the ductile-brittle transformation process under low-temperature environments has been mostly ignored. There is a lack of constitutive models that characterize the evolution process of the low-temperature mechanical properties of resins. At the same time, the internal action mechanism of the low-temperature lateral and shear mechanical response of composite materials is complex, and the evolution law and action mechanism of the mechanical properties are unclear, which seriously threatens the low-temperature bearing safety of the structure. Therefore, it is urgent to establish a temperature-dependent constitutive model of the resin to describe its failure behavior and the transformation process of elastic-plastic characteristics, develop a multi-scale prediction method for the macroscopic mechanical properties of composite materials in the entire temperature range, and solve the problems of poor prediction accuracy and applicability of ultra-low temperature mechanical properties analysis models of composite materials. Summary of the invention

[0005] In view of the shortcomings of existing methods and the needs of practical applications, in order to establish a temperature-dependent constitutive model of the resin to describe its failure behavior and the transformation process of elastic-plastic characteristics, a multi-scale prediction method for the macroscopic mechanical properties of composite materials in the full temperature range is developed. On the one hand, the present invention provides a multi-scale analysis method for ultra-low temperature mechanical properties of composite materials, comprising the following steps:

[0006] According to the matrix of the composite material, a constitutive model is established; a temperature parameter is introduced into the constitutive model to obtain a low-temperature constitutive model; the low-temperature constitutive model is used as a new matrix of the composite material, and a representative volume element model of the composite material is constructed based on the fiber of the composite material; the representative volume element model of the composite material is solved to obtain the ultra-low temperature multi-scale mechanical performance index of the composite material. The present invention establishes a temperature-related elastic-plastic constitutive model by introducing the ultra-low temperature influence effect, accurately characterizes the mechanical properties and failure behavior of the composite material under a low temperature environment, and solves the problem of poor prediction accuracy and poor applicability of the ultra-low temperature mechanical performance analysis model of the composite material.

[0007] Optionally, the step of introducing a temperature parameter into the constitutive model to obtain a low-temperature constitutive model comprises the following steps:

[0008] The temperature parameter is introduced into the Young's modulus to obtain the Young's modulus evolving with temperature; the temperature parameter is introduced into the yield function to obtain the yield function evolving with temperature; the temperature parameter is introduced into the tensile strength and the compressive strength to obtain the low-temperature tensile strength and the low-temperature compressive strength; the low-temperature constitutive model is obtained by combining the Young's modulus evolving with temperature, the yield function evolving with temperature, the low-temperature tensile strength and the low-temperature compressive strength. The present invention introduces the temperature parameter into the Young's modulus, the yield function, the tensile strength and the compressive strength of the traditional multi-scale constitutive model, and then constructs a low-temperature constitutive model, which is conducive to accurately characterizing the mechanical properties and failure behavior of composite materials under low-temperature environments.

[0009] Optionally, the temperature parameter is introduced into the Young's modulus to obtain the Young's modulus evolving with temperature, satisfying the following formula:

[0010] ,in, Indicates temperature Young's modulus of the lower matrix, Indicates reference temperature Young's modulus of the lower matrix, , The invention fits the Young's modulus evolving with temperature by means of test data, which is helpful to accurately describe the evolution trend of the Young's modulus of the resin material with temperature.

[0011] Optionally, the temperature parameter is introduced into the yield function to obtain a yield function evolving with temperature, which satisfies the following formula:

[0012] ,in, represents the temperature-dependent yield function of the matrix, represents the second invariant of the stress deviator tensor, represents the first invariant of the stress tensor, Indicates that the substrate is at temperature The compressive yield strength under Indicates that the substrate is at temperature The present invention uses the modified parabolic yield criterion to judge the onset and development of the plastic behavior of the resin, which is further conducive to accurately characterizing the mechanical properties and failure behavior of the composite material under low temperature environment.

[0013] Optionally, the substrate is at a temperature The tensile yield strength under the condition satisfies the following formula:

[0014] , the substrate is at temperature The compressive yield strength under the condition of , satisfies the following formula: ,

[0015] in, Indicates that the substrate is at temperature The tensile yield strength under Indicates reference temperature The tensile yield stress of the lower matrix, Indicates reference temperature The tensile hardening modulus of the lower matrix, represents the temperature and hardening modulus fitting parameters based on experimental data, , represents the fitting parameters of temperature and tensile yield strength based on experimental data, and represents the fitting parameters of temperature and compressive yield strength based on experimental data, represents the equivalent plastic strain, Indicates that the substrate is at temperature The compressive yield strength under Indicates reference temperature The compressive yield stress of the lower matrix, Indicates reference temperature The present invention introduces temperature parameters into the tensile strength and compressive strength, which is conducive to characterizing the yield and hardening behavior of the resin under tensile and compressive states at different temperatures.

[0016] Optionally, the equivalent plastic strain satisfies the following formula:

[0017] ,in, represents the equivalent plastic strain increment, represents the plastic strain increment, represents the dot multiplication operation, Represents the plastic Poisson's ratio of the matrix. The present invention uses the plastic Poisson's ratio to construct a correlation model between the equivalent plastic strain increment and the plastic strain increment, and further characterizes the equivalent plastic strain behavior of the matrix material.

[0018] Optionally, a temperature parameter is introduced into the tensile strength to obtain the low-temperature tensile strength, which satisfies the following formula:

[0019] ,in, represents the low temperature tensile strength of the matrix, Indicates the reference degree, Indicates the current temperature. represents the fitting parameters for tensile strength and temperature based on experimental data, Indicates the base material at the reference temperature Tensile strength under

[0020] Introducing the temperature parameter into the compression strength, the low-temperature compression strength is obtained, which satisfies the following formula:

[0021] ,in, represents the low temperature compressive strength of the matrix, Indicates the base material at the reference temperature The compressive strength under , It represents the fitting parameters of compressive strength and temperature based on experimental data. The low-temperature expansion strength and low-temperature compression strength constructed by the present invention are further conducive to accurately characterizing the low-temperature characteristics of material strength, modulus and other parameters.

[0022] Optionally, the low-temperature constitutive model is used as a new matrix of the composite material, and a representative volume element model of the composite material is constructed based on the fibers of the composite material, comprising the following steps:

[0023] A small number of initial fibers are randomly generated in the fiber distribution space; the distribution distance is determined based on the first nearest neighbor distance, the second fiber is determined using the first random angle, and the third fiber is generated based on the second nearest neighbor distance and the second random angle; the second or first adjacent fibers are iteratively generated using the second or third fiber as the new initial fiber until the distribution area is filled or the target volume fraction is reached; the representative volume element model of the composite material is obtained by combining the fiber generation result and the new matrix. The present invention adopts the nearest neighbor algorithm to realize the modeling process, and introduces the neighboring distribution characteristics of the fiber in the modeling process using the nearest neighbor algorithm, which is conducive to quickly revealing the evolution law and internal action mechanism of the mechanical properties of the composite material under ultra-low temperature environment.

[0024] Optionally, solving the representative volume element model of the composite material to obtain the ultra-low temperature multi-scale mechanical performance index of the composite material comprises the following steps:

[0025] A cooling analysis step and a loading analysis step are set; in the cooling analysis step, the initial temperature and the target low temperature of the composite material are set; in the loading analysis step, the load and the boundary conditions are applied; the representative volume element model of the composite material is solved in combination with the initial temperature, the target low temperature, the load and the boundary conditions to obtain the ultra-low temperature multi-scale mechanical performance index of the composite material. The present invention achieves an accurate prediction of the macroscopic mechanical response and failure behavior of the composite material in the low temperature range by solving the representative volume element model of the composite material.

[0026] In the second aspect, in order to efficiently perform the multi-scale analysis method of ultra-low temperature mechanical properties of composite materials provided by the present invention, the present invention also provides a multi-scale analysis system of ultra-low temperature mechanical properties of composite materials, including a processor, an input device, an output device and a memory, wherein the processor, the input device, the output device and the memory are interconnected, wherein the memory is used to store a computer program, the computer program includes program instructions, and the processor is configured to call the program instructions to execute the multi-scale analysis method of ultra-low temperature mechanical properties of composite materials as described in the first aspect of the present invention. The multi-scale analysis system of ultra-low temperature mechanical properties of composite materials of the present invention has a compact structure and stable performance, and can stably execute the multi-scale analysis method of ultra-low temperature mechanical properties of composite materials provided by the present invention, further improving the overall applicability and practical application ability of the present invention. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Figure 1 A flow chart of a multi-scale analysis method for ultra-low temperature mechanical properties of a composite material provided by an embodiment of the present invention;

[0028] Figure 2A comparison chart of numerical calculation results and experimental results of stress-strain response of a certain type of epoxy resin provided in an embodiment of the present invention;

[0029] Figure 3 A flow chart of constructing a composite material representative volume element model provided by an embodiment of the present invention;

[0030] Figure 4 A representative volume element model diagram of a composite material provided by an embodiment of the present invention;

[0031] Figure 5 A schematic diagram of a load application method provided in an embodiment of the present invention;

[0032] Figure 6 A failure morphology diagram of a certain type of composite material calculation model provided in an embodiment of the present invention;

[0033] Figure 7 A comparison chart of the calculation results and test results of the low-temperature longitudinal tensile mechanical response provided by an embodiment of the present invention;

[0034] Figure 8 A framework diagram of a multi-scale analysis system for ultra-low temperature mechanical properties of composite materials provided by an embodiment of the present invention;

[0035] Fig. 9 A schematic diagram of the structure of a multi-scale analysis device for ultra-low temperature mechanical properties of composite materials provided in an embodiment of the present invention. DETAILED DESCRIPTION

[0036] The specific embodiments of the present invention will be described in detail below. It should be noted that the embodiments described herein are only for illustration and are not intended to limit the present invention. In the following description, a large number of specific details are set forth in order to provide a thorough understanding of the present invention. However, it is obvious to those of ordinary skill in the art that these specific details do not need to be adopted to implement the present invention. In other examples, in order to avoid confusing the present invention, known circuits, software or methods are not specifically described.

[0037] Throughout the specification, references to "one embodiment," "an embodiment," "an example," or "an example" mean that a particular feature, structure, or characteristic described in conjunction with the embodiment or example is included in at least one embodiment of the present invention. Therefore, the phrases "in one embodiment," "in an embodiment," "an example," or "an example" appearing in various places throughout the specification do not necessarily all refer to the same embodiment or example. In addition, particular features, structures, or characteristics may be combined in one or more embodiments or examples in any suitable combination and / or subcombination. In addition, it should be understood by those of ordinary skill in the art that the figures provided herein are for illustrative purposes and that the figures are not necessarily drawn to scale.

[0038] See also Figure 1 In order to establish a temperature-dependent constitutive model of resin to describe its failure behavior and the transformation process of elastic-plastic characteristics, a multi-scale prediction method for the macroscopic mechanical properties of composite materials in the whole temperature range is developed to solve the problems of poor prediction accuracy and poor applicability of the ultra-low temperature mechanical properties analysis model of composite materials. The present invention provides a multi-scale analysis method for ultra-low temperature mechanical properties of composite materials, such as Figure 1 As shown, the method comprises the following steps:

[0039] S1. Establish a constitutive model based on the matrix of the composite material.

[0040] Specifically, when establishing the constitutive model of resin composites, it is first necessary to understand the mechanical properties of its matrix material and the interaction between the fiber and the matrix in the composite material. Resin composites are usually composed of resin matrix and reinforcing fibers (such as carbon fiber, glass fiber, etc.), and their mechanical properties are affected by many factors such as matrix material, fiber type, fiber arrangement direction and fiber volume fraction.

[0041] The resin matrix is ​​usually regarded as an elastic-plastic material, and its constitutive relationship can be described by an elastic-plastic model. The total strain of the commonly used elastic-plastic resin matrix is can be decomposed into elastic strain and plastic strain ,satisfy: .

[0042] Further, for elastic strain, the stress-strain relationship of the resin in the elastic stage can be defined as:

[0043] ,in represents the stress tensor, For resin materials at temperature The flexibility matrix under satisfies:

[0044] , in the matrix and Temperature Young's modulus and shear modulus of the resin below, Represents the Poisson's ratio of the resin matrix.

[0045] S2. Introducing a temperature parameter into the constitutive model to obtain a low-temperature constitutive model.

[0046] In the embodiment, the step S2 introduces a temperature parameter into the constitutive model to obtain a low-temperature constitutive model, comprising the following steps:

[0047] S21. Introduce the temperature parameter into Young's modulus to obtain the Young's modulus evolving with temperature.

[0048] Based on the test data, a logarithmic function can be used to describe the evolution trend of the Young's modulus of the resin material with temperature, satisfying the following formula:

[0049] ,

[0050] in, Indicates temperature Young's modulus of the lower matrix, Indicates reference temperature Young's modulus of the lower matrix, , represents the fitting parameters of Young’s modulus evolving with temperature.

[0051] S22. Introduce a temperature parameter into the yield function to obtain a yield function that evolves with temperature.

[0052] In the embodiment, the temperature parameter is introduced into the yield function to obtain a yield function evolving with temperature, which satisfies the following formula:

[0053] ,

[0054] in, represents the temperature-dependent yield function of the matrix, represents the second invariant of the stress deviator tensor, represents the first invariant of the stress tensor, Indicates that the substrate is at temperature The compressive yield strength under Indicates that the substrate is at temperature The tensile yield strength under .

[0055] The first invariant of the stress tensor satisfies: , the second invariant of the stress deviator satisfies: , , , They represent the maximum principal stress, the intermediate principal stress, and the minimum principal stress respectively;

[0056] Furthermore, in order to maintain the volumetric plastic strain under hydrostatic pressure, a non-associative flow rule can be introduced to define the plastic potential for: ,

[0057] in is the Von Mises stress, satisfying: , represents the hydrostatic pressure, satisfying: , The parameter that represents the volume flow deformation of the material can be expressed by the plastic Poisson's ratio of the material. calculate:

[0058] ,

[0059] Furthermore, according to the definition of plastic potential energy, the material flow rule is derived as follows:

[0060] ,

[0061] in, and denote the increments of plastic strain and plastic multiplier respectively, represents the stress deviator, is the unit tensor.

[0062] Furthermore, the plastic strain increment can be decomposed, namely: , represents the plastic strain increment deviator, Represents the volume component of the plastic strain increment.

[0063] Furthermore, the substrate is at a temperature The tensile yield strength under the condition satisfies the following formula:

[0064] ,

[0065] The substrate is at temperature The compressive yield strength under the condition of , satisfies the following formula:

[0066] ,

[0067] in, Indicates that the substrate is at temperature The tensile yield strength under Indicates reference temperature The tensile yield stress of the lower matrix, Indicates reference temperature The tensile hardening modulus of the lower matrix, represents the temperature and hardening modulus fitting parameters based on experimental data, , represents the fitting parameters of temperature and tensile yield strength based on experimental data, and represents the fitting parameters of temperature and compressive yield strength based on experimental data, represents the equivalent plastic strain, Indicates that the substrate is at temperature The compressive yield strength under Indicates reference temperature The compressive yield stress of the lower matrix, Indicates reference temperature The compressive hardening modulus of the lower matrix.

[0068] Understandably, , , , , They are all parameters that reflect the temperature dependence of the hardening function, and the corresponding values ​​can be obtained by fitting the experimental results data.

[0069] Furthermore, the equivalent plastic strain satisfies the following formula:

[0070] ,in, represents the equivalent plastic strain increment, represents the plastic strain increment, represents the dot multiplication operation, represents the plastic Poisson's ratio of the matrix.

[0071] S23. Introducing temperature parameters into the tensile strength and the compressive strength to obtain low-temperature tensile strength and low-temperature compressive strength.

[0072] Specifically, the tensile strength of the resin at different temperatures usually changes approximately like a power function, while the evolution trend of the compressive strength is similar to the compressive yield strength, which increases linearly with temperature. Therefore, the temperature parameter is introduced into the tensile strength to obtain the low-temperature tensile strength, which satisfies the following formula:

[0073] ,

[0074] in, represents the low temperature tensile strength of the matrix, Indicates the reference degree, Indicates the current temperature. represents the fitting parameters for tensile strength and temperature based on experimental data, Indicates the base material at the reference temperature The tensile strength under low temperature is obtained by introducing the temperature parameter into the compressive strength, and the low temperature compressive strength satisfies the following formula:

[0075] ,

[0076] in, represents the low temperature compressive strength of the matrix, Indicates the base material at the reference temperature The compressive strength under , represents the fitting parameters for compressive strength and temperature based on experimental data.

[0077] S24. Combining the temperature-evolving Young's modulus, the temperature-evolving yield function, the low-temperature tensile strength and the low-temperature compressive strength, obtain the low-temperature constitutive model.

[0078] The low-temperature constitutive model can be obtained by replacing the Young's modulus, yield function, tensile strength and compressive strength in the constitutive model with the temperature-evolving Young's modulus, the temperature-evolving yield function, the low-temperature tensile strength and the low-temperature compressive strength.

[0079] Furthermore, the material subroutine of the finite element software is used to realize the low-temperature elastic-plastic damage constitutive model of the resin, that is, the low-temperature constitutive model, considering the finite element unit at time During the calculation process, the stress state of the material in the yield stage is often measured by the test stress Calculated with plastic correction term, where the test stress can be Stress state at the moment and the material stiffness matrix The calculation results are:

[0080] ,

[0081] and Stress state at the moment satisfy:

[0082] , that is: , thus, through The stress state of the material at the moment , With plastic multiplier increment The material current Plastic stress at time.

[0083] Furthermore, considering that the material stress tensor can be decomposed into its stress deviator and hydrostatic pressure , stress state It is also decomposed into its partial and the hydrostatic pressure component , and satisfy: ,

[0084] , understandably, got and The iterative form only needs to calculate the plastic multiplier increment The current stress can be iteratively calculated through the stress state of the previous analysis step.

[0085] To satisfy the loading criterion of the yield surface, the yield function is kept in the plastic deformation process. Always 0, coupling can be obtained:

[0086] ,

[0087] In the formula and The equivalent plastic strain Calculate the equivalent plastic strain increment With plastic multiplier increment The calculation relationship satisfies:

[0088] ,

[0089] So far, we can solve The solution process can be completed with the help of Newton–Raphson iterative algorithm. After that, the current stress state and equivalent plastic strain can be updated to complete the plastic calculation process of the current analysis step.

[0090] Furthermore, in terms of material failure behavior, in order to characterize the damage behavior and failure state of the resin, the damage activation function of the material satisfies: ,

[0091] in, Indicates the loading status function, is the internal damage variable of the material, used to record the damage process, satisfying:

[0092] , the loading state function in the formula still has the characteristics of tension and compression anisotropy, where and They are based on the material effective stress tensor The obtained second invariant and the first invariant of the stress tensor, the effective stress tensor before material failure is the current stress tensor.

[0093] When the stress state meets the damage activation condition, it is considered that material damage occurs and the corresponding damage factor will also change accordingly, and its evolution criteria satisfy:

[0094] ,

[0095] in, It is the damage softening factor that determines the reduced stiffness of the material. In order to ensure the same energy release rate during failure of units of different sizes and avoid the influence of mesh dependence on the analysis results, the softening factor is calculated by the unit characteristic length and fracture toughness Jointly decide to meet:

[0096] ,

[0097] in It is the tensile or compressive strength of the resin, which is determined by the damage state of the material.

[0098] When the damage factor is When the flexibility matrix of the resin writing: ;

[0099] See also Figure 2 The numerical calculation and experimental characterization results of the stress-strain curves of a certain type of resin under tension and compression at different temperatures are shown in Figure 2 As shown, the low-temperature tensile response process in the calculation results is highly consistent with the experimental results. By comparing with the experimental results, it is verified that the low-temperature constitutive model proposed in the present invention can accurately describe the evolution process of the mechanical behavior of the resin matrix performance at low temperatures.

[0100] S3. Using the low-temperature constitutive model as a new matrix of the composite material, and constructing a representative volume element model of the composite material based on the fibers of the composite material.

[0101] See also Figure 3 In an embodiment, the step S3 uses the low temperature constitutive model as a new matrix of the composite material, and constructs a composite material representative volume element model based on the fibers of the composite material, including the following steps:

[0102] A small number of initial fibers are randomly generated in the fiber distribution space; the distribution distance is determined based on the first nearest neighbor distance, and the first random angle is used Determine the second fiber based on the second nearest neighbor distance and the second random angle Generate a third fiber; iteratively generate the second adjacent fiber or the first adjacent fiber with the second fiber or the third fiber as the new initial fiber until the distribution area is filled or the target volume fraction is reached; combine the fiber generation result and the new matrix to obtain the representative volume element model of the composite material.

[0103] It should be understood that the neighbor distance can be obtained by the nearest neighbor algorithm. For any fiber that passes through the boundary, a corresponding symmetrical fiber is placed at the corresponding boundary to maintain the geometric periodicity of the model. During the iteration process, it should be ensured that no fibers overlap with each other and that the fibers are located within the selected sample area. If overlap occurs or the fibers are located outside the sample area, the fiber spacing and direction angles are redistributed until a suitable distribution position is found.

[0104] See also Figure 4In one embodiment, a fiber geometry model with randomly distributed fibers and periodic characteristics can be established in ABAQUS / Standard commercial finite element software, and a three-dimensional representative volume element model with a size of 55 μm×55 μm×5 μm, namely, a composite material representative volume element RVE model, is generated, wherein the diameter of the carbon fiber is set to 7 μm. The RVE model of this size is sufficient to show the microstructural deformation characteristics of the composite material. The model uses an eight-node hexahedral full integration unit (C3D8) to mesh the RVE model. After mesh convergence analysis, the model finally contains approximately 163,000 units, and the unit mesh size is approximately 0.6 μm. The periodicity of the boundary grid nodes is maintained during the meshing process, and periodic boundary conditions are imposed on the RVE model through the multi-point constraint method to avoid the influence of stress distribution at the model boundary on the calculation results. A general contact algorithm is introduced into the calculation model, and the friction coefficient inside the model is set to 0.15 to consider the friction effect of mutual squeezing between the matrix and the fiber after interface damage. The mechanical properties of carbon fiber in the RVE model can be considered to be difficult to change at low temperatures. At the same time, due to the significant difference in thermal expansion coefficients between the matrix and the fiber, the thermal expansion coefficients of the fiber and the matrix must also be set.

[0105] S4. Solve the representative volume element model of the composite material to obtain the ultra-low temperature multi-scale mechanical performance index of the composite material.

[0106] In an embodiment, solving the representative volume element model of the composite material to obtain the ultra-low temperature multi-scale mechanical performance index of the composite material comprises the following steps:

[0107] A cooling analysis step and a loading analysis step are set; in the cooling analysis step, the initial temperature and the target low-temperature temperature of the composite material are set; in the loading analysis step, the load and the boundary conditions are applied; and the representative volume element model of the composite material is solved in combination with the initial temperature, the target low-temperature temperature, the load and the boundary conditions to obtain the ultra-low-temperature multi-scale mechanical performance indicators of the composite material.

[0108] In the embodiment, in the Abaqus finite element analysis software, a cooling analysis step and a loading analysis step are set for the established composite material representative volume element model; in the cooling analysis step, the initial temperature and the target low temperature of the material are set; in the loading analysis step, corresponding loads and boundary conditions are applied respectively for the mechanical properties to be calculated, and various load application methods are as follows: Figure 5 The calculation results of the transverse tensile failure process of a certain type of composite material at 293K, 193K and 93K are shown in Figure 6 As shown in the results, a typical transverse tensile cracking failure morphology of the composite material was obtained. At the same time, the matrix cracking was more severe in the failure morphology of 193K and 93K results, which reflects the introduced temperature effect. Figure 7The comparison between the stress-strain response obtained by the representative volume element model of the composite material at different temperatures and the actual test results is demonstrated. The calculation results of the present invention are highly consistent with the actual test results. The proposed method introduces the low-temperature performance evolution of the resin matrix and the thermal stress effect between the fiber and the matrix, which can characterize the mechanical response of the one-way plate under various stress states in an ultra-low temperature environment, and thus can calculate the low-temperature mechanical properties and failure behavior of the composite material at any temperature.

[0109] See also Figure 8 In an embodiment, in order to efficiently execute a multi-scale analysis method for ultra-low temperature mechanical properties of a composite material provided by the present invention, the present invention also provides a multi-scale analysis system for ultra-low temperature mechanical properties of a composite material, including: an input device, an output device, a processor, and a memory, wherein the input device, the output device, the processor, and the memory are interconnected, and the memory contains program instructions, and the program instructions are used for the steps of the multi-scale analysis method for ultra-low temperature mechanical properties of a composite material. The multi-scale analysis system for ultra-low temperature mechanical properties of a composite material of the present invention has a compact structure and stable performance, and can stably execute a multi-scale analysis method for ultra-low temperature mechanical properties of a composite material of the present invention, further improving the overall applicability and practical application capabilities of the present invention.

[0110] In an embodiment, the processor may be a central processing unit (CPU), and the processor may also be other general-purpose processors, digital signal processors (DSP), application-specific integrated circuits (ASIC), field-programmable gate arrays (FPGA) or other programmable logic devices, discrete gates or transistor logic devices, discrete hardware components, etc. A general-purpose processor may be a microprocessor or the processor may also be any conventional processor, etc. An input device may be used to obtain data information. An output device may be used to output the results obtained by storing program instructions contained in a computer program in a memory provided by the present invention. The memory may include a read-only memory and a random access memory, and provide instructions and data to the processor. A portion of the memory may also include a non-volatile random access memory.

[0111] In yet another alternative embodiment, see Fig. 9 In order to efficiently perform the multi-scale analysis method for ultra-low temperature mechanical properties of composite materials provided by the present invention, this embodiment also provides a multi-scale analysis device for ultra-low temperature mechanical properties of composite materials, such as Fig. 9 As shown, including:

[0112] The memory 10 is used to store computer programs; the processor 20 is used to execute the computer programs to implement the above-mentioned multi-scale analysis method of ultra-low temperature mechanical properties of composite materials. The memory 10, the processor 20, the communication interface 31 and the communication bus 32. The memory 10, the processor 20, and the communication interface 31 all communicate with each other through the communication bus 32.

[0113] In an embodiment, the memory 10 is used to store one or more program instructions. The memory 10 may store program instructions for implementing the following functions:

[0114] According to the matrix of the composite material, a constitutive model is established; a temperature parameter is introduced into the constitutive model to obtain a low-temperature constitutive model; the low-temperature constitutive model is used as a new matrix of the composite material, and a representative volume element model of the composite material is constructed based on the fibers of the composite material; the representative volume element model of the composite material is solved to obtain ultra-low temperature multi-scale mechanical performance indicators of the composite material.

[0115] In one possible implementation, the memory 10 may include a program storage area and a data storage area, wherein the program storage area may store an operating system, and at least one application required for a function, etc.; the data storage area may store data created during use. In addition, the memory 10 may include a read-only memory and a random access memory, and provide instructions and data to the processor. A portion of the memory may also include NVRAM. The memory stores an operating system and operating instructions, executable modules or data structures, or a subset thereof, or an extended set thereof, wherein the operating instructions may include various operating instructions for implementing various operations. The operating system may include various system programs for implementing various basic tasks and processing hardware-based tasks.

[0116] The processor 20 may be a central processing unit (CPU), an application specific integrated circuit, a digital signal processor, a field programmable gate array or other programmable logic device, and the processor 20 may be a microprocessor or any conventional processor, etc. The processor 20 may call a program stored in the memory 10. The communication interface 31 may be an interface of a communication module, and is used to connect with other devices or systems.

[0117] Of course, it should be noted that Fig. 9 The structure shown does not constitute a limitation on the multi-scale analysis device for ultra-low temperature mechanical properties of composite materials in this embodiment. In actual applications, the multi-scale analysis device for ultra-low temperature mechanical properties of composite materials may include Fig. 9 More or fewer components than shown, or combinations of certain components.

[0118] The embodiment also provides a storage medium having a computer program stored thereon, and when the computer program is executed by a processor, the steps of the multi-scale analysis method for ultra-low temperature mechanical properties of composite materials are implemented.

[0119] The storage medium may include: a USB flash drive, a mobile hard disk, a read-only memory (ROM), a random access memory (RAM), a magnetic disk or an optical disk, and other media that can store program codes.

[0120] In summary, the present invention develops a multi-scale analysis method for ultra-low temperature mechanical properties of composite materials, innovatively establishes a temperature-dependent elastic-plastic constitutive model of resins, characterizes the modulus, strength evolution, tension-compression anisotropy, tough-brittle conversion and other characteristics of resins under ultra-low temperature environments, realizes numerical calculations in the material custom subroutine of finite element software, and establishes a representative volume element model of composite one-way plates on this basis, reveals the evolution law and internal action mechanism of mechanical properties of composite materials under ultra-low temperature environments, realizes the accurate prediction of macroscopic mechanical response and failure behavior of composite materials in low temperature temperature zones, provides an effective technical method for analyzing the low-temperature bearing characteristics of composite structures, greatly improves the accuracy and efficiency of low-temperature structural performance analysis and safety evaluation of composite materials, and solves the problems of poor prediction accuracy and poor applicability of ultra-low temperature mechanical properties analysis models of composite materials. Therefore, the present invention effectively overcomes various shortcomings in the prior art and has a high industrial utilization value.

[0121] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or replace some or all of the technical features therein by equivalents. These modifications or replacements do not deviate the essence of the corresponding technical solutions from the scope of the technical solutions of the embodiments of the present invention, and they should all be included in the scope recorded in the present invention.

Claims

1. A multi-scale analysis method for ultra-low temperature mechanical properties of composite materials, characterized in that: The following steps are involved: According to the matrix of the composite material, a constitutive model is established; Introducing a temperature parameter into the constitutive model to obtain a low-temperature constitutive model; Using the low-temperature constitutive model as a new matrix of the composite material, and constructing a representative volume element model of the composite material based on the fibers of the composite material; Solving the representative volume element model of the composite material to obtain ultra-low temperature multi-scale mechanical performance indicators of the composite material; The step of introducing a temperature parameter into the constitutive model to obtain a low-temperature constitutive model comprises the following steps: The temperature parameter is introduced into Young's modulus to obtain the Young's modulus evolving with temperature; Introducing temperature parameters into the yield function, the yield function evolving with temperature is obtained; Introducing temperature parameters into tensile strength and compressive strength to obtain low-temperature tensile strength and low-temperature compressive strength; Combining the temperature-evolving Young's modulus, the temperature-evolving yield function, the low-temperature tensile strength, and the low-temperature compressive strength, to obtain the low-temperature constitutive model; The step of combining the temperature-evolving Young's modulus, the temperature-evolving yield function, the low-temperature tensile strength, and the low-temperature compressive strength to obtain the low-temperature constitutive model comprises: Using the temperature-evolving Young's modulus, the temperature-evolving yield function, the low-temperature tensile strength, and the low-temperature compressive strength to replace the Young's modulus, the yield function, the tensile strength, and the compressive strength in the constitutive model; The material subroutine of the finite element software is used to realize the low-temperature elastic-plastic damage constitutive model of the resin, that is, the low-temperature constitutive model. Considering the finite element unit at time [t n ,t n+1 ], the stress state of the material in the yield stage is often measured by the test stress Calculated with plastic correction term, where the test stress Can be obtained by n The stress state at time σ m,n and the material stiffness matrix The calculation results are: Among them, : represents the dot multiplication operation; And t n+1 The stress state at time σ m,n+1 satisfy: That is: Therefore, through t n+1 The stress state of the material at the moment S n+1 、(I1) n+1 The current material t can be calculated by adding the plastic multiplier increment Δγ n Plastic stress at time Stress state σ m,n+1 Decomposed into its deviator S n+1 and the hydrostatic pressure component p n+1 , and satisfy: Got S n+1 and p n+1 The iterative form of the solution calculates the plastic multiplier increments and iteratively calculates the current stress via the stress state of the previous analysis step.

2. The multi-scale analysis method for ultra-low temperature mechanical properties of composite materials according to claim 1, characterized in that: The temperature parameter is introduced into the Young's modulus to obtain the Young's modulus evolving with temperature, which satisfies the following formula: in, represents the Young's modulus of the matrix at temperature T, represents the Young's modulus of the matrix at reference temperature T0, a m,0 , b m,0 represents the fitting parameters of Young’s modulus evolving with temperature.

3. The multi-scale analysis method for ultra-low temperature mechanical properties of composite materials according to claim 1, characterized in that: The temperature parameter is introduced into the yield function to obtain the yield function evolving with temperature, which satisfies the following formula: in, represents the temperature-evolving yield function of the matrix, J2 represents the second invariant of the stress deviator, I1 represents the first invariant of the stress tensor, represents the compressive yield strength of the matrix at temperature T, It represents the tensile yield strength of the matrix at temperature T.

4. The multi-scale analysis method for ultra-low temperature mechanical properties of composite materials according to claim 1, characterized in that: The tensile yield strength of the substrate at temperature T satisfies the following formula: The compressive yield strength of the matrix at temperature T satisfies the following formula: in, represents the tensile yield strength of the matrix at temperature T, represents the tensile yield stress of the matrix at the reference temperature T0, represents the tensile hardening modulus of the matrix at reference temperature T0, n T represents the temperature and hardening modulus fitting parameters based on experimental data, a m,t , b m,t represents the fitting parameters of temperature and tensile yield strength based on experimental data, a m,c and b m,c represents the fitting parameters of temperature and compressive yield strength based on experimental data, represents the equivalent plastic strain, represents the compressive yield strength of the matrix at temperature T, represents the compressive yield stress of the matrix at the reference temperature T0, represents the compression hardening modulus of the matrix at the reference temperature T0.

5. The multi-scale analysis method for ultra-low temperature mechanical properties of composite materials according to claim 4, characterized in that: The equivalent plastic strain satisfies the following formula: in, represents the equivalent plastic strain increment, represents the plastic strain increment, : represents the dot product operation, v p represents the plastic Poisson's ratio of the matrix.

6. The multi-scale analysis method for ultra-low temperature mechanical properties of composite materials according to claim 1, characterized in that: Introducing the temperature parameter into the tensile strength, the low-temperature tensile strength is obtained, which satisfies the following formula: in, represents the low temperature tensile strength of the matrix, T0 represents the reference temperature, T represents the current temperature, a m,X , b m,X represents the fitting parameters for tensile strength and temperature based on experimental data, Indicates the tensile strength of the matrix material at the reference temperature T0; Introducing the temperature parameter into the compressive strength, the low-temperature compressive strength is obtained, which satisfies the following formula: in, represents the low temperature compressive strength of the matrix, Indicates the compressive strength of the base material at the reference temperature T0, a m,c , b m,c represents the fitting parameters for compressive strength and temperature based on experimental data.

7. The multi-scale analysis method for ultra-low temperature mechanical properties of composite materials according to claim 1, characterized in that: The method of solving the representative volume element model of the composite material to obtain the ultra-low temperature multi-scale mechanical performance index of the composite material comprises the following steps: Set cooling analysis step and loading analysis step; In the temperature reduction analysis step, the initial temperature and the target low temperature of the composite material are set; In the loading analysis step, loads and boundary conditions are applied; The representative volume element model of the composite material is solved in combination with the initial temperature, the target low-temperature temperature, the load and the boundary conditions to obtain the ultra-low-temperature multi-scale mechanical performance index of the composite material.

8. The multi-scale analysis method for ultra-low temperature mechanical properties of composite materials according to claim 1, characterized in that: The method of using the low temperature constitutive model as a new matrix of the composite material and constructing a composite material representative volume element model based on the fibers of the composite material comprises the following steps: A small number of initial fibers are randomly generated in the fiber distribution space; determining a distribution distance based on a first nearest neighbor distance, determining a second fiber using a first random angle, and generating a third fiber based on a second nearest neighbor distance and a second random angle; Iteratively generating the second adjacent fiber or the first adjacent fiber by taking the second fiber or the third fiber as a new initial fiber until the distribution area is filled or the target volume fraction is reached; The fiber generation results and the new matrix are combined to obtain a representative volume element model of the composite material.

9. A multi-scale analysis system for ultra-low temperature mechanical properties of composite materials, characterized in that: The multi-scale analysis system for ultra-low temperature mechanical properties of composite materials comprises: an input device, an output device, a processor, and a memory, wherein the input device, the output device, the processor, and the memory are interconnected, and the memory comprises program instructions, and the program instructions are used to execute the multi-scale analysis method for ultra-low temperature mechanical properties of composite materials according to any one of claims 1 to 8.

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