Moisture-heat cycle damage constitutive model of resin-based composite material and failure judgment method

Abstract

The invention discloses a resin-based composite material damp-heat cycle damage constitutive model and a failure judgment method. The method comprises the following steps: firstly, acquiring mechanical property change data of a resin material under different damp-heat cycle conditions through a test, and establishing a degradation model of mechanical property parameters changing along with damp-heat cycle; then, a mixing rate method is adopted to be combined with the volume fraction of the fiber and the matrix to deduce equivalent performance parameters of the single-layer plate, the equivalent performance parameters comprise a damp-heat expansion coefficient, a rigidity performance parameter and a strength performance parameter, and a constitutive equation considering the damp-heat deformation effect is constructed on the basis of a laminated plate theory; and finally, judging possible fiber, matrix and shear failure modes of the laminated plate by utilizing an improved three-dimensional Hashin failure criterion. The method can effectively predict the multi-mode damage behavior of the composite material in the humid and hot environment, and is suitable for strength evaluation and life prediction of the composite material structure.

Description

[Technical Field]

[0001] This invention belongs to the field of materials mechanics and environmental adaptability engineering, specifically relating to a constitutive model of damp heat cycle damage and a failure determination method for resin-based composite materials, which can be used for life prediction and service evaluation of composite material structures. [Background Technology]

[0002] Resin-based composite materials are widely used in aerospace, rail transportation, and marine engineering due to their high specific strength, excellent formability, and good corrosion resistance. However, in actual service, these composite materials are often exposed to harsh environments with alternating high humidity and high temperature, leading to material performance degradation and affecting their structural safety. Currently, most existing literature and engineering models only consider single environmental factors or linear degradation effects, lacking a systematic description of the material damage evolution under the cumulative effects of hygrothermal cycling. Furthermore, there is a lack of calculable and verifiable damage constitutive relations and failure criteria for the coupled behavior of hygrothermal environment and mechanical response. Therefore, it is urgent to establish a constitutive model that can comprehensively consider environmental influences and multi-scale damage mechanisms of materials, and to propose corresponding failure determination methods. [Summary of the Invention]

[0003] The purpose of this invention is to provide a constitutive model and failure determination method for hygrothermal cycling damage of resin-based composite materials, and to establish a failure determination criterion based on multiple parameters, in order to solve the problems of poor adaptability and weak failure prediction ability of existing models under non-constant environmental conditions. Firstly, based on mechanical experimental data, data fitting is performed to construct a mechanical property degradation model of resin materials under different hygrothermal cycling conditions at the microscopic level. Then, combining the volume fraction of fibers and matrix, the equivalent performance parameters of a single-layer plate are derived using the blending rate method, including the coefficient of hygrothermal expansion, stiffness parameters, and strength parameters. The overall stiffness characteristics are calculated based on laminate theory, and a constitutive relationship considering hygrothermal deformation is introduced to obtain the stress-strain response. Furthermore, for various failure modes that may occur in laminates under actual loads, such as tensile, compressive, and shear failure of fibers and matrix, as well as delamination, a three-dimensional failure criterion is constructed using an improved Hashin criterion to achieve the identification and judgment of various failure modes.

[0004] This invention proposes the following technical solution, comprising four steps:

[0005] Step 1: Degradation Model of Mechanical Properties of Resin Materials under Humid-Heat Cycling

[0006] The mechanical properties of resin-based composite laminates are mainly affected by two factors: changes in the mechanical properties of the component materials and free expansion caused by humid and hot environments. The Arrhenius model is used to reflect the effects of temperature on the aging, performance degradation, and reaction rate of composite materials; its standard form is as follows:

[0007]

[0008] Where k is the degradation rate coefficient, A is the frequency factor, representing the rate of reaction without the influence of temperature, Ea is the activation energy, R is the gas constant (8.314 J / mol·K), and T is the temperature.

[0009] Considering the influence of relative humidity H, the Arrhenius model can be extended as follows:

[0010]

[0011] Where n is the humidity influence factor.

[0012] Considering the influence of the number of cycles, a model for the degradation of the mechanical properties of resin materials under hygrothermal cycling conditions is established:

[0013] P(N)=P0·exp[-N·(k1t1+k2t2)] (3)

[0014] In the formula, P is the mechanical property value of the resin material, P0 is the initial mechanical property value, k1 is the degradation rate coefficient of environmental stage 1 in the hygrothermal cycle, t1 is the aging time of stage 1, k2 is the degradation rate coefficient of environmental stage 2 in the hygrothermal cycle, t2 is the aging time of stage 2, and N is the number of cycles.

[0015] Step 2: Derivation of equivalent performance parameters for single-layer boards

[0016] For the mechanical properties of single-layer boards, this method uses the blending ratio method to calculate the coefficient of hygrothermal expansion, stiffness parameters, and strength parameters of the single-layer board based on the volume fraction of fibers and matrix. The specific formulas are as follows:

[0017] Coefficient of thermal expansion:

[0018]

[0019] α2=α3=V f (1+ν f )α f +V m (1+ν m )α m -(V f ν f +V m ν m )α1 (5)

[0020] Coefficient of moisture expansion:

[0021]

[0022] in,

[0023] ρ=V f ρ f +V m ρ m (8)

[0024] Elastic modulus:

[0025] E 11 =E f V f +E m V m (9)

[0026]

[0027] Poisson's ratio:

[0028] v 12 =v 13 =V f v f +V m v m (11)

[0029]

[0030] Shear modulus:

[0031]

[0032] G 23 =E 22 / 2(1+v 23 (14)

[0033] In the formula, α f ρ f V f E f v f G f These represent the fiber's coefficient of thermal expansion, density, volume fraction, elastic modulus, Poisson's ratio, and shear modulus, respectively. α m β m ρ m V m E m v m G m These represent the thermal expansion coefficient, wet expansion coefficient, density, volume fraction, elastic modulus, Poisson's ratio, and shear modulus of the matrix, respectively, while ρ represents the density of the composite material.

[0034] Fibers are the primary load-bearing component in composite laminates, playing a dominant role, especially in the tensile direction. The matrix, on the other hand, serves to transfer loads, support the fibers, and protect the material, influencing shear strength and transverse strength. Working synergistically through interfacial bonding, both fibers and the matrix jointly determine the overall strength of the composite laminate. Therefore, theoretical analysis can estimate the impact of various performance parameters of fibers and the matrix on the strength of unidirectional fiber composites.

[0035] For the longitudinal tensile strength X of composite materials t :

[0036]

[0037] In the formula, X f This represents the tensile strength of the fiber.

[0038] For the longitudinal compressive strength X of composite materials c :

[0039]

[0040] For the transverse tensile strength Y of composite materials t The strain amplification factor method is used to determine:

[0041]

[0042] Where, ε mt M represents the tensile failure strain of the matrix. Y The transverse strain amplification factor is determined by the following formula:

[0043]

[0044] For the transverse compressive strength Y of composite materials c :

[0045]

[0046] Where, ε mc The compressive failure strain of the matrix is ​​denoted as .

[0047] For the in-plane shear strength S of the composite material 12 The following formula is used:

[0048]

[0049] In the formula, γ ms M represents the shear failure strain of the matrix. S This is the shear strain amplification factor.

[0050] For the transverse shear strength S of composite materials 23 The following formula is used:

[0051]

[0052] In the formula S m The matrix shear strength is denoted as .

[0053] For transversely isotropic composite materials:

[0054] Z t =Y t Z c =Y c S 13 =S 12 (twenty two)

[0055] In the formula Z t Z c S 13 These represent the normal tensile, compressive, and shear strengths of the composite material, respectively.

[0056] Step 3: Constitutive Equation Considering Humid-Heat Effects

[0057] The stress state at any point in the material is represented by stress components. Using an orthogonal coordinate system, with the coordinate axes x, y, and z corresponding to the numbers 1, 2, and 3, the stress tensor σ can be expressed as:

[0058]

[0059] Where, σ ij (i,j=1,2,3) represents the stress components, σ 12 =σ 21 , σ 13 =σ 31 , σ 23 =σ 32 .

[0060] The strain state at any point is represented by strain components, and the strain tensor ε can be expressed as:

[0061]

[0062] Where, ε ij (i,j=1,2,3) represents the strain components. γ 12 ,γ 23 ,γ 31 For engineering shear strain.

[0063] For orthotropic composite materials, when the temperature changes from T0 to T, the thermal free line strain in the principal directions of the material is: and Thermal shear strain Let ΔT = T - T0. T0 is the initial temperature. From the definition of the coefficient of thermal expansion, the coefficient of thermal expansion in the principal direction of the single-layer plate material can be obtained as:

[0064]

[0065] The unit is 1 / ℃ or 1 / K.

[0066] The thermal free strain in the principal directions of a single-layer material is:

[0067]

[0068] The moisture absorption rate C of a material is defined as:

[0069]

[0070] Where W is the mass of the sample after moisture absorption, W d Let be the dry mass of the sample. Referring to the definitions of the principal direction thermal expansion coefficient and thermal free strain of a single-layer plate material, and considering the moisture absorption rate C of the single-layer plate, the wet free strain in the principal direction of the material is:

[0071]

[0072] In the formula, β1, β2, and β3 are the coefficients of hygroscopic expansion in the principal directions of the single-layer plate material. and Indicates wet free line strain. and This represents wet shear strain.

[0073] By the superposition principle, the total strain is the sum of the strain caused by force and the free strain under humid heat, that is:

[0074]

[0075] In the formula, and The linear strain caused by force, and Let be the shear strain caused by force. That is:

[0076]

[0077] In the formula, {ε} is the total strain vector, {ε M} represents the strain vector caused by the force, {ε T} represents the thermal strain vector, {ε H} represents the wet strain vector.

[0078] Therefore, under the combined effects of external load and humid heat, the constitutive relation of the single-layer plate in the principal material direction is:

[0079] {ε}=S{σ}+{ε T}+{ε H} (31)

[0080] In the formula, {σ} is the total stress vector, and S is the compliance matrix of a single-layer plate. For transversely isotropic composite materials, the relationship between the measured engineering elastic constants and the compliance matrix is ​​as follows:

[0081]

[0082] Therefore:

[0083] {σ}=Q{ε-ε T -ε H} (33)

[0084] In the formula, Q is the stiffness matrix of a single-layer plate, satisfying Q = S -1 .

[0085] The constitutive model for orthotropic materials considering hydrothermal deformation is as follows:

[0086]

[0087] Step 4: Failure Judgment Criteria

[0088] Considering that composite laminates have multiple failure modes under external loads, including fiber tensile failure, fiber compression failure, matrix tensile failure, matrix compression failure, fiber-matrix shear failure, delamination failure, and various combinations of failures, a three-dimensional failure criterion based on the Hashin criterion is used to determine the stress state of the local volume elements of the material.

[0089] Fiber tensile failure:

[0090]

[0091] Fiber compression failure:

[0092]

[0093] Matrix tensile failure:

[0094]

[0095] Matrix compression failure:

[0096]

[0097] Matrix-fiber shear failure:

[0098]

[0099] Layering failure:

[0100]

[0101] When the stress state of a local volume element of a material (the smallest computational region obtained after discretizing the structure in finite element analysis, usually a three-dimensional solid element) meets a certain failure criterion, the element is determined to have failed. For failures occurring within internal material elements, a sudden drop in stiffness is adopted, with the specific degradation mechanism as follows:

[0102] (a) Fiber tensile failure: Assuming no further load is applied to the element, the mechanical property parameter E related to stiffness... 11 E 22 G 12 G 23 G 13 v 12 v 23 v 13 Multiply by the stiffness degradation factor k1, k1 = 0.07;

[0103] (b) Fiber compression failure: Assuming no further load is applied to the element, the mechanical property parameter E related to stiffness... 11 E 22 G 12 G 23 G 13 v 12 v 23 v 13 Multiply by the stiffness degradation factor k2, k2 = 0.14;

[0104] (c) Matrix tensile failure: Assuming that the transverse load will no longer act on the element, the mechanical property parameter E related to stiffness... 22 G 12 G 23 Multiply all by the stiffness degradation factor k3, k3 = 0.2;

[0105] (d) Matrix compressive failure: Assuming that the lateral load will no longer act on the element, the mechanical property parameter E related to stiffness... 22 G 12 G 23 Multiply all by the stiffness degradation factor k4, k4 = 0.4;

[0106] (e) Matrix-fiber shear failure: Assuming that the shear load will no longer act on the element, the mechanical property parameter G related to stiffness... 12 v 12 Degenerate to 0;

[0107] (f) Delamination failure: Assuming the normal load will no longer act on the element, the mechanical property parameter E related to stiffness...33 G 23 G 31 v 23 v 13 It degenerates to 0.

[0108] Considering that various failure modes can induce and couple with each other, when a unit experiences several different failure modes, a repeated degradation method is adopted to degrade the material properties.

[0109] Compared with the prior art, the present invention has the following advantages:

[0110] (1) A composite material damage modeling path from mesoscopic to macroscopic is proposed, covering material property degradation, laminate mechanical properties and environmental coupling;

[0111] (2) The constitutive relation considers the coupling between the environmental field and the damage variable, which is more in line with the actual working conditions;

[0112] (3) Multi-failure mode coupling judgment significantly improves the accuracy of failure prediction for composite laminate structures;

[0113] (4) It can be directly embedded into the finite element analysis process, providing a practical tool for structural engineering design and evaluation. [Attached Image Description]

[0114] Figure 1 This is a schematic diagram of the overall process of the method of the present invention.

Detailed Implementation Methods

[0115] To further clarify the technical solution of the present invention, the present invention will be described below with reference to a typical embodiment, but it should not be construed as a limitation on the scope of protection of the present invention.

[0116] This embodiment discloses a constitutive model for damp-heat cycling damage and a failure determination method for resin-based composite materials, the flowchart of which is shown below. Figure 1 As shown, the main steps include:

[0117] Step 1: Establishment of a model for the degradation of the mechanical properties of the resin matrix under damp heat cycling

[0118] In this embodiment, a certain type of carbon fiber / epoxy resin prepreg is used to prepare the layup as [0]. 25 A laminate sample with dimensions of 150mm × 15mm × 3mm and a fiber volume content of 60% was prepared. Corresponding epoxy resin test specimens with dimensions of 150mm × 15mm × 3mm were also prepared. The component material properties under standard laboratory conditions are shown in Table 1 below.

[0119] Table 1. Material performance parameters of carbon fiber / epoxy resin composite components

[0120]

[0121]

[0122] First, the composite material and epoxy resin samples of this model were subjected to cyclic treatment in different humid and hot environments using an environmental testing platform. Then, the mechanical properties of the treated composite material samples were tested (such as tensile or bending tests) to obtain relevant strength information for subsequent comparison with the simulation calculation results based on this invention. Tensile tests were performed on the treated resin samples to obtain the corresponding elastic modulus. Based on the resin test data, the parameters of equations (2) and (3) were fitted, and the fitted parameters are shown in Table 2 below.

[0123] Table 2 Parameters of the mechanical property degradation model for resin materials under damp heat cycling

[0124] <![CDATA[A(h -1 )]]> Ea(kJ / mol) n <![CDATA[9.5×10 3 ]]> 48 1.2

[0125] The initial elastic modulus E of epoxy resin is known. m0 = 3.45 GPa, R is 8.314 J / mol·K, then the performance degradation model of the epoxy resin under humid and hot cycling is:

[0126]

[0127] E m (N)=3.45·exp[-N·(k1t1+k2t2)] (43)

[0128] Where k is the degradation rate coefficient, T is the temperature, and H is the relative humidity. E m (N) is the elastic modulus of the epoxy resin material, k1 is the degradation rate coefficient of environmental stage 1 in the humid heat cycle, t1 is the aging time of stage 1, k2 is the degradation rate coefficient of environmental stage 2 in the humid heat cycle, t2 is the aging time of stage 2, and N is the number of cycles.

[0129] In a typical hot and humid cycle environment, assuming the hot and humid stage temperature T1 = 343 K (70℃), humidity H1 = 80%, and stage duration t1 = 8h, and the dry stage T2 = 298 K (25℃), humidity H2 = 50%, and stage duration t2 = 16h, substituting these values ​​into the calculation yields:

[0130]

[0131] The degradation model of the elastic modulus of the epoxy matrix under typical damp heat cycling conditions is as follows:

[0132] E m (N)=3.45×exp(-N×0.0031) (46)

[0133] The elastic modulus of the resin at different numbers of hygrothermal cycles can be calculated using equation (46), as shown in Table 3 below:

[0134] Table 3 Elastic modulus of resin materials after different cycles of damp heat

[0135] Number of wet and hot cycles N <![CDATA[Elastic modulus E of epoxy resin m (GPa)]]> 0 3.4500 10 3.3446 20 3.2424 50 2.9543 80 2.6917

[0136] Step 2: Derivation of equivalent performance parameters for single-layer boards

[0137] For the mechanical properties of single-layer boards, the coefficient of hygrothermal expansion, stiffness parameters, and strength parameters are calculated based on the volume fractions of fibers and matrix. Given V... f =0.6, V m =0.4 and the component material performance parameters of this model material under standard laboratory conditions, if the material has undergone 50 cycles of typical damp heat cycling in step one, the elastic modulus E of the matrix resin. m (50) = 2.9543 GPa, which can be calculated according to equations (4)-(22):

[0138] Coefficient of thermal expansion:

[0139]

[0140] Coefficient of moisture expansion:

[0141]

[0142] Elastic modulus:

[0143]

[0144] Poisson's ratio:

[0145] v 12 =v 13 =0.6×0.2+0.4×0.35=0.26 (53)

[0146]

[0147] Shear modulus:

[0148]

[0149] Longitudinal tensile strength X t :

[0150]

[0151] Longitudinal compressive strength X c :

[0152]

[0153] Transverse tensile strength Y t :

[0154]

[0155]

[0156] Lateral compressive strength Y c :

[0157]

[0158] In-plane shear strength S 12 :

[0159]

[0160] Transverse shear strength S 23 :

[0161]

[0162] Normal tensile strength Z t Compressive strength Z c and shear strength S 13 They are respectively:

[0163]

[0164] Step 3: Constitutive Equation Considering Humid-Heat Effects

[0165] For this type of resin-based composite laminate, after 50 typical humid heat cycles, the initial curing temperature of the material is known to be T0 = 133℃, and the working temperature is T = 23℃. Therefore, the temperature difference is ΔT = T - T0 = -110℃, and the water absorption rate is measured to be C = 0.01.

[0166] The flexibility matrix S of a single-layer plate is:

[0167]

[0168] From step two, we know that α1 = 0.1284(10 -6 K -1 ), α2=33.6914(10 -6 K -1 ),

[0169] α3=33.6914(10 -6 K -1 ), β1=0.0159(10 -6 ), β2=0.8780(10 -6 ),

[0170] β3=0.8780(10 -6 ).

[0171] If a composite material is subjected to a certain external load (such as tension or three-point bending), the strain state of the local volume element (a three-dimensional solid element in finite element analysis) of the material at a certain moment is ε. 11 =13.54×10 -3 , ε 22 =0.243×10 -3 , ε 33 =0.322×10 -3 γ 23 =0.455×10 -3 γ 31 =0.588×10 -3 γ 31 =0, and the stress can be calculated from the constitutive model of an orthotropic material considering hydrothermal deformation:

[0172]

[0173] The stress state of the element at this moment can then be obtained as follows:

[0174]

[0175] Step 4: Failure Judgment Criteria

[0176] Based on the stress analysis in step three, the three-dimensional Hashin criterion is used to determine the failure of each local volume element (three-dimensional solid element) of the composite material.

[0177] Given σ 11 >0, for fiber tensile failure:

[0178]

[0179] It can be determined that no fiber tensile failure has occurred.

[0180] Given σ 22 >0, for matrix tensile failure:

[0181]

[0182] Therefore, it can be determined that the unit has experienced matrix tensile failure.

[0183] Given σ 33 >0, for stratification failure:

[0184]

[0185] This indicates that the unit has experienced a layered failure.

[0186] For cases where matrix tensile failure and delamination failure occur within the internal units of a material, a corresponding stiffness drop principle is adopted, and the specific degradation mode is as follows:

[0187] (a) Matrix tensile failure: Assuming that the transverse load will no longer act on the element, the mechanical property parameter E related to stiffness... 22 G 12 G 23 Multiply all by the stiffness degradation factor k3, k3 = 0.2;

[0188] (b) Delamination failure: Assuming the normal load will no longer act on the element, the mechanical property parameter E related to stiffness... 33 G 23 G 31 v 23 v 13 It degenerates to 0.

[0189] The degenerate parameters are:

[0190]

[0191] In the formula E' 22 、E' 33 G' is the degraded elastic modulus. 12 G' 23 G' 31 v' is the degenerate shear modulus. 23 v' 13 This represents the degraded Poisson's ratio. The degraded parameters are substituted into the constitutive equation for repeated calculations until the material as a whole fails.

[0192] By embedding the above-mentioned mechanical property degradation model of resin materials under humid heat cycling, equivalent performance parameter model of single-layer plate, constitutive equation considering humid heat effect and failure judgment criteria into the finite element analysis platform (such as ABAQUS), the dynamic simulation of material properties evolving with humid heat aging is realized in the form of user subroutines, and the simulation is compared and verified with the measured mechanical response. This allows for the prediction of multi-mode failure behavior of composite materials in complex humid heat environments.

Claims

1. A method for determining the failure of a constitutive model of hydrothermal cycling damage in resin-based composite materials, characterized in that, Includes the following steps: Step 1: Based on the mechanical test data, perform data fitting to construct a mechanical property degradation model of the resin material under different humid heat cycling conditions from a microscopic level; Step 2: Combining the volume fraction of fibers and matrix, the equivalent performance parameters of the single-layer plate are derived using the blending rate method, including the coefficient of hygrothermal expansion, stiffness performance parameters, and strength performance parameters. Step 3: Calculate the overall stiffness characteristics based on the laminate theory, and introduce the constitutive relation considering hygrothermal deformation to obtain the stress-strain response; Step 4: Considering that composite laminates have multiple failure modes under external loads, including fiber tensile failure, fiber compression failure, matrix tensile failure, matrix compression failure, fiber-matrix shear failure, delamination failure, and various combinations of failures, a three-dimensional failure criterion based on the Hashin criterion is used to determine the stress state of the local volume elements of the material.

2. The failure determination method for a constitutive model of hydrothermal cycling damage of resin-based composite materials according to claim 1, characterized in that: Step one further includes: using the Arrhenius model to reflect the effects of temperature on the aging, performance degradation, and reaction rate of the composite material, in the form of: Where k is the degradation rate coefficient, A is the frequency factor, representing the rate of reaction without the influence of temperature, Ea is the activation energy, R is the gas constant (8.314 J / mol·K), and T is the temperature; Considering the influence of relative humidity H, the Arrhenius model can be extended as follows: Where n is the humidity influencing factor; Considering the influence of the number of cycles, a model for the degradation of the mechanical properties of resin materials under hygrothermal cycling conditions is established: P(N)=P0·exp[-N·(k1t1+k2t2)] (3) In the formula, P is the mechanical property value of the resin material, P0 is the initial mechanical property value, k1 is the degradation rate coefficient of environmental stage 1 in the hygrothermal cycle, t1 is the aging time of stage 1, k2 is the degradation rate coefficient of environmental stage 2 in the hygrothermal cycle, t2 is the aging time of stage 2, and N is the number of cycles.

3. The failure determination method for a constitutive model of hydrothermal cycling damage of resin-based composite materials according to claim 1, characterized in that: Step two further includes: using the blending ratio method, calculating the coefficient of hygrothermal expansion, stiffness parameters, and strength parameters of the single-layer board based on the volume fraction of fibers and matrix, with the specific formulas as follows: Coefficient of thermal expansion: α2=α3=V f (1+n f )a f +V m (1+n m )a m -(V f n f +V m n m )a1 (5) Coefficient of moisture expansion: in, p=V f r f +V m r m (8) Elastic modulus: E 11 =E f V f +E m V m (9) Poisson's ratio: v 12 =v 13 =V f v f +V m v m (11) Shear modulus: G 23 =E 22 / 2(1+v 23 ) (14) In the formula, α f ρ f V f E f v f G f These represent the fiber's coefficient of thermal expansion, density, volume fraction, elastic modulus, Poisson's ratio, and shear modulus, respectively. α m β m ρ m V m E m v m G m These represent the thermal expansion coefficient, wet expansion coefficient, density, volume fraction, elastic modulus, Poisson's ratio, and shear modulus of the matrix, respectively, while ρ represents the density of the composite material.

4. The failure determination method for a constitutive model of hydrothermal cycling damage of resin-based composite materials according to claim 3, characterized in that: Step one further includes: For the longitudinal tensile strength X of composite materials t : In the formula, X f The tensile strength of the fiber; For the longitudinal compressive strength X of composite materials c : For the transverse tensile strength Y of composite materials t The strain amplification factor method is used to determine: Where, ε mt M represents the tensile failure strain of the matrix. Y The transverse strain amplification factor is determined by the following formula: For the transverse compressive strength Y of composite materials c : Where, ε mc The compressive failure strain of the matrix is ​​denoted as .

5. The failure determination method for a constitutive model of hydrothermal cycling damage of a resin-based composite material according to claim 3 or 4, characterized in that: For the in-plane shear strength S of the composite material 12 The following formula is used: In the formula, γ ms M represents the shear failure strain of the matrix. S This is the shear strain amplification factor; For the transverse shear strength S of composite materials 23 The following formula is used: In the formula, S m The matrix shear strength; For transversely isotropic composite materials: Z t =Y t ,Z c =Y c ,S 13 =S 12 (22) In the formula, Z t Z c S 13 These represent the normal tensile, compressive, and shear strengths of the composite material, respectively.

6. The failure determination method for a constitutive model of hydrothermal cycling damage of resin-based composite materials according to claim 1, characterized in that: Step three further includes: representing the stress state at any point in the material using stress components, employing an orthogonal coordinate system, with the coordinate axes x, y, and z corresponding to the numbers 1, 2, and 3, and the stress tensor σ expressed as: Among them, σ ij (i, j = 1, 2, 3) represents the stress component, σ 12 = σ 21 , σ 13 = σ 31 , σ 23 = σ 32 ; The strain state at any point is represented by strain components, and the strain tensor ε is expressed as: Where, ε ij (i,j=1,2,3) represents the strain components. γ 12 ,γ 23 ,γ 31 For engineering shear strain.

7. The failure determination method for a constitutive model of hydrothermal cycling damage of resin-based composite materials according to claim 1, characterized in that: For orthotropic composite materials, when the temperature changes from T0 to T, the thermal free line strain in the principal directions of the material is: and Thermal shear strain Let ΔT = T - T0; T0 is the initial temperature. From the definition of the coefficient of thermal expansion, the coefficient of thermal expansion in the principal direction of the single-layer plate material is: The unit is 1 / ℃ or 1 / K; The thermal free strain in the principal directions of a single-layer material is: The moisture absorption rate C of a material is defined as: Where W is the mass of the sample after moisture absorption, W d Let C be the dry mass of the sample; referring to the definition of the thermal expansion coefficient and thermal free strain in the principal direction of a single-layer plate material, and considering the moisture absorption rate C of the single-layer plate, the wet free strain in the principal direction of the material is: In the formula, β1, β2, and β3 are the coefficients of hygroscopic expansion in the principal directions of the single-layer plate material. and Indicates wet free line strain. and Indicates wet shear strain; By the superposition principle, the total strain is the sum of the strain caused by force and the free strain under humid heat, that is: In the formula, and The linear strain caused by force, and The shear strain is caused by force; that is: {e}={e M }+{e T }+{e H } (30) In the formula, {ε} is the total strain vector, {ε M } represents the strain vector caused by the force, {ε T } represents the thermal strain vector, {ε H } represents the wet strain vector; Therefore, under the combined effects of external load and humid heat, the constitutive relation of the single-layer plate in the principal material direction is: {e}=S{σ}+{e} T }+{e H } (31) In the formula, {σ} is the total stress vector, and S is the compliance matrix of a single-layer plate.

8. The failure determination method for a constitutive model of hydrothermal cycling damage of resin-based composite materials according to claim 7, characterized in that: For transversely isotropic composite materials, the measured relationship between the engineering elastic constants and the compliance matrix is ​​as follows: Therefore: {σ}=Q{ε-ε T -ε H In equation (33), Q is the stiffness matrix of a single-layer plate, satisfying Q = S -1 ; The constitutive model for orthotropic materials considering hydrothermal deformation is as follows:

9. The failure determination method for a constitutive model of hydrothermal cycling damage of resin-based composite materials according to claim 1, characterized in that: Step four further includes: using a three-dimensional failure criterion developed based on the Hashin criterion to determine the failure state of the local volume element of the material; specifically: Fiber tensile failure: Fiber compression failure: Matrix tensile failure: Matrix compression failure: Matrix-fiber shear failure: Layering failure:

10. The failure determination method for a constitutive model of hydrothermal cycling damage of a resin-based composite material according to claim 1 or 9, characterized in that: When the specific stress state value of a local volume element of a material meets a certain failure criterion, a corresponding failure is determined to have occurred. For failures occurring within internal material elements, the stiffness drop principle is adopted, with the specific degradation method as follows: (a) Fiber tensile failure: Assuming that no load will be applied to the internal elements of the material, the mechanical property parameter E related to stiffness... 11 E 22 G 12 G 23 G 13 v 12 v 23 v 13 Multiply by the stiffness degradation factor k1, k1 = 0.07; (b) Fiber compression failure: Assuming that no load will be applied to the internal elements of the material, the mechanical property parameter E related to stiffness... 11 E 22 G 12 G 23 G 13 v 12 v 23 v 13 Multiply by the stiffness degradation factor k2, k2 = 0.14; (c) Matrix tensile failure: Assuming that the transverse load will no longer act on the internal elements of the material, the mechanical property parameter E related to stiffness... 22 G 12 G 23 Multiply all by the stiffness degradation factor k3, k3 = 0.2; (d) Matrix compressive failure: Assuming that the lateral load will no longer act on the internal elements of the material, the mechanical property parameter E related to stiffness... 22 G 12 G 23 Multiply all by the stiffness degradation factor k4, k4 = 0.4; (e) Matrix-fiber shear failure: Assuming that the shear load will no longer act on the internal elements of the material, the mechanical property parameter G related to stiffness... 12 v 12 Degenerate to 0; (f) Delamination failure: When the directed load no longer acts on the internal elements of the material, the mechanical property parameter E related to stiffness... 33 G 23 G 31 v 23 v 13 It degenerates to 0.

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