A method for simulating the elastic-damage of thermosetting resin based on the wet-thermal effect

Abstract

The application discloses a thermosetting resin elastoplastic-damage simulation method based on a hygrothermal effect. Under the hygrothermal effect, the corresponding relationship between the glass transition temperature of the thermosetting resin and the tensile and compression performance under uniaxial load is expressed through mathematical analysis means based on the judgment of the strength criterion and the plastic yield criterion, a constitutive model is established, the constitutive model is programmed, full-size modeling is carried out according to the pattern in the test, and the simulation result is verified. Compared with the prior art, the thermosetting resin elastoplastic-damage simulation method based on the hygrothermal effect has the characteristics of few parameters and high precision.

Description

Technical Field

[0001] This invention relates to the technical field of polymers, and more particularly to a method for simulating thermosetting resins. Background Technology

[0002] Thermosetting resins and other polymers are easily permeated by solvents such as water. When exposed to a humid and hot environment, water molecules in the environment diffuse into the resin under the influence of the water molecule concentration gradient, damaging the internal molecular chains and thus causing a decrease in its mechanical properties. Currently, most thermosetting resins exhibit a small fracture failure strain range under tensile loads, showing brittle fracture; under compressive loads, they can withstand large plastic deformation, exhibiting a typical tension / compression asymmetry phenomenon; thermoplastic resins, on the other hand, undergo large plastic deformation under both tensile and compressive loads. Thermosetting resins subjected to the combined effects of humid and hot environmental factors exhibit different failure modes and mechanical behaviors under compressive and tensile loads, therefore, constitutive models are needed to characterize their properties.

[0003] Currently, constitutive models that consider humid and thermal environmental factors exist, but these models require numerous parameters and various types of parameter verification tests. Furthermore, most models can only describe the humid-thermal-mechanical coupling effect in a one-dimensional state, which is not conducive to the evaluation and analysis of large-sized component structures in engineering applications. Yu Chao of Southwest Jiaotong University developed a viscoelastic-viscoplastic constitutive model for thermosetting resins considering the glass transition temperature and its humid-thermal-mechanical coupling. This model starts from the laws of thermodynamics and introduces a novel free energy function to characterize the influence of humid heat. However, it focuses primarily on the humid-thermal-mechanical interaction of thermosetting resins under cyclic loading / unloading, and the model has more than 50 material parameters, resulting in high complexity and cumbersome experimental verification steps. Bahrololoumi et al. of Michigan State University proposed a constitutive model that uses a multiphysics model to predict the mechanical behavior of thermosetting resins under environmental factors such as oxidation, moisture, and temperature. This model posits that the internal damage to thermosetting resins caused by humid-thermal aging is due to two parallel damage mechanisms: hydrolytic aging and thermo-oxidative aging. Moreover, the model assumes that these two aging mechanisms can be linearly superimposed. The model was developed by comparing experimental and theoretical analyses based on the changes in the microstructure of thermosetting resin crosslinked networks under humid heat aging. However, it still requires 15 parameters to characterize the changes in mechanical behavior. Moreover, the verification model is consistent with the method used by Yu Chao et al., which is to conduct numerical verification under a one-dimensional model.

[0004] Therefore, a new technical solution is needed to solve the above problems. Summary of the Invention

[0005] To address the problems arising from existing technologies, this invention provides a high-precision, low-parameter simulation method for thermosetting resin elastoplastic-damage based on the hygrothermal effect.

[0006] To achieve the above objectives, the present invention provides a thermosetting resin elastoplastic-damage simulation method based on the effect of damp heat, employing the following technical solution:

[0007] A method for elastoplastic-damage simulation of thermosetting resins based on the effect of damp heat includes the following steps:

[0008] 1) Full-size modeling of the dimensions used for the thermosetting resin specimens;

[0009] 2) Input glass transition temperature T g Tensile strength under uniaxial load X t Or compressive strength X c ;

[0010] 3) Obtain the stress σ and the corresponding simulated thermosetting resin strain ε;

[0011] 4) Construct stress-strain curves;

[0012] Among them, a strength criterion is proposed by combining the quadratic form of the parabolic shape, and the calculation formula is as follows:

[0013]

[0014] X c (T θ，g ) represents temperature T θ，g The compressive strength of simulated thermosetting resin, X t (T θ，g ) represents temperature T θ，g Simulated tensile strength of thermosetting resin; θ represents different hygrothermal states, g represents glass transition temperature. The first stress invariant represents the effective stress of the resin at time n+1. The second stress invariant represents the effective stress of the resin at time n+1;

[0015] If Φ d If the stress is greater than 0, then the material is damaged, and the damage stress and strain are updated:

[0016] Stress update:

[0017]

[0018] Response Update:

[0019] r is an internal parameter controlling the evolution of material damage, ν m This indicates the Poisson's ratio of the resin. For equivalent stress, I is the fourth-order unit tensor, 1 is the second-order unit tensor, and 1 = δ ij δ ij Kroneck1 = δ ij δ ij Symbol, ε n+1 Let ε be the total strain of the material at time n+1. n Let n be the total strain of the material at time n. Let Δε be the plastic strain tensor of the material at time n, and Δε be the strain increment at the current time.

[0020] If Φ d If the value is ≤0, then the material yields without damage. Referring to the plastic yield criterion proposed based on the parabolic yield behavior assumption, the formula is as follows:

[0021]

[0022] J 2，n+1 (σ) represents the second stress invariant of the resin at time n+1, I 1，n+1 (σ) represents the first stress invariant of the resin at time n+1. The glass transition temperature is expressed as T. g And the equivalent plastic strain is Uniaxial compressive strength of the resin at that time; The glass transition temperature is expressed as T. g And the equivalent plastic strain is Uniaxial tensile strength of the resin at that time;

[0023] If Φ d ≤0 and At this moment, the stress state at the material point is within the elastic domain. The elastic test stress at time n+1;

[0024] The stress is updated to:

[0025] The response has been updated to:

[0026] If Φ d ≤0 and At this moment, the stress state at the material point is within the plastic region, and the stress is updated as follows:

[0027]

[0028] The response has been updated to:

[0029]

[0030]

[0031] Gm S is the resin shear modulus, Δγ is the plasticity increment operator, and S n+1 Let K be the deviatoric stress tensor at time n+1. m Let be the bulk modulus of the resin, and α be a parameter controlling the plastic volumetric strain, (I1) n+1 The first invariant of stress at time n+1 is Δε. p For the plastic strain increment tensor, Let be the partial stress tensor at time n+1. Let ζ be the first invariant of the test stress at time n+1. s =1+6G m Δγ, ζ p =1+6G m Δγ.

[0032] Furthermore, the aforementioned plastic strain increment tensor By combining the definition of the flow direction of the plastic strain tensor, the equivalent plastic strain increment is obtained. Variable updates for the plastic yield criterion: ν p It is the plastic Poisson's ratio.

[0033] Furthermore, the small deformation strain decomposition theory decomposes the total deformation strain ε of the material into ε0. p elastic strain ε e and plastic strain ε p .

[0034] Furthermore, both the plastic yield criterion and the strength criterion mentioned above are based on T. g As a measure of the damp heat effect, it characterizes the influence of aging under damp heat on the failure strength of thermosetting resins.

[0035] Furthermore, the T g Different values ​​represent the conditions of no wet heat treatment, wet heat treatment, and repeated drying after wet heat treatment.

[0036] Furthermore, the aforementioned thermosetting resin elastoplastic-damage simulation method based on the hydrothermal effect is based on a continuous damage model and proposes a damage variable evolution equation:

[0037]

[0038] d represents the damage evolution control variable. When determining the damage evolution form after failure, a two-dimensional model is used, and the evolution variables and internal parameters are differentiated twice to consider the changes in the variables.

[0039] Furthermore, the value of A is obtained by the following formula:

[0040]

[0041] G f Indicates the fracture toughness of a material; e E represents the characteristic length of a unit cell; for a three-dimensional solid unit, it is the cube root of the unit volume; for a two-dimensional planar unit, it is the square root of the unit area. m A represents the elastic modulus of the resin; for each unit, the value of A is uniquely determined.

[0042] Furthermore, the thermosetting resin elastoplastic-damage simulation method based on the hygrothermal effect determines the relationship between the equivalent stress and the actual stress of isotropic materials after material damage, based on the assumption of equivalent strain:

[0043]

[0044] Furthermore, the method for establishing the thermosetting resin elastoplastic-damage simulation method based on the hygrothermal effect includes the following steps:

[0045] 1) Treat thermosetting resins under different humid and hot conditions, and use the heat changes caused by the absorption and release of heat by the thermosetting resins under different humid and hot conditions to calibrate and record their glass transition temperature.

[0046] 2) Conduct uniaxial tensile and compression tests on thermosetting resins under quasi-static loads under different humid and hot conditions, measure the deformation and compile it into stress-strain curves;

[0047] 3) Using mathematical analysis, the glass transition temperature is used as a parameter, and the plastic flow and strength values ​​of thermosetting resin under different humid and hot conditions are used as target quantities for optimization design. Combining the plastic yield criterion and the strength criterion, an elastoplastic-damage constitutive model of thermosetting resin considering the humid and hot effect is proposed.

[0048] 4) The above constitutive model is programmed using a programming language, and full-size modeling is performed on the test specimens, and the corresponding stress-strain curves are extracted.

[0049] Furthermore, in step 1), the glass transition temperature of thermosetting resins after different hygrothermal treatments is obtained using DSC or DMA; in step 2), the stress-strain curve is obtained using an MTS universal testing machine in conjunction with a video extensometer or DIC digital correlation strain testing technology.

[0050] The present invention has the following beneficial effects:

[0051] 1. Both the plastic yield criterion and the strength criterion are based on T. g As a measure of the hygrothermal effect, it characterizes the influence of aging under hygrothermal conditions on the deformation of thermosetting resins. It requires fewer parameters, has lower model complexity, and simplifies experimental verification procedures.

[0052] 2. Based on a three-dimensional continuous damage model and combined with mathematical partial derivative analysis, the influence of changes in damp heat-related variables on the mechanical behavior and failure mode of thermosetting resins is clearly identified with high accuracy. Attached Figure Description

[0053] Figure 1 This is the overall flowchart of the present invention;

[0054] Figure 2 This is a flowchart illustrating the numerical calculation process of the constitutive model used in this invention.

[0055] Figure 3 A comparison of glass transition temperature curves of thermosetting resins under different humid and hot conditions.

[0056] Figure 4 The graphs show the actual stress-strain curves of thermosetting resins under uniaxial tensile and compressive loads under different humid and hot conditions. The left graph shows the uniaxial tensile stress-strain curve, and the right graph shows the uniaxial compressive stress-strain curve.

[0057] Figure 5 The figures shown are for verifying the results of this invention. The left figure is a comparison of uniaxial tensile stress-strain curves, and the right figure is a comparison of uniaxial compressive stress-strain curves.

[0058] Among them, the plastic yield criterion is (1), the strength criterion is (4), the damage variable evolution equation is (7), and the relationship between equivalent stress and true stress is (10). Detailed Implementation

[0059] The present invention will be further illustrated below with reference to the accompanying drawings and specific embodiments. It should be understood that the following specific embodiments are for illustrative purposes only and are not intended to limit the scope of the invention. After reading the present invention, any modifications of the present invention in various equivalent forms by those skilled in the art will fall within the scope defined by the appended claims.

[0060] Please see Figure 1 As shown, this invention discloses an elasto-plastic-damage simulation method for thermosetting resins based on the hygrothermal effect. Based on the small deformation strain decomposition theory, this invention analyzes the glass transition temperature Tglass of thermosetting resins under the hygrothermal effect. g The influence of thermosetting resins on tensile and compressive properties under uniaxial load was investigated. A constitutive model was established, a simulation method was developed based on this model, and the simulation results were verified.

[0061] Strain refers to the local relative deformation of an object under the influence of external forces and non-uniform temperature fields. The deformation occurs in four stages: elastic deformation, yielding, strengthening, and necking. Elastic deformation occurs in the elastic stage; the object can return to its original shape after the applied external force is removed. Plastic deformation occurs in the yielding stage; the object cannot return to its original shape after the applied external force is removed. Strength is a mechanical indicator reflecting a material's load-bearing capacity; when necking reaches a certain extent, the material fails to withstand stress.

[0062] Stress refers to the internal forces generated between different parts of an object when it deforms due to external factors such as force, humidity, and temperature changes. These forces resist the external forces and attempt to restore the object from its deformed position to its original position. Stress values ​​represent the magnitude of strength. As the external force increases, the stress increases accordingly. When the bonding force between the particles within the material is insufficient to resist the applied external force, the material fails due to strength loss. Once the upper limit of the yield stress is reached, plastic flow occurs. Plastic flow refers to the flow of matter primarily through crystallization plastic deformation mechanisms.

[0063] This invention emphasizes the plastic flow behavior and strength variation law of thermosetting resins. Therefore, the glass transition temperature is used as a parameter, and the plastic flow and strength values ​​of thermosetting resins under different humid and hot conditions are used as target quantities. Combining the parabolic yield behavior assumption, plastic yield criteria and strength criteria are proposed and a constitutive model is established. Based on this constitutive model, a simulation method is then established.

[0064] See Figure 2 , Figure 3 The main calculation formulas of this invention are as follows:

[0065] 1) The formula for calculating the macroscopic phenomenological plastic yield criterion of thermosetting resins that include the hygrothermal effect is:

[0066]

[0067] Where J2(σ) represents the second stress invariant when the stress is σ, and I1(σ) represents the first stress invariant when the stress is σ. The glass transition temperature is represented by T. g And the equivalent plastic strain is Uniaxial compressive yield strength of the resin The glass transition temperature is represented by T. g And the equivalent plastic strain is Uniaxial tensile yield strength of the resin at that time;

[0068] The parameters in the above plastic yield criterion are obtained from the following formula:

[0069] Using the quasi-static tensile / compression test data of unaged thermosetting resin as the benchmark, the equivalent plastic strain and equivalent plastic stress under uniaxial compression and uniaxial tension of aged and aging-re-dried thermosetting resins were obtained by least squares optimization algorithm, which are (2) and (3) respectively:

[0070]

[0071]

[0072] Among them, T θ，g In the equation θ = (1, 2), 1 represents the T of the aged thermosetting resin. g 2 represents the T of the aging and repeated dry thermosetting resin. g T dry，g T represents unaged thermosetting resins g ξ asym This represents the correction factor for tension / compression asymmetry.

[0073] 2) This invention adopts a strength criterion (4) that is highly similar to the plastic yield criterion. Its form is also a parabolic quadratic form, and it is also based on T. g Using the damp heat effect as a measure to characterize the impact of aging on the failure strength of thermosetting resins, this invention achieves a high degree of consistency in the expression of the yield strength and failure strength of thermosetting resins under aging, further highlighting the advantages of T... g The superiority and simplicity of a phenomenological macroscopic constitutive model for thermosetting resins that considers the effects of hygrothermia are presented from the perspective of [missing information - likely a specific perspective or approach]. The calculation formula is as follows:

[0074]

[0075] X c (T θ，g ) represents temperature T θ，g The compressive strength of simulated thermosetting resin, X i (T θ，g ) represents temperature T θ，g The tensile strength of a simulated thermosetting resin is shown below, where θ represents different humid and hot conditions. Indicates the first stress invariant. Indicates the second stress invariant;

[0076] The parameters of the above strength criterion are obtained from the following formula:

[0077]

[0078]

[0079] Among them, X c (T θ，g ) and Xt (T θ，g (θ=(1,2)), where θ=1 represents the compressive strength and tensile strength of the thermosetting resin under aging, and θ=2 represents the compressive strength and tensile strength of the thermosetting resin after aging and repeated drying, respectively. X c (T dry，g ) and X t (T dry，g ) represent the compressive strength and tensile strength of the unaged thermosetting resin, respectively. asym This represents the asymmetry coefficient of tensile and compressive strength.

[0080] 3) After determining the strength criterion, according to the requirements of the continuous damage model, it is necessary to provide the damage evolution form of thermosetting resin after failure. The damage variable evolution equation (7) is as follows:

[0081]

[0082]

[0083] Where d is the damage evolution control variable; r is the internal parameter controlling the material damage evolution; G f Indicates the fracture toughness of a material; e E represents the characteristic length of a unit cell; for a three-dimensional solid unit, it is the cube root of the unit volume; for a two-dimensional planar unit, it is the square root of the unit area. m The elastic modulus of the resin; for each unit, the value of A is uniquely determined by (8).

[0084] 4) After determining the damage evolution law, it is necessary to determine the relationship between equivalent stress and actual stress in order to assign values ​​to the changed stress and update the stress. Based on the equivalent strain assumption, the relationship between the two can be obtained, given by formula (9):

[0085]

[0086] in, This represents the fourth-order elastic stiffness tensor of the undamaged thermosetting resin. The fourth-order flexibility tensor of the thermosetting resin without damage; This is the equivalent stress; for isotropic materials, the above relationship can be further expressed as:

[0087]

[0088] Where, ν m The value represents the Poisson's ratio of the resin, where I is the fourth-order unit tensor and 1 is the second-order unit tensor.

[0089] See Figure 2Based on the above formula at time n+1, the constitutive model is implemented as follows:

[0090] 1) Based on the classical small deformation strain decomposition theory, perform strain ε decomposition; and calculate the total deformation strain ε of the resin at time n+1. n+1 The elastic strain of the resin at time n is decomposed. Plastic strain of resin at time n The resin consists of three parts: the current strain increment Δε;

[0091] v = ε e +ε p (11)

[0092] 2) Calculate the test stress of the resin at time n+1.

[0093]

[0094] in, and are the point stress and total strain of the material at time n+1, respectively; C is the plastic strain tensor of the material at time n; m Let be a fourth-order isotropic elastic tensor, and its tensor expression is:

[0095]

[0096] Among them, G m and K m These represent the resin shear and bulk modulus, respectively; I is the fourth-order unit tensor; and 1 is the second-order unit tensor, where 1 = δ. ij δ ij For Kroneck's symbol.

[0097] 3) Combining the parabolic quadratic form, calculate whether the resin satisfies the following strength criterion at time n+1. The calculation formula is as follows:

[0098]

[0099] X c (T θ，g ) represents temperature T θ，g The compressive strength of simulated thermosetting resin, X t (T θ，g ) represents temperature T θ，g The tensile strength of a simulated thermosetting resin is calculated, where θ represents different humid and hot states, and the effective stress of the resin at time n+1 is... The first stress invariant represents the effective stress of the resin at time n+1. The second stress invariant represents the effective stress of the resin at time n+1.

[0100] 4) If Φ d If ≤0, it indicates that the resin is not damaged. Then it is necessary to further determine whether it has yielded. Based on the parabolic yield behavior assumption, the following resin plastic yield criterion is proposed. The formula (15) for the plastic yield criterion (1) at time n+1 is as follows:

[0101]

[0102] J 2，n+1 (σ) represents the second stress invariant of the resin at time n+1, I 1，n+1 (σ) represents the first stress invariant of the resin at time n+1. The glass transition temperature is expressed as T. g And the equivalent plastic strain is Uniaxial compressive yield strength of the resin The glass transition temperature is expressed as T. g And the equivalent plastic strain is The uniaxial tensile yield strength of the resin.

[0103] 5) If Φ d ≤0 and This indicates that the material point is located within the plastic domain, and it is necessary to solve for the plastic increment operator Δγ and the plastic strain increment tensor Δε. p The update steps are as follows:

[0104]

[0105]

[0106]

[0107] Among them, S n+1 Let (I1) be the deviatoric stress tensor at time n+1. n+1 The first invariant of stress at time n+1 is... Let be the partial stress tensor at time n+1. Let G be the first invariant of the test stress at time n+1. m K represents the resin shear modulus. m For the bulk modulus of resin, to make the formula more concise and elegant, the above formula is rearranged as follows:

[0108]

[0109]

[0110]

[0111] Where, ζ s =1+6Gm Δγ, ζ p =1+6G m Δγ.

[0112] The updated plastic strain tensor can be obtained by combining the above formula.

[0113]

[0114] Furthermore, by combining the definition of the flow direction of the plastic strain tensor, the equivalent plastic strain increment is obtained. Variable updates for the plastic yield criterion:

[0115]

[0116] The final strain stress is further updated as follows:

[0117]

[0118]

[0119] 6) If Φ d ≤0 and This indicates that the resin is within the elastic domain, so the final stress update is:

[0120]

[0121] The final strain update is as follows:

[0122]

[0123] 7) If Φ d If the value is greater than 0, it means that the resin has suffered material damage. Therefore, the damage variable d needs to be calculated first.

[0124]

[0125] d is the damage evolution control variable; r is the internal parameter controlling the material damage evolution; the value of A is a uniquely determined constant, which can be determined using the following expression (29):

[0126]

[0127] Among them, G f Indicates the fracture toughness of a material; e E represents the characteristic length of a unit cell; for a three-dimensional solid unit, it is the cube root of the unit volume; for a two-dimensional planar unit, it is the square root of the unit area. m This refers to the elastic modulus of the resin.

[0128] Furthermore, the thermosetting resin elastoplastic-damage simulation method based on the thermoplastic damage model determines the relationship between the equivalent stress and the true stress of isotropic materials based on the equivalent strain assumption, and can obtain the final stress update of the material at time n+1 as follows:

[0129]

[0130] Final Strain Update:

[0131] See Figure 1 , Figure 3 , Figure 4 , Figure 5 The present invention employs the verification steps of this thermosetting resin elastoplastic-damage simulation method based on the hydrothermal effect.

[0132] 1) The thermosetting resin is treated under different humid and hot conditions, including unaged, humid and hot treated followed by aging, and aging followed by repeated drying. The glass transition temperature is determined by using DSC or DMA testing equipment to analyze the changes in heat absorption and release generated by the thermosetting resin under different humid and hot conditions. In this embodiment, T g The different values ​​of 147.48℃, 103.86℃, and 118.72℃ represent the conditions of no wet heat treatment, wet heat treatment, and repeated drying after wet heat treatment, respectively.

[0133] 2) Using the MTS universal testing machine, uniaxial tensile and compression tests under quasi-static loads are carried out on thermosetting resins under different humid and hot conditions. During the test, video extensometers or digital correlation strain testing technologies such as DIC can be used to obtain the deformation of thermosetting resins under uniaxial tension or compression more accurately and obtain the true stress-strain curve.

[0134] 3) Based on the glass transition temperature of the resin under different humid heat conditions obtained in step 1) and the actual stress-strain curves under uniaxial tension and compression obtained in step 2), we comprehensively analyze the influence of the glass transition temperature of thermosetting resin under different humid heat conditions on the stress-strain curves under tension and compression, mainly involving plastic flow behavior and strength change law.

[0135] 4) Using mathematical analysis methods such as least squares optimization, the glass transition temperature is used as a parameter, and the plastic flow and strength values ​​of thermosetting resin under different humid and hot conditions are used as target quantities for optimization design. Combining the parabolic quadratic plastic yield and strength criteria, an elastoplastic-damage constitutive model for thermosetting resin considering the humid and hot effect is proposed. The main steps include numerical discretization under the small strain assumption, through strain decomposition, stress calculation, strength criterion and plastic yield criterion determination, and corresponding variable update.

[0136] 5) The constitutive model is programmed using the Fortran programming language and commercial finite element software. This embodiment is based on a commercial finite element platform and uses a written Fortran constitutive model subroutine to perform full-scale modeling with the dimensions of the specimen used in the experiment, conduct simulation, and extract the corresponding stress-strain curves.

[0137] 6) Comparison of experimental and simulated numerical values ​​of the actual stress-strain curves of thermosetting resins under uniaxial tension and compression under different humid and hot conditions: Under uniaxial tensile and compressive loads, the thermosetting resins under different humid and hot conditions are basically consistent in the early linear elastic segment, plastic flow segment and strength value, which can accurately describe the elastoplastic-damage behavior of thermosetting resins under different humid and hot conditions.

[0138] In summary, the thermosetting resin elastoplastic-damage simulation method based on the hygrothermal effect of this invention has the characteristics of fewer parameters and higher accuracy.

Claims

1. A method for elastoplastic-damage simulation of thermosetting resins based on the effect of damp heat, characterized in that, Includes the following steps: 1) Full-size modeling of the dimensions used for the thermosetting resin specimens; 2) Input glass transition temperature T g Tensile strength under uniaxial load X t Or compressive strength X c ; 3) Obtain the stress σ and the corresponding simulated thermosetting resin strain ε; 4) Construct stress-strain curves; Among them, a strength criterion is proposed by combining the quadratic form of the parabolic shape, and the calculation formula is as follows: X c (T θ，g ) represents temperature T θ，g The compressive strength of simulated thermosetting resin, X t (T θ，g ) represents temperature T θ，g Simulated tensile strength of thermosetting resin; θ represents different hygrothermal states, g represents glass transition temperature. The first stress invariant represents the effective stress of the resin at time n+1. The second stress invariant represents the effective stress of the resin at time n+1; If Φ d If the stress is greater than 0, then the material is damaged, and the damage stress and strain are updated: Stress update: Response Update: d is the control variable for damage evolution, ν m This indicates the Poisson's ratio of the resin. For equivalent stress, I is the fourth-order unit tensor, 1 is the second-order unit tensor, and 1 = δ ij δ ij For Kroneck's symbol, ε n+1 Let ε be the total strain of the material at time n+1. n Let n be the total strain of the material at time n. Let Δε be the plastic strain tensor of the material at time n, and Δε be the strain increment at the current time. If Φ d If the value is ≤0, then the material yields without damage. Referring to the plastic yield criterion proposed based on the parabolic yield behavior assumption, the formula is as follows: J 2，n+1 (σ) represents the second stress invariant of the resin at time n+1, I 1，n+1 (σ) represents the first stress invariant of the resin at time n+1. The glass transition temperature is expressed as T. g And the equivalent plastic strain is Uniaxial compressive strength of the resin at that time; The glass transition temperature is expressed as T. g And the equivalent plastic strain is Uniaxial tensile strength of the resin at that time; If Φ d ≤0 and At this moment, the stress state at the material point is within the elastic domain. The elastic test stress at time n+1; The stress is updated to: The strain has been updated to: If Φ d ≤0 and At this moment, the stress state at the material point is within the plastic region, and the stress is updated as follows: The strain has been updated to: G m S is the resin shear modulus, Δγ is the plasticity increment operator, and S n+1 Let K be the deviatoric stress tensor at time n+1. m Let be the bulk modulus of the resin, and α be a parameter controlling the plastic volumetric strain, (I1) n+1 The first invariant of stress at time n+1 is Δε. p For the plastic strain increment tensor, Let be the partial stress tensor at time n+1. Let ζ be the first invariant of the test stress at time n+1. s =1+6G m Δγ, ζ p =1+6G m Δγ.

2. The thermosetting resin elastoplastic-damage simulation method based on the damp-heat effect according to claim 1, characterized in that, The plastic strain increment tensor By combining the definition of the flow direction of the plastic strain tensor, the equivalent plastic strain increment is obtained. Variable updates for the plastic yield criterion: v p It is the plastic Poisson's ratio.

3. The thermosetting resin elastoplastic-damage simulation method based on the damp-heat effect according to claim 1, characterized in that, Based on the small deformation strain decomposition theory, the total deformation strain ε of a material is decomposed into elastic strain ε. e and plastic strain ε p .

4. The thermosetting resin elastoplastic-damage simulation method based on the damp heat effect according to claim 1, characterized in that, Both the plastic yield criterion and the strength criterion mentioned above are based on T. g As a measure of the damp heat effect, it characterizes the influence of aging under damp heat on the failure strength of thermosetting resins.

5. The method for elastoplastic-damage simulation of thermosetting resins based on the effect of damp heat according to claim 1 or 4, characterized in that, The T g Different values ​​represent the conditions of no wet heat treatment, wet heat treatment, and repeated drying after wet heat treatment.

6. The method for elastoplastic-damage simulation of thermosetting resins based on the damp-heat effect according to claim 1, characterized in that, The aforementioned thermosetting resin elastoplastic-damage simulation method based on the damp heat effect is based on a continuous damage model and proposes a damage variable evolution equation: r is an internal parameter that controls the material damage evolution. When determining the damage evolution form after failure, a two-dimensional model is used, and the evolution variables and internal parameters are differentiated twice to consider the changes in variables.

7. The thermosetting resin elastoplastic-damage simulation method based on the damp heat effect according to claim 6, characterized in that, The value of A is obtained by the following formula: G f Indicates the fracture toughness of a material; e E represents the characteristic length of a unit cell; for a three-dimensional solid unit, it is the cube root of the unit volume; for a two-dimensional planar unit, it is the square root of the unit area. m A represents the elastic modulus of the resin; for each unit, the value of A is uniquely determined.

8. The method for elastoplastic-damage simulation of thermosetting resins based on the damp-heat effect according to claim 1, characterized in that, The aforementioned thermosetting resin elastoplastic-damage simulation method based on the hygrothermal effect determines the relationship between the equivalent stress and the actual stress of isotropic materials after material damage, based on the assumption of equivalent strain.

9. The method for elastoplastic-damage simulation of thermosetting resins based on the damp-heat effect according to claim 1, characterized in that, The method for establishing the thermosetting resin elastoplastic-damage simulation method based on the hygrothermal effect includes the following steps: 1) Treat thermosetting resins under different humid and hot conditions, and use the heat changes caused by the absorption and release of heat by the thermosetting resins under different humid and hot conditions to calibrate and record their glass transition temperature. 2) Conduct uniaxial tensile and compression tests on thermosetting resins under quasi-static loads under different humid and hot conditions, measure the deformation and compile it into stress-strain curves; 3) Using mathematical analysis, the glass transition temperature is used as a parameter, and the plastic flow and strength values ​​of thermosetting resin under different humid and hot conditions are used as target quantities for optimization design. Combining the plastic yield criterion and the strength criterion, an elastoplastic-damage constitutive model of thermosetting resin considering the humid and hot effect is proposed. 4) The above constitutive model is programmed using a programming language, and full-size modeling is performed on the test specimens, and the corresponding stress-strain curves are extracted.

10. The thermosetting resin elastoplastic-damage simulation method based on the hydrothermal effect according to claim 9, characterized in that, Step 1) uses DSC or DMA to obtain the glass transition temperature of thermosetting resins after different hygrothermal treatments; Step 2) uses an MTS universal testing machine and video extensometer or DIC digital correlation strain testing technology to obtain stress-strain curves.

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