Method for reducing interface stress between conductor and epoxy resin based on numerical simulation

Abstract

The conductor and epoxy resin interface stress reduction method based on numerical simulation disclosed by the present invention comprises the following steps: step 1: setting the thermal and mechanical parameters of the conductor and epoxy resin materials, and establishing the conductor and epoxy resin interface model; step 2: performing multi-physical field coupling on the curing dynamics module, the heat conduction module and the stress strain module, and calculating the curing degree, temperature and stress change of the epoxy resin material during the curing process; step 3: performing parameter optimization on the curing process, establishing the design variables, the objective function and the constraint conditions, optimizing the temperature and the uniformity of the curing degree on the basis of the original process, and reducing the residual stress before and after curing; step 4: substituting the optimal solution into the conductor and epoxy resin interface model for inspection, if the calculated result of the response does not meet the accuracy requirement, then returning the optimal solution and the model calculation result to step 3, reselecting the parameters for calculation, if the accuracy requirement is met, the optimization ends. The method can reduce the interface defects caused by residual stress.

Description

Technical Field

[0001] The invention belongs to the technical field of electric power equipment manufacturing, and in particular relates to a method for reducing interface stress between a conductor and epoxy resin based on numerical simulation. Background Art

[0002] The insulation reliability of power equipment is a complex electrical, thermal and mechanical stress problem. Insulation defects caused by mechanical stress have become a problem that cannot be ignored in high-voltage power equipment. In power equipment such as power cables, dry bushings, gas-insulated metal-enclosed switchgear (GIS), and gas-insulated metal-enclosed transmission lines (GIL), there is a coaxial structure in which the central conductor is bonded to the epoxy-based composite material. Due to the differences between the conductor and the insulating material, the interface formed by the two becomes a weak link in the electrical, thermal and stress fields. During the curing process, the epoxy resin composite material will produce curing shrinkage stress and thermal stress on the insulator during the pouring process due to the uneven distribution of temperature and curing degree. These internal stresses will cause insulation defects. In actual operation, electrical accidents such as insulation cracking and interface peeling caused by the interface will occur, resulting in surface flashover and even insulator failure. The interface stress concentration between the metal conductor and the resin insulating material is an important cause of interface problems. Therefore, it is necessary to study the residual stress at the interface between the conductor and the solid insulation in power equipment, and minimize the temperature overshoot and residual stress by optimizing the parameters of the curing process of the resin-based insulating material.

[0003] Current research on residual stress numerical simulation mainly focuses on epoxy-based solid insulating materials, and there is little research on numerical simulation of stress at the interface between metal conductors and solid insulation. For example, invention patent CN201810448171.9 discloses a multi-scale numerical simulation method for residual stress of composite material curing, which mainly considers the residual stress changes inside the composite material, but has not yet paid attention to the metal-insulation interface and its residual stress optimization in power equipment. At the same time, this method does not involve the process of reducing stress through optimization algorithms. Summary of the invention

[0004] The purpose of the present invention is to provide a method for reducing the interface stress between a conductor and epoxy resin based on numerical simulation, taking into account the influence of the curing process and structural dimensions on the interface structure, and optimizing the temperature and curing degree gradient to minimize the residual stress and reduce the interface defects caused by the residual stress.

[0005] The technical solution adopted by the present invention is a method for reducing the interface stress between a conductor and epoxy resin based on numerical simulation, comprising the following steps:

[0006] Step 1: Set the thermal and mechanical parameters of the conductor and epoxy resin materials, and establish the interface model between the conductor and epoxy resin;

[0007] Step 2: Perform multi-physics field coupling on the curing dynamics module, heat conduction module and stress-strain module to calculate the curing degree, temperature and stress changes of the epoxy resin material during the curing process;

[0008] Step 3: Optimize the curing process parameters, establish design variables, objective functions and constraints, optimize the temperature and curing uniformity based on the original process, and reduce the residual stress before and after curing;

[0009] Step 4: Substitute the optimal solution into the conductor and epoxy resin interface model for verification. If the calculated result of the response does not meet the accuracy requirements, return the optimal solution and the model calculation results to step 3, reselect the parameters for calculation, and if the accuracy requirements are met, the optimization ends.

[0010] The present invention is also characterized in that

[0011] Step 1 is implemented according to the following steps:

[0012] Step 1.1: Set up the curing kinetics model parameters

[0013] Dynamic differential scanning calorimetry tests were performed on epoxy resin at heating rates of 5K / min, 10K / min, 20K / min and 30K / min. The experimental data were processed and the activation energy at different curing degrees was fitted using the Straink model and the average was taken to obtain the activation energy E a ;

[0014] The Straink model fitting formula is:

[0015]

[0016] Where β is the heating rate, E a is the activation energy, T f is the absolute temperature corresponding to different heating rates and the same degree of curing, R is the molar gas constant, and C is a constant;

[0017] According to the experimental results, the curing kinetic equation fitting formula of the classic autocatalytic reaction model was adopted;

[0018] The curing kinetics fitting formula of the autocatalytic model is:

[0019]

[0020] Where A is the pre-exponential factor, m is the autocatalytic reaction order, n is the curing agent reaction order, α is the degree of curing, and T is the temperature;

[0021] The parameters in the curing kinetics fitting formula of the autocatalytic model are nonlinearly fitted and the average value is taken, and finally the curing kinetics model fitting at different heating rates is obtained;

[0022] The curing kinetic model fitted with different heating rates is:

[0023]

[0024] Step 1.2: Measure the thermal and mechanical properties of the conductor and epoxy resin materials through thermodynamic tests, including thermal conductivity, density, constant pressure heat capacity, thermal expansion coefficient, storage modulus and Poisson's ratio of the two materials; establish the curing time-varying characteristics of the epoxy resin material parameters;

[0025] The time-varying characteristics of various parameters in the epoxy resin curing process are expressed as:

[0026] k(α)=k0(1-α)+k1

[0027] C P (α) = C P0 (1-α)+C P1

[0028] ρ(α)=ρ0(1-α)+ρ1

[0029]

[0030]

[0031] Among them, k0, C p0 , ρ0, E0 are the thermal conductivity, constant pressure heat capacity, density and storage modulus of the uncured epoxy resin, k1, C p1 , ρ1, and E1 are the thermal conductivity, constant pressure heat capacity, density, and storage modulus of the epoxy resin after curing, respectively; α0 is the degree of curing before the glass transition point, α1 is the degree of curing after the glass transition point, and α gel The corresponding degree of solidification when it is the gel point;

[0032] Step 1.3: Establish a geometric model of the interface between the conductor and the epoxy resin and perform mesh division; the geometric model of the interface between the conductor and the epoxy resin is a coaxial cylindrical model; the coaxial cylindrical model is a two-dimensional axisymmetric structure, specifically including a conductor, epoxy resin, an aluminum plate base, and a steel ring container, and mesh division is performed on it;

[0033] Step 1.4: Establish a conductor-epoxy interface model and set initial values ​​and boundary conditions; the conductor-epoxy interface model consists of a curing dynamics module, a heat conduction module, and a stress-strain module.

[0034] Step 1.4 is implemented as follows:

[0035] Step 1.4.1: The essence of the curing kinetics module is to solve the heat conduction problem of nonlinear heat sources. It can be coupled through coefficient-type equations and ODE equations. Therefore, it is only necessary to match the derived curing kinetics model to the ODE interface to achieve the bidirectional coupling between temperature and curing degree.

[0036] The general form of an ODE equation is:

[0037]

[0038] Among them, u and f are the dependent variable and source term, t is the instantaneous time, e a and d a are the mass coefficient and damping coefficient;

[0039] The mass coefficient and damping coefficient are set to 0 and 1 respectively, the dependent variable is set to the curing degree α, and the left side of the equation is expressed as the curing rate dα / dt; the source term is set to the curing kinetics model equation of the epoxy resin material. Through the above settings, the curing kinetics model is matched to the ODE interface;

[0040] Step 1.4.2: The heat conduction module is used to solve the temperature change during the curing process of epoxy resin material. The temperature change follows Fourier's heat conduction law.

[0041] Fourier's law of heat conduction equation is expressed as:

[0042]

[0043] Among them, K xx , K yy , K zz are the thermal conductivity in the x, y, and z directions respectively, ρ is the density, C p is the specific heat capacity, Q is the heat flux density;

[0044] Step 1.4.3: The stress-strain module is used to calculate the stress and strain generated during the curing process of epoxy resin, and the stress-strain relationship is established using the linear elastic constitutive model;

[0045] The general expression of the linear elastic constitutive model is:

[0046] {σ}=[E]({ε}-{ε0})+{σ0}

[0047] Among them, {σ}, {σ0} are the residual stress and the initial stress respectively; {ε}, {ε0} are the total strain and the internal total strain respectively; [E] is the tensor of elastic modulus.

[0048] Step 2 is implemented as follows:

[0049] The curing dynamics module and the heat conduction module respectively calculate the changes of the curing degree and temperature of the epoxy resin with time, and then the above two modules are coupled to the stress-strain module through thermal contraction and curing reaction contraction, so as to solve the stress-strain changes in the epoxy resin curing process; through the above steps, the maximum temperature gradient and curing degree gradient of the curing process are calculated. Due to the large difference in material properties on both sides of the interface, the temperature gradient has a maximum value at the interface, and the curing degree gradient is the largest inside the epoxy resin. The maximum first principal stress of the curing process appears at the upper and lower edges of the interface. The above temperature and curing degree gradient maximum values ​​and the maximum first principal stress results are called for step 4).

[0050] Step 3 is implemented as follows:

[0051] Establish design variables: curing parameters include the temperature T of the first stage C1 , the first stage insulation time t C , the second stage temperature T C2 , the heating rate from the first stage to the second stage K C ; Interface structure dimensions include insulation thickness h, aluminum conductor radius r al and the overall model radius r in ;

[0052] The objective function is the minimum residual stress min{Δε} before and after curing;

[0053] The constraints are:

[0054] X L ≤X i ≤X U

[0055]

[0056] Among them, X i are parameter variables, including T C1 ,t C , T C2 , K C ,h,r al 、r in ;X L and X U Respectively represent the upper and lower limits of the parameter variables; Δα k max , ΔT k max Δα is the maximum curing degree gradient and maximum temperature gradient after optimization. 0 max , ΔT 0 max is the maximum curing degree gradient and maximum temperature gradient of the initial curing process, α endT0 is the curing time of the original curing process.

[0057] The beneficial effects of the present invention are:

[0058] The method of the present invention comprehensively considers the influence of curing process parameters and interface structure dimensions on the residual stress at the interface between the metal conductor and the epoxy resin material, can provide a comprehensive optimization design scheme for the conductor insulation interface in power equipment, effectively reduce the interface defects caused by residual stress, and can greatly improve the reliability of the bonding between the metal and the epoxy resin in the power equipment, thereby improving the performance of the power equipment, and has certain practicality and economy. BRIEF DESCRIPTION OF THE DRAWINGS

[0059] Figure 1 It is a schematic flow chart of the method for reducing the interface stress between a conductor and epoxy resin based on numerical simulation of the present invention;

[0060] Figure 2 is the fitting result of epoxy resin curing kinetics in the present invention;

[0061] Figure 3 It is the geometric model of the interface between the conductor and the epoxy resin and its grid schematic diagram in the present invention;

[0062] Figure 4 Thermal boundary for the conductor and epoxy resin interface model;

[0063] Figure 5 It is the maximum temperature gradient distribution diagram of the initial curing process;

[0064] Figure 6 It is the maximum curing degree gradient distribution diagram of the initial curing process;

[0065] Figure 7 This is the maximum first principal stress distribution diagram at the end of curing in the present invention;

[0066] Figure 8 This is a comparison chart of temperature and stress during the curing process before and after optimization. DETAILED DESCRIPTION

[0067] The present invention is described in detail below with reference to the accompanying drawings and specific embodiments.

[0068] The present invention provides a method for reducing the stress at the interface between a conductor and epoxy resin based on numerical simulation, such as Figure 1 As shown, the following steps are included:

[0069] 1) Set the thermal and mechanical parameters of the conductor and epoxy resin materials, and establish the interface model between the conductor and epoxy resin.

[0070] 1.1) Set the parameters of the curing kinetics model. Dynamic differential scanning calorimetry tests were performed on epoxy resin at heating rates of 5K / min, 10K / min, 20K / min and 30K / min. The experimental data were processed and the activation energy at different curing degrees was fitted using the Straink model and averaged to obtain the activation energy E a .

[0071] The Straink model fitting formula is:

[0072]

[0073] Where β is the heating rate, E a is the activation energy, T f is the absolute temperature corresponding to different heating rates and the same degree of curing, R is the molar gas constant, and C is a constant.

[0074] The curing kinetics equation fitting formula of the classic autocatalytic reaction model is adopted according to the experimental results. The curing kinetics fitting formula of the autocatalytic model is:

[0075]

[0076] Among them, A is the pre-exponential factor, m is the autocatalytic reaction order, n is the curing agent reaction order, α is the degree of curing, and T is the temperature.

[0077] The parameters in the curing kinetics fitting formula of the autocatalytic model are nonlinearly fitted and the average value is taken, and finally the curing kinetics model fitting at different heating rates is obtained, such as Figure 2 As shown, the experimental values ​​are well matched with the model values.

[0078] The curing kinetic model fitted with different heating rates is:

[0079]

[0080] 1.2) The thermal and mechanical performance parameters of the conductor and epoxy resin materials are measured through thermodynamic tests, including the thermal conductivity, density, constant pressure heat capacity, thermal expansion coefficient, storage modulus and Poisson's ratio of the two materials. Since epoxy resin materials undergo multiple state changes during the curing process, their thermal and mechanical parameters are not constants. The parameters in different states are related to the degree of curing, so the curing time-varying characteristics of epoxy resin material parameters are established.

[0081] The time-varying characteristics of various parameters in the epoxy resin curing process are expressed as:

[0082] k(α)=k0(1-α)+k1

[0083] C P (α) = C P0 (1-α)+CP1

[0084] ρ(α)=ρ0(1-α)+ρ1

[0085]

[0086]

[0087] Among them, k0, C p0 , ρ0, E0 are the thermal conductivity, constant pressure heat capacity, density and storage modulus of the uncured epoxy resin, k1, C p1 , ρ1, and E1 are the thermal conductivity, constant pressure heat capacity, density, and storage modulus of the epoxy resin after curing. α0 is the degree of curing before the glass transition point, α1 is the degree of curing after the glass transition point, and α gel The degree of solidification corresponding to the gel point.

[0088] 1.3) Establish the geometric model of the interface between the conductor and epoxy resin and perform mesh division. Figure 3 As shown, the geometric model of the conductor and epoxy resin interface is a coaxial cylindrical model. The coaxial cylindrical model is a two-dimensional axisymmetric structure, which specifically includes a conductor, epoxy resin, an aluminum plate base, and a steel ring container. It is meshed, wherein the epoxy resin unit is ultra-finely processed. The refined grid is conducive to the correctness of the calculation. The conductor, aluminum plate base, and steel ring container units are roughly divided to prevent the calculation time from being too long, which causes a decrease in calculation efficiency.

[0089] 1.4) Establish the conductor-epoxy interface model and set the initial values ​​and boundary conditions. The conductor-epoxy interface model consists of a curing kinetics module, a heat conduction module, and a stress-strain module.

[0090] 1.4.1) The essence of the curing kinetics module is to solve the heat conduction problem of nonlinear heat sources. It can be coupled through coefficient-type equations and domain ordinary differential equations (ODEs). Therefore, it is only necessary to match the derived curing kinetics model to the ODE interface to achieve bidirectional coupling between temperature and curing degree.

[0091] The general form of an ODE equation is:

[0092]

[0093] Among them, u and f are the dependent variable and source term, t is the instantaneous time, e a and d a are the mass coefficient and the damping coefficient.

[0094] The mass coefficient and damping coefficient are set to 0 and 1 respectively, the dependent variable is set to the curing degree α, and the left side of the equation is expressed as the curing rate dα / dt; the source term is set to the curing kinetics model equation of the epoxy resin material. Through the above settings, the curing kinetics model is matched to the ODE interface.

[0095] 1.4.2) The heat conduction module is used to solve the temperature change during the curing process of epoxy resin materials. The temperature change follows Fourier's heat conduction law.

[0096] Fourier's law of heat conduction equation is expressed as:

[0097]

[0098] Among them, K xx , K yy , K zz are the thermal conductivity in the x, y, and z directions respectively, ρ is the density, C p is the specific heat capacity and Q is the heat flux.

[0099] like Figure 4 As shown in the figure, the outer boundary of the entire conductor and epoxy resin interface model is set as a convection heat flux boundary, and the internal model, such as the conductor and epoxy resin, the aluminum plate base and epoxy resin, and the steel ring container and epoxy resin, is set as a continuity boundary. The above boundary condition selection principle is because the entire conductor and epoxy resin interface model has natural convection with the air during the experiment, and the internal material part is closely connected.

[0100] 1.4.3) The stress-strain module is used to calculate the stress and strain generated during the curing process of epoxy resin, and the stress-strain relationship is established using the linear elastic constitutive model.

[0101] The general expression of the linear elastic constitutive model is:

[0102] {σ}=[E]({ε}-{ε0})+{σ0}

[0103] Among them, {σ}, {σ0} are the residual stress and the initial stress respectively; {ε}, {ε0} are the total strain and the internal total strain respectively; [E] is the tensor of elastic modulus.

[0104] Epoxy resin materials undergo multiple state changes during the curing process, including the flow stage and gel stage. The thermal expansion coefficients in this stage are set to 0. The thermal expansion coefficients in the glassy stage, post-heating stage, and cooling stage use the epoxy resin parameters measured in step 1.1). The outer boundary of the aluminum plate base is set as a roller support, the contact surface between the epoxy resin and the conductor is set as a contact pair, and the contact method uses a penalty function. The coordinate system uses the global coordinate system, and the initial displacement field and structural velocity field are both 0 in the axial and radial directions. The volume reference temperature of the thermal expansion interface is the temperature at the glass transition point of the curing process, and the input type is the secant thermal expansion coefficient.

[0105] 2) Perform multi-physics field coupling on the curing kinetics module, heat conduction module and stress-strain module to calculate the curing degree, temperature and stress changes of the epoxy resin material during the curing process. The curing kinetics module and heat conduction module can respectively calculate the changes in the curing degree and temperature of the epoxy resin over time. The higher the degree of curing, the more heat the epoxy resin releases, and thus the higher the temperature. The curing degree and temperature are interconnected, thereby achieving bidirectional coupling of the two modules. The above two modules are then coupled to the stress-strain module through thermal contraction and curing reaction contraction, thereby solving the stress-strain changes in the epoxy resin curing process. Through the above steps, the maximum temperature gradient and curing degree gradient of the curing process can be calculated, such as Figure 5 and Figure 6 As shown in Figure 2, due to the large difference in material properties on both sides of the interface, the temperature gradient reaches its maximum at the interface, while the curing degree gradient is maximum inside the epoxy resin. The maximum first principal stress during the curing process is shown in Figure 2. Figure 7 As shown, the maximum first principal stress appears at the upper and lower edges of the interface, and the above-mentioned maximum values ​​of temperature and curing degree gradient and the maximum first principal stress results are called for use in step 4).

[0106] 3) Optimize the curing process parameters, establish design variables, objective functions and constraints, optimize the temperature and curing uniformity based on the original process, and reduce the residual stress before and after curing.

[0107] Establish design variables: curing parameters include the temperature T of the first stage C1 , the first stage insulation time t C , the second stage temperature T C2 , the heating rate from the first stage to the second stage K C ; Interface structure dimensions include insulation thickness h, aluminum conductor radius r al and the overall model radius r in

[0108] The objective function is to minimize the residual stress min{Δε} before and after curing.

[0109] The constraints are:

[0110] X L ≤Xi ≤X U

[0111]

[0112] Among them, X i are parameter variables, including T C1 ,t C , T C2 , K C ,h,r al 、r in ;X L and X U Respectively represent the upper and lower limits of the parameter variables; Δα k max , ΔT k max Δα is the maximum curing degree gradient and maximum temperature gradient after optimization. 0 max , ΔT 0 max is the maximum curing degree gradient and maximum temperature gradient of the initial curing process, α end T0 is the curing time of the original curing process.

[0113] 4) Substitute the optimal solution into the conductor and epoxy resin interface model for verification. If the calculated result of the response does not meet the accuracy requirements, return the optimal solution and the model calculation results to step 3) and reselect the parameters for calculation. If the accuracy requirements are met, the optimization ends. Adjust different curing process parameters and structural dimensions for stress calculation. From the trend of change, the interface edge stress and k C Proportional to T C1 and t C Inversely proportional to T C2 No relation; in terms of impact, in descending order, it is t C , T C1 , K C The first principal stress at the interface edge under different insulation thicknesses is quite different and is proportional to the insulation thickness. The stress at the interface edge decreases slightly with the increase of the conductor radius.

[0114] The original size parameters are used before optimization, T C1 ,t C , T C2 , K C ,h,r al 、r in They are 80℃, 120min, 120℃, 40mm, 12.5mm, and 50mm respectively. After optimization, the peak values ​​of each temperature and the final value of strain have decreased to a certain extent, such as Figure 8As shown, by optimizing the curing parameters and structural dimensions, the temperature peak value is reduced by 3.35%, the strain final value is reduced by 6.19%, and the first principal stress at the interface edge is reduced by 3.15%. The present invention can effectively improve the residual stress introduced by the production process between the conductor and the epoxy resin, reduce the temperature overshoot during the curing process, and the method can be applied to reduce the interface stress between metal and thermosetting materials in power equipment and optimize the design process of the interface structure.

Claims

1. A method for reducing interface stress between conductor and epoxy resin based on numerical simulation, characterized in that: The steps include: Step 1: Set the thermal and mechanical parameters of the conductor and epoxy resin materials, and establish the interface model between the conductor and epoxy resin; Step 1 is implemented as follows: Step 1.1: Set up the curing kinetics model parameters Dynamic differential scanning calorimetry tests were performed on epoxy resin at heating rates of 5K / min, 10K / min, 20K / min and 30K / min. The experimental data were processed and the activation energy at different curing degrees was fitted using the Straink model and the average was taken to obtain the activation energy E a ; The Straink model fitting formula is: Where β is the heating rate, E a is the activation energy, T f is the absolute temperature corresponding to different heating rates and the same degree of curing, R is the molar gas constant, and C is a constant; According to the experimental results, the curing kinetic equation fitting formula of the classic autocatalytic reaction model was adopted; The curing kinetics fitting formula of the autocatalytic model is: Where A is the pre-exponential factor, m is the autocatalytic reaction order, n is the curing agent reaction order, α is the degree of curing, and T is the temperature; The parameters in the curing kinetics fitting formula of the autocatalytic model are nonlinearly fitted and the average value is taken, and finally the curing kinetics model fitting at different heating rates is obtained; The curing kinetic model fitted with different heating rates is: Step 1.2: Measure the thermal and mechanical properties of the conductor and epoxy resin materials through thermodynamic tests, including thermal conductivity, density, constant pressure heat capacity, thermal expansion coefficient, storage modulus and Poisson's ratio of the two materials; establish the curing time-varying characteristics of the epoxy resin material parameters; The time-varying characteristics of various parameters in the epoxy resin curing process are expressed as: k(α)=k0(1-α)+k1 C P (a)=C P0 (1-a)+C P1 ρ(α)=ρ0(1-α)+ρ1 Among them, k0, C p0 , ρ0, E0 are the thermal conductivity, constant pressure heat capacity, density and storage modulus of the uncured epoxy resin, k1, C p1 , ρ1, and E1 are the thermal conductivity, constant pressure heat capacity, density, and storage modulus of the epoxy resin after curing, respectively; α0 is the degree of curing before the glass transition point, α1 is the degree of curing after the glass transition point, and α gel The corresponding degree of solidification when it is the gel point; Step 1.3: Establish a geometric model of the interface between the conductor and the epoxy resin and perform mesh division; the geometric model of the interface between the conductor and the epoxy resin is a coaxial cylindrical model; the coaxial cylindrical model is a two-dimensional axisymmetric structure, specifically including a conductor, epoxy resin, an aluminum plate base, and a steel ring container, and mesh division is performed on it; Step 1.4: Establish a conductor-epoxy interface model and set initial values ​​and boundary conditions; the conductor-epoxy interface model consists of a curing dynamics module, a heat conduction module, and a stress-strain module; Step 2: Perform multi-physics field coupling on the curing dynamics module, heat conduction module and stress-strain module to calculate the curing degree, temperature and stress changes of the epoxy resin material during the curing process; Step 3: Optimize the curing process parameters, establish design variables, objective functions and constraints, optimize the temperature and curing uniformity based on the original process, and reduce the residual stress before and after curing; Step 3 is implemented as follows: Establish design variables: curing parameters include the temperature T of the first stage C1 , the first stage insulation time t C , the second stage temperature T C2 , the heating rate from the first stage to the second stage K C ; Interface structure dimensions include insulation thickness h, aluminum conductor radius r al and the overall model radius r in ; The objective function is the minimum residual stress min{Δε} before and after curing; The constraints are: X L ≤X i ≤X U Among them, X i are parameter variables, including T C1 ,t C , T C2 , K C ,h,r al 、r in ;X L and X U Respectively represent the upper and lower limits of the parameter variables; Δα k max , ΔT k max Δα is the maximum curing degree gradient and maximum temperature gradient after optimization. 0 max , ΔT 0 max is the maximum curing degree gradient and maximum temperature gradient of the initial curing process, α end is the degree of curing at the end of curing, T0 is the curing time of the original curing process; Step 4: Substitute the optimal solution into the conductor and epoxy resin interface model for verification. If the calculated result of the response does not meet the accuracy requirements, return the optimal solution and the model calculation results to step 3, reselect the parameters for calculation, and if the accuracy requirements are met, the optimization ends.

2. The method for reducing interface stress between conductor and epoxy resin based on numerical simulation according to claim 1, characterized in that: Step 1.4 is implemented as follows: Step 1.4.1: The essence of the curing kinetics module is to solve the heat conduction problem of nonlinear heat sources. It is coupled by coefficient-type equations and ODE equations. Therefore, it is only necessary to match the derived curing kinetics model to the ODE interface to achieve bidirectional coupling between temperature and curing degree. The general form of an ODE equation is: Among them, u and f are the dependent variable and source term, t is the instantaneous time, e a and d a are the mass coefficient and damping coefficient; The mass coefficient and damping coefficient are set to 0 and 1 respectively, the dependent variable is set to the curing degree α, and the left side of the equation is expressed as the curing rate dα / dt; the source term is set to the curing kinetics model equation of the epoxy resin material. Through the above settings, the curing kinetics model is matched to the ODE interface; Step 1.4.2: The heat conduction module is used to solve the temperature change during the curing process of epoxy resin material. The temperature change follows Fourier's heat conduction law. Fourier's law of heat conduction equation is expressed as: Among them, K xx , K yy , K zz are the thermal conductivity in the x, y, and z directions respectively, ρ is the density, C p is the specific heat capacity, Q is the heat flux density; Step 1.4.3: The stress-strain module is used to calculate the stress and strain generated during the curing process of epoxy resin, and the stress-strain relationship is established using the linear elastic constitutive model; The general expression of the linear elastic constitutive model is: {σ}=[E]({ε}-{ε0})+{σ0} Among them, {σ}, {σ0} are the residual stress and the initial stress respectively; {ε}, {ε0} are the total strain and the internal total strain respectively; [E] is the tensor of elastic modulus.

3. The method for reducing interface stress between conductor and epoxy resin based on numerical simulation according to claim 2, characterized in that: Step 2 is implemented as follows: The curing dynamics module and the heat conduction module respectively calculate the changes of the curing degree and temperature of the epoxy resin with time, and then the above two modules are coupled to the stress-strain module through thermal contraction and curing reaction contraction, so as to solve the stress-strain changes in the epoxy resin curing process; through the above steps, the maximum temperature gradient and curing degree gradient of the curing process are calculated. Due to the large difference in material properties on both sides of the interface, the temperature gradient has a maximum value at the interface, and the curing degree gradient is the largest inside the epoxy resin. The maximum first principal stress of the curing process appears at the upper and lower edges of the interface. The above temperature and curing degree gradient maximum values ​​and the maximum first principal stress results are called for step 4).

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