A method for predicting material mechanical properties based on a microstructure unit cell model

Abstract

The present application relates to a kind of material mechanics characteristic prediction method based on microstructure unit cell model, belong to aircraft heat protection technical field, by the residual carbon rate of material and the pyrolysis degree data of temperature variation obtained from thermogravimetric test result;By the volume fraction of each component of material, the volume fraction of each component corresponding to different pyrolysis degree is obtained using pyrolysis degree conversion;Parallel model is used to calculate the change of elastic modulus with pyrolysis degree;Based on the volume fraction of each component with pyrolysis degree, the distribution of mesoscopic size and elastic modulus, establish mesoscopic unit cell model under different pyrolysis degree;For the established unit cell model, load displacement boundary condition and periodic boundary condition, the equivalent elastic modulus of material is obtained;Combined with the pyrolysis degree variation data of material with temperature variation, the elastic modulus of material corresponding to different temperature or pyrolysis degree is obtained, solve the problem that the mechanical property parameters of different stages of pyrolysis process of resin-based heat protection material cannot be effectively predicted in prior art.

Description

TECHNICAL FIELD

[0001] The application relates to a material mechanical property prediction method based on a microstructure unit cell model and belongs to the technical field of aircraft thermal protection. BACKGROUND

[0002] The development of the thermal protection technology of an aircraft has experienced several processes. Initially, heat sink type thermal protection is used to block heat by using the heat absorption of a metal heat sink. However, as the aerodynamic heating is severe, the heat sink type thermal protection cannot meet the requirements. Then, the ablation thermal protection is developed to absorb heat by using evaporation, melting, sublimation and chemical reaction of materials. The ablation thermal protection is widely applied to reentry satellites and spaceships due to its high thermal protection effect. The ablation thermal protection is simple in form, has good thermal protection effect and high reliability, and is still widely applied to return satellites, spaceships and other aircrafts. In order to improve the heat insulation effect while considering the thermal protection efficiency and mechanical properties, the resin-based thermal protection material developed at present is a composite material of various hollow microspheres, fibers and matrices, which can significantly reduce the thermal conductivity and density of the material without affecting the thermal protection effect and mechanical strength.

[0003] The mechanical properties of the current homogeneous material are relatively mature. The mechanical properties of the original material can be effectively predicted by using the mechanical property test method or the finite element calculation. The physical properties and material microstructure of the material change significantly at different stages of the pyrolysis process. The test research on the mechanical parameters such as the elastic modulus of the material in the pyrolysis process is relatively complex, and cannot achieve the purpose of quickly predicting the mechanical properties of the material. Most of the tests still focus on the physical property parameters of the original material and the material after complete carbonization, and the change of the mechanical properties of the material at different stages of the pyrolysis process is less studied. SUMMARY

[0004] The technical problem of the application is to overcome the shortcomings of the prior art, provide a material mechanical property prediction method based on a microstructure unit cell model, and solve the problem that the mechanical property parameters at different stages of the pyrolysis process of the resin-based thermal protection material cannot be effectively predicted in the prior art.

[0005] The technical solution of the application is as follows:

[0006] A material mechanical property prediction method based on a microstructure unit cell model comprises the following steps:

[0007] Performing a thermogravimetric test on the resin-based thermal protection material to obtain the pyrolysis degree and the carbon residue rate changing with temperature;

[0008] According to the volume fraction of each component of the resin-based thermal protection material and the carbon residue rate changing with temperature obtained by the thermogravimetric test, the volume fraction of each component changing with the pyrolysis degree is obtained;

[0009] For each component of the resin-based heat protection material, a parallel model is used to calculate the elastic modulus corresponding to different degrees of pyrolysis;

[0010] According to the volume fraction of each component changing with the degree of pyrolysis and the elastic modulus corresponding to different degrees of pyrolysis, and the distribution of the mesoscopic size, a mesoscopic mechanics unit cell model corresponding to different degrees of pyrolysis is established based on the finite element method;

[0011] The established unit cell model is divided into a body grid;

[0012] For the finite element model after the body grid division, displacement boundary conditions and periodic boundary conditions are applied, and the equivalent elastic modulus of the resin-based heat protection material corresponding to different degrees of pyrolysis is obtained by solving;

[0013] According to the degree of pyrolysis changing with temperature obtained by the thermogravimetric experiment and the equivalent elastic modulus of the resin-based heat protection material corresponding to different degrees of pyrolysis, the equivalent elastic modulus of the resin-based heat protection material corresponding to different temperatures is obtained.

[0014] In the above material mechanics property prediction method based on the microstructure unit cell model, the thermogravimetric experiment is performed on the resin-based heat protection material to obtain the degree of pyrolysis changing with temperature and the residual carbon rate as follows:

[0015]

[0016] Wherein, α(T) is the degree of pyrolysis changing with temperature, A is the residual carbon rate, m0 is the initial mass, m ∞ is the mass after pyrolysis, and m(T) is the mass changing with temperature during the pyrolysis process.

[0017] In the above material mechanics property prediction method based on the microstructure unit cell model, the volume fraction of each component changing with the degree of pyrolysis is obtained based on the volume fraction of each component of the resin-based heat protection material and the residual carbon rate obtained by the thermogravimetric experiment, including the volume fraction of the resin matrix and the pore changing with the degree of pyrolysis;

[0018] The volume fraction of the resin matrix changing with the degree of pyrolysis is expressed as follows:

[0019]

[0020] Wherein: B is the volume ratio, α is the degree of pyrolysis, m1 is the mass of the resin, ρ1 is the density, V1 is the volume, m2 is the mass after carbonization, m2=Am1, A is the residual carbon rate, ρ2 is the density, and V2 is the volume;

[0021] The volume fraction of the pore changing with the degree of pyrolysis is expressed as follows:

[0022]

[0023] wherein, is the hollow resin microsphere volume fraction, is the fiber volume fraction, is the glass microsphere volume fraction.

[0024] In the above material mechanical property prediction method based on the microstructure unit cell model, for each component of the resin-based heat-proof material, a parallel model is used to calculate the elastic modulus corresponding to different degrees of pyrolysis, including the elastic modulus of the hollow resin microsphere wall and the elastic modulus of the resin matrix:

[0025] The hollow resin microsphere wall will have pores during the carbonization process, and the material property parameters will change. The residual carbon of the resin matrix part of the hollow resin microsphere wall after carbonization is in parallel with the small pores formed, and the elastic modulus E ms is expressed as:

[0026] E ms = E0(1-α) + BαE c + (1-B)αE g

[0027] wherein E0is the thermal conductivity of the resin matrix, E c is the thermal conductivity after complete carbonization; E g is the elastic modulus of air, B is the volume ratio, and α is the degree of pyrolysis.

[0028] The elastic modulus E m of the resin matrix changes with the degree of pyrolysis and is expressed as:

[0029] E m = E0(1-α) + E c α.

[0030] In the above material mechanical property prediction method based on the microstructure unit cell model, the microstructure mechanical unit cell model corresponding to different degrees of pyrolysis is established based on the finite element method, including: according to the size distribution law of the hollow resin microspheres, the size distribution law of the hollow glass microspheres, the size distribution law of the fibers, and the volume fraction of each component changing with the degree of pyrolysis and the elastic modulus corresponding to different degrees of pyrolysis, a unit cell model is established.

[0031] In the above material mechanical property prediction method based on the microstructure unit cell model, the established unit cell model is divided into a body grid, and the grid size of the microstructure component is equal to 1 / 50-1 / 30 times the diameter of the microspheres; the control body is a cube, and the side length of the cube is greater than twenty times the average diameter of the microspheres.

[0032] In the above material mechanical property prediction method based on the microstructure unit cell model, the finite element model after body meshing is subjected to displacement boundary conditions and periodic boundary conditions, and is solved to obtain the equivalent elastic modulus corresponding to different pyrolysis degrees, including:

[0033] Periodic boundary conditions are loaded on the side edges:

[0034]

[0035] Displacement boundary conditions are loaded on the upper and lower surfaces:

[0036]

[0037] Where u1, u2, u4, u5 respectively represent the displacement of the corresponding vertex of the control body along the x direction, v1, v4, v2, v5 respectively represent the displacement of the corresponding vertex of the control body along the y direction, w1, w2, w4, w5 respectively represent the displacement of the corresponding vertex of the control body along the z direction, u x1 , v x1 , w x1 respectively represent the displacement of each point on the plane x=0 along the x, y, z directions, u x2 , v x2 , w x2 respectively represent the displacement of each point on the plane x=L along the x, y, z directions, u y1 , v y1 , w y1 respectively represent the displacement of each point on the plane y=0 along the x, y, z directions, u y2 , v y2 , w y2 respectively represent the displacement of each point on the plane y=L along the x, y, z directions, u z1 , v z1 , w z1 respectively represent the displacement of each point on the plane z=0 along the x, y, z directions, u z2 , v z2 , w z2 respectively represent the displacement of each point on the plane z=L along the x, y, z directions.

[0038] The equivalent elastic modulus E corresponding to different pyrolysis degrees is represented as follows:

[0039]

[0040] Where F is the normal force of the cross section, S is the cross-sectional area of the control body, L is the side length of the control body, and Δl is the axial deformation.

[0041] In the material mechanical property prediction method based on the microstructure unit cell model, the pyrolysis degree and the equivalent elastic modulus E(alpha) corresponding to different pyrolysis degrees are obtained according to the pyrolysis degree alpha(T) changing with temperature and the equivalent elastic modulus E(alpha) corresponding to different pyrolysis degrees obtained by the thermogravimetric test.

[0042] A material mechanical property prediction system based on a microstructure unit cell model, comprising:

[0043] A pyrolysis degree and residual carbon rate acquisition module, performing a thermogravimetric test on a resin-based heat protection material to obtain a pyrolysis degree and a residual carbon rate changing with temperature;

[0044] A volume fraction acquisition module, obtaining a volume fraction of each component of the resin-based heat protection material changing with the pyrolysis degree according to the volume fraction of each component of the resin-based heat protection material and the residual carbon rate changing with temperature obtained by the thermogravimetric test;

[0045] An elastic modulus acquisition module, calculating an elastic modulus corresponding to different pyrolysis degrees for each component of the resin-based heat protection material by using a parallel model;

[0046] A unit cell model acquisition module, establishing a mesoscopic mechanical unit cell model corresponding to different pyrolysis degrees based on a finite element method according to the volume fraction of each component changing with the pyrolysis degree and the elastic modulus corresponding to different pyrolysis degrees, and a mesoscopic size distribution;

[0047] A mesh division module, dividing the established unit cell model into a body mesh;

[0048] A first equivalent elastic modulus acquisition module, applying a displacement boundary condition and a periodic boundary condition to the finite element model after the body mesh division to obtain an equivalent elastic modulus of the resin-based heat protection material corresponding to different pyrolysis degrees by solving;

[0049] A second equivalent elastic modulus acquisition module, obtaining an equivalent elastic modulus of the resin-based heat protection material corresponding to different temperatures according to the pyrolysis degree changing with temperature obtained by the thermogravimetric test and the equivalent elastic modulus of the resin-based heat protection material corresponding to different pyrolysis degrees.

[0050] A computer program product, comprising a computer program, which, when executed by a processor, implements the steps of the above method.

[0051] Compared with the prior art, the present application at least has the following beneficial effects:

[0052] (1) The embodiment of the present application provides a material mechanical property prediction method based on a microstructure unit cell model, wherein a residual carbon rate and pyrolysis degree data changing with temperature of a material are obtained from a thermogravimetric test result; volume fractions of each component of the material are used to obtain volume fractions of each component corresponding to different pyrolysis degrees by using pyrolysis degree conversion; parallel model calculation is used to obtain changes of elastic modulus of phenolic hollow microspheres and a resin matrix with pyrolysis degree; based on the volume fractions of each component changing with pyrolysis degree, the micro size distribution and the elastic modulus, a micro cell model is established at different pyrolysis degrees; for the established cell model, displacement boundary conditions and periodic boundary conditions are loaded, and the equivalent elastic modulus of the material is obtained; in combination with the test data of the material pyrolysis degree changing with temperature, the elastic modulus of the material corresponding to different temperatures or pyrolysis degrees is obtained, and the problem that the mechanical property parameters of the resin-based heat-proof material at different stages of the pyrolysis process cannot be effectively predicted in the prior art is solved.

[0053] (2) The embodiment of the present application aims at the problem that in the mechanical property calculation model of the resin-based heat-proof material, the mechanical properties at different stages of pyrolysis are obtained by heating the material to a certain temperature and then cooling, and then testing the mechanical properties, so that the mechanical property parameters at different stages of pyrolysis cannot be obtained. Based on this, the present application combines thermogravimetric test, micro parameter analysis and finite element modeling to predict the elastic modulus of the resin-based heat-proof material at different stages of the pyrolysis process, and solves the problem that the mechanical parameters of the resin-based heat-proof material at different stages of the pyrolysis process cannot be effectively predicted in the prior art. BRIEF DESCRIPTION OF DRAWINGS

[0054] Figure 1 The step flow chart of the material mechanical property prediction method based on the microstructure unit cell model in the embodiment of the present application is shown in the figure;

[0055] Figure 2 The finite element model in the embodiment of the present application is shown in the figure;

[0056] Figure 3 The schematic diagram of the mechanical cell boundary condition in the embodiment of the present application is shown in the figure;

[0057] Figure 4 The deformation cloud chart at 573K temperature in the embodiment of the present application is shown in the figure;

[0058] Figure 5 The stress cloud chart at 573K temperature in the embodiment of the present application is shown in the figure;

[0059] Figure 6 The figure of the material elastic modulus changing with temperature in the embodiment of the present application is shown in the figure. DETAILED DESCRIPTION

[0060] The present application will be further described in detail in combination with the drawings and specific embodiments:

[0061] like Figure 1 As shown, the material mechanical property prediction method based on the microstructure unit cell model in this embodiment of the invention includes the following steps:

[0062] Step 1: Conduct thermogravimetric analysis on the resin-based heat-resistant material to obtain the degree of pyrolysis and residual carbon rate as a function of temperature. For example, phenolic resin is used as an example in this embodiment.

[0063] In this embodiment of the invention, a thermogravimetric analysis was conducted on the resin-based heat-resistant material to obtain the degree of pyrolysis and residual carbon content as a function of temperature, including the initial mass m0 and the mass m after pyrolysis. ∞ The change in mass with temperature during pyrolysis is m(T), therefore the change in degree of pyrolysis with temperature is:

[0064]

[0065] Residual carbon content:

[0066]

[0067] Where α(T) is the degree of pyrolysis as a function of temperature, and A is the residual carbon content.

[0068] Step 2: Based on the volume fraction of each component of the resin-based heat-resistant material and the residual carbon rate of the resin components as a function of temperature obtained from thermogravimetric analysis, obtain the volume fraction of each component as a function of pyrolysis, including the volume fraction of the resin matrix and pores as a function of pyrolysis. For example, phenolic resin is used as an example in this embodiment.

[0069] In this embodiment of the invention, the mass of the resin is m1, the density is ρ1, and the volume is V1. The mass of the carbonized resin is m2, the density is ρ2, and the volume is V2. From the residual char rate, m2 = A·m1, and the volume ratio is:

[0070]

[0071] Volume fraction of resin matrix as a function of pyrolysis degree Represented as:

[0072]

[0073] Volume fraction of pores as a function of pyrolysis degree Represented as:

[0074] in, This represents the volume fraction of the resin matrix. This represents the volume fraction of hollow resin microspheres. This represents the fiber volume fraction. The volume fraction of the glass microspheres is denoted as .

[0075] Step three, for each component of the resin-based heat-resistant material, the elastic modulus corresponding to different degrees of pyrolysis is calculated by using a parallel model, including the elastic modulus of the hollow resin microsphere wall and the elastic modulus of the resin matrix, for example, in this embodiment, taking phenolic resin as an example.

[0076] In the embodiment of the application, after carbonization, the volume of the hollow glass microspheres and the volume fraction of the hollow phenolic microspheres remain unchanged, but small pores will be formed in the microsphere wall during the carbonization process, so the material property parameters will change. The microsphere wall is a phenolic resin matrix, and the residual carbon in the resin matrix part of the microsphere wall after carbonization is connected in parallel with the small pores formed, and the elastic modulus E ms of the microsphere wall is:

[0077] E ms = E0(1-α) + BαE c +(1-B)αE g

[0078] Wherein, E0 is the thermal conductivity of the resin matrix, E c is the thermal conductivity after complete carbonization, E g is the elastic modulus of air, B is the volume ratio, and α is the degree of pyrolysis.

[0079] For the resin matrix, the elastic modulus E m changes with the degree of pyrolysis α and is expressed as:

[0080] E m = E0(1-α) + E c α

[0081] Step four, according to the volume fraction of each component changing with the degree of pyrolysis and the elastic modulus corresponding to different degrees of pyrolysis, and the micro-size distribution, a micro-mechanical unit cell model corresponding to different degrees of pyrolysis is established based on the finite element method, for example, in this embodiment, taking phenolic resin as an example.

[0082] In the embodiment of the application, according to the size distribution law of the hollow phenolic microspheres, the size distribution law of the hollow glass microspheres, the size distribution law of the fibers, and the volume fraction of each component changing with the degree of pyrolysis and the elastic modulus corresponding to different degrees of pyrolysis, a unit cell model is established, as shown in Figure 2 .

[0083] Step five, the established unit cell model is divided into a body grid, for example, in this embodiment, taking phenolic resin as an example.

[0084] In the embodiment of the application, the control body is used to simulate the resin-based heat-resistant material. The control body is a cube, and the side length of the cube is greater than twenty times the diameter of the pores, and the grid size of the microstructure component is equal to 1 / 50-1 / 30 times the diameter of the microspheres.

[0085] Step 6: Apply displacement boundary conditions and periodic boundary conditions to the finite element model after volume mesh generation in Step 5, and perform post-processing to obtain the equivalent elastic modulus corresponding to different degrees of pyrolysis.

[0086] like Figure 3 As shown, in this embodiment of the invention, since the air inside the pores does not transmit mechanical loads, its stiffness effect is ignored. Periodic boundary conditions are applied to the sides:

[0087]

[0088] Displacement boundary conditions applied to the upper and lower surfaces:

[0089]

[0090] Where u1, u2, u4, and u5 represent the appendix, respectively. Figure 2 The displacements of the corresponding vertices of the central control volume along the x-direction, v1, v4, v2, and v5 respectively represent the displacements of the adjacent vertices. Figure 2 The displacements w1, w2, w4, and w5 of the corresponding vertices of the central control volume along the y-direction represent the attached... Figure 2 The displacement of the corresponding vertex of the control volume along the z-direction, u x1 v x1 w x1 Let u represent the displacements of points on the plane where x = 0 along the x, y, and z directions, respectively. x2 v x2 w x2 Let u represent the displacements of points on the plane x = L along the x, y, and z directions, respectively. y1 v y1 w y1 Let u represent the displacements of points on the plane where y = 0 along the x, y, and z directions, respectively. y2 v y2 w y2 Let u represent the displacements of points on the plane y = L along the x, y, and z directions, respectively. z1 v z1 w z1 Let u represent the displacements of points on the plane where z = 0 along the x, y, and z directions, respectively. z2 v z2 w z2 These represent the displacements of points on the plane z = L along the x, y, and z directions, respectively.

[0091] like Figure 4 , Figure 5 The figures shown are deformation cloud diagrams and stress cloud diagrams at a temperature of 573K in an embodiment of the present invention.

[0092] The equivalent elastic modulus E corresponding to different degrees of pyrolysis is expressed as follows:

[0093]

[0094] In the formula, F is the cross-sectional normal force, S is the cross-sectional area, L is the side length, and Δl is the axial deformation, the equivalent elastic modulus of the material at different pyrolysis degrees is calculated by the formula, and the equivalent elastic modulus at different temperatures is obtained in combination with the change relationship of the pyrolysis degree with the temperature in step one.

[0095] Step seven, the equivalent elastic modulus E(T) of the resin-based heat-proof material at different temperatures is obtained according to the pyrolysis degree α(T) changing with the temperature obtained by the thermogravimetric test and the equivalent elastic modulus E(α) of the resin-based heat-proof material corresponding to different pyrolysis degrees, as shown in the following formula. Figure 6

[0096] The application further provides a material mechanical property prediction system based on a microstructure unit cell model, comprising:

[0097] A pyrolysis degree and residual carbon rate acquisition module performs a thermogravimetric test on the resin-based heat-proof material to obtain a pyrolysis degree and a residual carbon rate changing with the temperature;

[0098] A volume fraction acquisition module obtains the volume fraction of each component of the resin-based heat-proof material changing with the pyrolysis degree according to the volume fraction of each component of the resin-based heat-proof material and the residual carbon rate changing with the temperature obtained by the thermogravimetric test;

[0099] An elastic modulus acquisition module calculates the elastic modulus corresponding to different pyrolysis degrees for each component of the resin-based heat-proof material by using a parallel model;

[0100] A unit cell model acquisition module establishes a mesoscopic mechanical unit cell model corresponding to different pyrolysis degrees based on a finite element method according to the volume fraction of each component changing with the pyrolysis degree and the elastic modulus corresponding to different pyrolysis degrees and the mesoscopic size distribution;

[0101] A mesh division module divides the established unit cell model into a body mesh;

[0102] A first equivalent elastic modulus acquisition module applies displacement boundary conditions and periodic boundary conditions to the finite element model after the body mesh division to obtain the equivalent elastic modulus of the resin-based heat-proof material corresponding to different pyrolysis degrees by solving;

[0103] A second equivalent elastic modulus acquisition module obtains the equivalent elastic modulus of the resin-based heat-proof material at different temperatures according to the pyrolysis degree changing with the temperature obtained by the thermogravimetric test and the equivalent elastic modulus of the resin-based heat-proof material corresponding to different pyrolysis degrees.

[0104] The application further provides a computer program product comprising a computer program, which, when executed by a processor, implements the steps of the above method.

[0105] ​The application is based on the application requirement and present situation of resin-based heat-proof materials, and aims at the deficiency in the calculation of mechanical properties in different pyrolysis stages of the resin-based heat-proof materials, and combines with the microstructure characteristics of the heat-proof materials, and proposes a material mechanical property prediction method of resin-based materials based on the microstructure unit cell model. The analysis object of the application is the resin-based heat-proof material, the inner surface of which is fixedly installed on the aircraft skin, the outer surface of which is in contact with the atmosphere, and the resin material is between the inner surface and the outer surface, and there are pores, fibers, hollow phenolic microspheres and hollow glass microspheres in the resin material. Firstly, the thermogravimetric test is carried out on the resin-based heat-proof material to obtain the relationship between the degree of pyrolysis and the temperature and the carbon residue rate of the resin; then, the volume percentage of each component in the pyrolysis process is calculated based on the pyrolysis carbon residue rate and the volume percentage of each component of the material, and the elastic modulus of the resin component is calculated by using the parallel model under different degrees of pyrolysis; finally, based on the component volume fraction corresponding to different degrees of pyrolysis, the elastic modulus and the micro-size distribution law, the finite element unit cell model is established, the body grid is divided, the displacement boundary condition and the periodic boundary condition are loaded, and the equivalent elastic modulus is solved.

[0106] The above is only the best specific embodiment of the application, but the protection scope of the application is not limited to this, any person skilled in the art can easily think of the changes or replacements within the technical range disclosed by the application, which should be covered in the protection scope of the application.

[0107] The contents not described in detail in the specification of the application belong to the known technology of the person skilled in the art.

Claims

1. A method for predicting mechanical properties of a material based on a microstructure unit cell model, characterized by, The method comprises the following steps: The thermal gravimetric test is performed on the resin-based heat protection material to obtain the pyrolysis degree and the residual carbon rate varying with temperature; The volume fraction of each component varying with the pyrolysis degree is obtained according to the volume fraction of each component of the resin-based heat protection material and the residual carbon rate obtained by the thermal gravimetric test; The elastic modulus corresponding to different pyrolysis degrees is calculated for each component of the resin-based heat protection material by using a parallel model; The mesoscopic mechanical unit cell model corresponding to different pyrolysis degrees is established based on the finite element method according to the volume fraction of each component varying with the pyrolysis degree, the elastic modulus corresponding to different pyrolysis degrees and the mesoscopic size distribution; The established unit cell model is divided into volume grids, and the grid size of the microstructure component is equal to 1 / 50-1 / 30 times the diameter of the microsphere. The finite element model after the volume grid division is subjected to displacement boundary conditions and periodic boundary conditions, and is solved to obtain the equivalent elastic modulus of the resin-based heat protection material corresponding to different pyrolysis degrees. The equivalent elastic modulus of the resin-based heat protection material at different temperatures is obtained according to the pyrolysis degree varying with temperature obtained by the thermal gravimetric test and the equivalent elastic modulus of the resin-based heat protection material corresponding to different pyrolysis degrees. 2.The method of claim 1, wherein, The thermal gravimetric test is performed on the resin-based heat protection material to obtain the pyrolysis degree and the residual carbon rate varying with temperature as follows: where a(T) is the degree of pyrolysis as a function of temperature, A is the residual carbon yield, m0is the initial mass, m ∞ is the mass after pyrolysis, and m(T) is the mass as a function of temperature during pyrolysis. 3.The method of claim 1, wherein, The volume fraction of each component varying with the pyrolysis degree is obtained according to the volume fraction of each component of the resin-based heat protection material and the residual carbon rate obtained by the thermal gravimetric test, including the volume fraction of the resin matrix and the pore varying with the pyrolysis degree; Volume fraction of resin matrix as a function of pyrolysis degree is represented as follows: Wherein: B is the volume ratio, α is the pyrolysis degree, m1 is the mass of the resin, ρ1 is the density, V1 is the volume, m2 is the mass after carbonization, m2=A·m1, A is the residual carbon rate, ρ2 is the density, V2 is the volume; Volume fraction of pores as a function of pyrolysis degree is represented as follows: wherein, is the volume fraction of hollow resin microspheres, is the volume fraction of fibers, is the volume fraction of glass microspheres. 4.The method of claim 1, wherein, The elastic modulus corresponding to different pyrolysis degrees is calculated for each component of the resin-based heat protection material by using a parallel model, including the elastic modulus of the hollow resin microsphere wall and the elastic modulus of the resin matrix: The hollow resin microsphere wall will have pores during the carbonization process, and the base material parameters will change. The residual carbon of the resin matrix part of the hollow resin microsphere wall after carbonization is connected in parallel with the small pores formed, and the elastic modulus E of the hollow resin microsphere wall is represented as: ms is represented as: E ms = E0(1 - a) + B a E c + (1 - B) a E g where E0is the thermal conductivity of the resin matrix, E c Thermal conductivity after complete carbonization; E g Elastic modulus for air, B is the volume ratio, and a is the degree of pyrolysis; Elastic modulus E of the resin matrix m expressed as a function of the degree of pyrolysis: E m = E0(1 - a) + E c a. 5.The method for predicting material mechanical properties based on a microstructure unit cell model according to claim 1, characterized in that, The mesoscopic mechanical unit cell model corresponding to different pyrolysis degrees is established based on the finite element method according to the size distribution of the hollow resin microsphere, the size distribution of the hollow glass microsphere, the size distribution of the fiber, and the volume fraction of each component varying with the pyrolysis degree and the elastic modulus corresponding to different pyrolysis degrees. 6.The method of predicting material mechanical properties based on a microstructure unit cell model according to claim 1, wherein, The established unit cell model is divided into volume grids, and the grid size of the microstructure component is equal to 1 / 50-1 / 30 times the diameter of the microsphere; the control body is a cube, and the side length of the cube is greater than twenty times the average diameter of the microsphere. 7.The method of claim 1, wherein, The finite element model after the volume grid division is subjected to displacement boundary conditions and periodic boundary conditions, and is solved to obtain the equivalent elastic modulus corresponding to different pyrolysis degrees, including: Periodic boundary conditions are loaded on the side edges: Displacement boundary conditions are loaded on the upper and lower surfaces: wherein u1, u2, u4, u5 represent the displacement of the corresponding vertex of the control body along the x direction, v1, v4, v2, v5 represent the displacement of the corresponding vertex of the control body along the y direction, w1, w2, w4, w5 represent the displacement of the corresponding vertex of the control body along the z direction, respectively, u x1 , v x1 , w x1 represent the displacement of the points on the plane of x=0 along the x, y, z directions, respectively, u x2 , v x2 , w x2 represent the displacement of the points on the plane of x=L along the x, y, z directions, respectively, u y1 , v y1 , w y1 represent the displacement of the points on the plane of y=0 along the x, y, z directions, respectively, u y2 , v y2 , w y2 represent the displacement of the points on the plane of y=L along the x, y, z directions, respectively, u z1 , v z1 , w z1 represent the displacement of the points on the plane of z=0 along the x, y, z directions, respectively, u z2 , v z2 , w z2 represent the displacement of the points on the plane of z=L along the x, y, z directions, respectively. The equivalent elastic modulus E corresponding to different pyrolysis degrees is represented as follows: Wherein, F is the cross-sectional normal force, S is the control body cross-sectional area, L is the control body side length, and Δl is the axial deformation. 8.The method of claim 1, wherein, The equivalent elastic modulus E(T) of the resin-based heat protection material at different temperatures is obtained according to the pyrolysis degree α(T) varying with temperature obtained by the thermal gravimetric test and the equivalent elastic modulus E(α) of the resin-based heat protection material corresponding to different pyrolysis degrees.

9. A microstructure unit cell model based material mechanical property prediction system, characterized in that, The method comprises the following steps: The pyrolysis degree and residual carbon rate obtaining module obtains the pyrolysis degree and residual carbon rate varying with temperature by performing a thermogravimetric test on the resin-based heat protection material; The volume fraction obtaining module obtains the volume fraction of each component varying with the pyrolysis degree according to the volume fraction of each component of the resin-based heat protection material and the residual carbon rate varying with temperature obtained by the thermogravimetric test; The elastic modulus obtaining module calculates the elastic modulus corresponding to different pyrolysis degrees for each component of the resin-based heat protection material by using a parallel model; The unit cell model obtaining module establishes a micromechanics unit cell model corresponding to different pyrolysis degrees based on a finite element method according to the volume fraction of each component varying with the pyrolysis degree and the elastic modulus corresponding to different pyrolysis degrees and the micro-size distribution; The mesh division module divides the established unit cell model into a body mesh; The first equivalent elastic modulus obtaining module applies displacement boundary conditions and periodic boundary conditions to the finite element model after the body mesh division and solves to obtain the equivalent elastic modulus of the resin-based heat protection material corresponding to different pyrolysis degrees; The second equivalent elastic modulus obtaining module obtains the equivalent elastic modulus of the resin-based heat protection material at different temperatures according to the pyrolysis degree varying with temperature obtained by the thermogravimetric test and the equivalent elastic modulus of the resin-based heat protection material corresponding to different pyrolysis degrees.

10. A computer program product comprising a computer program, characterized in that, The computer program is executed by a processor to realize the steps of the method of claim 1. The computer program is executed by a processor to realize the steps of the method of claim 1.

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