Nano-micro-macro pore structure modeling and pyrolysis gas mass flow rate calculation method

Abstract

The invention discloses a nano-micro-macro pore structure modeling and pyrolysis gas mass flow rate calculation method, and relates to the technical field of thermal protection material performance evaluation. The method comprises the following steps: preparing a resin-based heat-proof material; carrying out an ablation test on the resin-based heat-proof material; establishing a nano-micro-macro multi-scale pore structure model of the resin-based heat-proof material containing pores of a carbonization area, a pyrolysis area and an original material area; and calculating the mass flow rate of the pyrolysis gas of the nano-micro-macroscopic multi-scale pore structure model based on the internal mass conservation, energy conservation and pyrolysis gas generation and diffusion rules of the resin-based heat-proof material. According to the method, the generation amount of the gas in the pyrolysis process of the resin-based heat-proof material is accurately calculated by establishing the nano-micro-macro multi-scale pore structure model, the blank in the prior art is filled, and a new thought is provided for design and optimization of the heat-proof material.

Description

Technical Field

[0001] The present invention relates to the technical field of thermal protection material performance evaluation, and in particular to a method for nano-micro-macro pore structure modeling and pyrolysis gas mass flow rate calculation. Background Art

[0002] The resin matrix inside the resin-based heat-resistant material will undergo thermal decomposition reaction under high temperature environment, and absorb a large amount of heat through its own pyrolysis. The physical and chemical changes in the pyrolysis process include: melting, gasification, sublimation, pyrolysis, and oxidation of silicone resin; cracking of organic matter; decomposition of inorganic matter and its reaction with products; combustion of charcoal of silicone pyrolysis products, etc. Under extreme environments, the pore structure inside the heat-resistant material will evolve with the changes of temperature, pressure, time and other factors. According to the degree of pyrolysis reaction of the resin, the material can be divided into three regions along the thickness direction, namely, carbonization zone, pyrolysis zone and original material zone. The different degrees of pyrolysis make the microstructure of each region have great differences. The carbonization zone where the pyrolysis reaction is basically completed has a loose structure and defects such as cracks and pores will appear; holes of different sizes appear on the undecomposed phenolic resin matrix in the pyrolysis zone; the original material zone maintains the original structural form of the composite material, and there are also micro-nano pores of different scales inside the material. The performance of heat-resistant materials is closely related to their internal pore structure. The distribution and evolution of pore structure at nano, micro and macro scales directly affect the key properties of materials such as thermal conductivity, mechanical strength and thermal expansion coefficient. The pyrolysis of materials will produce a large amount of pyrolysis gas, which flows in the pores. As the pyrolysis gas gathers, the gas pressure inside the material rises. When the internal pressure is greater than the external environment pressure, the pyrolysis gas will overflow the surface along the complex pore structure inside the material. In this process, pore structures of different scales will have a certain impact on the generation and flow of pyrolysis gas. During the flow of pyrolysis gas inside the heat-resistant material, convection heat transfer and diffusion heat transfer will occur between the pyrolysis gas and the internal pore structure wall. Therefore, accurately establishing a model of the multi-scale pore structure inside the resin-based heat-resistant material under extreme environment and calculating the amount of pyrolysis gas generated in the pore structure model can provide a basis for the analysis of the flow law of pyrolysis gas inside the multi-scale pore structure, which is the basis and prerequisite for evaluating the ablation / thermal response characteristics of resin-based heat-resistant materials.

[0003] Existing research on resin-based heat-resistant materials mainly focuses on thermal stability and mechanical properties, but the evolution mechanism of the internal pore structure under extreme environments is not studied in depth. Moreover, the pore structure analysis methods are mostly limited to a single scale, which makes it difficult to fully reflect the complexity and dynamic evolution of the internal pore structure of the material. In addition, most of the current calculations of pyrolysis gas mass flow rate are based on equivalent porosity, and a true pore structure geometric model has not been established, which makes the calculation of gas mass flow rate inaccurate, which is not conducive to the subsequent analysis of pyrolysis gas flow law and the analysis of microscopic ablation / thermal response characteristics of resin-based heat-resistant materials.

[0004] In summary, there is currently a lack of a method that can effectively couple the establishment of nano-, micron- and macro-scale pore structure models and the calculation of the internal pyrolysis gas mass flow rate, so as to fully reveal the formation of the internal nano-micro-macro multi-scale pore structure of heat-resistant materials under extreme environments and the generation rules of pyrolysis gases. Summary of the invention

[0005] In view of the deficiencies in the above-mentioned background technology, the present invention mainly solves the problem that the existing pore structure analysis method cannot simultaneously couple the nano, micron and macro scales and the pyrolysis gas mass flow rate calculation is based on the equivalent porosity.

[0006] The present invention provides a nano-micro-macro pore structure modeling and pyrolysis gas mass flow rate calculation method. The method can effectively reveal the formation and evolution law of the internal pore structure of heat-proof materials under extreme environments, determine the difference in the internal pore structure of completely carbonized, partially carbonized, and uncarbonized heat-proof materials, clarify the relationship between the carbonization degree of heat-proof materials and the microstructure morphology and temperature, establish a nano-micro-macro multi-scale pore structure model of resin-based heat-proof materials containing pores in carbonized areas, pyrolysis areas, and original material areas, accurately calculate the amount of gas generated during the pyrolysis of resin-based heat-proof materials, fill the gap in the prior art, and provide new ideas for the design and optimization of heat-proof materials.

[0007] The present invention aims to provide a method for nano-micro-macro pore structure modeling and pyrolysis gas mass flow rate calculation, comprising: Preparation of resin-based heat-resistant materials; Conducting ablation test on resin-based heat-resistant materials, obtaining a specimen after ablation, and dividing the specimen after ablation into a carbonization zone and a pyrolysis zone; Mercury intrusion tests are performed on the ablated specimen and the specimen without ablation to obtain the pore structure parameters, mercury injection curves and pore size distribution curves corresponding to the ablated specimen and the specimen without ablation respectively; Obtain the millimeter-scale pore structure morphology inside the carbonization zone of the specimen after ablation, the micrometer-scale pore structure morphology inside the pyrolysis zone, and the nanometer-scale pore structure morphology inside the specimen without ablation; According to the pore structure parameters, mercury intrusion curves and pore size distribution curves corresponding to the ablated specimens and the unablated specimens, as well as the millimeter-scale pore structure morphology inside the carbonization zone of the ablated specimens, the micrometer-scale pore structure morphology inside the pyrolysis zone, and the nanometer-scale pore structure morphology inside the unablated specimens, a nano-micro-macro multi-scale pore structure model of the resin-based heat-resistant material containing pores in the carbonization zone, pyrolysis zone and original material zone is established; A thermal load boundary is applied to the nano-micro-macro multiscale pore structure model. Based on the conservation of mass and energy inside the resin-based thermal protection material, as well as the generation and diffusion laws of pyrolysis gas, the mass flow rate of the pyrolysis gas in the nano-micro-macro multiscale pore structure model is calculated.

[0008] Preferably, the ablation test is an oxyacetylene flame ablation test, and the thermal environment condition is 1.0~2.0MW / m 2 Ablation was performed for 100 to 300 seconds under heat flow conditions.

[0009] Preferably, the carbonization zone and the pyrolysis zone are divided according to the macroscopic morphology in the thickness direction of the specimen after ablation and the temperature at different positions.

[0010] Preferably, the millimeter-scale pore structure morphology inside the carbonization zone of the ablated specimen, the micrometer-scale pore structure morphology inside the pyrolysis zone, and the nanometer-scale pore structure morphology inside the unablated specimen are obtained according to the following steps: The ablated specimens and the unablated specimens were subjected to gold spraying treatment respectively; SEM imaging tests were performed on the ablated specimens after gold spraying and the specimens without ablation. The overall fiber arrangement of the material was first observed, and then the typical pore structure inside the heat-resistant material was gradually enlarged to obtain SEM electron microscope images. The SEM electron microscope images were processed and analyzed to obtain the millimeter-scale pore structure morphology inside the carbonization zone of the specimen after ablation, the micron-scale pore structure morphology inside the pyrolysis zone, and the nanometer-scale pore structure morphology inside the specimen without ablation.

[0011] Preferably, the millimeter-scale, micrometer-scale and nanometer-scale pore structure morphologies are all based on electron microscope images, using arbitrary polygons to depict the pores on the electron microscope images, and measuring the length and width of the pores according to the scale given by the electron microscope images; wherein the SEM imaging test uses a field emission scanning electron microscope.

[0012] Preferably, the pore structure parameters include porosity, median pore diameter, and average pore diameter.

[0013] Preferably, the mercury intrusion test is performed using a mercury intrusion porosimeter.

[0014] Preferably, the resin-based heat-resistant material is obtained by impregnating a phenolic resin matrix into a 2D woven fiber skeleton, wherein the phenolic resin matrix is ​​prepared by a molding foaming process and contains a large number of micro-nano pores inside.

[0015] Preferably, the nano-micro-macro multi-scale pore structure model is obtained according to the following steps: Obtain the distribution of fibers inside the resin-based heat-resistant material and the size of the fiber bundles, and establish the fiber component phase of a specific weaving method; A complementary set of fiber phases is established according to the fiber component phases of a specific weaving method, that is, a matrix phase of the resin-based heat-resistant material, so that the fiber phase is wrapped inside the matrix phase; According to the pore structure parameters, mercury intrusion curves and pore size distribution curves corresponding to the ablated specimens and the unablated specimens respectively, as well as the millimeter-scale pore structure morphology inside the carbonization zone of the ablated specimens, the micron-scale pore structure morphology inside the pyrolysis zone, and the nanometer-scale pore structure morphology inside the unablated specimens, the random function method is used to arrange pores of different sizes and numbers in different areas of the matrix phase, thereby obtaining a nano-micro-macro multi-scale pore structure model of the resin-based heat-resistant material containing pores in the carbonization zone, pyrolysis zone and original material zone.

[0016] Preferably, the mass flow rate of the pyrolysis gas in the nano-micro-macro multi-scale pore structure model is calculated by the following formula:

[0017] in, and are the density of the material at any temperature and the density of the material after complete carbonization, A , E a and are the pre-exponential factor, activation energy and mechanism function of the material, R is the ideal gas constant, T is the temperature, S For the area.

[0018] Compared with the prior art, the present invention has the following beneficial effects: The present invention provides a method for modeling nano-micro-macroscopic pore structure and calculating the mass flow rate of pyrolysis gas. The present invention obtains carbonization zones, pyrolysis zones and original material zones of resin-based heat-resistant materials with different degrees of pyrolysis by conducting ablation tests; obtains macroscopic porosity, pore size distribution and other data of the material by conducting mercury injection tests on the heat-resistant materials before and after ablation; obtains millimeter-level pore structure morphology of the carbonization zone of the resin-based heat-resistant materials, micrometer-level pore structure morphology of the pyrolysis zone, and nanometer-level pore structure morphology of the original material zone by conducting SEM imaging tests on the carbonization zone, pyrolysis zone and original material zone; establishes a nano-micro-macroscopic multi-scale pore structure model of pores in the carbonization zone, pyrolysis zone and original material zone of the resin-based heat-resistant materials based on the porosity and pore structure micro-morphology obtained by the test; applies a heat load boundary to the model, and considers the conservation of mass, conservation of energy and the generation and diffusion laws of pyrolysis gas inside it, and calculates the mass flow rate of pyrolysis gas in the nano-micro-macroscopic multi-scale pore structure model. This method can effectively reveal the formation and evolution of the internal pore structure of heat-resistant materials under extreme environments, determine the differences in the internal pore structure of completely carbonized, partially carbonized, and uncarbonized heat-resistant materials, clarify the relationship between the carbonization degree of heat-resistant materials and the microstructure morphology and temperature, accurately calculate the amount of pyrolysis gas generated inside the heat-resistant materials, fill the gap in the existing technology, and provide new ideas for the design and optimization of heat-resistant materials. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Figure 1 A flow chart of the nano-micro-macro multi-scale pore structure modeling and the calculation method of the pyrolysis gas mass flow rate provided by the present invention.

[0020] Figure 2 The test pieces, test process and test results of the oxyacetylene ablation test; (a) is the test piece of the oxyacetylene ablation test, with a size of 30mm×30mm×15mm, (b) is the ablation process when the oxyacetylene flame reaches the surface of the test piece, (c) is the macroscopic morphology of the surface of the test piece after the ablation, and (d) is the macroscopic morphology of the side of the test piece after the ablation.

[0021] Figure 3 The mercury penetration curves and pore size distribution curves of the resin-based heat-resistant material before and after ablation; wherein, (a) is the mercury penetration curve of the original material, (b) is the pore size distribution curve of the original material, (c) is the mercury penetration curve of the material after ablation, and (d) is the pore size distribution curve of the material after ablation.

[0022] Figure 4 The figure shows the process of establishing the nano-micro-macro multi-scale pore structure model of resin-based heat-resistant materials; (a) is the fiber phase geometry model, (b) is the matrix geometry model without pores, (c) is the pore phase geometry model, and (d) is the matrix geometry model with pores.

[0023] Figure 5 Nano-micro-macro multi-scale pore structure model of resin-based thermal protection materials under a given heat flux density of 1.1 MW / m 2 The mass flow rate of pyrolysis gas. DETAILED DESCRIPTION

[0024] In order to enable those skilled in the art to better understand and implement the technical solution of the present invention, the present invention is further described below in conjunction with specific embodiments and drawings, but the embodiments are not intended to limit the present invention.

[0025] The purpose of the present invention is to provide a model that can accurately establish the nano-micro-macro multi-scale pore structure inside the heat-resistant material under extreme environment, and a method for calculating the mass flow rate of pyrolysis gas in the model, to determine the difference in the internal pore structure of completely carbonized, partially carbonized and uncarbonized heat-resistant materials, to clarify the relationship between the carbonization degree of the heat-resistant material and the microstructure morphology and temperature, to establish a nano-micro-macro multi-scale pore structure model of the pores of the carbonized zone, pyrolysis zone and original material zone of the resin-based heat-resistant material, to calculate the amount of gas generated during the pyrolysis of the resin-based heat-resistant material, to lay a theoretical foundation for the analysis and evaluation of the flow of pyrolysis gas of the resin-based heat-resistant material and the ablation / thermal response characteristics, and to have very important scientific significance.

[0026] To achieve the above purpose, see Figure 1 As shown, the present invention provides a nano-micro-macro pore structure modeling and pyrolysis gas mass flow rate calculation method, which is used to establish a nano-micro-macro multi-scale pore structure model of a resin-based heat-resistant material before and after ablation and calculate the pyrolysis gas mass flow rate in the structure model under the action of a thermal load environment, including: S1. preparing resin-based heat-resistant materials; The resin-based heat-resistant material is obtained by impregnating a phenolic resin matrix in a 2D woven fiber skeleton, wherein the phenolic resin matrix is ​​prepared by a molding foaming process and contains a large number of micro-nano pores inside.

[0027] In this embodiment, the fiber skeleton is prepared in a 2D plain weave manner, that is, each warp yarn and each weft yarn are interwoven with each other; the matrix is ​​prepared by a molded foaming process, and the resin sample and the foaming agent material are placed in a molded foaming device, and pressure is applied to the foaming agent, which will generate a large amount of gas and diffuse into the resin. When enough gas is dissolved in the resin, the pressure is quickly released, and a stereotyped micro-nanoporous resin matrix is ​​obtained after the sample is cooled; a resin-based heat-resistant composite material can be obtained by impregnating a micro-nanoporous resin matrix in a 2D woven fiber skeleton. The prepared resin-based heat-resistant material is processed into two cubes, one of which is kept in its original state, and the other needs to be subjected to an ablation test.

[0028] See also Figure 2As shown in (a), the original material of the resin-based heat-resistant material is processed into two cubes of 30mm×30mm×15mm.

[0029] One of the pieces was kept in its original state and cut into 15 mm × 15 mm × 15 mm cubes for mercury intrusion and SEM imaging tests of the original material.

[0030] The other specimen that needs to undergo ablation test is first subjected to an oxyacetylene flame ablation test, and thermocouples are inserted at different positions in the thickness direction in order to measure and record the temperature changes at different positions of the specimen during the ablation process.

[0031] S2. Perform an ablation test on the resin-based heat-resistant material to obtain a test piece after ablation, and divide the test piece after ablation into a carbonization zone and a pyrolysis zone; The ablation test is an oxyacetylene flame ablation test, and the thermal environment condition is 1.0~2.0MW / m 2 Ablation under heat flow conditions lasts 100~300s. Among them, under hot environment conditions, the 2 The ablation was carried out for 200 s under the heat flow condition, and the flow rates of oxygen and acetylene were 12.06 m 3 / h and 7.03m 3 / h. Under this experimental state, the surface temperature of the material increased rapidly and gradually stabilized at around 1460°C. The temperatures at other locations also showed a gradual increase. After the experiment, the temperatures at 6mm, 10mm and 15mm from the material surface were 990°C, 810°C and 636°C respectively.

[0032] The carbonization zone and the pyrolysis zone are divided according to the macroscopic morphology in the thickness direction of the specimen after ablation and the temperature at different positions.

[0033] See also Figure 2 As shown in (b), during the ablation test, the specimen is placed on the fixture of the oxyacetylene flame ablation platform, and the flow rates of oxygen and acetylene and the distance between the flame and the specimen are set so that the test heat flux is 1.1 MW / m 2 , ablation was carried out for 200s under this heat flow condition.

[0034] After the ablation test, see Figure 2As shown in (c) and (d), observing the macroscopic morphology of the specimen surface, i.e., the side, it can be found that the specimen surface is covered with a large amount of white material, which is the quartz fiber exposed after the resin ablation, and there is an obvious stratification phenomenon in the thickness direction. The upper layer is more obviously exposed with more cracks, and is relatively loose overall, while the lower layer is relatively flat, with more phenolic resin matrix, and is relatively dense overall. According to the macroscopic morphology of the side of the specimen and the temperature data measured by the thermocouple, the upper layer of the specimen after ablation can be defined as the carbonization zone, and the lower layer can be defined as the pyrolysis zone. The specimen after the ablation test was cut into 15mm×15mm×15mm cubes for subsequent mercury injection and SEM imaging tests.

[0035] S3, performing mercury intrusion tests on the ablated specimen and the specimen without ablation, respectively, to obtain the pore structure parameters, mercury injection curves, and pore size distribution curves corresponding to the ablated specimen and the specimen without ablation; The mercury intrusion test is carried out using a mercury intrusion instrument.

[0036] The pore structure parameters include porosity, median pore diameter, and average pore diameter.

[0037] In this embodiment, mercury injection tests are performed on the ablated specimens and the unablated specimens of the resin-based heat-resistant material to obtain their pore structure parameters such as porosity, intermediate pore size, average pore size, as well as the mercury injection curve and pore size distribution curve during the test.

[0038] Mercury intrusion tests were performed on the ablated specimen and the unablated specimen (15 mm × 15 mm × 15 mm) using a mercury intrusion instrument (AutoPore IV 9500 V1.09). The volume of mercury entering the specimen was recorded as the pressure increased and plotted as shown in the figure. Figure 3 (a) and Figure 3 In addition, the pore size distribution data obtained from the mercury injection experiment is plotted into a pore size distribution curve, such as Figure 3 (b) and Figure 3 By sorting the obtained pore diameter and pore volume data, the overall porosity of the original specimen of the resin-based heat-resistant material can be obtained, and the pore volume and pore area can be sorted by size, and the pore diameter corresponding to the median pore volume and pore area can be obtained.

[0039] It should be noted that, because the specimens after the ablation test are divided into a carbonization zone and a pyrolysis zone in the thickness direction, the mercury injection test is carried out on the specimens after the ablation test. Therefore, the mercury injection test measures the porosity of the carbonization zone and the pyrolysis zone as a whole.

[0040] S4, obtaining the millimeter-scale pore structure morphology inside the carbonization zone of the specimen after ablation, the micrometer-scale pore structure morphology inside the pyrolysis zone, and the nanometer-scale pore structure morphology inside the specimen without ablation; The millimeter-scale pore structure morphology inside the carbonized zone of the ablated specimen, the micrometer-scale pore structure morphology inside the pyrolysis zone, and the nanometer-scale pore structure morphology inside the unablated specimen are obtained according to the following steps: The ablated specimens and the unablated specimens were subjected to gold spraying treatment respectively; SEM imaging tests were performed on the ablated specimens after gold spraying and the specimens without ablation. The overall fiber arrangement of the material was first observed, and then the typical pore structure inside the heat-resistant material was gradually enlarged to obtain SEM electron microscope images. The SEM electron microscope images were processed and analyzed to obtain the millimeter-scale pore structure morphology inside the carbonization zone of the specimen after ablation, the micron-scale pore structure morphology inside the pyrolysis zone, and the nanometer-scale pore structure morphology inside the specimen without ablation.

[0041] Among them, the millimeter-level, micrometer-level and nanometer-level pore structure morphologies are all based on electron microscope images, using arbitrary polygons to depict the pores on the electron microscope images, and measuring the length and width of the pores according to the scale given by the electron microscope images; wherein the SEM imaging test uses a field emission scanning electron microscope.

[0042] In this embodiment, SEM imaging tests are performed on the specimens of the resin-based heat-resistant material after gold spraying and before and after ablation. The overall fiber arrangement of the material is first observed, and then the typical pore structure inside the heat-resistant material is gradually magnified to obtain its microscopic morphology.

[0043] Among them, a Sigma 300 field emission scanning electron microscope from the German ZEISS company was used to observe the morphology of the original specimens of the resin-based heat-resistant material and the carbonization zone and pyrolysis zone after ablation from the macro scale to the micro scale.

[0044] The test sample with a size of 15mm×15mm×15mm was placed on a copper plate with conductive glue, and tested after gold spraying for 180s. The test voltage was 10.00kV, and the magnification was from small to large, ranging from 200 to 10000 times. When the magnification is small, the overall morphology of the heat-resistant material and the distribution of the fibers inside the material can be observed. A larger magnification is used to observe the area where the matrix is ​​distributed in large quantities, and the typical pore area is gradually enlarged until the pores inside the material can be better imaged in the entire field of view, and this state is photographed.

[0045] In this embodiment, the obtained SEM electron microscope images are processed and analyzed to obtain the microscopic morphology of nanoscale pores inside the original specimen of the resin-based heat-resistant material, the microscopic morphology of millimeter-scale pores inside the carbonization zone of the resin-based heat-resistant material after ablation, and the microscopic morphology of micrometer-scale pores inside the pyrolysis zone.

[0046] The SEM electron microscope image is processed, the holes are marked in the image, and the diameter of the hole is measured according to the ruler in the electron microscope image.

[0047] By analyzing the microscopic morphology of the specimens after ablation and those without ablation, we can obtain the microscopic morphology of nanoscale pores inside the original specimens of the resin-based heat-resistant material, the microscopic morphology of micron-scale pores inside the pyrolysis zone, which are distributed in the pyrolysis layer in spherical and ellipsoidal shapes, with a diameter of about 50~100 microns and a relatively dense distribution. The microscopic morphology of millimeter-scale pores inside the carbonization zone, which are mainly distributed at the junction of the 0° and 90° fiber plies, grow along the fiber bundles perpendicular to the thickness direction, and are slender irregular geometric bodies with a length of about 1~3 mm and a thickness of 200~300 microns.

[0048] S5. According to the pore structure parameters, mercury intrusion curves and pore size distribution curves corresponding to the ablated specimen and the unablated specimen, respectively, as well as the millimeter-scale pore structure morphology inside the carbonization zone of the ablated specimen, the micrometer-scale pore structure morphology inside the pyrolysis zone, and the nanometer-scale pore structure morphology inside the unablated specimen, a nano-micro-macro multi-scale pore structure model of the resin-based heat-resistant material containing pores in the carbonization zone, pyrolysis zone and original material zone is established; Based on the pore structure morphology of each region, a nano-micro-macro multi-scale pore structure model of the resin-based heat-resistant material containing pores in the carbonization zone, pyrolysis zone and original material zone is established. Among them, the original material zone refers to the area of ​​the specimen that has not been ablated. It should be noted that the resin-based heat-resistant material is composed of three components: fiber, matrix and pores, and most of the pores are distributed inside the matrix.

[0049] The process of establishing the nano-micro-macro multi-scale pore structure model includes: Obtain the distribution of fibers inside the resin-based heat-resistant material and the size of the fiber bundles, and establish the fiber component phase of a specific weaving method; A complementary set of fiber phases is established according to the fiber component phases of a specific weaving method, that is, a matrix phase of the resin-based heat-resistant material, so that the fiber phase is wrapped inside the matrix phase; According to the pore structure parameters, mercury intrusion curves and pore size distribution curves corresponding to the ablated specimens and the unablated specimens respectively, as well as the millimeter-scale pore structure morphology inside the carbonization zone of the ablated specimens, the micron-scale pore structure morphology inside the pyrolysis zone, and the nanometer-scale pore structure morphology inside the unablated specimens, the random function method is used to arrange pores of different sizes and numbers in different areas of the matrix phase, thereby obtaining a nano-micro-macro multi-scale pore structure model of the resin-based heat-resistant material containing pores in the carbonization zone, pyrolysis zone and original material zone.

[0050] In this embodiment, the process of establishing the nano-micro-macro multi-scale pore structure model includes: Firstly, based on the distribution of fibers inside the material obtained by SEM imaging test and the size of the observed fiber bundles, the fiber component phase of 2D weaving is established, such as Figure 4 As shown in (a), the warp yarns and weft yarns are interwoven to form a 2D woven plain fabric, wherein the cross-section of the warp and weft yarns is elliptical, with a major semi-axis of 0.4 mm, a minor semi-axis of 0.1 mm, and a surface density of 6 yarns / cm.

[0051] Secondly, the complement of the fiber phase is established, that is, the resin-based heat-resistant material does not contain a matrix phase with pores, so that the fiber phase is wrapped inside the matrix phase, such as Figure 4 As shown in (b).

[0052] Finally, based on the porosity and pore size distribution obtained from the mercury injection test and the size morphology of the pore structure obtained from the SEM test, the random function method was used to arrange spherical pores of different sizes and numbers in different regions of the matrix phase, such as Figure 4 As shown in (c), by cutting off the intersection of the spherical pores and the matrix phase without pores, a nano-micro-macro multi-scale pore structure model of the resin-based heat-resistant material containing pores in the carbonization zone, pyrolysis zone and original material zone can be obtained, as shown in Figure 4 As shown in (d).

[0053] S6. Apply a thermal load boundary to the nano-micro-macro multi-scale pore structure model, and calculate the mass flow rate of the pyrolysis gas in the nano-micro-macro multi-scale pore structure model based on the conservation of mass and energy inside the resin-based heat-resistant material and the generation and diffusion laws of the pyrolysis gas.

[0054] The mass flow rate of pyrolysis gas in the nano-micro-macro multi-scale pore structure model is calculated by the following formula:

[0055] in, and are the density of the material at any temperature and the density of the material after complete carbonization; A , E a and They are the pre-exponential factor, activation energy and mechanism function of the material respectively; R is the ideal gas constant; T is temperature; S For the area.

[0056] In this embodiment, the phenolic resin matrix inside the resin-based heat-resistant material will undergo thermal decomposition under high temperature, generating a large amount of pyrolysis gas. The thermal load boundary condition is applied to the nano-micro-macro multi-scale pore structure model, and the upper surface is given a heat flux density of 1.1 MW / m 2, and all other surfaces are adiabatic boundaries. Assign the thermal decomposition equation to the matrix phase of the model , and obtain the thermal decomposition degree of the matrix The density of the matrix phase is obtained by changing the law of time and temperature. , as follows:

[0057] In addition, considering the mass conservation law of the solid phase and the gas phase, the internal energy conservation law, and the gas generation and diffusion law, the temperature at each position of the structural model under a given heat flux density is calculated. T By integrating the density change formula over the wall of the model pore structure, the mass flow rate of the pyrolysis gas inside the material during the heat flux density process can be calculated. .

[0058] Figure 5 Nano-micro-macro multi-scale pore structure model of resin-based thermal protection materials under a given heat flux density of 1.1 MW / m 2 The mass flow rate of the pyrolysis gas. Figure 5 It can be seen that the change of the mass flow rate of pyrolysis gas over time shows that in the initial stage of heating, the mass flow rate of pyrolysis gas is small, which means that the pyrolysis reaction of the material occurs very slowly when the temperature is low, and the amount of pyrolysis gas generated is very small. As the pyrolysis reaction continues, the generation rate of pyrolysis gas increases rapidly and reaches a peak value. When most areas of the test material are pyrolyzed, the pyrolysis rate of the material slows down and the mass flow rate of the pyrolysis gas decreases. The generation and flow of pyrolysis gas can consume part of the heat and reduce the heat entering the material, which is an important heat-insulating mechanism for heat-resistant materials.

[0059] The present invention provides a method for modeling nano-micro-macro multi-scale pore structure and calculating the mass flow rate of pyrolysis gas. By carrying out ablation test, the carbonization zone, pyrolysis zone and original material zone of the resin-based heat-resistant material with different degrees of pyrolysis are obtained; by carrying out mercury injection test on the heat-resistant material before and after ablation, the macroscopic porosity, pore size distribution and other data of the material are obtained; by carrying out SEM imaging test on the carbonization zone, pyrolysis zone and original material zone, the millimeter-level pore structure morphology of the carbonization zone of the resin-based heat-resistant material, the micron-level pore structure morphology of the pyrolysis zone, and the nanometer-level pore structure morphology of the original material zone are obtained; based on the porosity and pore structure microscopic morphology obtained by the experiment, a nano-micro-macro multi-scale pore structure model of the resin-based heat-resistant material containing pores in the carbonization zone, pyrolysis zone and original material zone is established; a heat load boundary is applied to the model, and considering the mass conservation, energy conservation and pyrolysis gas generation and diffusion law inside it, the mass flow rate of the pyrolysis gas of the nano-micro-macro multi-scale pore structure model is calculated. This method can effectively reveal the formation and evolution of the internal pore structure of heat-resistant materials under extreme environments, determine the differences in the internal pore structure of completely carbonized, partially carbonized, and uncarbonized heat-resistant materials, clarify the relationship between the carbonization degree and microstructure morphology and temperature of heat-resistant materials, and accurately calculate the amount of pyrolysis gas generated inside heat-resistant materials.

[0060] The above description is only a preferred specific implementation manner of the present invention, but the protection scope of the present invention is not limited thereto. Any technician familiar with the technical field can make equivalent replacements or changes according to the technical scheme and inventive concept of the present invention within the technical scope disclosed by the present invention, which should be covered by the protection scope of the present invention.

Claims

1. A method for nano-micro-macro pore structure modeling and pyrolysis gas mass flow rate calculation, characterized in that: include: Preparation of resin-based heat-resistant materials; Conducting ablation test on resin-based heat-resistant materials, obtaining a specimen after ablation, and dividing the specimen after ablation into a carbonization zone and a pyrolysis zone; Mercury intrusion tests are performed on the ablated specimen and the specimen without ablation to obtain the pore structure parameters, mercury injection curves and pore size distribution curves corresponding to the ablated specimen and the specimen without ablation respectively; Obtain the millimeter-scale pore structure morphology inside the carbonization zone of the specimen after ablation, the micrometer-scale pore structure morphology inside the pyrolysis zone, and the nanometer-scale pore structure morphology inside the specimen without ablation; According to the pore structure parameters, mercury intrusion curves and pore size distribution curves of the ablated specimens and the unablated specimens, as well as the millimeter-scale pore structure morphology inside the carbonization zone of the ablated specimens, the micrometer-scale pore structure morphology inside the pyrolysis zone, and the nanometer-scale pore structure morphology inside the unablated specimens, a nano-micro-macro multi-scale pore structure model of the resin-based heat-resistant material containing pores in the carbonization zone, pyrolysis zone and original material zone is established; A thermal load boundary is applied to the nano-micro-macro multiscale pore structure model. Based on the conservation of mass and energy inside the resin-based thermal protection material, as well as the generation and diffusion laws of pyrolysis gas, the mass flow rate of the pyrolysis gas in the nano-micro-macro multiscale pore structure model is calculated.

2. The method for nano-micro-macro pore structure modeling and pyrolysis gas mass flow rate calculation according to claim 1, characterized in that: The ablation test is an oxyacetylene flame ablation test, and the thermal environment condition is 1.0~2.0MW / m 2 Ablation was performed for 100 to 300 seconds under heat flow conditions.

3. The method for nano-micro-macro pore structure modeling and pyrolysis gas mass flow rate calculation according to claim 1, characterized in that: The carbonization zone and the pyrolysis zone are divided according to the macroscopic morphology in the thickness direction of the specimen after ablation and the temperature at different positions.

4. The method for nano-micro-macro pore structure modeling and pyrolysis gas mass flow rate calculation according to claim 1, characterized in that: The millimeter-scale pore structure morphology inside the carbonized zone of the ablated specimen, the micrometer-scale pore structure morphology inside the pyrolysis zone, and the nanometer-scale pore structure morphology inside the unablated specimen are obtained according to the following steps: The ablated specimens and the unablated specimens were subjected to gold spraying treatment respectively; SEM imaging tests were performed on the ablated specimens after gold spraying and the specimens without ablation. The overall fiber arrangement of the material was first observed, and then the typical pore structure inside the heat-resistant material was gradually enlarged to obtain SEM electron microscope images. The SEM electron microscope images were processed and analyzed to obtain the millimeter-scale pore structure morphology inside the carbonization zone of the specimen after ablation, the micron-scale pore structure morphology inside the pyrolysis zone, and the nanometer-scale pore structure morphology inside the specimen without ablation.

5. The method for nano-micro-macro pore structure modeling and pyrolysis gas mass flow rate calculation according to claim 4, characterized in that: The millimeter-scale, micrometer-scale and nanometer-scale pore structure morphologies are all based on electron microscope images, using arbitrary polygons to depict the pores on the electron microscope images, and measuring the length and width of the pores according to the scale given by the electron microscope images; wherein the SEM imaging test uses a field emission scanning electron microscope.

6. The method for nano-micro-macro pore structure modeling and pyrolysis gas mass flow rate calculation according to claim 1, characterized in that: The pore structure parameters include porosity, median pore diameter, and average pore diameter.

7. The method for nano-micro-macro pore structure modeling and pyrolysis gas mass flow rate calculation according to claim 1, characterized in that: The mercury intrusion test is carried out using a mercury intrusion instrument.

8. The method for nano-micro-macro pore structure modeling and pyrolysis gas mass flow rate calculation according to claim 1, characterized in that: The resin-based heat-resistant material is obtained by impregnating a phenolic resin matrix in a 2D woven fiber skeleton, wherein the phenolic resin matrix is ​​prepared by a molding foaming process and contains a large number of micro-nano pores inside.

9. The method for nano-micro-macro pore structure modeling and pyrolysis gas mass flow rate calculation according to claim 1, characterized in that: The nano-micro-macro multi-scale pore structure model is obtained according to the following steps: Obtain the distribution of fibers inside the resin-based heat-resistant material and the size of the fiber bundles, and establish the fiber component phase of a specific weaving method; A complementary set of fiber phases is established according to the fiber component phases of a specific weaving method, that is, a matrix phase of the resin-based heat-resistant material, so that the fiber phase is wrapped inside the matrix phase; According to the pore structure parameters, mercury intrusion curves and pore size distribution curves corresponding to the ablated specimens and the unablated specimens respectively, as well as the millimeter-scale pore structure morphology inside the carbonization zone of the ablated specimens, the micron-scale pore structure morphology inside the pyrolysis zone, and the nanometer-scale pore structure morphology inside the unablated specimens, the random function method is used to arrange pores of different sizes and numbers in different areas of the matrix phase, thereby obtaining a nano-micro-macro multi-scale pore structure model of the resin-based heat-resistant material containing pores in the carbonization zone, pyrolysis zone and original material zone.

10. The method for nano-micro-macro pore structure modeling and pyrolysis gas mass flow rate calculation according to claim 1, characterized in that: The mass flow rate of pyrolysis gas in the nano-micro-macro multi-scale pore structure model is calculated by the following formula: in, and are the density of the material at any temperature and the density of the material after complete carbonization; A , E a and They are the pre-exponential factor, activation energy and mechanism function of the material respectively; R is the ideal gas constant; T is temperature; S For the area.

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