Modeling of nano-micro-macro pore structures and calculation method of pyrolysis gas mass flow rate

Abstract

The present invention discloses a method for nano-micro-macro pore structure modeling and pyrolysis gas mass flow rate calculation, which relates to the technical field of thermal protection material performance evaluation. The method includes preparing a resin-based thermal protection material; conducting an ablation test on the resin-based thermal protection material; establishing a nano-micro-macro multi-scale pore structure model of the resin-based thermal protection material with pores in the carbonized zone, pyrolysis zone, and original material zone; and calculating the mass flow rate of pyrolysis gas in the nano-micro-macro multi-scale pore structure model based on the internal mass conservation, energy conservation, and pyrolysis gas generation and diffusion laws of the resin-based thermal protection material. By establishing a nano-micro-macro multi-scale pore structure model, the present invention accurately calculates the gas generation amount during the pyrolysis of the resin-based thermal protection material, fills the gap in the existing technology, and provides new ideas for the design and optimization of thermal protection materials.

Description

Technical Field

[0001] The present invention relates to the technical field of performance evaluation of thermal protection materials, and particularly relates to a method for modeling nano-micro-macro pore structures and calculating the mass flow rate of pyrolysis gas. Background Art

[0002] The resin matrix inside the resin-based thermal protection material will undergo a pyrolysis reaction under high-temperature environments, absorbing a large amount of heat through its own pyrolysis. The physical and chemical changes during its pyrolysis process include: melting and gasification, sublimation, pyrolysis, oxidation of silicone resin; cracking of organic substances; decomposition of inorganic substances and reactions between them and products; combustion of carbon produced by pyrolysis products of silicone. In extreme environments, the pore structure inside the thermal protection material will evolve with the changes of factors such as temperature, pressure, and time. According to the degree of pyrolysis reaction of the resin, the material can be divided into three regions along the thickness direction, namely the carbonization region, the pyrolysis region, and the original material region. The different degrees of pyrolysis result in significant differences in the microstructures of each region. In the carbonization region where the pyrolysis reaction is basically completed, the structure is loose, and defects such as crack pores will appear; pores of different sizes appear on the unfragmented phenolic resin matrix in the pyrolysis region; the original material region maintains the original structure form of the composite material, and there are also micro-nano pores of different scales inside the material. The performance of the thermal protection material is closely related to its internal pore structure. The distribution and evolution of the pore structure at the nano, micro, and macro scales directly affect key properties such as the thermal conductivity, mechanical strength, and thermal expansion coefficient of the material. The pyrolysis of the material will generate a large amount of pyrolysis gas, and these gases flow inside the pores. As the pyrolysis gas accumulates, the gas pressure inside the material will rise. When the internal pressure is greater than the external environmental pressure, the pyrolysis gas will overflow to the surface along the complex pore structure inside the material. During this process, pore structures of different scales will have a certain impact on the generation and flow law of pyrolysis gas, and convective heat transfer and diffusion heat transfer will occur between the pyrolysis gas and the inner wall surface of the pore structure during the flow of the pyrolysis gas inside the thermal protection material. Therefore, accurately establishing a model of the internal multi-scale pore structure of the resin-based thermal protection material under extreme environments and calculating the generation amount of pyrolysis gas in the pore structure model can provide a basis for analyzing the flow law of pyrolysis gas inside the multi-scale pore structure, and is the basis and prerequisite for evaluating the ablation / thermal response characteristics of the resin-based thermal protection material.

[0003] The research on existing resin-based thermal protection materials mainly focuses on thermal stability and mechanical properties. The research on the evolution mechanism of the pore structure inside them under extreme environments is not deep enough, and most of the pore structure analysis methods are limited to a single scale, making it difficult to comprehensively reflect the complexity and dynamic evolution law of the internal pore structure of the materials. In addition, most of the current calculations of pyrolysis gas mass flow rate are based on the equivalent porosity, and a real geometric model of the pore structure has not been established, resulting in inaccurate calculation of the gas mass flow rate, which is not conducive to the subsequent analysis of the pyrolysis gas flow law and the micro-meso-scale ablation / thermal response characteristics analysis of resin-based thermal protection materials.

[0004] In summary, there is currently a lack of a method that can effectively couple the establishment of pore structure models at the nano, micro, and macro scales and the calculation of the internal pyrolysis gas mass flow rate to comprehensively reveal the formation of the internal nano-micro-macro multi-scale pore structure and the generation law of pyrolysis gas in thermal protection materials under extreme environments. Summary of the Invention

[0005] Aiming at the deficiencies in the above-mentioned background technology, the present invention mainly solves the problems that the existing pore structure analysis methods cannot couple the nano, micro, and macro scales at the same time and the pyrolysis gas mass flow rate calculation is based on the equivalent porosity.

[0006] The present invention provides a method for nano-micro-macro pore structure modeling and pyrolysis gas mass flow rate calculation. This method can effectively reveal the formation and evolution law of the internal pore structure of thermal protection materials under extreme environments, determine the differences in the internal pore structures of fully carbonized, partially carbonized, and non-carbonized thermal protection materials, clarify the relationship between the carbonization degree of thermal protection materials, microstructure morphology, and temperature, establish a nano-micro-macro multi-scale pore structure model of the pores in resin-based thermal protection materials including carbonized areas, pyrolysis areas, and original material areas, accurately calculate the gas generation amount during the pyrolysis process of resin-based thermal protection materials, fill the gaps in the existing technology, and provide new ideas for the design and optimization of thermal protection materials.

[0007] The purpose of the present invention is to provide a method for nano-micro-macro pore structure modeling and pyrolysis gas mass flow rate calculation, including:

[0008] Prepare resin-based thermal protection materials;

[0009] Conduct ablation tests on the resin-based thermal protection materials, obtain the ablated specimens, and divide the ablated specimens into carbonized areas and pyrolysis areas;

[0010] Conduct mercury intrusion tests on the ablated specimens and the non-ablated specimens respectively, and obtain the corresponding pore structure parameters, mercury intrusion curves, and pore size distribution curves of the ablated specimens and the non-ablated specimens respectively;

[0011] Obtain the millimeter-scale pore structure morphology inside the carbonized zone of the ablated specimen, the micron-scale pore structure morphology inside the pyrolysis zone, and the nanoscale pore structure morphology inside the non-ablated specimen;

[0012] Based on the pore structure parameters, mercury intrusion curves, and pore size distribution curves corresponding to the ablated specimens and non-ablated specimens respectively, as well as the millimeter-scale pore structure morphology inside the carbonized zone of the ablated specimen, the micron-scale pore structure morphology inside the pyrolysis zone, and the nanoscale pore structure morphology inside the non-ablated specimen, establish a nano-micro-macro multi-scale pore structure model of the resin-based thermal protection material with pores in the carbonized zone, pyrolysis zone, and original material zone;

[0013] 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 mass conservation, energy conservation, and the generation and diffusion laws of pyrolysis gas inside the resin-based thermal protection material.

[0014] Preferably, the ablation test is an oxyacetylene flame ablation test, and the thermal environment condition is ablation for 100 - 300 s under a heat flux condition of 1.0 - 2.0 MW / m 2 heat flux.

[0015] Preferably, the carbonized zone and the pyrolysis zone are obtained by dividing according to the macroscopic morphology in the thickness direction of the specimen after ablation and the temperatures at different positions.

[0016] Preferably, the millimeter-scale pore structure morphology inside the carbonized zone of the ablated specimen, the micron-scale pore structure morphology inside the pyrolysis zone, and the nanoscale pore structure morphology inside the non-ablated specimen are obtained according to the following steps:

[0017] Perform sputtering treatment on the ablated specimen and the non-ablated specimen respectively;

[0018] Perform SEM imaging tests on the sputtered ablated specimen and non-ablated specimen respectively. First, observe the overall fiber arrangement pattern of the material, and then gradually magnify the typical pore structures inside the thermal protection material to obtain SEM electron micrographs;

[0019] Process and analyze the SEM electron micrographs to obtain the millimeter-scale pore structure morphology inside the carbonized zone of the ablated specimen, the micron-scale pore structure morphology inside the pyrolysis zone, and the nanoscale pore structure morphology inside the non-ablated specimen.

[0020] Preferably, the pore structure morphologies at the millimeter scale, micron scale, and nanoscale are all based on the electron micrographs. Use arbitrary polygons to depict the pores on the electron micrographs, and measure the length and width of the pores according to the scale given in the electron micrographs; among them, the SEM imaging test uses a field emission scanning electron microscope.

[0021] Preferably, the pore structure parameters include porosity, median pore diameter, and average pore diameter.

[0022] Preferably, the mercury intrusion test is carried out using a mercury intrusion porosimeter.

[0023] Preferably, the resin-based thermal protection 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 and foaming process and contains a large number of micro-nano pores inside.

[0024] Preferably, the nano-micro-macro multi-scale pore structure model is obtained according to the following steps:

[0025] Obtain the distribution of fibers inside the resin-based thermal protection material and the size of fiber bundles, and establish a fiber component phase with a specific weaving pattern;

[0026] According to the fiber component phase with a specific weaving pattern, establish the complement of the fiber phase, that is, the matrix phase of the resin-based thermal protection material, so that the fiber phase is wrapped inside the matrix phase;

[0027] According to the pore structure parameters, mercury intrusion curve, and pore size distribution curve corresponding to the ablated specimen and the non-ablated specimen respectively, and according to the millimeter-scale pore structure morphology in the carbonized area, micron-scale pore structure morphology in the pyrolysis area, and nano-scale pore structure morphology inside the non-ablated specimen of the ablated specimen, use the method of random function to arrange pores of different sizes and different numbers in different regions of the matrix phase, so as to obtain the nano-micro-macro multi-scale pore structure model of the resin-based thermal protection material containing pores in the carbonized area, pyrolysis area, and original material area.

[0028] Preferably, the mass flow rate of the pyrolysis gas of the nano-micro-macro multi-scale pore structure model is calculated by the following formula:

[0029]

[0030] Wherein, and are the density of the material at any temperature and the density of the material after complete carbonization respectively, A , E a and are the pre-exponential factor, activation energy, and mechanism function of the material respectively, R is the ideal gas constant, T is the temperature, S is the area.

[0031] Compared with the prior art, the beneficial effects of the present invention are:

[0032] A method for modeling the nano-micro-macro pore structure and calculating the mass flow rate of pyrolysis gas provided by the present invention. Through conducting ablation experiments, carbonized zones, pyrolysis zones, and original material zones with different degrees of pyrolysis of resin-based thermal protection materials are obtained; through carrying out mercury intrusion experiments on the thermal protection materials before and after ablation, data such as the macroscopic porosity and pore size distribution of the materials are obtained; through carrying out SEM imaging experiments on the carbonized zone, pyrolysis zone, and original material zone, the millimeter-scale pore structure morphology of the carbonized zone of the resin-based thermal protection material, the micron-scale pore structure morphology of the pyrolysis zone, and the nano-scale pore structure morphology of the original material zone are obtained; based on the porosity and microscopic morphology of the pore structure obtained from the experiments, a nano-micro-macro multi-scale pore structure model of the resin-based thermal protection material containing carbonized zones, pyrolysis zones, and original material zones is established; applying a heat load boundary to this model, and considering the mass conservation, energy conservation, and pyrolysis gas generation and diffusion laws inside it, the mass flow rate of pyrolysis gas in the nano-micro-macro multi-scale pore structure model is calculated. This method can effectively reveal the formation and evolution laws of the internal pore structure of thermal protection materials under extreme environments, determine the differences in the internal pore structures of fully carbonized, partially carbonized, and non-carbonized thermal protection materials, clarify the relationship between the carbonization degree of thermal protection materials, microstructure morphology, and temperature, accurately calculate the generation amount of pyrolysis gas inside thermal protection materials, fill the gaps in the existing technology, and provide new ideas for the design and optimization of thermal protection materials. Brief Description of the Drawings

[0033] Figure 1 It is a flow chart of the method for modeling the nano-micro-macro multi-scale pore structure and calculating the mass flow rate of pyrolysis gas provided by the present invention.

[0034] Figure 2 They are the specimens, test processes, and test results of the oxyacetylene ablation experiment; among them, (a) is the specimen of the oxyacetylene ablation experiment 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 ablation, and (d) is the macroscopic morphology of the side of the test piece after ablation.

[0035] Figure 3 They are the mercury intrusion curves and pore size distribution curves of the resin-based thermal protection material before and after ablation; among them, (a) is the mercury intrusion curve of the original material, (b) is the pore size distribution curve of the original material, (c) is the mercury intrusion curve of the material after ablation, and (d) is the pore size distribution curve of the material after ablation.

[0036] Figure 4 They are the establishment process of the nano-micro-macro multi-scale pore structure model of the resin-based thermal protection material; among them, (a) is the geometric structure model of the fiber phase, (b) is the geometric structure model of the matrix without pores, (c) is the geometric structure model of the pore phase, and (d) is the geometric structure model of the matrix with pores.

[0037] Figure 5 For the mass flow rate of pyrolysis gas in the 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 below. Specific implementation mode

[0038] In order to enable those skilled in the art to better understand and implement the technical solution of the present invention, the present invention will be further described below in conjunction with specific embodiments and drawings, but the embodiments cited do not limit the present invention.

[0039] The object of the present invention is to provide a method that can accurately establish a nano-micro-macro multi-scale pore structure model inside a thermal protection material under extreme environments, calculate the mass flow rate of pyrolysis gas in this model, determine the differences in the internal pore structures of fully carbonized, partially carbonized, and uncarbonized thermal protection materials, clarify the relationship between the carbonization degree of thermal protection materials, microstructural morphology, and temperature, establish a nano-micro-macro multi-scale pore structure model of the pores in resin-based thermal protection materials including carbonized areas, pyrolysis areas, and original material areas, calculate the gas generation amount during the pyrolysis process of resin-based thermal protection materials, and lay a theoretical foundation for the analysis and evaluation of the flow of pyrolysis gas and ablation / thermal response characteristics of resin-based thermal protection materials, which has very important scientific significance.

[0040] To achieve the above object, as shown in Figure 1 shown, a nano-micro-macro pore structure modeling and pyrolysis gas mass flow rate calculation method provided by the present invention is used for the establishment of a nano-micro-macro multi-scale pore structure model of resin-based thermal protection materials before and after ablation and the calculation of the mass flow rate of pyrolysis gas in this structure model under the action of a thermal load environment, including:

[0041] S1. Prepare resin-based thermal protection materials;

[0042] The resin-based thermal protection material is obtained by impregnating a phenolic resin matrix in a 2D woven fiber skeleton. Among them, the phenolic resin matrix is prepared by a molding and foaming process and contains a large number of micro-nano pores.

[0043] In this embodiment, the fiber skeleton is prepared in the 2D plain weave pattern, that is, each warp yarn and each weft yarn are interwoven with each other; the matrix is prepared by a molding and foaming process. The resin sample and the foaming agent material are placed in a molding and foaming device, pressure is applied to the foaming agent, and it 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. After the sample cools down, a shaped micro-nano pore resin matrix is obtained; the resin-based thermal protection composite material can be obtained by impregnating the micro-nano pore resin matrix in the 2D woven fiber skeleton. The prepared resin-based thermal protection material is processed into two cubes, one is kept in the original state, and the other needs to undergo an ablation test.

[0044] SeeFigure 2 As shown in (a), the original resin-based heat-resistant material is processed into two 30mm×30mm×15mm cubes.

[0045] One of them is kept in its original state and cut into a 15mm×15mm×15mm cube for mercury intrusion and SEM imaging tests of the original material.

[0046] For the other specimen to be subjected to ablation test, it is first subjected to oxyacetylene flame ablation test, and thermocouples are inserted at different positions in the thickness direction to measure and record the temperature changes at different positions of the specimen during the ablation process.

[0047] S2. Conduct ablation tests on the resin-based heat-resistant material to obtain the ablated specimens, and divide the ablated specimens into a carbonized zone and a pyrolysis zone;

[0048] The ablation test is an oxyacetylene flame ablation test, and the thermal environment condition is ablation for 100 - 300 s under a heat flux condition of 1.0 - 2.0 MW / m 2 Among them, under a heat flux condition of 1.1 MW / m 2 ablation is carried out for 200 s, and the flow rates of oxygen and acetylene are 12.06 m 3 / h and 7.03 m 3 / h respectively. Under this experimental condition, the surface temperature of the material rises rapidly and gradually stabilizes at about 1460 °C, and the temperatures at other positions also show a gradually increasing change law. After the experiment, the temperatures at 6 mm, 10 mm, and 15 mm away from the material surface are 990 °C, 810 °C, and 636 °C respectively.

[0049] The carbonized zone and the pyrolysis zone are obtained by dividing according to the macroscopic morphology in the thickness direction of the specimen after ablation and the temperatures at different positions.

[0050] See 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 , and ablation is carried out for 200 s under this heat flux condition.

[0051] 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.

[0052] 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;

[0053] The mercury intrusion test is carried out using a mercury intrusion instrument.

[0054] The pore structure parameters include porosity, median pore diameter, and average pore diameter.

[0055] 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.

[0056] 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.

[0057] 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.

[0058] S4. Obtain the millimeter-scale pore structure morphology inside the carbonized zone of the ablated specimen, the micron-scale pore structure morphology inside the pyrolysis zone, and the nanometer-scale pore structure morphology inside the unablated specimen;

[0059] The millimeter-scale pore structure morphology inside the carbonized zone of the ablated specimen, the micron-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:

[0060] Perform sputtering coating on the ablated specimen and the unablated specimen respectively;

[0061] Perform SEM imaging tests on the sputtered-coated ablated specimen and unablated specimen respectively. First, observe the overall fiber arrangement pattern of the material, and then gradually magnify the typical pore structures inside the thermal protection material to obtain SEM electron micrographs;

[0062] Process and analyze the SEM electron micrographs to obtain the millimeter-scale pore structure morphology inside the carbonized zone of the ablated specimen, the micron-scale pore structure morphology inside the pyrolysis zone, and the nanometer-scale pore structure morphology inside the unablated specimen.

[0063] Among them, the pore structure morphologies at the millimeter scale, micron scale, and nanometer scale are all based on the electron micrographs. Use arbitrary polygons to depict the pores on the electron micrographs, and measure the length and width of the pores according to the scale given in the electron micrographs; among them, the SEM imaging test uses a field emission scanning electron microscope.

[0064] In this embodiment, perform SEM imaging tests on the specimens of the resin-based thermal protection material before and after ablation after sputtering coating. First, observe the overall fiber arrangement pattern of the material, and then gradually magnify the typical pore structures inside the thermal protection material to obtain its microscopic morphology.

[0065] Among them, use the Sigma 300 field emission scanning electron microscope of Carl Zeiss AG in Germany to observe the morphology of the original specimen of the resin-based thermal protection material and the carbonized zone and pyrolysis zone after ablation from the macroscopic scale to the microscopic scale.

[0066] Place a test sample with dimensions of 15 mm × 15 mm × 15 mm on a copper plate adhered with conductive adhesive, and perform tests after sputtering coating for 180 s. The applied voltage for the test is 10.00 kV, and the magnification factor ranges from small to large, from 200 to 10,000 times. When the magnification factor is small, the overall morphology of the thermal protection material and the distribution of fibers inside the material can be observed. Use a larger magnification factor to observe the area with a large number of matrices, and gradually magnify the typical pore areas until the pores inside the material can be imaged well in the entire field of view, and take pictures of this state.

[0067] In this embodiment, the obtained SEM images are processed and analyzed to obtain the microscopic morphology of nanoscale pores inside the original specimen of the resin-based thermal protection material, the microscopic morphology of millimeter-scale pores inside the carbonized zone after ablation of the resin-based thermal protection material, and the microscopic morphology of micron-scale pores inside the pyrolysis zone.

[0068] Among them, the taken SEM images are processed, the holes are marked in the images, and the diameters of the holes are measured according to the scale in the SEM images.

[0069] By analyzing the microscopic morphologies of the ablated specimen and the non-ablated specimen, the microscopic morphology of nanoscale pores inside the original specimen of the resin-based thermal protection material and the microscopic morphology of micron-scale pores inside the pyrolysis zone can be obtained. These pores are distributed in the pyrolysis layer in the form of spheres and ellipsoids, with diameters of approximately 50 - 100 microns and a relatively dense distribution. The microscopic morphology of millimeter-scale pores inside the carbonized zone is also obtained. These pores are mainly distributed at the junction of the 0° and 90° fiber plies and grow perpendicular to the thickness direction along the fiber bundles, being elongated irregular geometric bodies with a length of about 1 - 3 millimeters and a thickness of 200 - 300 microns.

[0070] S5. Based on the pore structure parameters, mercury intrusion curves, and pore size distribution curves corresponding to the ablated specimen and the non-ablated specimen respectively, as well as the millimeter-scale pore structure morphology inside the carbonized zone of the ablated specimen, the micron-scale pore structure morphology inside the pyrolysis zone, and the nanoscale pore structure morphology inside the non-ablated specimen, establish a nano-micro-macro multi-scale pore structure model of the resin-based thermal protection material containing carbonized zone, pyrolysis zone, and original material zone;

[0071] Based on the pore structure morphologies of each region, establish a nano-micro-macro multi-scale pore structure model of the resin-based thermal protection material containing carbonized zone, pyrolysis zone, and original material zone. Among them, the original material zone refers to the region of the non-ablated specimen. It should be noted that the resin-based thermal protection material is composed of three component phases: fibers, matrix, and pores, and most of the pores are distributed inside the matrix.

[0072] The process of establishing the nano-micro-macro multi-scale pore structure model includes:

[0073] Obtain the distribution of fibers inside the resin-based thermal protection material and the size of fiber bundles, and establish a fiber component phase with a specific weaving pattern;

[0074] Based on the fiber component phase with a specific weaving pattern, establish the complement of the fiber phase, that is, the matrix phase of the resin-based thermal protection material, so that the fiber phase is wrapped inside the matrix phase;

[0075] According to the pore structure parameters corresponding to the specimens after ablation and the specimens without ablation, the mercury intrusion curve and the pore size distribution curve, and according to the millimeter-scale pore structure morphology inside the carbonized zone of the ablated specimen, the micron-scale pore structure morphology inside the pyrolysis zone, and the nanoscale pore structure morphology inside the specimen without ablation, the method of random function is used to arrange pores of different sizes and different numbers in different regions of the matrix phase, so as to obtain a nano-micro-macro multi-scale pore structure model of the resin-based thermal protection material containing pores in the carbonized zone, pyrolysis zone and original material zone.

[0076] In this embodiment, the process of establishing the nano-micro-macro multi-scale pore structure model includes:

[0077] First, based on the distribution of fibers inside the material obtained from the SEM imaging test and the observed size of the fiber bundles, a 2D woven fiber component phase is established, such as Figure 4 shown in (a) of the figure. The warp and weft yarns are intertwined to form a 2D woven plain cloth, where the cross-section of the warp and weft yarns is elliptical, the major semi-axis is 0.4 mm, the minor semi-axis is 0.1 mm, and the areal density is 6 yarns / cm.

[0078] Secondly, the complement of the fiber phase is established, that is, the matrix phase of the resin-based thermal protection material without pores, so that the fiber phase is wrapped inside the matrix phase, such as Figure 4 shown in (b) of the figure.

[0079] Finally, based on the porosity, pore size distribution obtained from the mercury intrusion test and the size and morphology of the pore structure obtained from the SEM test, the method of random function is used to arrange spherical pores of different sizes and different numbers in different regions of the matrix phase, such as Figure 4 shown in (c) of the figure. The intersection of the spherical pores and the matrix phase without pores is cut off, and a nano-micro-macro multi-scale pore structure model of the resin-based thermal protection material containing pores in the carbonized zone, pyrolysis zone and original material zone can be obtained, such as Figure 4 shown in (d) of the figure.

[0080] 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 mass conservation, energy conservation inside the resin-based thermal protection material and the generation and diffusion laws of pyrolysis gas.

[0081] The mass flow rate of the pyrolysis gas in the nano-micro-macro multi-scale pore structure model is calculated by the following formula:

[0082]

[0083] Among them, and are the density of the material at any temperature and the density of the material after complete carbonization, respectively;A , E a and are the pre-exponential factor, activation energy, and mechanism function of the material, respectively; R is the ideal gas constant; T is the temperature; S is the area.

[0084] In this embodiment, under the action of high temperature, the phenolic resin matrix inside the resin-based thermal protection material will undergo thermal decomposition, generating a large amount of pyrolysis gas. A heat load boundary condition is applied to the nano-micro-macro multi-scale pore structure model, with a given heat flux density of 1.1 MW / m 2 on the upper surface, and adiabatic boundaries on other surfaces. A thermal decomposition equation is assigned to the matrix phase of the model to obtain the pyrolysis degree of the matrix varying with time and temperature, and then the density of the matrix phase is obtained, which is specifically as follows:

[0085]

[0086] In addition, considering the mass conservation law of the solid phase and gas phase, the internal energy conservation law, and the gas generation and diffusion law, the temperature T at each position of the structure model under the given heat flux density is calculated. Integrating the density change formula over the pore structure wall surface of the model can calculate the mass flow rate of the pyrolysis gas inside the material during the action of the heat flux density.

[0087] Figure 5 is the mass flow rate of the pyrolysis gas of the nano-micro-macro multi-scale pore structure model of the resin-based thermal protection material under the given heat flux density of 1.1 MW / m 2 . It can be seen from Figure 5 that the variation of the mass flow rate of the pyrolysis gas with time shows that at the initial stage of heating, the mass flow rate of the pyrolysis gas is small, indicating that the pyrolysis reaction of the material occurs very slowly at low temperatures and the amount of pyrolysis gas generated is very small. As the pyrolysis reaction proceeds continuously, the generation rate of the pyrolysis gas increases rapidly and reaches a peak. When most regions of the test material have undergone pyrolysis, the pyrolysis rate of the material slows down and the mass flow rate of the pyrolysis gas decreases. The generation and flow of the pyrolysis gas can consume a part of the heat and reduce the heat entering the material interior, which is an important heat insulation mechanism of the thermal protection material.

[0088] The present invention provides a method for modeling the nano-micro-macro multi-scale pore structure and calculating the mass flow rate of pyrolysis gas. By conducting ablation tests, carbonized zones, pyrolysis zones, and original material zones with different degrees of pyrolysis of resin-based thermal protection materials are obtained; by carrying out mercury intrusion experiments on the thermal protection materials before and after ablation, data such as the macroscopic porosity and pore size distribution of the materials are obtained; by conducting SEM imaging experiments on the carbonized zone, pyrolysis zone, and original material zone, the millimeter-scale pore structure morphology of the carbonized zone of the resin-based thermal protection material, the micron-scale pore structure morphology of the pyrolysis zone, and the nano-scale pore structure morphology of the original material zone are obtained; based on the porosity and microscopic morphology of the pore structure obtained from the experiments, a nano-micro-macro multi-scale pore structure model of the resin-based thermal protection material containing pores in the carbonized zone, pyrolysis zone, and original material zone is established; a thermal load boundary is applied to this model, and considering the mass conservation, energy conservation, and the generation and diffusion laws of pyrolysis gas inside it, the mass flow rate of pyrolysis gas in the nano-micro-macro multi-scale pore structure model is calculated. This method can effectively reveal the formation and evolution laws of the internal pore structure of thermal protection materials under extreme environments, determine the differences in the internal pore structures of fully carbonized, partially carbonized, and non-carbonized thermal protection materials, clarify the relationship between the carbonization degree of thermal protection materials, microstructure morphology, and temperature, and accurately calculate the generation amount of pyrolysis gas inside the thermal protection materials.

[0089] As described above, only the preferred specific embodiments of the present invention are given, but the protection scope of the present invention is not limited thereto. Any person skilled in the art within the technical scope disclosed by the present invention, according to the technical solution and inventive concept of the present invention, makes equivalent substitutions or changes, and all should be covered within 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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