Accelerated life test method for expanded polytetrafluoroethylene for aviation

Abstract

The invention discloses an accelerated life test method for expanded polytetrafluoroethylene for aviation, and belongs to the technical field of aircraft maintenance and detection. Comprising the following steps: mounting a sample, and performing at least one accelerated working condition simulation test including repeated compression, medium soaking, heat-moisture treatment, salt spray corrosion, solar radiation and the like; performing thermal aging on the test sample subjected to the simulation test at different temperatures; testing the mechanical property of the sample after thermal aging, and determining a critical value of the mechanical property by taking sealing failure as a judgment standard; and calculating the time when the performance reaches the critical value at different temperatures, and drawing an Amenius diagram to obtain the service life. According to the test method, complex working conditions can be accurately simulated, the service life of the material is efficiently obtained through scientific testing and calculation, a basis is provided for safe replacement of expanded polytetrafluoroethylene for aviation, the problems that a traditional method is difficult to adapt to actual scenes and service life prediction is not accurate are solved, and the reliability of an aircraft sealing system is guaranteed.

Description

Technical Field

[0001] This application belongs to the field of aircraft maintenance and testing technology, specifically involving an accelerated life test method for expanded polytetrafluoroethylene for aviation. Background Technology

[0002] In the aerospace field, the reliability of sealing materials is directly related to the safe operation of aircraft systems. Expanded polytetrafluoroethylene (PTFE) has become an ideal material for aerospace sealing components due to its stable high and low temperature resistance over a wide temperature range of -200℃ to 260℃, excellent aging resistance, and superior sealing performance. However, current research on this material mainly focuses on optimizing the production process, and there is still a significant gap in the assessment of its service life under complex aerospace conditions. In actual operation of aviation equipment, expanded PTFE seals must withstand the combined effects of various complex environmental factors, including alternating high and low temperatures, mechanical vibration, media corrosion, and radiation. Current research lacks a standardized accelerated aging test system for such complex operating conditions, making it impossible to effectively simulate real service environments. Furthermore, the lack of unified accelerated aging test methods and performance evaluation standards makes it difficult to accurately predict the material's service life under extreme conditions through accelerated testing, and to determine the quantitative relationship between seal performance degradation and service life. This directly leads to the inability to promptly identify expanded PTFE seals in a critical failure state during aviation equipment maintenance. Premature seal replacement increases maintenance costs and unnecessary downtime; delayed replacement may lead to serious safety hazards such as fuel leaks and hydraulic system failures due to seal failure.

[0003] Therefore, there is an urgent need to develop an accelerated testing method that can simulate real aviation operating conditions and quantitatively assess material lifespan, in order to fill the gaps in existing technologies and ensure the safe and reliable operation of aviation sealing systems. Summary of the Invention

[0004] The purpose of this application is to provide an accelerated life test method for expanded polytetrafluoroethylene (PTFE) for aviation, which can obtain the service life of expanded PTFE under complex operating conditions through a shorter accelerated life test.

[0005] To achieve the above objectives, this application provides an accelerated life testing method for expanded polytetrafluoroethylene (PTFE) for aviation applications, comprising the following steps: Install the test specimen and conduct accelerated operating condition simulation tests on the specimen; wherein, the accelerated operating condition simulation tests include at least one of repeated compression simulation tests, medium immersion simulation tests, damp heat treatment simulation tests, salt spray corrosion simulation tests, and solar radiation simulation tests; The sample that passed the accelerated operating condition simulation test was placed under different temperature conditions for thermal aging test. The mechanical properties of the material of the specimen that passed the thermal aging test were tested, and the critical values ​​of the mechanical properties of the material under different working conditions were determined with sealing failure as the criterion. Calculate the time it takes for the mechanical properties of the material to reach the corresponding critical values ​​at different temperatures, plot the Arrhenius diagram, and obtain the service life of the expanded polytetrafluoroethylene for aviation.

[0006] Furthermore, the repeated compression simulation test shall be repeated no less than 20 times, and the torque of repeated compression shall be 3.0 N·m to 7.0 N·m.

[0007] Furthermore, the media used in the media immersion simulation test includes at least one of distilled water, mixed oil, and No. 3 jet fuel, wherein the mixed oil includes equal masses of No. 15 hydraulic oil and 4109 lubricating oil. The soaking temperature is 33℃~37℃ when the medium is distilled water, 68℃~72℃ when the medium is mixed oil, and 58℃~62℃ when the medium is No. 3 jet fuel; the soaking time is not less than 24 hours.

[0008] Furthermore, the temperature of the damp heat treatment simulation test is 40℃~60℃, and the humidity is 85%~100%.

[0009] Furthermore, the salt solution used in the salt spray corrosion simulation test is a 4wt%~6wt% sodium chloride solution, and the corrosion temperature is 30℃~40℃.

[0010] Furthermore, the irradiance of the solar radiation simulation experiment was 1000 W / m². 2 ~2000W / m 2 The radiation temperature is 30℃~50℃.

[0011] Furthermore, the test temperature range of the thermal aging test is -75℃ to 260℃, and the test temperature is not less than 3 sets.

[0012] Furthermore, the mechanical properties of the material include tensile strength, resilience, dry stress relaxation, and sealing performance.

[0013] Furthermore, the horizontal axis of the Arrhenius plot is 1 / T, and the vertical axis is lnt, where t is the time to reach the corresponding critical value in hours. T represents the test temperature of the thermal aging test, in K.

[0014] Furthermore, the method for obtaining the service life of the expanded polytetrafluoroethylene for aviation applications includes: The slope m and intercept c are obtained by fitting the Arrhenius plot using the fitting function. A formula is established using the slope m and intercept c, and the service life t of the expanded polytetrafluoroethylene for aviation is calculated based on the formula. 实际 The formula is as follows: ln(t) 实际 =m / T 实际 +c; where T 实际 The absolute temperature of the target operating environment.

[0015] In summary, this application has the following advantages: This application discloses an accelerated life test method for expanded polytetrafluoroethylene for aviation, which achieves accurate simulation of the aviation service environment by constructing a pretreatment system with the synergistic effect of multiple factors.

[0016] Specifically, this application first designs a combination of pretreatment schemes for different environmental factors based on the complex working conditions faced by expanded polytetrafluoroethylene in actual service, such as high and low temperature alternation, mechanical stress, and chemical media corrosion. Multiple stress conditions are superimposed in the order of actual action, so that the material undergoes a degradation process in the laboratory environment that is highly similar to that in actual service, thereby effectively restoring the real path of material performance degradation.

[0017] Secondly, by precisely controlling high-temperature accelerated conditions, this application significantly shortens the performance degradation cycle while maintaining the consistency between the material aging mechanism and actual service conditions. This enables the acquisition of life data under long-term service conditions within a shorter test cycle, effectively solving the technical problem of excessively long test cycles in traditional test methods.

[0018] Finally, in the life assessment phase, multi-dimensional sealing performance tests were conducted on samples treated under the same accelerated conditions to establish a quantitative relationship between changes in the material's microstructure and the decline in macroscopic sealing performance. Based on the mechanical and physicochemical properties of the material's critical failure state, key performance parameters and their critical thresholds that can accurately characterize the material's remaining life were selected, forming a complete evaluation system from experimental simulation to data verification. This completely changes the current situation where traditional accelerated aging methods are divorced from practical application scenarios and lack effective verification methods, providing scientific and reliable technical support for the life prediction of aerospace sealing components. Attached Figure Description

[0019] Figure 1 A flowchart illustrating an accelerated life test method for expanded polytetrafluoroethylene (PTFE) for aviation applications provided in this application; Figure 2 This is a schematic diagram of the tooling used in the repeated compression simulation test of this application. Detailed Implementation

[0020] The principles and features of this application are described below with reference to embodiments. The examples are for illustrative purposes only and are not intended to limit the scope of this application. Unless otherwise specified in the embodiments, conventional conditions or conditions recommended by the manufacturer shall apply. Reagents or instruments whose manufacturers are not specified are all commercially available conventional products.

[0021] This application provides an accelerated life testing method for expanded polytetrafluoroethylene (PTFE) used in aviation, such as... Figure 1 As shown, it includes the following steps: S1. Install the test specimen and conduct an accelerated operating condition simulation test on the specimen.

[0022] The accelerated operating condition simulation test includes at least one of the following: repeated compression simulation test, medium immersion simulation test, damp heat treatment simulation test, salt spray corrosion simulation test, and solar radiation simulation test.

[0023] This application conducts accelerated operating condition simulation based on actual usage conditions. Through arbitrary combinations of various operating conditions (repeated compression, medium immersion, damp heat treatment, salt spray corrosion, solar radiation), it can comprehensively and realistically simulate the complex stress conditions faced by expanded polytetrafluoroethylene in the aerospace service environment.

[0024] As an optional implementation of this application, the repeated compression simulation test involves no less than 20 repeated compressions, with a torque of 3.0 N·m to 7.0 N·m during each compression. That is, by using a tooling to repeatedly compress the material a certain number of times to simulate the effect of repeated disassembly on expanded polytetrafluoroethylene (PTFE), and by simulating the frequent mechanical stresses experienced by aerospace seals during long-term use, the performance changes of the material under repeated stress can be tested, thus assessing its fatigue life.

[0025] In a specific implementation, the tooling structure is as follows: Figure 2 As shown, a metal fixture is used to compress expanded polytetrafluoroethylene (PTFE). The screw pitch on the fixture is similar to that of an aircraft hatch, conforming to actual operating conditions and avoiding the problem of conventional fixtures having larger screw pitches that cannot fully compress the material. The fixture mainly consists of a long strip-shaped upper structure and a flat plate-shaped lower structure, presenting a split design for sample installation and positioning. Through the cooperation of the upper and lower structures, the sample can be fixed or used for functional testing. Figure 2As shown, the upper structure is a rectangular strip with a length dimension of 205mm and a thickness dimension of 2.5mm. Serving as a pressure strip or positioning strip, it is used to apply pressure to the sample or define the sample's position along its length. Its flat structure ensures stable contact with the sample, and its small thickness facilitates precise pressure transmission control. The lower structure is a rectangular plate, with its width dimension marked, and its length is adapted to the upper strip. There are a total of 8 mounting holes, distributed in two columns (left and right). The left column holes have transverse spacing of 25.625mm (first hole from edge) and 51.25mm (interval between adjacent holes); longitudinally, they are distributed in width areas of 15mm and 40mm. The right column holes are marked R3.2, and the number of holes is symmetrical to the left column. They are used for bolt / pin connections to the upper structure or external equipment to achieve overall fixture fixation or sample clamping. The upper strip and the lower plate can be assembled using fasteners such as bolts to form a clamping space for the sample; it can also be used to fix the tooling on the test bench or equipment to ensure the stability of the tooling position during the test.

[0026] As an optional embodiment of this application, the medium used in the medium immersion simulation test includes at least one of distilled water, mixed oil, and No. 3 jet fuel, wherein the mixed oil includes equal masses of No. 15 hydraulic oil and 4109 lubricating oil; the immersion temperature is 33℃~37℃ when the medium is distilled water, 68℃~72℃ when the medium is mixed oil, and 58℃~62℃ when the medium is No. 3 jet fuel; the immersion time is not less than 24 hours. That is, immersing in a medium at a certain temperature for a certain time simulates long-term medium erosion. This application determines the medium type, immersion temperature, and time based on actual operating conditions, selecting media such as distilled water, mixed oil, or jet fuel, and immersing for not less than 24 hours at corresponding extreme operating temperatures. This effectively simulates the chemical corrosion and swelling phenomena of materials after long-term contact with the medium, and explores the influence of the medium on the sealing performance and mechanical properties of the material.

[0027] As an optional embodiment of this application, the treatment temperature of the damp heat treatment simulation test is 40℃~60℃, and the treatment humidity is 85%~100%. That is, the material is treated under certain damp heat conditions in a damp heat test chamber for a certain period of time to simulate long-term damp heat exposure. This application controls the treatment temperature at 40℃~60℃ and the humidity at 85%~100%, and particularly prefers the combination of 40℃ and 93% humidity, which can simulate the erosion of materials by high humidity and temperature fluctuation environments, thereby studying the aging behavior of materials in damp heat environments.

[0028] As an optional embodiment of this application, the salt solution used in the salt spray corrosion simulation test is a 4wt%~6wt% sodium chloride solution, and the corrosion temperature is 30℃~40℃. That is, long-term salt spray exposure is simulated by subjecting the material to salt spray corrosion at a certain temperature and concentration for a certain period of time in a salt spray test chamber. This application sets the salt solution concentration to 4wt%~6wt% and the corrosion temperature to 30℃~40℃, preferably a 5wt% concentration and 35℃, which can simulate the corrosive effect of coastal or high-salt-spray environments on materials, thereby evaluating the corrosion resistance of the materials.

[0029] As an optional embodiment of this application, the irradiance of the solar radiation simulation experiment is 1000 W / m². 2 ~2000W / m 2 The radiation temperature is 30℃~50℃. This means that long-term natural light irradiation is simulated by solar radiation of a certain intensity for a certain period of time in a solar radiation chamber. This application sets the irradiance at 1000W / m². 2 ~2000W / m 2 Radiation temperature 30℃~50℃, preferably 49℃, irradiance 1120W / m 2 It can simulate extreme solar radiation conditions and study the effects of ultraviolet radiation and other radiation on material properties.

[0030] As a preferred embodiment of this application, when simulating multiple operating conditions, the simulation should be carried out in the order of repeated compression, medium immersion, damp heat treatment, salt spray corrosion, and solar radiation. This order corresponds to the sequence in which expanded polytetrafluoroethylene comes into contact with the corresponding operating conditions during actual use.

[0031] S2. The sample that has passed the accelerated operating condition simulation test is placed under different temperature conditions for thermal aging test.

[0032] As an optional implementation of this application, the test temperature range of the thermal aging test is -75℃ to 260℃, and the test temperature is not less than 3 sets. This application places the accelerated operating condition simulated sample into thermal aging test chambers at different temperatures for thermal aging, with no less than 3 temperatures and maximizing the difference within the long-term service temperature range of the material. Based on the Arrhenius reaction rate theory, temperature is used to accelerate the aging reaction rate such as molecular chain degradation and cross-linking within the material. While maintaining the consistency between the material aging mechanism and actual service, the performance decay cycle is significantly shortened, enabling the acquisition of life data under long-term service conditions within a shorter test cycle, effectively improving test efficiency and reducing test costs.

[0033] S3. Test the mechanical properties of the material of the sample that has passed the thermal aging test, and determine the critical values ​​of the mechanical properties of the material under different working conditions, with sealing failure as the criterion.

[0034] As an optional implementation of this application, the mechanical properties of the material include tensile strength, resilience, dry stress relaxation, and sealing performance. This application tests the material properties after thermal aging, covering multiple aspects such as tensile strength, resilience, and dry stress relaxation, comprehensively evaluating the performance changes of the material during the aging process from a mechanical performance perspective. Tensile strength reflects the material's ability to resist tensile failure, resilience reflects the material's recovery ability after deformation under stress, and dry stress relaxation characterizes the attenuation of stress over time under constant deformation. These performance parameters can intuitively reflect the degree of mechanical property degradation after material aging, providing basic data for subsequent analysis of the relationship between material performance and service life. Then, the sealing performance of the material after thermal aging under the same conditions is tested, and the critical value is determined according to the critical point of material performance corresponding to the unqualified sealing performance. When the critical values ​​are inconsistent under different conditions, the critical value that is less likely to fail to seal is selected. Sealing performance is a key indicator for the application of expanded polytetrafluoroethylene in the aerospace field. In this way, a quantitative relationship between the macroscopic sealing performance of the material and microstructural changes and other mechanical properties is established, and key performance parameters and their critical thresholds that can accurately characterize the remaining service life of the material are screened out, providing a reliable basis for material life assessment.

[0035] S4. Calculate the time it takes for the mechanical properties of the material to reach the corresponding critical values ​​at different temperatures, plot the Arrhenius diagram, and obtain the service life of the expanded polytetrafluoroethylene for aviation.

[0036] This application calculates the time it takes for material properties to reach critical values ​​at different temperatures, plots Arrhenius diagrams, and then calculates service life. By using the Arrhenius equation to correlate temperature with material aging rate, and through mathematical modeling, integrates and analyzes the material property data obtained in the preceding steps at different temperatures, it achieves a scientific prediction of the material's service life at actual service temperatures, providing theoretical guidance for the replacement and maintenance of expanded polytetrafluoroethylene (PTFE) for aviation applications.

[0037] In a specific implementation, the sealing performance of the material is tested after thermal aging under the same conditions, and the material properties corresponding to the point where the sealing performance fails are used as the critical value. For example: Table 1

[0038] As shown in Table 1, if the sealing performance fails when the thermal aging time is t5, then L4, H4, and G4 should be selected as critical values. When the critical values ​​under different conditions are inconsistent, the critical value that is less likely to cause sealing failure should be selected. Taking tensile strength as an example, the maximum critical value under different working conditions is 9 MPa, and the minimum critical value is 7 MPa. Therefore, 8 MPa should be uniformly selected when calculating the critical value for the corresponding working conditions.

[0039] As an optional implementation of this application, the horizontal axis of the Arrhenius plot is 1 / T, and the vertical axis is lnt, where t is the time to reach the corresponding critical value in hours; and T is the test temperature of the thermal aging test in K, which is the absolute temperature.

[0040] The method for obtaining the service life of the expanded polytetrafluoroethylene for aviation applications includes: The slope m and intercept c are obtained by fitting the Arrhenius plot using the fitting function. A formula is established using the slope m and intercept c, and the service life t of the expanded polytetrafluoroethylene for aviation is calculated based on the formula. 实际 The formula is as follows: ln(t) 实际 =m / T 实际 +c; where T 实际 The absolute temperature of the target operating environment.

[0041] Specifically, the Arrhenius equation is widely used in the study of polymer aging processes and is a commonly used empirical formula. This application modifies the Arrhenius equation to calculate the actual service life of materials. The calculation process and examples are shown below: 1) The initial formula for the Arrhenius equation is: k = A * e -Ea / RT , Where k is the reaction rate constant, and the unit depends on the reaction order; A refers to the pre-factor (frequency factor), which is related to the frequency of molecular collisions; Ea is the activation energy, measured in J / mol, which represents the energy barrier that the reaction needs to overcome. R is the molar gas constant, 8.134 J·mol⁻¹ -1 ·K -1 ; T refers to absolute temperature, measured in Kelvin (K).

[0042] 2) In the field of material aging, the time t for material properties to decay to a critical value can be regarded as the reciprocal of the reaction rate (t∝1 / k), therefore t=B*e Ea / RT ; Linearization after taking the natural logarithm: ln(t) = (Ea / R) * (1 / T) + ln(B); That is, ln(t) is linearly related to 1 / T, with a slope of Ea / R and an intercept of ln(B).

[0043] 3) To draw an Arrhenius diagram, you need to obtain at least three temperature points (such as T1, T2, and T3) and the times t1, t2, and t3 when the material properties (such as tensile strength, resilience, etc.) reach their critical values.

[0044] For example: T1 = 100℃ (373K), t1 = 100 hours; T2 = 120℃ (393K), t2 = 50 hours; T3 = 140℃ (413K), t3 = 25 hours.

[0045] 4) Calculate 1 / T and ln(t), as shown in the table below:

[0046] With 1 / T*10 -3 Plot a scatter plot with ln(t) as the x-axis and ln(t) as the y-axis. Fit the line by linear regression to obtain the equation: ln(t) = m * 1 / T + c; where the slope m = Ea / R and the intercept c = ln(B).

[0047] 5) Calculate the activation energy from the slope m of the fitted line: Ea=m*R. For example, if m=10000, then Ea=10000*8.314=83.14kJ / mol.

[0048] Determine the actual operating temperature T 实际 For example, in an aerospace environment, the long-term operating temperature of materials is 50℃ (323K). The actual service life (t) is calculated. 实际 , will T 实际 Substitute into the fitting equation: ln(t) 实际 = m * 1 / T 实际 +c; For example: If m = 10000, c = -20, T 实际 =323K, then ln(t) 实际 = 10000 * 1 / 323 - 20 ≈ 11.02; Then t 实际 =e 11.02 ≈60,000 hours.

[0049] The above process achieves the purpose of obtaining the (actual) service life of the expanded polytetrafluoroethylene for aviation purposes as described in this application.

[0050] In this application, the Arrhenius plot is a graph drawn based on the Arrhenius equation, using data related to the time it takes for the material's mechanical properties to reach their critical values ​​at different temperatures. Specifically, ln(t) (where t is the time it takes for the material's mechanical properties to reach their critical values, taken as the natural logarithm) is plotted on the ordinate, and 1 / T (where T is the absolute temperature of the thermal aging test, taken as the reciprocal) is plotted on the abscissa. In principle, the Arrhenius equation describes the relationship between the reaction rate constant and temperature. This application correlates the "rate" (reflected by time; the shorter the time, the faster the decay) of the material's properties to decay to their critical values ​​with temperature. After plotting, the slope of the straight line in the graph is related to the activation energy of the material's aging, and the intercept is related to parameters such as the pre-exponential factor. This graph visually presents the influence of temperature on the time it takes for the material's properties to decay to their critical values. Furthermore, based on this graph, extrapolation calculations can be performed to obtain the material's performance at the actual operating temperature T. 实际 The time t for mechanical properties to reach the critical value at the accelerated temperature of (non-thermal aging test) 实际 Ultimately, the service life of expanded polytetrafluoroethylene (PTFE) for aerospace applications was determined, enabling a scientific prediction of material lifespan. In simple terms, this application uses a graphical method, based on the relationship between temperature and performance degradation time, to help calculate the material's service life under real-world operating conditions.

[0051] In summary, this application artificially accelerates the aging rate of expanded polytetrafluoroethylene (ePTFE) under simulated multiple stress factors in actual working conditions (such as mechanical compression, media corrosion, damp heat, salt spray, solar radiation, etc.), thereby shortening the testing cycle. The core logic of this application's accelerated life testing method for expanded polytetrafluoroethylene for aviation applications lies in the fact that under harsher environments than actual usage conditions, the material's performance degrades more rapidly, thus allowing for the extrapolation of long-term service life from short-term test data.

[0052] The technical solutions described above in this application will be explained in detail below with reference to specific embodiments.

[0053] Example 1 This embodiment discloses an accelerated life test method for expanded polytetrafluoroethylene (PTFE) used in aviation, including the following steps: S101. Prepare the test specimen from waterproof, high-strength expanded polytetrafluoroethylene. S102, Install the sample onto Figure 2 In the fixture shown, the compression was repeated 20 times to keep the sample in a compressed state throughout the process. S103. Soak the repeatedly compressed sample in distilled water at 35°C for 1 day. S104. The sample after being soaked in the medium is treated in a damp heat test chamber at 40℃ and 93% humidity for 3.5 days. S105. The sample after wet heat treatment was corroded in a salt spray test chamber at 35℃ and 5wt% salt solution for 4 days. S106. The sample after salt spray corrosion was subjected to a temperature of 49℃ and an irradiance of 1120W / m². 2 Radiation was conducted in a solar radiation test chamber for 3 days. S107. The solar-irradiated samples are placed in thermal aging test chambers at 100℃, 180℃ and 260℃ respectively for thermal aging, and samples are taken from them periodically to test the tensile strength, resilience and dry stress relaxation of the samples. The appropriate material properties and their critical values ​​are selected through the corresponding sealing performance tests. S108. Using the linear relationship between material properties and thermal aging time, calculate the time t it takes for material properties to decrease to the critical value at thermal aging temperature T. S109. Calculate the critical time t. 100 t 180 and t 260 ; S110. Plot the relationship between lnt and 1 / T, i.e., the Arrhenius plot, and obtain the slope m and intercept c by fitting the function. S111, via ln(t) 实际 = m * 1 / T 实际 +c Calculates the target using ambient temperature T 实际 The following service life t 实际 .

[0054] Example 2 This embodiment discloses an accelerated life test method for expanded polytetrafluoroethylene (PTFE) used in aviation, including the following steps: S1201. Prepare the test specimen from waterproof and environmentally resistant expanded polytetrafluoroethylene. S202, Install the sample onto Figure 2 In the fixture shown, the compression was repeated 20 times to keep the sample in a compressed state throughout the process. S203. The repeatedly compressed sample was immersed in an oil mixture of No. 15 hydraulic oil and 4109 lubricating oil at a mass ratio of 1:1 at 70°C for 1 day. S204. The sample after being soaked in the medium is treated in a damp heat test chamber at 40℃ and 93% humidity for 3.5 days. S205. The sample after wet heat treatment was corroded in a salt spray test chamber at 35℃ and 5wt% salt solution for 4 days. S206. The sample after salt spray corrosion was subjected to a temperature of 49℃ and an irradiance of 1120W / m². 2 Radiation was conducted in a solar radiation test chamber for 3 days. S207. The solar-irradiated samples are placed in thermal aging test chambers at 100℃, 180℃ and 260℃ respectively for thermal aging, and samples are taken from them periodically to test the tensile strength, resilience and dry stress relaxation of the samples. The appropriate material properties and their critical values ​​are selected through the corresponding sealing performance tests. S208. Using the linear relationship between material properties and thermal aging time, calculate the time t it takes for material properties to decrease to the critical value at thermal aging temperature T. S209. The critical time t is calculated. 100 t 180 and t 260 ; S210. Plot the relationship between lnt and 1 / T, i.e., the Arrhenius plot, and obtain the slope m and intercept c by fitting the function. S211, via ln(t) 实际 = m * 1 / T 实际 +c, calculates the target ambient temperature T. 实际 The following service life t 实际 .

[0055] Example 3 This embodiment discloses an accelerated life test method for expanded polytetrafluoroethylene (PTFE) used in aviation, including the following steps: S301. Prepare the test specimen from fire-resistant expanded polytetrafluoroethylene. S302, Install the sample onto Figure 2 In the fixture shown, the compression was repeated 20 times to keep the sample in a compressed state throughout the process. S303. Immerse the repeatedly compressed sample in No. 3 jet fuel at 60°C for 1 day; S304. The sample after being soaked in the medium is treated in a damp heat test chamber at 40℃ and 93% humidity for 3.5 days. S305. The sample after wet heat treatment was corroded in a salt spray test chamber at 35℃ and 5wt% salt solution for 4 days. S306. The sample after salt spray corrosion is subjected to a temperature of 49℃ and an irradiance of 1120W / m². 2 Radiation was conducted in a solar radiation test chamber for 3 days. S307. The solar-irradiated samples are placed in thermal aging test chambers at 100℃, 140℃ and 180℃ respectively for thermal aging, and samples are taken from them periodically to test the tensile strength, resilience and dry stress relaxation of the samples. The appropriate material properties and their critical values ​​are selected through the corresponding sealing performance tests. S308. Using the linear relationship between material properties and thermal aging time, calculate the time t it takes for material properties to decrease to the critical value at thermal aging temperature T. S309. Calculate the critical time t.100 t 140 and t 180 ; S310. Plot the relationship between lnt and 1 / T, i.e., the Arrhenius plot, and obtain the slope m and intercept c by fitting the function. S311, via ln(t) 实际 = m * 1 / T 实际 +c, calculates the target ambient temperature T. 实际 The following service life t 实际 .

[0056] While specific embodiments of this application have been described in detail, this should not be construed as limiting the scope of protection of this application. Various modifications and variations that can be made by those skilled in the art without inventive effort within the scope described in the claims still fall within the scope of protection of this application.

Claims

1. A method for accelerated life testing of expanded polytetrafluoroethylene (PTFE) for aviation applications, characterized in that, Includes the following steps: Install the test specimen and conduct accelerated operating condition simulation tests on the specimen; wherein, the accelerated operating condition simulation tests include at least one of repeated compression simulation tests, medium immersion simulation tests, damp heat treatment simulation tests, salt spray corrosion simulation tests, and solar radiation simulation tests; The sample that passed the accelerated operating condition simulation test was placed under different temperature conditions for thermal aging test. The mechanical properties of the material of the specimen that passed the thermal aging test were tested, and the critical values ​​of the mechanical properties of the material under different working conditions were determined with sealing failure as the criterion. Calculate the time it takes for the mechanical properties of the material to reach the corresponding critical values ​​at different temperatures, plot the Arrhenius diagram, and obtain the service life of the expanded polytetrafluoroethylene for aviation.

2. The accelerated life test method for expanded polytetrafluoroethylene for aviation use according to claim 1, characterized in that, The repeated compression simulation test shall be repeated no less than 20 times, and the torque of repeated compression shall be 3.0 N·m to 7.0 N·m.

3. The accelerated life test method for expanded polytetrafluoroethylene for aviation use according to claim 1, characterized in that, The medium used in the medium immersion simulation test includes at least one of distilled water, mixed oil, and No. 3 jet fuel, wherein the mixed oil includes equal masses of No. 15 hydraulic oil and 4109 lubricating oil. The soaking temperature is 33℃~37℃ when the medium is distilled water, 68℃~72℃ when the medium is mixed oil, and 58℃~62℃ when the medium is No. 3 jet fuel; the soaking time is not less than 24 hours.

4. The accelerated life test method for expanded polytetrafluoroethylene for aviation use according to claim 1, characterized in that, The temperature range for the simulated damp heat treatment was 40℃~60℃, and the humidity range was 85%~100%.

5. The accelerated life test method for expanded polytetrafluoroethylene for aviation use according to claim 1, characterized in that, The salt solution used in the salt spray corrosion simulation test was a 4wt%~6wt% sodium chloride solution, and the corrosion temperature was 30℃~40℃.

6. The accelerated life test method for expanded polytetrafluoroethylene for aviation use according to claim 1, characterized in that, The irradiance of the solar radiation simulation experiment was 1000 W / m². 2 ~2000W / m 2 The radiation temperature is 30℃~50℃.

7. The accelerated life test method for expanded polytetrafluoroethylene for aviation use according to claim 1, characterized in that, The test temperature range for the thermal aging test is -75℃ to 260℃, and the test temperature is not less than 3 sets.

8. The accelerated life test method for expanded polytetrafluoroethylene for aviation use according to claim 1, characterized in that, The mechanical properties of the material include tensile strength, resilience, dry stress relaxation, and sealing performance.

9. The accelerated life test method for expanded polytetrafluoroethylene for aviation use according to claim 1, characterized in that, The horizontal axis of the Arrhenius plot is 1 / T, and the vertical axis is lnt, where t is the time to reach the corresponding critical value in hours; and T is the test temperature of the thermal aging test in K.

10. The accelerated life test method for expanded polytetrafluoroethylene for aviation use according to claim 1, characterized in that, The method for obtaining the service life of the expanded polytetrafluoroethylene for aviation applications includes: The slope m and intercept c are obtained through the fitting function of the Arrhenius plot; A formula is established using the slope m and intercept c, and the service life t of the expanded polytetrafluoroethylene for aviation is calculated based on the formula. 实际 The formula is as follows: ln(t) 实际 =m / T 实际 +c; where T 实际 The absolute temperature of the target operating environment.

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