A test method for helicopter connection structures in high-altitude cold and sandy atmospheric environments

Abstract

This invention provides a method for testing helicopter connection structures in an atmospheric environment characterized by sequentially subjecting test pieces to low-temperature fatigue testing, sand and dust testing, temperature shock (low-temperature) testing, UV-condensation testing, and salt solution spray-drying testing. This method significantly improves the effectiveness of these tests, enabling a more rapid and accurate assessment of the adaptability of helicopter skin riveted structures in such an environment. The results closely match those obtained from tests conducted in a natural parking state. A single test cycle can simulate a helicopter riveted structure parked outdoors in an atmospheric environment characterized by high temperatures, dust, and sand.

Description

Technical Field

[0001] The present invention relates to the technical field of helicopter environmental testing, and in particular to a method for testing a helicopter connection structure in an alpine and sandy atmospheric environment. Background Art

[0002] Helicopters spend approximately 96% of their total operational time parked on the ground. During these extended periods, they are constantly subjected to the combined effects of a complex external environment. Due to the harsh ground parking environment, such as low temperatures and dust, typical environmental adaptability issues frequently occur in helicopters operating in high-altitude desert environments, including wear and seizure of moving parts, circuit degradation, and seal failure. Due to insufficient verification of corrosion and aging resistance, the research foundation for equivalent accelerated testing technology for helicopter ground parking environments is weak. This lack of practical application in converting helicopter ground parking environmental spectra into laboratory accelerated simulation spectra makes it difficult to meet the requirements for rapid assessment and verification of the environmental adaptability of critical helicopter components, hindering the safe and reliable use of helicopters.

[0003] At present, the test of helicopter connection structure mainly adopts the method of exposing to natural environment or laboratory simulated environment for a certain period of time to conduct tensile performance or fatigue performance test to characterize the environmental resistance of helicopter connection structure. The test cycle of the method of natural environment test plus mechanical performance test is long, and it is difficult to achieve rapid evaluation; the currently commonly used laboratory simulation plus mechanical performance test method does not fully consider the main environmental factors affecting helicopter connection structure in high-altitude cold and sandy areas, and does not reflect the interactive application scheme of environment and load, resulting in insufficient simulation effect.

[0004] While some test methods have been developed for helicopter materials, processes, and structures, drawing on research from fixed-wing aircraft, these environmental damage assessment and verification methods primarily rely on single-factor testing. Furthermore, the environmental stress profiles employed differ significantly from actual conditions, leaving room for improvement in the accuracy of these results. In particular, research on the combined effects of low temperatures, dust, and other environmental factors on helicopter connection structures in complex, cold, and sandy environments is insufficient. Consequently, there is an urgent need to develop scientifically validated laboratory simulation accelerated test methods for helicopters operating in these environments. Summary of the Invention

[0005] The present invention aims to provide a method for testing a helicopter connection structure in a high-altitude cold and sandy atmospheric environment, which is at least used to quickly and accurately evaluate the adaptability of the helicopter connection structure in a high-altitude cold and sandy atmospheric environment.

[0006] In order to achieve the above-mentioned purpose, the present invention adopts the following technical solution.

[0007] A method for testing a helicopter connection structure in a high-altitude cold and sandy atmosphere environment, characterized in that a test piece is subjected to a low-temperature fatigue test, a sand and dust test, a temperature shock (low-temperature) test, an ultraviolet-condensation test, and a salt solution spray-drying test in sequence;

[0008] The low temperature fatigue test is to apply a pull-pull sinusoidal fatigue load equivalent to one year of flight strength to the test piece.

[0009] The sand and dust test is a combination test of normal temperature dust blowing, high temperature dust blowing, and high temperature sand blowing.

[0010] The temperature shock test is a shock test conducted under the extreme temperature atmosphere of the area where the helicopter is in service.

[0011] The UV-condensation test is an alternating UV-condensation test conducted on helicopter connection structure test pieces in combination with the highest temperature and the maximum annual solar UV radiation value measured in the area where the helicopter is in service.

[0012] The salt solution spray-drying test is an alternating salt spray-drying test conducted on helicopter connection structure test pieces in combination with the maximum chloride ion content and rainwater pH value measured in the area where the helicopter is in service.

[0013] Preferably, the specific steps of implementing the salt solution spray-drying test include: obtaining the ratio of the wetting time to the drying time measured throughout the year in the area where the helicopter is in service, using the maximum value of the ratio as the cycle time ratio of spraying and drying, and selecting the highest temperature measured in the area where the helicopter is in service as the spray temperature.

[0014] In the present invention, the helicopter connection structure is the riveted portion of the helicopter skin side panel.

[0015] In order to further improve the reliability of the test, when implementing the dust test, the test surface of the test piece is perpendicular to the dust blowing direction.

[0016] To further improve the accuracy of the test, the test conditions of the low-temperature fatigue test are as follows: the test frequency is 16 Hz based on the movement law of the helicopter rotor, the stress peak is 75 MPa based on the maximum design load of the helicopter fuselage skin structure, the stress valley is 4.5 MPa, the number of fatigue load cycles is 8,000 times, and the test temperature is 12°C lower than the lowest temperature in the area where the helicopter is in service;

[0017] The test conditions of the dust blowing test are as follows: the temperature of the high-temperature dust blowing test and the sand blowing test are both the highest temperature in the area where the helicopter is in service, the relative humidity is ≤30%, the wind speed of the dust blowing test is 8.9 m / s, and the wind speed of the sand blowing test is the maximum hourly average wind speed on the ground in the area where the helicopter is in service ±2 m / s. The diameter of the dust and the diameter of the sand in the dust blowing test are both controlled within the range of the measured particle size in the area where the helicopter is in service. The concentration of the dust blowing test is (10.6±7) g / m 3 , sand blowing test concentration is (2.2±0.5)g / m 3 , the duration of dust blowing test is 12h, and the duration of sand blowing test is 1.5h;

[0018] The test conditions of the temperature shock test are: continuous shock for 4 hours at a low temperature of -31±2°C, continuous shock for 2 hours at a high temperature of 43±1°C, and 3 cycles of shock.

[0019] The test conditions of the UV-condensation test are: irradiance level of 1.1 W / (m 2 / nm), each 12h cycle includes 8h of ultraviolet test at (60±1)℃ and 4h of condensation test at (50±1)℃, and the test time is 9 days;

[0020] The test conditions of the salt solution spray-drying test are as follows: the corrosive medium is a mixed solution of 0.05% Na2SO4 and 0.01% NaCl, the pH value is adjusted to 6-8 with dilute sulfuric acid or NaOH solution, and the sedimentation rate of the salt solution is controlled to 1-3 mL / (80 cm 2 h); During the wet-drying test, in each 24-hour cycle, salt spraying was performed for 3 hours and ventilation drying was performed for 21 hours. The salt spraying temperature was set to T = (35 ± 1) ° C according to the highest temperature measured, the drying temperature was set to T = (35 ± 1) ° C, and the drying humidity was set to RH = (50 ± 3)%. The test time for one cycle of the salt solution spray-drying test was 7 days;

[0021] The total duration of each test cycle is 18 days.

[0022] To further improve the accuracy of the test, the sand and dust test and UV irradiation are only performed on the test surface of the test piece.

[0023] Beneficial effects: The scheme of the present invention can effectively simulate the actual situation when a helicopter is parked on the ground in a high-altitude, cold and sandy environment, where the outdoor atmospheric environment temperature is low, the temperature difference between day and night is large, there is a lot of dust and sand, there is high solar radiation during the day, condensation at night, alternating dry and wet conditions, and erosion by corrosive media, and the flight process is subject to fatigue loads. The adoption of the scheme of the present invention significantly improves the effectiveness of the simulated high-altitude, cold and sandy environment test, and can more quickly and accurately evaluate the adaptability of the helicopter skin riveted structure in the high-altitude, cold and sandy atmospheric environment, which is very close to the test results under the natural parking state. One cycle test can simulate the situation of the riveted structure of a helicopter parked outdoors in a high-altitude, cold and sandy area for one year. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 2. It is a schematic diagram of a helicopter skin connection structure test piece in an embodiment;

[0025] Figure 2 This is the environmental spectrum of the laboratory accelerated test of the helicopter riveted structure in the embodiment simulating the high-altitude cold and high-sand atmospheric environment. DETAILED DESCRIPTION

[0026] The present invention will be further described below with reference to the accompanying drawings and specific embodiments. However, the following embodiments are only intended to help understand the principles and core concepts of the present invention and are not intended to limit the scope of protection of the present invention. It should be noted that for those skilled in the art, improvements made to the present invention without departing from the principles of the present invention also fall within the scope of protection of the claims of the present invention.

[0027] Example

[0028] like Figure 1 and Figure 2 As shown, a method for testing a helicopter connection structure in a high-altitude cold and sandy atmospheric environment is provided. The test piece is subjected to a low-temperature fatigue (sub-test), a sand and dust (sub-test), a temperature shock (sub-test), an ultraviolet-condensation (sub-test), and a salt solution spray-drying (sub-test) in sequence. The method is used to simulate the actual conditions when a helicopter connection structure is parked on the ground in a high-altitude cold and sandy area, where the connection structure is exposed to low outdoor atmospheric temperature, large temperature difference between day and night, heavy dust and sand, high solar radiation during the day, condensation at night, alternating dry and wet conditions, and erosion by corrosive media, and is subjected to fatigue loads during flight. Figure 1 Shown is the riveted structure of the helicopter skin side panel.

[0029] Among them, low-temperature fatigue test: The dynamic and static alternating load environmental factors that the helicopter connection structure is subjected to during the ground parking stage and the flight stage will affect the surface protective coating and riveted parts. A tension-tension sinusoidal fatigue load equivalent to one-year flight strength is applied to the riveted structure test piece using a material testing machine. The frequency is 16Hz based on the motion law of the helicopter rotor. The stress peak is 75MPa based on the maximum design load of a certain helicopter fuselage skin structure, and the stress valley is 4.5MPa based on 0.06. The number of fatigue load cycles is based on 500 times based on the CASS spectrum, and is set at 8000 times considering the relevant helicopter design requirements and the strengthening proportional coefficient. Considering the extreme conditions of helicopter flight, the fatigue test is designed to be carried out under low temperature conditions. According to the minimum ground temperature of a certain high-altitude and cold sandy area is -31.2℃, considering that the helicopter usually flies at an altitude of about 2000m, the temperature during flight is about 12℃ lower than the ground temperature. Therefore, the fatigue test is designed to be carried out under (-43±2)℃.

[0030] The dust test: In a ground-parked environment, the surface coating of helicopter connection structures is affected by environmental factors such as dust and sand in two main ways. First, the impact of large particles such as dust and sand can easily cause the coating to break and fall off at the structural connection points. Second, the soluble and insoluble components in dust and sand can change the surface state of the structural components, leading to moisture absorption and a decrease in the critical wetting humidity. In particular, the highly corrosive chlorine, when dissolved in rainwater (snow), dew, and the surface wetting film, can accelerate corrosion and aging reactions at the coating / metal interface. Referring to the relevant test conditions of GJB 150.12A-2009, "Military Equipment Laboratory Environmental Test Methods Part 12: Dust and Sand Test," a combination test of normal temperature (23±1°C) dust blowing, high temperature dust blowing, and high temperature sand blowing was designed to simulate the effects of dust and sand on the riveted structural components of the helicopter fuselage skin. The temperature of the high-temperature dust and sand blowing tests was designed to be (43±1)°C based on the maximum ground temperature of 42.6°C in a certain high-altitude and high-dust area, and the relative humidity was ≤30%. The wind speed of the dust blowing test was the higher speed of the typical desert wind given in the standard, 8.9 m / s. The wind speed of the sand blowing test was controlled at (11±2) m / s based on the maximum hourly average wind speed of 11.0 m / s in a certain high-altitude and high-dust area. The diameter of the dust in the dust blowing test was controlled at (30-149) μm with reference to the average median diameter of 32.64 μm of sand dust measured in a certain high-altitude and high-dust area. The diameter of the sand in the sand blowing test was controlled at (150-400) μm with reference to the maximum particle size range of sand dust measured in a certain high-altitude and high-dust area, (116.1-390.2) μm. The concentration of the dust blowing test was (10.6±7) g / m 3 , sand blowing test concentration is (2.2±0.5)g / m 3The installation direction of dust blowing and sand blowing tests is that the test surface is perpendicular to the blowing direction of sand and dust (so that the specimen is subjected to the maximum abrasive effect). The duration of dust blowing test is 12 hours (6 hours at normal temperature + 6 hours at high temperature), and the duration of sand blowing test is 1.5 hours (it is recommended to carry out sand blowing pre-test and adjust the sand blowing test time as appropriate according to the pre-test results).

[0031] Among them, temperature shock (low temperature) test: under the action of continuous low temperature, the surface coating of the helicopter fuselage skin structural parts tends to become brittle and hard (resulting in reduced flexibility). At the same time, under the action of cold and hot temperature cycle impact, the surface coating of the structural parts tends to produce microcracks; according to the highest ground temperature (42.6℃) and the lowest ground temperature (-31.2℃) in a certain high-altitude and cold sandy area, the constant extreme temperature shock test is designed with a low temperature of (-31±2)℃ and a low temperature duration of 4h; the high temperature is (43±1)℃, the high temperature duration is 2h, and the number of cyclic impacts is 3 times.

[0032] Among them, UV-condensation test: The effect of solar radiation spectrum on organic coating is mainly the photodegradation of coating caused by ultraviolet rays. The test conditions of UV condensation test are as follows: irradiation level is 1.1W / (m 2 ·nm), each 12h cycle includes an 8h ultraviolet test at (60±1)℃ and a 4h condensation test at (50±1)℃; considering that the helicopter is parked outdoors for only a few hours a year to receive sunlight, it is reasonable to assume that the outdoor parking time is all sunshine time, and the total solar ultraviolet radiation can be evenly distributed within the sunshine time (that is, the change of solar radiation within the sunshine time is not considered), so as to estimate the total ultraviolet radiation that the coating sample may receive throughout the year. In this embodiment, the total solar ultraviolet radiation measured in the high-altitude and high-sand area where the helicopter is in service is 249MJ / m 2 The annual sunshine hours are 2388 hours, the outdoor parking time is 300 hours, and the irradiance level is 1.1W / (m 2 ·nm) The total UV radiation equivalent to UV light is 60W / m 2 Therefore, the total time of the UV condensation test is designed to be 9 days (249MJ / m 2 × 1 / 8 (the ratio of outdoor parking time to total annual sunshine hours: 300h / 2388h) ÷ 60W / m 2 ÷3600s÷16h (16h of UV irradiation per 24h)≈9d) to simulate the total UV radiation received by the coating sample throughout the year.

[0033] Among them, the salt solution spray-drying test: Corrosive media (pollutants) in the atmospheric environment include chlorine-containing gases, sulfur oxide gases, and nitrogen oxide gases, which can also affect the aging and adhesion loss of helicopter structural surface coatings. On the one hand, pollutants can dissolve into the water film formed on the surface of the organic coating, forming a conductive electrolyte solution. This then enters the coating / metal interface, causing corrosion reactions. The corrosion products react with groups on the molecular chain. On the other hand, the pollutants diffuse into the coating, where the active groups in the gas react with certain groups on the molecular chain, changing the molecular chain structure and causing degradation of the organic coating. In humid air environments, condensation forms a water film on the surface of the coating sample. Analysis of rainwater in the high-altitude, cold, and sandy regions where helicopters are used shows that the pH value of rainfall is as low as 6.38, averages 6.79, and reaches a maximum of 7.77. Rainwater (snow) also contains high concentrations of sulfate and chloride ions. Therefore, the experimental conditions of the salt solution spray-drying test are determined as follows: using a 0.05% Na2SO4 + 0.01% NaCl mixed solution, adjusting the pH value to 6-8 (neutral) with dilute sulfuric acid or NaOH solution to simulate the corrosive medium in the atmospheric environment, and controlling the sedimentation rate of the salt solution to 1-3 mL / (80 cm 2 ·h). Moreover, coatings exposed to the atmospheric environment will undergo repeated wetting-drying processes, which will continuously increase the concentration of corrosive media on the coating surface and accelerate corrosion. According to the statistical results of the relative humidity of the atmosphere in the high-altitude and sandy areas where helicopters are in service, the ratio of the wetting time throughout the year (wetting is defined as temperatures above 0°C and relative humidity ≥80%) to the drying time is approximately 1:11 to 1:7. Therefore, the larger value of 1:7 is used as the spray / drying cycle time ratio, that is, 3 hours of spraying and 21 hours of ventilation and drying in each 24-hour cycle to highlight the impact of alternating wet and dry conditions on the coating. The spray temperature is determined to be T = (35±1)°C, taking into account the ground temperature in the high-altitude and sandy areas and the dissolved oxygen concentration in the salt solution. The drying temperature is determined to be T = (35±1)°C, and the drying humidity RH is ≤ (50±3)%. The test time for one cycle is 7 days.

[0034] During the test, each cycle test lasts about 18 days in total. After the test, the test pieces are tested for appearance, gloss, color difference, thickness, infrared and other performance. One cycle test can simulate the outdoor use of a helicopter riveted structure in a high-altitude, cold and sandy area for one year.

[0035] This embodiment uses the helicopter skin riveted structure ( Figure 1 The experimental results are shown in Table 1-4.

[0036] Table 1 Appearance test results of skin flat plate coating samples

[0037]

[0038] Table 2 Appearance rating results of flat coating samples with direct machine skin riveting structure

[0039]

[0040] Table 3 60° gloss loss data and gloss loss degree levels of flat coating samples with direct machine skin riveting structure

[0041]

[0042] Table 4 Color difference data and discoloration grade of coating samples of flat plate with direct machine skin riveting structure

[0043]

[0044] Tables 1 to 4 show that after 12 months of exposure to a high-altitude, high-dust, and sandy outdoor atmospheric environment (8000 fatigue loading cycles before testing), the gloss loss rate and color difference values ​​of the typical helicopter skin riveted flat-plate coating specimens gradually increased with exposure time. The macroscopic corrosion morphology mainly showed slight staining, very slight gloss loss, very slight discoloration, and very slight damage to the topcoat at the rivet location. Both gloss loss and discoloration levels were graded 1, with no other significant changes. In contrast, after one cycle of laboratory accelerated testing, the macroscopic corrosion morphology of the typical helicopter skin riveted flat-plate coating specimens mainly showed slight staining, slight gloss loss, slight discoloration, and slight damage to the topcoat at the rivet location. This indicates that the laboratory test results are generally consistent with those of the natural environment test in the high-altitude, high-dust, and sandy region. Testing according to the given laboratory accelerated test environmental profile for helicopter riveted structures simulates the high-altitude, high-dust, and sandy atmospheric environment, providing very accurate simulation results at high acceleration rates and significantly shortening test assessment time.

Claims

1. A method for testing helicopter connection structures in a high-altitude, cold, and sandy atmospheric environment, characterized by: The test pieces were subjected to low-temperature fatigue test, sand and dust test, temperature shock test, UV-condensation test and salt solution spray-drying test in sequence; The low temperature fatigue test is to apply a pull-pull sinusoidal fatigue load equivalent to one year of flight strength to the test piece. The sand and dust test is a combination test of normal temperature dust blowing, high temperature dust blowing, and high temperature sand blowing. The temperature shock test is a shock test conducted under the extreme temperature atmosphere of the area where the helicopter is in service. The UV-condensation test is an alternating UV-condensation test conducted on helicopter connection structure test pieces in combination with the highest temperature and the maximum annual solar UV radiation value measured in the area where the helicopter is in service. The salt solution spray-drying test is a salt spray-drying alternating test conducted on helicopter connection structure test pieces in combination with the highest chloride ion content and rainwater pH value measured in the area where the helicopter is in service; The test conditions of the low-temperature fatigue test are as follows: the test frequency is 16 Hz according to the movement law of the helicopter rotor, the stress peak is 75 MPa with reference to the maximum design load that the helicopter fuselage skin structure can withstand, the stress valley is 4.5 MPa, the number of fatigue load cycles is 8,000 times, and the test temperature is 12°C lower than the lowest temperature in the area where the helicopter is in service; The test conditions of the dust and sand test are as follows: the temperature of the high-temperature dust blowing test and the sand blowing test are both the highest temperature in the area where the helicopter is in service, the relative humidity is ≤30%, the wind speed of the dust blowing test is 8.9 m / s, and the wind speed of the sand blowing test is the maximum hourly average wind speed on the ground in the area where the helicopter is in service ±2 m / s. The diameter of the dust and sand in the dust blowing test are both controlled within the range of the measured particle size in the area where the helicopter is in service. The concentration of the dust blowing test is (10.6±7) g / m 3 , sand blowing test concentration is (2.2±0.5) g / m 3 , the duration of dust blowing test is 12h, and the duration of sand blowing test is 1.5h; The test conditions of the temperature shock test are: continuous shock for 4 hours at a low temperature of -31±2°C, continuous shock for 2 hours at a high temperature of 43±1°C, and 3 cycles of shock. The test conditions of the UV-condensation test are: irradiance level at 340 nm 1.1 W / (m 2 / nm), each 12h cycle includes 8h of ultraviolet test at (60±1)℃ and 4h of condensation test at (50±1)℃, and the test time is 9 days; The test conditions of the salt solution spray-drying test are as follows: the corrosive medium is a mixed solution of 0.05% Na2SO4 and 0.01% NaCl, the pH value is adjusted to 6-8 with dilute sulfuric acid or NaOH solution, and the sedimentation rate of the salt solution is controlled to 1-3 mL / (80 cm2·h); During the wet-drying test, in each 24-hour cycle, salt spraying is performed for 3 hours and ventilation drying is performed for 21 hours. The salt spraying temperature is set at T = (35 ± 1) °C according to the highest temperature measured, the drying temperature is set at T = (35 ± 1) °C, and the drying humidity is RH = (50 ± 3)%. The test time for one cycle of the salt solution spray-drying test is 7 days. The total duration of each test cycle is 18 days.

2. The test method according to claim 1, characterized in that The specific steps of implementing the salt solution spray-drying test include: obtaining the ratio of the wetting time to the drying time measured throughout the year in the area where the helicopter is in service, using the maximum value of the ratio as the cycle time ratio of spraying and drying, and selecting the highest temperature measured in the area where the helicopter is in service as the spray temperature.

3. The test method according to claim 2, characterized in that: The helicopter connection structure is the riveted part of the helicopter skin side panel.

4. The test method according to claim 3, characterized in that: When performing the dust test, the test surface of the test piece is perpendicular to the dust blowing direction.

5. The test method according to claim 4, characterized in that: The sand and dust test and UV irradiation are only performed on the test surface of the test piece.

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