Test and measurement system and method for the electrical breakdown ignition characteristics of ignition sources for aircraft composite fuel tank fasteners

Abstract

This invention discloses a test and measurement system and method for the electrical breakdown and ignition characteristics of fasteners in aircraft composite fuel tanks. The test and measurement system includes a pulse electrical breakdown test power supply, a carbon fiber composite laminate for fasteners, an electrical breakdown injection clamping mechanism and adjustment unit, a control, measurement and analysis unit for the electrical breakdown test, and an electrical breakdown spark monitoring unit. By obtaining test data on the electrical breakdown and spark state characteristics of the fastener-composite material laminate under pulse voltage, the correlation between the electrical breakdown and ignition source characteristics of the fastener-composite material interface and factors such as the moisture content of the fastener-composite material interface sample, the fastener structure, and the electrical parameters of the pulse voltage is obtained. The correlation law between the ignition source characteristics of typical fastener structures in fuel tanks and lightning electrical parameters, action conditions, and flight environment characteristics is obtained, laying the foundation for quantitative prediction and safety assessment research of ignition sources of fasteners in large aircraft fuel tanks.

Description

Technical Field

[0001] This invention relates to the field of composite material testing, specifically to test methods for the properties of carbon fiber composite fasteners, and particularly to a test and measurement system and method for the electrical breakdown ignition characteristics of fasteners in aircraft composite fuel tanks. Background Technology

[0002] Carbon fiber composites possess properties such as low density, high strength, high modulus, high temperature resistance, and chemical corrosion resistance, while also exhibiting the flexibility and processability of textile fibers. They are widely used in aerospace, military, and civilian industries. With improvements in aircraft design and advancements in carbon fiber composite technology, the use of carbon fiber reinforced polymer (CFRP) composites in large civil aircraft, military aircraft, drones, and stealth aircraft is continuously increasing. Currently, CFRP materials account for 50% of the main wing, tail, fuselage, and floor structures of the Boeing B787; 53% of the materials on the Airbus A350XWA; 12% on the Chinese C919; and the second-generation C929 will use 50% CFRP materials, with composite fuel tanks explicitly being used.

[0003] Lightning is a multi-stage, continuous discharge process involving high-voltage shock waves induced by large currents, magnetic fields, and Joule heating effects. The strong currents, magnetic fields, and accompanying shock waves generated by lightning cause combustion, erosion, and explosions in aircraft materials, leading to structural distortion and reduced strength, posing a serious threat to the safe operation of aircraft. Fuel tanks are a crucial component of complex aircraft systems, responsible for storing fuel, adjusting the center of gravity, and cooling equipment. In the past 50 years, there have been 18 fuel tank explosions in civil transport aircraft worldwide, resulting in 542 deaths. The fuel system, composed of integral fuselage or wing fuel tanks, is the most vulnerable system in an aircraft, and fuel tank explosions have become one of the major threats to civil aviation safety, drawing serious attention from airworthiness authorities worldwide.

[0004] To significantly reduce the probability of fuel tank explosions in civil aircraft, the U.S. Federal Aviation Administration, the European Aviation Safety Agency, and the Civil Aviation Administration of China have all issued clear regulations on the test methods and airworthiness requirements for ignition sources of aircraft fuel tanks. Ignition sources for aircraft fuel tanks include filament heating caused by current-carrying wires, electrostatic breakdown, lightning strikes causing hot spots, frictional heating, edge corona formation, and electric arcs / sparks. Ignition mechanisms can be broadly categorized into "electric ignition" and "hot spot ignition."

[0005] In the new carbon fiber composite aircraft fuel tank structure, the assembly structure and interface characteristics of the fasteners themselves are the main factors leading to electric field breakdown and current conduction hot spots. Sparks, temperature rises, and air jet phenomena caused at the structural interface become the source of fuel tank ignition.

[0006] The existing ignition source for large aircraft fuel tanks mainly uses a spark source of a certain energy to test the combustion method of combustible gas with a predetermined concentration. The energy of the spark discharge is obtained by calculating the energy of various components such as inductance and resistance in the discharge circuit. However, the judgment result is a digital quantity, with only two results: "combustible" and "non-combustible". It is impossible to achieve quantitative prediction and safety assessment of the ignition source. Summary of the Invention

[0007] To address the shortcomings of existing technologies, the present invention aims to provide a test and measurement system and method for the electrical breakdown ignition characteristics of fasteners in aircraft composite fuel tanks, laying the foundation for the structural design and risk assessment of ignition sources for fuel tanks struck by lightning.

[0008] This invention is achieved through the following technical solution:

[0009] A test and measurement system for the electrical breakdown ignition characteristics of fasteners in aircraft composite fuel tanks includes a pulse electrical breakdown test power supply, a carbon fiber composite laminate for fasteners, an electrical breakdown injection clamping mechanism and adjustment unit, a control, measurement and analysis unit for electrical breakdown tests, and an electrical breakdown spark monitoring unit.

[0010] The pulse electrical breakdown test power supply is used to generate pulse voltage waves with adjustable rise time. It includes an adjustable high-voltage DC charging power supply and an adjustable rise time pulse voltage generating unit. The charging voltage of the adjustable high-voltage DC charging power supply to the adjustable rise time pulse voltage generating unit is monitored online by a charging voltage monitoring sensor, and the analog charging voltage is transmitted to the control unit of the control and measurement analysis unit of the electrical breakdown ignition test.

[0011] The fastener carbon fiber composite laminate sample is clamped and pulsed voltage is conducted into the fastener carbon fiber composite laminate sample through an electrical breakdown injection clamping mechanism and adjustment unit.

[0012] The electrical breakdown injection clamping mechanism and adjustment unit are used to clamp the fastener carbon fiber composite laminate sample and apply pulse voltage to the fastener carbon fiber composite laminate sample.

[0013] The control and measurement analysis unit for the electrical breakdown ignition test is used to control the ignition characteristics test of the fastener carbon fiber composite laminate ignition source and to measure and analyze the electrical breakdown pulse parameters, including a control unit and an electrical breakdown measurement and analysis unit.

[0014] The electrical breakdown spark monitoring unit is used to observe the occurrence and development process of the electrical spark of the fastener carbon fiber ignition source, and to obtain the electrical spark process of the fastener carbon fiber ignition source.

[0015] The fastener carbon fiber composite laminate is clamped by an electrical breakdown injection clamping mechanism and adjustment unit, and a pulse voltage is applied to the sample by a pulse electrical breakdown test power supply. The occurrence and development process of the electrical spark of the fastener carbon fiber ignition source is obtained by the electrical breakdown spark monitoring unit. The control and measurement analysis unit of the electrical breakdown ignition test controls the ignition characteristics test of the fastener carbon fiber composite laminate and measures and analyzes the electrical breakdown pulse parameters. Finally, a correlation database is obtained between the electrical breakdown and electrical spark characteristics of the fastener carbon fiber composite laminate and the fastener-composite material mating structure, temperature and humidity, and pulse voltage electrical parameters. This forms a database of electrical breakdown and ignition source characteristics of the fastener ignition source of the composite fuel tank simulating the flight environment of a large aircraft.

[0016] Furthermore, the adjustable high-voltage DC charging power supply consists of an electronically controlled voltage regulator T1, a transformer T2, a rectifier silicon stack D, and a current-limiting resistor Rc;

[0017] The adjustable rise time pulse voltage generating unit consists of a main pulse energy storage capacitor C1, a high voltage discharge switch G, an adjustable waveform forming resistor R1, an adjustable waveform forming resistor R2, and a forming capacitor C2. The fastener carbon fiber composite laminate is connected to the output terminal of the adjustable rise time pulse voltage generating unit through an electrical breakdown injection clamping mechanism and an adjustment unit.

[0018] Furthermore, the electrical breakdown injection clamping mechanism and adjustment unit are mounted on an adjustable-position double-sided structure clamp on an insulating plate. The double-sided structure clamp consists of two insulating baffles connected by bolts. Plate-shaped high-voltage injection electrode HV and low-voltage return electrode LV are installed on the inner side of each double-sided insulating baffle. The high-voltage end of the pulse electrical breakdown test power supply is connected to the high-voltage injection electrode HV, and the low-voltage end is connected to the low-voltage return electrode LV of the electrode structure.

[0019] Furthermore, the control unit includes a charging voltage monitoring circuit and a programmable controller; the charging voltage monitoring circuit of the control unit receives the signal transmitted from the charging voltage monitoring sensor, and after processing by the programmable controller, controls the discharge of the high-voltage discharge switch G of the pulse voltage generating unit with adjustable rise time.

[0020] The programmable controller is also combined with the industrial control computer of the electrical breakdown measurement and analysis unit to control the connection / disconnection, high voltage rise / fall, and high voltage discharge switch G of the charging process for the ignition characteristics test of the fastener carbon fiber composite laminate, thereby realizing the automatic control of the ignition characteristics test process of the fastener carbon fiber composite laminate.

[0021] Furthermore, the electrical breakdown measurement and analysis unit includes a pulse voltage sensor, a digital oscilloscope, and an industrial control computer;

[0022] The pulse voltage sensor, in conjunction with an array digital oscilloscope, measures the pulse voltage between the high-pressure injection point and the low-pressure return point of the carbon fiber composite laminate of the fastener. The industrial control computer processes and analyzes the pulse voltage signal measured by the digital oscilloscope to obtain the electrical breakdown voltage U under various parameters, including the fastener assembly method and ambient temperature and humidity.

[0023] Furthermore, the electrical breakdown spark monitoring unit includes a high-speed camera monitoring instrument and a high-speed camera control computer; the high-speed camera monitoring instrument observes the occurrence and development process of the electrical spark of the fastener carbon fiber ignition source, and its imaging process is controlled by the high-speed camera control computer.

[0024] The test and measurement methods for the ignition source breakdown ignition characteristics of fasteners for aircraft composite fuel tanks include the following steps:

[0025] 1) Sample selection and treatment: Multiple fastener composite laminate samples were selected and subjected to temperature and humidity treatment to simulate the actual flight environment of large aircraft.

[0026] 2) Install the first fastener composite laminate sample with different humidity in the electrical breakdown injection clamping mechanism and adjustment unit, and connect the high voltage injection electrode HV and low voltage return electrode LV of the electrical breakdown injection clamping mechanism and adjustment unit to the high voltage and low voltage output ports of the adjustable rise time pulse voltage generation unit.

[0027] 3) Apply lightning voltage pulses to the fastener composite laminate, and change the pulse voltage time while keeping the peak value of the pulse voltage constant to obtain the breakdown characteristics and electrical breakdown ignition characteristics of the fastener carbon fiber composite laminate under different humidity conditions. The breakdown electric spark characteristics are detected by pulse voltage sensor and electrical breakdown spark monitoring unit.

[0028] 4) While keeping the pulse voltage rise time constant, the peak value of the pulse voltage was changed to obtain the breakdown characteristics and electrical breakdown ignition characteristics of the fastener carbon fiber composite laminate under different humidity conditions. The breakdown electric spark characteristics were detected by using a pulse voltage sensor and an electrical breakdown spark monitoring unit.

[0029] 5) Repeat process 2) to process 4) sequentially using fastener carbon fiber composite laminates with different humidity, temperature and assembly methods to obtain a correlation database between the breakdown voltage, breakdown electric spark characteristics and sample temperature and humidity, pulse voltage rise rate, duration, peak value and assembly method of the fastener carbon fiber composite laminate.

[0030] 6) Perform multi-factor regression statistical analysis on all lightning strike test results to obtain the correlation between the ignition source characteristics of typical fastener structures of fuel tanks and lightning electrical parameters, temperature and humidity flight environment characteristics, and assembly structure.

[0031] Furthermore, the assembly method includes achieving clearance fit and interference fit by adjusting the distance between the bilateral insulating baffles, and filling the space between the high-voltage injection electrode HV and the low-voltage return electrode LV and the carbon fiber composite material with insulating materials having different dielectric constants.

[0032] The present invention has the following beneficial effects:

[0033] This invention establishes an experimental system for electrical breakdown and spark characteristics of fastener-composite material interfaces, proposes an experimental method for ignition source characteristics of fastener-composite material interfaces, and obtains experimental data on the electrical breakdown and spark state characteristics of fastener-composite material laminates under pulse voltage. Through the observation results of the electrical breakdown and spark process monitoring unit, the correlation between the electrical breakdown and ignition source characteristics of fastener-composite material interfaces and factors such as the moisture content of the fastener-composite material interface sample, fastener structure, and pulse voltage electrical parameters is finally obtained. This forms a database of electrical breakdown and spark characteristics of fuel tank ignition sources simulating the flight environment of large aircraft, and obtains the correlation law between the ignition source characteristics of typical fastener structures in fuel tanks and lightning electrical parameters, action conditions, and flight environment characteristics, laying the foundation for quantitative prediction and safety assessment research of fastener ignition sources in large aircraft fuel tanks. Attached Figure Description

[0034] Figure 1 This is a structural block diagram of the composite fastener ignition source ignition characteristic test system of the present invention;

[0035] Figure 2 This is a circuit block diagram of the composite fastener ignition source ignition characteristic test system of the present invention;

[0036] Figure 3 This is a schematic diagram of the clamping structure for testing the ignition characteristics of the composite fasteners of the present invention.

[0037] Figure 4 This is a flowchart of the test and analysis method for the ignition characteristics of fastener composite materials. Detailed Implementation

[0038] The present invention will be further described in detail below with reference to specific embodiments. These descriptions are for explanation purposes only and are not intended to limit the scope of the invention.

[0039] join Figure 1 , Figure 2The present invention provides a test and measurement system for the electrical breakdown ignition characteristics of fasteners in aircraft composite fuel tanks. The system consists of a pulse electrical breakdown test power supply 1, a carbon fiber composite laminate fastener 2, an electrical breakdown injection clamping mechanism and adjustment unit, an electrical breakdown test control, measurement and analysis unit 3, and an electrical breakdown spark monitoring unit 4.

[0040] The pulse electrical breakdown test power supply 1 mainly consists of an adjustable high-voltage DC charging power supply 1-1 and an adjustable rise time pulse voltage generating unit 1-2, used to generate pulse voltage waves with adjustable rise times. During actual testing, the charging voltage of the adjustable high-voltage DC charging power supply 1-1 to the adjustable rise time pulse voltage generating unit 1-2 is monitored online by a charging voltage monitoring sensor 1-3, and the analog charging voltage is transmitted to the control unit 31 of the electrical breakdown ignition test control and measurement analysis unit 3. The function of the adjustable rise time pulse voltage generating unit 1-2 is to generate pulse voltage waves with adjustable rise times.

[0041] See Figure 2 The circuit diagram of the pulse electrical breakdown test power supply 1 for testing the spark characteristics of the carbon fiber ignition source of the fastener of the present invention mainly consists of two parts: an adjustable high voltage DC charging power supply 1-1 and an adjustable rise time pulse voltage generating unit 1-2.

[0042] The adjustable high-voltage DC charging power supply 1-1 mainly consists of an electronically controlled voltage regulator T1, a transformer T2, a rectifier silicon stack D, and a current-limiting resistor Rc.

[0043] The adjustable rise time pulse voltage generating unit 1-2 mainly consists of a main pulse energy storage capacitor C1, a high voltage discharge switch G, adjustable waveform forming resistors R1 and R2, and a forming capacitor C2. They are electrically connected in series and parallel, and the fastener carbon fiber composite laminate plate 2 sample and its connecting fixture are connected in parallel to the output terminal of the adjustable rise time pulse voltage generating unit 1-2.

[0044] The control and measurement analysis unit 3 for the electrical breakdown ignition test is responsible for controlling the ignition characteristics test of the fastener carbon fiber composite ignition source and measuring and analyzing the electrical breakdown pulse parameters. It mainly consists of a control unit 31 and an electrical breakdown measurement and analysis unit 32. The control unit 31 primarily comprises a charging voltage monitoring circuit 31-1 and a programmable controller 31-2. The charging voltage monitoring circuit 31-1 of the control unit 31 receives signals from the charging voltage monitoring sensor 1-3, and after processing by the programmable controller 31-2, controls the discharge of the high-voltage discharge switch G of the adjustable rise time pulse voltage generating unit 1-2. Furthermore, the programmable controller 31-2, in conjunction with the industrial control computer 32-4 of the electrical breakdown measurement and analysis unit 32, controls the connection / disconnection, high voltage rise / fall, and conduction of the high-voltage discharge switch G during the charging process of the fastener carbon fiber composite ignition source ignition characteristics test, thus achieving automatic control of the fastener carbon fiber composite ignition source ignition characteristics test process.

[0045] The electrical breakdown measurement and analysis unit 32 is used to control the ignition characteristic test of the fastener carbon fiber ignition source and to measure and analyze the electrical breakdown pulse parameters. It also enables process control of the ignition characteristic test of the fastener carbon fiber composite material and the measurement and analysis of the electrical breakdown pulse parameters. The electrical breakdown measurement and analysis unit 32 mainly consists of a pulse voltage sensor 32-1, a digital oscilloscope 32-3, and an industrial control computer 32-4. The pulse voltage sensor 32-1, in conjunction with the array digital oscilloscope 32-3, measures the pulse voltage between the high-pressure injection point and the low-pressure return point of the fastener carbon fiber composite material. The industrial control computer 32-4 processes and analyzes the pulse voltage signal measured by the digital oscilloscope 32-3 to obtain the electrical breakdown voltage U under parameters including fastener assembly method and ambient temperature and humidity.

[0046] The electrical breakdown spark monitoring unit 4 observes the occurrence and development process of the electric spark from the ignition source of the fastener carbon fiber. It mainly consists of a high-speed camera monitoring instrument 41-1 and a high-speed camera control computer 41-2. The main function of the high-speed camera monitoring instrument 41-1 is to observe the occurrence and development process of the electric spark from the ignition source of the fastener carbon fiber. Its imaging process is controlled by the high-speed camera control computer 41-2, and the electric spark process of the fastener carbon fiber ignition source is obtained through the electrical breakdown spark monitoring unit 4.

[0047] The carbon fiber composite material 2 of the sample fastener is clamped and pulsed voltage is conducted and injected into the sample fastener carbon fiber composite material 2 through an electrical breakdown injection clamping mechanism and adjustment unit.

[0048] See Figure 3As shown, the electrical breakdown injection clamping mechanism and adjustment unit are used to clamp the fastener carbon fiber composite laminate specimen and apply pulse voltage to it. The electrical breakdown injection clamping mechanism and adjustment unit is a double-sided clamp A2 mounted on an insulating plate A1 with an adjustable locking position. The double-sided clamp A2 consists of two insulating baffles connected by bolts. The installation position of the insulating baffles is adjusted by nuts A3 and screws A4 to clamp the different fastener carbon fiber composite laminate specimens. A high-voltage injection electrode HV and a low-voltage return electrode LV are installed inside each of the double-sided insulating baffles. The high-voltage injection electrode HV and the low-voltage return electrode LV are mounted on the insulating plate. Their function is to connect the fastener carbon fiber composite laminate specimen to the pulse electrical breakdown test power supply circuit. The high-voltage end of the pulse electrical breakdown test power supply is connected to the high-voltage injection electrode HV of the electrical breakdown injection clamping mechanism and adjustment unit. The high-voltage injection electrode HV is a plate-shaped electrode with a certain thickness. The low-voltage end of the pulse electrical breakdown test power supply is connected to the low-voltage return electrode of the electrode structure.

[0049] See Figure 4 The test and measurement methods for the ignition characteristics of carbon fiber composite fasteners are as follows:

[0050] 1) Sample Selection and Treatment: Fastener composite laminate samples were selected and treated, mainly including temperature and humidity control, to simulate the actual flight environment of a large aircraft. The sample temperature and humidity conditions were measured at least five points, denoted as S. m1 To S m5 .

[0051] 2) Install the first fastener composite laminate sample with different humidity in the electrical breakdown injection clamping mechanism and adjustment unit, and connect the high voltage injection electrode HV and the low voltage return electrode LV of the electrical breakdown injection clamping mechanism and adjustment unit to the high voltage and low voltage output ports of the adjustable rise time pulse voltage generation unit 2.

[0052] 3) For the fastener composite material laminate 2, under the condition of keeping the peak value of the pulse voltage constant, the pulse voltage time is changed to obtain the breakdown characteristics and electrical breakdown ignition characteristics of the fastener carbon fiber composite material laminate 2 under different humidity conditions, and the breakdown electric spark characteristics are detected by pulse voltage sensor 32-1 and electrical breakdown spark monitoring unit 4.

[0053] 4) While keeping the pulse voltage rise time constant, the peak value of the pulse voltage is changed to obtain the breakdown characteristics and electrical breakdown ignition characteristics of the fastener carbon fiber composite laminate under different humidity conditions. The breakdown electric spark characteristics are detected by pulse voltage sensor 32-1 and electrical breakdown spark monitoring unit 4.

[0054] 5) Change the humidity of the fastener carbon fiber composite material and repeat process 2) to 4) to obtain a database of the correlation between the breakdown voltage, breakdown electric spark characteristics and multiple factors such as sample temperature and humidity, pulse voltage rise rate, duration, peak value, and assembly structure of the fastener carbon fiber composite material.

[0055] 6) Similarly, the influencing factors of fastener EDM characteristics can also include the assembly method of fastener and carbon fiber composite material, including clearance fit, interference fit, and filling the space between the high-voltage injection electrode HV and the low-voltage return electrode LV and the carbon fiber composite material with insulating materials of different dielectric constants, etc.

[0056] 7) Perform multi-factor regression statistical analysis on all lightning strike test results to obtain the correlation between the ignition source characteristics of typical fastener structures of fuel tanks and lightning electrical parameters, temperature and humidity flight environment characteristics.

[0057] 8) Statistical analysis of electrical breakdown and electric spark characteristics test structures, including research on the electrical breakdown and breakdown electric spark characteristics and influencing factors of carbon fiber composite fasteners, mainly including two aspects:

[0058] First, the temperature and humidity of the fastener carbon fiber composite laminate were adjusted to simulate different flight electrical environments of large aircraft, and pulse voltage waves with different rise rates and intensities were applied. The electrical breakdown characteristics and electrical breakdown ignition characteristics of the fastener carbon fiber composite laminate were obtained through pulse voltage sensors and electrical breakdown spark monitoring units, as well as the attachment area of ​​lightning on the end face of the standing trees in the sample forest.

[0059] Secondly, the electrical breakdown ignition source characteristics of the fastener carbon fiber composite laminate were analyzed. Through experiments, a correlation database was established between the electrical breakdown, electrical breakdown ignition source and other factors of the fastener carbon fiber composite laminate. The multi-factor regression method was used to obtain the correlation regularity between the ignition source characteristics of typical fastener structures and lightning electrical parameters, temperature and humidity flight environment characteristics, and the evaluation method of ignition source characteristics.

Claims

1. A test and measurement system for the electrical breakdown ignition characteristics of fasteners for aircraft composite fuel tanks, characterized in that: It includes a pulse electrical breakdown test power supply (1), a fastener carbon fiber composite laminate (2), an electrical breakdown injection clamping mechanism and adjustment unit, an electrical breakdown test control, measurement and analysis unit (3), and an electrical breakdown spark monitoring unit (4); The pulse electrical breakdown test power supply (1) is used to generate pulse voltage waves with adjustable rise time. It includes an adjustable high voltage DC charging power supply (1-1) and an adjustable rise time pulse voltage generating unit (1-2). The adjustable high voltage DC charging power supply (1-1) monitors the charging voltage of the adjustable rise time pulse voltage generating unit (1-2) online by the charging voltage monitoring sensor (1-3) and transmits the analog charging voltage to the control unit (31) of the control and measurement analysis unit (3) of the electrical breakdown ignition test. The fastener carbon fiber composite laminate (2) sample is clamped and pulsed voltage is conducted into the fastener carbon fiber composite laminate (2) sample through an electrical breakdown injection clamping mechanism and adjustment unit; The electrical breakdown injection clamping mechanism and adjustment unit are used to clamp the fastener carbon fiber composite laminate (2) sample and apply pulse voltage to the fastener carbon fiber composite laminate sample. The control and measurement analysis unit (3) for the electrical breakdown ignition test is used to control the ignition characteristics test of the fastener carbon fiber composite laminate ignition source and to measure and analyze the electrical breakdown pulse parameters, including a control unit (31) and an electrical breakdown measurement and analysis unit (32). The electrical breakdown spark monitoring unit (4) is used to observe the occurrence and development process of the electrical spark of the fastener carbon fiber ignition source and obtain the electrical spark process of the fastener carbon fiber ignition source. The fastener carbon fiber composite laminate (2) is clamped by the electrical breakdown injection clamping mechanism and adjustment unit, and a pulse voltage is applied to the sample by the pulse electrical breakdown test power supply (1). The occurrence and development process of the electrical spark of the fastener carbon fiber ignition source is obtained by the electrical breakdown spark monitoring unit (4). The control and measurement analysis unit (3) of the electrical breakdown ignition test controls the ignition characteristics test of the fastener carbon fiber composite laminate and measures and analyzes the electrical breakdown pulse parameters. The test is repeated with fastener carbon fiber composite laminates with different humidity, temperature and assembly methods to obtain the correlation database between the breakdown voltage and breakdown electrical spark characteristics of the fastener carbon fiber composite laminate and the sample temperature and humidity, pulse voltage rise rate, duration, peak value and assembly method. Finally, the correlation database between the electrical breakdown and electrical spark characteristics of the fastener carbon fiber composite laminate and the fastener-composite material mating structure, temperature and humidity, pulse voltage electrical parameters is obtained, forming a database of electrical breakdown and ignition source characteristics of the fastener ignition source of composite fuel tank simulating the flight environment of a large aircraft.

2. The test and measurement system for the electrical breakdown ignition characteristics of aircraft composite fuel tank fasteners according to claim 1, characterized in that: The adjustable high-voltage DC charging power supply (1-1) consists of an electronically controlled voltage regulator T1, a transformer T2, a rectifier silicon stack D, and a current-limiting resistor Rc. The adjustable rise time pulse voltage generating unit (1-2) consists of a main pulse energy storage capacitor C1, a high voltage discharge switch G, an adjustable waveform forming resistor R1, an adjustable waveform forming resistor R2, and a forming capacitor C2. The fastener carbon fiber composite laminate (2) is connected to the output terminal of the adjustable rise time pulse voltage generating unit (1-2) through an electrical breakdown injection clamping mechanism and an adjustment unit.

3. The test and measurement system for the electrical breakdown ignition characteristics of aircraft composite fuel tank fasteners according to claim 1, characterized in that: The electrical breakdown injection clamping mechanism and adjustment unit are mounted on an insulating plate (A1) with an adjustable locking position double-sided structure clamp (A2). The double-sided structure clamp (A2) consists of two insulating baffles connected by bolts. Plate-shaped high-voltage injection electrode HV and low-voltage return electrode LV are installed on the inner side of the double-sided insulating baffles respectively. The high-voltage end of the pulse electrical breakdown test power supply (1) is connected to the high-voltage injection electrode HV, and the low-voltage end is connected to the low-voltage return electrode LV of the electrode structure.

4. The test and measurement system for the electrical breakdown ignition characteristics of aircraft composite fuel tank fasteners according to claim 2, characterized in that: The control unit (31) includes a charging voltage monitoring circuit (31-1) and a programmable controller (31-2); the charging voltage monitoring circuit (31-1) of the control unit (31) receives the signal transmitted from the charging voltage monitoring sensor (1-3), and after processing by the programmable controller (31-2), it controls the discharge of the high-voltage discharge switch G of the pulse voltage generating unit (1-2) with adjustable rise time. The programmable controller (31-2) is also combined with the industrial control computer (32-4) of the electrical breakdown measurement and analysis unit (32) to control the connection / disconnection, high voltage rise / fall and high voltage discharge switch G of the fastener carbon fiber composite laminate ignition source ignition characteristic test charging process, thereby realizing the automatic control of the fastener carbon fiber composite laminate ignition source ignition characteristic test process.

5. The test and measurement system for the electrical breakdown ignition characteristics of aircraft composite fuel tank fasteners according to claim 2, characterized in that: The electrical breakdown measurement and analysis unit (32) includes a pulse voltage sensor (32-1), a digital oscilloscope (32-3), and an industrial control computer (32-4); The pulse voltage sensor (32-1) and the array digital oscilloscope (32-3) are used together to measure the pulse voltage between the high-pressure injection point and the low-pressure return point of the fastener carbon fiber composite laminate. The industrial control computer (32-4) processes and analyzes the pulse voltage signal measured by the digital oscilloscope (32-3) to obtain the electrical breakdown voltage U under the fastener assembly method and ambient temperature and humidity parameters.

6. The test and measurement system for the electrical breakdown ignition characteristics of aircraft composite fuel tank fasteners according to claim 4 or 5, characterized in that: The electrical breakdown spark monitoring unit (4) includes a high-speed camera monitoring instrument (41-1) and a high-speed camera control computer (41-2); the high-speed camera monitoring instrument (41-1) observes the occurrence and development process of the electrical spark of the fastener carbon fiber ignition source, and its imaging process is controlled by the high-speed camera control computer (41-2).

7. A method for testing and measuring the electrical breakdown ignition characteristics of fasteners in aircraft composite fuel tanks based on the test and measurement system described in claim 6, characterized in that... Includes the following steps: 1) Sample selection and treatment: Multiple fastener composite laminate samples were selected and subjected to temperature and humidity treatment to simulate the actual flight environment of large aircraft. 2) Install the first fastener composite laminate sample with different humidity in the electrical breakdown injection clamping mechanism and adjustment unit, and connect the high voltage injection electrode HV and low voltage return electrode LV of the electrical breakdown injection clamping mechanism and adjustment unit to the high voltage and low voltage output ports of the adjustable rise time pulse voltage generation unit (1-2). 3) Apply lightning voltage pulses to the fastener composite laminate (2), and change the pulse voltage time while keeping the peak value of the pulse voltage constant, to obtain the breakdown characteristics and electrical breakdown ignition characteristics of the fastener carbon fiber composite laminate (2) under different humidity conditions, and use pulse voltage sensor (32-1) and electrical breakdown spark monitoring unit (4) to detect the breakdown electric spark characteristics. 4) Under the condition of keeping the pulse voltage rise time constant, change the peak value of the pulse voltage to obtain the breakdown characteristics and electrical breakdown ignition characteristics of the fastener carbon fiber composite laminate under different humidity conditions, and use a pulse voltage sensor (32-1) and an electrical breakdown spark monitoring unit (4) to detect the breakdown electric spark characteristics. 5) Repeat process 2) to process 4) sequentially using fastener carbon fiber composite laminates with different humidity, temperature and assembly methods to obtain a correlation database between the breakdown voltage, breakdown electric spark characteristics and sample temperature and humidity, pulse voltage rise rate, duration, peak value and assembly method of the fastener carbon fiber composite laminate. 6) Perform multi-factor regression statistical analysis on all lightning strike test results to obtain the correlation between the ignition source characteristics of typical fastener structures of fuel tanks and lightning electrical parameters, temperature and humidity flight environment characteristics, and assembly structure.

8. The test and measurement method for the electrical breakdown ignition characteristics of aircraft composite fuel tank fasteners according to the test and measurement system of claim 7, characterized in that: Assembly methods include achieving clearance fit and interference fit by adjusting the distance between the double-sided insulating baffles, and filling the space between the high-voltage injection electrode HV and the low-voltage return electrode LV and the carbon fiber composite material with insulating materials having different dielectric constants.

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