Test and measurement system and method for ignition characteristics of thermal jet ignition source of aircraft composite fuel tank fasteners

Abstract

This invention discloses a test and measurement system and method for the thermal injection ignition characteristics of fasteners in aircraft composite fuel tanks. The test system includes an adjustable high-voltage DC charging power supply, a lightning current discharge unit simulating a natural lightning environment, and a control, measurement, and analysis unit for the thermal injection ignition test. Based on the mating structure characteristics of the fastener carbon fiber composite laminate, the system obtains the correlation between the impact force and thermal spark characteristics of the thermal injection high-temperature airflow at the interface of the fastener carbon fiber composite laminate and factors such as the mating structure of the fastener carbon fiber composite laminate, climatic environment such as temperature and humidity, and lightning current electrical parameters. This forms a database of thermal injection ignition characteristics of fasteners in composite fuel tanks simulating the flight environment of large aircraft, laying the foundation for the research on multi-physics modeling, ignition mechanism, and prediction algorithms for lightning strikes on ignition sources of large aircraft composite fuel tanks.

Description

Technical Field

[0001] This invention relates to carbon fiber composite material testing technology, specifically to testing methods for the properties of carbon fiber composite fasteners, and particularly to a testing and measurement system and method for the thermal jet ignition characteristics of aircraft composite fuel tank fasteners. 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, static heat injection, lightning-induced hot spots, frictional heating, edge corona formation, and electric arcs / sparks, but the 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 method 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 thermal jet ignition characteristics of fasteners for aircraft composite fuel tanks, laying the foundation for the structural design and risk assessment of ignition sources for lightning-damaged fuel tanks.

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

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

[0010] The pulsed thermal spray test power supply includes an adjustable high-voltage DC charging power supply and a lightning current generation unit that simulates a natural lightning environment. The lightning current generation unit that simulates a natural lightning environment generates a lightning current wave with an adjustable rise time. The charging voltage of the adjustable high-voltage DC charging power supply to the lightning current generation unit that simulates a natural lightning environment is monitored online by a charging voltage monitoring sensor, and the analog charging voltage is transmitted to the control and measurement analysis unit of the thermal spray ignition test.

[0011] The control and measurement analysis unit for the thermal injection ignition test is used for the control of the test and the measurement and analysis of thermal injection pulse parameters, including a control unit and a thermal injection measurement and analysis unit;

[0012] The thermal jet spark monitoring unit is used to obtain the occurrence and development process of the electric spark from the carbon fiber ignition source of the fastener. It includes a high-speed camera monitoring instrument and a high-speed camera control computer. The high-speed camera monitoring instrument's imaging process is controlled by the high-speed camera control computer.

[0013] The thermal injection clamping mechanism and adjustment unit are used for clamping the fastener carbon fiber composite laminate sample and for applying lightning current to the fastener carbon fiber composite laminate sample via arc and conduction injection.

[0014] Lightning current waves of different intensities are applied to the fastener carbon fiber composite laminate sample by a pulsed thermal jet test power supply. The lightning current is applied to the fastener carbon fiber composite laminate by arc and conduction injection through the thermal jet injection clamping mechanism and adjustment unit to form thermal jet sparks. The thermal jet spark monitoring unit is used to obtain the occurrence and development process of the electric spark of the fastener carbon fiber ignition source. The correlation between the thermal jet high temperature airflow impact force and thermal spark characteristics of the fastener carbon fiber composite laminate interface and the fastener carbon fiber composite laminate mating structure, temperature and humidity, and lightning current electrical parameters is obtained, forming a thermal jet ignition characteristic database of composite fuel tank fastener ignition source simulating the flight environment of a large aircraft.

[0015] 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;

[0016] The simulated natural lightning environment lightning current generation unit consists of a main pulse energy storage capacitor C, a high-voltage discharge switch G, a waveform forming resistor R, and a waveform forming inductor L. The fastener carbon fiber composite laminate, the thermal injection clamping mechanism, and the adjustment unit are connected in series in the simulated natural lightning environment lightning current generation unit circuit.

[0017] Furthermore, the control unit includes a charging voltage monitoring circuit and a programmable logic controller (PLC). The charging voltage monitoring circuit of the control unit receives the signal transmitted from the charging voltage monitoring sensor, and after processing by the PLC, outputs a control signal to control the discharge of the high-voltage discharge switch G of the lightning current generating unit in the simulated natural lightning environment.

[0018] In addition, the programmable logic controller (PLC) is combined with the industrial control computer of the thermal spray 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.

[0019] Furthermore, the thermal spray measurement and analysis unit includes a pulse current sensor, a digital oscilloscope, and an industrial control computer. The pulse current sensor and the array oscilloscope jointly measure the lightning current between the high-voltage injection point and the low-voltage return point of the fastener carbon fiber composite laminate. The industrial control computer processes and analyzes the lightning current signal measured by the oscilloscope to obtain the thermal spray voltage U under the fastener assembly method and ambient temperature and humidity parameters.

[0020] Furthermore, the thermal injection clamping mechanism and adjustment unit include a thermal injection conduction clamping mechanism and a thermal injection arc injection clamping mechanism;

[0021] The thermal jet conduction injection clamping mechanism includes a double-sided structure clamp with adjustable locking position mounted on an insulating plate. The double-sided structure clamp consists of two insulating baffles connected by bolts. The installation position between the two insulating baffles is adjusted by bolts to achieve the clamping of carbon fiber composite laminates with different fasteners. Plate-shaped high-voltage injection electrodes and low-voltage return electrodes are respectively installed on the inner side of the double-sided insulating baffles. The high-voltage end of the pulse power supply simulating a natural lightning environment is connected to the high-voltage injection electrode, and the low-voltage end is connected to the low-voltage return electrode of the electrode structure.

[0022] The thermal jet arc injection clamping mechanism includes a clamp and adjustment mechanism and an electrode adjustment mechanism. The clamp and adjustment mechanism includes a double-sided structure clamp with adjustable locking position mounted on an insulating plate. The double-sided structure clamp consists of two insulating baffles connected by bolts. The installation position between the two insulating baffles is adjusted by the bolts to achieve the clamping of carbon fiber composite laminates with different fasteners. The electrode adjustment mechanism includes an electrode gap distance adjustment mechanism, a high-voltage injection electrode, and two low-voltage return electrodes. The high-voltage injection electrode is mounted directly above the carbon fiber composite laminate with fasteners through the electrode gap distance adjustment mechanism. The gap between the high-voltage injection electrode and the carbon fiber composite laminate sample with fasteners is adjusted by the electrode gap distance adjustment mechanism. The two low-voltage return electrodes are set on the inner side of the insulating baffles on both sides of the double-sided structure clamp. The carbon fiber composite laminate sample with fasteners is in close electrical contact with the low-voltage return electrode plates on both sides, and the installation position of the baffles is adjusted by screws to achieve fixed clamping.

[0023] Furthermore, the electrode gap adjustment mechanism is a lifting mechanism located on one side of the fixture and adjustment mechanism. The high-pressure injection electrode is mounted on the lifting mechanism. The height of the high-pressure injection electrode is adjusted by the lifting mechanism to adjust the gap between the high-pressure injection electrode and the fastener carbon fiber composite laminate sample.

[0024] A test and measurement method for the ignition characteristics of thermal jet ignition of aircraft composite fuel tank fasteners includes the following steps:

[0025] 1) Selection and treatment of test specimens: Multiple carbon fiber composite laminates for fasteners of large aircraft and fuel tanks were selected and subjected to temperature and humidity treatment to simulate the actual structure of aircraft fuel tanks and flight environment.

[0026] 2) Install the fastener carbon fiber composite laminate in the thermal injection clamping mechanism and adjustment unit, and connect the high-voltage injection electrode and low-voltage return electrode of the thermal injection clamping mechanism and adjustment unit to the lightning current generation unit circuit in the simulated natural lightning environment;

[0027] 3) Apply lightning current pulses with different peak values ​​to the carbon fiber composite laminate of the fastener, and measure the lightning current data flowing through the carbon fiber composite laminate of the fastener through the pulse current sensor;

[0028] 4) The thermal jet high-temperature airflow impact force detection unit (4-21) and analysis and processing unit of the thermal jet spark monitoring unit record the airflow impact force generated by the high-temperature gas pyrolysis at the interface of the fastener carbon fiber composite laminate caused by lightning current arc and Joule heating effect; the high-speed camera monitoring instrument and high-speed camera control computer (41-2) of the thermal jet spark monitoring unit collect and store the thermal spark phenomenon at the interface of the fastener carbon fiber composite laminate.

[0029] 5) Using fastener carbon fiber composite laminates with different humidity and temperature, repeat steps 2) to 4), and record the lightning current parameters flowing through the fastener carbon fiber composite laminate, the thermal spray pressure at the interface of the fastener carbon fiber composite laminate, and the hot spot phenomenon.

[0030] 6). Change the assembly method of the fastener carbon fiber composite laminate interface, that is, adjust the gap between the high-pressure injection electrode and the fastener carbon fiber composite laminate sample, repeat steps 1) to 5), and record the lightning current parameters flowing through the fastener carbon fiber composite laminate, as well as the airflow impact force and thermal spark phenomenon generated by the pyrolysis high-temperature gas at the fastener carbon fiber composite laminate interface.

[0031] 7) The hot spot ignition state of the fastener carbon fiber composite laminate interface is treated to establish the correlation between the hot jet air pressure and spark morphology of the fastener ignition source thermal jet characteristics and the assembly method, temperature and humidity, lightning current electrical parameters.

[0032] 8) Statistical analysis of the thermal jet ignition source test results, including research on the thermal jet airflow pressure, spark characteristics and influencing factors of the fastener carbon fiber composite laminate, establishing a correlation database between the thermal jet ignition characteristics of the fastener ignition source and other factors, and using multi-factor regression method to obtain an evaluation method for the thermal jet ignition characteristics of the fastener ignition source.

[0033] The present invention has the following beneficial effects:

[0034] A test and measurement system and method for the thermal jet ignition characteristics of fasteners in aircraft composite fuel tanks are disclosed. The test system includes an adjustable high-voltage DC charging power supply, a lightning current discharge unit simulating a natural lightning environment, and a control, measurement, and analysis unit for the thermal jet ignition test. Lightning current waves of different intensities are applied to the carbon fiber composite laminate of the fasteners via arcing and conductive injection through a pulsed thermal jet test power supply to form thermal jet sparks. The occurrence and development process of the electrical sparks from the carbon fiber ignition source of the fasteners are obtained, and the correlation between the impact force of the high-temperature airflow and the thermal spark characteristics at the interface of the carbon fiber composite laminate and the mating structure, temperature and humidity, and lightning current electrical parameters of the carbon fiber composite laminate are obtained.

[0035] The experimental and measurement analysis method for thermal jet ignition characteristics is based on the mating structure characteristics of fastener carbon fiber composite laminates. Through experimental data on the thermal jet ignition state characteristics of fastener carbon fiber composite laminates under lightning current, and using statistical methods, the correlation between the impact force and thermal spark characteristics of the high-temperature airflow at the interface of the fastener carbon fiber composite laminate and factors such as the mating structure of the fastener carbon fiber composite laminate, climatic environment (temperature and humidity), and lightning current electrical parameters is obtained. This forms a database of thermal jet ignition characteristics of composite fuel tank fasteners simulating the flight environment of large aircraft, laying the foundation for multi-physics modeling, ignition mechanism, and prediction algorithms for lightning strikes on large aircraft composite fuel tank ignition sources. It also provides a basis for the structural design and risk assessment of lightning-struck fuel tank ignition sources. Attached Figure Description

[0036] Figure 1 This is a structural block diagram of the composite fastener ignition source ignition characteristic test system of the present invention.

[0037] Figure 2 This is a circuit block diagram of the composite fastener ignition source ignition characteristic test system of the present invention;

[0038] Figure 3 shows the clamping structure for the ignition characteristics test of the composite fastener of the present invention.

[0039] Figure 3a This is a schematic diagram of the thermal jet conduction injection clamping mechanism in this invention;

[0040] Figure 3b This is a schematic diagram of the thermal jet arc injection clamping mechanism in this invention;

[0041] Figure 4 This is a flowchart of the test and analysis method for the ignition characteristics of fastener composite materials. Detailed Implementation

[0042] 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.

[0043] See Figure 1 As shown, the test and measurement system for the thermal jet ignition characteristics of the aircraft composite fuel tank fastener of the present invention consists of a pulse thermal jet test power supply 1, a carbon fiber composite laminate fastener 2, a thermal jet injection clamping mechanism and adjustment unit, a thermal jet ignition test control and measurement analysis unit 3, and a thermal jet spark monitoring unit 4.

[0044] The pulsed thermal spray test power supply 1 mainly consists of an adjustable high-voltage DC charging power supply 1-1 and a lightning current generation unit 1-2 simulating a natural lightning environment. During actual testing, the charging voltage of the adjustable high-voltage DC charging power supply 1-1 to the lightning current generation 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 thermal spray ignition test control and measurement analysis unit 3. The function of the lightning current generation unit 1-2 simulating a natural lightning environment is to generate a lightning current wave with an adjustable rise time.

[0045] See Figure 2 The diagram shows the principle circuit of the pulse thermal jet test power supply 1 for testing the electric spark characteristics of the carbon fiber ignition source of the fastener according to the present invention. It mainly consists of two parts: an adjustable high-voltage DC charging power supply 1-1 and a lightning current generation unit 1-2 that simulates a natural lightning environment.

[0046] 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. The lightning current generation unit 1-2 simulating a natural lightning environment mainly consists of a main pulse energy storage capacitor C, a high-voltage discharge switch G, a waveform forming resistor R, and a waveform forming inductor L. They are electrically connected in series, and the fastener carbon fiber composite laminate plate 2 sample and its connecting fixture thermal injection clamping mechanism and adjustment unit are connected in series in the circuit of the lightning current generation unit 1-2 simulating a natural lightning environment.

[0047] See Figure 1As shown, the control and measurement analysis unit 3 for the thermal spray ignition test is responsible for controlling the ignition characteristics test of the fastener carbon fiber composite laminate ignition source and measuring and analyzing the thermal spray pulse parameters. It mainly consists of a control unit 31 and a thermal spray measurement and analysis unit 32. The control unit 31 primarily comprises a charging voltage monitoring circuit 31-1 and a programmable logic controller (PLC) 31-2. The charging voltage monitoring circuit 31-1 of the control unit 31 receives signals from the charging voltage monitoring sensor 1-3, which are then processed by the PLC 31-2. The PLC 31-2 then outputs control signals to control the discharge of the high-voltage discharge switch G in the simulated natural lightning environment lightning current generation unit 1-2.

[0048] In addition, the programmable controller 31-2 is combined with the industrial control computer 32-3 of the thermal spray measurement and analysis unit 32 to control the connection / disconnection, high voltage rise / fall, and high voltage discharge switch G of the charging process of the fastener carbon fiber composite laminate ignition source ignition characteristic test, thereby realizing the automatic control of the fastener carbon fiber composite laminate ignition source ignition characteristic test process.

[0049] The function of the thermal spray measurement and analysis unit 32 is to control the ignition characteristic test of the fastener carbon fiber ignition source and to measure and analyze the thermal spray pulse parameters. It also enables process control of the ignition characteristic test of the fastener carbon fiber composite laminate and the measurement and analysis of the thermal spray pulse parameters. The thermal spray measurement and analysis unit 32 mainly consists of a pulse current sensor 32-1, a digital oscilloscope 32-2, and an industrial control computer 32-3. The pulse current sensor 32-1, in conjunction with the array oscilloscope 32-2, measures the lightning current between the high-voltage injection point and the low-voltage return point of the fastener carbon fiber composite laminate. The industrial control computer 32-3 processes and analyzes the lightning current signal measured by the oscilloscope to obtain the thermal spray voltage U under parameters including fastener assembly method and ambient temperature and humidity.

[0050] See Figure 3a and Figure 3b As shown, the thermal jet injection clamping mechanism and adjustment unit are used to clamp the fastener carbon fiber composite laminate sample. The thermal jet injection clamping mechanism and adjustment unit include a thermal jet conduction injection clamping mechanism and a thermal jet arc injection clamping mechanism, which realizes the application of lightning current to the fastener carbon fiber composite laminate sample by arc and conduction injection.

[0051] See Figure 3aAs shown, the thermal jet injection clamping mechanism is a double-sided clamp A2 with an adjustable locking position, mounted on an insulating plate A1. The double-sided clamp A2 consists of two insulating baffles connected by bolts. The installation position of the baffles is adjusted by nuts A3 and screws A4 to clamp the carbon fiber composite laminate 2 sample with different fasteners. A high-voltage injection electrode HV and a low-voltage return electrode LV are installed inside each of the double-sided insulating baffles. Their function is to connect the carbon fiber composite laminate sample with fasteners to the simulated natural lightning environment pulse power supply circuit 1-2. The high-voltage end of the simulated natural lightning environment pulse power supply 1-2 is connected to the high-voltage injection electrode HV of the thermal jet injection clamping mechanism. The high-voltage injection electrode is a plate-shaped electrode with a certain thickness. The low-voltage end of the simulated natural lightning environment pulse power supply is connected to the low-voltage return electrode LV of the electrode structure.

[0052] See Figure 3b As shown, the thermal jet arc injection clamping mechanism consists of a clamp and adjustment mechanism and an electrode adjustment mechanism. The clamp and adjustment mechanism is a double-sided clamp A2 with adjustable locking position mounted on an insulating plate A1. The double-sided clamp A2 consists of two insulating baffles connected by bolts. The installation position of the baffles is adjusted by nuts A3 and screws A4 to achieve the clamping of carbon fiber composite laminate 2 samples with different fasteners.

[0053] The electrode adjustment mechanism includes a set of metal electrodes and an electrode gap adjustment mechanism. The high-voltage injection electrode HV of the high-voltage arc in the thermal spray test is fixedly installed above the fastener of the fastener carbon fiber composite laminate plate sample, and there is a certain adjustable gap distance between it and the fastener carbon fiber composite laminate plate 2. The two low-voltage return electrodes LV are set on the inner side of the insulating baffles on both sides of the double-sided structure clamp. The fastener carbon fiber composite laminate plate sample is in close electrical contact with the low-voltage return electrode plate on both sides, and the installation position of the baffle is adjusted by the screw to achieve fixed clamping.

[0054] The electrode gap adjustment mechanism is a lifting mechanism located on one side of the fixture and adjustment mechanism. The high-pressure injection electrode HV is mounted on the lifting mechanism. The height of the high-pressure injection electrode is adjusted by the lifting mechanism, thereby adjusting the gap between the high-pressure injection electrode and the carbon fiber composite laminate sample 2. The lifting mechanism can be a hydraulic lifting mechanism, a motor-driven screw lifting mechanism, or a cylinder-driven pneumatic lifting mechanism.

[0055] like Figure 1As shown, the thermal jet spark monitoring unit 4 observes the occurrence and development process of the electric spark from the fastener carbon fiber ignition source. It mainly consists of a high-speed camera monitoring instrument 41-1, a high-speed camera control computer 41-2, a thermal jet high-temperature airflow impact force detection unit 4-21, and an impact force analysis and processing unit 4-22. 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 fastener carbon fiber ignition source. Its imaging process is controlled by the high-speed camera control computer 41-2. The thermal jet spark monitoring unit 4 obtains the electric spark process of the fastener carbon fiber ignition source. The thermal jet high-temperature airflow impact force detection unit 4-21 and the impact force analysis and processing unit 4-22 record the airflow impact force generated by the high-temperature gas at the interface of the fastener carbon fiber composite laminate, caused by lightning current arc and Joule heating effect. The thermal jet high-temperature airflow impact force detection unit 4-21 consists of an impact sensor and a signal conditioning circuit. The impact sensor is installed at a certain distance from the side of the carbon fiber laminate fastener, and there can be one or more of them. Its function is to detect the thermal impact force generated by the high-temperature gas ejected from the interface of the carbon fiber composite laminate sample, the insulating material, the sealing material, and the resin pyrolysis between the carbon fiber laminate layers. The impact force analysis and processing unit 4-22 is used to analyze the correlation between the thermal impact force and the assembly structure of the carbon fiber composite laminate sample, the electrical parameters of the lightning impact force, etc.

[0056] See Figure 4 The test and measurement methods for the ignition characteristics of carbon fiber composite laminate fasteners are as follows:

[0057] 1) Sample Selection and Treatment: Fastener carbon fiber composite laminate samples were selected and treated, mainly including temperature and humidity (especially humidity), to simulate the actual flight environment of a large aircraft. The sample temperature and humidity conditions had at least five points, denoted as S. m1 To S m1 .

[0058] 2) Install the first fastener carbon fiber composite laminate sample with different humidity in the thermal spray injection clamping mechanism, and electrically connect the thermal spray injection clamping mechanism and the adjustment unit to the circuit of the thermal spray simulated natural lightning environment lightning current generation unit.

[0059] 3) By changing the peak value of the applied lightning current, the impact force and ignition characteristics of the thermal jet airflow of the fastener carbon fiber composite laminate under different humidity conditions are obtained. A pulse current sensor is used to detect the lightning current flowing through the fastener carbon fiber composite laminate 2, and a thermal jet spark monitoring unit 4 is used to detect the impact force and thermal spark characteristics of the thermal jet airflow of the fastener carbon fiber composite laminate 2.

[0060] 4) Change the humidity of the fastener carbon fiber composite laminate and repeat process 2) to 4) to obtain a database of the correlation between the lightning current flowing through the fastener carbon fiber composite laminate, the electric arc generated by the lightning current, the impact force of the high-temperature thermal jet airflow generated at the interface of the fastener carbon fiber composite laminate by Joule heat, and the thermal spark characteristics and multiple factors such as sample temperature and humidity, and lightning current peak value.

[0061] 5) Similarly, the influencing factors of the impact force and thermal spark characteristics of the high-temperature airflow of the fastener thermal jet can also include the assembly method of the fastener and the carbon fiber composite material, including clearance fit, interference fit, and filling the gap between the fastener and the carbon fiber composite material with insulating materials with different dielectric constants, etc.

[0062] 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 in fuel tanks and lightning electrical parameters, temperature and humidity flight environment characteristics.

[0063] Statistical analysis was conducted on the test results of thermal spraying and thermal spark characteristics, including research on the impact force and thermal spark characteristics and influencing factors of high-temperature airflow during thermal spraying of fastener carbon fiber composite laminates. This mainly included two aspects: First, adjusting the temperature and humidity of the fastener carbon fiber composite laminates to simulate different flight electrical environments of large aircraft, and applying lightning current waves of different intensities. The lightning current waves flowing through the fastener carbon fiber composite laminates were measured using a pulse current sensor, and the impact force characteristics and thermal spark characteristics of the high-temperature airflow during thermal spraying at the interface of the fastener carbon fiber composite laminates were detected using a thermal spraying spark monitoring unit 4. Second, the impact force characteristics and thermal spark characteristics of the high-temperature airflow during thermal spraying of the fastener carbon fiber composite laminates were analyzed. A correlation database was established between the impact force of the high-temperature airflow during thermal spraying, the thermal spark characteristics, and multiple factors such as temperature and humidity, lightning current parameters, and interface assembly methods. A multi-factor regression method was used to obtain an evaluation method for the impact force of the high-temperature airflow during thermal spraying and the thermal spark characteristics at the interface of the fastener carbon fiber composite laminates.

Claims

1. A test and measurement system for the ignition characteristics of thermal jet ignition of fasteners for aircraft composite fuel tanks, characterized in that: It includes a pulse thermal spray test power supply (1), a fastener carbon fiber composite laminate (2), a thermal spray injection clamping mechanism and adjustment unit, a thermal spray ignition test control and measurement analysis unit (3) and a thermal spray spark monitoring unit (4); The pulsed thermal spray test power supply (1) includes an adjustable high-voltage DC charging power supply (1-1) and a lightning current generation unit (1-2) simulating a natural lightning environment. The lightning current generation unit (1-2) simulating a natural lightning environment generates a lightning current wave with an adjustable rise time. The charging voltage of the lightning current generation unit (1-2) simulating a natural lightning environment is monitored online by the charging voltage monitoring sensor (1-3) of the adjustable high-voltage DC charging power supply (1-1), and the analog charging voltage is transmitted to the control and measurement analysis unit (3) of the thermal spray ignition test. The control and measurement analysis unit (3) for the thermal injection ignition test is used for the control of the test and the measurement and analysis of the thermal injection pulse parameters, including a control unit (31) and a thermal injection measurement and analysis unit (32); The thermal jet spark monitoring unit (4) is used to obtain the occurrence and development process of the electric spark of the fastener carbon fiber ignition source. It 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) is controlled by the high-speed camera control computer (41-2) during the imaging process. The thermal injection clamping mechanism and adjustment unit are used for clamping the fastener carbon fiber composite laminate (2) specimen and for applying lightning current to the fastener carbon fiber composite laminate (2) specimen by arc and conduction injection. The pulsed thermal jet test power supply (1) applies lightning current waves of different intensities to the fastener carbon fiber composite laminate (2) sample. The lightning current is applied to the fastener carbon fiber composite laminate (2) by electric arc and conduction injection through the thermal jet injection clamping mechanism and adjustment unit to form thermal jet sparks. The thermal jet spark monitoring unit (4) is used to obtain the occurrence and development process of the fastener carbon fiber ignition source electric spark. The experiment was repeated using fastener carbon fiber composite laminates with different humidity and temperature conditions. The lightning current parameters flowing through the fastener carbon fiber composite laminates, the thermal spray pressure at the interface of the fastener carbon fiber composite laminates, and the hot spot phenomenon were recorded. Adjust the gap between the high-pressure injection electrode and the fastener carbon fiber composite laminate (2) sample, repeat the test, record the lightning current parameters flowing through the fastener carbon fiber composite laminate, as well as the airflow impact force and thermal spark phenomenon generated by the pyrolysis high-temperature gas at the interface of the fastener carbon fiber composite laminate; process the hot ignition state at the interface of the fastener carbon fiber composite laminate to form the correlation between the thermal jet airflow pressure and spark morphology of the fastener ignition source thermal jet characteristics and the assembly method, temperature and humidity, and lightning current electrical parameters. Statistical analysis was conducted on the test results of thermal jet ignition source, including the study of thermal jet gas pressure, spark characteristics and influencing factors of fastener carbon fiber composite laminate, and a correlation database between the thermal jet ignition characteristics of fastener ignition source and multiple factors was established. The correlation between the thermal jet high-temperature airflow impact force and thermal spark characteristics of the fastener carbon fiber composite laminate interface and the fastener carbon fiber composite laminate mating structure, temperature and humidity, lightning current electrical parameters is obtained, forming a database of thermal jet ignition characteristics of composite fuel tank fasteners simulating the flight environment of large aircraft.

2. The test and measurement system for the ignition characteristics of aircraft composite fuel tank fasteners using thermal jet ignition as described in 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 simulated natural lightning environment lightning current generating unit (1-2) consists of a main pulse energy storage capacitor C, a high-voltage discharge switch G, a waveform forming resistor R and a waveform forming inductor L. The fastener carbon fiber composite laminate (2) and the thermal injection clamping mechanism and adjustment unit are connected in series in the circuit of the simulated natural lightning environment lightning current generating unit (1-2).

3. The test and measurement system for the ignition characteristics of aircraft composite fuel tank fasteners using thermal jet ignition as described in 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 outputs a control signal after processing by the programmable controller (31-2) to discharge control the high-voltage discharge switch G of the lightning current generating unit (1-2) in the simulated natural lightning environment. In addition, the programmable logic controller (31-2) is combined with the industrial control computer (32-3) of the thermal spray 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.

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

5. The test and measurement system for the ignition characteristics of aircraft composite fuel tank fasteners using thermal jet ignition as described in claim 4, characterized in that: The thermal injection clamping mechanism and adjustment unit include a thermal injection conduction clamping mechanism and a thermal injection arc injection clamping mechanism. The thermal jet conduction injection clamping mechanism includes a double-sided structure clamp (A2) with adjustable locking position mounted on an insulating plate (A1). The double-sided structure clamp (A2) consists of two insulating baffles connected by bolts. The installation position between the two insulating baffles is adjusted by bolts to achieve the clamping of carbon fiber composite laminate (2) with different fasteners. Plate-shaped high-voltage injection electrodes (HV) and low-voltage return electrodes (LV) are respectively installed on the inner side of the double-sided insulating baffles. The high-voltage end of the pulse power supply (1-2) simulating natural lightning environment 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. The thermal jet arc injection clamping mechanism includes a clamp and adjustment mechanism and an electrode adjustment mechanism. The clamp and adjustment mechanism includes a double-sided structure clamp (A2) with adjustable locking position mounted on an insulating plate (A1). The double-sided structure clamp (A2) consists of two insulating baffles connected by bolts. The installation position between the two insulating baffles is adjusted by bolts to achieve the clamping of different fastener carbon fiber composite laminates (2). The electrode adjustment mechanism includes an electrode gap distance adjustment mechanism, a high-voltage injection electrode (HV), and two low-voltage return electrodes (LV). The high-voltage injection electrode (HV) is mounted directly above the fastener carbon fiber composite laminate (2) through the electrode gap distance adjustment mechanism. The gap between the high-voltage injection electrode and the fastener carbon fiber composite laminate (2) sample is adjusted by the electrode gap distance adjustment mechanism. The two low-voltage return electrodes (LV) are set on the inner side of the insulating baffles on both sides of the double-sided structure clamp. The fastener carbon fiber composite laminate sample is in close electrical contact with the low-voltage return electrode plate on both sides, and the installation position of the baffles is adjusted by screws to achieve fixed clamping.

6. The test and measurement system for the ignition characteristics of aircraft composite fuel tank fasteners using thermal jet ignition as described in claim 5, characterized in that: The electrode gap adjustment mechanism is a lifting mechanism set on one side of the fixture and adjustment mechanism. The high-pressure injection electrode (HV) is installed on the lifting mechanism. The height of the high-pressure injection electrode is adjusted by the lifting mechanism to adjust the gap between the high-pressure injection electrode and the fastener carbon fiber composite laminate (2) sample.

7. A method for testing and measuring the ignition characteristics of aircraft composite fuel tank fasteners based on the test and measurement system of claim 6, characterized in that... Includes the following steps: 1). Selection and treatment of test specimens: Multiple carbon fiber composite laminates (2) for fasteners of large aircraft and fuel tanks were selected for temperature and humidity treatment to simulate the actual structure of aircraft fuel tanks and flight environment; 2). Install the fastener carbon fiber composite laminate (2) in the thermal injection clamping mechanism and adjustment unit, and connect the high-voltage injection electrode (HV) and low-voltage return electrode (LV) of the thermal injection clamping mechanism and adjustment unit to the circuit of the simulated natural lightning environment lightning current generation unit (1-2); 3). Apply lightning current pulses with different peak values ​​to the fastener carbon fiber composite laminate (2), and measure the lightning current data flowing through the tested fastener carbon fiber laminate through the pulse current sensor (32-1); 4). The thermal jet spark monitoring unit (4) uses the thermal jet high-temperature airflow impact force detection unit (4-21) and analysis and processing unit (4-22) to record the airflow impact force generated by the high-temperature gas at the interface of the fastener carbon fiber composite laminate caused by lightning current arc and Joule heating effect. The high-speed camera monitoring instrument (41-1) and high-speed camera control computer (41-2) of the thermal jet spark monitoring unit (4) collect and store the thermal spark phenomenon at the interface of the fastener carbon fiber composite laminate. 5) Using fastener carbon fiber composite laminates with different humidity and temperature, repeat steps 2) to 4), and record the lightning current parameters flowing through the fastener carbon fiber composite laminate, the thermal spray pressure at the interface of the fastener carbon fiber composite laminate, and the hot spot phenomenon. 6). Change the assembly method of the fastener carbon fiber composite laminate interface, that is, adjust the gap between the high-pressure injection electrode and the fastener carbon fiber composite laminate (2) sample, repeat steps 1) to 5), record the lightning current parameters flowing through the fastener carbon fiber composite laminate, as well as the airflow impact force and thermal spark phenomenon generated by the pyrolysis high temperature gas at the fastener carbon fiber composite laminate interface. 7) The hot spot ignition state of the fastener carbon fiber composite laminate interface is treated to establish the correlation between the hot jet air pressure and spark morphology of the fastener ignition source thermal jet characteristics and the assembly method, temperature and humidity, lightning current electrical parameters. 8) Statistical analysis of the thermal jet ignition source test results, including the study of thermal jet airflow pressure, spark characteristics and influencing factors of fastener carbon fiber composite laminate (2), establishing a correlation database between the thermal jet ignition characteristics of fastener ignition source and multiple factors, and using the multi-factor regression method to obtain the evaluation method of the thermal jet ignition characteristics of fastener ignition source.

Images