Method for measuring ablation amount of heat-proof layer of metal cabin of aircraft

Abstract

The invention relates to a method for measuring the ablation amount of a heat-proof layer of a metal cabin of an aircraft, and belongs to the technical field of aerospace special parameter measurement. Comprising the following steps: simulating a measurement temperature environment, transmitting ultrasonic signals to an aircraft metal cabin according to a fixed frequency and a fixed period, and establishing a first interpolation function and a second interpolation function; heating the metal cabin body, transmitting an ultrasonic signal to the cabin body, and acquiring an ultrasonic echo signal diagram to obtain metal layer transit time; calculating the average propagation speed of the ultrasonic signal in the metal layer; according to the first interpolation function and the average propagation speed of the ultrasonic signal in the metal layer, obtaining the corresponding average temperature of the metal layer; measuring the temperature of the inner surface of the metal layer; calculating the interface temperature of the metal layer and the heat-proof layer; calculating the average temperature of an unablated layer; according to the second interpolation function and the average temperature of the non-ablated layer, acquiring the propagation velocity of the corresponding ultrasonic signal in the non-ablated layer; ultrasonic echo signal diagrams are continuously collected, the transition time of the non-ablated layer is obtained, and the ablative amount of the heat-proof layer is calculated.

Description

Technical Field

[0001] The invention relates to the technical field of special parameter measurement in aerospace, and in particular to a method for measuring the ablation amount of a heat protection layer of a metal cabin of an aircraft. Background Art

[0002] When a spacecraft enters the atmosphere, the outer surface of the structure is subjected to the high temperature environment caused by high-speed flight, and the maximum temperature can exceed 2000℃. It is difficult for general metal structures to withstand such high temperatures, so it is generally necessary to cover the outside of the metal structure with a layer of high-temperature resistant composite material structure, called a heat shield. When the aircraft flies in the air for a long time at a high Mach number, the problem of aerodynamic heating is very prominent, and the body material will ablate and deform in a high temperature environment, seriously endangering the life safety of the pilot. Therefore, it is necessary to evaluate the thermal performance of the material through experiments, and the amount of ablation is one of the important bases for its evaluation.

[0003] Spacecraft with high maneuverability requirements need to maintain their aerodynamic shape during flight, and the ablative material needs to maintain its shape and strength during the ablation phase change process. This type of ablative material is called a dimensional ablative material. Dimensional ablative materials are different from ordinary ablative materials that rely on chemical reactions and mechanical stripping. They are essentially a reinforced phenolic resin material. The ablation process is actually the process of carbonization of the material. The shape and strength of the material hardly change during the ablation and carbonization process and after complete carbonization. Therefore, the traditional wire-laying detection technology relies on the method of measuring the ablation amount by the ablative material scouring and destroying the embedded sensitive element, and the method of measuring the ablation amount by the embedded resistance wire fusing the resistance wire, both of which cannot measure the ablation amount of dimensional ablative materials.

[0004] At present, the commonly used method for measuring the ablation amount of dimensional ablative materials in the industry is to use an embedded ablation sensor. This embedded ablation sensor method requires the design of installation holes on the metal cabin and non-metallic wall in advance, which destroys the integrity of the aircraft cabin structure. At the same time, there is a gap between the sensor and the cabin opening, and the outer wall surface is mostly curved and difficult to completely correspond to the sensor. The sensor and the thermal protection layer ablate asynchronously, resulting in poor synchronization between the sensor and the measured thermal protection layer. Therefore, it is urgent to propose a method for measuring the ablation amount of the aircraft metal cabin thermal protection layer without destroying the cabin and the ablation layer structure. Summary of the invention

[0005] In view of the above analysis, the present invention aims to provide a method for measuring the ablation amount of the thermal protection layer of the aircraft's metal cabin, so as to solve at least one of the following problems: 1. The existing method for measuring the ablation amount of dimensional ablative materials destroys the structural integrity of the aircraft's metal cabin; 2. The existing method for measuring the ablation amount of dimensional ablative materials has poor synchronization between the sensor and the thermal protection layer being measured.

[0006] The purpose of the present invention is mainly achieved through the following technical solutions:

[0007] The present invention provides a method for measuring the ablation amount of a heat protection layer of a metal cabin of an aircraft, comprising the following steps:

[0008] S1: simulating the temperature measurement environment, transmitting ultrasonic signals to the aircraft metal cabin at a fixed frequency and period, establishing a first interpolation function between the propagation speed of the ultrasonic signal in the metal layer material of the aircraft metal cabin and the average temperature of the metal layer, and a second interpolation function between the propagation speed of the ultrasonic signal in the heat protection layer material of the aircraft metal cabin and the average temperature of the unablated layer;

[0009] S2: Heat the metal cabin of the aircraft, transmit ultrasonic signals to the metal cabin of the aircraft according to the fixed frequency and period in step S1, collect ultrasonic signal echo signal graphs, and obtain the metal layer transition time t 12 ;

[0010] S3: Calculate the average propagation speed V of the ultrasonic signal in the metal layer of the aircraft metal cabin according to the metal layer transit time and the metal layer thickness of the aircraft metal cabin. 金属 ;

[0011] S4: According to the first interpolation function and the average speed V of the ultrasonic signal propagating in the metal layer of the aircraft metal cabin 金属 , obtain the average temperature of the metal layer of the aircraft's metal cabin corresponding to the average velocity propagating in the metal layer of the aircraft's metal cabin

[0012] S5: Measure and obtain the inner surface temperature Tc of the metal layer of the aircraft metal cabin;

[0013] S6: Based on the average temperature of the metal layer of the aircraft's metal cabin and the inner surface temperature Tc of the metal layer of the aircraft metal cabin, the temperature Tc of the interface between the metal layer of the aircraft metal cabin and the heat protection layer is calculated J ;

[0014] S7: According to the temperature T of the interface between the metal layer of the aircraft metal cabin and the heat protection layer J and the carbonization temperature T of the aircraft metal cabin heat protection layer material s , the average temperature of the unablated layer of the aircraft metal cabin is calculated

[0015] S8: acquiring a propagation velocity V(T) of an ultrasonic signal in the unablated layer of the aircraft metal cabin body corresponding to the average temperature of the unablated layer of the aircraft metal cabin body according to the second interpolation function and the average temperature of the unablated layer of the aircraft metal cabin body;

[0016] S9: Continuously collect ultrasonic signal echo signal diagrams to obtain the non-ablated layer transition time t Δ, according to the total thickness of the aircraft thermal protection layer X 0 , the propagation velocity V(T) in the unablated layer of the aircraft metal cabin and the unablated layer transit time t Δ , calculate and obtain the ablation amount X of the aircraft metal cabin thermal protection layer.

[0017] Furthermore, in step S1, the fixed transmission frequency is 1-10 Hz.

[0018] Further, in step S1, the fixed period is 0.1s-1s.

[0019] Furthermore, in step S1, the transmitting vibration frequency of the ultrasonic signal is 0.5-3 MHz.

[0020] Furthermore, in step S3, the average speed of the ultrasonic signal propagating in the metal layer of the aircraft metal cabin is calculated by the following formula:

[0021]

[0022] Wherein, L is the thickness of the metal layer of the aircraft metal cabin, mm;

[0023] t 12 —Metal layer transition time, μs;

[0024] V 金属 —The average speed at which ultrasonic signals propagate in the metal layer of the aircraft’s metal cabin, m / s.

[0025] Furthermore, in step S6, the temperature of the interface between the metal layer of the aircraft metal cabin and the heat protection layer is calculated by the following formula:

[0026]

[0027] in, —Average temperature of the metal layer of the aircraft metal cabin, °C;

[0028] Tc—the inner surface temperature of the metal layer of the aircraft metal cabin, °C;

[0029] T J —The temperature of the interface between the metal layer and the thermal protection layer of the aircraft's metal cabin, ℃.

[0030] Furthermore, in step S7, the average temperature of the unablated layer of the aircraft metal cabin is calculated by the following formula:

[0031]

[0032] Among them, T J —Temperature of the interface between the metal layer of the aircraft metal cabin and the heat protection layer, °C;

[0033] T s —Carbonization temperature of the heat protection layer material of the aircraft metal cabin, °C;

[0034] —The average temperature of the unablated layer of the aircraft's metal cabin.

[0035] Furthermore, in step S9, the ablation amount of the aircraft metal cabin heat protection layer is calculated by the following formula:

[0036]

[0037] Where, X—ablation thickness, mm;

[0038] X 0 —Total thickness of heat protection layer, mm;

[0039] V(T)—the propagation velocity of ultrasonic signal in the unablated layer of the aircraft metal cabin, m / s;

[0040] t Δ —Transit time of unablated layer, μs.

[0041] Furthermore, in step S1, the simulated measurement temperature environment is achieved by a high and low temperature test chamber or a tubular furnace.

[0042] Furthermore, in step S5, the inner surface temperature of the metal layer of the aircraft metal cabin is measured by a temperature sensor.

[0043] Compared with the prior art, the present invention can achieve at least one of the following beneficial effects:

[0044] 1. The measuring method of the present invention can complete the measurement without destroying the wall structure, without destroying the integrity of the metal cabin, and without causing any damage to the metal cabin of the aircraft, which is convenient and fast.

[0045] 2. The method of the present invention directly measures the heat protection layer of the metal cabin. Compared with the existing hole measurement method, it breaks through the limitation of the traditional hole measurement method on the measurement position, has good synchronization, and does not affect the heat transfer of the material.

[0046] In the present invention, the above-mentioned technical solutions can also be combined with each other to achieve more preferred combination solutions. Other features and advantages of the present invention will be described in the subsequent description, and some advantages can become obvious from the description, or can be understood by practicing the present invention. The purpose and other advantages of the present invention can be realized and obtained through the contents particularly pointed out in the description and the drawings. BRIEF DESCRIPTION OF THE DRAWINGS

[0047] The drawings are only for the purpose of illustrating particular embodiments and are not to be considered limiting of the present invention. Like reference symbols denote like components throughout the drawings.

[0048] Figure 1 It is a flow chart of the measuring method of the present invention;

[0049] Figure 2 This is a schematic diagram of the echo signal collected during the measurement of the present invention;

[0050] Figure 3 It is an interpolation curve diagram of the first interpolation function and the second interpolation function according to an embodiment of the present invention;

[0051] Figure 4 This is a schematic diagram of the specific structure of the measurement system of Example 2 of the present invention;

[0052] Figure 5 Schematic diagram of the measurement principle when using the measurement system of Example 2 of the present invention to perform measurement.

[0053] Reference numerals:

[0054] 1-aircraft metal cabin wall; 2-threaded hole; 3-spring; 4-screw; 5-special fixture; 6-ultrasonic transducer; 7-high temperature resistant coupling agent; 8-temperature sensor; 9-ultrasonic signal transceiver; 10-data acquisition device; 11-power supply; 12-data processing and display device; 13-heat protection layer; 14-ablation layer; 15-unablated layer. DETAILED DESCRIPTION

[0055] The preferred embodiments of the present invention are described in detail below in conjunction with the accompanying drawings, wherein the accompanying drawings constitute a part of this application and are used together with the embodiments of the present invention to illustrate the principles of the present invention, but are not used to limit the scope of the present invention.

[0056] Ablation materials have the advantages of high heat protection efficiency, reliable operation, and strong ability to adapt to flow field changes. They are widely used in aviation, aerospace, missiles, nuclear industry, heating furnace manufacturing, and industries with very demanding working conditions. The performance of ablative materials will directly affect the working state, reliability, and signal characteristics of the aircraft. The ablation amount is one of the important bases for evaluating its performance. Rapid, accurate, and complete testing of its ablation amount is of great significance for the research and use of ablative materials.

[0057] Dimensional ablative materials are different from ordinary ablative materials that rely on chemical reactions and mechanical stripping. They are essentially a reinforced phenolic resin material. The material's external dimensions and strength hardly change during the carbonization process and after complete carbonization. Usually, the thermal protection layer of dimensional ablative materials is bonded to the metal cabin wall of the aircraft through a colloid to form a thinner adhesive layer. The properties of the colloid are similar to those of the thermal protection layer of dimensional ablative materials. The traditional wire-laying detection technology relies on the method of measuring the ablation amount by the ablative material eroding and destroying the embedded sensitive elements, and the method of measuring the ablation amount by the embedded resistance wire fusing the resistance wire. Both methods cannot measure the ablation amount of dimensional ablative materials. At present, the commonly used method for measuring the ablation amount of dimensional ablative materials in the industry is to use an embedded ablation sensor. This method of embedded ablation sensors requires the design of installation holes on the metal cabin and non-metallic wall in advance, destroying the original wall structure. The measurement method of the present invention does not need to destroy the wall structure, does not destroy the integrity of the metal cabin, directly measures the heat protection layer of the metal cabin, and can complete the measurement without causing any damage to the metal cabin of the aircraft. It breaks through the limitations of the traditional hole measurement method on the measurement position and has good synchronization.

[0058] Specifically, the present invention provides a method for measuring the ablation amount of an aircraft thermal protection layer, comprising the following steps:

[0059] S1: simulating the temperature measurement environment, transmitting ultrasonic signals to the aircraft metal cabin at a fixed frequency and period, establishing a first interpolation function between the propagation speed of the ultrasonic signal in the metal layer material of the aircraft metal cabin and the average temperature of the metal layer, and a second interpolation function between the propagation speed of the ultrasonic signal in the heat protection layer material of the aircraft metal cabin and the average temperature of the unablated layer;

[0060] S2: Heat the metal cabin of the aircraft, transmit ultrasonic signals to the metal cabin of the aircraft according to the fixed frequency and period in step S1, collect ultrasonic signal echo signal graphs, and obtain the metal layer transition time t 12 ;

[0061] S3: Calculate the average propagation speed V of the ultrasonic signal in the metal layer of the aircraft metal cabin according to the metal layer transit time and the metal layer thickness of the aircraft metal cabin. 金属 ;

[0062] S4: According to the first interpolation function and the average speed V of the ultrasonic signal propagating in the metal layer of the aircraft metal cabin 金属 , obtain the average temperature of the metal layer of the aircraft's metal cabin corresponding to the average velocity propagating in the metal layer of the aircraft's metal cabin

[0063] S5: Measure and obtain the inner surface temperature Tc of the metal layer of the aircraft metal cabin;

[0064] S6: Based on the average temperature of the metal layer of the aircraft's metal cabin and the inner surface temperature Tc of the metal layer of the aircraft metal cabin, the temperature Tc of the interface between the metal layer of the aircraft metal cabin and the heat protection layer is calculated J ;

[0065] S7: According to the temperature T of the interface between the metal layer of the aircraft metal cabin and the heat protection layer J and the carbonization temperature T of the aircraft metal cabin heat protection layer material s , the average temperature of the unablated layer of the aircraft metal cabin is calculated

[0066] S8: acquiring a propagation velocity V(T) of an ultrasonic signal in the unablated layer of the aircraft metal cabin body corresponding to the average temperature of the unablated layer of the aircraft metal cabin body according to the second interpolation function and the average temperature of the unablated layer of the aircraft metal cabin body;

[0067] S9: Continuously collect ultrasonic signal echo signal diagrams to obtain the non-ablated layer transition time t Δ , according to the total thickness of the aircraft thermal protection layer X 0 , the propagation velocity V(T) in the unablated layer of the aircraft metal cabin and the unablated layer transit time t Δ , calculate and obtain the ablation amount X of the aircraft metal cabin thermal protection layer.

[0068] Specifically, in step S1, before the aircraft metal cabin is heated at high temperature for ablation, the temperature environment is first simulated and measured to establish a first interpolation function between the propagation speed of the ultrasonic signal in the metal layer material of the aircraft metal cabin and the average temperature of the metal layer and a second interpolation function between the propagation speed of the ultrasonic signal in the heat-resistant layer material of the aircraft metal cabin and the average temperature of the unablated layer.

[0069] It should be noted that in step S1, the average temperature of the metal layer of the metal cabin is generally lower than 400°C. Therefore, according to GB / T23900-2009 "Method for measuring ultrasonic velocity of non-destructive inspection materials", a high and low temperature test chamber is used to provide the required temperature environment, and a database is established between the propagation velocity of the ultrasonic signal in the metal layer material of the aircraft metal cabin and the average temperature of the metal layer. Then, the first interpolation function is obtained by fitting according to the least squares method. The carbonization temperature of the aircraft metal cabin thermal protection layer material is greater than 400℃, so it is necessary to first make a standard sample and use a tubular furnace to provide the required temperature environment. The test section of the standard sample is placed in the constant temperature zone of the tubular furnace. The standard sample waveguide section is used to guide the ultrasonic probe to transmit and receive ultrasonic waves in a lower temperature area. After intercepting the echo signal of the test section, the sound velocity of the ultrasonic signal at the current temperature is obtained according to GB / T23900-2009 "Method for Measurement of Ultrasonic Velocity of Non-destructive Inspection Materials", and a database is established between the propagation velocity of the ultrasonic signal in the aircraft metal cabin thermal protection layer material and the average temperature of the unablated layer. Then, the second interpolation function is obtained by fitting according to the least squares method.

[0070] Specifically, in step S1, the fixed transmission frequency is 1-10 Hz, and the fixed period is 0.1s-1s; the vibration frequency of the ultrasonic transmission signal is 0.5-3 MHz. Exemplarily, the vibration frequency of the ultrasonic transmission signal is 0.8 MHz, 1 MHz, 1.5 MHz, 2 MHz, and 2.5 MHz. The higher the measurement accuracy requirement, the higher the transmitting and receiving device with the ultrasonic transmission signal vibration frequency is used.

[0071] It should be noted that a complete ultrasonic signal cycle typically has a time interval of only a few microseconds, but it will contain multiple peaks, such as Figure 2 As shown, the first wave peak is the wave excited when the ultrasonic signal is emitted; the second wave peak is the reflected wave generated when the ultrasonic signal passes through the metal cabin of the aircraft and enters the glue layer and the unablated layer. The time difference between the first wave peak and the second wave peak is the "metal layer transition time". Since the glue layer between the metal cabin wall of the aircraft and the unablated layer is very thin, and there is no obvious boundary between the glue layer and the unablated layer and the properties of the materials are similar, there will be a small fluctuation after the second wave peak; the third wave peak is the reflected wave generated when the ultrasonic signal enters the transition layer from the unablated layer, and the time difference between the second wave peak and the third wave peak is the "unablated layer transition time"; the fourth wave peak is the reflected wave generated when the ultrasonic signal enters the carbonized layer from the transition layer, and the fifth wave peak is the reflected wave when the ultrasonic signal enters the air interface from the carbonized layer. There are many clutters after the third wave peak, and the fourth and fifth wave peaks are easily submerged by clutters. The transition layer is in a state of being ablated. Therefore, when measuring the ablation amount of the aircraft metal cabin thermal protection layer, the ablation amount of the aircraft metal cabin thermal protection layer can be obtained by subtracting the un-ablated thickness of the ablated layer from the known total thickness of the aircraft metal cabin ablation layer.

[0072] Specifically, in step S2, the metal cabin of the aircraft is heated, the temperature of the metal cabin of the aircraft is gradually increased, an ultrasonic signal is emitted to the metal cabin of the aircraft according to the fixed frequency and period in step S1, and an ultrasonic signal echo signal graph is collected. Through the ultrasonic signal echo signal graph, the metal layer transition time t can be obtained. 12 (i.e., the time difference between the 1st peak and the 2nd peak); it should be noted that, at the beginning of heating, the heating temperature has not yet reached the carbonization temperature of the aircraft's metal cabin thermal protection layer, then the 1st peak, the 2nd peak, and the 3rd peak can be seen from the ultrasonic signal echo signal diagram, but the time difference between the 2nd peak and the 3rd peak at this stage is very small, infinitely close to 0, at this time, ablation has not yet begun, the thickness of the unablated layer is approximately equal to the total thickness of the thermal protection layer, and the ablation amount of the thermal protection layer is infinitely close to 0. As the heating continues, the temperature of the outer surface of the aircraft's metal cabin reaches the carbonization temperature of the thermal protection layer, and the thermal protection layer begins to ablate, then the 1st peak, the 2nd peak, the 3rd peak, the 4th peak, and the 5th peak can be seen from the ultrasonic signal echo signal diagram, thereby calculating and obtaining the "metal layer transition time t of the aircraft's metal cabin material echo," 12 ” and “transit time of unablated layer t Δ ”.

[0073] Specifically, in step S3, the metal layer transition time t 12 The ultrasonic signal echo signal diagram in step S2 is obtained. The thickness L of the metal layer of the aircraft metal cabin is known. According to formula 1, the average speed V of the ultrasonic signal propagating in the metal layer of the aircraft metal cabin is calculated. 金属 :

[0074]

[0075] Wherein, L is the thickness of the metal layer of the aircraft metal cabin, mm;

[0076] t 12 —Metal layer transition time, μs;

[0077] V 金属 —The average speed at which ultrasonic signals propagate in the metal layer of the aircraft’s metal cabin, m / s.

[0078] Specifically, in step S4, the average velocity V of the ultrasonic signal propagating in the metal layer of the aircraft metal cabin obtained in step S3 is calculated by using the first interpolation function. 金属 , get the average temperature of the metal layer of the aircraft metal cabin corresponding to the average speed

[0079] Specifically, in step S5, a temperature sensor may be used to directly measure and obtain the inner surface temperature Tc of the metal layer of the aircraft metal cabin.

[0080] Specifically, in step S6, according to the average temperature of the metal layer of the aircraft metal cabin obtained in step S4 The temperature Tc of the interface between the metal layer of the metal cabin of the aircraft and the heat protection layer is calculated by formula 2. J :

[0081]

[0082] in, —Average temperature of the metal layer of the aircraft metal cabin, °C;

[0083] Tc—the inner surface temperature of the metal layer of the aircraft metal cabin, °C;

[0084] T J —The temperature of the interface between the metal layer of the spacecraft's metal cabin and the thermal protection layer, ℃.

[0085] Specifically, in step S7, according to the temperature T of the interface between the metal layer of the aircraft metal cabin and the heat protection layer obtained in step S6 J and the carbonization temperature T of the aircraft metal cabin heat protection layer material s , the average temperature of the unablated layer of the metal cabin of the traveler is calculated by formula 3

[0086]

[0087] Among them, T J —Temperature of the interface between the metal layer of the aircraft metal cabin and the heat protection layer, °C;

[0088] T s —Carbonization temperature of the heat protection layer material of the aircraft metal cabin, °C;

[0089] —Average temperature of the unablated layer of the aircraft metal cabin, ℃.

[0090] It should be noted that, usually when taking measurements, the material used for the thermal protection layer of the aircraft's metal cabin is known, and its carbonization temperature can be known based on the type of thermal protection layer material. When the thermal protection layer material is determined, the carbonization temperature of the material (i.e., the temperature at which ablation begins) is known and fixed.

[0091] Specifically, in step S8, the second interpolation function is used to calculate the average temperature of the unablated layer of the aircraft metal cabin obtained in step S7. Obtain the propagation velocity V(T) of the ultrasonic signal in the unablated layer of the aircraft metal cabin at the average temperature.

[0092] Specifically, in step S9, the unablated layer transition time t is obtained by collecting the ultrasonic signal echo signal diagram. Δ , according to the total thickness of the aircraft thermal protection layer X 0 , the propagation velocity V(T) in the unablated layer of the aircraft metal cabin obtained in step S8 and the unablated layer transit time t Δ , the ablation amount X of the aircraft metal cabin thermal protection layer is calculated by formula 4:

[0093]

[0094] Where, X—ablation thickness, mm;

[0095] X′—unablated layer thickness, mm;

[0096] X 0 —Total thickness of heat protection layer, mm;

[0097] V(T)—the sound velocity of the ultrasonic signal in the unablated layer of the aircraft metal cabin, m / s;

[0098] t Δ —Unablated layer transition time (i.e., the time difference between the second and third wave peaks), μs. Figure 1 Shown is a flow chart of the measuring method of the present invention.

[0099] The measurement method of the present invention can be completed by a system for measuring the ablation amount of the heat protection layer of the aircraft metal cabin, the measurement system comprising: a temperature simulation unit, an ultrasonic transducer unit, a temperature measurement unit, an ultrasonic signal transceiver unit, and a data acquisition and analysis unit;

[0100] Specifically, the temperature simulation unit includes a high and low temperature test chamber and a tubular furnace, which are used to provide different temperature environments to simulate the temperature when the metal cabin of the aircraft is actually heated; and is communicated with the data acquisition and analysis unit.

[0101] The ultrasonic transducer unit includes an ultrasonic transducer, which can be fixed on the metal bulkhead of the aircraft by a special clamp, and the special clamp can be connected to the metal bulkhead bolts of the aircraft by screws; a spring can be added between the special clamp and the screws to adjust the pressure between the ultrasonic transducer and the metal bulkhead surface of the aircraft; the gap between the ultrasonic transducer and the metal bulkhead of the aircraft can be filled by a high-temperature resistant coupling agent; the ultrasonic transducer and the ultrasonic signal transceiver unit are connected by a cable to realize the output and reception of ultrasonic signals.

[0102] The temperature measuring unit comprises a temperature sensor which is crimped onto the metal cabin wall of the aircraft and is used to measure the inner surface temperature of the metal layer of the metal cabin of the aircraft.

[0103] The ultrasonic signal transceiver unit comprises an ultrasonic signal transceiver device for outputting and receiving alternating voltage.

[0104] The data acquisition and analysis unit includes a data acquisition device and a data analysis module. The data acquisition device includes a signal amplifier, an oscilloscope, and a filter, which are used to obtain the time difference between the peaks in the ultrasonic echo signal; the data analysis module includes a first interpolation function, a second interpolation function, a measurement program, and a temperature-correction program, which are used to calculate and output the ablation amount of the thermal protection layer in real time.

[0105] It should be noted that the temperature sensor, the ultrasonic signal transceiver, and the data analysis module are all connected to the data acquisition device for communication.

[0106] It should be noted that the ultrasonic transducer includes a piezoelectric element, which is excited by a short electrical pulse to generate an ultrasonic pulse; the ultrasonic transducer and the ultrasonic signal transceiver are connected by a cable to realize the output and reception of ultrasonic signals. The output of ultrasonic signals refers to the ultrasonic signal transceiver outputting an alternating voltage with a fixed period through the ultrasonic transducer to excite the ultrasonic signal; the reception of ultrasonic signals refers to the ultrasonic transducer converting the structural vibration generated by the pressure or deformation of the piezoelectric element into an electrical signal and inputting it into the ultrasonic signal transceiver for storage or outputting it to the data acquisition device. The signal amplifier in the data acquisition device amplifies the ultrasonic signal, and the filter filters out signals that are less than 80% of the transmission signal frequency and higher than 120% of the transmission signal frequency. The oscilloscope displays each peak (the horizontal axis represents time, and the vertical axis represents voltage). The ultrasonic echo signal schematic diagram collected by the data acquisition device can be used to obtain the "metal layer transition time t 12 ” and “transit time of unablated layer t Δ ; Ultrasonic waves in the megahertz range cannot be effectively transmitted through the air, so a high-temperature resistant coupling agent is used between the ultrasonic transducer and the metal bulkhead of the aircraft to achieve good ultrasonic transmission; threaded holes can be pre-processed on the metal bulkhead of the aircraft for special fixtures to be connected to the metal bulkhead bolts of the aircraft through screws; the ultrasonic signal transmitting and receiving device is connected to the power supply through a cable, and the power supply can be the power supply on the aircraft or an external power supply on the ground.

[0107] It should be noted that the data analysis module includes a first interpolation function, a second interpolation function and a temperature-correction program; the first interpolation function and the second interpolation function simulate the temperature of the actual heating of the aircraft metal cabin through the temperature simulation unit, and are established according to the method of the above step S1. The measurement program is the formula 4 described in the above step S9, which is edited by C language, matlab or labview. The temperature-correction program is established according to the formulas 1-3 in the above steps S2-S8, and is edited by C language, matlab or labview.

[0108] During measurement, the ultrasonic signal transmitting and receiving device outputs an alternating voltage with a fixed period according to the setting to excite an ultrasonic signal (i.e., a transmitting signal) through the ultrasonic transducer. The ultrasonic signal passes through the high-temperature resistant coupling agent-aircraft metal cabin wall-glue layer-unablated layer-transition layer-completely ablated layer (carbonized layer)-air layer in sequence. Each time the ultrasonic wave passes through the boundary of the two layers, transmission and reflection will occur. The transmitted wave continues to propagate, and the reflected wave propagates back to the ultrasonic transducer. The ultrasonic transducer converts the sound energy into electrical energy, which is then stored or output by the ultrasonic signal transceiver to the data acquisition device to obtain the time difference between the peaks in the ultrasonic echo signal; based on the echo signal of the transmitting signal received by the ultrasonic transducer, the data acquisition device extracts the time difference between the peaks from the echo signal and inputs it to the data analysis module through a communication connection. The data analysis module calculates the degree of ablation according to the time domain of each period echo signal, and outputs the ablation amount of the heat protection layer in real time.

[0109] The measurement method of the present invention does not need to destroy the wall structure, does not destroy the integrity of the metal cabin, directly measures the heat protection layer of the metal cabin, does not affect the heat transfer of the material, and can complete the measurement without causing any damage to the metal cabin of the aircraft. It breaks through the limitations of the traditional hole measurement method on the measurement position and has good synchronization.

[0110] Example 1

[0111] In this embodiment, it is known that the metal layer material of a certain aircraft metal cabin is aluminum alloy, with a thickness L of 20 mm; the heat protection layer material is phenolic resin, with a thickness X 0 The carbonization temperature of the heat protection layer is 20 mm. s It is 650℃.

[0112] The method for measuring the ablation amount of the aircraft heat protection layer proposed by the present invention measures the ablation amount of the heat protection layer of the aircraft metal cabin after the heat protection layer is heated, comprising the following steps:

[0113] S1: simulate the temperature measurement environment, transmit ultrasonic signals to the aircraft metal cabin at a fixed frequency and period, establish a first interpolation function between the propagation speed of the ultrasonic signal in the metal layer material of the aircraft metal cabin and the average temperature of the metal layer, and a second interpolation function between the propagation speed of the ultrasonic signal in the heat protection layer material of the aircraft metal cabin and the average temperature of the unablated layer; Figure 3 shown.

[0114] Among them, the fixed transmission frequency is 10 Hz, the fixed transmission period is 0.1 s, and the vibration frequency of the ultrasonic transmission signal is 2.5 MHz.

[0115] S2: heating the metal cabin of the aircraft, transmitting an ultrasonic signal to the metal cabin of the aircraft according to the fixed frequency and period in step S1, collecting an ultrasonic signal echo signal graph, and obtaining a metal layer transition time;

[0116] The ultrasonic signal echo signal diagram is collected, and it can be seen that the echo signal shows 2-3 peaks at the beginning, indicating that the heat protection layer material has not reached the carbonization temperature at this time, has not started to ablate, and the ablation amount is 0mm.

[0117] When the echo signal displayed in the ultrasonic signal echo signal diagram shows the fourth peak, it means that the heat protection layer begins to ablate. Take a certain moment as an example:

[0118] At this moment, the data acquisition device 10 displays the first peak, the second peak, the third peak, the fourth peak, and the fifth peak. Figure 2 As shown; it can be seen that the time difference between the first peak and the second peak, that is, the metal layer transition time t 12 =8.08μs; the time difference between the second and third peaks, i.e. the unablated layer transit time t Δ =11.76μs.

[0119] S3: Calculate the average propagation speed of the ultrasonic signal in the metal layer of the aircraft's metal cabin based on the metal layer transit time and the thickness of the metal layer of the aircraft's metal cabin:

[0120]

[0121] S4: Through the first interpolation function, according to the average speed V of the ultrasonic signal propagating in the aluminum alloy layer of the aircraft metal cabin 铝 , obtain the average temperature of the aluminum alloy layer of the aircraft metal cabin corresponding to the average speed

[0122] S5: Using a temperature sensor to measure, the inner surface temperature Tc of the aluminum alloy layer of the aircraft metal cabin is obtained to be 50° C.

[0123] S6: According to the average temperature of the metal layer of the aircraft metal cabin and the inner surface temperature of the metal layer of the aircraft metal cabin, the temperature of the interface between the metal layer of the aircraft metal cabin and the heat protection layer is calculated:

[0124]

[0125] S7: By T J The carbonization temperature of the aircraft metal cabin heat protection layer material is 650℃. Calculate the average temperature of the unburned layer of the aircraft metal cabin

[0126]

[0127] S8: Through the second interpolation function, according to the average temperature of the unablated layer of the aircraft metal cabin Obtain the propagation velocity of the ultrasonic signal in the unablated layer of the aircraft metal cabin at the average temperature V(T) = 2586 m / s;

[0128] S9: According to the total thickness of the aircraft's thermal protection layer, the propagation velocity in the unablated layer of the aircraft's metal cabin, and the unablated layer transit time, the ablation amount of the aircraft's metal cabin's thermal protection layer is calculated:

[0129] Thickness of unablated layer of heat protection layer

[0130] Thermal protection layer ablation amount X = X 0 -X'=4.8mm.

[0131] When the thermal protection layer reaches the ablation temperature, the ultrasonic signal echo signal diagram is continuously collected to obtain the transition time of the unablated layer. The ablation amount of the thermal protection layer of the aircraft metal cabin is calculated based on the total thickness of the aircraft thermal protection layer, the propagation speed in the unablated layer of the aircraft metal cabin and the transition time of the unablated layer.

[0132] Example 2

[0133] This embodiment provides a specific implementation device of a system for measuring the ablation amount of a heat protection layer of a metal cabin of an aircraft, such as Figure 4 shown.

[0134] The measuring system comprises: a temperature simulation unit, an ultrasonic transducer unit, a temperature measuring unit, an ultrasonic signal transceiver unit, and a data acquisition and analysis unit;

[0135] The temperature simulation unit includes a high and low temperature test chamber and a tube furnace, which are used to provide different temperature environments to simulate the temperature when the metal cabin of the aircraft is actually heated;

[0136] The ultrasonic transducer unit includes an ultrasonic transducer 6, which is used to output and receive ultrasonic signals. The ultrasonic transducer 6 is fixed to the aircraft metal bulkhead 1 through a special fixture 5, and the special fixture 5 can be bolted to the aircraft metal bulkhead 1 through a screw 4; a spring 3 can be added between the special fixture 5 and the screw 4 to adjust the pressure between the ultrasonic transducer and the aircraft metal bulkhead surface; the gap between the ultrasonic transducer 6 and the aircraft metal bulkhead 1 can be filled by a high-temperature resistant coupling agent 7; a threaded hole 2 is pre-processed on the aircraft metal bulkhead 1, which is used for the special fixture 5 to be bolted to the aircraft metal bulkhead 1 through the screw 4;

[0137] The temperature measurement unit comprises a temperature sensor 8, which is in communication connection with a data acquisition device 10 in the data acquisition and analysis unit and is used to measure the inner surface temperature of a metal layer of a metal cabin of an aircraft;

[0138] The ultrasonic signal transceiver unit includes an ultrasonic signal transceiver 9, which is connected to the ultrasonic transducer 6 through a cable. The ultrasonic signal transceiver 9 excites the ultrasonic signal through the ultrasonic transducer 6 according to the alternating voltage with a fixed period output according to the setting. The ultrasonic transducer 6 converts the structural vibration generated by the pressure or deformation of the piezoelectric element into an electrical signal and inputs it into the ultrasonic signal transceiver 9 for storage or outputs it to the data acquisition device 10; the ultrasonic signal transmitting and receiving device 9 is connected to the power supply 11 through a cable;

[0139] The data acquisition and analysis unit includes a data acquisition device 10 and a data analysis module 12. The data acquisition device 10 includes a signal amplifier, an oscilloscope, and a filter, and is used to obtain the time difference between the peaks in the ultrasonic echo signal; the data analysis module 12 includes a first interpolation function, a second interpolation function, a measurement program, and a temperature-correction program, and is used to calculate and output the ablation thickness of the thermal protection layer in real time; the data acquisition device 10 and the data analysis module 12 are communicatively connected.

[0140] The schematic diagram of using the measurement system of this embodiment to measure the ablation amount of the thermal protection layer of the aircraft metal cabin is as follows: Figure 5 shown.

[0141] The above description is only a preferred specific implementation manner of the present invention, but the protection scope of the present invention is not limited thereto. Any changes or substitutions that can be easily conceived by any technician familiar with the technical field within the technical scope disclosed by the present invention should be covered within the protection scope of the present invention.

Claims

1. A method for measuring the ablation amount of the heat protection layer of the aircraft metal cabin, characterized in that: The following steps are involved: S1: simulating the temperature measurement environment, transmitting ultrasonic signals to the aircraft metal cabin at a fixed frequency and period, establishing a first interpolation function between the propagation speed of the ultrasonic signal in the metal layer material of the aircraft metal cabin and the average temperature of the metal layer, and a second interpolation function between the propagation speed of the ultrasonic signal in the heat protection layer material of the aircraft metal cabin and the average temperature of the unablated layer; S2: Heat the metal cabin of the aircraft, transmit ultrasonic signals to the metal cabin of the aircraft according to the fixed frequency and period in step S1, collect ultrasonic signal echo signal graphs, and obtain the metal layer transition time t 12 ; S3: Calculate the average propagation speed V of the ultrasonic signal in the metal layer of the aircraft metal cabin according to the metal layer transit time and the metal layer thickness of the aircraft metal cabin. 金属 ; S4: According to the first interpolation function and the average speed V of the ultrasonic signal propagating in the metal layer of the aircraft metal cabin 金属 , obtain the average temperature of the metal layer of the aircraft's metal cabin corresponding to the average velocity propagating in the metal layer of the aircraft's metal cabin S5: Measure and obtain the inner surface temperature Tc of the metal layer of the aircraft metal cabin; S6: Based on the average temperature of the metal layer of the aircraft's metal cabin and the inner surface temperature Tc of the metal layer of the aircraft metal cabin, the temperature Tc of the interface between the metal layer of the aircraft metal cabin and the heat protection layer is calculated J ; S7: According to the temperature T of the interface between the metal layer of the aircraft metal cabin and the heat protection layer J and the carbonization temperature T of the aircraft metal cabin heat protection layer material s , the average temperature of the unablated layer of the aircraft metal cabin is calculated S8: acquiring a propagation velocity V(T) of an ultrasonic signal in the unablated layer of the aircraft metal cabin body corresponding to the average temperature of the unablated layer of the aircraft metal cabin body according to the second interpolation function and the average temperature of the unablated layer of the aircraft metal cabin body; S9: Continuously collect ultrasonic signal echo signal diagrams to obtain the non-ablated layer transition time t Δ According to the total thickness of the aircraft thermal protection layer X0, the propagation velocity V(T) in the unablated layer of the aircraft metal cabin, and the unablated layer transit time t Δ , calculate and obtain the ablation amount X of the aircraft metal cabin thermal protection layer.

2. The measuring method according to claim 1, characterized in that: In step S1, the fixed transmission frequency is 1-10 Hz.

3. The measuring method according to claim 2, characterized in that: In step S1, the fixed period is 0.1s-1s.

4. The measuring method according to claim 3, characterized in that: In step S1, the transmitting vibration frequency of the ultrasonic signal is 0.5-3 MHz.

5. The measuring method according to claim 1, characterized in that: In step S3, the average speed of the ultrasonic signal propagating in the metal layer of the aircraft metal cabin is calculated by the following formula: Wherein, L is the thickness of the metal layer of the aircraft metal cabin, mm; t 12 —Metal layer transition time, μs; V 金属 —The average speed at which ultrasonic signals propagate in the metal layer of the aircraft’s metal cabin, m / s.

6. The measuring method according to claim 1, characterized in that: In step S6, the temperature of the interface between the metal layer of the aircraft metal cabin and the heat protection layer is calculated by the following formula: in, —Average temperature of the metal layer of the aircraft metal cabin, °C; Tc—the inner surface temperature of the metal layer of the aircraft metal cabin, °C; T J —The temperature of the interface between the metal layer and the thermal protection layer of the aircraft's metal cabin, ℃.

7. The measuring method according to claim 1, characterized in that: In step S7, the average temperature of the unablated layer of the aircraft metal cabin is calculated by the following formula: Among them, T J —Temperature of the interface between the metal layer of the aircraft metal cabin and the heat protection layer, °C; T s —Carbonization temperature of the heat protection layer material of the aircraft metal cabin, °C; —The average temperature of the unablated layer of the aircraft's metal cabin.

8. The measuring method according to claim 1, characterized in that: In step S9, the ablation amount of the aircraft metal cabin heat protection layer is calculated by the following formula: Where, X—ablation thickness, mm; X0—total thickness of heat protection layer, mm; V(T)—the propagation velocity of ultrasonic signal in the unablated layer of the aircraft metal cabin, m / s; t Δ —Transit time of unablated layer, μs.

9. The measuring method according to any one of claims 1 to 8, characterized in that: In step S1, the simulated measurement temperature environment is achieved by a high and low temperature test box or a tube furnace.

10. The measuring method according to any one of claims 1 to 9, characterized in that: In step S5, the inner surface temperature of the metal layer of the aircraft metal cabin is measured by a temperature sensor.

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