System and method for measuring ablation thickness of aircraft ablation heat-proof layer

Abstract

The invention relates to a system and a method for measuring the ablation thickness of an aircraft ablation heat-proof layer, and belongs to the technical field of aerospace special parameter measurement. The measurement system comprises a temperature simulation unit, an ultrasonic transduction unit, a temperature measurement unit, an ultrasonic signal transceiving unit and a data acquisition and analysis unit. The temperature simulation unit comprises a high and low temperature test box and a tube furnace, and is used for providing different temperature environments and simulating the temperature when the aircraft cabin is actually heated; the ultrasonic transduction unit comprises an ultrasonic transducer and is used for outputting and receiving ultrasonic signals; the temperature measuring unit comprises a temperature sensor used for measuring the temperature of the inner surface of the aircraft cabin metal layer. The ultrasonic signal receiving and transmitting unit comprises an ultrasonic signal receiving and transmitting device and is used for outputting and receiving alternating voltage; the data acquisition and analysis unit comprises a data acquisition device and a data analysis module; the data acquisition device is used for acquiring a time difference between wave crests in the ultrasonic echo signals; and the data analysis module is used for calculating and outputting the ablation thickness of the heat-proof layer in real time.

Description

Technical Field

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

[0002] Ablation refers to the material consumption phenomenon of solid surface caused by thermochemical and mechanical processes under the action of heat flow when missiles and aircraft re-enter the atmosphere. Ablative materials, also known as heat shields, can undergo physical and chemical changes such as decomposition, melting, evaporation, sublimation, and erosion under the action of heat flow. A large amount of heat is taken away by the mass consumption of the material surface to cool the large amount of heat energy generated when the aircraft re-enters the atmosphere, and prevent the heat flow from entering the interior of the aircraft and causing fatal damage. Ablation thickness is an important parameter in the design of re-entry vehicles in aerospace engineering. The necessary thickness of ablative materials is very important to ensure the safety of equipment and personnel in the aircraft. The ablation rate and ablation amount of the thermal protection layer must be mastered. If the ablative thermal protection layer is burned through during flight, aerodynamic heating will cause the surface temperature of the spacecraft to be too high, resulting in damage to the spacecraft or causing the temperature inside the spacecraft to be too high, and the instruments cannot work properly.

[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 material is 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 eroding 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 thickness of dimensional ablative materials.

[0004] At present, the commonly used method for measuring the ablation thickness of dimensional ablative materials in the industry is to use an embedded ablation sensor. This embedded ablation sensor method requires designing installation holes on the metal cabin and non-metallic wall in advance, which destroys the original wall structure and has poor synchronization. Summary of the invention

[0005] In view of the above analysis, the present invention aims to provide a system and method for measuring the ablation thickness of an aircraft ablative thermal protection layer, so as to solve at least one of the following problems: 1. The measurement of the ablation thickness of existing dimensional ablative materials is generally achieved by embedding ablation sensors, which will damage the cabin wall and the ablation layer structure; 2. The existing method for measuring the ablation thickness 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 system for measuring the ablation thickness of an aircraft ablative heat protection layer, 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;

[0008] 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;

[0009] The ultrasonic transducer unit includes an ultrasonic transducer for outputting and receiving ultrasonic signals;

[0010] The temperature measurement unit includes a temperature sensor for measuring the inner surface temperature of a metal layer of a metal cabin of an aircraft;

[0011] The ultrasonic signal transceiver unit includes an ultrasonic signal transceiver device for outputting and receiving an alternating voltage, and the output ultrasonic signal sequentially passes through the aircraft metal bulkhead, the unablated layer, the transition layer, the completely ablated layer and the air layer to generate an echo signal;

[0012] 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 thickness of the thermal protection layer in real time.

[0013] Furthermore, the temperature simulation unit is communicatively connected to the data acquisition and analysis unit; the ultrasonic transducer unit is connected to the ultrasonic signal transceiver unit via a cable; the temperature measurement unit is communicatively connected to the data acquisition device in the data acquisition and analysis unit; the ultrasonic signal transceiver unit is communicatively connected to the data acquisition device in the data acquisition and analysis unit, and is connected to the power supply via a cable; the data acquisition device in the data acquisition and analysis unit is communicatively connected to the data analysis module.

[0014] Furthermore, the first interpolation function is a relationship 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;

[0015] The second interpolation function is a function of the relationship between the propagation speed of the ultrasonic signal in the thermal protection layer material of the aircraft metal cabin and the average temperature of the unablated layer.

[0016] Furthermore, the data analysis module calculates the ablation thickness of the heat protection layer according to the following formula:

[0017]

[0018] Where, X—ablation thickness, mm;

[0019] X0—total thickness of heat protection layer, mm;

[0020] V(T)—the sound velocity of the ultrasonic signal in the unablated layer of the aircraft metal cabin, m / s;

[0021] t Δ —Transit time of unablated layer, μs.

[0022] The present invention also provides a method for measuring the ablation thickness of an aircraft ablative heat protection layer, which is completed by the above-mentioned measurement system and includes the following steps:

[0023] S1: simulate and measure the temperature environment, transmit ultrasonic signals to the metal cabin of the aircraft 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, and import the first interpolation function and the second interpolation function into the data analysis module in the data acquisition and analysis unit;

[0024] S2: Establishing the measurement program and the temperature-sound velocity correction program and importing them into the data analysis module in the data acquisition and analysis unit;

[0025] S3: Heat the metal cabin of the aircraft, and transmit ultrasonic signals to the metal cabin of the aircraft according to the fixed frequency and period in step S1. The data acquisition device extracts the "metal layer transition time" and "unablated layer transition time" of the echo of the metal cabin material of the aircraft from the echo signal and inputs them into the data analysis module. The data analysis module completes data processing in real time according to the measurement program and the temperature-sound velocity correction program and outputs the thickness of the unablated layer.

[0026] Further, in step S2, the measurement procedure includes:

[0027]

[0028] Where, X—ablation thickness, mm;

[0029] X0—total thickness of heat protection layer, mm;

[0030] V(T)—the sound velocity of the ultrasonic signal in the unablated layer of the aircraft metal cabin, m / s;

[0031] t Δ —Transit time of unablated layer, μs.

[0032] Furthermore, in step S2, the principle of establishing the temperature-sound velocity correction program includes: according to the metal layer thickness L of the aircraft metal cabin and the metal layer transition time t12 , calculate the average speed of ultrasonic signal propagation in the metal layer of the aircraft metal cabin:

[0033]

[0034] Wherein, L is the thickness of the metal layer of the aircraft metal cabin, mm;

[0035] t 12 —Metal layer transition time, μs;

[0036] V 金属 —The average speed at which ultrasonic signals propagate in the metal layer of the aircraft’s metal cabin, m / s.

[0037] Furthermore, in step S3, the principle of establishing the temperature-sound velocity correction program also includes: using a first interpolation function, according to the average speed V of the ultrasonic signal propagating in the metal layer of the aircraft metal cabin 金属 , get the average temperature of the metal layer of the aircraft metal cabin corresponding to the average speed

[0038] Furthermore, in step S3, the principle of establishing the temperature-sound velocity correction program also includes: obtaining the inner surface temperature Tc of the metal layer of the aircraft metal cabin by measuring with a temperature sensor in the measuring device, and Tc to calculate the temperature T of the interface between the metal layer of the aircraft metal cabin and the heat protection layer J :

[0039]

[0040] in, —Average temperature of the metal layer of the aircraft metal cabin, °C;

[0041] Tc—the inner surface temperature of the metal layer of the aircraft metal cabin, °C;

[0042] T J —The temperature of the interface between the metal layer and the thermal protection layer of the aircraft's metal cabin, ℃.

[0043] By T J and the carbonization temperature T of the aircraft metal cabin heat protection layer material s Calculate the average temperature of the unablated layer of the aircraft metal cabin

[0044]

[0045] Among them, T J —Temperature of the interface between the metal layer of the aircraft metal cabin and the heat protection layer, °C;

[0046] T s—Carbonization temperature of the heat protection layer material of the aircraft metal cabin, °C;

[0047] —Average temperature of the unablated layer of the aircraft metal cabin, ℃.

[0048] Furthermore, in step S3, the temperature-sound velocity correction program establishment principle also includes: using a second interpolation function, according to the average temperature of the unablated layer of the aircraft metal cabin The propagation velocity V(T) of the ultrasonic signal in the unablated layer of the aircraft metal cabin at the average temperature is obtained.

[0049] Compared with the prior art, the present invention can achieve at least one of the following beneficial effects:

[0050] 1. The existing method of measuring the ablation thickness of dimensional ablative materials is mainly achieved by embedding ablation sensors. This method requires designing installation holes on the metal cabin and non-metal wall in advance, destroying the original wall structure and having poor synchronization. The measurement system and measurement method of the present invention do not require designing installation holes on the metal cabin and non-metal wall, will not cause any damage to the metal cabin of the aircraft, and the measurement system is easy to install; the method of the present invention directly measures the heat protection layer of the metal cabin, breaking through the limitations of the traditional hole measurement method on the measurement position, and has good synchronization.

[0051] 2. The existing method of measuring the ablation thickness of the aircraft metal cabin thermal protection layer by embedding the ablation sensor. The embedded metal sensitive line affects the one-dimensional heat transfer. The method of the present invention does not perform any processing on the metal cabin thermal protection layer and directly measures it, which does not affect the heat transfer of the material.

[0052] 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

[0053] 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.

[0054] Figure 1 It is a schematic diagram of the structure of the measurement system of the present invention;

[0055] Figure 2 This is a schematic diagram of the echo signal collected during the measurement of the present invention;

[0056] Figure 3The interpolation curve diagram of the first interpolation function and the second interpolation function in Embodiment 1 of the present invention;

[0057] Figure 4 This is a schematic diagram of the specific structure of the measurement system of Example 2 of the present invention;

[0058] Figure 5 Schematic diagram of the measurement principle when using the measurement system of Example 2 of the present invention to perform measurement.

[0059] Reference numerals:

[0060] 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

[0061] 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.

[0062] The present invention provides a system for measuring the ablation thickness of an aircraft ablative heat protection layer, 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;

[0063] 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;

[0064] The ultrasonic transducer unit includes an ultrasonic transducer for outputting and receiving ultrasonic signals;

[0065] The temperature measurement unit includes a temperature sensor for measuring the inner surface temperature of a metal layer of a metal cabin of an aircraft;

[0066] The ultrasonic signal transceiver unit includes an ultrasonic signal transceiver device for outputting and receiving an alternating voltage;

[0067] 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 thickness of the thermal protection layer in real time.

[0068] Specifically, the temperature simulation unit is communicatively connected with the data acquisition and analysis unit. The ultrasonic transducer of the ultrasonic transducer unit can be fixed on the metal bulkhead of the aircraft by a special fixture, and the special fixture can be bolted to the metal bulkhead of the aircraft by screws; a spring can be added between the special fixture and the screw 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 temperature measurement unit is crimped onto the metal bulkhead of the aircraft and is communicatively connected with the data acquisition device in the data acquisition and analysis unit. The ultrasonic signal transceiver unit is communicatively connected with the data acquisition device in the data acquisition and analysis unit, and is connected to the power supply through a cable. The data acquisition device in the data acquisition and analysis unit is communicatively connected with the data analysis module.

[0069] Usually, the heat-resistant layer of dimensional ablative material 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 heat-resistant layer of dimensional ablative material. Dimensional ablative material is essentially a reinforced phenolic resin material. The ablation process is essentially a process of carbonization of the material. The material's external dimensions and strength hardly change during and after carbonization. The traditional wire-laying detection technology relies on the method of measuring the ablation amount by eroding the embedded sensitive element by the ablative material and the method of measuring the ablation amount by fusing the embedded resistance wire. Both of them cannot measure the ablation thickness of dimensional ablative material. At present, the commonly used method for measuring the ablation thickness of dimensional ablative material in the industry is to use the method of embedding ablation sensors, which requires the design of installation holes on the metal cabin and non-metallic wall surfaces in advance, destroying the integrity of the cabin structure. When using the measurement system of the present invention for measurement, there is no need to design installation holes on the metal cabin and non-metallic wall surfaces, and the integrity of the metal cabin is not destroyed. The measurement can be completed without causing any damage to the metal cabin of the aircraft, and the installation is quick.

[0070] It should be noted that the ultrasonic transducer of the ultrasonic transducer unit 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 in the ultrasonic signal transceiver unit 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 in the data acquisition and analysis unit to obtain the time difference between the peaks in the ultrasonic echo signal; ultrasonic waves in the megahertz range cannot be effectively transmitted through the air, so the gap between the ultrasonic transducer and the metal bulkhead of the aircraft is filled with a high-temperature resistant coupling agent to achieve good ultrasonic transmission; threaded holes are pre-processed on the metal bulkhead of the aircraft for special fixtures to be connected to the metal bulkhead 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 the external power supply on the ground.

[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, during the measurement process, multiple peaks of the ultrasonic signal are filtered and displayed by the data acquisition device; Figure 2 Among them, the first peak is generated when the ultrasonic transducer excites the ultrasonic signal, the second 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, and the time difference between the first peak and the second 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 peak; the third 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 peak and the third peak is the "unablated layer transition time"; the fourth peak is the reflected wave generated when the ultrasonic signal enters the carbonized layer from the transition layer, and the fifth peak is the reflected wave when the ultrasonic signal enters the air interface from the carbonized layer. There are many clutters after the third peak, and the fourth and fifth peaks are easily submerged by clutters. The transition layer is in a state of being ablated. Therefore, when measuring the ablation thickness of the aircraft metal cabin thermal protection layer, the ablation thickness of the aircraft metal cabin thermal protection layer can be obtained by subtracting the un-ablated thickness of the ablation layer from the total thickness of the ablation layer.

[0072] When the above measurement system is used to measure the ablation thickness of the aircraft thermal protection layer, the ultrasonic signal transmitting and receiving device excites the ultrasonic signal (i.e., the transmitting signal) through the ultrasonic transducer according to the setting output of the alternating voltage with a fixed period, and 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 transmission 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 to the data by the ultrasonic signal transceiver. The acquisition device obtains the time difference between the peaks in the ultrasonic echo signal; based on the echo signal of the transmission signal received by the ultrasonic transducer, the signal amplifier in the data acquisition device amplifies the echo signal, the filter filters out the 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 time difference between the peaks is extracted from the echo signal and input into the data analysis module through the communication connection, the data analysis module calculates the ablation degree according to the time domain of each cycle echo signal, and outputs the ablation thickness of the thermal protection layer in real time.

[0073] Specifically, the present invention also provides a method for measuring the ablation thickness of an aircraft ablative heat protection layer, and the measurement is completed by the above-mentioned measurement system, comprising the following steps:

[0074] S1: simulate and measure the temperature environment, transmit ultrasonic signals to the metal cabin of the aircraft 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, and import the first interpolation function and the second interpolation function into the data analysis module in the data acquisition and analysis unit;

[0075] S2: Establishing the measurement program and the temperature-sound velocity correction program and importing them into the data analysis module in the data acquisition and analysis unit;

[0076] S3: Heat the metal cabin of the aircraft, and transmit ultrasonic signals to the metal cabin of the aircraft according to the fixed frequency and period in step S1. The data acquisition device extracts the "metal layer transition time" and "unablated layer transition time" of the echo of the metal cabin material of the aircraft from the echo signal and inputs them into the data analysis module. The data analysis module completes data processing in real time according to the measurement program and the temperature-sound velocity correction program and outputs the thickness of the unablated layer.

[0077] Specifically, before the aircraft metal cabin is heated at high temperature for ablation, the temperature environment is first simulated and measured, and 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 are established and imported into the data analysis module. At the same time, before the aircraft metal cabin is heated at high temperature for ablation, a measurement program and a temperature-sound speed correction program are established and imported into the data analysis module.

[0078] 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. At the same time, since the gap between the ultrasonic transducer and the metal cabin wall of the aircraft is filled with a high-temperature resistant coupling agent, the temperature resistance of the high-temperature resistant coupling agent is 800°C, and the carbonization temperature of the aircraft metal cabin thermal protection layer material is greater than 400°C, 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 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 is established. Then, the second interpolation function is obtained by fitting according to the least squares method.

[0079] 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.

[0080] Specifically, in step S2, the measurement program is established based on the principle that:

[0081]

[0082] Where, X—ablation thickness, mm;

[0083] X′—unablated layer thickness, mm;

[0084] X0—total thickness of heat protection layer, mm;

[0085] V(T)—the sound velocity of the ultrasonic signal in the unablated layer of the aircraft metal cabin, m / s;

[0086] t Δ —Unablated layer transition time, (i.e., the time difference between the second and third wave peaks), μs.

[0087] According to formula 1, edit using C language, matlab or labview, create a measurement program and import it into the data analysis module.

[0088] It should be noted that V(T) is the sound velocity of the ultrasonic signal in the thermal protection layer material of the aircraft metal cabin. It changes with the temperature of the thermal protection layer. Therefore, proper temperature correction can greatly improve the measurement accuracy. Therefore, before the measurement begins, a temperature-sound velocity correction program is established. The establishment principle is:

[0089] The first step is to calculate the thickness of the metal layer L of the aircraft metal cabin and the metal layer transition time t according to formula 2. 12 , calculate the average speed of ultrasonic signal propagation in the metal layer of the aircraft metal cabin:

[0090]

[0091] Wherein, L is the thickness of the metal layer of the aircraft metal cabin, mm;

[0092] t 12 —Metal layer transition time, μs;

[0093] V 金属 —The average speed at which ultrasonic signals propagate in the metal layer of the aircraft’s metal cabin, m / s.

[0094] In the second step, the first interpolation function in the data analysis module is used to calculate the average velocity V of the ultrasonic signal propagating in the metal layer of the aircraft metal cabin. 金属 , get the average temperature of the metal layer of the aircraft metal cabin corresponding to the average speed

[0095] The third step is to measure the temperature of the inner surface of the metal layer of the aircraft metal cabin through the temperature sensor in the temperature measurement unit to obtain Tc. According to formula 3, and Tc to calculate the temperature T of the interface between the metal layer of the aircraft metal cabin and the heat protection layer J :

[0096]

[0097] in, —Average temperature of the metal layer of the aircraft metal cabin, °C;

[0098] Tc—the inner surface temperature of the metal layer of the aircraft metal cabin, °C;

[0099] T J —The temperature of the interface between the metal layer of the spacecraft's metal cabin and the thermal protection layer, ℃.

[0100] Step 4: According to formula 4, through T J and the carbonization temperature T of the aircraft metal cabin heat protection layer material s Calculate the average temperature of the unablated layer of the aircraft metal cabin

[0101]

[0102] Among them, T J —Temperature of the interface between the metal layer of the aircraft metal cabin and the heat protection layer, °C;

[0103] T s —Carbonization temperature of the heat protection layer material of the aircraft metal cabin, °C;

[0104] —Average temperature of the unablated layer of the aircraft metal cabin, ℃.

[0105] 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 fixed.

[0106] The fifth step is to use the second interpolation function in the data analysis module to calculate the average temperature of the unablated layer of the aircraft metal cabin. Obtaining the propagation velocity V(T) of the ultrasonic signal in the unablated layer of the aircraft metal cabin at the average temperature;

[0107] According to the above principles, the editing is completed through C language, matlab or labview, the temperature-sound velocity correction program is established and imported into the data analysis module.

[0108] Specifically, in step S3, the aircraft metal cabin is heated, and an ultrasonic signal is emitted to the aircraft metal cabin according to the fixed frequency and period in step S1, and the data acquisition device extracts the "metal layer transition time t" of the aircraft metal cabin material echo from the echo signal. 12 ” and “transit time of unablated layer t Δ " and input into the data analysis module, which completes data processing in real time according to the measurement program and temperature-sound velocity correction program and outputs the thickness of the unablated layer, including the following stages:

[0109] In the first stage, at room temperature, an ultrasonic signal is emitted to the metal cabin of the aircraft according to the fixed frequency and period in step S1. At this time, the metal cabin of the aircraft has not yet started to be heated, and the ultrasonic signal passes through the high temperature resistant coupling agent-aircraft metal cabin wall-glue layer-unablated layer-air layer in sequence, generating the first peak and the second peak; the data acquisition device extracts the "metal layer transition time t" of the echo of the aircraft metal cabin material from the echo signal. 12 " and the total thickness of the heat protection layer X0, as the initial value of the measurement;

[0110] In the second stage, the aircraft metal cabin starts to be heated, and the temperature of the aircraft metal cabin gradually increases. The ultrasonic signal is emitted to the aircraft metal cabin according to the fixed frequency and period in step S1, and the heating starts until the aircraft metal cabin heat protection layer begins to ablate. The ultrasonic signal passes through the high temperature resistant coupling agent-aircraft metal cabin wall-glue layer-unablated layer-transition layer-air layer in sequence, generating the first wave peak, the second wave peak, and the third wave peak. However, the time difference t between the second wave peak and the third wave peak in this stage is Δ It is very small and infinitely close to 0. Therefore, at this stage, the temperature-sound velocity correction program does not intervene in the measurement. The thickness of the unablated layer X′ is approximately equal to the total thickness of the heat protection layer X0, and the ablated thickness X is 0 mm.

[0111] In the third stage, the outer surface temperature of the aircraft metal cabin reaches the carbonization temperature of the heat protection layer, and the heat protection layer begins to ablate. The ultrasonic signal is emitted to the aircraft metal cabin at the fixed frequency and period in step S1. 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, generating the first peak, the second peak, the third peak, the fourth peak and the fifth peak. The data acquisition device extracts the "metal layer transition time t" of the aircraft metal cabin material echo from the echo signal. 12 ” and “transit time of unablated layer t Δ " and input it into the data analysis module. When the measurement system observes the generation of the fourth wave peak, it means that the heat protection layer begins to ablate. The temperature-sound velocity correction program starts and the measurement is intervened. The data analysis module completes the data processing in real time according to the measurement program and outputs the thickness of the unablated layer. At this time, the thickness of the unablated layer is X'. As the measurement proceeds, the data processing and display device displays in real time and ablation thickness X.

[0112] Example 1

[0113] In this embodiment, it is known that the metal layer material of a certain aircraft metal cabin is aluminum alloy, and the thickness L is 20 mm; the heat protection layer material is phenolic resin, and the thickness X0 is 20 mm. The carbonization temperature of the heat protection layer is T s It is 650℃.

[0114] The ablation thickness of the heat protection layer of the aircraft metal cabin is measured by the measurement system and method of the ablation thickness of the aircraft heat protection layer proposed by the present invention, which includes the following steps:

[0115] Step 1: Follow the measurement system diagram (such as Figure 1 As shown), arrange the components of the measurement system;

[0116] Step 2: simulate and measure the temperature environment, transmit ultrasonic signals to the metal cabin of the aircraft 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, and import the first interpolation function and the second interpolation function into the data analysis module in the data acquisition and analysis unit;

[0117] The fixed transmission frequency is 10Hz, the fixed transmission period is 0.1s, and the vibration frequency of the ultrasonic transmission signal is 2.5MHz;

[0118] The interpolation curve diagram of the first interpolation function and the second interpolation function is as follows: Figure 3 shown.

[0119] Step 3: Before the measurement begins, build and import the data analysis module in the data acquisition and analysis unit, and establish the principles of the measurement program and the temperature-sound velocity correction program as described in the manual;

[0120] Step 4: measurement starts, heating the metal cabin of the aircraft begins, and ultrasonic signals are emitted to the metal cabin of the aircraft according to the fixed frequency and period in step S1;

[0121] The data acquisition device displays the waveform of the echo signal. At the beginning, the echo signal shows 2-3 peaks, indicating that the heat protection layer material has not yet reached the carbonization temperature and has not started to ablate. The temperature-sound velocity correction program is not started, and the ablation thickness is 0mm.

[0122] When the waveform of the echo signal displayed by the data acquisition device shows the fourth peak, it means that the thermal protection layer begins to ablate. The temperature-sound velocity correction program is started and the measurement is intervened. Take a certain moment as an example:

[0123] At this moment, the waveform of the echo signal displayed by the data acquisition device shows 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. The data acquisition device measures the metal layer transition time t 12 and the unablated layer transit time t Δ Transmit to the data analysis module.

[0124] At this moment, the temperature sensor measured the inner surface temperature Tc of the aluminum alloy layer of the aircraft metal cabin to be 50°C.

[0125] The internal operations of the data analysis module are as follows:

[0126] The average speed of ultrasonic signal propagation in the aluminum alloy layer of the aircraft metal cabin:

[0127]

[0128] 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

[0129] pass and Tc to calculate the temperature T of the interface between the metal layer of the aircraft metal cabin and the heat protection layer J :

[0130]

[0131] 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

[0132]

[0133] 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;

[0134] Thickness of unablated layer of heat protection layer

[0135] The ablation thickness of the heat protection layer is X=X0-X'=4.8mm.

[0136] When the heat protection layer reaches the ablation temperature, the data analysis module performs the above calculations and outputs the ablation thickness in real time each time the data acquisition device receives an echo signal.

[0137] Example 2

[0138] 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.

[0139] 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;

[0140] 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;

[0141] 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;

[0142] 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;

[0143] 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;

[0144] 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.

[0145] 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.

[0146] 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 system for measuring the ablation thickness of an aircraft ablative heat protection layer, characterized in that: It includes a temperature simulation unit, an ultrasonic transducer unit, a temperature measurement unit, an ultrasonic signal transceiver unit, and a data acquisition and analysis unit; 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; The ultrasonic transducer unit includes an ultrasonic transducer for outputting and receiving ultrasonic signals; The temperature measurement unit includes a temperature sensor for measuring the inner surface temperature of a metal layer of a metal cabin of an aircraft; The ultrasonic signal transceiver unit includes an ultrasonic signal transceiver device for outputting and receiving an alternating voltage, and the output ultrasonic signal sequentially passes through the aircraft metal bulkhead, the unablated layer, the transition layer, the completely ablated layer and the air layer to generate an echo signal; 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 thickness of the thermal protection layer in real time.

2. The measuring system according to claim 1, characterized in that The temperature simulation unit is communicatively connected to the data acquisition and analysis unit; the ultrasonic transducer unit is connected to the ultrasonic signal transceiver unit via a cable; the temperature measurement unit is communicatively connected to the data acquisition device in the data acquisition and analysis unit; the ultrasonic signal transceiver unit is communicatively connected to the data acquisition device in the data acquisition and analysis unit, and is connected to the power supply via a cable; the data acquisition device in the data acquisition and analysis unit is communicatively connected to the data analysis module.

3. The measuring system according to claim 1 or 2, characterized in that: The first interpolation function is a function of the relationship 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; The second interpolation function is a function of the relationship between the propagation speed of the ultrasonic signal in the thermal protection layer material of the aircraft metal cabin and the average temperature of the unablated layer.

4. The measuring system according to any one of claims 1 to 3, characterized in that: The data analysis module calculates the ablation thickness of the heat protection layer according to the following formula: Where, X—ablation thickness, mm; X0—total thickness of heat protection layer, mm; V(T)—the sound velocity of the ultrasonic signal in the unablated layer of the aircraft metal cabin, m / s; t Δ —Transit time of unablated layer, μs.

5. A method for measuring the ablation thickness of an aircraft ablative heat protection layer, accomplished by the measurement system according to any one of claims 1 to 4, characterized in that: The following steps are involved: S1: simulate and measure the temperature environment, transmit ultrasonic signals to the metal cabin of the aircraft 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, and import the first interpolation function and the second interpolation function into the data analysis module in the data acquisition and analysis unit; S2: Establishing the measurement program and the temperature-sound velocity correction program and importing them into the data analysis module in the data acquisition and analysis unit; S3: Heat the metal cabin of the aircraft, and transmit ultrasonic signals to the metal cabin of the aircraft according to the fixed frequency and period in step S1. The data acquisition device extracts the "metal layer transition time" and "unablated layer transition time" of the echo of the metal cabin material of the aircraft from the echo signal and inputs them into the data analysis module. The data analysis module completes data processing in real time according to the measurement program and the temperature-sound velocity correction program and outputs the thickness of the unablated layer.

6. The measuring method according to claim 5, characterized in that: In step S2, the measurement procedure includes: Where, X—ablation thickness, mm; X0—total thickness of heat protection layer, mm; V(T)—the sound velocity of the ultrasonic signal in the unablated layer of the aircraft metal cabin, m / s; t Δ —Transit time of unablated layer, μs.

7. The measuring method according to claim 6, characterized in that: In step S2, the principle of establishing the temperature-sound velocity correction program includes: according to the metal layer thickness L of the aircraft metal cabin and the metal layer transition time t 12 , calculate the average speed of ultrasonic signal propagation in the metal layer of the aircraft metal cabin: 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.

8. The measuring method according to claim 7, characterized in that: In step S3, the principle of establishing the temperature-sound velocity correction program also includes: using a first interpolation function, according to the average speed V of the ultrasonic signal propagating in the metal layer of the aircraft metal cabin 金属 , get the average temperature of the metal layer of the aircraft metal cabin corresponding to the average speed 9. The measuring method according to claim 8, characterized in that: In step S3, the principle of establishing the temperature-sound velocity correction program also includes: obtaining the inner surface temperature Tc of the metal layer of the aircraft metal cabin through the temperature sensor in the measuring device, and obtaining the inner surface temperature Tc of the metal layer of the aircraft metal cabin through the temperature sensor in the measuring device. and Tc to calculate the temperature T of the interface between the metal layer of the aircraft metal cabin and the heat protection layer J : 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, ℃. By T J and the carbonization temperature T of the aircraft metal cabin heat protection layer material s Calculate the average temperature of the unablated layer of the aircraft metal cabin 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; —Average temperature of the unablated layer of the aircraft metal cabin, ℃.

10. The measuring method according to claim 9, characterized in that: In step S3, the temperature-sound velocity correction program establishment principle also includes: using a second interpolation function, according to the average temperature of the unablated layer of the aircraft metal cabin The propagation velocity V(T) of the ultrasonic signal in the unablated layer of the aircraft metal cabin at the average temperature is obtained.

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