A diagnostic method and device for fatigue crack failure of aircraft engine accessory pipeline

Abstract

The present invention provides a method and device for diagnosing fatigue crack faults of aircraft engine accessory pipelines, belonging to the field of aircraft engines; the method steps are to evaluate the state of the aircraft engine accessory pipelines, select the installation position of the acceleration sensor according to the evaluation results; collect the signal of the aircraft engine accessory pipelines through the acceleration sensor; process the signal of the aircraft engine accessory pipelines; calculate the fault characteristics of the aircraft engine accessory pipelines according to the signal processing results of step 3; diagnose the faults of the aircraft engine accessory pipelines according to the fault characteristics. The present invention considers the actual nonlinear boundaries and constraints of the aircraft engine accessory pipelines, takes the local structure of the accessory pipelines as the object of analysis and diagnosis, and solves the shortcomings of the existing method based on nonlinear transfer function in the process of diagnosing fatigue crack faults of aircraft engine accessory pipelines.

Description

Technical Field

[0001] The invention belongs to the field of aeroengines, and in particular relates to a method and equipment for diagnosing fatigue crack faults of accessory pipelines of aeroengines. Background Art

[0002] Aircraft engine accessory pipelines are mainly used for the transmission of fuel, lubricating oil, air and other media. They are called the "heart" of the engine and are an important part of the aircraft engine. The single-tube structure is composed of a single tube or several tubes in series, while the piping structure is composed of two or more tubes connected by clamps or multi-way joints. Since the operation of aircraft engines is often accompanied by dynamic excitations such as rotor vibration, fluid pulsation and oscillating combustion, the vibration failure problem of accessory pipelines has always been very prominent.

[0003] Fatigue cracks are one of the common vibration failures, which mainly arise from tiny structural defects (loose welds and surface scratches, etc.) generated during pipeline processing and installation. Under the action of the alternating vibration load of the aircraft engine, the stress concentration generated at the root of the initial crack continuously tears the structure and promotes the slow expansion of the crack. When the mechanical properties of the crack area drop to the point where it cannot withstand the alternating load, the pipeline structure suddenly breaks and fails. Fatigue fracture failure can seriously damage the integrity of the accessory pipeline, affect the structural reliability of the aircraft engine, and even cause catastrophic accidents with the destruction of the aircraft and the loss of life. For example, the hydraulic conduit of a certain type of aircraft engine broke and leaked oil, causing a fire in the aircraft fuel tank; the oil delivery conduit of a certain type of aircraft engine broke, causing a serious safety accident.

[0004] It takes a certain amount of time for fatigue cracks to develop into fatigue fractures. Therefore, by making full use of this "time difference" and timely diagnosing fatigue crack failures in aircraft engine accessory pipelines, it is possible to eliminate potential failure hazards before fatigue fractures occur in the pipeline structure, thus ensuring the stable and safe operation of the engine. At the same time, the diagnosis results of fatigue cracks also play an important reference role in the early design and later maintenance of aircraft engine accessory pipelines.

[0005] According to the structural form and vibration characteristics of the aircraft engine accessory pipeline, its mechanical model is often simplified to a beam-like structure with two ends supported. The diagnosis of pipeline cracks is correspondingly transformed into the identification of cracks in the beam-like structure. The main principle of the mechanical model-based diagnosis method is that fatigue cracks will change the geometric and physical properties of the local structure, thereby affecting the vibration characteristics of the entire structure. Therefore, fatigue cracks can be reversely diagnosed by monitoring the changes in the structural vibration characteristics. The transfer function is generally defined as the ratio of the output spectra at different locations of the structure. Compared with other vibration characteristics (modal parameters, frequency response function, and output spectrum), the transfer function has obvious advantages. For example, the transfer function is directly calculated from the output spectrum, avoiding structural modal analysis and input excitation measurement; the transfer function only depends on the structural zero point, is more sensitive to changes in local structural parameters, and is more suitable for the diagnosis of local fatigue cracks.

[0006] At present, fatigue crack faults are simulated as elastic forces with cubic stiffness nonlinearity, and the corresponding nonlinear transfer functions are used to determine the location of fatigue cracks in pipeline structures. In order to reduce the interference of external excitation and frequency range, the existing technology uses natural logarithm normalization and total coefficient of output response weight to increase the difference of nonlinear transfer functions between healthy structures and cracked structures. Considering the difficulty of processing non-stationary signals, the transfer functions are defined by nonlinear working modes, coherence functions and wavelet transform coefficients, respectively, and fatigue crack units in beam structures are diagnosed. Based on the Volterra series theory, multiple nonlinear crack units in one-dimensional beam structures are diagnosed by using transfer functions based on nonlinear output frequency response functions. In order to avoid the decomposition calculation of nonlinear output frequency response functions, the transfer function is directly defined by nonlinear output spectrum, and a diagnostic method that can distinguish the number of crack faults is proposed. In order to improve the accuracy of fatigue crack diagnosis results, a transfer function based on second-order output spectrum is defined and fatigue crack faults of different degrees in beam structures are located.

[0007] For fatigue crack failures in aircraft engine accessory pipelines, the diagnosis method based on nonlinear transfer function continuously improves the crack identification sensitivity while striving to provide more accurate crack location information. However, the existing diagnosis method still has the following three shortcomings.

[0008] (1) Most diagnostic methods ignore the nonlinear boundaries and constraints of accessory pipelines, which results in large errors in the diagnosis of fatigue crack failures in actual aircraft engine accessory pipelines.

[0009] (2) Most diagnostic methods require the accessory pipeline as a whole to be analyzed and diagnosed, which increases the difficulty of accessory pipeline dynamics modeling, analysis, and calculation, and also increases the workload of fault diagnosis;

[0010] (3) Most diagnostic methods require the reference state of the accessory pipeline as a diagnostic benchmark, which severely limits the effective monitoring of some aircraft engine accessory pipelines where the reference state is unknown or difficult to measure. Summary of the invention

[0011] Technical issues to be solved:

[0012] In order to avoid the shortcomings of the prior art, the present invention provides a method for diagnosing fatigue crack faults of aircraft engine accessory pipelines, taking into account the actual nonlinear boundaries and constraints of the aircraft engine accessory pipelines, taking the local structure of the accessory pipelines as the object of analysis and diagnosis, and solving the shortcomings of the existing methods based on nonlinear transfer functions in the process of diagnosing fatigue crack faults of aircraft engine accessory pipelines.

[0013] The technical solution of the present invention is: a method for diagnosing fatigue crack faults of aircraft engine accessory pipelines, characterized by the following specific steps:

[0014] Step 1: Evaluate the status of the aircraft engine accessory pipelines and select the acceleration sensor installation location based on the evaluation results;

[0015] Step 2: collecting signals from the aircraft engine accessory pipeline through the acceleration sensor;

[0016] Step 3: Process the signal of the aircraft engine accessory pipeline;

[0017] Step 4: Calculate the fault characteristics of the aircraft engine accessory pipeline according to the signal processing result of step 3;

[0018] Step 5: Diagnose the fault of aircraft engine accessory pipeline through fault characteristics.

[0019] A further technical solution of the present invention is: in the step 1, the state and environment assessment is performed according to the structural form and support method of a certain type of aircraft engine accessory pipeline to be diagnosed, and the acceleration sensor is installed at a location where fatigue cracks are prone to occur.

[0020] A further technical solution of the present invention is: in step 2, the acceleration sensor is installed at a selected position and connected to a host computer through a signal conditioner; an excitation system is installed on the accessory casing, and the excitation system is connected to the host computer; and the pipeline vibration acceleration time domain signal is collected through the host computer.

[0021] A further technical solution of the present invention is: in step 3, the vibration acceleration time domain signal is subjected to noise reduction processing, the time domain signal is transformed into frequency domain data, and the output spectrum and transfer function are calculated.

[0022] A further technical solution of the present invention is: the output spectrum is The superscript n represents the nth set of measured data, n = 1, 2, 3, the subscript a represents different sensor channels, a = 1, 2, ..., j is the complex frequency domain parameter, ω = 64π is the complex frequency;

[0023] The transfer function Subscripts a, b represent different sensor channels, a, b = 1, 2, ..., a ≠ b.

[0024] A further technical solution of the present invention is: in step 4, the fault characteristics of the accessory pipeline are calculated according to the obtained transfer function. c=A, B, A and B represent different diagnostic areas;

[0025] Based on the transfer function calculated from the first and second groups of data, the fault characteristics are:

[0026]

[0027] Among them, the superscript 12 represents the first group of data and the second group of data;

[0028] According to the transfer function calculated from the second and third groups of data, the fault characteristics are:

[0029]

[0030] The superscript 23 represents the second and third groups of data.

[0031] A further technical solution of the present invention is: in step 5, according to the obtained fault characteristics, the diagnostic characteristics are calculated to determine the crack fault in each diagnostic area of ​​the pipeline; the diagnostic characteristic calculation formula is as follows:

[0032]

[0033] According to whether the diagnostic characteristic value is close to zero, it is judged whether there is a crack fault in each diagnostic area of ​​the pipeline.

[0034] A diagnostic device for fatigue crack faults in an aircraft engine accessory pipeline, characterized in that it comprises an acceleration sensor, a signal conditioner, a host computer, and an excitation system; the acceleration sensors are installed at both ends of the pipeline, corresponding to the locations where fatigue cracks are most likely to occur, and are connected to the host computer through the signal conditioner; the excitation system is installed on the accessory casing, the excitation system comprises an exciter and a signal amplifier, and the exciter is connected to the host computer through the signal amplifier;

[0035] The excitation frequency and amplitude, sensor sensitivity, signal sampling frequency and signal sampling time are set on the software side of the host computer to collect the pipeline vibration acceleration time domain signal.

[0036] A further technical solution of the present invention is: the two ends of the pipeline are respectively an A diagnostic area and a B diagnostic area, and three acceleration sensors are installed in the two diagnostic areas respectively. The acceleration sensor model is B&K AS-020S / N, and the sensitivity is 100mv / g; the signal conditioner has a 204.8kHz synchronous sampling frequency and a 24-bit resolution.

[0037] A further technical solution of the present invention is: the excitation system is a B&K 4842 modal excitation system, the maximum output load is 100N, the frequency range is DC-5000Hz, and the peak-to-peak value of the stroke displacement is 1inch; the sampling frequency is set to 8192Hz, and the sampling time is 14s.

[0038] Beneficial Effects

[0039] The beneficial effects of the present invention are as follows: the present invention considers the actual nonlinear boundaries and constraints of the aircraft engine accessory pipeline, takes the local structure of the accessory pipeline as the object of analysis and diagnosis, and simplifies the difficulty of pipeline dynamics modeling, analysis and calculation. At the same time, the diagnostic method only considers the aircraft engine accessory pipeline to be diagnosed, without the need for reference state and reference characteristics, thus reducing the workload of crack fault diagnosis and improving the practicality of the diagnostic method. BRIEF DESCRIPTION OF THE DRAWINGS

[0040] Figure 1 It is a flow chart of the diagnostic method.

[0041] Figure 2 It is a schematic diagram of signal acquisition.

[0042] Figure 3 is a bar graph of diagnosis results.

[0043] Explanation of the accompanying drawings: 1. Accessory pipeline; 2. Threaded joint; 3. Acceleration sensor; 4. Signal conditioner; 5. Computer; 6. Accessory receiver; 7. Diagnostic area A; 8. Diagnostic area B; 9. Exciter; 10. Signal amplifier, 11. Horizontal axis (diagnostic area); 12. Vertical axis (diagnostic characteristic value); 13. Coordinate origin; 14. Diagnostic characteristic value of diagnostic area A; 15. Diagnostic characteristic value of diagnostic area B; 16. Graphic annotation. DETAILED DESCRIPTION

[0044] The embodiments described below with reference to the accompanying drawings are exemplary and are intended to be used to explain the present invention, but should not be construed as limiting the present invention.

[0045] This embodiment is a method for diagnosing fatigue crack failures in the accessory pipeline of a certain type of aircraft engine. The specific operation process is based on Figure 1 As shown below:

[0046] Step 1, assessing the status of aircraft engine accessory pipelines;

[0047] According to the structural form and support mode of the accessory pipeline of a certain type of aircraft engine to be diagnosed, the state and environment assessment are carried out, and the vibration acceleration sensor is installed at the selected measuring point.

[0048] In this embodiment, a certain type of aircraft engine accessory pipeline to be diagnosed is a single-tube simply supported beam structure, and both ends of the pipeline are connected to the aircraft engine accessory casing through threaded joints. The acceleration sensor measurement points are selected at both ends of the pipeline where fatigue cracks are prone to occur.

[0049] Step 2, collecting signals from the aircraft engine accessory pipeline;

[0050] Install a vibration exciter on the accessory housing to provide a vibration source, and connect the vibration exciter to the computer through a signal amplifier. Install a vibration acceleration sensor in the diagnostic area, and connect the sensor to the computer through a signal conditioner. Set the excitation frequency and amplitude, sensor sensitivity, signal sampling frequency and signal sampling time on the computer software to collect the pipeline vibration acceleration time domain signal.

[0051] In this implementation example, Figure 2 As shown, a total of 6 acceleration sensor signals in diagnostic areas A and B are connected to the computer through a signal conditioner. The acceleration sensor model is B&K AS-020S / N, with a sensitivity of 100mv / g. The signal conditioner is independently developed, with a synchronous sampling frequency of 204.8kHz and a resolution of 24 bits. The signal acquisition software is independently developed and can simultaneously collect vibration time domain data of 8 channels. The excitation system (exciter and signal amplifier) ​​is a B&K 4842 modal excitation system with a maximum output load of 100N, a frequency range of DC-5000Hz, and a peak-to-peak stroke displacement of 1inch. The sampling frequency is set to 8192Hz and the sampling time is 14s.

[0052] For the first set of data, the excitation frequency and amplitude were set to 16 Hz and 3.98 V respectively, and the time domain signals of 6 acceleration sensors were collected.

[0053] For the second set of data, the excitation frequency and amplitude were set to 16 Hz and 9.97 V respectively, and the time domain signals of 6 acceleration sensors were collected.

[0054] For the third set of data, the excitation frequency and amplitude were set to 16 Hz and 5.98 V respectively, and the time domain signals of 6 acceleration sensors were collected.

[0055] Step 3, processing the signal of the aircraft engine accessory pipeline;

[0056] The vibration acceleration time domain signal is denoised, the time domain signal is transformed into frequency domain data, and the output spectrum and transfer function are calculated.

[0057] In this implementation example,

[0058] For the first set of data, the 14s duration data of each sensor channel is divided into 14 segments of 1s duration data, and a 1s duration noise-reduced data is obtained by averaging in the time domain. The 1s duration data is transformed into frequency domain data through a self-written Fourier transform program, and the vibration amplitude at a frequency of 32Hz is selected to calculate the transfer function shown in the following formula.

[0059]

[0060] in, is the output spectrum, the superscript 1 represents the first set of data, the subscript a represents different sensor channels, j is the complex frequency domain parameter, and ω=64π is the complex frequency. is the transfer function, the superscript 1 represents the first set of data, and the subscripts a and b represent different sensor channels.

[0061] The second set of data, split the 14s duration data of each sensor channel into 14 segments of 1s duration data, and obtain a 1s duration noise-reduced data by averaging in the time domain. The 1s duration data is transformed into frequency domain data through a self-written Fourier transform program, and the vibration amplitude at a frequency of 32Hz is selected to calculate the transfer function shown in the following formula.

[0062]

[0063] in, is the output spectrum, the superscript 2 represents the second set of data, the subscript a represents different sensor channels, j is the complex frequency domain parameter, and ω=64π is the complex frequency. is the transfer function, the superscript 2 represents the second set of data, and the subscripts a and b represent different sensor channels.

[0064] The third set of data, split the 14s data of each sensor channel into 14 segments of 1s data, and get a 1s segment of noise-reduced data by averaging in the time domain. The 1s data is transformed into frequency domain data through a self-written Fourier transform program, and the vibration amplitude at a frequency of 32Hz is selected to calculate the transfer function shown in the following formula.

[0065]

[0066] in, is the output spectrum, the superscript 3 represents the third set of data, the subscript a represents different sensor channels, j is the complex frequency domain parameter, and ω=64π is the complex frequency. is the transfer function, the superscript 3 represents the third set of data, and the subscripts a and b represent different sensor channels.

[0067] Step 4, calculating the characteristics of the aircraft engine accessory pipeline;

[0068] According to the obtained transfer function, the fault characteristics of the accessory pipeline are calculated.

[0069] In this implementation example, the fault characteristics shown in the following formula are calculated based on the transfer function calculated based on the first set of data and the second set of data.

[0070]

[0071] in, is the fault feature, the superscript 12 represents the first set of data and the second set of data, and the subscript c represents different diagnosis areas.

[0072] Based on the transfer function calculated from the second and third sets of data, the fault characteristics are calculated as shown in the following formula.

[0073]

[0074] in, are fault features, the superscript 23 represents the second and third sets of data, and the subscript c represents different diagnostic areas.

[0075] Step 5, diagnose the fault of the aircraft engine accessory pipeline.

[0076] According to the obtained fault characteristics, the diagnostic characteristics are calculated to determine the crack faults in each diagnostic area of ​​the pipeline.

[0077] In this implementation example, the diagnostic feature shown in the following formula is calculated: Whether there is a crack fault in each diagnostic area of ​​the pipeline is determined based on whether the feature value is close to zero.

[0078]

[0079] Among them, β c (jω)(c=A,B) is the diagnostic feature, and the subscript c represents different diagnostic areas.

[0080] like Figure 3 As shown, the diagnostic feature β A (jω) is significantly greater than zero, while the diagnostic characteristic β B (jω) obviously approaches zero. Therefore, the crack fault only exists in the diagnosis area A.

[0081] At this point, the diagnosis of fatigue crack failure in the accessory pipeline of a certain type of aircraft engine has been completed.

[0082] Although the embodiments of the present invention have been shown and described above, it is to be understood that the above embodiments are exemplary and are not to be construed as limitations on the present invention. A person skilled in the art may change, modify, replace and modify the above embodiments within the scope of the present invention without departing from the principles and intent of the present invention.

Claims

1. A method for diagnosing fatigue crack failure of an aircraft engine accessory pipeline, characterized in that The specific steps are as follows: Step 1: Evaluate the status of the aircraft engine accessory pipeline, and select the installation position of the acceleration sensor based on the evaluation results; the aircraft engine accessory pipeline to be diagnosed is a single-tube simply supported beam structure, and both ends of the pipeline are connected to the aircraft engine accessory casing through threaded joints. The acceleration sensor measurement points are selected at both ends of the pipeline where fatigue cracks are prone to occur; Step 2: Collect signals of the aircraft engine accessory pipeline through the acceleration sensor; install the acceleration sensor at a selected position and connect it to the host computer through a signal conditioner; install a vibration excitation system on the accessory casing, and connect the vibration excitation system to the host computer; collect pipeline vibration acceleration time domain signals through the host computer; Step 3: Process the signal of the aircraft engine accessory pipeline; reduce the noise of the vibration acceleration time domain signal, transform the time domain signal into frequency domain data, and calculate the output spectrum and transfer function; the output spectrum is , the superscript n represents the nth set of measured data, n=1, 2, 3, and the subscript a represents different sensor channels, a=1, 2, ..., is the complex frequency domain parameter, is the complex frequency; the transfer function , subscripts a, b represent different sensor channels, a, b = 1, 2, …, a ≠ b; Step 4: Calculate the fault characteristics of the aircraft engine accessory pipeline based on the signal processing results of step 3; calculate the fault characteristics of the accessory pipeline based on the obtained transfer function ,c=A, B, A, B represent different diagnostic areas; Based on the transfer function calculated from the first and second groups of data, the fault characteristics are: Among them, the superscript 12 represents the first group of data and the second group of data; According to the transfer function calculated from the second and third groups of data, the fault characteristics are: Among them, the superscript 23 represents the second and third groups of data; Step 5: diagnose the fault of the aircraft engine accessory pipeline through the fault characteristics; calculate the diagnostic characteristics according to the obtained fault characteristics, and judge the crack fault in each diagnostic area of ​​the pipeline; the diagnostic characteristic calculation formula is as follows: According to whether the diagnostic characteristic value is close to zero, it is judged whether there is a crack fault in each diagnostic area of ​​the pipeline.

2. A device for implementing the method for diagnosing fatigue crack faults of aircraft engine accessory pipelines as claimed in claim 1, characterized in that: The invention comprises an acceleration sensor, a signal conditioner, a host computer and an excitation system; the acceleration sensor is installed at both ends of the pipeline, corresponding to the places where fatigue cracks are most likely to occur, and connected to the host computer through the signal conditioner; the excitation system is installed on the accessory casing, the excitation system comprises an exciter and a signal amplifier, and the exciter is connected to the host computer through the signal amplifier; The excitation frequency and amplitude, sensor sensitivity, signal sampling frequency and signal sampling time are set on the software side of the host computer to collect the pipeline vibration acceleration time domain signal.

3. The device according to claim 2, characterized in that: The two ends of the pipeline are respectively the A diagnostic area and the B diagnostic area. Three acceleration sensors are installed in the two diagnostic areas respectively. The acceleration sensor model is B&K AS-020 S / N with a sensitivity of 100mv / g. The signal conditioner has a synchronous sampling frequency of 204.8kHz and a resolution of 24 bits.

4. The device according to claim 2, characterized in that: The excitation system is a B&K 4842 modal excitation system with a maximum output load of 100N, a frequency range of DC-5000Hz, and a peak-to-peak value of stroke displacement of 1inch; the sampling frequency is set to 8192Hz, and the sampling time is 14s.

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