CN113552223B - Torsion shaft multichannel acoustic emission detection system and defect detection method based on optical fiber interferometer - Google Patents
Torsion shaft multichannel acoustic emission detection system and defect detection method based on optical fiber interferometer Download PDFInfo
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- CN113552223B CN113552223B CN202110822146.4A CN202110822146A CN113552223B CN 113552223 B CN113552223 B CN 113552223B CN 202110822146 A CN202110822146 A CN 202110822146A CN 113552223 B CN113552223 B CN 113552223B
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
- G01N29/00—Investigating or analysing materials by the use of ultrasonic, sonic or infrasonic waves; Visualisation of the interior of objects by transmitting ultrasonic or sonic waves through the object
- G01N29/14—Investigating or analysing materials by the use of ultrasonic, sonic or infrasonic waves; Visualisation of the interior of objects by transmitting ultrasonic or sonic waves through the object using acoustic emission techniques
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
- G01N2291/00—Indexing codes associated with group G01N29/00
- G01N2291/02—Indexing codes associated with the analysed material
- G01N2291/023—Solids
- G01N2291/0234—Metals, e.g. steel
Abstract
The invention provides a torsion shaft multichannel acoustic emission detection system based on an optical fiber interferometer, which comprises: the high-temperature-resistant optical fiber loop acoustic emission sensor comprises a narrow-band light source, a first optical fiber coupler group, a second optical fiber coupler group, a photoelectric detector group, a filter group, an acquisition card and an industrial measurement and control computer. The torsion shaft defect detection method is provided by utilizing the torsion shaft multichannel acoustic emission detection system based on the optical fiber interferometer, acoustic emission signals generated inside the torsion shaft in the loading process can be measured on line in real time, the growth rate of acoustic emission events on the torsion shaft, the growth rate of acoustic emission energy and the positioning concentration of acoustic emission events are analyzed according to the signals, the activity state of the acoustic emission events inside the torsion shaft is further judged, and the detection of the torsion shaft internal defects under the conditions of real time and high temperature in service is realized.
Description
Technical Field
The invention belongs to the technical field of acoustic emission nondestructive detection, and particularly relates to a torsion axis multichannel acoustic emission detection system and a defect detection method based on an optical fiber interferometer.
Background
Torsion axles are the main elastic elements and key components of a vehicle suspension system, and are broken frequently due to small volume, large energy storage and severe working conditions, so that the torsion axles become one of the important reasons for vehicle faults. The torsion shaft is subjected to high stress random torsional loads during operation, and fatigue fracture is a common failure mode. The torsion shaft, after being subjected to a disturbance load a sufficient number of times, forms crack nuclei from high stress or high strain parts and gradually progresses from micro cracks to macro cracks. Thereafter, under a disturbance load, the crack further propagates until the critical dimension is reached and complete fracture occurs. According to the fatigue failure theory, the fatigue failure process can be roughly divided into four phases: crack nucleation, micro-crack propagation, macro-crack propagation and transient fracture stages. In each stage, the internal structure of the material is significantly changed.
The transient elastic wave generated by the rapid release of the local source energy is an acoustic emission wave. In actual operation, under the action of stress generated by externally applied load, acoustic emission waves are generated in the process of changing internal structures such as torsion shaft deformation, crack expansion and the like. The acoustic emission wave signal is a weak signal that needs to be detected by means of highly sensitive devices. The method for detecting acoustic emission waves in the torsion shaft fatigue research process is to detect, record and analyze acoustic emission wave signals by using acoustic emission detection equipment and utilize the characteristics of the signals to characterize the material fatigue and defect development of the torsion shaft.
The conventional nondestructive detection method, such as eddy current detection, ultrasonic detection, magnetic powder detection and the like, needs the torsion shaft to stop working when being applied to torsion shaft defect detection, so that the real-time defect condition during the operation of the torsion shaft cannot be dynamically measured in the working process of an armored vehicle, and the online monitoring requirement cannot be met. The acoustic emission detection technology can realize the real-time monitoring of the defects of the torsion shaft, however, the existing acoustic emission detection technology cannot be used in a high-temperature environment generated during the operation of the torsion shaft due to the adoption of the piezoelectric ceramic acoustic emission sensor, so that the application of the existing acoustic emission detection technology is limited.
Disclosure of Invention
The invention mainly solves the technical problem that the existing acoustic emission detection technology cannot be applied to the technical blank in a high-temperature environment, and provides a torsion shaft multichannel acoustic emission detection system and a defect detection method based on an interferometer. The method has the advantages of simple equipment and low cost, can realize in-service real-time and continuous monitoring of the torsion shaft defects in the vehicle operation, has high defect detection rate, high equipment sensitivity and good stability, and can resist extreme environments such as high temperature, strong electromagnetic interference and the like.
The technical scheme adopted for solving the technical problems is as follows: an interferometer-based torsion axis multi-channel acoustic emission detection system, comprising: the device comprises a narrow-band light source, a first optical fiber coupler group, a high-temperature resistant reference optical fiber ring group, a high-temperature resistant sensing optical fiber ring group, a second optical fiber coupler group, a photoelectric detector group, a filter group, an acquisition card and an industrial measurement and control computer. The narrow-band light source is connected with one group of input ends of the first optical fiber coupler group, and one group of output ends of the first optical fiber coupler group are connected with the high-temperature-resistant reference optical fiber ring group to form a reference arm of the interferometer; the other output end of the first optical fiber coupler group is connected with the input end of the high-temperature resistant sensing optical fiber ring group to form a sensing arm of the interferometer; one group of input ends of the second optical fiber coupler group are connected with the output ends of the high-temperature-resistant sensing optical fiber ring group, the other group of input ends of the second optical fiber coupler group are connected with the output ends of the high-temperature-resistant reference optical fiber ring group, one group of output ends of the second optical fiber coupler group are connected with the input ends of the photoelectric detector group, and the output ends of the photoelectric detector group are connected with the input ends of the filter group; the output end of the filter bank is connected to the acquisition card and the industrial measurement and control computer.
The invention provides a torsion shaft multichannel acoustic emission detection system based on an interferometer, which provides a corresponding defect detection method: 1) arranging a plurality of high-temperature-resistant optical fiber ring acoustic emission sensors on a torsion shaft at the same time, monitoring acoustic emission signals generated in the torsion shaft in real time by using an acquisition card and an industrial measurement and control computer, 2) calculating the amplitude, energy, arrival time, rise time, duration and ringing times of the acoustic emission signals according to the signals acquired by the optical fiber ring acoustic emission sensors, 3) calculating the growth rate of the acoustic emission events of the torsion shaft and the growth rate of the acoustic emission energy according to the acquired acoustic emission signals and the characteristics thereof, realizing line positioning of the acoustic emission events of the torsion shaft by using multipath acoustic emission signals, and calculating the line positioning concentration, thereby further judging the active state of the acoustic emission events in the torsion shaft and detecting defects on line.
Further, the center wavelength range of the narrow-band light is 1500-1630nm, the wavelength stability is less than +/-1 pm, the bandwidth is less than 200kHz, the output power is more than or equal to 100mW, and the long-term stability of the output light power is +/-0.01 dB; the power of the output light power of the light source, which is limited by the input light power of the photoelectric conversion module, is distributed to each path of optical fiber ring sensor, and the power cannot exceed 10mW.
Furthermore, the radius of the framework of the high-temperature-resistant sensing optical fiber ring and the high-temperature-resistant reference optical fiber ring is not smaller than 20mm, and the optical fibers are reliably adhered to the surface of the framework by using high-temperature-resistant glue.
Compared with the prior art, the invention has the advantages that: the traditional nondestructive testing method can not monitor the defect condition of the torsion shaft in real time in the running process of the armored vehicle, and can not meet the online monitoring requirement in the motor operation of the armored vehicle; in the existing method for detecting the torsion shaft defect by utilizing the acoustic emission signal, piezoelectric ceramics are taken as a sensor, the sensor is not high-temperature resistant, the high-temperature surface of the torsion shaft in operation cannot be installed, and weak partial discharge signals in the torsion shaft are difficult to detect. Compared with the traditional nondestructive detection method and the piezoelectric ceramic acoustic emission detection method, the system has the dual advantages of on-line continuous monitoring and high temperature resistance, so that the torsion shaft multichannel acoustic emission detection system based on the interferometer can work in an extreme environment, and has higher flexibility and environmental adaptability.
Drawings
Fig. 1 is a block diagram of the structure of the present invention.
In the figure: 1. the device comprises a narrow-band light source, a first optical fiber coupler group, a high-temperature-resistant reference optical fiber ring group, a high-temperature-resistant sensing optical fiber ring group, a second optical fiber coupler group, a photoelectric detector group, a filter group, an acquisition card and an industrial measurement and control computer, wherein the narrow-band light source, the first optical fiber coupler group, the high-temperature-resistant reference optical fiber ring group, the high-temperature-resistant sensing optical fiber ring group, the second optical fiber coupler group, the photoelectric detector group, the filter group, the acquisition card and the industrial measurement and control computer are arranged in sequence.
FIG. 2 is a schematic diagram of the structure of a high temperature resistant fiber optic ring acoustic emission sensor used in the present invention.
In the figure: a is an optical fiber input end, and b is an optical fiber output end.
FIG. 3 is a schematic diagram illustrating steps of a defect detection method.
Detailed Description
In order to make the objects, technical solutions and advantages of the present invention more apparent, the present invention will be further described with reference to the accompanying drawings and specific embodiments. It is to be understood that the description herein is only for the purpose of illustrating the invention and is not to be construed as limiting the invention.
As shown in FIG. 1, the interferometer-based torsion axis multichannel acoustic emission detection system comprises a narrow-band light source 1, a narrow-band light source 2, a first optical fiber coupler group 3, a high-temperature-resistant reference optical fiber ring group 4, a high-temperature-resistant sensing optical fiber ring group 5, a second optical fiber coupler group 6, a photoelectric detector group 7, a filter group 8, an acquisition card and an industrial measurement and control computer; the light emitted by the narrow-band light source 1 enters the first optical fiber coupler group 2, 50% of the light enters the high-temperature-resistant reference optical fiber ring group 3 from one group of output ends, which is a reference arm of the interferometer, and the other 50% of the light enters the input end of the high-temperature-resistant sensing optical fiber ring group 4 from the other group of output ends, which is a sensing arm of the interferometer, and acoustic emission signals generated by defect expansion on a torsion shaft are sensed; the light coming out of the high-temperature-resistant sensing optical fiber ring group and the high-temperature-resistant reference optical fiber ring group interfere with each other in the second optical fiber coupler 5 group; the light after interference enters the photoelectric detector group 6 to be converted into an electric signal; the acoustic emission signals after denoising are obtained through the band-pass filtering of the filter bank 7; the denoised acoustic emission signals are processed by the acquisition card and finally displayed on the industrial measurement and control computer 8.
As shown in figure 2, when an acoustic emission signal exists outside, an optical fiber ring acoustic emission sensor on a sensing arm of the interferometer receives the acoustic emission signal, the acoustic pressure changes the length of an optical fiber to cause partial phase shift, and the acoustic pressure generates a photoelastic effect on the optical fiber, so that the phase of an optical wave of the optical fiber is modulated, the magnitude of the phase modulation is related to the magnitude of the acoustic pressure, the light interferes with the light passing through a phase modulator of a reference arm, the light is converted into a current signal with varying intensity after passing through a photoelectric detector, the current signal is sent into a band-pass filter, and the detected acoustic emission signal is obtained through signal analysis and processing of the signal of the filter.
As shown in fig. 3, the defect detection method specifically includes three steps: 1) Considering that the slenderness ratio of the torsion shaft is very large, the torsion shaft can be approximately regarded as a linear region, in order to accurately measure all acoustic emission signals and position information of the linear region when the torsion shaft works, two ends of the torsion shaft are simultaneously provided with a high-temperature-resistant optical fiber ring acoustic emission sensor respectively, and an acoustic emission signal generated in the torsion shaft during the work is monitored in real time by utilizing an acquisition card and an industrial measurement and control computer;
2) According to signals acquired by the two-channel optical fiber ring acoustic emission sensors, the amplitude, energy, arrival time, rise time, duration and ringing times of acoustic emission signals of each channel are calculated, and the meanings of the parameters are as follows:
amplitude: maximum amplitude value (dB) of the acoustic emission signal; energy: an area under the acoustic emission signal detection envelope (J); arrival time: time (μs) for an acoustic emission wave to reach the sensor; rise time: the time interval (mus) that elapses from the first crossing of the threshold to the reaching of the maximum amplitude of the acoustic emission signal; duration of time: the time interval (mus) that the acoustic emission signal passes the threshold for the first time until eventually falling to the threshold; number of rings: the acoustic emission signal is passed a threshold number of times within the duration.
3) According to the collected acoustic emission signal and its characteristics, calculating the growth rate alpha of torsion axis acoustic emission event and the growth rate beta of acoustic emission energy, the calculation method is that
Where N is the acoustic emission event count and E is the acoustic emission energy count, and considering that the acoustic emission event has a duration of a certain length and the signal processing capability of the sampling system is limited, the average growth rate over a period of time Δt can be calculated as the growth rate α of the torsion axis acoustic emission event and the growth rate β of the acoustic emission energy in practical calculation. Setting a rate threshold alpha 0 ，β 0 The current growth rate exceeds a threshold, i.e. alpha > alpha 0 Or beta > beta 0 When the acoustic emission event activity inside the torsion axis is considered to be strong, internal structural changes occur, and attention should be paid.
In addition to analyzing the acoustic emission signal for the degree, defect detection also requires obtaining positional information of the acoustic emission event. Line positioning of torsion axis acoustic emission events is realized by utilizing the arrival time difference of two paths of acoustic emission signals and adopting a time difference positioning method, positioning results for a period of time are accumulated, the spatial distribution rule of the positioning results is researched, and the line positioning concentration sigma% is calculated
Wherein N is the cumulative positioning number of acoustic emission events, N x For locating coordinates in [ x, x+Deltax]Cumulative number of locations of acoustic emission events within a range. Setting a positioning concentration threshold sigma 0 In percent, the current positioning concentration exceeds a threshold, i.e., sigma% > sigma 0 % of the time, the acoustic emission events inside the torsion axis are considered to be more concentrated, and fatigue fracture is likely to occur near the location concentration point, and attention should be paid.
The choice of the narrowband light source is critical, it directly affects the interferometer output, narrowband light requires stable power, and the bandwidth is small with a sufficiently long coherence length. The wavelength range of the selected narrow-band optical center is 1500-1630nm, the wavelength stability is less than +/-1 pm, the bandwidth is less than 200kHz, the output power is more than or equal to 100mW, the long-term stability of the output optical power is +/-0.01 dB, the output stability of the interferometer is good, and the signal to noise ratio is high.
The main element of the photodetector is a photodiode, which is a semiconductor device that converts an optical signal into an electrical signal. The core part of the diode is also a PN junction, and compared with a common diode, the diode is structurally different in that the PN junction area is made larger as much as possible, the electrode area is made smaller as much as possible, and the photodiode works under the action of reverse voltage. In the absence of illumination, the reverse current is small (typically less than 0.1 microamperes), referred to as dark current. When light is irradiated, photons carrying energy enter the PN junction, and then the energy is transferred to bound electrons on the covalent bond, so that part of the electrons break loose the covalent bond, and electron-hole pairs, called photo-generated carriers, are generated. They participate in drifting movement under the action of reverse voltage, so that the reverse current is obviously increased, and the greater the intensity of light, the greater the reverse current. This property is known as "photoconductive". The photodiode generates a current called photocurrent when irradiated by light of a general illuminance. If a load is placed on the external circuit, an electrical signal is obtained on the load and this electrical signal changes accordingly with the change in light. The photodiodes used in the invention are PIN tubes, and the response wavelength is 600 nm-1800 nm.
The optical fiber coupler is an optical passive device, which is used for connecting two or more optical fibers, so that optical signals transmitted in the optical fibers are coupled in a special coupling area, and power or wavelength distribution is performed. At present, there is a single-mode fiber coupler prepared by a fusion tapering method, which is to draw two (or more than two) optical fibers with coating layers removed together in a certain way, fuse the optical fibers under high-temperature heating, simultaneously stretch the optical fibers to two sides, and finally form a special waveguide structure in a biconic form in a heating area. The spectral ratio of the optical fiber coupler in the invention is 50:50.
The acquisition card is a device which acquires an analog electric signal and leads the analog electric signal to a computer after analog-digital conversion. The acquisition card integrates an analog input channel, a signal conditioning circuit, a sampling hold, a conversion and control logic unit clock, a bus interface and a controller into a whole, thereby realizing a hardware circuit of a complete measurement system. The main performance parameters of the acquisition card include: channel number, sampling frequency, resolution, accuracy, range, and gain. In the invention, the number of the acquisition card channels is consistent with the number of the sensor channels. As the frequency of the acoustic emission signal generated in the torsion shaft fatigue loading process is not more than 500kHz, the sampling frequency of the acquisition card is higher than 1MHz according to the Nyquist sampling theorem, and the acquisition card with the maximum sampling frequency of 10MHz is adopted in the invention.
The technical content not disclosed in the invention belongs to the technical field of the prior art.
While the foregoing describes illustrative embodiments of the present invention to facilitate an understanding of the present invention by those skilled in the art, it should be understood that the present invention is not limited to the scope of the embodiments, but is to be construed as protected by the accompanying claims insofar as various changes are within the spirit and scope of the present invention as defined and defined by the appended claims.
Claims (1)
1. A torsion axis defect detection method based on an optical fiber interferometer, which is characterized in that a detection system used by the method comprises the following steps: the device comprises a narrow-band light source (1), a first optical fiber coupler group (2), a high-temperature-resistant reference optical fiber ring group (3), a high-temperature-resistant sensing optical fiber ring group (4), a second optical fiber coupler group (5), a photoelectric detector group (6), a filter group (7), an acquisition card and an industrial measurement and control computer (8);
the high-temperature-resistant reference optical fiber ring set (3) and the high-temperature-resistant sensing optical fiber ring set (4) determine whether the method can accurately measure acoustic emission signals generated by the torsion shaft at high temperature; the high-temperature-resistant reference optical fiber ring set (3) and the high-temperature-resistant sensing optical fiber ring set (4) comprise a plurality of high-temperature-resistant optical fiber ring acoustic emission sensors with the same structure, the sensor framework material is made of high-temperature-resistant metal, a coating high-temperature-resistant bending-resistant optical fiber is wound on the metal framework, and the optical fibers are reliably adhered to the surface of the framework by using high-temperature-resistant glue; the high-temperature-resistant sensing optical fiber ring and the high-temperature-resistant reference optical fiber ring are used in pairs, when the high-temperature-resistant sensing optical fiber ring is used, a coupling agent with high viscosity and high temperature resistance is used and reliably fixed on the torsion shaft, and the high-temperature-resistant reference optical fiber ring is placed in an environment without vibration interference;
the torsion shaft defect detection method based on the optical fiber interferometer comprises the following steps: 1) simultaneously arranging a plurality of high-temperature-resistant optical fiber ring acoustic emission sensors on a torsion shaft, and monitoring acoustic emission signals generated in the torsion shaft in real time by using an acquisition card and an industrial measurement and control computer, 2) calculating the amplitude, energy, arrival time, rise time, duration time and ringing times of the acoustic emission signals according to the signals acquired by the optical fiber ring acoustic emission sensors, 3) calculating the growth rate of acoustic emission events of the torsion shaft and the growth rate of acoustic emission energy according to the acquired acoustic emission signals and the characteristics thereof; line positioning of torsion axis acoustic emission events is realized by utilizing the arrival time difference of two paths of acoustic emission signals and adopting a time difference positioning method, positioning results for a period of time are accumulated, the spatial distribution rule of the positioning results is researched, and the line positioning concentration sigma% is calculated
Wherein N is the cumulative positioning number of acoustic emission events, N x For locating coordinates in [ x, x+Deltax]Accumulating a positioning number of acoustic emission events within a range; setting a positioning concentration threshold sigma 0 In percent, the current positioning concentration exceeds a threshold, i.e., sigma% > sigma 0 % of the acoustic emission events inside the torsion axis are considered to be concentrated, and fatigue fracture is likely to occur near the location concentration pointCracking should be of concern.
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