CN112946077A - Carbon fiber composite material surface critical refraction longitudinal wave excitation detection system and method - Google Patents
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Abstract
The invention provides a system and a method for detecting excitation of critical refraction longitudinal waves on the surface of a carbon fiber composite material. The invention can measure the optimal incident angle of the excited critical refraction longitudinal wave, thereby ensuring that the standard critical refraction longitudinal wave is excited in the material, having more accurate propagation direction and smaller attenuation and scattering, and improving the accuracy of a nondestructive testing measurement area. The optimal received signal is obtained, the amplitude is large, the characteristics are clear, and the analysis and the utilization are convenient.
Description
Technical Field
The invention relates to the field of ultrasonic nondestructive testing and structural health monitoring, in particular to a system and a method for detecting surface critical refraction longitudinal wave excitation of a carbon fiber composite material based on a received wave amplitude value.
Background
The detection of material surfaces using critical Refracted Longitudinal waves (LCR wave) is a common practice in ultrasonic non-destructive testing. The critical refracted longitudinal wave is a longitudinal wave propagating along the surface of the material formed with a first critical incident angle based on snell's law. The detection of material surfaces using ultrasound critical refraction longitudinal waves is a common practice in ultrasonic non-destructive testing. The critical refracted longitudinal wave is a longitudinal wave propagating along the surface of the material formed with a first critical incident angle based on snell's law. In recent years, the research fields of applying LCR waves to materials are mainly pipeline welding stress, residual stress of complex curved surfaces, residual stress of track surfaces and the like. In summary, the current research and application field of ultrasonic detection using LCR waves is mainly isotropic materials such as metals.
The LCR wave method has high application potential in nondestructive testing of the carbon fiber composite material. The method has strict requirements on the incident angle of the ultrasound and the receiving angle of the sensor, and the internal structure of the carbon fiber composite material as an anisotropic material can greatly influence the transmission of the ultrasound. Different from isotropic materials, in order to excite an LCR wave on a carbon fiber composite material and obtain a good wave receiving effect, the optimal excitation angle of the LCR wave in the corresponding carbon fiber composite material needs to be calibrated.
Disclosure of Invention
The invention provides a system and a method for detecting excitation of critical refraction longitudinal waves on the surface of a carbon fiber composite material based on a received wave amplitude value.
The specific technical scheme of the invention is as follows:
(1) the components of the detection system provided by the invention are shown in figure 1. The whole system consists of an industrial personal computer system, a pulse excitation card, a variable-angle ultrasonic wedge, an ultrasonic transducer and a data acquisition card.
The industrial personal computer system is a computer system directly interacting with human, is directly connected with the pulse excitation card and the data acquisition card, sends a command to the pulse excitation card through self-developed ultrasonic nondestructive testing software, analyzes and displays ultrasonic data recorded by the data acquisition card, and displays the acquired ultrasonic waveform on a screen, wherein a software flow chart is shown in fig. 2.
One end of the pulse excitation card is connected with the industrial personal computer system, the other end of the pulse excitation card is connected with the ultrasonic transducer, and after the command of the industrial personal computer system is received, pulse waves are sent to the ultrasonic transducer;
the data acquisition card is connected with the ultrasonic transducer which is responsible for receiving information, acquires the related electrical signal information of the ultrasonic transducer and sends the information to the industrial personal computer system.
The ultrasonic transducer can convert the input electric power into mechanical power (i.e. ultrasonic wave) and then transmit the mechanical power, and can also convert the received mechanical power into electrical power. The system applies 2 ultrasonic transducers and 2 variable-angle ultrasonic wedges, wherein 1 group of ultrasonic transducers and the variable-angle wedges receive pulse waves from a pulse excitation card and emit ultrasonic waves into a material, and the other 1 group of ultrasonic transducers and the variable-angle wedges receive waveforms transmitted from the material.
The angle-variable ultrasonic wedge is an auxiliary module between the ultrasonic transducer and the material to be measured, and is used for fixing the ultrasonic transducer to form a stable position relation with the surface of the material to be measured, and the structural schematic diagram of the angle-variable ultrasonic wedge is shown in fig. 3. In order to reduce the influence of air between the surfaces on the propagation of ultrasonic waves, the variable-angle ultrasonic wedge is simultaneously coupled with an ultrasonic transducer and the surface of the material by using a coupling agent. When the ultrasonic wedge block is used, ultrasonic waves are emitted from the ultrasonic transducer, pass through the inside of the variable-angle ultrasonic wedge block to reach the surface of a material, are refracted and then spread inside the material, and are received by the other set of variable-angle ultrasonic wedge block and the ultrasonic transducer.
(2) One of the core methods for exciting the ultrasonic critical refraction longitudinal wave in the invention is to change the angle of the ultrasonic wave incident on the surface of the material by adjusting the variable-angle ultrasonic wedge. The structural principle schematic diagram of the variable-angle ultrasonic wedge is shown in fig. 3. When in use, the ultrasonic transducer is coupled and fixed with the upper surface of the sliding block. When the incident angle is changed, the fixing knob is firstly adjusted to loosen the sliding block and the sliding curved surface, then the sliding block is rotated for a certain angle along the axis, and then the fixing knob is screwed again to fix a new angle.
(3) According to snell's law, when the ultrasonic incident angle is smaller than the first critical angle, both refracted longitudinal waves and refracted transverse waves exist in the material. According to snell's law and related research, the main lobe direction of the refracted longitudinal wave gradually shifts toward the surface as the incident angle gradually increases, and the refracted longitudinal wave propagates below the surface in the surface-parallel direction when the first critical angle is reached. In anisotropic materials, the angle of refraction of ultrasound is not calculated according to snell's law, but the refracted longitudinal wave approaches the surface as the angle of incidence increases, while the amplitude of the refracted longitudinal wave induced in the receiving wedge increases the closer the longitudinal wave mainlobe is to the surface.
The principle of exciting the critical refraction longitudinal wave in the invention is that when the ultrasonic wave is incident on the surface of the material at the optimal angle and successfully excites the critical refraction longitudinal wave, the received waveform amplitude is maximum. The core step of the excitation method is to continuously adjust the ultrasonic incident angle until the amplitude of the received waveform reaches the maximum value, and to use the corresponding ultrasonic incident angle as the optimal angle for exciting the critical refraction longitudinal wave.
(4) When the angle of the variable-angle ultrasonic wedge is adjusted, the excitation angle of the critical refraction longitudinal wave needs to be roughly estimated so as to reduce the range of the test angle. In the invention, the initial angle is estimated by a finite element simulation method for the propagation of the ultrasound in the carbon fiber composite material. After the initial angle is obtained, the amplitude of the received waveform is observed after the variable-angle ultrasonic wedge is adjusted by about 1 degree each time within the range from 0 degree to the initial angle plus 10 degrees until the amplitude reaches the maximum value.
The following detailed description will be made on the technical scheme of the method for exciting the surface critical refraction longitudinal wave of the carbon fiber composite material, which is disclosed by the invention:
the method comprises the following steps: determining the testing angle range of critical refraction longitudinal wave excitation test by simulation
The COMSOL was used to simulate the propagation of ultrasonic waves in an ultrasonic wedge (not an actual experimental variable angle ultrasonic wedge, but an alternative to the design in the simulation) and a carbon fiber material. Ultrasound is excited from the left wedge, and upon entering the carbon fiber material, refracted longitudinal and transverse waves, bow waves, etc. are excited. Wherein the refracted longitudinal wave again enters the wedge on the right by refraction and is received by the sensor. The ultrasonic wedge block material is organic glass (PMMA), the sound velocity in the material is 2700m/s, and the elastic matrix of the carbon fiber material is as follows:
the left wedge was excited with a single period of 1.5MHz and the receive waveform in the receive wedge was observed.
LCR waves are observed in CFRP materials when the ultrasound incidence angle is set at around 14.5 degrees.
When the incident angle changes between 0-90 degrees, the received waveform can reach an extreme value for many times because the refracted longitudinal wave and the refracted transverse wave have different critical refraction angles. Therefore, in the excitation test, the test range of the ultrasonic incident angle is determined according to the simulation result.
Step two: preparation of the test
And (3) carrying out ultrasonic detection on three carbon fiber composite material plates of 0-degree ply, 0/90 ply and 0/45/-45/90 ply respectively by using a test system consisting of an industrial personal computer system, a pulse excitation card, a data acquisition card, a variable-angle ultrasonic wedge and an ultrasonic transducer.
The material used in the test is a carbon fiber plate, the thickness of the carbon fiber plate is more than 5mm, and the surface of the plate is not specially treated. The carbon fiber material plate is placed on a horizontal plane, two variable-angle ultrasonic wedges which are respectively responsible for transmitting and receiving are placed on the surface of the plate, and an ultrasonic coupling agent is used for coupling the surface of the material with the surface of each variable-angle ultrasonic wedge, each variable-angle ultrasonic wedge and the ultrasonic transducer. The edges of the two variable angle ultrasonic wedges are aligned with the edges of the sheet material to ensure that the centers of the wedges are collinear. According to different fiber laying modes of the carbon fiber plates, the propagation direction of the ultrasonic refraction wave is parallel to the fiber direction of one of the plates when the wedge block is placed. The distance between the two wedges should not exceed 100mm, since the ultrasound is strongly attenuated in the carbon fibre material.
After the detection system is built, the current received waveform is displayed in software, and the next test is started.
Step three: adjusting the variable angle ultrasonic wedge block and searching the maximum point of the received wave amplitude
When the waveform is observed for the first time, the incidence angle of the wedge block is set at 0 degree, the current received wave waveform is recorded, and the ultrasonic incidence angle is adjusted. The receiving wedge block and the transmitting wedge block are adjusted simultaneously, the amplitude of the variable-angle ultrasonic wedge block is adjusted to be 1 degree each time, and the current wave-receiving waveform is recorded after adjustment. The adjustment and recording operations were repeated until angles in the range of (0-14 ° +10 °) were tested.
And comparing all recorded waveform data, and searching the corresponding ultrasonic incident angle when the waveform amplitude reaches the maximum value for the first time. It is believed that the LCR wave is successfully excited at the surface of the material, and that this angle is the optimal angle for exciting the LCR wave.
The invention has the advantages and beneficial effects that: it is known from many studies and experiments that the optimal excitation angle of the critical refracted longitudinal wave is not the first critical angle directly calculated by snell's law, but is several degrees different from the first critical angle. For the carbon fiber composite material, because of the internal layered structure and the layering characteristics, the refracted longitudinal wave excited by the excitation angle calculated by using the snell's law cannot ensure the criticality. In addition, the attenuation and scattering of ultrasound are large when the ultrasound propagates in the material, so that the difference of the incident angle of the ultrasound has a large influence on the amplitude of the received waveform. The invention can measure the optimal incident angle of the excited critical refraction longitudinal wave, thereby ensuring that: 1. the standard critical refraction longitudinal wave is excited in the material, so that the material has more accurate propagation direction and smaller attenuation and scattering, and the accuracy of a nondestructive testing measurement area is improved. 2. The optimal received signal is obtained, the amplitude is large, the characteristics are clear, and the analysis and the utilization are convenient.
Drawings
FIG. 1 is a schematic diagram of a detection system of the present invention.
FIG. 2 is a flow chart of software used in the assay.
Fig. 3 is a structural schematic diagram of an ultrasonic wedge with variable angles.
Fig. 4 is a diagram of propagation paths of critical refraction longitudinal waves of ultrasound.
Detailed Description
The following detailed description of the embodiments of the invention:
the method comprises the following steps: determining the testing angle range of critical refraction longitudinal wave excitation test by simulation
The COMSOL was used to simulate the propagation of ultrasonic waves in an ultrasonic wedge (not an actual experimental variable angle ultrasonic wedge, but an alternative to the design in the simulation) and a carbon fiber material. The propagation path of the ultrasound is shown in fig. 4, and the ultrasound is excited from the left wedge, and when entering the carbon fiber material, refracted longitudinal waves and refracted transverse waves, head waves and the like are excited. Where the refracted longitudinal wave again enters the wedge on the right by refraction and is received by the sensor. The ultrasonic wedge block material is organic glass (PMMA) in simulation, the internal sound velocity of the material is 2700m/s, and the elastic matrix of the carbon fiber material is as follows:
the left wedge was excited with a single period of 1.5MHz and the receive waveform in the receive wedge was observed.
LCR waves are observed in CFRP materials when the ultrasound incidence angle is set at around 14.5 degrees.
In the simulation, the highest amplitudes of the received waveforms at different incident angles were tested within a certain range of 14.5 degrees, and the results are shown in table 1. The results show that the amplitude of the received waveform gradually increases as the ultrasound incidence angle approaches the first critical angle. Analysis of the simulation results revealed that the excitation angle of the critical refracted longitudinal wave in this material was approximately 14 degrees.
When the incident angle changes between 0-90 degrees, the received waveform can reach an extreme value for many times because the refracted longitudinal wave and the refracted transverse wave have different critical refraction angles. Therefore, in the excitation test, the test range of the ultrasonic incident angle is determined according to the simulation result. According to the simulation result, the angle test range of the test is (0-14 degrees +10 degrees).
TABLE 1 amplitude of received waveform at different incident angles
Step two: preparation of the test
And (3) carrying out ultrasonic detection on three carbon fiber composite material plates of 0-degree ply, 0/90 ply and 0/45/-45/90 ply by using a test system consisting of an industrial personal computer system, a pulse excitation card, a data acquisition card, a variable-angle ultrasonic wedge and an ultrasonic transducer.
The material used in the test is a carbon fiber plate, the thickness of the carbon fiber plate is more than 5mm, and the surface of the plate is not specially treated. The carbon fiber material plate is placed on a horizontal plane, two variable-angle ultrasonic wedges which are respectively responsible for transmitting and receiving are placed on the surface of the plate, and an ultrasonic coupling agent is used for coupling the surface of the material with the surface of each variable-angle ultrasonic wedge, each variable-angle ultrasonic wedge and the ultrasonic transducer. The edges of the two variable angle ultrasonic wedges are aligned with the edges of the sheet material to ensure that the centers of the wedges are collinear. According to different fiber laying modes of the carbon fiber plates, the propagation direction of the ultrasonic refraction wave is parallel to the fiber direction of one of the plates when the wedge block is placed. The distance between the two wedges should not exceed 100mm, since the ultrasound is strongly attenuated in the carbon fibre material.
After the detection system is built, the current received waveform is displayed in software, and the next test is started.
Step three: adjusting the variable angle ultrasonic wedge block and searching the maximum point of the received wave amplitude
When the waveform is observed for the first time, the incidence angle of the wedge block is set at 0 degree, the current received wave waveform is recorded, and the ultrasonic incidence angle is adjusted. The receiving wedge block and the transmitting wedge block are adjusted simultaneously, the amplitude of the variable-angle ultrasonic wedge block is adjusted to be 1 degree each time, and the current wave-receiving waveform is recorded after adjustment. The adjustment and recording operations were repeated until angles in the range of (0-14 ° +10 °) were tested.
And comparing all recorded waveform data, and searching the corresponding ultrasonic incident angle when the waveform amplitude reaches the maximum value for the first time. It is believed that the LCR wave is successfully excited at the surface of the material, and that this angle is the optimal angle for exciting the LCR wave.
Through experiments, the sound velocity of the carbon fiber composite materials of the three layers in all directions is shown in the table 2. The incidence angles (approximate values) at which LCR waves were excited in the fiber direction on the carbon fiber composite plates of the three plies are shown in table 3. Meanwhile, the angle calculated by the ultrasonic sound velocity in the fiber direction directly according to the Snell's law is used to compare with the angle obtained by the experiment.
TABLE 2 carbon fiber Sound velocity test results
TABLE 3 first critical angle corresponding to three kinds of carbon fiber composite boards
This result confirms the viewpoint that the first critical angle calculated from snell's law cannot be used when the carbon fiber composite material excites the LCR wave, and confirms the feasibility of exciting the LCR wave on the surface layer of the carbon fiber composite material by observing the amplitude of the received waveform.
Claims (10)
1. A carbon fiber composite material surface critical refraction longitudinal wave excitation detection system is characterized in that:
the detection system consists of an industrial personal computer system, a pulse excitation card, a variable-angle ultrasonic wedge block, an ultrasonic transducer and a data acquisition card;
the industrial personal computer system is a computer system directly interacting with human, is directly connected with the pulse excitation card and the data acquisition card, sends a command to the pulse excitation card through the ultrasonic nondestructive testing software, analyzes and displays ultrasonic data recorded by the data acquisition card, and displays the acquired ultrasonic waveform on a screen;
one end of the pulse excitation card is connected with the industrial personal computer system, the other end of the pulse excitation card is connected with the ultrasonic transducer, and after the command of the industrial personal computer system is received, pulse waves are sent to the ultrasonic transducer;
the data acquisition card is connected with the ultrasonic transducer responsible for receiving information, acquires the related electrical signal information of the ultrasonic transducer and sends the information to the industrial personal computer system;
the ultrasonic transducer converts the input electric power into mechanical power, namely ultrasonic waves, and then transmits the mechanical power, or converts the received mechanical power into electrical energy;
the angle-variable ultrasonic wedge is an auxiliary module between the ultrasonic transducer and the material to be measured and is used for fixing the ultrasonic transducer to form a stable position relation with the surface of the material to be measured.
2. The carbon fiber composite surface critical refraction longitudinal wave excitation detection system according to claim 1, characterized in that: 2 ultrasonic transducers and 2 variable-angle ultrasonic wedges are adopted, wherein 1 group of ultrasonic transducers and the variable-angle wedges receive pulse waves from a pulse excitation card and emit ultrasonic waves into a material; another set of 1 ultrasonic transducer and variable angle wedge receive the wave form coming out of the material.
3. The carbon fiber composite surface critical refraction longitudinal wave excitation detection system according to claim 1, characterized in that: in order to reduce the influence of air between surfaces on ultrasonic wave propagation, the variable-angle ultrasonic wedge block is coupled with an ultrasonic transducer and the surface of a material by using a coupling agent; the ultrasonic wave reaches the surface of the material through the inside of the variable-angle ultrasonic wedge after being emitted from the ultrasonic transducer, is transmitted in the material after being refracted, and is received by the other set of variable-angle ultrasonic wedge and the ultrasonic transducer.
4. The carbon fiber composite surface critical refraction longitudinal wave excitation detection system according to claim 3, characterized in that: changing the angle of the surface of the ultrasonic incident material by adjusting the variable-angle ultrasonic wedge; when in use, the ultrasonic transducer is coupled and fixed with the upper surface of the sliding block; when the incident angle is changed, the fixing knob is firstly adjusted to loosen the sliding block and the sliding curved surface, then the sliding block is rotated for a certain angle along the axis, and then the fixing knob is screwed again to fix a new angle.
5. The carbon fiber composite surface critical refraction longitudinal wave excitation detection system according to claim 4, characterized in that: when the ultrasonic waves are incident on the surface of the material at the optimal angle and successfully excite the critical refraction longitudinal waves, the amplitude of the received waveform is maximum; therefore, the ultrasonic incident angle needs to be adjusted continuously until the amplitude of the received waveform reaches the maximum value, and the corresponding ultrasonic incident angle at this time is used as the optimal angle for exciting the critical refraction longitudinal wave.
6. The carbon fiber composite surface critical refraction longitudinal wave excitation detection system according to claim 5, characterized in that: and in the range from 0 degrees to the initial angle of +10 degrees, the amplitude of the received waveform is observed after the variable-angle ultrasonic wedge is adjusted by about 1 degree each time until the amplitude reaches the maximum value.
7. The detection method of the carbon fiber composite material surface critical refraction longitudinal wave excitation detection system according to claim 1, characterized in that:
the method comprises the following steps: determining the testing angle range of critical refraction longitudinal wave excitation test by simulation
Simulating the propagation of ultrasonic waves in the ultrasonic wedge and the carbon fiber material by using COMSOL; the ultrasonic wave is excited from the wedge block on the left, and when entering the carbon fiber material, refracted longitudinal waves, refracted transverse waves and head waves are excited; the refracted longitudinal wave enters the wedge block on the right side through refraction again and is received by the sensor; the ultrasonic wedge block material is organic glass PMMA, the sound velocity in the material is 2700m/s, and the elastic matrix of the carbon fiber material is as follows:
exciting the left wedge block by using a single period with the period of 1.5MHz, and observing a receiving waveform in the receiving wedge block;
step two: preparation of the test
Respectively carrying out ultrasonic detection on three carbon fiber composite material plates of 0-degree ply, [0/90] ply and [0/45/-45/90] ply by using a detection system;
the material used in the test is a carbon fiber plate, the carbon fiber plate is placed on a horizontal plane, two variable-angle ultrasonic wedges which are respectively responsible for transmitting and receiving are placed on the surface of the plate, and an ultrasonic coupling agent is used for coupling the surface of the material with the surface of the variable-angle ultrasonic wedges, the variable-angle ultrasonic wedges and an ultrasonic transducer; the edges of the two variable-angle ultrasonic wedges are aligned with the edge of the plate, so that the centers of the wedges are collinear;
after the detection system is built, displaying the current received waveform in software, and starting the next test;
step three: adjusting the variable angle ultrasonic wedge block and searching the maximum point of the received wave amplitude
When the waveform is observed for the first time, the incidence angle of the wedge block is set at 0 ℃, the current received wave waveform is recorded, and the ultrasonic incidence angle is adjusted; the receiving wedge block and the transmitting wedge block are adjusted simultaneously, the amplitude of the variable-angle ultrasonic wedge block is adjusted to be 1 degree each time, and the current wave-receiving waveform is recorded after adjustment; repeating the adjustment and recording operation until the angles within the range of 0-14 degrees plus 10 degrees are tested once;
comparing all recorded waveform data, and searching the corresponding ultrasonic incident angle when the waveform amplitude reaches the maximum value for the first time; it is believed that the LCR wave is successfully excited at the surface of the material, and that this angle is the optimal angle for exciting the LCR wave.
8. The carbon fiber composite surface critical refraction longitudinal wave excitation detection system according to claim 7, characterized in that: in step one, when the ultrasonic incidence angle is set to be about 14.5 degrees, LCR waves are observed in the CFRP material; when the incident angle changes between 0-90 degrees, the received waveform can reach an extreme value for many times because the refracted longitudinal wave and the refracted transverse wave have different critical refraction angles; therefore, in the excitation test, the test range of the ultrasonic incident angle is determined according to the simulation result.
9. The carbon fiber composite surface critical refraction longitudinal wave excitation detection system according to claim 7, characterized in that: the thickness of the carbon fiber plate is more than 5mm, and the surface of the plate is not specially treated.
10. The carbon fiber composite surface critical refraction longitudinal wave excitation detection system according to claim 7, characterized in that: when the wedge block is placed, the propagation direction of the ultrasonic refraction wave is ensured to be parallel to the fiber direction of one of the plates; the distance between the two wedges should not exceed 100 mm.
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Cited By (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN114034420A (en) * | 2021-10-20 | 2022-02-11 | 哈尔滨工业大学 | Linkage device with synchronously adjustable distance and angle, transceiving module, plane stress field detection device and plane stress field detection method |
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