CN110568064A - Resonant eddy current detection method and system for damage of carbon fiber composite material - Google Patents
Resonant eddy current detection method and system for damage of carbon fiber composite material Download PDFInfo
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- G01N27/90—Investigating or analysing materials by the use of electric, electrochemical, or magnetic means by investigating magnetic variables for investigating the presence of flaws using eddy currents
- G01N27/9046—Investigating or analysing materials by the use of electric, electrochemical, or magnetic means by investigating magnetic variables for investigating the presence of flaws using eddy currents by analysing electrical signals
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Abstract
The invention discloses a resonant eddy current detection method and a resonant eddy current detection system for damage of a carbon fiber composite material. In the method and the system, an eddy current detection coil and a resonant capacitor are connected in parallel to form a resonant eddy current probe, and then a sine wave of resonant frequency is generated through a self-resonant circuit. Under the sine wave excitation, the resonant eddy current probe can be equivalent to a pure resistor. The damage condition in the carbon fiber composite material can be evaluated by measuring the change of the equivalent resistance of the resonant eddy current probe. The invention is very suitable for the nondestructive testing of the high-resistivity weak conductive material such as the carbon fiber composite material; the detection effect is rather poor for metal materials with good conductivity.
Description
Technical Field
The invention relates to a nondestructive testing method and a nondestructive testing system for damage of a carbon fiber composite material, in particular to a resonant eddy current testing method and a resonant eddy current testing system for damage of a carbon fiber composite material, and belongs to the field of electromagnetic nondestructive testing of composite materials.
Background
The carbon fiber composite material is a novel structural material, has superior performances of high strength and light weight, and is widely applied to the fields of civil use, military use, aerospace and the like. Due to the structural characteristics of the carbon fiber composite material, the structural damage of the carbon fiber composite material cannot be avoided in the processing and using processes. Therefore, in order to ensure the quality of the carbon fiber composite material, the development of nondestructive testing of the carbon fiber composite material is receiving more and more attention.
Eddy current testing is a conventional non-destructive testing method that utilizes the electromagnetic induction principle for testing. The method utilizes the coil to excite the eddy current in the conductor, if the damage exists in the eddy current area, the distribution of the eddy current field in the area can be influenced, and corresponding voltage change is induced on the coil. The eddy current detection has good detection effect on the conductor, so that the eddy current detection is very suitable for metal materials. However, carbon fiber composite materials are weakly conductive materials, and have a resistivity 3 orders of magnitude higher than that of metal materials. The eddy current generated in the carbon fiber composite material by the conventional low-frequency eddy current detection technology is very weak, and the eddy current signal and the sensitivity thereof are poor and are difficult to be picked up by a probe.
In order to overcome the above difficulties, a high frequency eddy current detection method of 10MHz or more is generally used. However, the high-frequency eddy current detection system is difficult to implement, and the signal processing and amplifying circuit is susceptible to external interference and coil lift-off.
chinese patent CN201510243769 discloses a high-frequency electromagnetic eddy current detection system for damage detection of carbon fiber composite material, which comprises an upper computer, a displacement platform, an eddy current probe, an analog signal processing unit and a digital signal processing unit. The whole detection system works at high frequency, can reach the excitation frequency of 10MHz, has high detection sensitivity, can carry out damage positioning on tiny damages in the carbon fiber composite material, and has high integration degree and small volume.
Chinese patent CN 104897775B discloses a medium frequency eddy current testing system of carbon fiber resin matrix composite, which comprises a signal generating module, an eddy current sensing unit, a phase-locked amplifying module and a signal collecting module. In order to overcome the problems of weak sensing signals and poor sensitivity, the invention adopts a means of improving the sensitivity and amplification gain of a post-processing circuit; meanwhile, the design of each module has high sensitivity and strong detection capability on tiny signals, and the purpose of medium-frequency eddy current detection is achieved.
Chinese patent CN103760234B discloses a design method for improving the extreme sensitivity of eddy current detection by using the change of resonant frequency. Compared with a conventional eddy current detection impedance signal image, the resonance eddy current detection impedance signal image obtained by the method is added with frequency change information besides amplitude and phase information; with this information, the detection sensitivity for the minute defect is further improved.
Shenzhong, Chen Shi cheap et al [ resonant eddy current testing of metal microcracks, university of Petroleum, 1993,05:126-129 ] measured the propagation of microcracks on metal surfaces using eddy current resonance testing. By increasing the quality factor of the resonant circuit, the micro surface cracks and defects can obtain larger signal voltage output.
through related reports, the eddy current detection of the carbon fiber composite material has the problems of weak signal and poor sensitivity. There are two approaches to overcome at present: the first is to increase the eddy current detection frequency, and a high-frequency eddy current detection system with the frequency of more than 10MHz is used for achieving the aim; the second method is to increase the sensitivity and amplification gain of the processing circuit and to increase the signal strength by using a high-precision amplifier.
The resonance method is also applied to the field of eddy current detection, but is mainly used for additionally providing frequency change information or improving signal output through resonance quality factor.
disclosure of Invention
In view of the above problems, the present invention provides a resonant eddy current testing method and system for detecting damage in a carbon fiber composite material in a low-medium frequency range, aiming at the characteristic of high resistivity of the carbon fiber composite material.
One object of the present invention is to provide a resonance type eddy current testing method for damage of a carbon fiber composite material, which is characterized in that:
firstly, an eddy current detection coil L is connected with a resonance capacitor C in parallel, the resonance capacitor can be a fixed capacitor, and the LC parallel circuit is used as the resonance type eddy current probe of the invention to replace a single detection coil of the conventional eddy current detection; because the end voltage V and the total current I in the LC parallel resonance circuit have the characteristic of the same phase, the resonant eddy current probe is shown as pure resistance under the parallel resonance frequency.
Then, the resonant eddy current probe is connected into a self-resonant circuit to generate a sine wave with the excitation frequency f changing along with the inductance L of the detection coil; under the sine wave excitation of the frequency, the resonant eddy current probe can always keep pure resistance.
At this time, in the eddy current signal output by the eddy current detection coil L, the imaginary part Δ Vy of the signal change is cancelled by the resonant capacitor, and the real part Δ Vx of the signal change is superimposed on the equivalent resistance R of the eddy current probe.
Further, by means of online measurement of the voltage V or the total current I of the eddy current probe end by the resonance mode, the equivalent resistance R corresponding to the resonance mode eddy current probe at different positions in the material structure to be measured can be obtained by utilizing the ohm theorem.
And finally, scanning and detecting the surface of the material to be detected by using the resonant eddy current probe. If the material structure is damaged, the conductivity of the material at the position is reduced, the resistivity is improved, the current phase of the eddy current detection coil is relatively moved backwards, the real part Vx of an eddy current signal is increased, and the equivalent resistance R of the resonant eddy current probe is correspondingly increased. By sampling or observing the change of the equivalent resistance R of the resonant eddy current probe, whether the material is damaged or not can be judged and the damage condition can be evaluated.
The resonant eddy current detection system designed by the method is insensitive to the intensity change of an eddy current field in the material to be detected and sensitive to the current phase change caused by the resistivity change in the material to be detected; the resistivity change in the material is directly mapped to a change in the equivalent resistance R of the resonant eddy current probe. Therefore, the invention is very suitable for nondestructive testing of the high-resistivity weak conducting materials such as carbon fiber composite materials.
According to another aspect of the present invention, there is provided a resonant eddy current testing system for damage to a carbon fiber composite material, comprising: the device comprises an eddy current probe, a resonator, a voltage detector, a current detector, a data collector, an upper computer and a displacement platform.
the eddy current probe is a resonant eddy current probe, and comprises: the device comprises a shell, an eddy current detection coil, a resonant capacitor and a shielding wire; the eddy current detection coil and the resonance capacitor are connected in parallel to form an LC parallel circuit, and the LC parallel circuit is arranged in the shell and led out of the parallel circuit through a shielding wire.
The resonator is an LC parallel self-resonant circuit or module and is connected with the eddy current probe through a shielding wire. On one hand, an eddy current probe provides an LC parallel resonance condition to generate a sinusoidal signal with the excitation frequency f changing along with the inductance L of the detection coil; on the other hand, the excitation current is provided for the eddy current probe.
The voltage detector is used for detecting the terminal voltage V of the eddy current probe; the AC voltage applied to the eddy current probe is taken out, the effective value or peak-to-peak value of the terminal voltage V is detected, and the terminal voltage V is converted into a DC level form. If the resonator is implemented as a constant voltage LC parallel resonant circuit, where the terminal voltage V acting on the eddy current probe is constant and known, the voltage detector can be eliminated.
The current detector is used for detecting the total current I of the eddy current probe; the AC current applied to the eddy current probe is taken out through the sampling resistor, the effective value or peak-to-peak value of the total current I is detected, and the total current I is converted into a DC level form.
The data acquisition unit is a multi-channel data acquisition system and is used for converting output results of the voltage detector and the current detector into corresponding digital quantities and uploading the digital quantities to an upper computer through a data bus.
the eddy current probe is arranged on a sliding block of the displacement platform; and the displacement platform is controlled by the upper computer.
the upper computer has two functions, on one hand, the movement track of the displacement platform is controlled by sending a movement instruction, and the scanning of the workpiece to be detected by the eddy current probe is realized; and on the other hand, according to the acquired data, calculating the equivalent resistance R of the eddy current probe in real time, evaluating whether damage exists or not and the damage degree, and simultaneously displaying the detection result in real time.
Compared with the conventional eddy current detection probe, the resonant eddy current probe has three obvious characteristics: firstly, under the condition of parallel resonance frequency, the terminal voltage V and the total current I in the resonant eddy current probe have the characteristic of the same phase, and the resonant eddy current probe is expressed as pure resistance. Secondly, the imaginary part Δ Vy of the eddy current signal change caused by material damage is offset by the resonant capacitor, and the real part Δ Vx of the eddy current signal change is superimposed on the equivalent resistance R of the resonant eddy current probe. Therefore, the damage condition of the material structure can be reflected by the change of the equivalent resistance R of the eddy current probe. Thirdly, the resonant eddy current probe works in an LC parallel self-resonance mode, so that an additional high-frequency signal source and an amplifier are not needed to generate an excitation current.
from the above, the beneficial effects of the present invention are: in the detection method and the system, LC parallel resonance is utilized to convert the eddy current detection coil into a purely resistive resonant eddy current probe. The resonant eddy current probe is insensitive to the intensity change of an eddy current field in a detected material and sensitive to the current phase change caused by the resistivity change in the detected material; the resistivity change in the material is directly mapped to a change in the equivalent resistance R of the resonant eddy current probe. Therefore, the invention is very suitable for nondestructive testing of the high-resistivity weak conducting materials such as carbon fiber composite materials; the detection effect is rather poor for metal materials with good conductivity.
Drawings
FIG. 1 is a block diagram of a detection system according to an embodiment of the present invention;
FIG. 2 is a schematic diagram illustrating the detection principle of the eddy current probe according to the embodiment of the present invention;
FIG. 3 is a schematic diagram of the electrical circuit of the connections between the eddy current probe, the resonator, the voltage detector, and the current detector in an embodiment of the present invention;
Reference numbers for the various components in the figures: 1. an eddy current probe; 2. a resonator; 3. a voltage detector; 4. a current detector; 5. a data acquisition unit; 6. an upper computer; 7. a displacement platform; 8. a carbon fiber composite material.
Detailed Description
The technical scheme provided by the invention is further explained by combining the attached drawings.
Referring to fig. 1, a resonant eddy current testing system for damage to a carbon fiber composite material includes: the device comprises an eddy current probe 1, a resonator 2, a voltage detector 3, a current detector 4, a data acquisition unit 5, an upper computer 6 and a displacement platform 7.
The eddy current probe 1 is a resonant eddy current probe, including: a housing 11, an eddy current detection coil 12, a resonance capacitor 13, and a shield wire 14; the eddy current detection coil 12 and the resonance capacitor 13 are connected in parallel to form an LC parallel circuit, and are arranged in the shell 11, and the parallel circuit is led out through the shielding wire 14. Because the end voltage V and the total current I in the LC parallel resonance circuit have the same phase characteristic, the eddy current probe is shown to be pure resistance under the parallel resonance frequency.
The resonator 2 is an LC parallel self-resonant circuit and is connected to the eddy current probe 1 via a shield wire 14. On one hand, the eddy current probe 1 provides an LC parallel resonance condition to generate a sinusoidal signal with the excitation frequency f changing along with the inductance L of the detection coil. On the other hand, the excitation current is provided for the eddy current probe 1; under the action of the frequency excitation current, the eddy current probe 1 can always keep pure resistance.
The voltage detector 3 is used for adopting the output voltage of the resonator 2, namely the terminal voltage V of the eddy current probe 1; the ac voltage output from the resonator 2 is taken out, and the effective value or peak-to-peak value of the terminal voltage V is detected and converted into a dc level form.
The current detector 4 is used for detecting the total current I of the eddy current probe 1; the total current I acting on the eddy current probe 1 is taken out, the effective value or peak-to-peak value of the total current I is detected, and converted into a dc level form.
The data acquisition unit 5 is a two-way data acquisition system, converts the output results of the voltage detector 3 and the current detector 4 into corresponding digital quantities, and uploads the digital quantities to the upper computer 6 through a data bus.
the eddy current probe 1 is arranged on a slide block of a displacement platform 7, and the motion trail of the displacement platform 7 is controlled by sending a motion command by an upper computer 6.
the upper computer 6 has two functions, on one hand, the movement track of the displacement platform 7 is controlled by sending a movement instruction, and the scanning detection of the eddy current probe 1 on the workpiece to be detected is realized; and on the other hand, according to the acquired data and ohm's law, calculating in real time to obtain equivalent resistances R corresponding to eddy current probes at different positions in the structure of the carbon fiber composite material 8 to be detected.
If damage exists in the carbon fiber composite material structure, the carbon fiber is broken, so that the conductivity of the carbon fiber composite material at the position is directly reduced, and the resistivity is improved; the current phase relative backward shift is shown on the eddy current detection coil, the real part Vx of the eddy current signal is increased, and the equivalent resistance R of the eddy current probe is correspondingly increased. Therefore, the upper computer 6 monitors the change of the equivalent resistance R of the eddy current probe 1 in real time, and can judge whether the carbon fiber composite material is damaged or not and evaluate the damage condition.
Referring to fig. 2, the detection principle of the resonant eddy current probe in the embodiment of the present invention is as follows: when the eddy current detection coil 12 is applied with an angular frequencyAt the time of excitation current of (2), the self-impedance of the eddy current detection coil 12 isWhereinIs the static internal resistance of the eddy current detecting coil 12. Since the eddy current detecting coil 12 is placed above the test piece to be tested, an eddy current is induced inside the test piece. According to the mirror image principle, the presence of another induction coil inside the test piece corresponds to the presence of eddy currents in the induction coil. The self-impedance of the induction coil can be set asThe mutual inductance with the eddy current detection coil 12 is M. The impedance of the eddy current detection coil 12 affected by the eddy current is as follows from the mutual inductance relationship of the two coils in space。
when the test piece is made of metal material, the conductivity of the material is good, and at the moment, the material has good conductivity(ii) a The impedance of the eddy current detection coil 12 after being affected by the eddy current is approximated to. In the resonant eddy current probe of the present invention, the imaginary part of the impedance of the coil 12 is offset by the resonant capacitor C, and the equivalent resistance of the resonant eddy current probe is obtainedTherefore, the invention has poor detection effect on metal materials with good conductivity.
When the piece to be tested is a carbon fiber composite material with weak conductivity, the material has high resistivity, and at the moment(ii) a The impedance of the eddy current detection coil 12 after being affected by the eddy current is approximated to. In the resonant eddy current probe of the invention, the equivalent resistance. Internal resistance caused by material structure damageIs directly mapped to the change in the equivalent resistance R of the resonant eddy current probe. Therefore, the invention is very suitable for the nondestructive detection of the carbon fiber composite material.
Referring to fig. 3, in this embodiment, the eddy current detection coil 12 is formed by winding 125 turns of a copper enameled wire with a wire diameter of 0.1mm, and the external dimensions of the eddy current detection coil 12 are as follows: height 1mm, external diameter 3.5mm, internal diameter 1mm, and equipped with the magnetic core of diameter phi 1mm 8mm in the coil centre bore. An intermediate tap is left at 25 turns of the eddy current detection coil 12. The resonant capacitor 13 is a ceramic chip capacitor of 440pF and is connected in parallel with the eddy current detection coil 12. The natural frequency of the LC resonant circuit is at 1 MHz. The eddy current detection coil 12 is enclosed in a plastic case 11 together with a resonance capacitor 13, and the parallel circuit is led out through a shield wire 14. The outer dimensions of the housing 11 are: diameter Φ 8mm 30 mm.
The resonator 2 is preferably an inductive three-point LC oscillating circuit. The triode in the circuit is a 9018 low-power high-frequency tube. The resonant probe is connected into an LC oscillating circuit driven by a triode 9018. In this circuit, the transistor 9018 is common base connected, so that the net input to the emitter junction is reduced, the collector current is reduced, and the phase condition of positive feedback is met, so that a sine wave with an excitation frequency f of about 1MHz can be generated.
The voltage detector 3 preferably includes an effective value level detection circuit AD 8362. In fig. 3, the terminal voltage V of the resonant probe is extracted from the resonator 2 and then input to the input port INH1 of the AD8362-1 through the operational amplifier OPA 695. The circuit detects the effective value of the terminal voltage V, converts the effective value into a direct current level and outputs the direct current level through a VOUT port.
the current detector 4 is preferably another piece of AD 8362. In fig. 3, since the total current I of the resonant probe flows through the emitter of the transistor 9018, the emitter voltage of the transistor 9018 may be used as the sampling of the total current I, and at this time, the emitter resistance 1.3k Ω of the transistor 9018 is a sampling resistance. This voltage is also input to the input port INH1 of the AD8362-2 via the op amp OPA 695. And outputs the current detection result through the VOUT port of the AD 8362-2.
The data acquisition device 5 preferably adopts a USB3210 data acquisition card, wherein the first channel is connected with a VOUT port (namely voltage detection output) of the AD 8362-1; the second channel is connected to the VOUT port (i.e., the current sense output) of AD 8362-2. And output results of the voltage detector 3 and the current detector 4 are converted into corresponding 16-bit digital quantities, and the digital quantities are uploaded to the upper computer 6 through a USB bus.
The upper computer 6 is preferably an industrial personal computer with a USB bus. The displacement platform 7 is preferably a desktop gantry type 2-axis displacement platform and is connected with the upper computer 6 through a USB bus. And the upper computer 6 controls the resonant eddy current probe 1 to scan on the carbon fiber composite material sample by sending a motion command.
Claims (2)
1. A resonant eddy current testing method for damage of carbon fiber composite materials is characterized in that: the method comprises the following steps:
Connecting an eddy current detection coil L with a resonance capacitor C in parallel, and using the LC parallel circuit as a resonance type eddy current probe;
The resonant eddy current probe is connected into a self-resonant circuit to generate a sine wave with the excitation frequency f changing along with the inductance L of the detection coil; under the excitation frequency f, the resonant eddy current probe is pure resistive, and the equivalent resistance of the resonant eddy current probe is R;
The equivalent resistance R corresponding to the resonant eddy current probe can be calculated by measuring the voltage V or the total current I of the resonant eddy current probe end on line;
When the resonant eddy current probe is used for scanning and detecting the surface of the carbon fiber composite material sample, if damage exists in the structure of the carbon fiber composite material sample, the equivalent resistance R corresponding to the resonant eddy current probe at the position is increased; by sampling or observing the change of the equivalent resistance R of the resonant eddy current probe, whether the carbon fiber composite material sample has damage or not can be judged and the damage condition can be evaluated.
2. A resonant eddy current testing system for damage to carbon fiber composites, comprising: an eddy current probe (1), a resonator (2), a voltage detector (3), a current detector (4), a data collector (5), an upper computer (6) and a displacement platform (7),
The eddy current probe (1) is a resonant eddy current probe, and comprises: a shell (11), an eddy current detection coil (12), a resonance capacitor (13) and a shielding wire (14); the eddy current detection coil (12) and the resonance capacitor (13) are connected in parallel to form an LC parallel resonance circuit, and the LC parallel resonance circuit is arranged in the shell and led out through a shielding wire (14);
The resonator (2) is an LC parallel self-resonant circuit or module and is connected with the eddy current probe (1); according to the LC parallel resonance condition provided by the eddy current probe (1), the excitation frequency f generated by the resonator (2) is a sinusoidal signal which changes along with the inductance L of the detection coil, and provides excitation current for the eddy current probe (1);
The voltage detector (3) is connected with the resonator (2) or the eddy current probe (1) and is used for detecting a terminal voltage V acting on the eddy current probe (1); the voltage detector (3) extracts the effective value or peak-to-peak value of the terminal voltage V and converts the effective value or peak-to-peak value into a direct current level form;
the current detector (4) is connected with the resonator (2) or the eddy current probe (1) and is used for detecting the total current I actually flowing through the eddy current probe (1); the current detector (4) extracts the total current I through a sampling resistor and converts the effective value or the peak-to-peak value of the total current I into a direct current level form;
the data acquisition unit (5) is a data acquisition system with more than two paths and is used for converting output results of the voltage detector (3) and the current detector (4) into corresponding digital quantities and uploading the digital quantities to the upper computer (6) through a data bus;
The upper computer (6) is connected with the data acquisition unit (5) and the displacement platform (7) through a bus; the upper computer (6) controls the motion trail of the displacement platform (7) by sending a motion instruction; meanwhile, according to the acquired data, calculating the equivalent resistance R of the eddy current probe (1) in real time, and evaluating the damage degree in the sample structure according to the change of the equivalent resistance R;
The eddy current probe (1) is assembled on the sliding block of the displacement platform (7), and the upper computer (6) controls the movement of the sliding block, so that the eddy current probe (1) can scan a sample to be tested.
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| CN111796020A (en) * | 2020-08-27 | 2020-10-20 | 厦门大学 | Eddy current detection method and system for layering defects of carbon fiber composite material |
| CN113138422A (en) * | 2020-01-16 | 2021-07-20 | 图尔克控股有限责任公司 | Proximity switch and method for detecting an object to be detected |
| KR102478600B1 (en) * | 2021-12-27 | 2022-12-15 | 재단법인 한국섬유기계융합연구원 | Fiber arrangement uniformity measurement system of spread carbon fiber using eddy current sensor and method terefor |
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