CN107870196B - Electromagnetic intelligent interlayer for monitoring fatigue cracks around bolt hole - Google Patents
Electromagnetic intelligent interlayer for monitoring fatigue cracks around bolt hole Download PDFInfo
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- CN107870196B CN107870196B CN201711262455.0A CN201711262455A CN107870196B CN 107870196 B CN107870196 B CN 107870196B CN 201711262455 A CN201711262455 A CN 201711262455A CN 107870196 B CN107870196 B CN 107870196B
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- G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
- G01N27/00—Investigating or analysing materials by the use of electric, electrochemical, or magnetic means
- G01N27/72—Investigating or analysing materials by the use of electric, electrochemical, or magnetic means by investigating magnetic variables
- G01N27/82—Investigating or analysing materials by the use of electric, electrochemical, or magnetic means by investigating magnetic variables for investigating the presence of flaws
- 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
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Abstract
The invention discloses an electromagnetic intelligent interlayer for monitoring fatigue cracks on the periphery of a bolt hole, which comprises an excitation coil, a signal pickup coil and a fatigue crack direction identification module; the exciting coils are concentric circles at certain intervals, and the winding mode of the exciting coils ensures that exciting currents in the exciting coils have the same flowing direction at the same time; the signal pickup coil is arranged in a staggered mode from the center to the outside of induction areas of different areas, and the fatigue crack direction identification module identifies the direction of the fatigue crack according to the change rate of output signals when the signals output by the different induction areas of the signal pickup coil are relatively crack-free. The invention can improve the eddy current flowing direction and improve the sensitivity of the eddy current sensor for monitoring the fatigue cracks around the bolt hole.
Description
Technical Field
The invention belongs to the field of nondestructive testing and structural health monitoring, and particularly relates to a planar eddy current sensor interlayer for monitoring fatigue cracks around bolt holes in real time.
Background
In order to ensure the safe operation of machines and equipment, the service life and reliability are closely concerned indexes of the mechanical structure in the whole life cycle. Fatigue damage is one of the common injuries. Bolting and riveting are common mechanical structural joints, and the joints are also important areas for stress concentration and even fatigue crack initiation and propagation. Therefore, health monitoring of fatigue cracks around bolt holes and staking holes is essential.
The eddy current method based on the electromagnetic induction principle is one of the common detection methods for nondestructive detection due to the characteristics of low manufacturing cost, simple structure, high efficiency and the like. This method has also been applied in recent years to the field of health monitoring of mechanical structures. An intelligent sandwich structure for detecting fatigue cracks on the periphery of a bolt hole mainly exists in a planar calyx-shaped eddy current sensor in the literature, namely, a calyx-shaped eddy current sensor and an airplane metal structure fatigue damage monitoring test research. The sensor is an excitation coil with a certain spacing, but the direction of the excitation current in adjacent spaced excitation coils is opposite, so the eddy currents induced under the excitation coils also have opposite directions. When the fatigue crack expands to a certain length from inside to outside, the eddy current disturbed at the inner side and the eddy current at the outer side form a local loop, and the disturbance does not increase along with the increase of the length of the crack any more. And the signal pickup coils of the inner layer and the outer layer of the array structure adopt a radial alignment arrangement mode, when a crack is expanded to the outer layer, although the channels of the response of the sensor are increased, the crack direction information in the output signals of the array coils is not increased.
Disclosure of Invention
In view of the above, the present invention provides an electromagnetic intelligent interlayer for monitoring fatigue cracks around bolt holes, which can improve the eddy current flowing direction and improve the sensitivity of eddy current sensors for monitoring fatigue cracks around bolt holes.
An electromagnetic intelligent interlayer for monitoring fatigue cracks around bolt holes comprises an excitation coil, a signal pickup coil and a fatigue crack direction identification module;
the excitation coils are concentric circles at certain intervals, and the winding mode of the excitation coils ensures that excitation currents in the excitation coils have the same flowing direction at the same moment so as to ensure that the disturbance to eddy current is continuously enhanced when the length of fatigue cracks around the bolt hole is continuously increased;
the signal pickup coils are arranged in a staggered manner from the center to the outside in the induction areas of different areas, so that the recognition capability of the sensor to the crack direction is improved;
the fatigue crack direction identification module identifies the direction of the fatigue crack according to the change rate of output signals of different induction areas of the signal pickup coil when the signals are relatively crack-free.
Furthermore, the excitation coil is wound in a concentric circle mode, the adjacent coils complete continuous winding of the concentric circles in a lead bending mode, the positive pole of the lead and the concentric circles of the excitation coil are located in the same plane, and the negative pole of the lead is led out after being bent through the concentric circle at the innermost circle.
Furthermore, the positive and negative poles of the exciting coil are two parallel leads, and the concentric circles of the exciting coil are respectively lapped on the positive and negative leads.
Further, the diameters of the wires forming the concentric circles in the excitation coil are sequentially reduced from inside to outside.
Further, the signal pickup coil is located in a sector area below the exciting coil, and the sector areas of the signal pickup coil in the radial direction area are in a staggered arrangement.
Further, the fatigue crack direction identification module abstracts the angular regions into angular region nodes, denoted by AD1, AD2, AD3, … …; abstracting signal pickup coils of different channels as sensor nodes, and indicating Ch1, Ch2, Ch3 and … …; abstracting the relationship between the sensor nodes and the signal pickup coil nodes into a weighted directed graph, wherein each sensor node points to the occupied angle region, the weight of the ith sensor node pointing to the jth angle region node is defined as the percentage of the area of the ith channel in the jth angle region, and P is usedijRepresents; the crack signal of the ith channel of the sensor is the percentage of the amplitude of the output signal of the channel relative to the amplitude of the output signal without cracks, and u is usediThat means that the crack signatures of all channels form a column vector U ═ U1,u2,u3,……]T(ii) a Setting the crack characteristic signal of the jth angle region as qjThe crack characteristic signals of all angle regions form a column vector Q ═ Q1,q2,q3,……]TThe calculation mode is Q-UP, wherein the element of the ith row and the jth column of the matrix U is Pij。
Has the advantages that:
1. the defect that the eddy current induced by a traditional calyx-shaped plane eddy current sensor is disturbed by fatigue cracks and the eddy current forms a local loop so that the disturbance of the eddy current by the cracks is not increased along with the increase of the length of the fatigue cracks is overcome, and the sensitivity of the eddy current sensor for monitoring the fatigue cracks at the periphery of the bolt hole is improved by improving the flowing direction of the eddy current.
2. The signal pickup coils in the inner and outer regions are arranged, so that the recognition capability of the sensor on the fatigue crack direction is realized under the condition that the number of channels of the signal pickup coils of the eddy current array sensor is not increased, and when the fatigue crack expands in the inner region, the fatigue crack is the same as that of the traditional calyx-shaped eddy current sensor; the direction recognition capability of the sensor doubles when fatigue cracks propagate to the outer region.
3. The invention provides a graph theory-based authorized directed graph, which converts crack characteristic signals output by each channel of a sensor into crack characteristic signals of each angle area and realizes intelligent angle identification of fatigue cracks.
Drawings
FIG. 1: eddy current sensor exciting coil with series connection relation
FIG. 2: eddy current sensor exciting coil with parallel connection relation
FIG. 3: different line width parallel eddy current sensor exciting coil
FIG. 4: 8 1-turn signal pickup coils
FIG. 5: typical eddy current sensor excitation and signal pickup coil structure and its normal magnetic field distribution
FIG. 6: conversion algorithm schematic diagram of weighted directed graph for crack direction identification
FIG. 7: typical experimental system structure block diagram
FIG. 8: variation of crack characteristic signals output by 8 channels of sensor along with stretching times
FIG. 9: variation of crack characteristic signal of 8-angle area along with stretching times
Detailed Description
The invention is described in detail below by way of example with reference to the accompanying drawings.
The invention provides an electromagnetic intelligent interlayer for monitoring fatigue cracks around bolt holes, which comprises an excitation coil, a signal pickup coil and a fatigue crack direction identification module;
the excitation coils are concentric circles at certain intervals, and the winding mode of the excitation coils ensures that excitation currents in the excitation coils have the same flowing direction at the same moment so as to ensure that the disturbance to eddy current is continuously enhanced when the length of fatigue cracks around the bolt hole is continuously increased;
the signal pickup coils are arranged in a staggered manner from the center to the outside in the induction areas of different areas, so that the recognition capability of the sensor to the crack direction is improved;
the fatigue crack direction identification module identifies the direction of the fatigue crack according to the change rate of output signals of different induction areas of the signal pickup coil when the signals are relatively crack-free.
The exciting coil and the signal pickup coil are respectively arranged on the front surface and the back surface of the flexible substrate, a central hole for a bolt to pass through is processed on the flexible substrate, the electromagnetic intelligent interlayer is clamped between two structural members to be tested and fixed by the bolt, and the structural members are tested by tensile test equipment.
As shown in fig. 1, the excitation coils are wound in a concentric circle mode, adjacent coils complete continuous winding of concentric circles in a lead bending mode, the positive pole of the lead and the concentric circles of the excitation coils are located in the same plane, and the negative pole of the lead is led out after being bent through the concentric circle at the innermost circle. Compared with the traditional excitation current in the positive and negative directions, the defect that eddy disturbance does not change obviously when the crack extends because eddy current is not generated to form a local loop is overcome.
As shown in fig. 2, the positive electrode and the negative electrode of the excitation coil are two parallel wires, and the concentric circles of the excitation coil are respectively lapped on the positive electrode and the negative electrode wires.
As shown in fig. 3, the diameters of the wires constituting the concentric circles in the excitation coil are sequentially decreased from inside to outside.
The exciting coil and the signal pickup coil shown in fig. 5 are arranged on two layers in the middle of the four-layer circuit board, and the exciting coil and the signal pickup coil are connected to the first layer through holes for loading exciting current and picking up induction signals of each channel.
As shown in figure 7, the exciting current of the electromagnetic intelligent interlayer, namely the eddy current sensor, is realized by amplifying 30KHz sinusoidal alternating current generated by a function generator through an external power amplifier, and the effective value of the exciting current in the experiment is 0.956A. And the output signal of the signal pickup coil is amplified and filtered by an amplifying and filtering circuit consisting of 4 AD620 chips to improve the signal-to-noise ratio of the signal. The output signal of the amplifying circuit is connected to an oscilloscope. 8129 signal points of the oscilloscope are stored for 2.5ms each time, the signal points are copied into the computer, FFT conversion is carried out through matlab, and the peak value of 30kHz after the FFT conversion represents the amplitude of the detection signal. The output signals of 8 channels are obtained by means of manual switching. The peak value of the cyclic pulsating pulling force is set to be 1.1KN, and the frequency is set to be 3 Hz. The reference axis of the fatigue tensile test piece is arranged on a connecting line between the bolt hole and the prefabricated microcrack, when data are obtained, the pulling machine stops working, an included angle between the reference axis of the sensor (on a ray from the center of the sensor to the midpoint of the excitation current input terminal of the sensor) and the reference axis of the test piece is 15 degrees, and cracks are expanded in the channel 1 and the channel 8 of the signal pickup coil. Before stretching, 8 channel signals are saved as reference signals when no crack exists; when the number of times of stretching is more than 4500, the output signals of 8 channels are saved every 50 times of stopping.
The rate of change of the signal amplitude with fatigue crack length is obtained as shown in fig. 8. U ═ U1,u2,u3,u4,u5,u6,u7,u8]TCrack signature output for 8 channels, Q ═ Q1,q2,q3,q4,q5,q6,q7,q8]TAnd outputting crack characteristic signals of 8 angular regions for 8 channels. The conversion between the two is realized by the formula Q-UP, wherein
The value of each element in P is determined by the sensor structure. The crack signature signals for the 8 angular regions output after the conversion are shown in fig. 9.
In summary, the above description is only a preferred embodiment of the present invention, and is not intended to limit the scope of the present invention. Any modification, equivalent replacement, or improvement made within the spirit and principle of the present invention should be included in the protection scope of the present invention.
Claims (5)
1. The electromagnetic intelligent interlayer is characterized by comprising an excitation coil, a signal pickup coil and a fatigue crack direction identification module;
the exciting coils are concentric circles at certain intervals, and the winding mode of the exciting coils ensures that exciting currents in the exciting coils have the same flowing direction at the same time;
the signal pickup coils are arranged in a staggered mode from induction areas of different areas with the centers facing outwards;
the fatigue crack direction identification module identifies the direction of the fatigue crack according to the change rate of output signals of different induction areas of the signal pickup coil when the signals are relatively crack-free;
the fatigue crack direction identification module abstracts the angle region into angle region nodes, and the angle region nodes are represented by AD1, AD2, AD3 and … …; abstracting signal pickup coils of different channels as sensor nodes, and indicating Ch1, Ch2, Ch3 and … …; abstracting the relationship between the sensor nodes and the signal pickup coil nodes into a weighted directed graph, wherein each sensor node points to the occupied angle region, the weight of the ith sensor node pointing to the jth angle region node is defined as the percentage of the area of the ith channel in the jth angle region, and P is usedijRepresents; the crack signal of the ith channel of the sensor is the percentage of the amplitude of the output signal of the channel relative to the amplitude of the output signal without cracks, and u is usediThat means that the crack signatures of all channels form a column vector U ═ U1,u2,u3,……]T(ii) a Setting the crack characteristic signal of the jth angle region as qjWhat is, what isThe crack characteristic signals of the angular region form a column vector Q ═ Q1,q2,q3,……]TThe calculation mode is Q-UP, wherein the element of the ith row and the jth column of the matrix U is PijWhere i represents the ith channel of the sensor signal pickup coil and j is the jth of the angular region over which the crack may propagate.
2. The electromagnetic intelligent interlayer for monitoring the fatigue crack at the periphery of the bolt hole as claimed in claim 1, wherein the excitation coil is wound in a concentric circle mode, the adjacent coils complete continuous winding of concentric circles in a lead bending mode, the positive pole of the lead and the concentric circles of the excitation coil are in the same plane, and the negative pole of the lead is led out after being bent through the concentric circle at the innermost circle.
3. The electromagnetic intelligent interlayer for monitoring the fatigue crack around the bolt hole according to claim 1, wherein the positive and negative electrodes of the excitation coil are two parallel wires, and the concentric circles of the excitation coil are respectively lapped on the positive and negative wires.
4. The electromagnetic intelligent interlayer for monitoring the fatigue crack around the bolt hole according to claim 3, wherein the diameters of the wires forming concentric circles in the excitation coil are reduced from inside to outside in sequence.
5. The electromagnetic intelligent interlayer for monitoring the fatigue crack around the bolt hole according to claim 1, wherein the signal pickup coil is located in a sector area below the exciting coil, and the sector areas of the signal pickup coil in the radial direction area are in a staggered arrangement.
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| CN109030622A (en) * | 2018-08-08 | 2018-12-18 | 中国人民解放军空军工程大学 | A kind of highly sensitive flexible eddy current array sensor and its monitoring method |
| CN109541018A (en) * | 2018-11-19 | 2019-03-29 | 厦门大学 | A kind of method of flexible circumferential crossed array currents sensing film and its monitoring crack |
| CN110031545A (en) * | 2019-05-17 | 2019-07-19 | 何舒扬 | It is capable of the intelligent gasket of real-time monitoring metal structure crackle |
| CN110346447B (en) * | 2019-07-09 | 2022-12-16 | 兰州理工大学 | Optimization method of calyx-shaped planar eddy current sensor |
| CN110596235B (en) * | 2019-08-02 | 2022-12-16 | 兰州理工大学 | Planar eddy current sensor based on similar Taiji diagram |
| CN110333284B (en) * | 2019-08-02 | 2022-12-16 | 兰州理工大学 | Series type plane eddy current sensor |
| CN112730603A (en) * | 2020-10-13 | 2021-04-30 | 爱德森（厦门）电子有限公司 | Method and system device for improving eddy current detection crack depth detection range |
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