1. A flexible eddy current sensing film based on a trapezoidal coil array is characterized by comprising an excitation coil layer, a receiving coil layer and an insulating film layer; the excitation coil layer and the receiving coil layer are respectively wired on two sides of the insulating film layer and connected through blind holes, the receiving coil layer is formed by an array of trapezoid-like receiving coil units, each trapezoid-like receiving coil unit is wound by a conducting wire, the excitation coil layer is formed by an array of parallelogram-like excitation coil units, and each parallelogram-like excitation coil unit is wound by a conducting wire.

2. The trapezoidal coil array based flexible eddy current sensing film as claimed in claim 1, wherein the insulating film layer is a polyimide film.

3. The trapezoidal coil array-based flexible eddy current sensing film as claimed in claim 1, wherein the number of the parallelogram-like excitation coil units is 1 × n, where n is the number of the axial arrays; the number of the trapezoid-like receiving coil units is m multiplied by n, wherein m is the number of the circumferential arrays.

4. The trapezoidal coil array-based flexible eddy current sensing film as claimed in claim 3, wherein the number of the axial arrays is determined by the number of layers or the thickness of the device under test, and the number of the circumferential arrays is determined by the aperture of the device under test.

5. A detection device based on a trapezoidal coil array flexible eddy current sensing film is characterized by comprising a sensing film, a high-frequency alternating signal source, a switch converter and an oscilloscope; wherein the content of the first and second substances,

the high-frequency alternating signal source is connected in series with the exciting coil layer of the sensing film, and the receiving coil layer of the sensing film is connected in series with the oscilloscope through the switch converter.

6. A use method of a flexible eddy current sensing film based on a trapezoidal coil array is characterized by comprising the following specific steps:

winding and pasting a sensing film on a bolt, enabling a receiving coil layer to be close to a piece to be tested, enabling an exciting coil layer to be close to the bolt, and enabling a high-frequency alternating current source to send an alternating signal to the exciting coil layer;

the receiving coil layer is connected to an oscilloscope through a switch converter, and the switch converter is switched, so that the induced voltage of the receiving coil layer is sequentially input into the oscilloscope;

and comparing the induced voltage variation before and after the damage of the receiving coil layer in the cross area, judging the axial or radial expansion condition of the crack of the piece to be detected, and calculating the circumferential angle of the crack of the piece to be detected.

7. The use method of the ladder-shaped coil array-based flexible eddy current sensing film as claimed in claim 6, wherein the frequency of the alternating current sent by the high-frequency alternating current source is set to be 100kHz-15 MHz.

8. The use method of the trapezoidal coil array-based flexible eddy current sensing film according to claim 6, wherein the formula for calculating the circumferential angle of the crack of the workpiece to be measured is as follows:

wherein k is the ratio of the variation,ΔU₁is the change of the induced voltage of the first coil in the same cross region, delta U₂The induced voltage variation of the second coil in the same cross region; n is the number of crossing regions before the crack occurs.

Background

The bolt connection structure is a common connection mode of main bearing structures of aerospace, rail transit, civil engineering and the like, and the integrity of the bolt connection structure often directly influences the reliability and safety of a system. However, the bolted connection inevitably has changes of connection states such as stress concentration at the bolt hole edge under a long-term complex working environment, so that the bolted connection structure is easy to have hole edge cracks to further cause loss of structural functions. Therefore, the method has very important significance for effectively monitoring and preventing the hole edge cracks of the bolt connecting structure and predicting the residual life of the bolt connecting structure, ensuring the reliability of the engineering structure, guaranteeing the life and property safety of people and guaranteeing the stable and healthy development of social economy.

In recent years, with the attempt of engineering application of the structural health monitoring technology, the contradiction between the quantitative monitoring requirement of engineering technicians and the insufficient quantitative level of the monitoring technology becomes a main contradiction which restricts the further application of the structural health monitoring technology. The method for monitoring the cracks at the hole edge of the bolt connection structure mainly comprises a vacuum comparison monitoring method, an intelligent coating method and an optical fiber sensor strain monitoring method which belong to direct measurement methods, and an electromechanical impedance method, an acoustic emission method, an ultrasonic guided wave method based on a piezoelectric sensor and an eddy current detection method which belong to indirect measurement methods. However, the detection method in the prior art cannot accurately identify the circumferential angle of crack propagation and the crack propagation in the axial direction or the radial direction. Therefore, overcoming the defect of weak coil monitoring capability and enhancing the identification capability of axial expansion and radial expansion is a problem to be solved urgently for those skilled in the art.

Disclosure of Invention

In view of the above, the invention provides a flexible eddy current sensing film based on a trapezoidal coil array, a detection device and a detection method, which improve the identification capability of axial expansion and radial expansion and accurately and quantitatively monitor the circumferential angle, the radial direction and the axial expansion of a hole edge crack.

In order to achieve the purpose, the invention adopts the following technical scheme: in a first aspect, a trapezoidal coil array-based flexible eddy current sensing film is provided, which comprises an excitation coil layer, a receiving coil layer and an insulating film layer; the excitation coil layer and the receiving coil layer are respectively wired on two sides of the insulating film layer and connected through blind holes, the receiving coil layer is formed by an array of trapezoid-like receiving coil units, each trapezoid-like receiving coil unit is wound by a conducting wire, the excitation coil layer is formed by an array of parallelogram-like excitation coil units, and each parallelogram-like excitation coil unit is wound by a conducting wire.

By adopting the technical scheme, the method has the following beneficial technical effects: the receiving coil layer adopts the trapezoidal coil to replace the triangular coil, the monitoring area at the corner is increased, the defects that the circumferential position of the crack cannot be accurately identified and the induced voltage variation does not obviously change along with the crack expansion are overcome, and the circumferential identification capability and the radial and axial expansion tracking capabilities of the flexible film are improved. The exciting coil adopts the irregular parallelogram coil to replace the traditional rectangular coil, and the defect of poor monitoring capability of the coil at the corner caused by inconsistent action ranges of the exciting coil unit and the receiving coil unit in the flexible film of the triangular coil is overcome.

Preferably, the insulating film layer is a polyimide film.

By adopting the technical scheme, the method has the following beneficial technical effects: the polyimide film has the characteristics of outstanding high temperature resistance, radiation resistance, chemical corrosion resistance and electrical insulation performance.

Preferably, the number of the parallelogram-like excitation coil units is 1 × n, wherein n is the number of the axial arrays; the number of the trapezoid-like receiving coil units is m multiplied by n, wherein m is the number of the circumferential arrays.

Preferably, the number of the axial arrays is determined by the number of layers or the thickness of the piece to be measured, and the number of the circumferential arrays is determined by the aperture of the piece to be measured.

In a second aspect, a detection device based on a trapezoidal coil array flexible eddy current sensing film is provided, which comprises a sensing film, a high-frequency alternating signal source, a switch converter and an oscilloscope; wherein the content of the first and second substances,

the high-frequency alternating signal source is connected in series with the exciting coil layer of the sensing film, and the receiving coil layer of the sensing film is connected in series with the oscilloscope through the switch converter.

In a third aspect, a method for using a trapezoidal coil array-based flexible eddy current sensing film is provided, which specifically comprises the following steps:

winding and pasting a sensing film on a bolt, enabling a receiving coil layer to be close to a piece to be tested, enabling an exciting coil layer to be close to the bolt, and enabling a high-frequency alternating current source to send an alternating signal to the exciting coil layer;

the receiving coil layer is connected to an oscilloscope through a switch converter, and the switch converter is switched, so that the induced voltage of the receiving coil layer is sequentially input into the oscilloscope;

and comparing the induced voltage variation before and after the damage of the receiving coil layer in the cross area, judging the axial or radial expansion condition of the crack of the piece to be detected, and calculating the circumferential angle of the crack of the piece to be detected.

Preferably, the frequency of the alternating current sent by the high-frequency alternating current source is set to be 100kHz-15 MHz.

Preferably, the formula for calculating the circumferential angle of the crack of the workpiece to be measured is as follows:

wherein k is the ratio of the variation,ΔU₁is the change of the induced voltage of the first coil in the same cross region, delta U₂The induced voltage variation of the second coil in the same cross region; n is the number of crossing regions before the crack occurs.

According to the technical scheme, compared with the prior art, the invention discloses and provides the flexible eddy current sensing film based on the trapezoidal coil array, the detection device and the detection method, overcomes the defects of weak corner monitoring capability and weak corner identification capability of the triangular coil flexible eddy current sensing film, and improves the identification precision of the circumferential angle of the hole edge crack and the expansion capability of tracking the radial and axial cracks; the quantitative monitoring level of the cracks on the hole edge of the bolt connecting structure is effectively improved, and data support is provided for accurately predicting the residual service life of the bolt connecting structure.

Drawings

In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings used in the description of the embodiments or the prior art will be briefly described below, it is obvious that the drawings in the following description are only embodiments of the present invention, and for those skilled in the art, other drawings can be obtained according to the provided drawings without creative efforts.

FIG. 1 is a schematic view of a flexible eddy current sensing film in accordance with the present invention;

FIG. 2 is a schematic diagram of the trace of the excitation coil layer in the flexible eddy current sensing film according to the present invention;

FIG. 3a is a schematic diagram of a local routing of the No. 1 excitation coil layer in the flexible eddy current sensing film according to the present invention;

FIG. 3b is a schematic diagram of a partial routing of the No. 2 excitation coil layer in the flexible eddy current sensing film according to the present invention;

FIG. 4 is a schematic diagram of the routing of the receive coil layer in the flexible eddy current sensor film of the present invention;

FIG. 5a is a schematic diagram of a partial trace of the receiving coil layer No. 1 in the flexible eddy current sensing film according to the present invention;

FIG. 5b is a schematic diagram of a partial trace of the receiving coil layer No. 2 in the flexible eddy current sensing film according to the present invention;

FIG. 6 is a schematic view of the composition distribution of the flexible eddy current sensing film according to the present invention;

FIG. 7 is a schematic view of a flexible eddy current sensing film according to the present invention in use;

FIG. 8a is a schematic view of a prior art coil shape of the present invention;

FIG. 8b is a schematic view of the trapezoidal coil shape of the present invention;

FIG. 9 is a schematic structural diagram of an apparatus for monitoring hole edge cracking using a flexible eddy current sensing film according to the present invention;

the device comprises a flexible eddy current sensing film 1, a bolt 2, a to-be-detected part 3, a high-frequency alternating signal source 4, a switching converter 5, an oscilloscope 6, an excitation coil layer 17, an excitation coil layer 2, an insulation film 9, a receiving coil layer 1 10, a receiving coil layer 2 11, a first blind hole 12, an excitation coil in the excitation coil layer 1, an excitation coil of the excitation coil layer 2 14, a fourth receiving coil 15, a fifth blind hole 16, a third receiving coil 17, a fourth blind hole 18, a second receiving coil 19, a third blind hole 20, a first receiving coil 21, a second blind hole 22, a fifth receiving coil 23, a sixth receiving coil 24, a seventh receiving coil 25 and an eighth receiving coil 26.

Detailed Description

The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the drawings in the embodiments of the present invention, and it is obvious that the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present invention.

The embodiment 1 of the invention discloses a flexible eddy current sensing film based on a trapezoidal coil array, which is schematically shown in fig. 1, the specific composition distribution of the sensing film is shown in fig. 6, the sensing film in the embodiment comprises 9 layers of films, and comprises 5 layers of insulating films, 2 layers of excitation coil layers and 2 layers of receiving coil layers, and the excitation coil layers and the receiving coil layers are mutually isolated through insulating film layers. In fig. 6, from top to bottom: insulating film 9, excitation coil layer No. 17, insulating film 9, excitation coil layer No. 2 8, insulating film 9, receiving coil layer No. 1 10, insulating film 9, receiving coil layer No. 2 11, insulating film 9. The No. 1 excitation coil layer 7 and the No. 2 excitation coil layer 8 form an excitation part of the sensing film; the No. 1 receiving coil layer 10 and the No. 2 receiving coil layer 11 constitute a receiving portion of the sensor film.

The insulating film 9 is a polyimide film having outstanding high-temperature resistance, radiation resistance, chemical resistance, and electrical insulating properties.

Furthermore, the receiving coil layer is formed by an array of trapezoid-like receiving coil units, each receiving coil in the same row is wound by a conducting wire, the exciting coil layer is formed by an array of parallelogram-like exciting coil units, and each exciting coil in the same row is wound by a conducting wire.

In an excitation coil layer, n parallelogram coils are axially arrayed, the number of n is determined by the specification of a to-be-monitored piece, and n is 3 in the embodiment; for an excitation coil, each circumferential coil is wound by a conducting wire, m trapezoidal coils are arranged in a circumferential array in a receiving coil layer, n parallelogram coils are arranged in an axial array, the number of m is determined by the aperture size of a to-be-monitored piece, and m is equal to n and equal to 3 in the embodiment; for the receiver coil, each coil unit is wound from a single wire.

Specifically, the routing of the excitation coil layer is shown in fig. 2, and in order to better explain the routing manner of the excitation coil layer, a local routing diagram of the excitation coil layer No. 1 in fig. 3a and a local routing diagram of the excitation coil layer No. 2 in fig. 3b are used for detailed explanation. In this case, the insulating films laminated in the two excitation coil layers are not shown. The exciting coil layer and the receiving coil layer are both of a double-coil structure. The lead is led in from the right side of the exciting coil 13 in the No. 1 exciting coil layer and is clockwise wound to the first blind hole 12, passes through the insulating film to the first blind hole 12 of the exciting coil 14 in the No. 2 exciting coil layer, and the lead is clockwise wound to the periphery of the exciting coil 14 and then is led out from the left side.

The driving coil routing is a routing path of the driving coil in the 1 st row of the driving part in this embodiment, and the routing paths of the driving coils in the other rows are consistent with the routing path of the driving coil in the 1 st row.

The routing of the receiving coil layer is shown in fig. 4, and in order to better illustrate the routing manner of the receiving coil, the following is described in detail with reference to fig. 5a and 5 b. In which the insulating films laminated in the two receiving coil layers are not shown. The lead is led in from the right side of the first receiving coil 21 in the receiving coil layer No. 1, clockwise surrounds to the second blind hole 22, passes through the insulating film to the second blind hole 22 of the fifth receiving coil 23 of the receiving coil layer No. 2, and is led out from the lower part of the fifth receiving coil 23 to the left side after clockwise surrounding to the periphery of the coil; a wire is led into the second receiving coil 19 from the lower side of the first receiving coil 21 in the receiving coil layer No. 1, and is wound to the third blind hole 20 clockwise, and penetrates through the insulating film to the third blind hole 20 of the sixth receiving coil 24 of the receiving coil layer No. 2, and the wire is wound to the periphery of the coil clockwise and then is led out by routing below the sixth receiving coil 24; a wire is led into the third receiving coil 17 from the lower side of the first receiving coil 21 and the second receiving coil 19 in the receiving coil layer 1 to clockwise surround the wire to the fourth blind hole 18 and pass through the insulating film to the fourth blind hole 18 of the seventh receiving coil of the receiving coil layer 2 11, and the wire is led out by routing below the seventh receiving coil 25 after clockwise surrounding the wire to the periphery of the coil; the last wire is led into the fourth receiving coil 15 from the lower side of the first receiving coil 21, the second receiving coil 19 and the third receiving coil 17 in the receiving coil layer 1, and is wound to the fifth blind hole 16 clockwise, and passes through the insulating film to the fifth blind hole 16 of the eighth receiving coil 26 of the receiving coil layer 2, and the wire is wound to the periphery of the coil clockwise and then is led out by routing below the eighth receiving coil 26.

The receiving coil routing is a routing path of a receiving coil in the 1 st row of the receiving part in this embodiment, and routing paths of the receiving coils in the other rows are consistent with the routing paths of the coils.

The main differences of the excitation and receiving coil routing are as follows: the exciting coils in the same row are wound by the same wire, that is, in the embodiment, the exciting part is wound by 3 wires, and 3 pairs of interfaces are formed; each receiver coil in the same row is wound from one wire, i.e. in this embodiment, the receiver portion has a total of 12 wire windings, 12 pairs of interfaces.

The embodiment 2 of the invention discloses a detection device based on a trapezoidal coil array flexible eddy current sensing film, which comprises a sensing film 1, a high-frequency alternating signal source 4, a switch converter 5 and an oscilloscope 6; wherein the content of the first and second substances,

the high-frequency alternating signal source 4 is connected in series with the exciting coil layer of the sensing film 1, and the receiving coil layer of the sensing film 1 is connected in series with the oscilloscope 6 through the switch converter 5.

The embodiment 3 of the invention discloses a use method of a flexible eddy current sensing film based on a trapezoidal coil array, and as shown in fig. 9, the use of the flexible eddy current sensing film for monitoring a hole edge crack device is schematically illustrated, and the specific steps include the following steps:

the flexible eddy current sensing film 1 is wound and adhered on a bolt 2, a receiving coil layer is close to a piece to be tested 3, an exciting coil layer is close to the bolt 2, 15 leads are led out of the flexible eddy current sensing film 1, a pair of interfaces of an exciting part 3 are connected into a high-frequency alternating signal source 4 in series, the frequency of alternating current is set to be 100kHz-15MHz, proper frequency can be selected according to the number of turns of the leads in the sensing film, and a pair of leads of a receiving part 9 are connected into an oscilloscope 6 through a connecting switch converter 5.

It should be noted that, the use method of the flexible eddy current sensing film is realized based on the eddy current effect, and the piece to be measured needs to have conductivity.

The use process can be divided into two stages: 1. in the reference stage, when the hole edge is not damaged, the high-frequency alternating signal source 4 sends an alternating signal to an excitation part of the flexible eddy current sensing film 1, due to the eddy current effect, induced voltage is received on each receiving coil of the receiving part, and the induced voltage value of each receiving coil is obtained on the oscilloscope 6 by controlling the switch corresponding to each coil on the switch converter 5 and recorded as reference voltage; 2. in the comparison stage, during real-time monitoring, the high-frequency alternating signal source 4 sends alternating signals to an excitation part of the flexible eddy current sensing film 1, due to the eddy current effect, induced voltages can be received on all receiving coils of a receiving part, induced voltage values of all receiving coils are obtained on the oscilloscope 6 by controlling switches corresponding to all coils on the switch converter 5, and whether cracks occur in the piece to be detected 3 can be preliminarily judged by comparing reference voltages; according to the magnitude of the induced voltage variation of the receiving coils in each crossing region, the circumferential angle of the crack can be accurately identified through calculation, and the radial and axial expansion degrees are judged.

Fig. 7 is a schematic circumferential development of the flexible eddy current sensing film according to the present invention in use, in which the sensing film is divided into 12 intersecting zones, and since the development is in the circumferential direction, each row of intersecting zones bisects 360 °, i.e., 90 °. In this embodiment, the left boundary of the workpiece 3 is defined as 0 °, and a crack may be initiated at any circumferential position and may propagate in the radial and axial directions.

In this embodiment, the induced voltage of the adjacent coils in the crossing region where the crack is located will change significantly, and the ratio of the change amountsΔU₁Is the change of the induced voltage of the first coil in the same cross region, delta U₂The induced voltage variation of the second coil in the same cross region; taking an intersection area in fig. 8 as an example, the first coil is a thickened portion coil, and the second coil is an un-thickened portion coil. By the formula:

wherein n is the number of cross areas before the crack appears, and the circumferential angle of the crack can be obtained; when the crack axially expands, the induced voltage of the right coil in the crossing area where the crack is located is changed, and then the induced voltage of the left coil is changed, so that the length of the crack is preliminarily judged, and then the length is accurately judged according to the property that the induced voltage change of the coil linearly increases along with the expansion of the crack in the monitoring area of the coil; when the crack radially expands, the induced voltage variation of the coil in the intersection region where the crack is located increases as the radial expansion length increases, so that the degree of radial expansion of the crack can be determined.

As shown in fig. 8a, a schematic diagram of the shape of the conventional coil is shown, and fig. 8b is a schematic diagram of the shape of the trapezoidal coil of the present invention, as can be seen from a comparison between fig. 8a and fig. 8b, the receiving coil adopts the trapezoidal coil instead of the triangular coil, so that the monitoring area at the corner is increased, the defects that the corner of the triangular coil cannot accurately identify the circumferential position of a crack and the induced voltage variation does not change obviously along with the crack extension are overcome, and the circumferential identification capability and the radial and axial extension tracking capabilities of the flexible thin film are improved.

The embodiments in the present description are described in a progressive manner, each embodiment focuses on differences from other embodiments, and the same and similar parts among the embodiments are referred to each other. The device disclosed by the embodiment corresponds to the method disclosed by the embodiment, so that the description is simple, and the relevant points can be referred to the method part for description.

The previous description of the disclosed embodiments is provided to enable any person skilled in the art to make or use the present invention. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the generic principles defined herein may be applied to other embodiments without departing from the spirit or scope of the invention. Thus, the present invention is not intended to be limited to the embodiments shown herein but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.