Flexible attached conductive grating sensor for online detection of fatigue cracks and crack detection system
Through the three-layer composite structure and conductive channel design of flexible attached conductive grille sensor, the integration problem of existing potential/resistance sensors on complex structural parts is solved, and the monitoring of crack length, direction and expansion path is achieved, reducing cost and accuracy requirements.
Patent Information
- Application Number
- CN202510401680.6
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2025-04-01
- Publication Date
- 2025-07-11
AI Technical Summary
The existing potential/resistance method crack monitoring sensors are difficult to integrate on complex structural parts, and can only monitor the length and direction of the crack, and cannot determine the crack propagation path, and require reference models and high-precision circuits.
A flexible attached conductive grille sensor is designed, adopting a three-layer composite structure, including a flexible insulating support layer, a conductive channel layer and a protection and signal transmission layer. The crack length and direction are monitored through the upper and lower double-layer orthogonal conductive channels, and the crack expansion path is judged by the Arduino UNO upper computer.
It enables easy integration on complex structural parts, enables the determination of crack length, direction and expansion path, reduces cost and accuracy requirements, is not affected by the conductive properties of the measured material, and does not require a specific reference model.
Smart Images
Figure CN120293190A_ABST
Abstract
Description
Technical Field
[0001] The present invention belongs to the technical field of real-time monitoring of fatigue cracks in engineering load-bearing structural members. Specifically, it relates to a flexible attached conductive grid sensor for online detection of fatigue cracks and a crack detection system. Background Art
[0002] With the development of aviation technology and the application of new materials and new processes, the structures of aircraft and engine load-bearing components tend to be increasingly complex. In addition, the improvement of equipment performance, the extension of service life, and the diversification and integration of service tasks have all added uncertainties to flight safety management. In order to cope with the new challenges of safety and reliability, structural health monitoring technology has gradually developed and been applied to the use and maintenance of high-reliability equipment such as aircraft and engines. While ensuring structural safety, it reduces maintenance costs and improves economy. The fatigue crack online quantitative monitoring sensor is an important part of the structural health monitoring system. Developing sensors that are easy to integrate with the structure, have high sensitivity, and can reliably serve in harsh environments is the focus of research on damage tolerance design based on structural health monitoring technology.
[0003] According to different damage monitoring principles, sensors that can be applied to the structural health monitoring system include piezoelectric sensors, fiber optic sensors, eddy current sensors, potential / resistance sensors, etc. The potential / resistance method monitoring technology has great application prospects in the field of crack monitoring of aircraft and engine structures due to its advantages such as simple system, easy signal processing, and easy integration with the structure, and has become an important branch of structural health monitoring technology research.
[0004] The principle of monitoring cracks by the potential / resistance method is that the electric field / resistance of a conductive structure is a function of its geometric shape, especially the crack size. The initiation and propagation of fatigue cracks will cause changes in the electric field / resistance of the structure. By applying a constant current, the changes in the potential / resistance of the structure can be measured.
[0005] According to the relationship between the potential / resistance change and the crack length, the crack length can be indirectly and quantitatively inferred through the measured potential / resistance change. Some sensors based on the potential method need to be integrated into structural components through processes such as PECVD. The process is relatively complex, the processing difficulty is large, and the cost is high, making it difficult to apply to structural components with complex configurations. Some can detect the length and direction of cracks, but cannot determine the crack propagation process, such as the strip resistance encoded crack sensor, as Figure 1 shown.
[0006] There are some deficiencies in directly monitoring cracks using the potential / resistance method: 1) The structure to be measured must be conductive; 2) A reference model of the quantitative relationship between the potential / resistance change and crack length of the structure needs to be obtained through reference experiments or theoretical derivations. During the crack monitoring process, the circuit for measuring the potential / resistance change must be exactly the same as that of the reference model, which greatly increases the operation difficulty and accuracy requirements of the monitoring system. This reference model can only be applied to the crack monitoring of specific structures; 3) Only the crack length and direction can be obtained, and the crack propagation path cannot be determined. Summary of the Invention
[0007] To overcome the deficiencies of the traditional potential / resistance method for indirectly monitoring crack length, the present invention proposes a flexible attached conductive grid sensor and a crack detection system for online detection of fatigue cracks. This sensor can not only determine the crack length and direction but also determine the crack propagation path based on the historical information detected by the sensor.
[0008] The present invention is achieved through the following technical solutions:
[0009] A flexible attached conductive grid sensor for online detection of fatigue cracks:
[0010] The flexible attached conductive grid sensor has a three-layer composite structure;
[0011] The bottom layer is a flexible insulating support layer, which is used to support the middle layer and the top layer, adheres to the surface of the material to be measured through an adhesive, and transmits the stress and strain of the material to be measured, so that the flexible attached conductive grid sensor has the characteristic of accompanying damage;
[0012] The middle layer is a conductive channel layer, which is composed of multiple conductive channels arranged in a specific geometric shape according to the morphology and propagation direction of the fatigue cracks to be monitored;
[0013] The top layer is a protection and signal transmission layer, which is used to protect the conductive channel layer, prevent external physical damage, chemical corrosion, and moisture erosion, integrates an Arduino UNO upper computer to collect the electrical signals of the conductive channel layer, and transmits the electrical signals to an external signal acquisition and processing module to perform real-time analysis and processing of the crack information and achieve online quantitative detection of fatigue cracks.
[0014] Furthermore, the bottom layer is insulated from the metal surface to avoid the influence of external interference on the crack detection signal.
[0015] Furthermore, the adhesive is a high-strength and high-bonding epoxy resin glue to ensure no relative displacement or looseness between the flexible attached conductive grid sensor and the material to be measured.
[0016] Further, the conductive channels with a specific geometry are upper and lower double-layer orthogonal conductive channels, realizing quantitative monitoring of crack length in two dimensions.
[0017] Further, when the crack front passes through the conductive channel layer, based on the fracture characteristics of the material and the accompanying damage effect of the flexible attached conductive grid sensor, the conductive channels are affected and their electrical properties change, thereby judging the crack propagation direction.
[0018] Further, when the fatigue crack does not pass through the conductive channels corresponding to the flexible attached conductive grid sensor, the conductive channels can be normally powered on, and the output level measured by the corresponding pin of the Arduino host computer is high. When the crack passes through and damages the conductive channels through the accompanying damage characteristics, the channels cannot conduct electricity and the output level is low. By analyzing the output level, it is judged whether the crack passes through the corresponding conductive channels.
[0019] Further, during the operation of the sensor, the crack propagation will change the level value of the conductive channels measured by the Arduino UNO host computer. By analyzing the output level, the propagation path of the fatigue crack front is obtained, and the crack propagation length is calculated according to the spacing of the conductive channels.
[0020] A crack detection system for a flexible attached conductive grid sensor for online detection of fatigue cracks:
[0021] The crack detection system includes a fatigue testing machine, a signal acquisition and processing module, an optical crack observation module, and a specimen integrated with a sensor;
[0022] The fatigue testing machine is used to simulate the alternating stress that the specimen bears during actual use, prompting the specimen to generate fatigue cracks;
[0023] The signal acquisition and processing module collects the signals of the sensor, processes and analyzes these signals, and converts the level changes detected by the sensor into a data form that can be recognized and analyzed by a computer or other data processing devices;
[0024] The optical crack observation module is used to directly observe the generation and propagation of fatigue cracks on the surface of the specimen, and mutually verify with the results detected by the sensor;
[0025] The specimen integrated with the sensor is the test material with a flexible attached conductive grid sensor attached to its surface.
[0026] Further, after the flexible attached conductive grid sensor is attached to the test material without cracks, first check whether the sensor is intact through self-check. If the electrical levels of all conductive channels measured by the Arduino UNO host computer are high, it means the sensor is intact; if there is a low level, it means that there is a damaged conductive channel in the sensor.
[0027] Further, the optical observation crack module uses a digital microscope to observe the fatigue crack propagation in real time. If it is difficult to accurately observe the crack front on the surface of the specimen on the side where the sensor is attached, the crack propagation on the surface of the other side of the specimen is observed through the digital microscope.
[0028] Advantages of the present invention
[0029] When the sensor designed by the present invention is in use, it is not affected by the conductivity of the measured material, does not require the establishment of a reference model, and has the advantages of being easy to integrate with the structure, light in weight, thin in thickness, not affecting the force of the measured material, and low in cost; based on the FPCB technology, multi-channel conductive channels with different geometric forms are arranged on the flexible insulating substrate, and the upper and lower double-layer orthogonal conductive channels are used to monitor the crack length in two dimensions. It is attached to the surface of the measured material through epoxy resin adhesive, which can not only determine the crack length and direction, but also determine the crack propagation path based on historical information, and can better cope with the problem of the change of the crack propagation direction.
[0030] The present invention is based on the detection of the open circuit of the conductive channel. When the fatigue crack front passes through the conductive channel of the sensor, the channel is opened due to its accompanying damage characteristics. The crack length is judged according to the opening and closing of different conductive channels. Each conductive channel is connected to the Arduino UNO host computer, and whether the crack passes through is determined by detecting the change of the channel level (high level indicates not broken, low level indicates broken), and then the crack propagation path is judged. Description of the drawings
[0031] Figure 1 It is a bar resistor coded crack sensor.
[0032] Figure 2 It is a schematic structural diagram of the flexible attachment type conductive grid sensor of the present invention.
[0033] Figure 3 It is a schematic circuit diagram of the connection between the conductive channel of the sensor and the Arduino host computer.
[0034] Figure 4 It is for crack propagation display and microscopic observation of crack propagation, where (a) the fatigue crack passes through the first conductive channel parallel to the tensile direction, and (b) the fatigue crack passes through the 3rd conductive channel parallel to the tensile direction.
[0035] Figure 5 It is an example diagram of the change of the fatigue crack propagation direction. Detailed implementation manners
[0036] The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts shall fall within the protection scope of the present invention.
[0037] The experimental methods used in the following embodiments are all conventional methods unless otherwise specified. The materials, reagents, methods and instruments used are all conventional materials, reagents, methods and instruments in the art unless otherwise specified, and those skilled in the art can obtain them through commercial channels.
[0038] A flexible attached conductive grid sensor for online detection of fatigue cracks:
[0039] The flexible attached conductive grid sensor has a three-layer composite structure;
[0040] The bottom layer is a flexible insulating support layer (flexible insulating substrate), which is used to support the middle layer and the top layer, adheres to the surface of the measured material through an adhesive, transmits the stress and strain of the measured material, and enables the flexible attached conductive grid sensor to have the characteristic of accompanying damage; the bottom layer is insulated from the metal surface to avoid the influence of external interference on the crack detection signal. The adhesive is a high-strength and high-adhesion epoxy resin glue to ensure no relative displacement or looseness between the flexible attached conductive grid sensor and the measured material.
[0041] The middle layer is a conductive channel layer. According to the shape and propagation direction of the fatigue crack to be monitored, the attached crack monitoring sensor based on FPCB technology arranges multi-channel conductive channels with different geometric forms on the flexible insulating substrate. When the leading edge of the fatigue crack of the measured material passes through the conductive channels of the sensor, due to the characteristic of accompanying damage of the sensor attached to the material surface, the corresponding conductive channels of the sensor are opened. According to the opening and closing of different conductive channels of the sensor, the length of the crack can be quantitatively judged;
[0042] In the embodiment, as Figure 2 shown, the conductive channels are set as upper and lower double-layer orthogonal conductive channels to realize quantitative monitoring of the crack length in two dimensions.
[0043] The top layer is a protection and signal transmission layer, which is used to protect the conductive channel layer, prevent external physical damage, chemical corrosion and moisture erosion, integrates an Arduino UNO host computer to collect the electrical signals of the conductive channel layer, and transmits the electrical signals to an external signal acquisition and processing module to perform real-time analysis and processing on the crack information, so as to realize online quantitative detection of fatigue cracks.
[0044] The crack propagation visualization software Crack Monitor uses the Arduino UNO development board as the host computer, which can realize the acquisition and processing of signals at the back end of the sensor and the visual display of the crack propagation situation. The schematic diagram of the connection circuit between each conductive channel of the sensor and the Arduino UNO host computer is as shown in Figure 3 shown
[0045] When the crack front passes through the conductive channel layer, based on the fracture characteristics of the material and the accompanying damage effect of the flexible attached conductive grid sensor, the conductive channel is affected and its electrical properties change, so as to judge the propagation direction of the crack.
[0046] When the fatigue crack does not pass through the conductive channel corresponding to the flexible attached conductive grid sensor, the conductive channel can be normally powered on, and the output level measured by the corresponding pin of the Arduino host computer is high level (the serial communication data is 1). When the crack passes through and destroys the conductive channel through the accompanying damage characteristics, this channel cannot conduct electricity, and the output level is low level (the serial communication data is 0). By analyzing the output level, it is judged whether the crack passes through the corresponding conductive channel.
[0047] During the working process of the sensor, the crack propagation will change the conductive channel level value measured by the Arduino UNO host computer. By analyzing the output level, the propagation path of the fatigue crack front is obtained, and the crack propagation length is calculated according to the spacing of the conductive channels.
[0048] A crack detection system for a flexible attached conductive grid sensor for online detection of fatigue cracks:
[0049] The crack detection system includes a fatigue testing machine, a signal acquisition and processing module, an optical crack observation module, and a specimen integrated with a sensor;
[0050] The fatigue testing machine is used to simulate the alternating stress borne by the specimen during actual use, and to cause fatigue cracks in the specimen;
[0051] The signal acquisition and processing module collects the signals of the sensor, processes and analyzes these signals, and converts the detected level changes of the sensor into a data form that can be recognized and analyzed by a computer or other data processing devices;
[0052] The optical crack observation module is used to directly observe the generation and propagation of fatigue cracks on the surface of the specimen, and mutually verify with the results detected by the sensor to improve the accuracy and reliability of crack detection;
[0053] The specimen integrated with the sensor is the test material with a flexible attached conductive grid sensor attached to the surface of the specimen.
[0054] After the flexible attached conductive grid sensor is attached to the material under test without cracks, first perform a self-check to see if the sensor is intact. If the average electrical level of the conductive channels measured by the Arduino UNO host computer is high, it indicates that the sensor is intact; if there is a low level, it means that there is damage to the conductive channels of the sensor.
[0055] In the actual experiment, first, select an epoxy resin adhesive with strong adhesion and good curing effect, and attach the sensor to the stress concentration area of the specimen. Install the specimen on the material testing machine, and set the digital microscope to observe the fatigue crack propagation in real time. If it is difficult to accurately observe the crack front on the surface of the specimen on the side where the sensor is attached, then observe the crack propagation on the other side of the specimen through the digital microscope. At this time, it is assumed that the crack propagation on the front and back surfaces of the specimen is the same. Connect the sensor to the Arduino UNO host computer and connect the serial port to communicate with the software. Then turn on the material testing machine to apply a load to the specimen, and observe the crack propagation through the digital microscope until the specimen breaks.
[0056] The fatigue crack front of the specimen passes through the first conductive channel of the attached sensor that is parallel to the tensile direction. At this time, the conductive channel of the sensor is broken due to accompanying damage, and the output level of the pin of the Arduino host computer connected to this channel is low (the serial communication data is 0). The crack propagation area indicates that the crack has propagated 1 mm, as Figure 4 (a) shows. At this time, draw the crack propagation area through the software and draw it in red. When the crack propagates through different conductive channels of the sensor in sequence, correctly calculate the crack length and display the crack propagation situation.
[0057] When the propagation direction of the crack front changes, such as when the fatigue crack propagates upward after passing through the 6th longitudinal channel of the sensor, the corresponding crack propagation is shown as Figure 5 shown. At the same time, the corresponding square area is filled with red, indicating that the crack front has propagated to this area, and the crack propagation length is displayed as 7 mm. Thus, it can be seen that this sensor can detect the length and propagation direction of the crack.
[0058] The above has introduced in detail a flexible attached conductive grid sensor and a crack detection system for online detection of fatigue cracks proposed by the present invention, and has elaborated on the principle and implementation method of the present invention. The description of the above embodiments is only used to help understand the method and its core idea of the present invention; at the same time, for those of ordinary skill in the art, according to the idea of the present invention, there will be changes in the specific implementation method and application scope. In summary, the content of this specification should not be construed as a limitation to the present invention.
Claims
1. A flexible attached conductive grid sensor for online detection of fatigue cracks, characterized in that: The flexible attached conductive grid sensor has a three-layer composite structure; The bottom layer is a flexible insulating support layer, which is used to support the middle layer and the top layer, adheres to the surface of the material to be measured through an adhesive, transmits the stress and strain of the material to be measured, and enables the flexible attached conductive grid sensor to have the characteristic of accompanying damage; The middle layer is a conductive channel layer, which is composed of a plurality of conductive channels in a specific geometric shape according to the morphology and propagation direction of the fatigue crack to be monitored; The top layer is a protection and signal transmission layer, which is used to protect the conductive channel layer, prevent external physical damage, chemical corrosion and moisture erosion, integrates an Arduino UNO host computer to collect the electrical signals of the conductive channel layer, transmits the electrical signals to an external signal acquisition and processing module, and performs real-time analysis and processing on the crack information to realize online quantitative detection of fatigue cracks.
2. The flexible attached conductive grid sensor according to claim 1, characterized in that: The bottom layer is insulated from the metal surface to avoid the influence of external interference on the crack detection signal.
3. The flexible attached conductive grid sensor according to claim 2, characterized in that: The adhesive is a high-strength and high-bonding epoxy resin glue to ensure no relative displacement or looseness between the flexible attached conductive grid sensor and the material to be measured.
4. The flexible attached conductive grid sensor according to claim 3, characterized in that: The conductive channels in the specific geometric shape are upper and lower double-layer orthogonal conductive channels, which realize quantitative monitoring of the crack length in two dimensions.
5. The flexible attached conductive grid sensor according to claim 4, characterized in that: When the crack front passes through the conductive channel layer, based on the fracture characteristics of the material and the accompanying damage effect of the flexible attached conductive grid sensor, the conductive channels are affected and their electrical properties are changed, so as to judge the propagation direction of the crack.
6. The flexible attached conductive grid sensor according to claim 5, characterized in that: When the fatigue crack does not pass through the corresponding conductive channel of the flexible attached conductive grid sensor, the conductive channel can be normally energized, and the output level measured by the corresponding pin of the Arduino host computer is high. When the crack passes through and damages the conductive channel through the accompanying damage characteristic, the channel cannot conduct electricity and the output level is low. Whether the crack passes through the corresponding conductive channel is judged by analyzing the output level.
7. The flexible attached conductive grid sensor according to claim 6, characterized in that: During the working process of the sensor, the crack propagation will change the electrical level value of the conductive channel measured by the Arduino UNO host computer. The propagation path of the fatigue crack front is obtained by analyzing the output level, and the crack propagation length is calculated according to the spacing of the conductive channels.
8. A crack detection system for a flexible attached conductive grid sensor for online detection of fatigue cracks according to any one of claims 1 to 7, characterized in that: The crack detection system includes a fatigue testing machine, a signal acquisition and processing module, an optical crack observation module, and a specimen integrated with the sensor; The fatigue testing machine is used to simulate the alternating stress endured by the test piece during actual use, and to prompt the test piece to generate fatigue cracks; The signal acquisition and processing module collects the signals from the sensors, processes and analyzes these signals, and converts the detected level changes of the sensors into a data form that can be recognized and analyzed by a computer or other data processing devices; The optical crack observation module is used to directly observe the generation and propagation of fatigue cracks on the surface of the test piece, and mutually verify the results detected by the sensors; The test piece integrated with sensors is the material under test with a flexible attached conductive grid sensor attached to its surface.
9. The crack detection system according to claim 8, wherein: After the flexible attached conductive grid sensor is attached to the material under test without cracks, first check whether the sensor is intact through self-check. If the electrical levels of all conductive channels measured by the Arduino UNO host computer are high, it indicates that the sensor is intact; if there is a low level, it indicates that there is a damaged conductive channel in the sensor.
10. The crack detection system according to claim 9, wherein: The optical crack observation module uses a digital microscope to observe the propagation of fatigue cracks in real time. If it is difficult to accurately observe the crack front on the surface of the test piece on the side where the sensor is attached, the digital microscope is used to observe the propagation of cracks on the other side surface of the test piece.