A crack propagation testing device and method

Abstract

The application discloses a crack propagation testing device and method, which comprises a crack propagation meter, a parallel resistance R1, a series resistance R2 and a strain gauge; the crack propagation meter is connected with the strain gauge in a 1 / 4 bridge mode, the series resistance R2 is connected in series between the crack propagation meter and the strain gauge, and the parallel resistance R1 is connected in parallel at both ends of the crack propagation meter. The signal can be amplified, the signal output is still maintained after all the silk grids of the crack propagation meter are broken, the crack propagation meter can be tested by using the existing strain measuring instrument on site, and the equipment cost is saved.

Description

Technical Field

[0001] This invention belongs to the field of crack propagation testing, and relates to a crack propagation testing device and method. Background Technology

[0002] Infrastructure projects such as highways, bridges, and tunnels generally cannot avoid developing cracks during long-term service. Fatigue loads can induce small cracks in the foundation of highway infrastructure. Initially, these cracks are usually insufficient to affect the overall safety of the infrastructure. However, with prolonged fatigue loading and the influence of environmental factors such as wind and rain erosion, these small cracks will gradually propagate. Once the cracks have expanded to a certain extent, they can cause large-scale structural damage to the infrastructure foundation, posing a serious threat to its safe service performance. Therefore, monitoring the crack propagation status of highway infrastructure is one of the key tasks in ensuring its safe service.

[0003] The mainstream technologies in the field of crack testing can be divided into radiographic and ultrasonic testing, imaging methods, and electrical testing methods. Radiographic and ultrasonic crack testing technologies are mainly used for flaw detection. Imaging methods are easily affected by environmental factors such as dust, vibration, and noise at the testing site, making them unsuitable for long-term monitoring. Electrical testing methods generally use crack propagation meters for long-term crack monitoring. The main structure of this method's testing element is a set of parallel resistance wire grids. After being glued and installed, as the crack propagates, the wire grids break one by one along a certain direction, resulting in a change in resistance. By real-time detection of the crack propagation meter's resistance, the length and rate of crack propagation can be deduced based on information such as the wire grid spacing and the time points of resistance changes. However, it still has the following shortcomings:

[0004] When the crack propagation meter first shows a wire grid breakage phenomenon, the resistance change is too small, and the initiation signal of crack propagation is easily masked by signal noise and cannot be identified, which can easily lead to misjudgment of the crack propagation initiation time.

[0005] After all the wire grids of the crack propagation meter break, an open circuit is formed, resulting in an excessively large step change in resistance caused by the last broken wire grid, which exceeds the instrument's measurement range.

[0006] The testing sites of infrastructure generally do not have high-precision and high-stability resistance measurement equipment. Real-time monitoring of the resistance of crack propagation meters requires additional testing equipment, which is too costly and lacks engineering practicality. Summary of the Invention

[0007] The purpose of this invention is to overcome the shortcomings of the prior art, such as the inability to identify the starting signal, the exceeding of the instrument's range after all the crack propagation gauge wires break, and the need for additional testing equipment. This invention provides a crack propagation testing device and method that can amplify the signal and ensure that the signal output is maintained even after all the crack propagation gauge wires break. It can also use existing strain measurement instruments on site to test the crack propagation gauge, thus saving equipment costs.

[0008] To achieve the above objectives, the present invention employs the following technical solution:

[0009] A crack propagation testing device includes a crack propagation meter, a parallel resistor R1, a series resistor R2, and a strain gauge;

[0010] The crack propagation gauge is connected to the strain gauge in a 1 / 4 bridge configuration. A series resistor R2 is connected in series between the crack propagation gauge and the strain gauge, and a parallel resistor R1 is connected in parallel across the crack propagation gauge.

[0011] Preferably, when the strain gauge channel bridge resistance is 120Ω, in order to keep ε within 6000με, the parallel resistor R1 of the crack propagation meter has a minimum resistance of 1Ω and a maximum resistance not exceeding 60% of the initial resistance of the crack propagation meter; when the strain gauge channel bridge resistance is 350Ω, the parallel resistor R1 has a minimum resistance of 1Ω and a maximum resistance not exceeding the initial resistance of the crack propagation meter.

[0012] Preferably, the resistance value of the series resistor R2 is equal to the resistance value of the strain gauge channel bridge.

[0013] Preferably, the series resistor R2 is a resistance strain gauge.

[0014] Preferably, the crack propagation gauge is connected to the strain gauge using a three-wire system.

[0015] Preferably, both the parallel resistor R1 and the series resistor R2 are mounted on the PCB board, which is equipped with a crack propagation meter interface, a strain gauge channel interface, a parallel resistor interface, and a series resistor interface.

[0016] Preferably, the crack propagation meter is a trapezoidal parallel wire grid crack propagation meter or an equal-length parallel wire grid crack propagation meter.

[0017] A crack propagation testing method for the aforementioned device involves mounting a crack propagation meter on a substrate, connecting the crack propagation meter to a parallel resistor R1, a series resistor R2, and a strain gauge. With the substrate unaffected by external force, the wire grids are cut sequentially from one side of the crack propagation meter. The strain gauge records the strain step data after each wire grid fracture, forming standard wire grid fracture data for the tested crack propagation meter. When performing actual crack propagation tests using this crack propagation meter, the measured strain data is compared with the standard wire grid fracture data to determine the time point of crack propagation. The crack propagation length and propagation speed are calculated by combining the number of wire grid fractures, the wire grid spacing, and the wire grid fracture interval.

[0018] Preferably, during the fracture process of the crack propagation gauge wire grid, the relationship between the resistance change and the strain output of the strain gauge is as follows:

[0019]

[0020] In the formula, ΔR is the change in resistance of the test circuit during the crack propagation gauge wire grid fracture process; R is the bridge resistance of the 1 / 4 bridge test channel of the strain gauge; ε is the output strain of the strain gauge; K 仪 Set the sensitivity coefficient for the strain gauge.

[0021] Preferably, when generating standard wire grid fracture data, the sampling frequency of the strain gauge is 5-10Hz; during actual crack propagation testing, the sampling frequency of the strain gauge is not less than 10Hz.

[0022] Compared with the prior art, the present invention has the following beneficial effects:

[0023] This invention converts the resistance signal of the test circuit into a strain signal, amplifying the signal and making the initial signal easy to identify. A standard resistor is connected in parallel to the crack propagation gauge, ensuring that even after the entire wire grid breaks, the change in the resistance of the test circuit remains within the strain gauge's range, and the total strain is controlled within the range of the test channel, maintaining the output value. Directly connecting the crack propagation gauge to the strain gauge channel with a 1 / 4 bridge would cause the bridge circuit to become unbalanced, making testing impossible. Therefore, a standard resistor is connected in series with the crack propagation gauge to ensure the bridge circuit is balanced after connecting the crack propagation gauge to the strain gauge channel. Since strain testing instruments are generally available at testing sites for infrastructure such as highways, bridges, and tunnels, the testing method proposed in this invention can utilize existing strain measurement instruments to test the crack propagation gauge, saving equipment costs. Crack testing is not limited by the type of material being tested, making it highly adaptable.

[0024] Furthermore, the test signal line connected to the strain gauge via a 1 / 4 bridge adopts a three-wire system to eliminate measurement errors caused by wire resistance.

[0025] Furthermore, integrating the circuitry onto the PCB board facilitates rapid device assembly and improves testing efficiency. Attached Figure Description

[0026] Figure 1 This is a schematic diagram of the crack propagation testing device of the present invention;

[0027] Figure 2 This is a schematic diagram of the wiring PCB board of the crack propagation testing device of the present invention;

[0028] Figure 3 This is a schematic diagram of the trapezoidal parallel wire grid crack propagation meter structure of the present invention;

[0029] Figure 4 This is a schematic diagram of the equal-length parallel wire grid crack propagation meter structure of the present invention;

[0030] Figure 5 This is a step diagram of the fracture strain of the trapezoidal parallel wire grid crack propagation meter of the present invention.

[0031] Figure 6 This is a step diagram of the fracture strain of the equal-length parallel wire grid crack propagation meter of the present invention.

[0032] Figure 7 This is a schematic diagram of the tensile cracking test of the present invention;

[0033] Figure 8 The strain step diagram of the actual test of the trapezoidal parallel wire grid crack propagation meter of the present invention is shown.

[0034] Wherein: 1-Crack propagation gauge; 2-Strain gauge; 3-Crack propagation gauge interface; 4-Strain gauge channel interface; 5-Parallel resistor interface; 6-Series resistor interface; 7-PCB board; 8-Standard crack specimen. Detailed Implementation

[0035] The technical solutions of the present invention will be clearly and completely described below with reference to the accompanying drawings of the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without creative effort are within the scope of protection of the present invention.

[0036] It should be noted that the terms “front,” “back,” “left,” “right,” “up,” and “down” used in the following description refer to the directions shown in the attached diagram, while the terms “inside” and “outside” refer to the directions toward or away from the geometric center of a specific component, respectively.

[0037] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains. The terminology used herein in the specification of this invention is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention. The term "and / or" as used herein includes any and all combinations of one or more of the associated listed items.

[0038] like Figure 1 As shown, the crack propagation testing device of the present invention includes a crack propagation meter 1, a parallel resistor R1, a series resistor R2, and a strain gauge 2.

[0039] The initial resistance of crack propagation gauge 1 is typically 3Ω to 8Ω. The standard resistance of the 1 / 4 bridge strain gauge channel in a conventional strain gauge 2 is 120Ω or 350Ω. Directly connecting crack propagation gauge 1 to the strain gauge 2 channel with a 1 / 4 bridge connection will cause the bridge circuit to become unbalanced, making testing impossible. To ensure bridge circuit balance after connecting crack propagation gauge 1 to the strain gauge 2 channel, a standard resistor, R2, needs to be connected in series with crack propagation gauge 1. This ensures the overall resistance of the test circuit reaches or approaches the bridge circuit resistance (typically 120Ω or 350Ω). Furthermore, crack propagation gauge 1 typically has 10 to 30 wires. As these wires break one by one during testing, the resistance at both ends of crack propagation gauge 1 gradually increases until an open circuit occurs. This resistance change will exceed the range of strain gauge 2, rendering testing impossible. To ensure that the change in resistance of the test circuit remains within the range of the strain gauge 2 and maintains the output value after the crack propagation meter 1 has completely broken, a standard resistor R1 needs to be connected in parallel to the crack propagation meter 1.

[0040] The resistance values ​​of standard resistors connected in series and parallel in the test circuit are calculated using the following method:

[0041] The relationship between the resistance change and the output strain of strain gauge 2 during the fracture of the wire grid of crack propagation gauge 1 is shown in the following formula.

[0042]

[0043] In the formula,

[0044] ΔR—The change in resistance of the test circuit during the fracture of the crack propagation meter wire grid, in Ω;

[0045] R—Bridge resistance of the 1 / 4 bridge test channel of strain gauge 2, typically 120Ω and 350Ω;

[0046] ε—Strain gauge 2 output strain, με;

[0047] K 仪 — Set the sensitivity coefficient for strain gauge 2, typically 2.00.

[0048] The strain gauge 2 typically has a range of 20000 με. To improve measurement accuracy, 30% of the full scale is used as the limiting strain during the wire mesh fracture process of the crack propagation gauge 1, i.e., 6000 με. When the channel bridge resistance R is 120Ω, to keep ε within 6000 με, the parallel resistance R1 of the crack propagation gauge 1 should have a minimum value of 1Ω and a maximum value not exceeding 60% of the initial resistance of the crack propagation gauge 1. When the channel bridge resistance R is 350Ω, the parallel resistance R1 should have a minimum value of 1Ω and a maximum value not exceeding the initial resistance of the crack propagation gauge 1.

[0049] like Figure 2 As shown, the test circuit can be connected via PCB board 7. The designed PCB board 7 needs to have reserved interfaces for crack propagation gauge 3, strain gauge channel 4, parallel resistor 5, and series resistor 6. The reserved interfaces on PCB board 7 can be designed as pads, with circuits soldered using methods such as soldering or fusion soldering, or connected via connectors. A 120Ω or 350Ω resistance strain gauge can be used as the series resistor R2, mounted on the reserved copper foil area of ​​PCB board 7 and connected in series to the test circuit. To improve the stability of the test circuit and reduce the temperature drift of the resistance, the temperature self-compensation coefficient of the resistance strain gauge is selected as 16 based on the linear expansion coefficient of copper. The initial resistance of crack propagation gauge 1 is generally small (3Ω~8Ω). Crack monitoring in large facilities requires long connecting wires. The resistance of the wires is too high relative to the resistance of the test element, and its impact on the accuracy of the test results cannot be ignored. Therefore, when the test circuit is connected to strain gauge 2 via a 1 / 4 bridge, a three-wire system can be used to eliminate the influence of wire resistance on the test accuracy of crack propagation gauge 1. After the wiring of PCB board 7 is completed, the circuits, interfaces and resistors of PCB board 7 can be encapsulated and protected by means of gluing, covering with film, etc.

[0050] Crack propagation gauge 1 is mounted on a steel substrate, and then connected to a series resistor and a parallel resistor via the designed PCB board 7 circuitry. With the substrate unaffected by external force, the wire mesh of crack propagation gauge 1 is cut one by one from one side using the tip of a tool such as a steel needle or utility knife. Strain gauge 2 records the strain step data after each wire mesh breaks, forming the standard wire mesh fracture data for the tested crack propagation gauge 1. When performing actual crack propagation tests using the corresponding model crack propagation gauge 1, the measured strain data can be compared with the standard wire mesh fracture data to determine the time point of crack propagation. By combining the number of wire mesh breaks, the wire mesh spacing, and the wire mesh breakage interval of crack propagation gauge 1, the length and propagation speed of crack propagation can be quantitatively calculated.

[0051] During the wire grid cutting process, when standard wire grid fracture data is generated, the sampling frequency of strain gauge 2 is 5-10Hz; during actual crack propagation testing, the sampling frequency of strain gauge 2 is not less than 10Hz.

[0052] Example 1:

[0053] Embodiment 1 of this invention describes the wire grid fracture test of a trapezoidal parallel wire grid crack propagation meter. The structure of the trapezoidal parallel wire grid crack propagation meter is as follows: Figure 3 As shown. The crack propagation gauge 1 has an initial resistance of 5Ω and 15 wire grids. During testing, a standard resistor must first be connected in series with the crack propagation gauge 1 to match the resistance of the test circuit bridge of strain gauge 2. Secondly, to ensure that the resistance change in the test circuit caused by wire grid breakage during testing remains within the range of strain gauge 2, a resistor needs to be connected in parallel with the crack propagation gauge 1.

[0054] The strain gauge 21 / 4 bridge channel has a bridge resistance of 350Ω. The series standard resistor is a 350Ω resistance strain gauge with a temperature self-compensation coefficient of 16. The parallel resistor has a resistance range of 1Ω to 5Ω, and a 5Ω color-coded resistor is selected. After the crack propagation gauge's first wire grid completely breaks, the resulting resistance change is 2.5Ω, with a resistance change rate of 0.714%. Because... And K 仪 The typical value is 2.00. The calculated maximum strain after all the wire mesh breaks is 0.357% (3571 με).

[0055] The wiring principle of the test line is as follows Figure 1 As shown, during actual testing, the design... Figure 2 The PCB board 7 shown integrates the connection lines for the crack propagation meter 1. From top to bottom, the PCB board 7 consists of: the connection pad for the crack propagation meter 1, the connection pad for the parallel resistor, the connection pad for the series resistance strain gauge, the strain gauge patch area, and the connection pad for the strain gauge 2. The connection pad for the crack propagation meter 1 is connected to the pads at both ends of the crack propagation meter 1 via soldered wires; the two ends of the parallel color-coded resistor are connected to the circular pads; the series strain gauge is mounted in the patch area and then connected to the test circuit in series using enameled wire; the connection pad for the strain gauge 2 is designed as a three-wire system, connecting the strain gauge 2 in a 1 / 4 bridge configuration.

[0056] To verify the feasibility of the crack propagation meter 1 testing method, the crack propagation meter 1 was glued and mounted onto a steel substrate, and the test circuit was connected. Using the tip of a tool such as a steel needle or a utility knife, starting from one side of the crack propagation meter 1, the wire mesh of the crack propagation meter 1 was cut off one by one, and the strain step data formed after the breakage of each wire mesh was collected. The average strain data at which each step reached stability was calculated, so that the strain step data of each step corresponded one-to-one with each wire mesh of the crack propagation meter 1, such as... Figure 5 As shown, the test results produce clearly identifiable strain step data, and the total strain is consistent with the theoretical calculation results, indicating that the test method is feasible.

[0057] Example 2:

[0058] Embodiment 2 of the present invention describes the wire grid fracture test of an equal-length parallel wire grid crack propagation meter. The structure of the equal-length parallel wire grid crack propagation meter is as follows: Figure 4 As shown, the initial resistance is 3Ω, with 10 wire grids. The strain gauge 21 / 4 bridge channel has a bridge resistance of 120Ω. The series standard resistor is a 120Ω resistance strain gauge with a temperature self-compensation coefficient of 16. The parallel resistor has a resistance range of 1Ω to 1.8Ω, and a 1.5Ω color-coded resistor is selected. After all the wire grids of the crack propagation gauge break, the resulting resistance change is 0.5Ω, and the resistance change rate is 0.417%. Because... And K 仪 The value is typically 2.00. The maximum strain after all the wire mesh breaks is calculated to be 0.208% (2083 με).

[0059] In Example 2, the mounting method and PCB board 7 wire bonding method for the equal-length parallel wire grid crack propagation gauge are consistent with those in Example 1. Using tools such as steel needles and utility knives, the wire grid is cut strip by strip starting from one side of the crack propagation gauge 1. The resulting equal-length parallel wire grid crack propagation gauge wire grid fracture strain step diagram is shown below. Figure 6 As shown, it can be seen that the strain step data output by strain gauge 2 during the fracture process of the crack propagation gauge 1 wire grid shows obvious regularity, and the total strain is consistent with the calculation results.

[0060] Actual tensile testing was conducted on the crack propagation meter 1 in Example 1. The crack propagation meter 1 was attached and installed at the end of the pre-fabricated crack in the standard crack specimen 8, according to... Figure 7 Connect the circuit as shown. After the specimen is installed, turn on the tensile testing machine to perform a tensile crack test. Set the sampling frequency of strain gauge 2 to 10Hz.

[0061] Figure 8 The strain output data of the crack propagation meter 1, mounted on the standard crack specimen 8, during the actual tensile crack test is shown. It can be seen that the pre-existing crack in the standard crack specimen 8 began to propagate after 5 seconds, and all the wire grids broke after 42 seconds. The spacing between adjacent wire grids is 1.78 mm, with a total of 15 wire grids. The maximum test range for crack length is 24.92 mm, therefore the crack propagation rate is 0.67 mm / s.

[0062] It should be noted that, in this document, relational terms such as "first" and "second" are used only to distinguish one entity or operation from another, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Furthermore, the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such process, method, article, or apparatus.

[0063] It should be understood that the above description is for illustrative purposes and not for limitation. Many embodiments and applications beyond the provided examples will be apparent to those skilled in the art upon reading the above description. Therefore, the scope of this patent should not be determined by reference to the above description, but rather by reference to the foregoing claims and the full scope of their equivalents. For purposes of completeness, all articles and references, including patent applications and publications, are incorporated herein by reference. The omission of any aspect of the subject matter disclosed herein in the foregoing claims is not intended as a waiver of that subject matter, nor should it be construed as an indication that the applicant has not considered that subject matter as part of the disclosed inventive subject matter.

Claims

1. A crack propagation testing device, characterized in that, Includes a crack propagation meter (1), a parallel resistor R1, a series resistor R2, and a strain gauge (2); The crack propagation gauge (1) is connected to the strain gauge (2) in a 1 / 4 bridge configuration. A series resistor R2 is connected in series between the crack propagation gauge (1) and the strain gauge (2), and a parallel resistor R1 is connected in parallel across the crack propagation gauge (1).

2. The crack propagation testing device according to claim 1, characterized in that, When the resistance of the strain gauge (2) channel bridge is 120Ω, in order to keep ε within 6000με, the minimum resistance of the parallel resistor R1 of the crack propagation meter (1) is 1Ω, and the maximum resistance does not exceed 60% of the initial resistance of the crack propagation meter (1); when the resistance of the strain gauge (2) channel bridge is 350Ω, the minimum resistance of the parallel resistor R1 is 1Ω, and the maximum resistance does not exceed the initial resistance of the crack propagation meter (1).

3. The crack propagation testing device according to claim 1, characterized in that, The resistance of the series resistor R2 is equal to the resistance of the strain gauge (2) channel bridge.

4. The crack propagation testing device according to claim 1, characterized in that, The series resistor R2 is a resistance strain gauge.

5. The crack propagation testing device according to claim 1, characterized in that, The crack propagation gauge (1) is connected to the strain gauge (2) using a three-wire system.

6. The crack propagation testing device according to claim 1, characterized in that, The parallel resistor R1 and the series resistor R2 are both set on the PCB board (7). The PCB board (7) is provided with a crack propagation meter interface (3), a strain gauge channel interface (4), a parallel resistor interface (5), and a series resistor interface (6).

7. The crack propagation testing device according to claim 1, characterized in that, The crack propagation meter (1) adopts a trapezoidal parallel wire grid crack propagation meter or an equal-length parallel wire grid crack propagation meter.

8. A crack propagation testing method based on the device according to any one of claims 1-7, characterized in that, The crack propagation meter (1) is mounted on the substrate, and then the crack propagation meter (1) is connected to the parallel resistor R1, the series resistor R2 and the strain gauge (2). Under the condition that the substrate is not subjected to external force, the wire grid is cut off one by one from one side of the crack propagation meter (1). The strain gauge (2) records the strain step data after each wire grid breaks, forming the standard wire grid fracture data of the crack propagation meter (1) being tested. When using the crack propagation meter (1) to perform actual crack propagation test, the measured strain data is compared with the standard wire grid fracture data to determine the time point when the crack propagation occurs. Combined with the number of wire grid breaks, wire grid spacing and wire grid breakage interval of the crack propagation meter (1), the length and propagation speed of crack propagation are calculated.

9. The crack propagation test method according to claim 8, characterized in that, During the fracture process of the crack propagation gauge (1) wire grid, the relationship between the resistance change and the output strain of the strain gauge (2) is as follows: In the formula, ΔR is the change in resistance of the test circuit during the fracture of the wire grid of the crack propagation meter (1); R is the bridge resistance of the 1 / 4 bridge test channel of the strain gauge (2); ε is the output strain of the strain gauge (2); K 仪 Set the sensitivity coefficient for the strain gauge (2).

10. The crack propagation test method according to claim 8, characterized in that, When generating standard wire grid fracture data, the sampling frequency of the strain gauge (2) is 5-10Hz; during actual crack propagation testing, the sampling frequency of the strain gauge (2) is not less than 10Hz.

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