A method for measuring the position, length and angle of surface cracks based on surface waves

Abstract

The invention discloses a method for measuring the position, length and angle of surface cracks based on surface waves, comprising the following steps: S1. Sequentially arrange a pulsed laser probe and a laser vibrometer on the detected surface of the workpiece to be measured, and fix the pulsed laser probe; S2. The pulsed laser probe emits pulsed laser to obtain transmitted wave signals and reflected wave signals; S3. Extract the time of the lowest wave trough of the surface wave reflection signal and the time of the first wave trough of the oscillating part, and simultaneously extract the time corresponding to the wave trough of the oscillating part of the surface wave transmission signal; S4. Calculate the distance between the position where the crack is located and the laser vibrometer probe, the crack length, the distance between the bottom of the crack and the laser vibrometer probe, and the inclination angle α of the surface crack. This method quantitatively detects the position, length and angle of surface cracks generated in important components, evaluates the qualification of the manufactured components, or provides a reference for whether the components in service need to be replaced and how to repair them.

Description

Technical Field

[0001] The present invention relates to the technical field of quantitative non-destructive testing, and specifically refers to a method for measuring the position, length and angle of surface cracks based on surface waves. Background Art

[0002] With the progress of science and the development of industrial production technology, metal components and various high-performance materials are widely used in various fields of life and production. Especially, many major civilian equipment and weaponry have been elevated to the national security strategy level, such as civil airliners, high-speed trains, fighter jets and aero-engines, etc. During the processes of production, processing, assembly and service of these major equipment, micro-cracks often occur on the surfaces of components due to uneven stress. If these surface micro-cracks are not detected and discovered in time, not only will the various performances of the equipment decline, but also when the cracks continue to grow, it may cause the fracture and failure of components, leading to major safety accidents. Therefore, in order to ensure the reliability and safety of the equipment, it is necessary to regularly detect key structural components and timely discover the early micro-cracks in the component structures. Currently, many scholars are committed to researching methods for detecting surface micro-cracks, but most of them focus on studying the relationship between reflected surface waves and relevant parameters of vertical cracks. Regarding the research on transmitted waves, the frequency-domain transmission coefficient is also mostly used to fit and calculate the crack-related parameters.

[0003] In existing research, Wu Rui et al. studied the detection of microcracks at different depths in 6061 aluminum alloy by building a laser ultrasonic detection platform. It was found that at the same laser energy, the oscillation time difference of the reflected echoes of defects at different depths was linearly related to the defect depth. Therefore, through the fitting relationship between the oscillation time difference and the defect depth, quantitative detection of microcracks at different depths was achieved. This method analyzed the time-domain signal characteristics of defect signals from the reflected surface waves. Only by knowing the fitting relationship between the oscillation time difference of the reflected surface waves and the defect depth could the depth of surface microcracks be obtained from the detection data. Deng Jin et al. studied the relationship between the transmission coefficient and the geometric parameters of inclined cracks by analyzing the change in the maximum spectral amplitude of laser ultrasonic transmitted surface waves, and then used the curve fitting method to obtain the fitting equations of the laser ultrasonic surface wave transmission coefficient with depth, width, and angle respectively. This method was a summary of the empirical formula for the relationship between surface crack parameters and the transmission coefficient from the frequency domain. And to obtain the relevant geometric parameters of surface cracks from the detection data, relatively complicated data processing was required. Zhang Zaidong et al. measured the depth of surface-opening cracks at different depths using the surface wave spectrum method by establishing a two-dimensional plane strain finite element model with absorbing boundaries, and then processed the transmitted wave signals to obtain that the crack depth was approximately inversely proportional to the absorption frequency. This method still calculated the crack using the frequency-domain information of the transmitted wave. It not only required prior knowledge of the inverse relationship equation between the crack depth and the absorption frequency, but also the accuracy could only reach the millimeter level. In the detection of surface cracks, other non-destructive testing methods, such as traditional ultrasonic testing, although can detect various forms of crack defects, but need to contact the sample surface with a piezoelectric probe sensor, which is not suitable for detection in special environments such as high temperature, high pressure, and strong corrosion. Ray detection can detect volume-type cracks, but has a poor detection effect on plane cracks, requires self-adjustment of the best ray irradiation direction, and rays are harmful to the human body and the cost is expensive. Eddy current detection uses the eddy current effect and can detect surface and near-surface defects of materials with high detection sensitivity, but can only detect conductive materials. Penetrant testing can detect surface-opening defects of metals and non-metals, but the testing process is cumbersome and the repeatability of detecting defects is poor. Summary of the Invention

[0004] The object of the present invention is to propose a method for measuring the position, length, and angle of surface cracks based on surface waves, quantitatively detecting the position, length, and angle of surface cracks generated during the processing and service of important components, evaluating the qualification of the manufactured components, or providing a reference for whether the components during service need to be replaced and how to be repaired.

[0005] To solve the above technical problems, the technical solution of the present invention is as follows:

[0006] A method for measuring the position, length, and angle of surface cracks based on surface waves, comprising the following steps:

[0007] S1. Sequentially set a pulsed laser probe and a laser vibrometer on the surface to be detected of the workpiece to be measured, and fix the pulsed laser probe.

[0008] S2. The pulsed laser probe emits pulsed laser to excite surface waves on the surface of the workpiece to be measured. Move the laser vibrometer to obtain the transmitted wave signal TR and the reflected wave signal rR respectively.

[0009] S3. Extract the time t of the lowest trough of the surface wave reflection signal R1 and the time t of the first trough of the oscillating part R2 . At the same time, extract the corresponding times t R3 and t R4 of the troughs of the oscillating part of the surface wave transmission signal.

[0010] S4. Using the obtained times t R1 and t R2 , calculate the distance x between the position where the crack is located and the laser vibrometer probe when measuring the reflected wave; using the obtained times t R1 and t R4 , obtain the crack length l; using t R2 , t R3 , t R4 , obtain the distance m between the bottom of the crack and the laser vibrometer probe when receiving the transmitted wave; then combine x, l, and m to obtain the inclination angle α of the surface crack.

[0011] Preferably, in step S2, the methods for obtaining the transmitted wave signal TR and the reflected wave signal rR are as follows: Use the laser vibrometer probe to receive data once. If the first received signal is the transmitted wave signal TR, then the surface crack of the workpiece is between the pulsed laser probe and the laser vibrometer probe; then move the position of the laser vibrometer probe on the surface of the workpiece by a distance of x1 to make the pulsed laser probe and the laser vibrometer probe on the same side of the crack, and receive data once again. At this time, the received signal is the reflected wave signal rR; if the first received signal is the reflected wave signal rR, the position where the crack is located can be calculated according to the time of the reflected echo; then move the position of the laser vibrometer probe on the surface of the workpiece by a distance of x1 to make the crack between the pulsed laser probe and the laser vibrometer probe, and receive data once again. At this time, the received signal is the transmitted wave signal TR.

[0012] Preferably, in step S2, the method for exciting the ultrasonic surface wave is laser point source excitation, specifically, the pulsed laser emitted by the pulsed laser probe is focused into a point source laser through a convex lens, and irradiates on the surface of the workpiece to excite the ultrasonic surface wave.

[0013] Preferably, in the step S2, the excitation method of the surface acoustic wave is line source excitation. Specifically, the pulsed laser emitted by the pulsed laser probe passes through the cylindrical lens and is focused into line source laser, which is irradiated on the surface of the workpiece to excite the surface acoustic wave.

[0014] Preferably, in the step S4, the calculation method of the distance x between the position where the crack is located and the probe of the laser vibrometer is as follows:

[0015]

[0016] Calculate the crack length l, and the calculation method is as follows:

[0017]

[0018] Calculate the distance m between the bottom of the crack and the probe of the laser vibrometer, and the calculation method is as follows:

[0019]

[0020] Calculate the inclination angle α of the surface crack, and the calculation method is as follows:

[0021]

[0022] Where V R is the propagation speed of the surface wave excited by the laser on the surface of the workpiece to be measured; V s is the propagation speed of the shear wave excited by the laser inside the workpiece to be measured; x1 is the moving distance of the probe of the laser vibrometer during two measurements.

[0023] Preferably, the propagation speed V of the surface wave excited by the laser on the surface of the workpiece to be measured R is obtained by looking up the ultrasonic velocity table.

[0024] Preferably, the propagation speed V of the shear wave excited by the laser inside the workpiece to be measured s is obtained by looking up the ultrasonic velocity table.

[0025] Preferably, the laser vibrometer adopts a laser interferometer.

[0026] Preferably, when the length of the surface crack is greater than the wavelength of a surface wave, the surface crack is a surface rectangular inclined crack.

[0027] The present invention has the following characteristics and beneficial effects:

[0028] 1) The present invention is a non-contact measurement, without moving and disassembling the parts to be measured, improving the detection efficiency.

[0029] 2) The present invention only needs two sets of detected data to obtain the position, length and angle information of the crack, featuring a simple method, low cost and fast detection speed.

[0030] 3) The present invention uses transmitted waves and reflected waves to measure the position, length and angle of surface cracks, without the need to know in advance the relative distance between the pulsed laser probe and the laser vibrometer probe.

[0031] 4) The present invention is applicable to the measurement of the position, length and angle of surface cracks at most inclination angles, realizing the quantitative detection of surface cracks.

[0032] 5) Using laser ultrasonic transmitted surface waves to quantitatively measure the position, length and angle of surface crack defects can not only detect whether the equipment parts in service need to be replaced or repaired, but also evaluate the qualification of manufactured parts and optimize the processing technology.

[0033] 6) Using laser ultrasonic transmitted surface waves to quantitatively measure the position, length and angle of surface cracks only requires two positioning detections to obtain the position, length and angle information of the surface cracks, and is applicable to the measurement of the position, length and angle of surface cracks at most inclination angles, with a wide range of applications.

[0034] 7) It is simple to operate, has a fast detection speed and high precision. Moreover, since both the excitation and reception of ultrasonic waves use lasers, non-contact detection can be achieved, and it can be used for in-situ detection during the processing. Description of the Drawings

[0035] In order to more clearly illustrate the technical solutions in the embodiments of the present invention or in the prior art, the following will briefly introduce the drawings required for use in the description of the embodiments or the prior art. Obviously, the following drawings are only some embodiments of the present invention. For those of ordinary skill in the art, without creative efforts, other drawings can be obtained based on these drawings.

[0036] Figure 1 It is a schematic diagram of the detection state of a method for detecting the position, length and angle of surface cracks based on surface waves in an embodiment of the present invention.

[0037] Figure 2 It is a signal diagram of ultrasonic reflected surface waves detected by a laser vibrometer.

[0038] Figure 3 It is a signal diagram of ultrasonic transmitted surface waves detected by a laser vibrometer.

[0039] In the figure, 1 - workpiece to be measured, 2 - surface crack, 3 - pulsed laser probe, 4 - laser vibrometer. Detailed Embodiments

[0040] It should be noted that, without conflict, the embodiments in the present invention and the features in the embodiments can be combined with each other.

[0041] The present invention will be specifically described below in conjunction with the accompanying drawings and embodiments.

[0042] This embodiment is to detect the position, length, and angle of surface cracks generated in manufactured parts and service parts due to uneven stress, so as to be able to detect whether the equipment parts in service need to be replaced and repaired, or to evaluate the qualification of manufactured parts and optimize the processing technology.

[0043] A method for measuring the position, length, and angle of surface cracks based on surface waves proposed by the present invention has the following specific solutions:

[0044] This quantitative measurement method uses a surface crack quantitative measurement device based on laser ultrasonic surface waves, as Figure 1 shown, including a pulsed laser probe 3 and a laser vibrometer 4. The pulsed laser probe 3 is fixed on the detected surface of the workpiece 1 to be measured, and the laser vibrometer can be movably arranged on the detected surface of the workpiece 1.

[0045] The specific steps of this quantitative measurement method are as follows:

[0046] 1) Place the pulsed laser probe 3 and the laser vibrometer 4 at any surface position in the workpiece 1 to be measured, and keep the position of the pulsed laser probe 3 fixed;

[0047] 2) The pulsed laser probe 3 emits pulsed laser to irradiate the surface of the workpiece 1, and surface waves are excited on the surface of the workpiece. The laser vibrometer 4 is used to receive the first detection waveform diagram;

[0048] 3) If the first detection waveform diagram is a transmitted wave waveform diagram, it can be known that the surface crack 2 is between the pulsed laser probe 3 and the laser vibrometer 4. Then move the laser vibrometer 4 by a distance of x1 to make the crack on the same side of the pulsed laser probe 3 and the laser vibrometer 4, and repeat step 2) to receive the detection waveform diagram of the reflected surface wave. If the first detection waveform diagram is a reflected wave waveform diagram, the crack position can be preferentially calculated according to the detection waveform diagram, and then move the laser vibrometer 4 by a distance of x1 to make the crack between the pulsed laser probe 3 and the laser vibrometer 4, and repeat step 2) to receive the detection waveform diagram of the transmitted surface wave;

[0049] 4) Extract the lowest trough time t R1 of the surface wave reflection signal and the first trough time t R2 of the oscillating part, and the trough time t R3 and t R4 of the oscillating part of the surface wave transmission signal;

[0050] 5) Use the obtained time t R1 and t R2 to calculate the distance x between the position of the crack and the probe of the laser vibrometer when measuring the reflected wave; use the obtained time t R1 and t R4 to calculate the crack length l; use t R2 、t R3 、t R4 to calculate the distance m between the bottom of the crack and the probe of the laser vibrometer when receiving the transmitted wave; then, combining the parameters obtained from the above calculations, the inclination angle α of the surface crack can be calculated. The calculation formula is as follows:

[0051]

[0052]

[0053] where V R is the propagation speed of the surface wave excited by the laser on the surface of the workpiece to be measured; V s is the propagation speed of the shear wave excited by the laser inside the workpiece to be measured; x1 is the moving distance of the probe of the laser vibrometer during two measurements.

[0054] The following verifies the effect of the present invention in combination with a specific measurement experiment: Use the above measurement method to detect the surface crack of a medium carbon steel. The steel block is 150 mm long, 50 mm wide, and 15 mm high, and there is a surface crack on its upper surface. Place the steel block on the sample platform, and use the pulse laser probe and the laser vibrometer probe to excite the surface wave and receive the reflected wave signal on the same side of the surface crack of the steel block to obtain the arrival time t R1 and t R2 . Move the probe of the laser vibrometer by a distance x1, and use the pulse laser probe and the laser vibrometer probe to excite the surface wave and receive the transmitted wave signal on both sides of the surface crack of the steel block to obtain the arrival time t R3 and t R4 . Use the obtained t R1 、t R2 、t R3 、t R4 to calculate the position, length, and angle information of the surface crack.

[0055] The measurement results and their errors of the final embodiment are shown in the following table:

[0056] Crack parameter Crack position x (μm) Crack length l (μm) Crack inclination angle α (°) Reference value 3000 900 75 Measured value 3058.92 937.91 77.36 Relative error 1.96％ 4.21％ 3.15％

[0057] As can be seen from the table, the relative error of the quantitative detection of the position, length and angle of the surface crack in the present invention is within 5%, which has high precision. Moreover, this method is a non-contact non-destructive detection, which can realize in-situ detection during the processing or service process of parts, improving the detection efficiency.

[0058] The embodiments of the present invention have been described in detail above in conjunction with the accompanying drawings, but the present invention is not limited to the described embodiments. For those skilled in the art, without departing from the principle and spirit of the present invention, various changes, modifications, substitutions and variations of these embodiments including components still fall within the protection scope of the present invention.

Claims

1. A method for measuring the position, length, and angle of a surface crack based on surface waves, characterized in that, It includes the following steps: S1. Sequentially set a pulsed laser probe and a laser vibrometer on the surface to be detected of the workpiece to be measured, and fix the pulsed laser probe; S2. The pulsed laser probe emits pulsed laser to excite surface waves on the surface of the workpiece to be measured, and respectively obtain a transmitted wave signal TR and a reflected wave signal rR by moving the laser vibrometer; S3. Extract the lowest trough time t of the surface wave reflection signal R1 and the first trough time t of the oscillating part R2 , and at the same time extract the corresponding times t R3 and t R4 ; S4. Use the obtained time t R1 and t R2 , calculate the distance x between the position where the crack is located and the probe of the laser vibrometer when measuring the reflected wave; use the obtained time t R1 and t R4 to obtain the crack length l; use t R2 , t R3 , t R4 to obtain the distance m between the bottom of the crack and the probe of the laser vibrometer when receiving the transmitted wave; then, combining x, l, and m, the inclination angle α of the surface crack can be obtained In the step S4, the calculation method of the distance x between the position where the crack is located and the laser vibrometer probe is as follows: Calculate the crack length l, and the calculation method is as follows: Calculate the distance m between the crack bottom and the laser vibrometer probe, and the calculation method is as follows: Calculate the inclination angle α of the surface crack, and the calculation method is as follows: where V R is the propagation velocity of the surface wave excited by the laser on the surface of the workpiece to be measured; V s is the propagation velocity of the shear wave excited by the laser inside the workpiece to be measured; x1 is the moving distance of the probe of the laser vibrometer during two measurements.

2. The surface crack position, length and angle measurement method based on surface wave according to claim 1, characterized in that, In the step S2, the methods for obtaining the transmitted wave signal TR and the reflected wave signal rR are as follows: Use the laser vibrometer probe to receive data once. If the first received signal is the transmitted wave signal TR, then the surface crack of the workpiece is between the pulsed laser probe and the laser vibrometer probe; then move the position of the laser vibrometer probe on the surface of the workpiece by a distance of x1 to make the pulsed laser probe and the laser vibrometer probe on the same side of the crack, and receive data once again. At this time, the received signal is the reflected wave signal rR; if the first received signal is the reflected wave signal rR, the position where the crack is located can be calculated according to the time of the reflected echo; then move the position of the laser vibrometer probe on the surface of the workpiece by a distance of x1 to make the crack between the pulsed laser probe and the laser vibrometer probe, and receive data once again. At this time, the received signal is the transmitted wave signal TR.

3. The method for measuring the position, length and angle of a surface crack based on surface waves according to claim 1, characterized in that, In the step S2, the excitation method of the ultrasonic surface wave is laser point source excitation. Specifically, the pulsed laser emitted by the pulsed laser probe is focused into a point source laser through a convex lens, and irradiates on the surface of the workpiece to excite the ultrasonic surface wave.

4. The method for measuring the position, length and angle of a surface crack based on surface waves according to claim 1, characterized in that In the step S2, the excitation method of the ultrasonic surface wave is line source excitation. Specifically, the pulsed laser emitted by the pulsed laser probe is focused into a line source laser through a cylindrical lens, and irradiates on the surface of the workpiece to excite the ultrasonic surface wave.

5. The method for measuring the position, length and angle of a surface crack based on surface waves according to claim 1, characterized in that The propagation speed V of the laser-excited surface wave on the surface of the workpiece under test R is obtained by looking up the ultrasonic speed table.

6. The method for measuring the position, length and angle of a surface crack based on surface waves according to claim 1, characterized in that, The propagation velocity V of the laser-excited shear wave inside the workpiece under test s is obtained by referring to the ultrasonic velocity table.

7. The method for measuring the position, length and angle of a surface crack based on surface waves according to claim 1, characterized in that, The laser vibrometer described uses a laser interferometer.

8. The method for measuring the position, length and angle of a surface crack based on surface waves according to claim 1, characterized in that, When the length of the surface crack is greater than the wavelength of a surface wave, the surface crack is a surface rectangular inclined crack.

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