Quantitative detection method of subsurface inclined cracks based on laser ultrasonic transmission surface waves

Abstract

The present invention discloses a quantitative detection method for subsurface inclined cracks based on laser ultrasonic transmission surface waves, which includes the following steps: S1, placing a pulsed laser probe and a laser vibrometer probe on both sides of a subsurface inclined crack of a workpiece; S2, emitting a pulsed laser from the pulsed laser probe to irradiate the workpiece, thereby stimulating an ultrasonic surface wave on the workpiece surface, and using the laser vibrometer to measure a transmission surface wave signal TR of the surface wave passing through the subsurface inclined crack; S3, extracting the first peak t of the transmission surface wave signal TR. R1 , the time corresponding to the second trough t R2 , and the time corresponding to the third trough t R3 ; S4, using the extraction time t R1 , t R2 and t R3 , the subsurface inclined crack length l is calculated. This method effectively improves the detection accuracy of subsurface cracks at different inclination angles, especially the detection accuracy of small inclination angles.

Description

Technical Field

[0001] The present invention relates to the technical field of ultrasonic nondestructive testing, in particular to non-contact measurement and ultrasonic nondestructive testing, and specifically to a quantitative detection method for subsurface inclined cracks based on laser ultrasonic transmission surface waves. Background Art

[0002] With the advancement of industrial modernization, various materials and devices manufactured using advanced precision and ultra-precision machining technologies are widely used in a variety of fields, including aerospace, energy and chemical engineering, transportation, weaponry, and biomedicine. During manufacturing and service, these materials and devices are subject to harsh environments such as high temperature, high pressure, high load, and corrosion, which can easily cause microcracks beneath the surface of the materials. These cracks, which range in size from a few to tens of microns and are approximately a hundred microns below the surface, are known as subsurface cracks. If subsurface cracks are not identified promptly and effectively, and necessary measures are not taken, they may further develop and ultimately lead to fatigue fracture of the device. The presence of subsurface cracks seriously reduces the reliability and stability of materials and devices, and may even lead to highly dangerous and destructive accidents.

[0003] Laser ultrasonic testing is a new nondestructive testing technology that uses laser excitation to generate ultrasonic waves in various modes, enabling the detection of material defects. While sharing the advantages of conventional ultrasonic testing, such as accuracy, reliability, high sensitivity, and low cost, laser ultrasonic testing also offers non-contact, rich wave modes, and a wide bandwidth. This technology demonstrates excellent performance in the nondestructive detection of defects and is attracting increasing attention from experts and scholars. Currently, within the field of laser ultrasonic testing, relatively mature methods exist for the detection and location of subsurface cracks, and many scholars are also conducting research on vertical cracks. However, quantitatively measuring the length of subsurface inclined cracks remains a significant challenge.

[0004] In existing research, Takao Tanaka et al. built a laser ultrasonic detection system based on the confocal Fabry-Perot interferometry method. Using carbon steel samples with internal defects as research objects, they analyzed the transmitted longitudinal and shear wave signals and were able to detect micro-defects with an ultrasonic wave length ratio of approximately 0.07. This system has high sensitivity and resolution, but cannot achieve quantitative detection. Thevar et al. developed a laser ultrasonic system capable of long-distance detection. This system can be used to detect bonding defects in materials with extremely high acoustic attenuation and sub-surface defects in new foam materials, but cannot achieve quantitative detection of sub-surface defects. Coony used an optical scanning method in flaw detection tests to obtain the ultrasonic signal time displacement amplitude signal to detect material defects. However, this method can only detect sub-surface defects and cannot achieve quantitative detection.

[0005] Other existing nondestructive testing methods, such as infrared thermal imaging, use infrared light as a radiation source. Due to defects on the surface of a workpiece or discontinuous internal structures, the heat transferred to deeper layers can vary, causing variations in the surface temperature field. Thermal imaging is then used to detect surface and internal defects. However, this method suffers from low sensitivity and, due to the long wavelength of infrared light, insufficient penetration and a low detection depth. Radiographic testing requires penetrating the metal layer of a material to sensitize the film, but this is accompanied by attenuation. Furthermore, the radiation source for radiographic testing is easily worn out and must be replaced regularly. It is also difficult to carry, highly radioactive, and expensive, and has limitations such as the signal being unable to determine the specific dimensions of the defect, such as its depth and width. Eddy current testing, based on the principle of electromagnetic induction, is commonly used to detect defects in conductive materials. However, due to its significant limitations in detecting materials, weak penetration, and unstable sensitivity, this method is unable to determine the depth and width of defects.

[0006] Laser ultrasonic nondestructive testing is used to achieve quantitative detection of subsurface inclined crack defects, which can not only establish the relationship between crack defect parameters and processing parameters, realize the optimization of processing technology, but also facilitate the subsequent processing to remove subsurface inclined crack defects. However, among the existing nondestructive testing methods, there are few methods that can quantitatively measure the length of subsurface inclined cracks. In order to solve the above technical problems, China Patent Publication Application Number: 202111627531.X, named: A quantitative detection method for subsurface crack length based on laser-excited surface waves, using laser ultrasonic reflected waves to detect subsurface cracks. Its accuracy is good when the inclination angle is about 90°, but as the inclination angle of the subsurface crack decreases, the relative error of its length detection will increase significantly, especially for subsurface cracks with an inclination angle of less than 30°, the relative error of its length detection can even reach more than 30%. Summary of the Invention

[0007] The present invention proposes a quantitative detection method for subsurface inclined cracks based on laser ultrasonic transmission surface waves, which effectively improves the detection accuracy of subsurface cracks at different inclination angles.

[0008] In order to solve the above technical problems, the technical solution of the present invention is:

[0009] A quantitative detection method for subsurface inclined cracks based on laser ultrasonic transmission surface waves comprises the following steps:

[0010] S1. Place the pulsed laser probe and the laser vibrometer probe on both sides of the subsurface inclined crack of the workpiece respectively;

[0011] S2. The pulse laser probe emits a pulse laser to irradiate the workpiece, exciting an ultrasonic surface wave on the workpiece surface. The laser vibrometer is used to measure the transmitted surface wave signal TR of the surface wave passing through the subsurface inclined crack.

[0012] S3, extract the first peak t of the transmitted surface wave signal TR R1 , the time corresponding to the second trough t R2 , and the time corresponding to the third trough t R3 ;

[0013] S4, using the extracted time t R1 , t R2 and t R3 , the subsurface inclined crack length l is calculated as follows:

[0014]

[0015] where v R is the propagation velocity of ultrasonic surface waves on the workpiece surface, v S is the propagation velocity of ultrasonic shear wave in the workpiece, v P is the propagation speed of ultrasonic longitudinal waves in the workpiece.

[0016] Preferably, the ultrasonic surface wave is excited by laser point source excitation, specifically, a pulse laser probe emits a pulse laser which is focused into a point source laser through a convex lens, irradiates the workpiece surface and excites the ultrasonic surface wave.

[0017] Preferably, the ultrasonic surface wave is excited by line source excitation, specifically, a pulse laser probe emits a pulse laser which is focused into a line source laser through a cylindrical lens, irradiated on the workpiece surface and excited to generate ultrasonic surface waves.

[0018] Preferably, the subsurface crack is a rectangular crack, and the linear source laser is parallel to the axis of the subsurface crack.

[0019] Preferably, the propagation speeds of the ultrasonic surface wave, ultrasonic shear wave and ultrasonic longitudinal wave on the workpiece surface need to be found in advance by looking up an ultrasonic velocity table.

[0020] The present invention has the following characteristics and beneficial effects:

[0021] 1. The present invention is simple to operate and has high measurement accuracy. Only one measurement is required to quickly obtain the length information of the sub-surface inclined crack, which reduces the time cost of detection. 2. The present invention is a non-contact measurement, which can realize online detection during the processing process and improve detection efficiency. 3. When the crack inclination angle is 60° or less, the detection accuracy of the present invention is significantly improved compared with the existing sub-surface crack length detection method. 4. It has the characteristics of fast detection speed and high precision, and due to the characteristics of non-contact detection, it can be used for in-situ measurement during the processing process, or for quantitative detection of sub-surface inclined crack length in extreme environments such as high temperature and high pressure. It can be applied to any harsh scene and has a wide range of applications. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the embodiments or the description of the prior art. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative work.

[0023] Figure 1 3 is a schematic diagram of the detection state of the method for quantitatively detecting sub-surface inclined cracks based on laser ultrasonic transmission surface waves according to an embodiment of the present invention.

[0024] Figure 2 This is a graph of the transmitted surface wave ultrasonic signal detected by a laser vibrometer.

[0025] In the figure, 1-workpiece, 2-subsurface inclined crack, 3-pulsed laser probe, 4-laser vibrometer. DETAILED DESCRIPTION

[0026] It should be noted that, in the absence of conflict, the embodiments of the present invention and the features in the embodiments may be combined with each other.

[0027] The present invention will be described in detail below with reference to the accompanying drawings.

[0028] The implementation of the present invention relates to a quantitative detection method for sub-surface inclined cracks based on laser ultrasonic transmission surface waves. This method uses a pulsed laser focused into a point source to generate ultrasonic surface waves inside a workpiece. The surface waves transmit through the sub-surface inclined cracks to generate transmitted surface wave signals. The transmitted wave signals are received by a laser vibrometer and then analyzed to achieve quantitative detection of the length of the sub-surface inclined cracks in the workpiece.

[0029] The specific steps are as follows: Figure 1 As shown:

[0030] A pulsed laser probe 3 and a laser vibrometer probe 4 are placed on both sides of a subsurface inclined crack 2 in a workpiece 1;

[0031] The pulse laser probe 3 emits a pulse laser to irradiate the workpiece 1, exciting an ultrasonic surface wave on the workpiece surface. The laser vibrometer 4 measures the transmitted surface wave signal TR of the surface wave passing through the subsurface inclined crack.

[0032] Extract the first peak t of the transmitted surface wave signal TR R1 , the time corresponding to the second trough t R2 , and the time corresponding to the third trough t R3 ;

[0033] Using the extraction time t R1 , t R2 , t R3 , the subsurface inclined crack length l is calculated. The calculation formula is as follows:

[0034]

[0035] where v R is the propagation velocity of ultrasonic surface wave on the surface of the workpiece to be measured, v S is the propagation speed of ultrasonic shear wave in the workpiece to be measured, v P It is the propagation speed of ultrasonic longitudinal wave in the workpiece to be measured.

[0036] The following is a specific measurement experiment to verify the effectiveness of the present invention: the aforementioned method was used to measure the length of a subsurface inclined crack on an aluminum plate. The plate under test was 100 mm long, 50 mm wide, and 10 mm thick, and had a subsurface inclined crack below the workpiece surface. A pulsed laser probe 3 was placed on one side of the crack to excite the surface wave, and a laser vibrometer probe 4 was placed on the other side of the crack to receive the transmitted surface wave. Figure 1 As shown in the figure, the arrival times of the first and second characteristic troughs of the transmitted surface wave are extracted and used to calculate the subsurface inclined crack length. To verify that the detection accuracy of the present invention is significantly improved compared to the original method when the crack inclination angle is less than 60°, the pulsed laser probe 3 and the laser vibrometer probe 4 are placed on the same side of the crack, and the subsurface inclined crack length is detected using reflected surface waves.

[0037] The measurement results and relative errors of this embodiment are shown in the following table:

[0038]

[0039] As can be seen from the table, the embodiments of the present invention achieve higher accuracy in detecting inclined subsurface cracks. In particular, when the subsurface crack inclination angle is less than 60°, the quantitative detection of the subsurface inclined crack length using this method significantly improves detection accuracy compared to the original detection method. This present invention significantly improves detection of subsurface inclined crack length.

[0040] The embodiments of the present invention are described in detail above with reference to the accompanying drawings, but the present invention is not limited to the described embodiments. It will be apparent to those skilled in the art that various changes, modifications, substitutions, and variations of these embodiments, including components, without departing from the principles and spirit of the present invention are still within the scope of protection of the present invention.

Claims

1. A quantitative detection method for subsurface inclined cracks based on laser ultrasonic transmission surface waves, characterized in that: The steps include: S1. Place the pulsed laser probe and the laser vibrometer probe on both sides of the subsurface inclined crack of the workpiece respectively; S2. The pulse laser probe emits a pulse laser to irradiate the workpiece, exciting an ultrasonic surface wave on the workpiece surface. The laser vibrometer is used to measure the transmitted surface wave signal TR of the surface wave passing through the subsurface inclined crack. S3, extract the first peak t of the transmitted surface wave signal TR R1 , the time corresponding to the second trough t R2 , and the time corresponding to the third trough t R3 ; S4, using the extracted time t R1 , t R2 and t R3 , the subsurface inclined crack length l is calculated as follows: where v R is the propagation velocity of ultrasonic surface waves on the workpiece surface, v S is the propagation velocity of ultrasonic shear wave in the workpiece, v P is the propagation speed of ultrasonic longitudinal waves in the workpiece.

2. The method for quantitative detection of subsurface inclined cracks based on laser ultrasonic transmission surface waves according to claim 1, characterized in that: The ultrasonic surface wave excitation method is laser point source excitation, specifically, a pulse laser probe emits a pulse laser which is focused into a point source laser through a convex lens, irradiates the workpiece surface and excites the ultrasonic surface wave.

3. The method for quantitative detection of subsurface inclined cracks based on laser ultrasonic transmission surface waves according to claim 1, characterized in that: The ultrasonic surface wave excitation method is line source excitation, specifically, a pulse laser probe emits a pulse laser which is focused into a line source laser through a cylindrical lens, irradiated on the workpiece surface and excited to generate ultrasonic surface waves.

4. The method for quantitative detection of subsurface inclined cracks based on laser ultrasonic transmission surface waves according to claim 3, characterized in that: The subsurface crack is a rectangular crack, and the linear source laser is parallel to the axis direction of the subsurface crack.

5. The method for quantitative detection of subsurface inclined cracks based on laser ultrasonic transmission surface waves according to claim 1, characterized in that: The propagation speeds of the ultrasonic surface wave, ultrasonic shear wave, and ultrasonic longitudinal wave on the workpiece surface need to be found in advance by looking up an ultrasonic velocity table.

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