Defect detection method based on fast and slow wave chasing

Abstract

The invention relates to a defect detection method based on fast and slow wave chasing, and the method comprises the following steps: 1, calculating a guided wave frequency dispersion curve of a one-dimensional component, and determining the propagation speeds of guided waves under different frequencies, 2, selecting two excitation frequencies, respectively corresponding to different propagation speeds, recording a fast wave with a fast propagation speed as a fast wave, recording a wave speed as V1, recording a slow wave with a slow propagation speed as a slow wave, 3, when the fast waves reach the meeting point, if the point has defects, the defects are fully expanded under the stretching action of the slow waves, so that the reflection of the fast waves is improved, 4, the excitation time interval of the fast waves and the slow waves is delta t, and 5, the emission time interval is continuously changed, so that the fast waves and the slow waves meet at different positions d, and the reflection of the fast waves and the slow waves is improved. And step 6, extracting the intensity of the fast wave echo signals at different d positions as a (x), obtaining a corresponding relation curve of the echo intensity and the length of the component, and if the curve is obviously increased at a certain position, determining that the position has defects.

Description

Technical Field

[0001] The invention relates to a defect detection method based on fast and slow wave catching up, belonging to the technical field of ultrasonic defect detection. Background Art

[0002] Ultrasonic guided wave technology, due to its strong penetration, high sensitivity, and non-destructive nature, is widely used for nondestructive testing of various structural materials. It is particularly suitable for rapid screening of internal defects in one-dimensional or quasi-one-dimensional components, such as pipes, bars, rails, and guardrails. However, existing ultrasonic testing methods still face numerous technical bottlenecks when detecting tiny cracks, early fatigue damage, or closed defects. These include weak reflection intensity, which is easily masked by background noise. In many engineering applications, defects often appear closed, such as early cracks, cold welds, or partially debonded interfaces. These defects, when unstressed, adhere tightly to the surrounding material and fail to effectively disrupt the propagating ultrasonic waves, resulting in extremely weak reflected waves that are difficult to distinguish from the background waveform. Conventional linear detection methods lack sensitivity and rely primarily on linear propagation mechanisms, such as pulse-echo methods and phased array scanning under single-frequency or narrowband excitation. These methods struggle to focus energy on the target area, especially when the defect location is uncertain or deeply buried, where the echo signal is extremely weak, significantly reducing detection accuracy. Summary of the Invention

[0003] The present invention is aimed at the technical problems existing in the prior art and provides a defect detection method based on fast and slow wave chasing. By exciting two types of guided waves with fast and slow wave speeds at different frequencies and making them meet at a specified position, the first wave first opens the defect, triggering a strong reflection of the second wave that arrives subsequently.

[0004] In order to achieve the above object, the technical solution of the present invention is as follows: a defect detection method based on fast and slow wave catching up, the method comprising the following steps:

[0005] Step 1: Calculate the guided wave dispersion curve of the one-dimensional component to determine the propagation speed of the guided wave at different frequencies.

[0006] When guided waves propagate in a steel pipe, they exhibit three modes: longitudinal expansion, torsion, and bending. The radial, circumferential, and longitudinal displacement fields of the steel pipe are expressed as follows:

[0007] u r =U r (r)cosnθcos(wt+kz)(radial) (1)

[0008] u θ =U θ (r)sinnθcos(wt+kz)(circumferential direction) (2)

[0009] u z=U z (r)cosnθsin(wt+kz)(vertical) (3)

[0010] Where z is the depth of the pile, U r (r), U θ (r) and U z (r) are the amplitudes in radial, circumferential and longitudinal directions respectively. The longitudinal and torsional modes are axisymmetric, while the bending mode is non-axisymmetric.

[0011] For axisymmetric modes, n=0, and for bending modes, n=1, 2, 3, ...,

[0012] Therefore, the longitudinal mode is represented by L(0,m), the torsional mode is represented by T(0,m), and the bending mode is represented by F(n,m), where n=1, 2, 3, ..., and m=1, 2, 3, ...;

[0013] Step 2: Select two excitation frequencies, corresponding to different propagation speeds. The fast wave is recorded as the fast wave with a wave speed of V1, and the slow wave is recorded as the slow wave with a wave speed of V0. The slow wave is emitted first, and then the fast wave is emitted. By adjusting the time interval between the fast and slow waves, the fast wave can catch up with the slow wave at different positions.

[0014] Step 3: When the fast wave reaches the meeting point, if there is a defect at that point, the defect will be fully enlarged under the stretching action of the slow wave, thereby improving the reflection of the fast wave. Step 4: The time interval between the fast and slow wave excitation is Δt, where Δt is calculated by the following formula:

[0015] The distance d between the intersection point of the two ultrasonic waves and the incident position

[0016]

[0017] Δt is the time difference between the two ultrasonic waves, and t0 is the time for the slow wave to propagate when the two ultrasonic waves intersect.

[0018] t0=d / V0

[0019] V0 is the velocity of the ultrasonic wave emitted first, V1 is the velocity of the ultrasonic wave emitted later, and d is the distance between the focal point and the origin.

[0020] Step 5: Continuously change the emission time interval so that the fast wave and slow wave meet at different positions d.

[0021] Step 6: Extract the fast wave echo signal intensity at different d positions as a(x) and obtain a curve showing the corresponding relationship between echo intensity and component length. If the curve increases significantly at a certain point (for example, reaching twice the echo intensity at other d positions), it is considered that there is a defect at that location.

[0022] Compared with the existing technology, the advantages of the present invention are as follows: 1. It can actively stimulate closed defects and increase the intensity of reflected signals.

[0023] Utilizing two different waveguide velocities, fast and slow, the slow wave arrives first and exerts a stretching effect, creating a localized opening in the defect area, significantly enhancing the subsequent fast wave's reflected signal. Compared to traditional passive detection mechanisms, this method achieves "pre-activation" of the defect response, effectively overcoming the difficulty of detecting closed defects.

[0024] 2. Realize the spatiotemporal focusing of detection energy and improve the signal-to-noise ratio

[0025] By precisely controlling the emission time intervals of fast waves and slow waves, the two are made to "catch up and meet" at a designated location, forming a spatiotemporal focusing effect, concentrating the detection energy at any predetermined location of the structure, and greatly improving the signal strength and detection sensitivity at the defect location. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Figure 1 is a schematic diagram of the dispersion curve,

[0027] Figure 2 The incentive signal for the fast and slow waves to catch up,

[0028] Figure 3 Defect opening caused by slow wave stretching,

[0029] Figure 4 Detection device connection diagram. DETAILED DESCRIPTION

[0030] In order to deepen the understanding of the present invention, this embodiment is described in detail below with reference to the accompanying drawings.

[0031] Example 1: See Figures 1-4 , a defect detection method based on fast and slow wave catching up, the method comprising the following steps,

[0032] Step 1: Calculate the guided wave dispersion curve of the one-dimensional component to determine the propagation velocity of the guided wave at different frequencies. Figure 1 As shown in Figure 2, it can be seen that the propagation speed of ultrasonic waves in a one-dimensional component varies depending on the excitation frequency.

[0033] When guided waves propagate in a steel pipe, they exhibit three modes: longitudinal expansion, torsion, and bending. The radial, circumferential, and longitudinal displacement fields of the steel pipe are expressed as follows:

[0034] u r =U r (r)cosnθcos(wt+kz)(radial) (1)

[0035] u θ =U θ(r)sinnθcos(wt+kz)(circumferential direction) (2)

[0036] u z =U z (r)cosnθsin(wt+kz)(vertical) (3)

[0037] Where z is the depth of the pile, U r (r), U θ (r) and U z (r) are the amplitudes in radial, circumferential and longitudinal directions respectively. The longitudinal and torsional modes are axisymmetric, while the bending mode is non-axisymmetric.

[0038] For axisymmetric modes, n=0, and for bending modes, n=1, 2, 3, ...,

[0039] Therefore, the longitudinal mode is represented by L(0,m), the torsional mode is represented by T(0,m), and the bending mode is represented by F(n,m), where n=1, 2, 3, ..., and m=1, 2, 3, ...;

[0040] Step 2: Select two excitation frequencies, corresponding to different propagation speeds. The fast wave is recorded as the fast wave with a wave speed of V1, and the slow wave is recorded as the slow wave with a wave speed of V0. The slow wave is emitted first, and then the fast wave is emitted. By adjusting the time interval between the fast and slow waves, the fast wave can catch up with the slow wave at different positions.

[0041] Step 2: Select two excitation frequencies, corresponding to different propagation speeds. The faster propagation speed is recorded as the fast wave with a wave speed of V1, and the slower propagation speed is recorded as the slow wave with a wave speed of V0. The slow wave is emitted first, and then the fast wave is emitted. By adjusting the time interval between the fast wave and the slow wave, the fast wave can catch up with the slow wave at different positions. The slow wave is a tensile wave, and the fast wave can be a tensile wave or a compression wave, such as Figure 2 As shown,

[0042] Step 3: When the fast wave reaches the meeting point, if there is a defect at that point, the defect will be fully enlarged under the stretching effect of the slow wave, thereby enhancing the reflection of the fast wave, such as Figure 3 shown

[0043] Step 4: The time interval Δt between fast and slow wave excitation is calculated by the following formula:

[0044] The distance d between the intersection point of the two ultrasonic waves and the incident position

[0045]

[0046] Δt is the time difference between the two ultrasonic waves, and t0 is the time for the slow wave to propagate when the two ultrasonic waves intersect.

[0047] t0=D / V0

[0048] V0 is the velocity of the ultrasonic wave emitted first, V1 is the velocity of the ultrasonic wave emitted later, and d is the distance between the focal point and the origin.

[0049] Step 5: Continuously change the emission time interval so that the fast wave and slow wave meet at different positions d.

[0050] Step 6: Extract the fast wave echo signal intensity at different d positions as a(x). Obtain a curve showing the relationship between echo intensity and component length. If the curve increases significantly at a certain point (for example, reaching twice the echo intensity at other d positions), it is considered that there is a defect at that location.

[0051] In step 2: Based on the obtained dispersion curve, the group velocity of the guided wave propagating in the one-dimensional structure can be determined in the dispersion curve according to its frequency. First, a low-frequency ultrasonic guided wave with a low group velocity is emitted, and then an ultrasonic guided wave with a higher frequency with a high group velocity is emitted. The propagation time of the first emitted low-frequency ultrasonic wave in the one-dimensional structure is changed, and the emission time of the later emitted high-frequency wave is determined, thereby changing the convergence point of the two ultrasonic guided waves. Therefore, the entire one-dimensional structure can be scanned. When the fast wave reaches the meeting point, if there is a defect at that point, the defect is fully enlarged under the stretching action of the slow wave, thereby enhancing the reflection of the fast wave.

[0052] This application can inspect not only one-dimensional components but also two-dimensional components using similar principles. Applicable one-dimensional components include pipes, rods, beams, columns, and shafts. Fast and slow waves refer not only to guide waves but also to other ultrasonic waves with different wave speeds, such as p-waves, s-waves, and Rayleigh waves.

[0053] The transmission interval is continuously varied to allow the fast and slow waves to meet at different locations. The echo signal strength at each transmission interval is extracted as a(x). A curve is generated that plots echo intensity against component length. If the curve shows a significant increase at a certain point, a defect is assumed to exist there, allowing defect detection to be performed on the entire one-dimensional structure.

[0054] Example 2: See Figures 1-4 A defect detection device based on fast and slow wave catching up is designed. The test device includes a test object and a signal generator and receiver. The device integrates functional modules commonly found in traditional ultrasonic testing systems, such as a signal generator, power amplifier, preamplifier, and signal oscilloscope. A computer controls the generation of an excitation signal, which generates two ultrasonic guided waves in the test object. The excited ultrasonic waves propagate through the test object, and at the defective convergence point, the high-frequency waves generate a reflected echo. The reflected echo is then transmitted back to the sensor, which then acts as a receiving sensor to receive the signal. Figure 4 shown.

[0055] It should be noted that the above embodiments are not intended to limit the scope of protection of the present invention, and equivalent changes or substitutions made on the basis of the above technical solutions fall within the scope of protection of the claims of the present invention.

Claims

1. A defect detection method based on fast and slow wave catching up, characterized in that: The method comprises the following steps: Step 1, calculating the guided wave dispersion curve of the one-dimensional component to determine the propagation speed of the guided wave at different frequencies; When guided waves propagate in a steel pipe, they exhibit three modes: longitudinal expansion, torsion, and bending. The radial, circumferential, and longitudinal displacement fields of the steel pipe are expressed as follows: u r = U r (r)cos nθcos(wt + kz) (radial) (1) u θ =U θ (r)sin nθcos(wt+kz)(circumferential) (2) u z =U z (r)cos nθsin(wt+kz)(longitudinal) (3) Where z is the depth of the pile, U r (r), U θ (r) and U z (r) are the amplitudes in radial, circumferential and longitudinal directions respectively. The longitudinal and torsional modes are axisymmetric, while the bending mode is non-axisymmetric. For axisymmetric modes, n=0, and for bending modes, n=1, 2, 3, ..., Therefore, the longitudinal mode is represented by L(0,m), the torsional mode is represented by T(0,m), and the bending mode is represented by F(n,m), where n=1, 2, 3, ..., and m=1, 2, 3, ...; Step 2: Select two excitation frequencies, corresponding to different propagation speeds. The fast wave is recorded as the fast wave with a wave speed of V1, and the slow wave is recorded as the slow wave with a wave speed of V0. The slow wave is emitted first, and then the fast wave is emitted. By adjusting the time interval between the fast and slow waves, the fast wave can catch up with the slow wave at different positions. Step 3: When the fast wave reaches the meeting point, if there is a defect at that point, the defect will be fully enlarged under the stretching effect of the slow wave, thereby enhancing the reflection of the fast wave. Step 4: The time interval between fast and slow wave excitation is Δt, Step 5: Continuously change the emission time interval so that the fast wave and slow wave meet at different positions d. Step 6: Extract the fast wave echo signal intensity at different d positions as a(x) and obtain the corresponding relationship curve between echo intensity and component length. If the curve increases significantly at a certain location, it is considered that there is a defect at that location.

2. The defect detection method based on fast and slow wave catching up according to claim 1 is characterized in that: In step 2, the slow wave is a stretching wave, and the fast wave is a stretching wave or a compression wave.

3. The defect detection method based on fast and slow wave catching up according to claim 1 is characterized in that: In step 4, Δt is calculated by the following formula, The distance between the intersection point of the two ultrasonic waves and the incident position, Δt is the time difference between the two ultrasonic waves, and t0 is the time for the slow wave to propagate when the two ultrasonic waves intersect. t0=d / V0 V0 is the velocity of the ultrasonic wave emitted first, and V1 is the velocity of the ultrasonic wave emitted later. d is the distance between the focal point and the origin.

4. A defect detection device based on fast and slow wave catching up, characterized in that: The device is used to implement the method described in any one of claims 1 to 3, comprising a detection object and a signal generator receiver. The device integrates functional modules such as a signal generator, a power amplifier, a preamplifier, and a signal oscilloscope commonly found in traditional ultrasonic detection systems. The device is controlled by a computer to generate an excitation signal, and ultrasonic guided waves are emitted twice in succession in the detection object. The excited ultrasonic waves propagate in the detection object, and high-frequency waves generate reflected echoes at the defective convergence point. The reflected echoes are transmitted back to the sensor, and the sensor then serves as a receiving sensor to receive the signal.

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