阅读说明：本技术 基于激光超声表面波频域参数的亚表面裂纹定量测量方法 (Sub-surface crack quantitative measurement method based on laser ultrasonic surface wave frequency domain parameters ) 是由 王传勇 孔奕 王文 卢科青 陈占锋 居冰峰 于 2021-06-03 设计创作，主要内容包括：本发明公开了基于激光超声表面波频域参数的亚表面裂纹定量测量方法；该测量方法的步骤如下：一、在被测工件的被检测表面的同一侧设置依次排列的脉冲激光器探头、反射波接收器和透射波接收器。反射波接收器、透射波接收器分别位于被测的亚表面裂纹的相反侧。二、反射波接收器检测反射波中心频率的数值f-(r)。透射波接收器检测透射波中心频率的数值f-(t)。三、计算出亚表面裂纹的埋藏深度和高度。本发明利用亚表面裂纹反射和透射的表面波进行亚表面裂纹的深度和长度的测量,且准确度能够达到95％以上,实现了金属板亚表面裂纹的定量检测。此外,本发明仅通过检测反射波、透射波中心频率并代入对应表达式后即可获得亚表面裂纹的深度和长度。(The invention discloses a subsurface crack quantitative measurement method based on laser ultrasonic surface wave frequency domain parameters; the measuring method comprises the following steps: firstly, a pulse laser probe, a reflected wave receiver and a transmitted wave receiver which are sequentially arranged are arranged on the same side of the detected surface of the detected workpiece. The reflected wave receiver and the transmitted wave receiver are respectively positioned on the opposite sides of the measured subsurface crack. Secondly, the reflected wave receiver detects the value f of the center frequency of the reflected wave r . The transmitted wave receiver detects the value f of the center frequency of the transmitted wave t . And thirdly, calculating the buried depth and height of the subsurface crack. The invention uses the surface waves reflected and transmitted by the sub-surface crack to perform sub-surfaceThe depth and the length of the surface crack are measured, the accuracy can reach more than 95%, and the quantitative detection of the subsurface crack of the metal plate is realized. In addition, the depth and the length of the subsurface crack can be obtained only by detecting the central frequency of the reflected wave and the central frequency of the transmitted wave and substituting the central frequency into the corresponding expression.)

1. The subsurface crack quantitative measurement method based on the frequency domain parameters of the laser ultrasonic surface wave is characterized by comprising the following steps: step one, arranging a pulse laser probe (2), a reflected wave receiver (3) and a transmitted wave receiver (4) which are sequentially arranged on the same side of the detected surface of a detected workpiece; the reflected wave receiver (3) and the transmitted wave receiver (4) are respectively positioned on the opposite sides of the measured subsurface crack (5);

exciting a surface wave on the surface of the workpiece to be detected by using a pulse laser probe (2); the reflected wave receiver (3) detects the surface wave reflected at the subsurface crack (5) to obtain a value f of the center frequency of the reflected wave_r(ii) a A transmitted wave receiver (4) detects the surface wave transmitted through the subsurface crack (5) with a value f of the center frequency of the transmitted wave_t；

Step three, calculating the buried depth h of the subsurface crack (5)₁As shown in formula (1):

h₁＝-3.97×10^-4×f_r+1904.57 type (1)

Calculating the height h of the subsurface crack (5)₂As shown in formula (2):

2. the method for quantitatively measuring the subsurface crack based on the frequency domain parameters of the laser ultrasonic surface wave as claimed in claim 1, wherein: the material of the workpiece to be detected is aluminum.

3. The method for quantitatively measuring the subsurface crack based on the frequency domain parameters of the laser ultrasonic surface wave as claimed in claim 1, wherein: obtaining the value f of the center frequency of the reflected wave in the second step_rAnd the value f of the center frequency of the transmitted wave_tThe specific process is as follows: obtaining a reflection oscillogram and a transmission oscillogram according to the reflected wave received by the reflected wave receiver (3) and the transmitted wave receiver (4) and the arrival time and amplitude of the transmitted wave; fourier transform is respectively carried out on the reflection oscillogram and the transmission oscillogram to respectively obtain frequency domain images of the reflected wave and the transmission wave, and the numerical value f of the center frequency of the reflected wave is obtained through observation_rAnd the value f of the center frequency of the transmitted wave_t。

4. The method for quantitatively measuring the subsurface crack based on the frequency domain parameters of the laser ultrasonic surface wave as claimed in claim 1, wherein: the pulse laser probe (2) adopts one of a pulse laser probe, a piezoelectric ceramic surface wave probe, an electromagnetic acoustic transducer and an air coupling transducer.

5. The method for quantitatively measuring the subsurface crack based on the frequency domain parameters of the laser ultrasonic surface wave as claimed in claim 1, wherein: the reflected wave receiver (3) and the transmitted wave receiver (4) adopt one or two of a laser interferometer and a piezoelectric ceramic surface wave probe.

6. The method for quantitatively measuring the subsurface crack based on the frequency domain parameters of the laser ultrasonic surface wave as claimed in claim 1, wherein: and step one, detecting the position of the sub-surface crack by a line source laser scanning method or a point source laser fast scanning method through galvanometer scanning before executing.

7. The method for quantitatively measuring the subsurface crack based on the frequency domain parameters of the laser ultrasonic surface wave as claimed in claim 1, wherein: the transverse distances from the reflected wave receiver and the transmitted wave receiver to the subsurface crack are both greater than or equal to 5 mm; also, the bandwidth of the reflected wave receiver and the transmitted wave receiver is to include the spectral range of the reflected wave and the transmitted wave.

Technical Field

The invention relates to the field of nondestructive testing, in particular to a subsurface crack quantitative measurement method based on laser ultrasonic surface wave frequency domain parameters.

Background

In recent years, with the continuous emergence of new materials and new processes, a large number of precision instruments and equipment have been developed and put into production practice. However, in the fields of aerospace, metallurgy and the like with higher and higher requirements on processing materials, some subsurface cracks in the test piece can expand along the surface of the test piece under the action of stress, and finally have important influence on the mechanical properties of the test piece, even break the test piece, and cause serious accidents.

Laser ultrasound is a non-contact, high-precision, nondestructive novel ultrasonic detection technology, and is the leading-edge technology of nondestructive detection and evaluation of materials at present. By analyzing the processes of ultrasonic transmission, reflection, scattering and the like, the information of macroscopic defects, structural forms, mechanical properties and the like of the test piece can be obtained. In the existing research, some scholars analyze simulation data by using a short-time fourier transform and an EMD decomposition method in a time-frequency analysis method, and obtain the relationship between the defect depth and the characteristic quantities of the ultrasonic signal, such as frequency, energy and the like.

In the field of non-destructive inspection, it is also important to detect the depth and length of a defect. The depth and length of the subsurface crack are two important parameters for subsequent processing to remove the defect layer. However, in some existing laser detection, it is rare to simultaneously perform quantitative measurement on the depth and length of the defect. In addition, the conventional method for quantitatively detecting surface defects (such as the method using ultrasonic vibration amplitude) needs to perform detection on a plurality of known size defects in advance to obtain a fitting curve and then perform quantitative detection on other size defects, and the detection accuracy of the method is not high. The method using the ultrasonic propagation path has high detection precision, but is complex and difficult to acquire accurate propagation time for weak signals.

Disclosure of Invention

The invention provides a quantitative measurement method of subsurface cracks based on ultrasonic surface wave frequency domain parameters, which aims to quantitatively detect the depth and the length of the subsurface cracks generated in the machining of a precision machining material so as to facilitate the subsequent machining to remove a defect layer, and the specific scheme is as follows:

a subsurface crack quantitative measurement method based on ultrasonic surface wave frequency domain parameters comprises the following steps:

step one, arranging a pulse laser probe, a reflected wave receiver and a transmitted wave receiver which are sequentially arranged on the same side of the detected surface of the detected workpiece. The reflected wave receiver and the transmitted wave receiver are respectively positioned on the opposite sides of the measured subsurface crack.

And secondly, exciting a surface wave on the surface of the workpiece to be measured by using a pulse laser probe. The reflected wave receiver detects the surface wave reflected by the sub-surface crack to obtain the value f of the central frequency of the reflected wave_r. A transmitted wave receiver detects a surface wave transmitted through the subsurface crack, the value f of the center frequency of the transmitted wave_t。

Step three, calculating the buried depth h of the subsurface crack₁As shown in formula (1):

h₁＝-3.97×10^-4×f_r+1904.57 type (1)

Calculating the height h of the subsurface crack₂As shown in formula (2):

preferably, the workpiece to be measured is made of aluminum.

Preferably, the value f of the center frequency of the reflected wave is obtained in the second step_rAnd the value f of the center frequency of the transmitted wave_tThe specific process is as follows: based on reflected wave receiver, transmitted wave receiverAnd obtaining the arrival time and amplitude of the arriving reflected wave and transmitted wave to obtain a reflected oscillogram and a transmitted oscillogram. Fourier transform is respectively carried out on the reflection oscillogram and the transmission oscillogram to respectively obtain frequency domain images of the reflected wave and the transmission wave, and the numerical value f of the center frequency of the reflected wave is obtained through observation_rAnd the value f of the center frequency of the transmitted wave_t。

Preferably, the pulse laser probe is one of a pulse laser probe, a piezoelectric ceramic surface wave probe, an electromagnetic acoustic transducer and an air coupling transducer.

Preferably, the reflected wave receiver and the transmitted wave receiver are one or both of a laser interferometer and a piezoelectric ceramic surface wave probe.

Preferably, the first step is carried out by scanning the laser through a line source or scanning the point source laser through a galvanometer to detect the position of the sub-surface crack.

Preferably, the lateral distances from the reflected wave receiver and the transmitted wave receiver to the subsurface crack are both greater than or equal to 5 mm. Also, the bandwidth of the reflected wave receiver and the transmitted wave receiver is to include the spectral range of the reflected wave and the transmitted wave.

Compared with the prior art, the invention has the beneficial effects that:

1. the method utilizes the surface waves reflected and transmitted by the subsurface cracks to measure the depth and the length of the subsurface cracks, the accuracy can reach more than 95%, and the quantitative detection of the subsurface cracks of the metal plate is realized.

2. The depth and the length of the subsurface crack can be obtained only by detecting the central frequency of the reflected wave and the central frequency of the transmitted wave and substituting the central frequency into the corresponding expression, and the method has the characteristics of simplicity, lower cost and high measurement speed.

Drawings

FIG. 1 is a schematic illustration of the present invention for detecting sub-surface cracks;

FIG. 2a is a diagram of a waveform received by a reflected wave receiver in a specific measurement test;

FIG. 2b is a diagram of waveforms received by a transmitted wave receiver in a particular measurement experiment;

fig. 3a is a frequency domain signal diagram of a reflected wave receiver after fourier transform of a received waveform in a specific measurement test;

fig. 3b is a frequency domain signal diagram of a waveform received by a transmitted wave receiver after fourier transform in a specific measurement test.

In the figure, 1, a workpiece, 2, a pulse laser probe; 3. a reflected wave receiver; 4. a transmitted wave receiver; 5. sub-surface cracking.

Detailed Description

The present invention will be described in detail with reference to the accompanying drawings and examples.

The invention provides a subsurface crack quantitative measurement method based on ultrasonic surface wave frequency domain parameters, which aims to detect the depth and height of a subsurface crack generated in the process of processing a precision processing material so as to remove a defect layer in the subsequent processing, and the specific scheme is as follows:

the quantitative measurement method adopts a subsurface crack quantitative measurement device based on the frequency domain parameters of the ultrasonic surface waves, and comprises a pulse laser probe 2, a reflected wave receiver 3 and a transmitted wave receiver 4. The pulse laser probe 2 is used for emitting pulse laser to the workpiece, and the reflected wave receiver 3 is used for receiving a surface wave signal reflected by an internal crack of the workpiece; the transmission wave receiver 4 is used for receiving a surface wave signal penetrating through a crack in the workpiece; the depth and height of the defect in the workpiece 1 are acquired by combining the two surface wave signals. The pulse laser probe 2 is used for exciting the ultrasonic surface wave, and specifically adopts one of a pulse laser probe, a piezoelectric ceramic surface wave probe, an electromagnetic acoustic transducer and an air coupling transducer. The reflected wave receiver 3 and the transmitted wave receiver 4 adopt one or two of a laser interferometer and a piezoelectric ceramic surface wave probe. The frequency bandwidth of the reflected wave receiver 3 and the transmitted wave receiver 4 includes the spectral range of the reflected and transmitted surface waves, which is specifically 3-5 MHz. Therefore, incomplete signal reception is avoided, and the precision of the detection result is ensured.

The quantitative measurement method comprises the following specific steps:

1) the pulse laser probe 2, the reflected wave receiver 3 and the transmitted wave receiver 4 which are arranged in sequence are placed on the same side of the detected workpiece, and the reflected wave receiver 3 and the transmitted wave receiver 4 are respectively positioned on the opposite sides of the subsurface crack 5. The lateral distances from the reflected wave receiver and the transmitted wave receiver to the subsurface crack are both greater than or equal to 5 mm. The reflected wave receiver 3 near the pulse laser probe 2 receives the reflected wave information, and the transmitted wave receiver 4 far from the pulse laser probe 2 receives the transmitted wave information. The approximate location of the subsurface crack 5 is previously detected by prior art techniques (e.g., by ultrasonic detection).

2) Exciting a surface wave on the surface of the workpiece by using a pulse laser probe 2, and receiving the arrival time and amplitude of the reflected wave by using a reflected wave receiver 3 positioned in front of a subsurface crack 5 to obtain a oscillogram of the reflected wave; the time and amplitude of arrival of the transmitted wave at the receiver are received by the transmitted wave receiver 4 located behind the subsurface crack 5, and a waveform diagram of the transmitted wave is obtained.

3) Fourier transform is carried out on the oscillogram of the reflected wave and the transmitted wave received in the step 2 to obtain a frequency domain image of the reflected wave and the transmitted wave, and the numerical value f of the center frequency of the reflected wave is obtained through observation_rAnd the value f of the center frequency of the transmitted wave_t。

4) Calculating the buried depth h of the subsurface crack 5 by the numerical values of the central frequencies of the reflected wave and the transmitted wave obtained in the step 3₁As shown in formula (1):

h₁＝-3.97×10^-4×f_r+1904.57 type (1)

5) Then h is obtained by calculation in step 4₁Calculating the height h of the subsurface crack 5₂As shown in formula (2):

the center frequency f of the reflected wave_rAnd a transmitted wave center frequency f_tIn hertz; the formula and the calculation result unit are micrometer, and the method is suitable for quantitative detection of the subsurface cracks of the workpiece made of aluminum.

The following knotThe effect of the invention is verified by a specific measurement test: the sub-surface cracks of an aluminum plate are detected by the method, the length of the detected aluminum plate is 150mm, the height of the detected aluminum plate is 50mm, the width of the detected aluminum plate is 10mm, and the sub-surface cracks are arranged below the upper surface of the detected aluminum plate. A pulse laser 2 is placed on one side of the crack for excitation of the surface wave, a reflected wave receiver 3 is placed at a point on the line connecting the pulse laser 2 and the crack for receiving the incident and reflected surface waves, and a transmitted wave receiver 4 is placed on the extension of the line connecting the pulse laser 2 and the crack for receiving the transmitted surface wave, as shown in fig. 2a and 2 b. Extracting the reflected and transmitted surface waves for Fourier transform to obtain frequency domain signals of the reflected and transmitted surface waves, and extracting the center frequency f of the reflected and transmitted waves as shown in FIGS. 3a and 3b_rAnd f_t. And finally, obtaining the depth and the length of the subsurface crack by using the formula and calculation.

The final test results and their relative errors are shown in the following table:

parameters of cracking	Depth h of crack1(μm)	Height h of crack2(μm)
			Reference value	100.0	200
Measured value	95.4	194.4
			Relative error	4.6％	2.79％

As can be seen from the table, the quantitative detection of the length and the depth of the subsurface crack of the invention has the relative error within 5 percent and has high precision. The method has the advantage of greatly improving the detection of the depth and the length of the subsurface crack.