阅读说明：本技术 一种基于超声平面波成像和时间反转算子相结合的高分辨缺陷无损检测方法 (High-resolution defect nondestructive testing method based on combination of ultrasonic plane wave imaging and time reversal operator ) 是由 赵勃 韩梁 单奕萌 李佳鑫 于 2021-09-06 设计创作，主要内容包括：本发明是一种基于超声平面波成像和时间反转算子相结合的高分辨缺陷无损检测方法。本发明通过超声线性相控阵向被测工件发射一组平面波,利用超声相控阵采集各个平面波的反射回波数据,对回波数据进行时域滤波,滤除信号中的随机噪声；通过边缘提取方法取出扫描图像中各个缺陷的边缘信息,作为被测工件内部缺陷的基本信息,基本信息包括缺陷的位置信息、形状信息和大小范围信息；利用时间反转算子的特征向量对缺陷信号进行自动聚焦,在得到的各块缺陷区域进行精确成像,对整个被测工件缺陷的进行精确定位。(The invention relates to a high-resolution defect nondestructive testing method based on the combination of ultrasonic plane wave imaging and a time reversal operator. The method comprises the steps of transmitting a group of plane waves to a workpiece to be measured through an ultrasonic linear phased array, collecting reflection echo data of each plane wave by using the ultrasonic phased array, carrying out time domain filtering on the echo data, and filtering random noise in signals; extracting edge information of each defect in the scanned image by using an edge extraction method to serve as basic information of the internal defect of the detected workpiece, wherein the basic information comprises position information, shape information and size range information of the defect; and automatically focusing the defect signals by using the characteristic vectors of the time reversal operators, accurately imaging each obtained defect region, and accurately positioning the defects of the whole detected workpiece.)

1. A high-resolution defect nondestructive testing method based on the combination of ultrasonic plane wave imaging and time reversal operators is characterized in that: the method comprises the following steps:

step 1: transmitting a group of plane waves to a workpiece to be measured through an ultrasonic linear phased array, acquiring reflection echo data of each plane wave by using the ultrasonic phased array, performing time-domain filtering on the echo data, and filtering random noise in signals;

step 2: extracting edge information of each defect in the scanned image by using an edge extraction method to serve as basic information of the internal defect of the detected workpiece, wherein the basic information comprises position information, shape information and size range information of the defect;

and step 3: and automatically focusing the defect signals by using the characteristic vectors of the time reversal operators, accurately imaging each obtained defect region, and accurately positioning the defects of the whole detected workpiece.

2. The method of claim 1, wherein the method comprises the following steps: the step 1 specifically comprises the following steps:

step 1.1: transmitting a group of plane waves to a workpiece to be detected through an ultrasonic linear phased array, wherein the deflection angle alpha of each plane wave_iSatisfies the following conditions:

wherein lambda is the wavelength of the ultrasonic wave, and p is the distance between adjacent array elements of the ultrasonic phased array;

step 1.2: then, collecting reflection echo data of each plane wave by using an ultrasonic phased array, carrying out time domain filtering on the echo data, and filtering random noise in signals; setting a scanning plane, calculating the distance between a scanning pixel point and each array element of the phased array, and calculating the time t for each pixel point signal to return to each array element by using the propagation sound velocity of ultrasound in the detected workpiece₁Satisfies the following conditions:

wherein (x)_(j,k),y_(j,k),z_(j,k)) Is the position coordinate of the pixel point in the scanning plane (x)_n,y_n,z_n) Is the position coordinate of the nth array element, and c is the sound velocity of the ultrasonic wave;

step 1.3: calculating the time t from each transmitting plane wave to each pixel point₂：

t₂＝(xsin(α_i)+zcos(α_i))/c (3)

Obtaining the total time of the ultrasonic wave propagating in the tested workpiece, wherein the signals between any two adjacent points in the received waveform satisfy a linear relation, and the method comprises the following steps according to the linear interpolation principle:

the signal intensity of each pixel point in the scanning plane is obtained by utilizing the plane wave echo data received by each array element, so that successive imaging is carried out on the scanning plane, the coherence of the imaging result of each plane wave is calculated, and pixel signal coherent superposition is carried out:

wherein s is_ij,mAnd s_ij,nThe intensity values of the pixel in the ith row and the jth column obtained by imaging with the m-th emitted plane wave and the n-th emitted plane wave are respectively.

3. The method of claim 2, wherein the method comprises the following steps: the step 3 specifically comprises the following steps:

the method comprises the following steps of utilizing a characteristic vector of a time reversal operator to carry out automatic focusing on a defect signal, accurately imaging each defect area obtained fundamentally, regarding the whole ultrasonic detection system, enabling an input signal to be an excitation signal of Ne array elements, enabling an output signal to be a received echo signal of the Ne array elements, enabling the ultrasonic detection system to serve as an MIMO system, and enabling the input-output relation of the system to meet the following requirements:

r(t)＝K(t)e(t) (6)

wherein e (t) is the transmitting signal of Ne array elements, and r (t) is the receiving signal of Ne array elements;

let T (w) be K^*And (w) K (w) is a time reversal operator, a corresponding characteristic value and a corresponding characteristic vector are obtained through characteristic decomposition, and each defect position is subjected to successive focusing, so that each characteristic vector of the time reversal operator, which corresponds to each defect, is utilized, and amplitude and phase information of the characteristic vector are utilized to process a transmitting signal of an array element, and accurate focusing of the defect position in the workpiece to be measured is realized.

4. The method of claim 3, wherein the method comprises the following steps: the calculation method of the feature vector operator comprises the following steps: by using angle alpha of emission during plane wave imaging_iTaking an echo signal obtained by a plane wave of 0 as r (t), performing Fourier transform on the echo signal to obtain R (w), wherein the transmission signal of each array element is known as e (t), performing Fourier transform on the transmission signal of each array element to obtain E (w), calculating a transmission matrix of the system by using the principle of a half tensor matrix, selecting a transmission matrix of corresponding frequency according to the central frequency of the transmission signal, and calculating time reversal of the system by using the transmission matrix;

and obtaining a characteristic value and a characteristic vector of a time reversal operator by utilizing characteristic decomposition, and carrying out successive focusing imaging on the defect position so as to realize accurate positioning of the defect of the workpiece to be detected.

Technical Field

The invention relates to the technical field of nondestructive defect detection, in particular to a high-resolution nondestructive defect detection method based on the combination of ultrasonic plane wave imaging and a time reversal operator.

Background

On the basis of not damaging the material performance of the substance, the detection and imaging of the tiny defects of the material with complex geometric shape are very difficult problems. The alloy GH4169 is widely applied to key parts such as turbine discs, air compressor drums, casings and the like of aircraft engines, and even if the key parts have tiny defects and fatigue damage, the key parts can cause catastrophic results, so that the alloy GH4169 is very important for high-precision nondestructive testing. Ultrasonic detection is one of the most widely applied detection methods due to its advantages of low cost, rapid detection, no damage to material properties, and the like, and is an indispensable detection means particularly in the industrial fields of aviation, ships, nuclear industry, and the like. With the increasing requirement for the detection reliability in industrial detection, ultrasonic detection is also required to have faster detection speed, higher detection precision and more accurate description of defects, so that the technology for improving the performance of ultrasound in the aspect of nondestructive detection is more and more emphasized and becomes a research hotspot.

The general electric company proposes a solution (U.S. patent publication No. US20170199160a1), which first locates the position of the ultrasonic transducer relative to the measured object, then collects B-scan data of the measured object from at least one B-scan, then collects C-scan data of the measured object from at least one C-scan, then removes random noise and coherent noise of the data according to the predetermined geometry of the measured object to obtain filtered data, and finally generates a V-scan image, thereby determining a plurality of damage indexes of the measured object. The method has problems that: the geometric shape of the measured piece needs to be determined in advance, and B scanning and C scanning are needed to be carried out on the measured piece, so that rapid detection cannot be met.

University of great courseware proposed an ultrasonic TOFD blind zone suppression method based on synthetic aperture focusing and mode converted waves (ultrasonic TOFD blind zone suppression method based on synthetic aperture focusing and mode converted waves, publication No. CN 110243945A). The method adopts a TOFD detection system consisting of an ultrasonic flaw detector, a TOFD probe, an inclined organic glass wedge block and a scanning device to carry out scanning and image acquisition along the surface of a workpiece to be detected so as to obtain A scanning signal sets at different scanning positions. And when the mode converted wave shortest propagation sound at each position is solved according to the Fermat theorem, time delay and amplitude superposition processing are carried out on all A scanning signals, TOFD scanning image reconstruction is realized through point-by-point focusing, transverse redundant signals are weakened, and the imaging quality is improved. The method can inhibit the TOFD blind area and improve the defect quantification precision. The method has problems that: the defect positioning accuracy is related to the scanning accuracy of A scanning, step scanning and point-to-point focusing are needed to complete image reconstruction, the scanning time is long, and the requirement of quick scanning cannot be met.

Disclosure of Invention

The invention solves the problems of low defect nondestructive detection speed and low detection precision of a detected workpiece, thereby improving the quality control technology in industrial production, and provides a high-resolution defect nondestructive detection method based on the combination of ultrasonic plane wave imaging and a time reversal operator, and the invention provides the following technical scheme:

a high-resolution defect nondestructive testing method based on the combination of ultrasonic plane wave imaging and a time reversal operator comprises the following steps:

step 1: transmitting a group of plane waves to a workpiece to be measured through an ultrasonic linear phased array, acquiring reflection echo data of each plane wave by using the ultrasonic phased array, performing time-domain filtering on the echo data, and filtering random noise in signals;

step 2: extracting edge information of each defect in the scanned image by using an edge extraction method to serve as basic information of the internal defect of the detected workpiece, wherein the basic information comprises position information, shape information and size range information of the defect;

and step 3: and automatically focusing the defect signals by using the characteristic vectors of the time reversal operators, accurately imaging each obtained defect region, and accurately positioning the defects of the whole detected workpiece.

Preferably, the step 1 specifically comprises:

step 1.1: transmitting a group of plane waves to a workpiece to be detected through an ultrasonic linear phased array, wherein the deflection angle alpha of each plane wave_iSatisfies the following conditions:

wherein lambda is the wavelength of the ultrasonic wave, and p is the distance between adjacent array elements of the ultrasonic phased array;

step 1.2: then, collecting reflection echo data of each plane wave by using an ultrasonic phased array, carrying out time domain filtering on the echo data, and filtering random noise in signals; setting a scanning plane, calculating the distance between a scanning pixel point and each array element of the phased array, and calculating the time t for each pixel point signal to return to each array element by using the propagation sound velocity of ultrasound in the detected workpiece₁Satisfies the following conditions:

wherein (x)_(j,k),y_(j,k),z_(j,k)) Is the position coordinate of the pixel point in the scanning plane (x)_n,y_n,z_n) Is the position coordinate of the nth array element, and c is the sound velocity of the ultrasonic wave;

step 1.3: calculating the time t from each transmitting plane wave to each pixel point₂：

t₂＝(x sin(α_i)+z cos(α_i))/c (3)

Obtaining the total time of the ultrasonic wave propagating in the tested workpiece, wherein the signals between any two adjacent points in the received waveform satisfy a linear relation, and the method comprises the following steps according to the linear interpolation principle:

the signal intensity of each pixel point in the scanning plane is obtained by utilizing the plane wave echo data received by each array element, so that successive imaging is carried out on the scanning plane, the coherence of the imaging result of each plane wave is calculated, and pixel signal coherent superposition is carried out:

wherein s is_ij,mAnd s_ij,nThe intensity values of the pixel in the ith row and the jth column obtained by imaging with the m-th emitted plane wave and the n-th emitted plane wave are respectively.

Preferably, the step 3 specifically comprises:

the method comprises the following steps of utilizing a characteristic vector of a time reversal operator to carry out automatic focusing on a defect signal, accurately imaging each defect area obtained fundamentally, regarding the whole ultrasonic detection system, enabling an input signal to be an excitation signal of Ne array elements, enabling an output signal to be a received echo signal of the Ne array elements, enabling the ultrasonic detection system to serve as an MIMO system, and enabling the input-output relation of the system to meet the following requirements:

r(t)＝K(t)e(t) (6)

wherein e (t) is the transmitting signal of Ne array elements, and r (t) is the receiving signal of Ne array elements;

let T (w) be K^*And (w) K (w) is a time reversal operator, a corresponding characteristic value and a corresponding characteristic vector are obtained through characteristic decomposition, and each defect position is subjected to successive focusing, so that each characteristic vector of the time reversal operator, which corresponds to each defect, is utilized, and amplitude and phase information of the characteristic vector are utilized to process a transmitting signal of an array element, and accurate focusing of the defect position in the workpiece to be measured is realized.

Preferably, the feature vector operator calculation method is as follows: by using angle alpha of emission during plane wave imaging_iThe echo signal obtained by the plane wave of 0 is regarded as r (t), r (w) is obtained by performing fourier transform on the echo signal, the transmission signal of each array element is known as e (t), the transmission signal is subjected to fourier transform to be e (w), a transmission matrix of the system is obtained by calculating according to the principle of a half tensor matrix, and the transmission matrix is obtained according to the principle of a half tensor matrixSelecting a transfer matrix of corresponding frequency from the center frequency of the transmitted signal, and calculating the time reversal of the system by the transfer matrix;

and obtaining a characteristic value and a characteristic vector of a time reversal operator by utilizing characteristic decomposition, and carrying out successive focusing imaging on the defect position so as to realize accurate positioning of the defect of the workpiece to be detected.

The invention has the following beneficial effects:

the method comprises the steps of firstly carrying out rough imaging on the interior of a workpiece to be detected by utilizing a method of transmitting multi-angle plane waves by utilizing an ultrasonic phased array, roughly determining the structural characteristics of the interior of the workpiece to be detected, realizing ultrafast defect rough positioning due to the rapidity of plane wave imaging, then carrying out edge extraction by utilizing a digital image processing technology, and preliminarily determining the position information and the size range information of a defect, thereby greatly reducing the subsequent fine scanning range, further improving the detection speed, and finally carrying out high-precision focusing on the defect position in the workpiece to be detected by utilizing the characteristic vector of a time reversal operator. Finally, the defects of the detected workpiece are detected more quickly, more accurately and more accurately.

Drawings

FIG. 1 is a flow chart of a high-efficiency high-resolution defect nondestructive testing method based on a convolutional neural network;

FIG. 2 is a schematic diagram of an ultrasonic phased array;

fig. 3 is a schematic diagram of an ultrasonic plane wave.

Detailed Description

The present invention will be described in detail with reference to specific examples.

The first embodiment is as follows:

as shown in fig. 1 to 3, the present invention provides a high resolution defect nondestructive testing method based on the combination of ultrasonic plane wave imaging and time reversal operator, which comprises the following specific steps:

step 1, transmitting a group of planes to a workpiece to be detected through an ultrasonic linear phased arraySurface waves, in which the deflection angle alpha of the respective surface wave_iSatisfies the following conditions:

wherein lambda is the wavelength of the ultrasonic wave, and p is the distance between adjacent array elements of the ultrasonic phased array.

And then, collecting reflection echo data of each plane wave by using an ultrasonic phased array, carrying out time domain filtering on the echo data, and filtering random noise in the signals. Setting a scanning plane, calculating the distance between a scanning pixel point and each array element of the phased array, and calculating the time t1 for each pixel point signal to return to each array element by using the propagation sound velocity of the ultrasound in the tested workpiece to satisfy the following requirements:

wherein (x)_(j,k),y_(j,k),z_(j,k)) Is the position coordinate of the pixel point in the scanning plane (x)_n,y_n,z_n) Is the position coordinate of the nth array element, and c is the sound velocity of the ultrasonic wave.

Then, calculating the time t2 from each emission plane wave to each pixel point:

t₂＝(x sin(α_i)+z cos(α_i))/c (3)

therefore, the total time of the ultrasonic wave propagating in the tested workpiece is obtained, and if the signals between any two adjacent points in the received waveform satisfy a linear relation, the method has the following steps according to the linear interpolation principle:

the signal intensity of each pixel point in the scanning plane is obtained by utilizing the plane wave echo data received by each array element, the scanning plane is imaged successively, and because the position and the range of the workpiece to be detected are roughly scanned by utilizing the plane wave imaging, the pixel precision of the scanning plane is set to be lower, and the imaging time is reduced. Then, the coherence of the imaging result of each plane wave is calculated, and the pixel signals are coherently superposed:

and sij, m and sij, n are the intensity values of the pixels in the ith row and the jth column obtained by imaging the plane wave emitted at the mth time and the plane wave emitted at the nth time respectively.

Step 2: because the echo signal at the defect of the workpiece to be detected is enhanced, bright spots appear at the defect position in the scanned imaging image, the edge information of each defect in the scanned image can be extracted by using an edge extraction method in the digital image processing technology and used as the basic information of the internal defect of the workpiece to be detected, and the basic information comprises the position information, the shape information and the size range information of the defect.

And step 3: and automatically focusing the defect signals by using the characteristic vectors of the time reversal operators, and accurately imaging each defect region obtained in the process, thereby realizing the accurate positioning of the defects of the whole detected workpiece. The basic principle of the time reversal operator is as follows: the input signal of the whole ultrasonic detection system is the excitation signal of Ne array elements, and the output signal of the whole ultrasonic detection system is the receiving echo signal of Ne array elements, so that the ultrasonic detection system can be used as a MIMO system (multiple input multiple output system). The input-output relation of the system satisfies the following conditions:

r(t)＝K(t)e(t) (6)

where e (t) is the transmission signal of Ne array elements, and r (t) is the receiving signal of Ne array elements.

Let T (w) be K^*And (w) K (w) is a time reversal operator, corresponding characteristic values and characteristic vectors can be obtained through characteristic decomposition, and if the sequential focusing of each defect position is to be realized, each characteristic vector of the time reversal operator corresponding to each defect is used, and the amplitude and phase information of each characteristic vector are used for processing the transmitting signals of the array elements, so that the accurate focusing of the defect position in the workpiece to be measured is realized. Feature(s)The vector operator calculation method is as follows: by using angle alpha of emission during plane wave imaging_iThe echo signal obtained by the plane wave of 0 is regarded as r (t), the echo signal is subjected to Fourier transform to obtain R (w), the transmission signal of each array element is known as e (t), the transmission signal is subjected to Fourier transform to obtain E (w), a transmission matrix of the system is obtained by utilizing the principle of a half tensor matrix, then the transmission matrix of the corresponding frequency is selected according to the central frequency of the transmission signal, and then a time reversal operator of the system is calculated through the transmission matrix. And obtaining a characteristic value and a characteristic vector of a time reversal operator by utilizing characteristic decomposition, and then carrying out successive focusing imaging on the defect position, thereby realizing the accurate positioning of the defect of the workpiece to be detected.

Under the normal temperature condition, the tested object is an aluminum test block which is made of isotropic material, the speed of ultrasonic longitudinal wave propagating in the ultrasonic longitudinal wave test block is 6300m/s, the maximum detection depth is 100mm, an ultrasonic phased array with 64 array elements and 5MHz center frequency is used for detection, the interval of the phased array elements is 0.5mm, the wavelength of the ultrasonic longitudinal wave is 1.26mm, the deflection angle of the transmitted ultrasonic plane wave is calculated according to a formula, then the excitation delay of each array element is set in an ultrasonic phased array control system, the phased array is ensured to transmit the plane wave with the specified deflection angle, and all array elements of the phased array receive pulse echoes at the same time. Setting a target detection range of plane wave imaging, then imaging echo data obtained by single plane wave emission by using a flight time method to obtain plane wave imaging results of all deflection angles, and then linearly superposing a plurality of imaging results to obtain a final coarse scanning result. And then determining the number of the defects in the measured object by using an edge extraction algorithm based on a Canny operator, and simultaneously carrying out coarse positioning on the defect positions and carrying out coarse estimation on the defect sizes. Finally, a time reversal operator of the phased array detection system is estimated by utilizing echo data obtained by plane wave emission, a characteristic vector of the time reversal operator is calculated, delay time of each excitation array element is calculated according to amplitude information and phase information of the characteristic vector, accurate focusing on internal defects of the detected object is achieved, a high-precision focused image is obtained, and high-precision positioning and size representation are carried out on the internal defects of the detected object.

The invention provides a high-resolution defect nondestructive testing method based on the combination of ultrasonic plane wave imaging and a time reversal operator, which utilizes the ultra-fast imaging advantage of ultrasonic plane wave to realize the rough scanning of the internal structure of a tested object, then performs the approximate position and size of each defect through an edge extraction algorithm, and finally performs successive accurate focusing on the internal defects by utilizing the characteristic vector of the time reversal operator to obtain a high-resolution focused imaging result, thereby completing the high-precision positioning of the internal defects of the tested object on the size representation.

The above is only a preferred embodiment of the high-resolution defect nondestructive testing method based on the combination of the ultrasonic plane wave imaging and the time reversal operator, and the protection range of the high-resolution defect nondestructive testing method based on the combination of the ultrasonic plane wave imaging and the time reversal operator is not limited to the above embodiments, and all technical schemes belonging to the idea belong to the protection range of the invention. It should be noted that modifications and variations which do not depart from the gist of the invention will be those skilled in the art to which the invention pertains and which are intended to be within the scope of the invention.