CN102809610A - Phased array ultrasonic testing method based on improved dynamic depth focusing - Google Patents

Abstract

The invention belongs to the technical field of nondestructive testing, and specifically relates to a phased array ultrasonic testing method based on improved dynamic depth focusing. There are five steps in the post-processing step and the B-type map reconstruction step. The invention accurately focuses the ultrasonic echo signal to the defect position, which can solve the problem of difficult defect identification caused when the signal-to-noise ratio of the defect reflection echo signal is too low; The problem of deviation between the ideal focus and the actual focus, for the phased array ultrasonic detection of layered media and anisotropic media, can effectively improve the detection resolution; the invention can also reduce hardware system errors caused by phased array flaw detectors, etc. The ultrasonic imaging results are blurred and distorted, and the quality of phased array ultrasonic imaging is improved.

Description

A Phased Array Ultrasonic Inspection Method Based on Improved Dynamic Depth Focusing

technical field

The invention belongs to the technical field of nondestructive testing, and in particular relates to a phased array ultrasonic testing method based on improved dynamic depth focusing.

Background technique

Non-destructive testing (nondestructive testing), referred to as NDT, is based on the premise of not damaging the adaptability of the object to be tested, and uses a variety of physical principles and chemical phenomena to carry out effective inspection and testing of various engineering materials, parts, and structural parts. Evaluate their continuity, integrity, safety reliability and certain physical properties. The five conventional non-destructive testing methods mainly include radiographic testing, ultrasonic testing, penetrant testing, magnetic particle testing, and eddy current testing.

Ultrasonic testing (UT) is to use the probe to stimulate the ultrasonic wave to be transmitted into the workpiece to be inspected after being coupled by the coupling agent. When the ultrasonic wave encounters a defect, reflection and refraction will occur. By analyzing the energy amplitude, sound velocity, and The change of signal frequency and other methods are used to detect.

Phased array ultrasonic testing technology is to electronically control each array element in the transducer array, and regularly transmit and receive ultrasonic waves according to a certain delay time, so as to control the deflection and focus of the ultrasonic beam in the workpiece to be inspected, so as to realize the inspection of materials. Non-destructive testing, which includes phased array ultrasonic transmitting and receiving two parts. The working principle of phased array ultrasonic transmission is based on the Huygens-Fresnel principle. When each array element is excited by the pulse of the same frequency, the transmitted ultrasonic waves will interfere to form a synthetic wave front, thereby forming a stable wave front in space. Ultrasonic field; if the excitation pulse time of each array element is changed so that they are emitted according to a certain delay time, then according to the Huygens principle, the emitted ultrasonic waves will be superimposed in space to synthesize a new wave front, thereby realizing sound beam deflection or features such as focus. According to the principle of reciprocity, the reception of phased array is also achieved by delay method. According to the time difference when the echo arrives at each array element, the delay compensation is performed on the received information of each array element, and then superimposed to obtain the target direction. Reflection echo; at the same time, through the phase and amplitude control of each array element and sound beam forming and other methods, various phase control effects such as dynamic focusing, variable aperture, and apodization can be formed.

During phased array ultrasonic testing, due to the deviation between the actual sound velocity of the tested material and the assumed sound velocity, or the presence of coarse grains, anisotropy, and non-uniformity in the tested material, the non-uniformity of the sound beam when the ultrasonic signal propagates will cause It causes the distortion of the phased array ultrasonic synthesis signal in the process of ultrasonic signal propagation, which leads to the difficulty of beam focusing and beam synthesis during defect detection, and seriously affects the spatial resolution and contrast of phased array ultrasonic imaging.

Contents of the invention

Aiming at the problems existing in the prior art, the present invention proposes a phased array ultrasonic detection method based on improved dynamic depth focusing, using the ultrasonic echo signal received by each array element in the phased array straight probe as the feedback signal, and extracting The defect information in the signal obtains the time difference of the defect echo arriving at several adjacent array elements closest to the defect, and then according to the time difference of these array elements, there is no need to re-energize the ultrasonic wave, only need to Delay processing is performed on the received signals, so that the echo signals received by these array elements are focused on the defect position. The receiving delay time of the array element is adjusted according to the actually received echo signal to realize accurate focusing of the sound beam at the defect position, which can effectively improve the detection resolution of the defect.

The present invention proposes a phased array ultrasonic detection method based on improved dynamic depth focusing, wherein the detection device required by the detection method includes a phased array ultrasonic flaw detector and a phased array straight probe, wherein the phased array ultrasonic flaw detector and The phased array straight probe is electrically connected, and the phased array straight probe is a one-dimensional linear probe with multiple array elements. The detection method specifically includes the following steps:

Step 1, phased array ultrasonic transmitting and receiving steps. First, set up the phased array flaw detector, conduct phased array linear electronic scanning, set the number of array elements selected for one transmission/reception of ultrasonic waves (this value is generally 1/4 of the number of phased array straight probe array elements) and The step value of linear electronic scanning (this value takes 1 array element), and at the same time set the ultrasonic focus position emitted by the phased array straight probe as the lower surface of the detected workpiece (this value is determined by the thickness of the detected workpiece), phased array The way the straight probe receives ultrasonic echo signals is the dynamic depth focusing (DDF) mode. The setting of the dynamic depth focusing mode includes three parameters: the initial focus depth, the end focus depth and the focus depth step. The start focus depth and the end focus depth are determined by The thickness of the detected workpiece is determined, and the focus depth step is determined by the required detection accuracy. This method can make the ultrasonic echo signals from different focus depth positions in a focused state. Through the above settings, the phased array flaw detector converts multiple adjacent array elements in the phased array straight probe into a transmitting array aperture, and controls all array elements in each array aperture, and each array element in the array aperture follows the The delay time value calculated by the phased array flaw detector emits ultrasonic waves. At the same time, each array element in the array aperture receives ultrasonic echo signals. These ultrasonic echo signals include reflected echoes and defects on the upper and lower surfaces of the detected workpiece. According to the delay time value of each focal depth position calculated by the phased array flaw detector during dynamic depth focusing, the ultrasonic echo signals received by each array element in the array aperture are processed by dynamic depth focusing and combined into A beam of ultrasound signals is defined as the composite ultrasound signal of the array aperture. By sequentially controlling each array aperture to transmit and receive ultrasonic waves, the ultrasonic composite signal of each array aperture can be obtained.

Step 2, defect identification step. The data in the ultrasonic composite signal obtained by each array aperture in step 1 is characterized by brightness (or color), and a two-dimensional cross-sectional view of the detected workpiece is obtained, which is a B-type display. Since the B-type display contains the Detect the reflected echo information on the upper and lower surfaces of the workpiece, so the two-dimensional position information of the defect can be determined from the B-type map;

Step 3, the delay time calculation step. According to the defect position information initially identified in step 2, an array aperture closest to the defect position is selected, and according to the ultrasonic echo signals received by each element in the array aperture in step 1, add Rectangular time window or any window function used to extract information in a given interval in digital signal processing to extract the echo information of the defect position. Then, according to the principle that the ultrasonic echo signals reflected by the same defect received by each array element in the array aperture are correlated, the cross-correlation method is used to calculate the time difference for the ultrasonic wave to reach each array element in the array aperture from the defect position;

The specific operation of the cross-correlation method includes the following steps:

(1) Select an array aperture closest to the defect position, and use the data of the ultrasonic echo signal received by the array element closest to the defect in step 1 as the reference signal x(n)(n= 0,1,2...N-1), take the data of the ultrasonic echo signal received by any other element in the array aperture in step 1 as the measured signal y(n) (n=0,1,2 ...N-1), n represents the position in the sequence, and N is the number of collection points for each array element to receive the ultrasonic echo signal in step 1. For the detected workpiece with thickness h and longitudinal wave sound velocity c, when the phased array ultrasonic flaw detection When the sampling frequency of the instrument is M, N=(2h/c)*M;

(2) Set the cycle length of the cyclic correlation operation to L, L≥2N-1, the reference signal x(n)(n=0,1,2...N-1) and the measured signal y(n)(n =0,1,2…N-1) respectively padding to length L; for the reference signal x(n)(n=0,1,2…L-1) after zero padding and the measured signal x(n) after zero padding Signal y(n)(n=0,1,2...L-1) undergoes fast Fourier transform (FFT) to obtain X(k)(k=0,1,2...L-1) and Y(k) (k=0,1,2...L-1), where X(k) represents the zero-filled reference signal x(n) from the time-domain signal to the frequency-domain signal after Fast Fourier Transform (FFT) Sequence, Y(k) represents the sequence of the measured signal y(n) after the zero padding is changed from the time domain signal to the frequency domain signal after the fast Fourier transform (FFT), k represents the X(k ) and the position in the Y(k) sequence;

(3) Perform conjugate operation on X(k), multiply the result of the conjugate operation with Y(k) by complex numbers, the result of multiplication by complex numbers is the cross-correlation function R(k), and then perform R(k) Inverse Fast Fourier Transform (IFFT) extracts the real part R(τ), then the τ in the real part R(τ) corresponding to the maximum value of R(k) is the required reference signal and the measured signal time difference.

(4) The data of the ultrasonic echo signals received by other array elements in the array aperture in step 1 are used as the measured signals to perform the calculations (1) to (3) in turn, and obtain the array elements in the array aperture Relative to the time difference of the reference signal, these time differences are the delay time for each array element in the selected array aperture to receive the defect reflection echo signal.

Step 4, a post-processing step of the echo signal. Take the delay time value of the focus depth position closest to the defect when setting dynamic depth focusing in step 1, and replace it with the delay time value of each array element in the selected array aperture obtained in step 3, keeping The delay time values at other focal depth positions remain unchanged, so that the ultrasonic echo signals received by each array element in the selected array aperture are focused to the defect position. According to the delay time value after the above processing, the ultrasonic echo signals received by each array element in the selected array aperture are re-synthesized to form a new ultrasonic composite signal of the array aperture;

Step five, the reconstruction step of the B-type graph. Replace the ultrasonic composite signal obtained by the array aperture in step 1 with the new ultrasonic composite signal formed by the array aperture selected in step 4, and redraw the B-type map for defect identification.

The phased array ultrasonic detection method proposed by the present invention is not only applied to the detection of the detected workpiece with only one defect, but also applicable to the detection of the detected workpiece with more than two defects.

The advantages of the present invention are:

(1) The present invention proposes a phased array ultrasonic detection method based on improved dynamic depth focusing, which can accurately focus the ultrasonic echo signal to the defect position, and can solve the problem caused by the low signal-to-noise ratio of the defect reflected echo signal. The problem of difficult defect identification;

(2) The present invention proposes a phased array ultrasonic detection method based on improved dynamic depth focusing, which can effectively solve the problem of deviation between the ideal focus and the actual focus due to the uneven material of the workpiece to be inspected. For layered media and various Phased array ultrasonic testing of anisotropic media can effectively improve the detection resolution;

(3) The present invention proposes a phased array ultrasonic detection method based on improved dynamic depth focusing, which can reduce the blurring and distortion of ultrasonic imaging results caused by hardware system errors such as phased array flaw detectors, and improve the quality of phased array ultrasonic detection. image quality.

Description of drawings

Fig. 1 shows the phased array linear scanning mode;

Fig. 2 shows the phased array dynamic depth focusing mode;

Fig. 3 shows the synthesis method of the ultrasonic echo signal during the phased array dynamic depth focusing;

Fig. 4 shows the determination method of the array aperture closest to the defect;

Fig. 5 shows a schematic diagram of adjusting a focus position for a defect position.

Detailed ways

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

The invention uses a phased array straight probe to detect the workpiece to be detected, and obtains the time difference of the defect echo arriving at these several array elements by processing the ultrasonic echo signals received by several adjacent array elements, and then Delay processing is performed on the received signal to focus the received echo signal on the defect position. This detection method effectively corrects the problems of uneven sound velocity of the tested material, deviation between the actual sound velocity and the assumed sound velocity, and improves the accuracy of the focus point.

The present invention proposes a phased array ultrasonic detection method based on improved dynamic depth focusing, wherein the detection device required by the detection method includes a phased array ultrasonic flaw detector and a phased array straight probe, wherein the phased array ultrasonic flaw detector and The phased array straight probe is electrically connected, and the phased array straight probe is a one-dimensional linear probe with multiple array elements. The detection method specifically includes the following steps:

Step 1, phased array ultrasonic transmitting and receiving steps. First, set up the phased array flaw detector, conduct phased array linear electronic scanning, set the number of array elements selected for one transmission/reception of ultrasonic waves (this value is generally 1/4 of the number of phased array straight probe array elements) and The step value of linear electronic scanning (this value takes 1 array element), and at the same time set the ultrasonic focus position emitted by the phased array straight probe as the lower surface of the detected workpiece (this value is determined by the thickness of the detected workpiece), phased array The way the straight probe receives ultrasonic echo signals is the dynamic depth focusing (DDF) mode. The setting of the dynamic depth focusing mode includes three parameters: the initial focus depth, the end focus depth and the focus depth step. The start focus depth and the end focus depth are determined by The thickness of the detected workpiece is determined, and the focus depth step is determined by the required detection accuracy. This method can make the ultrasonic echo signals from different focus depth positions in a focused state. Through the above settings, the phased array flaw detector converts multiple adjacent array elements in the phased array straight probe into a transmitting array aperture, and controls all array elements in each array aperture, and each array element in the array aperture follows the The delay time value calculated by the phased array flaw detector emits ultrasonic waves. At the same time, each array element in the array aperture receives ultrasonic echo signals. These ultrasonic echo signals include reflected echoes and defects on the upper and lower surfaces of the detected workpiece. According to the delay time value of each focal depth position calculated by the phased array flaw detector during dynamic depth focusing, the ultrasonic echo signals received by each array element in the array aperture are processed by dynamic depth focusing and combined into A beam of ultrasound signals is defined as the composite ultrasound signal of the array aperture. By sequentially controlling each array aperture to transmit and receive ultrasonic waves, the ultrasonic composite signal of each array aperture can be obtained.

Step 2, defect identification step. The data in the ultrasonic composite signal obtained by each array aperture in step 1 is characterized by brightness (or color), and a two-dimensional cross-sectional view of the detected workpiece is obtained, which is a B-type display. Since the B-type display contains the Detect the reflected echo information on the upper and lower surfaces of the workpiece, so the two-dimensional position information of the defect can be determined from the B-type map.

Step 3, the delay time calculation step. According to the defect position information initially identified in step 2, an array aperture closest to the defect position is selected, and according to the ultrasonic echo signals received by each element in the array aperture in step 1, add Rectangular time window or any window function used to extract information in a given interval in digital signal processing to extract the echo information of the defect position. Then, according to the principle that the ultrasonic echo signals reflected by the same defect received by each array element in the array aperture are correlated, the cross-correlation method is used to calculate the time difference of the ultrasonic wave from the defect position to each array element in the array aperture.

The specific operation of the cross-correlation method includes the following steps:

(1) Select an array aperture closest to the defect position, and use the data of the ultrasonic echo signal received by the array element closest to the defect in step 1 as the reference signal x(n)(n= 0,1,2...N-1), take the data of the ultrasonic echo signal received by any other element in the array aperture in step 1 as the measured signal y(n) (n=0,1,2 ...N-1), n represents the position in the sequence, and N is the number of collection points for each array element to receive the ultrasonic echo signal in step 1. For the detected workpiece with thickness h and longitudinal wave sound velocity c, when the phased array ultrasonic flaw detection When the sampling frequency of the instrument is M, N=(2h/c)*M;

(2) Set the cycle length of the cyclic correlation operation to L, L≥2N-1, the reference signal x(n)(n=0,1,2...N-1) and the measured signal y(n)(n =0,1,2…N-1) respectively padding to length L; for the reference signal x(n)(n=0,1,2…L-1) after zero padding and the measured signal x(n) after zero padding Signal y(n)(n=0,1,2...L-1) undergoes fast Fourier transform (FFT) to obtain X(k)(k=0,1,2...L-1) and Y(k) (k=0,1,2...L-1), where X(k) represents the zero-filled reference signal x(n) from the time-domain signal to the frequency-domain signal after Fast Fourier Transform (FFT) Sequence, Y(k) represents the sequence of the measured signal y(n) after the zero padding is changed from the time domain signal to the frequency domain signal after the fast Fourier transform (FFT), k represents the X(k ) and the position in the Y(k) sequence;

(3) Perform conjugate operation on X(k), multiply the result of the conjugate operation with Y(k) by complex numbers, the result of multiplication by complex numbers is the cross-correlation function R(k), and then perform R(k) Inverse Fast Fourier Transform (IFFT) extracts the real part R(τ), then the τ in the real part R(τ) corresponding to the maximum value of R(k) is the required reference signal and the measured signal time difference;

(4) The data of the ultrasonic echo signals received by other array elements in the array aperture in step 1 are used as the measured signals to perform the calculations (1) to (3) in turn, and obtain the array elements in the array aperture Relative to the time difference of the reference signal, these time differences are the delay time for each array element in the selected array aperture to receive the defect reflection echo signal.

Step 4, a post-processing step of the echo signal. Take the delay time value of the focus depth position closest to the defect among the focus depth positions when setting dynamic depth focusing in step 1, and replace it with the delay time value of each array element in the selected array aperture obtained in step 3, and other If the delay time value of the focus depth position remains unchanged, the ultrasonic echo signals received by each array element in the selected array aperture are focused to the defect position. The ultrasonic echo signals received by each array element in the selected array aperture are re-synthesized according to the delay time value after the above processing to form a new ultrasonic composite signal for the array aperture.

Step five, the reconstruction step of the B-type graph. Replace the ultrasonic composite signal obtained by the array aperture in step 1 with the new ultrasonic composite signal formed by the array aperture selected in step 4, and redraw the B-type map for defect identification.

The phased array ultrasonic detection method proposed by the present invention is not only applied to the detection of the detected workpiece with only one defect, but also applicable to the detection of the detected workpiece with more than two defects.

Embodiment: This embodiment proposes a phased array ultrasonic detection method based on improved dynamic depth focusing, including the following steps:

Step 1. Take a phased array one-dimensional linear straight probe containing E (32) array element chips as an example, and use the phased array linear electronic scanning method to transmit ultrasonic waves. First, take No. 1~E/4 (1 ~No.8) array elements, these E/4 array elements form the first array aperture, and calculate the delay time of each array element in the array aperture, so that the ultrasonic beam emitted by each array element is vertically focused and incident on the detected workpiece lower surface. Then, select No. 2~(E/4+1) (No. 2~9), No. 3~(E/4+2) (No. 3~10), No. 4~(E/4+2) in the phased array straight probe respectively 4+3) (No. 4~11)...(3E/4+1)~E (No. 25~32) array elements form different array apertures, then the probes of E array element chips contain a total of 3E/4+ 1 (25) array apertures, the first array aperture completes the task of transmitting and receiving ultrasonic beams, and then the second array aperture completes the task of sending and receiving, and so on, so that 3E/4+1 array apertures are sequentially Sending and receiving are completed in turn, so as to realize a comprehensive scan within the range of the workpiece covered by the phased array straight probe. The linear electronic scanning method of the phased array is shown in Figure 1. In the figure, a phased array straight probe with E array element chips is taken as an example, and several array element chips are taken to form an array aperture, which is sequentially emitted along the linear scanning direction. ultrasound.

The phased array dynamic depth focusing (DDF) method is used to receive ultrasonic echo signals. The dynamic depth focusing method is realized by setting the initial focus depth, end focus depth and focus depth step of the phased array flaw detector. The initial focus depth and end focus depth are determined by the thickness of the workpiece to be detected, and the focus depth step is determined by the required detection accuracy. Through the above settings, the phased array flaw detector first calculates the delay time value of the ultrasonic echo signals reflected at different focal depth positions to reach each array element in each array aperture, and then after each array element receives the echo signal, through By controlling the delay time value of each focus depth position of dynamic depth focus, the echo beams from different focus depth positions can be in focus. The dynamic depth focus mode of phased array is shown in Figure 2, which shows Each focal depth position when an array aperture performs dynamic depth focusing. The signals received by each array element in each array aperture are synthesized in turn to obtain ultrasonic synthesized signals of 3E/4+1 array apertures. The signal synthesis method of one array aperture is shown in Figure 3, and the dynamic depth Taking the first and second focal depth positions in focusing as an example, it shows the process of combining ultrasonic echo signals received by each array element in an array aperture into a beam of ultrasonic signals through dynamic depth focusing processing.

Step 2. Characterize the data in the ultrasonic composite signal obtained by each array aperture in step 1 with brightness (or color), and obtain a two-dimensional cross-sectional view of the detected workpiece, which is a B-type display. Because the B-type display in the figure It contains the reflected echo information of the upper and lower surfaces of the detected workpiece, so the two-dimensional position information of the defect can be determined from the B-type map.

Step 3, the delay time calculation step. According to the defect position information initially judged in step 2, select an array aperture closest to the defect, and extract the echo information of the defect position according to the echo signals received by each array element in the array aperture, and according to the determined For the position information of the defect, a rectangular time window is added to the ultrasonic echo signal received by each array element in the selected array aperture in step 1 at the defect position, that is, the sampling value outside the time window is weighted as 0, and the time The sampled values within the window range are weighted by 1. The center position of the rectangular time window is determined from the initially determined position of the defect to the position of each array element in the selected array aperture.

When an array aperture transmits, although the echo signals of the same defect received by each array element in the array aperture have differences in time, they come from the same reflector and propagate in a medium with basically the same acoustic parameters. , so there is a correlation, which can be used to estimate the time difference of each array element in the selected array aperture receiving the defect reflection echo signal, and the specific operation is as follows:

(1) Select an array aperture closest to the defect position, and use the data of the ultrasonic echo signal received by the array element closest to the defect in step 1 as a reference signal, defined as x(n) (n=0,1,2...N-1), take the data of the ultrasonic echo signal received by any other element in the array aperture in step 1 as the measured signal, defined as y(n)(n =0,1,2...N-1), as shown in Figure 4, the phased array straight probe with 32 array elements is taken as an example, and the array aperture closest to the defect position is the 18th array aperture ( No. 18~25 array elements), with the data of the ultrasonic echo signal received by the array element (No. 21 array element) closest to the defect as the reference signal, and the other array elements (No. Array element) The data of the ultrasonic echo signal received by any array element in step 1 is used as the signal under test. The N value is the number of collection points for receiving ultrasonic echo signals, which is determined by the actual sound path of the workpiece under test. For a workpiece with a thickness of h and a sound velocity of longitudinal waves of c, when the sampling frequency of the phased array flaw detection equipment is M When, N=(2h/c)*M. For example, for a workpiece with a thickness of 60mm and a sound velocity of longitudinal wave of 5900m/s, when the sampling frequency of the phased array flaw detection equipment is 100MHz, the value of N is 2034;

(2) Set the cycle length of the cycle correlation operation to L, L≥2N-1, set x(n)(n=0,1,2...N-1) and y(n)(n=0,1, 2…N-1) are filled with zeros until the length is L, then it becomes x(n)(n=0,1,2…L-1) and y(n)(n=0,1,2…L- 1);

(3) Perform Fast Fourier Transform (FFT) on x(n)(n=0,1,2...L-1) and y(n)(n=0,1,2...L-1) respectively to get X(k)(k=0,1,2...,L-1) and Y(k)(k=0,1,2...,L-1);

(4) Perform conjugate operation on X(k), multiply the result of the conjugate operation with Y(k), and define the result of complex multiplication as the autocorrelation function R(k), and then calculate R(k) Perform inverse fast Fourier transform (IFFT) to extract its real part R(τ), then τ in the real part R(τ) corresponding to the maximum value of R(k) is the required measured signal and reference The time difference of the signal.

Take the data of the ultrasonic echo signals received by the remaining E/4-2 measured channels as the measured signal, and use the above four steps to obtain the time difference of each measured signal relative to the reference signal. These time differences The value is the delay time of each element in the selected array aperture.

Step 4. Take the delay time value of the focus depth position closest to the defect among the focus depth positions when setting dynamic depth focusing in step 1, and use the delay time value of each array element in the selected array aperture obtained in step 3 Instead, the delay time values at other focal depth positions remain unchanged, so that the ultrasonic echo signals received by each array element in the selected array aperture are focused to the defect position, as shown in Figure 5, an array aperture is used as a dynamic depth During focusing, the depth of focus position closest to the defect among the depth of focus positions is replaced by the defect position, while the other depth of focus positions remain unchanged. According to the delay time value after the above processing, the echo signals received by each array element are synthesized again to obtain a new ultrasonic synthesized signal of the array aperture.

Step 5. The new ultrasonic echo signal synthesized by the array aperture replaces the ultrasonic echo signal of the array aperture at the beginning of scanning in step 1, keeping the ultrasonic echo signals of other array apertures unchanged, and redrawing the B-type map.

Claims (6)

1. A phased array ultrasonic detection method based on improved dynamic depth focusing, characterized in that: comprise the following steps: Step 1. Phased array ultrasonic transmitting and receiving steps: Set the phased array flaw detector to perform phased array linear electronic scanning, set the number of array elements selected for transmitting/receiving ultrasonic waves and the step value of linear electronic scanning, and set the ultrasonic focus position of the phased array straight probe to be To detect the lower surface of the workpiece, the method of receiving ultrasonic echo signals by the phased array straight probe is the dynamic depth focusing mode. Through the above settings, the phased array flaw detector converts multiple adjacent array elements in the phased array straight probe into a transmitting array aperture , to control all array elements in each array aperture, each array element in the array aperture transmits ultrasonic waves according to the delay time value calculated by the phased array flaw detector, and at the same time, each array element in the array aperture receives ultrasonic echoes Signals, according to the delay time value of each focus depth position during dynamic depth focusing calculated by the phased array flaw detector, perform dynamic depth focus processing on these ultrasonic echo signals and combine them into a bundle of ultrasonic signals, which is the ultrasonic composite signal of the array aperture. Sequentially control each array aperture to transmit and receive ultrasonic waves, and obtain the ultrasonic composite signal of each array aperture; Step 2. Defect identification steps: The data in the ultrasonic composite signal obtained by each array aperture in step 1 is characterized by brightness or color, and the B-type display diagram of the detected workpiece is obtained, because the B-type display diagram contains the reflected echoes of the upper and lower surfaces of the detected workpiece information, so the two-dimensional position information of the defect can be determined from the B-type map; Step 3. Delay time calculation steps: According to the defect position information initially identified in step 2, select an array aperture closest to the defect position, and extract the echo signal of the defect position according to the ultrasonic echo signals received by each array element in step 1. Wave information, according to the principle that each array element in the array aperture receives the ultrasonic echo signal reflected by the same defect has correlation, and uses the cross-correlation method to calculate the time difference of the ultrasonic wave from the defect position to each array element in the array aperture; Step 4. Post-processing steps of the echo signal: According to the delay time of each array element in the selected array aperture closest to the defect obtained in step 3, adjust the focal depth positions of the dynamic depth focusing set in step 1, so that each array in the selected array aperture The ultrasonic echo signal received by the element is focused to the defect position, and the ultrasonic echo signal received by each array element in the selected array aperture is re-synthesized to form a new ultrasonic composite signal of the array aperture; Step 5, B-type diagram reconstruction steps: Replace the ultrasonic composite signal obtained by the array aperture in step 1 with the new ultrasonic composite signal formed by the array aperture selected in step 4, and redraw the B-type map for defect identification. 2. A phased array ultrasonic detection method based on improved dynamic depth focusing according to claim 1, characterized in that: in step 3, cross-correlation method is used to calculate that ultrasonic waves arrive at each array element in the array aperture from the defect position The specific time difference is: (1) Select an array aperture closest to the defect position, and use the data of the ultrasonic echo signal received by the array element closest to the defect in step 1 as the reference signal x(n)(n= 0,1,2...N-1), take the data of the ultrasonic echo signal received by any other element in the array aperture in step 1 as the measured signal y(n) (n=0,1,2 ...N-1), n represents the position in the sequence, and N is the number of collection points for each array element to receive the ultrasonic echo signal in step 1. For the detected workpiece with thickness h and longitudinal wave sound velocity c, when the phased array ultrasonic flaw detection When the sampling frequency of the instrument is M, N=(2h/c)*M; (2) Set the cycle length of the cyclic correlation operation to L, L≥2N-1, the reference signal x(n)(n=0,1,2...N-1) and the measured signal y(n)(n =0,1,2…N-1) respectively padding to length L; for the reference signal x(n)(n=0,1,2…L-1) after zero padding and the measured signal x(n) after zero padding Signal y(n)(n=0,1,2...L-1) undergoes fast Fourier transform to obtain X(k)(k=0,1,2...L-1) and Y(k)(k= 0,1,2...L-1), where X(k) represents the sequence of the reference signal x(n) after zero padding, which is changed from the time domain signal to the frequency domain signal after fast Fourier transform, Y(k) Indicates that the measured signal y(n) after zero padding is changed from the time domain signal to the sequence of the frequency domain signal after fast Fourier transform, and k represents the sequence of X(k) and Y(k) in the sequence after Fourier transform Location; (3) Perform conjugate operation on X(k), multiply the result of the conjugate operation with Y(k) by complex numbers, the result of multiplication by complex numbers is the cross-correlation function R(k), and then perform R(k) Fast Fourier inverse transform, extract the real part R(τ), then the τ in the real part R(τ) corresponding to the maximum value of R(k) is the time difference between the required reference signal and the measured signal ; (4) The data of the ultrasonic echo signals received by other array elements in the array aperture in step 1 are used as the measured signal to carry out the calculations in steps (1) to (3) respectively, and the array aperture in each array aperture is obtained. The time difference of the element relative to the reference signal, and the obtained time difference is the delay time for each element in the selected array aperture to receive the defect reflection echo signal. 3. A phased array ultrasonic testing method based on improved dynamic depth focusing according to claim 1, characterized in that: in the first step, the step value of linear electronic scanning is 1 array element. 4. A phased array ultrasonic detection method based on improved dynamic depth focusing according to claim 1, characterized in that: in the step 1, the number of array elements selected for one transmission/reception of ultrasonic waves is phased array 1/4 of the number of array elements of the straight probe. 5. A phased array ultrasonic detection method based on improved dynamic depth focusing according to claim 1, characterized in that: the method of extracting the echo information of the defect position in the third step is to add a rectangular time window Any window function used in digital signal processing to extract information in a given interval. 6. A phased array ultrasonic testing method based on improved dynamic depth focusing according to claim 1, characterized in that: the phased array ultrasonic testing method is not only applied to the detection of a detected workpiece with only one defect, It is also applied to the inspection of inspected workpieces with more than two defects.

Images