CN102818851B - Detection method for ultrasonic detection of arc-shaped corner of L-shaped workpeice - Google Patents

Abstract

A detection method for ultrasonic detection of an arc corner of an L-shaped workpiece by using a detection device, the detection method comprising the following steps: determining the parameters of a phased array straight probe from the arc corner of the L-shaped workpiece; The parameters of the curved corner and the phased array straight probe determined in the previous step determine the surface center position of the phased array straight probe placed along the bisector of the opening angle θ perpendicular to the curved corner and the position of the curved corner The distance D between the center positions; the step of determining the wedge, the arc surface of the wedge is determined by the arc corner of the detected L-shaped workpiece, and the surface of the phased array straight probe determined by the position is determined to be coupled with it. The flat surface of the wedge; the steps of ultrasonic beam emission, echo signal reception and image processing steps. With the application of the present invention, for different curved corner structures of L-shaped workpieces to be detected, the replacement wedge is used instead of the phased array straight probe, and the most common phased array straight probe is used to complete the detection, which greatly saves the hardware cost.

Description

Ultrasonic testing method for arc corners of L-shaped workpieces

technical field

The invention relates to an ultrasonic nondestructive testing method, in particular to a testing method for ultrasonic testing of arc corners of L-shaped workpieces based on phased array ultrasonic testing technology.

Background technique

Nondestructive testing (nondestructive test), referred to as NDT, is a technology that detects its performance, quality, and internal defects without destroying or damaging the object under test. Among the existing non-destructive testing methods, the conventional methods mainly include radiographic testing (RT) method, ultrasonic testing (UT) method, penetrant testing (PT) method, magnetic particle testing (MT) method, eddy current testing (ET) method, and of course There are unconventional ones, such as microwave detection method, potential detection method, etc.

Ultrasonic testing (UT) is to use the ultrasonic wave to propagate in the material to be tested, the acoustic characteristics of the material and the change of the internal structure have a certain influence on the propagation of the ultrasonic wave, and to understand the material performance and structural changes by detecting the degree and condition of the ultrasonic wave. . When an ultrasonic wave enters an object and encounters a defect, a part of the sound wave will be reflected. The receiver analyzes the reflected wave to measure the thickness of the material, to find hidden internal defects, or to analyze such as metal, plastic, composite material, ceramics, etc. properties of materials such as rubber, glass, etc.

Specifically, the phased array ultrasonic testing technology is to control each array element in the transducer array through the electronic system, and transmit and receive ultrasonic waves according to a certain delay time rule, so as to dynamically control the deflection and focusing of the ultrasonic beam in the workpiece. Non-destructive testing of materials. When the synthesized ultrasonic beam encounters the target, an echo signal will be generated, and the arrival time of each array element is different. According to the time difference of the echo arriving at each array element, the element signal is compensated for delay and synthesized, and the specific ultrasonic beam can be synthesized. The superposition of echo signals in one direction is enhanced, while the echo signals in other directions are weakened or even canceled to obtain an ultrasound scan. In order to make those skilled in the art more clearly understand the principle of deflection and focusing of the ultrasonic beam, FIG. 12( a ) and FIG. 12 ( b ) are used for illustration. Among them, Fig. 12(a) is a schematic diagram of a one-dimensional linear array probe to realize acoustic beam deflection through time delay control, wherein the excitation pulse respectively excites the N array elements in the transducer array elements with a certain time delay, and the synthesized The beam direction and the horizontal direction form a deflection angle θ. Correspondingly, the synthesized beam front forms an angle θ with the vertical direction, which forms the deflection of the acoustic beam; The time delay of is used to excite the N array elements in the transducer array elements respectively, which synthesize the wave front and focus on the point P, that is, form the acoustic beam focus.

Due to the complex structure of L-shaped workpieces, conventional ultrasonic testing methods are limited by equipment capabilities and methods, making it difficult to achieve accurate detection. At present, for its ultrasonic non-destructive testing, in addition to the traditional ultrasonic C-scan system, phased array probes with special shapes such as arc probes have been used to complete the ultrasonic testing of L-shaped structures. Because this method must design arc probes And processing, even for samples with slightly different arc corners, it is necessary to use phased array arc probes of different sizes, so the hardware cost is relatively high.

Contents of the invention

For this reason, in order to solve the above-mentioned technical problems, the present invention selects ordinary phased array straight probes and specially designs arc wedges to detect the arc corners of L-shaped workpieces. Like this, since the probes are selected from general parts, the wedges The manufacture of the block is relatively easy, so the cost is greatly saved. Furthermore, for L-shaped workpieces with slightly different arc radii, the present invention does not need to replace the phased array straight probe, and only needs to design arc wedges of different sizes to meet the good coupling with the inspected workpiece, which greatly reduces the hardware cost. cost.

A detection method for ultrasonic detection of arc corners of L-shaped workpieces using a detection device, wherein the detection device includes a phased array ultrasonic flaw detector, a phased array straight probe and a wedge, and the phased array ultrasonic The flaw detector is electrically connected to the phased array straight probe, the phased array straight probe has a plurality of array elements, and its geometric parameters include at least the number of array elements and the distance between array elements, and the wedge has a The curved surface coupled with the curved corner of the L-shaped workpiece and the straight surface coupled with the phased array straight probe; wherein the detection method comprises the following steps:

(a) the geometric parameter determining step of the phased array straight probe, the geometric parameter of the phased array straight probe is determined by the arc corner of the L-shaped workpiece;

(b) the step of determining the position of the phased array straight probe, the parameter determination of the phased array straight probe determined by the arc corner of the L-shaped workpiece and step (a) along the direction perpendicular to the arc corner The distance D between the center position of the phased array straight probe surface facing the arc-shaped corner and the center position of the arc-shaped corner placed on the bisector of the opening angle θ;

(c) The step of determining the wedge, the arc surface of the wedge is determined by the arc corner of the detected L-shaped workpiece, and the surface of the phased array straight probe determined by the position is determined to be coupled with it the flat surface of said wedge;

(d) Ultrasonic beam transmitting step, first select a plurality of said array elements respectively to form a plurality of sub-arrays, then carry out time delay between each said array elements in each sub-array of said plurality of sub-arrays, and then said The pulse signal sent by the phased array ultrasonic flaw detector excites each element of each sub-array in the plurality of sub-arrays to emit ultrasonic waves, and then the ultrasonic beam synthesized by each sub-array is vertically incident on the arc of the L-shaped workpiece to be detected. shape corner;

(e) Echo signal receiving step, the ultrasonic beam forms an echo signal after encountering an internal defect of the detected L-shaped workpiece, and the echo signal is received by each array element in the sub-array and forms an A scan signal;

(f) Image processing step, the A-scan signal is received by the phased array ultrasonic flaw detector, and converted into a C-scan image through a corresponding image processing program.

The beneficial effect of the invention is that the arc corner of the L-shaped workpiece is detected by selecting the phased array straight probe and designing the matching arc wedge, which greatly reduces the cost. Furthermore, for the slightly different structure of the curved corner of the L-shaped workpiece, the replacement wedge is used instead of the phased array straight probe, and the most common phased array straight probe is used to complete the detection, which greatly saves hardware costs and Design, test time.

Description of drawings

In order to explain the present invention, exemplary embodiments thereof will be described hereinafter with reference to the accompanying drawings, in which:

Figure 1 shows a schematic diagram of a phased array straight probe detecting an L-shaped workpiece with an arc corner radius of 4 mm;

Fig. 2 shows a schematic diagram of detecting an L-shaped workpiece with an opening angle greater than 90 degrees with a phased array straight probe;

Fig. 3 shows the schematic diagram of detecting an L-shaped workpiece with an opening angle less than 90 degrees with a phased array straight probe;

Fig. 4 shows the phased array straight probe position in Fig. 1 more specifically;

Fig. 5 schematically shows the arc wedge used in the present invention;

Fig. 6 shows the schematic diagram of carrying out right boundary detection with phased array straight probe;

Fig. 7 has shown the schematic diagram that carries out detection in the whole range with phased array straight probe;

Fig. 8 shows the schematic diagram of carrying out left boundary detection with phased array straight probe;

Figure 9 shows a schematic diagram of ultrasonic scanning imaging;

Figure 10 shows a schematic diagram of a 3D matrix;

Figure 11 shows a schematic diagram of scanning data filling;

Figure 12(a) shows a schematic diagram of acoustic beam deflection delay control;

Fig. 12(b) shows a schematic diagram of delay control of acoustic beam deflection and focus.

Detailed ways

In the present invention, in the ultrasonic detection of the arc corner of the L-shaped workpiece, the detection device includes a phased array ultrasonic flaw detector, a phased array straight probe and a wedge. Among them, the phased array ultrasonic flaw detector is electrically connected with the phased array straight probe, the phased array straight probe has a plurality of array elements, the wedge has an arc surface coupled with the arc corner of the L-shaped workpiece and is connected with the phase control A flat surface to which an array probe is coupled.

When using the above-mentioned phased array straight probe to detect defects on L-shaped workpieces, the phased array ultrasonic flaw detector is used to respectively excite each array element (chip) of the phased array straight probe with an electric pulse with a small time difference. In essence, it is a transducer of electro-acoustic and acoustic-electric conversion, so each array element of the phased array straight probe emits ultrasonic waves to form an ultrasonic composite beam and shoots to the inside of the arc corner of the L-shaped workpiece. When the ultrasonic wave encounters a defect It will be returned in the form of a flaw echo, and the flaw echo will return to each array element with a calculable time difference. Before the signals merge, there is a time difference between the echo signals received by each array element. The A-scan pattern formed after the signals are merged shows the echo characteristics of a focal point in the material.

In the present invention, the sound beam control focusing principle of the arc corner of the L-shaped workpiece is as follows, that is, by exciting different phased array straight probe array elements for different detection point positions, and controlling the excitation or reception pulse of each array element The time delay is different, and the phase control such as phased array deflection and focusing is realized, so that the sound beam is incident on the detected surface as vertically as possible, and the sound beam is adjusted to the arc corner area without moving the phased array straight probe laterally. Full coverage.

The present invention adopts ordinary phased array straight probes and specially designed arc wedges, aiming at the radii of different arc corners of L-shaped workpieces, by designing arc wedges of different sizes to meet the good coupling with the inspected workpiece, Reduced hardware costs. Regarding the selection of phased array straight probes and curved wedges, three factors are mainly considered: the radius of the curved corner of the workpiece to be inspected, the opening angle of the curved corner, and the thickness. The following steps can be followed:

First, according to the radius and opening angle of the arc corner of the L-shaped workpiece, determine the number of array elements, array element spacing and outer shell dimensions of the selected phased array straight probe. Figure 1 is a schematic diagram of the detection of an L-shaped workpiece with an arc corner radius of 4mm and an opening angle of 90°. The phased array straight probe is placed on the vertical plane of the bisector of the opening angle of the arc corner. The two ends of the arc-shaped corner detection area are S1 and S2. In order to ensure that the sound beam is perpendicular to the S1 and S2 points of the detected surface, the sound beam deflection direction is the normal direction of S1 and S2 points, so as to obtain the maximum deflection of the sound beam direction.

For an L-shaped workpiece with an opening angle of 90°, first determine the array element spacing p of the phased array straight probe to be selected (the array element spacing p is in mm), in order to obtain a good sound field when the sound beam is deflected at a large angle characteristics, the array element spacing p is usually equal to the wavelength λ, and only one decimal place is required, where the wavelength λ is equal to the ratio of the sound velocity of the workpiece to the frequency of the phased array straight probe (the frequency of the phased array probe is determined by the actual measured workpiece performance), for example, for a carbon fiber reinforced composite L-shaped workpiece with a sound velocity of 2950m/s, when the frequency of the phased array probe is selected to be 5MHz, its wavelength is equal to 0.59mm, and the array element spacing p is 0.6mm; then, according to geometric relationship Determine the number n of array elements in the sub-array, and determine the number N of array elements of the phased array straight probe to be selected according to the number n of array elements in the sub-array. In the above geometric relationship, n is the number of array elements in the phased array straight probe sub-array, and n can only choose 4, 8, 16..., which is the exponential multiple of 2; d is the phase separation of the array elements at both ends The distance from the edge of the shell of the array control straight probe is selected here as a small-profile probe, so d=3mm; r is the arc radius of the arc corner of the L-shaped workpiece, which is determined by the actual arc radius of the L-shaped workpiece; θ is the opening angle. When the opening angle of the L-shaped workpiece is equal to or greater than 90°, θ is equal to 90°. When the opening angle of the L-shaped workpiece is less than 90°, θ is equal to the opening angle of the L-shaped workpiece. The maximum value of n that can satisfy the above geometric relationship is the number n of array elements in the determined subarray. For example, for an L-shaped workpiece with a circular arc radius r of 4 mm and an opening angle of 90°, when the array element spacing When it is determined to be 0.6mm, n can be set to 8 to satisfy the above geometric relationship. The selection basis for the number of array elements N of the phased array straight probe and the number of array elements n of the sub-array is: the number of array elements N of the phased array straight probe is generally 16, 32, 64, 128, etc. For a phased array straight probe with 16 pieces, the number of array elements n of the selected sub-array is usually 4, and for a phased array straight probe with a number of array elements N of 32, the number of array elements n of the selected sub-array is usually 8, in order analogy. Therefore, after the number n of array elements of the sub-array is determined, according to the above relationship, the number N of array elements of the selected phased array straight probe can be inversely deduced. According to the above method, for an L-shaped workpiece with an arc corner radius r of 4 mm and an opening angle of 90°, a phased array straight probe with an array element number N of 32 and an array element spacing p of 0.6 mm can be selected.

As shown in Figure 2, for an L-shaped workpiece with an opening angle greater than 90°, since its arc detection area is smaller than that of the workpiece with an opening angle of 90°, the phased array of an L-shaped workpiece with an opening angle of 90° can still be used. Straight probe parameters.

As shown in Figure 3, for L-shaped workpieces with an opening angle of less than 90°, the selection method for L-shaped workpieces with an opening angle of 90° proposed above can be used to select the geometric parameters of the phased array straight probe. Since the arc detection area is larger than the arc detection area with an opening angle of 90°, this method can realize the detection of part of the arc area, that is, the area between S1 and S2 in Figure 3.

The shell length L is the product of the number of array elements N and the array element spacing p plus the distance d between the array elements at both ends and the edge of the shell. The shell width is the element width plus the distance between the element and the edge of the shell.

Secondly, determine the distance D between the center position of the phased array straight probe surface and the center position of the detection area of the arc-shaped corner. According to the geometric relationship, In the formula, N is the number of array elements of the phased array straight probe, n is the number of array elements of the selected sub-array, and p is the array element spacing. For L-shaped workpieces equal to and less than 90°, α is the opening angle θ, and for L-shaped workpieces greater than 90°, α=180°-θ. As shown in Figure 4, according to the parameters of the phased array straight probe selected above, N=32, n=8, α=π/2, p=0.6mm, that is, D is 7.2mm.

When changing to the next L-shaped workpiece with a slightly different arc corner for detection, the radius R of the arc corner of the next L-shaped workpiece is the same as the arc of the L-shaped workpiece selected when determining the geometric parameters of the phased array straight probe When the radius r of the corner part satisfies |R-r|≤1, the phased array straight probe determined above can still be used to detect the detected L-shaped workpiece, and only need to replace the curved wedges of different sizes.

Then, according to the arc corner of the detected L-shaped workpiece and the determined geometric parameters and placement positions of the phased array straight probe, the geometric dimensions of the required wedge are determined. The wedge size mainly includes the corner radius r', the angle ω, the maximum height h from the arc surface to the straight surface, and the wedge thickness w. 4 and 5, the curved wedge radius r' and angle ω are determined by the radius r and the opening angle θ of the arc corner of the L-shaped workpiece to be detected, that is, r'=r, ω=θ. The height h is the sum of the distance between the radius r' of the bend and the center position of the phased array straight probe surface and the center position of the wedge bend. Since r'=r, h=r+D. The wedge thickness w is determined by the shell width of the phased array straight probe.

By stimulating different array elements at different detection point positions, and controlling the time delay of each array element excitation or receiving pulse, phase control such as deflection and focusing of the phased array is realized, and the phased array straight probe is not moved laterally. Full coverage of the sound beam in the lateral area of the curved corner.

Below, take an L-shaped workpiece with a radius of 4mm at the arc corner as an example. Here, a phased array straight probe with 32 elements is selected, and the method of setting the time delay is as follows:

First select the 1st to 8th array elements, among which, these 8 array elements are synthesized into a sub-array, which can be called the first sub-array. As shown in Figure 6, in order to make the sound beam perpendicularly incident on the detection point P at the rightmost end of the arc corner area of the detected L-shaped workpiece, the deflection direction of the sound beam is determined by the position of the detection point P and the effective aperture of the selected first sub-array. The center position O is determined, so that the deflection angle α can be calculated. Then, according to the determined beam deflection angle α, according to the beam deflection focus delay control method shown in Figure 12(b), the excitation pulse respectively excites the 8 arrays in the transducer array elements element, its synthetic wavefront is focused on point P to realize the deflection and focus of the acoustic beam at the deflection angle α.

Adopt phased array linear scanning mode, respectively for the 2nd to 9th, 3rd to 10th, 4th to 11th...24th to 31st, a total of 23 sub-arrays (the center positions of each array element combination are O ₁ , O ₂ .. .O ₂₃ ) to motivate. In this way, the first sub-array completes receiving and sending of ultrasonic beams, and then the second sub-array completes sending and receiving, and so on, so that each sub-array takes turns sending and receiving until the 23rd sub-array completes sending and receiving, that is, the arc corner Scanning at different detection points within the detection area. As shown in Figure 7, by dividing the detection area at the corner of the arc into 24 equal parts, 23 detection points K ₁ , K ₂ ... K ₂₃ in the detection area can be obtained, passing through the center of the effective aperture of the selected sub-array respectively position (O ₁ , O ₂ ... O ₂₃ ) and the detection point (K ₁ , K ₂ ... K ₂₃ ) of the arc corner to draw a straight line, then the direction of the scanning sound beam on the detection area is sequentially determined ( 23 in total). Then, according to the calculation method of the deflection angle α _{above, each sound beam deflection angle β 1 , β 2} , β _{3 .} . . Finally, according to the determined sound beam deflection angle, according to the above-mentioned sound beam deflection focus delay control method, the deflection focus of the sound beam at each deflection angle is realized, thereby realizing the detection of the entire detection range.

For the calculation of the deflection angle γ of the leftmost detection point of the arc corner detection area, it is the same as the rightmost detection point of the arc corner area. The 25th to 32nd array elements are selected, and these 8 array elements synthesize the effective aperture. The point position Q and the center position of the effective aperture determine the deflection direction of the sound beam, and then the deflection angle γ is calculated by using the calculation method of the deflection angle α above, as shown in FIG. 8 . According to the determined deflection angle of the sound beam, the deflection focus of the sound beam at the deflection angle is realized according to the above-mentioned deflection focus delay control method of the sound beam.

Use the above-mentioned deflected and focused acoustic beam to scan for defects on L-shaped workpieces. The echo signals are received by the phased array system to obtain A-scan data. The image processing program in the flaw detector in the phased array system is based on the arc of the L-shaped workpiece. The corner shape adopts image processing to obtain the C-scan expansion diagram of the L-shaped workpiece. In this way, the internal defect state at the corner of the L-shaped workpiece can be accurately reflected, and defect quantification and positioning detection can be completed on this basis. Specifically, as described below, Fig. 9 is a schematic diagram of B-scan imaging and C-scan imaging of phased array ultrasonic scanning imaging. Here, taking an L-shaped workpiece with an arc corner radius of 4mm as an example, how to The scan data plots a C-scan development of the arc's corner region.

First, define the parameters. Specifically, the number of sound beams is 25, the amount of data collected by the sound beams is 50, and the sound velocity of the L-shaped workpiece is 2950m/s.

Then, a 3D matrix is established as shown in FIG. 10 . In this matrix, the length is the longitudinal length of the workpiece, and the grid in the length direction is divided according to the width of each scan of the phased array straight probe; The position of the detection point at the right end, the grid in the width direction is divided according to the number of sound beams synthesized by the arc-shaped corner detection area, respectively 1st to 8th, 2nd to 9th, 3rd to 10th, ..., 25th ~32, a total of 25 sub-arrays; the height is the workpiece thickness of the L-shaped workpiece, and the grid in the height direction is divided according to the amount of data collected by the sound beam. In this embodiment, the width of the 3D matrix is 25, the height is 50, and the width of each scan of the phased array straight probe is 6 mm.

Then, the A-scan data collected at each detection point is read into the 3D matrix according to the principle of taking the maximum value of the position superposition point. For example, the first group of sound beams is emitted, and then the A-scan echo data obtained by receiving is put into the 3D matrix, as shown in Figure 11, the positions where the x direction is 1 and the y direction is 1-50 are captured by the first group of A-scan data (50) filling, and so on, the A-scan data obtained from the 2nd to 25th sound beams along the x direction are respectively stored in the corresponding positions of the matrix in the y direction. Then the phased array straight probe moves along the longitudinal direction of the workpiece, that is, the z direction, repeats the above steps, and completes the A-scan data filling of the 3D matrix in turn; , project the data onto the upper surface to obtain a C-scan two-dimensional matrix, that is, obtain a top view of the surface of the detected workpiece; perform image filling on the data in the C-scan two-dimensional matrix, and preferably use image denoising and image segmentation at the same time The processing method processes the C-scan image; finally, draws the C-scan image of the arc corner detection area of the L-shaped workpiece according to the proportional relationship.

The beneficial effect of the present invention is that, for different arc-shaped corner structures of L-shaped workpieces, replacement wedges are used instead of phased array straight probes, and the most common phased array straight probes are used to complete the detection, which greatly saves hardware costs ;Adopt specific phased array focusing law to achieve sound beam deflection and focusing, and realize rapid detection of arc corner structure of L-shaped workpiece without moving the phased array straight probe; use C-scan expansion diagram to display the whole The arc-shaped corner detection area makes the defect display mode more intuitive and improves the ability to distinguish defects. This method has important practical value for ultrasonic nondestructive testing of L-shaped workpieces made of carbon fiber reinforced resin matrix composite materials.

The present invention is not limited in any way to the exemplary embodiments presented in the description and drawings. All combinations of (parts of) embodiments shown and described are expressly understood to be incorporated within this description and expressly understood to fall within the scope of the present invention. Moreover, many variations are possible within the scope of the invention as outlined by the claims. Furthermore, any reference signs in the claims should not be construed as limiting the scope of the invention.

Claims (7)

1. A method for ultrasonically detecting the arc corner of an L-shaped workpiece using a phased array ultrasonic testing device, wherein the phased array ultrasonic testing device includes a phased array ultrasonic flaw detector, a phased array straight probe and a phased array ultrasonic testing device. Wedge, the phased array ultrasonic flaw detector is electrically connected to the phased array straight probe, the phased array straight probe has a plurality of array elements, and its geometric parameters include at least the number of array elements and the distance between array elements. The wedge has an arc surface coupled with the arc corner of the L-shaped workpiece and a straight surface coupled with the phased array straight probe; wherein the detection method includes the following steps: (a) a step for determining the geometric parameters of the phased array straight probe, determining the geometric parameters of the phased array straight probe by the arc corner of the L-shaped workpiece; (b) the step of determining the position of the phased array straight probe, the parameter determination of the phased array straight probe determined by the arc corner of the L-shaped workpiece and step (a) along the direction perpendicular to the arc corner The distance D between the center position of the phased array straight probe surface facing the arc-shaped corner and the center position of the arc-shaped corner placed on the bisector of the opening angle θ; (c) The step of determining the wedge, the arc surface of the wedge is determined by the arc corner of the L-shaped workpiece, and the surface of the phased array straight probe determined by the position is determined to be coupled with it the flat surface of the wedge; (d) Ultrasonic beam transmitting step, first select a plurality of said array elements respectively to form a plurality of sub-arrays, then carry out time delay between each said array elements in each sub-array of said plurality of sub-arrays, and then said The pulse signal sent by the phased array ultrasonic flaw detector excites each element of each sub-array in the plurality of sub-arrays to emit ultrasonic waves, and then the ultrasonic beam synthesized by each sub-array is perpendicularly incident on the arc angle of the L-shaped workpiece. department; (e) an echo signal receiving step, the ultrasonic beam meets the L-shaped workpiece to form an echo signal, and the echo signal is received by each array element in the sub-array to form an A-scan signal; (f) Image processing step, the A-scan signal is received by the phased array ultrasonic flaw detector, and converted into a C-scan image through a corresponding image processing program. 2. The method according to claim 1, wherein in step (a), the array element spacing p of the straight probe of the phased array is determined earlier according to p≈v/f, wherein, v represents the distance of the L-shaped workpiece Speed of sound, f represent the frequency of the phased array straight probe; then according to the formula Determine the array element number n of the sub-array of the phased array straight probe, wherein, d represents the distance between the two ends of the array elements from the shell edge of the phased array straight probe, and r represents the arc of the L-shaped workpiece radius, when the opening angle of the L-shaped workpiece is equal to or greater than 90°, θ is equal to 90°, and when the opening angle of the L-shaped workpiece is less than 90°, θ is equal to the opening angle of the L-shaped workpiece; and then, according to the phase control The number n of array elements of the sub-array of the straight probe determines the number N of array elements of the phased array straight probe. 3. The method according to claim 1 or 2, wherein, in step (b), the center position of the surface of the phased array straight probe facing the curved corner is the same as that of the curved surface The distance D between the centers of the circles is given by the geometric relation To determine, wherein, when the opening angle θ of the L-shaped workpiece is less than or equal to 90°, α=θ, and when the opening angle θ of the L-shaped workpiece is greater than 90°, α=180°-θ. 4. The method according to claim 3, wherein in step (c), the arc length radius of the arc surface of the wedge and the corresponding arc length of the arc length are determined by the arc corner of the L-shaped workpiece. Central angle, the maximum height h of the wedge is calculated by the formula h=r+D, wherein r represents the arc radius of the L-shaped workpiece, and the thickness of the wedge is not less than the width of the phased array straight probe . 5. The method according to claim 1, wherein the image processing step includes a parameter definition substep, a 3D matrix establishment substep, and a C-scan image establishment substep, wherein the parameter definition substep defines the ultrasonic wave The number of beams, the amount of data collected by the ultrasonic beam, the start position and end position of the scan, and the sound velocity of the workpiece; The sub-step of establishing the 3D matrix, firstly, take the longitudinal length of the L-shaped workpiece as long, the arc length of the arc-shaped corner of the L-shaped workpiece as width, and the thickness of the arc-shaped corner of the workpiece as high Establish a matrix, wherein the step in the length direction is divided according to the size of each scan of the phased array straight probe, and the step in the width direction is according to the ultrasonic beam shot at the arc-shaped corner of the workpiece The number of divisions, the steps in the height direction are divided according to the amount of data collected by the ultrasonic beam, and then the A-scan data are respectively read into the 3D matrix to form a 3D matrix; The sub-step of establishing the C-scan image, firstly, taking the maximum value in the height direction of the 3D matrix and projecting the A-scan data onto the surface formed by the width and length of the 3D matrix to form a C-scan two-dimensional matrix, and then performing image Fill to get C-scan image. 6. The method according to claim 5, wherein the steps of image denoising and image segmentation processing are included in the C-scan image building sub-step. 7. The method according to claim 1, further comprising step (g) next L-shaped workpiece detection step, R represents the radius of the arc corner of the next L-shaped workpiece, and r represents the step (a) The radius in the geometric parameters of the arc corner of the L-shaped workpiece detected, when |R-r|≤1, the parameters and positions of the phased array straight probe remain unchanged, according to steps (c)-( f) Perform detection.