A defect location and quantitative detection method based on ultrasonic nondestructive testing

Abstract

This invention discloses a method for quantitative defect location detection based on ultrasonic nondestructive testing, comprising the following steps: performing a linear B-scan on the test block to acquire a B-scan signal including n A-scan signals; normalizing the defect-free reference signal and the B-scan signal to obtain the defect echo signal; extracting the defect longitudinal wave echo time from each A-scan signal from the defect echo signal; establishing a coordinate system with the first scan position as the origin, the scan direction as the positive x-axis, and the direction perpendicular to the surface of the test block as the positive y-axis; and obtaining the defect location and size based on the scan point coordinates, the defect longitudinal wave echo time, and the longitudinal wave velocity. The results of this invention can directly output the defect location and size, and plot the defect morphology in the coordinate system, providing a clear and intuitive output. This invention can obtain the defect size based on the data from the linear B-scan, significantly improving detection efficiency compared to C-scan methods.

Description

Technical Field

[0001] The present invention belongs to the defect detection technology of metal additive parts, and specifically relates to a defect positioning and quantitative detection method based on ultrasonic non-destructive testing. Background Art

[0002] Driven by the manufacturing needs of large-scale, lightweight, integrated and reliable parts in the aerospace field, metal additive manufacturing technology and equipment are constantly maturing. At present, it has been piloted in the aerospace field, and has significantly improved the manufacturing size and manufacturing efficiency compared with traditional manufacturing processes. Metal additive manufacturing manufactures physical parts by melting and accumulating metal powder or wire layer by layer, which greatly reduces the constraints of part structure complexity on manufacturing process, time and cost, and can even manufacture parts that cannot be processed by conventional manufacturing technology. It has a strategic position in the aerospace field and has a very broad application prospect. However, the metal additive manufacturing process is a very complex multi-physical field coupling strong non-equilibrium metallurgical process with very complex multi-physical field coupling, such as the interactive coupling of high-energy beams and materials, crystal growth under ultra-high rapid solidification conditions of micro-molten pools, and organizational evolution under repeated cyclic heating and cooling conditions. The temperature gradient is large during the forming process, the solidification speed of the molten pool is fast, and metallurgical defects such as pores and cracks are prone to appear inside the parts, which seriously affect the mechanical properties of the parts. At present, it is urgent to carry out research on defect detection technology for metal additive parts.

[0003] Ultrasonic testing refers to a non-destructive testing method that uses ultrasonic waves to inspect internal defects of metal components. Ultrasonic waves are emitted to the surface of the component through a coupling agent using a transmitting probe. When the ultrasonic wave propagates inside the component, it will have different echo signals when it encounters different interfaces. The time difference and signal attenuation of different reflected signals transmitted to the probe can be used to detect defects inside the component. The size, location and general nature of the defect can be determined based on the amplitude and propagation time of the echo signal. Since metal materials undergo repeated cycles of heating and cooling during the additive manufacturing process, pores are easily generated inside the product. Therefore, it is necessary to carry out research on ultrasonic quantitative detection technology for pore defects inside additive products.

[0004] The Chinese patent, publication number CN105973992A, discloses "Ultrasonic wavelet detection method for micro-pore defects in epoxy cast insulation parts", which realizes quantitative detection of bottom surface defects of parts, and obtains the defect size by the difference between the bottom surface position and the pore position. However, this method has a good detection effect and detection accuracy for bottom surface defects. For internal defects, this method can realize defect location, but cannot realize defect size measurement. Summary of the invention

[0005] In order to overcome the problems in the prior art, the purpose of the present invention is to provide a defect positioning and quantitative detection method based on ultrasonic non-destructive testing, which can effectively improve the defect detection accuracy and improve the detection efficiency.

[0006] To achieve the above object, the technical solution adopted by the present invention is:

[0007] A defect location quantitative detection method based on ultrasonic nondestructive testing comprises the following steps:

[0008] Perform a linear B scan in the area to be tested of the block to be tested, and obtain a B scan signal S including n A scan signals;

[0009] The defect-free reference signal S R Normalize the signal S with the B scan signal to obtain the defect echo signal S';

[0010] Extract the defect longitudinal wave echo time t in each A-scan signal from the defect echo signal S' i ; i represents the number of the scan point;

[0011] A coordinate system is established with the first scanning position as the origin, the scanning direction as the positive x direction, and the direction inside the test block perpendicular to the surface of the test block as the positive y direction;

[0012] The defect position and size are obtained based on the scanning point coordinates, the defect longitudinal wave echo time and the longitudinal wave velocity.

[0013] A further improvement of the present invention is that the longitudinal wave velocity V is obtained by measuring on a standard test block made of the same material as the block to be tested.

[0014] A further improvement of the present invention is that an A-scan experiment is carried out on the surface of a standard test block, the arrival times T2 and T4 of the secondary longitudinal wave and the fourth longitudinal wave echo signals are extracted from the signals, and the longitudinal wave velocity is determined based on the arrival times T2 and T4 of the secondary longitudinal wave and the fourth longitudinal wave echo signals.

[0015] A further improvement of the present invention is that the longitudinal wave velocity is calculated by the following formula:

[0016]

[0017] Where H is the thickness of the standard test block.

[0018] A further improvement of the present invention is that the defect-free reference signal S R It is obtained by taking an A scan at a defect-free area of ​​the test block.

[0019] A further improvement of the present invention is that the defect-free reference signal S RThe specific process of normalizing the B-scan signal S to obtain the defect echo signal S' is as follows: subtract the defect-free reference signal S from the B-scan signal S R , and obtain the defect echo signal S'.

[0020] A further improvement of the present invention is that the center of the defect position is calculated by the following formula:

[0021]

[0022] Where i is 1 to n, D(x D ,y D ) is the center of the defect position.

[0023] A further improvement of the present invention is that the defect size r D Calculated by the following formula:

[0024]

[0025] Compared with the prior art, the present invention has the following technical effects:

[0026] The results of the present invention can directly output the position and size of the defect, draw the defect morphology in the coordinate system, and the output result is intuitive. The present invention can obtain the defect size based on the data of the linear B scan, and the detection efficiency is significantly improved compared to the method of detecting defects through C scan. The detection method of the present invention is simple. Based on the B-scan detection, it can be simplified to selecting no less than 3 representative positions and defect echo moments for calculation in extreme cases. The data processing process of the present invention is simple, and no signal processing method is required to enhance the features of the defect echo signal. It only needs to collect a reference signal in the defect-free area and subtract it from the original B-scan signal. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Figure 1 is an implementation flow chart of an embodiment of the present invention;

[0028] Figure 2 is a structural diagram of a detection system in an embodiment of the present invention;

[0029] Figure 3 is the normalized ultrasonic B-scan signal in the embodiment of the present invention;

[0030] Figure 4 It is the result after being processed by the method of the present invention.

[0031] Figure 5 This is the geometric relationship diagram between the two scanning points and the defects. DETAILED DESCRIPTION

[0032] The method of the present invention is further described below with reference to the accompanying drawings and embodiments.

[0033] See also Figure 2 The detection system adopted by the present invention includes an industrial computer 1, a scanning device 2, a PLC 3, an ultrasonic transmitting device 4, a signal acquisition card 5 and an ultrasonic probe 6, wherein the scanning device 2, the PLC 3, the ultrasonic transmitting device 4, and the signal acquisition card 5 are all connected to the industrial computer 1, the scanning device 2 is connected to the ultrasonic probe 6, the ultrasonic transmitting device 4 is also connected to the ultrasonic probe 6, and the ultrasonic probe 6 is used to test the block to be tested 7.

[0034] The ultrasonic quantitative detection method of internal pore defects of a workpiece of the present invention comprises the following steps:

[0035] Step 1: Determine the longitudinal wave velocity V on a standard test block made of the same material as the block to be tested; specifically, the following steps are included:

[0036] Step 1.1, perform an A-scan experiment on the surface of a standard test block with a thickness of H through an ultrasonic probe 6, extract the arrival times T2, T4, etc. of the secondary longitudinal wave, the fourth longitudinal wave, etc. longitudinal wave echo signals from the signal, and measure the thickness H of the standard test block;

[0037] Step 1.2: Determine the longitudinal wave velocity

[0038] Step 2: Perform A scan at the defect-free part of the block to be tested to obtain the defect-free reference signal S R ;

[0039] Step 3: Apply coupling agent (model: Hongda CG-98 ultrasonic coupling agent) to the area to be tested of the block to be tested, perform a linear B scan, and obtain a B scan signal S including n A scan signals;

[0040] Step 4: Normalization: Subtract the defect-free reference signal S from the B-scan signal S R , enhance the defect echo signal, suppress the bottom echo of the longitudinal wave, and obtain the defect echo signal S';

[0041] Step 5: Extract the defect longitudinal wave echo time t in each A-scan signal from the defect echo signal S' i ; i represents the number of the scan point;

[0042] Step 6: Take the first scanning position as the origin, the scanning direction as the positive x direction, the inner direction of the test block and perpendicular to the upper surface as the positive y direction, and establish a coordinate system. Set the coordinates of the i-th scanning point as (x i ,y i );

[0043] Step 7: According to the scanning point coordinates, the time of the defect longitudinal wave echo and the longitudinal wave velocity, solve the defect position and size: the specific steps are as follows:

[0044] Step 7.1: Construct the system of equations Substitute the longitudinal wave velocity V, the scanning point coordinates (x i ,y i ), time t of defect longitudinal wave echo i , find the defect center position D(x D ,y D ); i is from 1 to n.

[0045] Step 7.2: Construct the equation Calculate the defect radius r D .

[0046] The detection principle of the present invention is:

[0047] Assuming that the defect is a point that completely reflects ultrasonic waves (ignoring shape and size), when the ultrasonic wave propagates to the defect, because the probe has both excitation and receiving functions, the defect echo signal collected by the probe is the ultrasonic signal returned along the original path of the ultrasonic propagation path. Therefore, the product of the propagation time t and the wave velocity V obtained from the ultrasonic signal is twice the distance from the probe to the defect. When the defect position is unknown, a circle is drawn with the probe position as the center and the distance from the probe to the defect as the radius. The point on this circle is the position of the defect (reflection point) (the accurate defect position cannot be obtained from a single signal).

[0048] When the defect is a pore, its cross-section is a circle. Since ultrasonic waves propagate along the shortest path in the medium, the line from the probe to the defect reflection point will pass through the center of the defect (that is, the three points of probe-reflection point-defect center are on the same straight line).

[0049] When there are 2 scanning points (probe positions), such as Figure 5 As shown, let A and B be the scanning points, and ⊙D shown by the dotted line is the defect. ⊙A is a circle drawn with scanning point A as the center and half of the product of the defect echo time and wave velocity (AM length) as the radius. The defect reflection point is on ⊙A. M is the reflection point corresponding to scanning point A, so M is on both ⊙A and ⊙D, and the three points AMD are on a straight line. Similarly, B is the second scanning point, N is the corresponding reflection point, and the three points BND are on a straight line.

[0050] |AD-BD|=|DM+MA-DN-NB|, because M and N are both on ⊙D, so DM=DN, so |AD-BD|=|MA-NB|. From the above derivation, it can be seen that when the defect ⊙D is unknown, from the relationship between A, B, M, and N, it can be seen that with A and B as the focus and |MA-NB| as the real axis, a hyperbola can be drawn, and the defect center D is located on this hyperbola, such as Figure 5 Shown as the dashed line segment.

[0051] To find the defect center, only three scans are needed and two hyperbolas are drawn. However, considering the accuracy of the detection, as many hyperbolas as possible are needed (corresponding to the equation group in step 7.1), and their intersection is the defect center. After finding the defect center, the defect radius r = AD-AM = BD-BN.

[0052] Example 1

[0053] This embodiment provides a defect location quantitative detection method based on ultrasonic nondestructive testing. The specific implementation process is as follows: Figure 1 As shown, the following steps are included:

[0054] 1. Preparation of standard test blocks and defect test blocks;

[0055] Two ER2319 aluminum alloy test blocks with dimensions of 100×100×10mm were prepared by arc welding additive manufacturing technology. One defect-free test block was marked as a standard test block, and the other test block was marked as a defective test block. The side processing radius was 1mm and the depth was 5mm (center position) The transverse through hole was marked as a defect.

[0056] 2. Measurement of longitudinal wave velocity;

[0057] Coupling agent was applied to the surface of the standard test block, and the ultrasonic probe was arranged for testing to obtain the A-scan signal. The first longitudinal wave bottom echo in the signal appeared at 3.4μs, and the second longitudinal wave bottom echo appeared at 6.9μs. Combined with the thickness of the standard test block of 10mm, the longitudinal wave propagation velocity was calculated to be 5840m / s.

[0058] 3. Obtain a defect-free reference signal

[0059] An A-scan experiment was performed on the defect-free part of the defective test block. In order to reduce the error, the signal was averaged in the time domain after 16 repeated experiments to obtain the reference signal S R In order to pursue the accuracy of the test results, it is recommended to select as much scanning data as possible.

[0060] 4. Obtain the original ultrasonic signal;

[0061] Place the defective test block on the scanning device, apply coupling agent to the area to be tested, and fix the ultrasonic probe on the scanning device. Set the scanning parameters in the computer: scanning points 5, scanning step length 1mm, sampling frequency 20MHz, time domain average times 16 times, signal length 160 points (8μs), and the normalized signal is as follows Figure 3 The longitudinal wave echoes of the defects appear at positions 58, 52, 47, 42, and 37, and the corresponding longitudinal wave echo times are 2.9μs, 2.6μs, 2.3μs, 2.1us, and 1.85μs.

[0062] 5. Substitute into the equation to calculate and solve the defect location;

[0063] Substitute the scanning point coordinates, echo time, and longitudinal wave velocity into the equation group

[0064]

[0065] Among them, i=1,2,3,4.

[0066] Taking the first scan position as the coordinate origin, the above four equations are used to draw hyperbolas as follows: Figure 4 As shown in the figure, 5 scanning points are marked on the x-axis, and the intersection of the four hyperbolas is the defect center position D (8.008, 5.006).

[0067] 6. Substitute into the equation to calculate the defect radius

[0068]

[0069] Five defect radius values ​​were obtained, and the average value was 1.0112 mm, which was consistent with the defect size.

Claims

1. A defect location quantitative detection method based on ultrasonic nondestructive testing, characterized in that: The following steps are involved: Perform a linear B scan in the area to be tested of the block to be tested, and obtain a B scan signal S including n A scan signals; The defect-free reference signal S R Normalize the signal S with the B scan signal to obtain the defect echo signal S'; Extract the defect longitudinal wave echo time t in each A-scan signal from the defect echo signal S' i ; i represents the number of the scan point; A coordinate system is established with the first scanning position as the origin, the scanning direction as the positive x direction, and the direction inside the test block perpendicular to the surface of the test block as the positive y direction; According to the scanning point coordinates, the time of the defect longitudinal wave echo and the longitudinal wave velocity, the defect position and size are obtained; The longitudinal wave velocity is calculated by the following formula: Where H is the thickness of the standard test block, T2 is the arrival time of the secondary longitudinal wave signal, and T4 is the arrival time of the fourth longitudinal wave signal; The center of the defect location is calculated by the following formula: Where i is 1 to n, D(x D ,y D ) is the center of the defect position, x D is the horizontal coordinate of the defect center, y D is the horizontal coordinate of the defect center, x i is the horizontal coordinate of the scan point coordinate, y i is the ordinate of the scan point, x i+1 The horizontal coordinate of the next scan point, y i+1 is the ordinate of the next scan point, t i is the time of defect longitudinal wave echo, t i+1 is the time of the next defect longitudinal wave echo, V is the longitudinal wave velocity; Defect size r D Calculated by the following formula:

2. A defect location quantitative detection method based on ultrasonic nondestructive testing according to claim 1, characterized in that: Defect-free reference signal S R It is obtained by taking an A scan at a defect-free area of ​​the test block.

3. The defect location quantitative detection method based on ultrasonic nondestructive testing according to claim 1 is characterized in that: The defect-free reference signal S R The specific process of normalizing the B-scan signal S to obtain the defect echo signal S' is as follows: subtract the defect-free reference signal S from the B-scan signal S R , and obtain the defect echo signal S'.

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