Composite material defect self-adaptive frequency selection method and ultrasonic detection method

Abstract

The invention provides a composite material defect self-adaptive frequency selection method. The method comprises the following steps: selecting a test block with defects; performing ultrasonic detection on the test block to obtain an ultrasonic detection signal diagram; according to the ultrasonic detection signal diagram, identifying a defect ultrasonic waveform and an interference waveform under a specific defect type; eliminating interference waveforms to obtain time intervals and time domain signals of defect ultrasonic waveforms; performing Fourier transform on the time domain signal to obtain a frequency domain signal; and according to the curve graph of the frequency domain signal, obtaining a frequency value corresponding to the maximum amplitude, and taking the frequency as the detection frequency corresponding to the specific defect. The invention further provides an ultrasonic detection method. The method can improve the detection precision.

Description

Technical Field

[0001] The present invention relates to the field of ultrasonic detection, and in particular to the field of ultrasonic detection of defects in composite materials. Background Art

[0002] Composite materials are composed of different component materials, and there are interface layers between the components. For fiber-reinforced resin-based composite materials, due to the gaps between fibers or fiber bundles, mesoscopic or microscopic structures such as pores are inevitably generated during the molding process. This composite material composed of multiple components and complex internal structures has different responses to ultrasound due to its different components and structures, such as different sound reflection coefficients, sound transmission coefficients, sound speeds, and sound attenuation coefficients, forming sound response characteristics different from those of homogeneous materials such as steel and aluminum. On the other hand, composite materials inevitably produce defects during the molding process, such as delamination, inclusions, pores, resin-rich, glue-poor, fiber breakage, fiber wrinkling, and other defects.

[0003] Therefore, when ultrasonic testing is performed on composite materials, different components, different structures and different internal defects have different responses to ultrasonic waves. Therefore, it is required to select different testing parameters for the testing of a certain type of special structure or composite materials with specific defects, and select different testing frequencies f for different structures and defects. The traditional ultrasonic testing method generally uses a fixed ultrasonic testing probe, such as a 2.5MHz, 5MHz and other frequency ultrasonic testing probe, to perform single-frequency ultrasonic testing on composite materials. This method does not take into account the different ultrasonic response characteristics of composite material components, internal structures and internal defects, and cannot set the optimal testing frequency for specific defect types inside the composite material for targeted testing. The accuracy and effectiveness of the test results cannot be guaranteed. Summary of the invention

[0004] An object of the present invention is to provide a composite material defect adaptive frequency selection method.

[0005] Another object of the present invention is to provide an ultrasonic detection method to improve the accuracy and reliability of detection.

[0006] The composite material defect adaptive frequency selection method for achieving the above-mentioned purpose comprises the following steps: selecting a test block with defects; performing ultrasonic detection on the test block to obtain an ultrasonic detection signal graph; identifying the defect ultrasonic waveform and interference waveform under a specific defect type according to the ultrasonic detection signal graph; eliminating the interference waveform to obtain the time interval and time domain signal of the defect ultrasonic waveform; performing Fourier transform on the time domain signal to obtain a frequency domain signal; and obtaining the frequency value corresponding to the maximum amplitude according to the curve graph of the frequency domain signal, and confirming the frequency as the detection frequency corresponding to the specific defect.

[0007] In one or more embodiments, the interference waveform includes a surface reflection wave, a bottom reflection wave, and a secondary reflection wave.

[0008] In one or more embodiments, the signal outside the time interval of the defect ultrasonic waveform of the ultrasonic detection signal diagram is reset to zero and reset to the basic amplitude.

[0009] In one or more embodiments, the specific defect types include delamination, debonding, dense porosity, air holes, inclusions, glue-rich, resin-rich, fiber wrinkles, and fiber breaks.

[0010] In one or more embodiments, the method further includes: adjusting the ultrasonic detection signal graph under the specific defect type to 80% of the full screen height, recording the ultrasonic detection gain value, and using the ultrasonic detection gain as the detection reference sensitivity for this type of defect.

[0011] In one or more embodiments, the detection frequency corresponding to each specific defect type is recorded to obtain a defect-detection frequency set.

[0012] In one or more embodiments, CT testing is performed to determine the type and location of defects before ultrasonic testing is performed on the test block.

[0013] An ultrasonic testing method for achieving the above-mentioned purpose is used to perform ultrasonic testing on a workpiece to be tested, and includes the following steps: according to the above-mentioned method, different testing frequencies corresponding to different types of defects are obtained; the testing frequencies corresponding to specific types of defects are selected in turn to perform ultrasonic testing on the workpiece to be tested, the testing frequency is used as the ultrasonic excitation frequency of an ultrasonic generator, and an ultrasonic testing probe with a center frequency equal to the testing frequency is selected to determine whether the workpiece to be tested has a specific type of defect corresponding to the testing frequency; and the testing is stopped when it is detected that the workpiece to be tested has a specific type of defect.

[0014] In one or more embodiments, reflection or penetration ultrasonic testing is performed.

[0015] In one or more embodiments, when it is detected that the sensitivity of the part to be detected exceeds the detection reference sensitivity, the detection is stopped.

[0016] The above-mentioned composite material defect adaptive frequency selection method performs waveform analysis on various types of specific defects, extracts the waveforms corresponding to typical defect signals, performs data processing on the acoustic wave time domain signals corresponding to the defects and obtains their frequency domain signals through Fourier transform, obtains the optimal ultrasonic detection frequency corresponding to each specific defect, and establishes a set of optimal ultrasonic detection parameters; various types of defects in composite materials are detected according to the detection frequencies obtained above, thereby realizing accurate detection of various types of defects in composite materials. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] The above and other features, properties and advantages of the present invention will become more apparent through the following description in conjunction with the accompanying drawings and embodiments, in which:

[0018] Figure 1 It is the ultrasonic testing signal diagram of composite materials with defects;

[0019] Figure 2 It is a schematic diagram of defect ultrasonic waveform and interference waveform under a specific defect type;

[0020] Figure 3 is an ultrasonic detection signal diagram after removing the interference waveform;

[0021] Figure 4 It is a frequency domain signal diagram;

[0022] Figure 5 It is a flow chart of the adaptive frequency selection method for composite material defects;

[0023] Figure 6 is a flow chart of a specific embodiment of the adaptive frequency selection method;

[0024] Figure 7 It is a flow chart of the ultrasonic testing method. DETAILED DESCRIPTION

[0025] The present invention is further described below in conjunction with specific embodiments and drawings. More details are elaborated in the following description to facilitate a full understanding of the present invention. However, the present invention can obviously be implemented in a variety of other ways different from the description herein. Those skilled in the art can make similar generalizations and deductions based on actual application situations without violating the connotation of the present invention. Therefore, the protection scope of the present invention should not be limited by the content of this specific embodiment.

[0026] It should be noted that these and other subsequent drawings are only examples and are not drawn to scale, and should not be used to limit the actual scope of protection required by the present invention.

[0027] Existing ultrasonic detection methods have the disadvantage of being unable to perform targeted detection of specific types of defects inside composite materials. The present invention proposes an adaptive frequency selection method for composite material defects, which can adaptively select frequencies for different defects, thereby using specific detection frequencies for various types of defects in composite materials to improve detection accuracy and reliability.

[0028] Reference Figures 1 to 6It is understood that the method includes the following steps: S1 selects a test block with defects; S2 performs ultrasonic testing on the test block to obtain an ultrasonic testing signal graph; S3 identifies the defect ultrasonic waveform and interference waveform under a specific defect type based on the ultrasonic testing signal graph; S4 eliminates the interference waveform to obtain the time interval and time domain signal of the defect ultrasonic waveform; S5 performs Fourier transform on the time domain signal to obtain a frequency domain signal; S6 obtains the frequency value corresponding to the maximum amplitude based on the curve graph of the frequency domain signal, and confirms the frequency as the detection frequency corresponding to the specific defect.

[0029] Specifically, in step S1, the test block is selected from the actual composite material parts to be tested and has typical defects. For example, a test block containing defects is cut from a defective composite material sample according to a certain size by mechanical cutting or the like. When cutting the test block, the defect position is located in the center area of ​​the test block to facilitate subsequent testing. The test block size should be as small as possible, but should not be less than the minimum detection area required for ultrasonic testing. For example, the test block size can be 50mm×50mm and the thickness can be 28mm. The thickness can be the same as that of the actual composite material to be tested, which is convenient for subsequent CT defect detection.

[0030] Typical defects include but are not limited to delamination, debonding, dense porosity, air holes, inclusions, glue or resin richness, fiber wrinkles, fiber breakage and other defects.

[0031] Preferably, before performing step S2, micro-focus or nano-focus CT is used to determine the type and location of the defect. CT testing is expensive and complicated to use, but it can better determine the type and location of the defect; while ultrasonic testing is convenient to use and has a low price. Predetermining the type and location of the defect through CT is helpful for judging the subsequent ultrasonic testing signal diagram.

[0032] After obtaining the defect information in the test block, the test block is subjected to ultrasonic testing to obtain an ultrasonic testing signal diagram. The ultrasonic testing signal diagram is as follows: Figure 1 The time-amplitude curve is shown in the figure. The ultrasonic generator generates a pulse wave, which enters the composite material through a broadband ultrasonic detection probe through a transmission medium such as water or air. The broadband ultrasonic detection probe acts as a transmitting probe to transmit ultrasonic waves; the ultrasonic waves emitted by the broadband ultrasonic probe are reflected from the upper surface, inside and bottom of the composite material, and are received by the broadband ultrasonic probe. The received ultrasonic time domain signal, i.e., the time-amplitude curve, is presented by the oscilloscope. When there are defects inside the composite material, the defect will also reflect ultrasonic waves and be received by the broadband ultrasonic detection probe. On the ultrasonic propagation path, the ultrasonic waves reflected at different sound paths (distances) are displayed in chronological order on their time-amplitude curves due to the different transmission times required. After receiving the ultrasonic detection signal, the broadband probe determines the ultrasonic waveform reflected by the defect by the position on the time baseline of the ultrasonic detection signal.

[0033] Typical reflection method ultrasonic echo curve of defective composite materials is as follows: Figure 1 As shown, it is necessary to identify the defect ultrasonic waveform A and the interference waveform B under a specific defect type i. The interference waveform includes but is not limited to the surface reflection wave B1, the bottom reflection wave B2 and the secondary reflection wave B3.

[0034] Perform steps S3 and S4 to correct the defect waveform s i (t) on t s -t n The signals corresponding to the time periods other than t are reset to zero. s -t n The signal amplitude outside is reset to the basic amplitude s0, and the interference waveform B is eliminated; the single waveform ultrasonic detection signal corresponding to the defect signal is obtained, and the time interval t of the defect ultrasonic waveform A is obtained. s -t n and the time domain signal s i '(t), such as Figure 3 shown.

[0035] Step S5 is performed to obtain the time domain signal s i '(t) Perform Fourier transform to obtain the frequency domain signal F i '(t), such as Figure 4 shown.

[0036] Finally, step S6 is performed, according to Figure 4 The frequency domain signal curve shown in the figure obtains the frequency value f corresponding to the maximum amplitude i-max , and confirm the frequency as the detection frequency corresponding to the specific defect. Figure 4 For a composite defect specimen shown in FIG. , the maximum amplitude is for the frequency value f i-max The value of is 0.96MHz, the frequency f i-max is the maximum ultrasonic response frequency corresponding to the specific defect i, that is, the optimal detection frequency f of the defect i_opt It is 0.96MHz.

[0037] Choose the center frequency as f i-opt =0.96MHz ultrasonic detection probe, used for ultrasonic detection of this type of defect i, adjust the ultrasonic excitation frequency of the ultrasonic generator to the optimal detection frequency f i-opt =0.96MHz, use reflection method or penetration method to carry out ultrasonic testing on defective test blocks.

[0038] In addition, the ultrasonic detection signal of the corresponding defect on the defect test block can be adjusted to 80% of the full screen height, and the ultrasonic detection gain at this time can be recorded. The gain value is the detection reference sensitivity of this type of defect. According to the detection reference sensitivity established in this step, the reflection method or penetration method ultrasonic detection is performed on the composite material to be tested, and the ultrasonic scanning of the composite material with defect type i is completed.

[0039] Each defect type i and its corresponding detection frequency are collected to obtain N defect-detection frequency sets. As shown in Table 1, the detection frequency corresponding to each defect is filled into the following typical defect type table of composite materials.

[0040] Table 1 Typical defect types of composite materials

[0041]

[0042] In this way, the above method analyzes the ultrasonic detection signals of typical defects, extracts the waveforms corresponding to the typical defect signals, processes the sound wave time domain signals corresponding to the defects and obtains their frequency domain signals through Fourier transform, obtains the optimal ultrasonic detection frequency, thereby obtaining the specific defects and the corresponding optimal detection frequencies, establishes the optimal ultrasonic detection parameters, and provides selection guidance for the actual detection process, solving the problems existing in traditional methods that the ultrasonic detection signals for specific defects cannot be effectively extracted and that ultrasonic detection test blocks for different defect types of composite materials are lacking.

[0043] According to the introduction of the above composite material defect adaptive frequency selection method, it is also possible to understand an ultrasonic testing method for testing the test piece, such as Figure 7 As shown, the following steps are included: different detection frequencies corresponding to different types of defects are obtained according to the above method; the detection frequencies corresponding to specific types of defects are selected in turn to perform ultrasonic detection on the part to be detected, the detection frequency is used as the ultrasonic excitation frequency of the ultrasonic generator, and an ultrasonic detection probe with a center frequency equal to the detection frequency is selected to perform reflection method or penetration method ultrasonic detection to determine whether the part to be detected has a specific type of defect corresponding to the detection frequency; and the detection is stopped when it is detected that the part to be detected has a specific type of defect.

[0044] That is, the test piece is tested multiple times using the same ultrasonic method and different testing frequencies to obtain information on different defect types.

[0045] For example, according to the defect types shown in Table 1 above, a detection frequency of 0.96 MHz is used for the first time to detect whether the test piece contains delamination defects. When it is detected that the sensitivity of the test piece exceeds the detection reference sensitivity, it indicates that the test piece has significant delamination defects, and the detection is stopped. When the test piece does not identify delamination defects at a detection frequency of 0.96 MHz, a second detection is performed. The second detection uses another detection frequency to detect the debonding defect type. After multiple detections, the ultrasonic scanning of the entire composite material test piece is completed, thereby realizing defect adaptive frequency selection ultrasonic detection of different defect types inside the composite material, achieving the best detection results of different defect types inside the composite material, and greatly improving the detection accuracy and reliability.

[0046] The present application uses specific words to describe the embodiments of the present application. For example, "one embodiment", "an embodiment", and / or "some embodiments" refer to a certain feature, structure or characteristic related to at least one embodiment of the present application. Therefore, it should be emphasized and noted that "one embodiment" or "an embodiment" or "an alternative embodiment" mentioned twice or multiple times in different positions in this specification does not necessarily refer to the same embodiment. In addition, some features, structures or characteristics in one or more embodiments of the present application can be appropriately combined.

[0047] Although the present invention is disclosed as above with preferred embodiments, it is not intended to limit the present invention. Any person skilled in the art may make possible changes and modifications without departing from the spirit and scope of the present invention. Therefore, any modification, equivalent change and modification made to the above embodiments according to the technical essence of the present invention without departing from the content of the technical solution of the present invention shall fall within the protection scope defined by the claims of the present invention.

Claims

1. Composite material defect adaptive frequency selection method, characterized in that: The steps include: Select a test block with defects; Performing ultrasonic testing on the test block to obtain an ultrasonic testing signal diagram; According to the ultrasonic detection signal diagram, identifying the defect ultrasonic waveform and interference waveform under a specific defect type; Eliminate the interference waveform to obtain the time interval and time domain signal of the defect ultrasonic waveform; Performing Fourier transform on the time domain signal to obtain a frequency domain signal; According to the curve graph of the frequency domain signal, the frequency value corresponding to the maximum amplitude is obtained, and the frequency is determined as the detection frequency corresponding to the specific defect.

2. The composite material defect adaptive frequency selection method according to claim 1, characterized in that: The interference waveform includes a surface reflection wave, a bottom reflection wave and a secondary reflection wave.

3. The composite material defect adaptive frequency selection method according to claim 1, characterized in that: The signals outside the time interval of the defect ultrasonic waveform in the ultrasonic detection signal diagram are reset to zero and reset to the basic amplitude.

4. The composite material defect adaptive frequency selection method according to claim 1, characterized in that: The specific defect types include delamination, debonding, dense pores, air holes, inclusions, glue-rich, resin-rich, fiber wrinkles, and fiber breaks.

5. The composite material defect adaptive frequency selection method according to claim 1, characterized in that: The method also includes: adjusting the ultrasonic detection signal diagram under the specific defect type to 80% of the full screen height, recording the ultrasonic detection gain value, and using the ultrasonic detection gain as the detection reference sensitivity of this type of defect.

6. The composite material defect adaptive frequency selection method according to claim 4, characterized in that: The detection frequency corresponding to each specific defect type is recorded to obtain a defect-detection frequency set.

7. The composite material defect adaptive frequency selection method according to claim 1, characterized in that: Before ultrasonic testing of the test blocks, CT testing is used to determine the type and location of defects.

8. An ultrasonic testing method for performing ultrasonic testing on a test piece, characterized in that: The steps include: According to the method described in any one of claims 1 to 7, different detection frequencies corresponding to different types of defects are obtained; Selecting detection frequencies corresponding to specific types of defects in sequence to perform ultrasonic detection on the part to be detected, using the detection frequency as the ultrasonic excitation frequency of the ultrasonic generator, and selecting an ultrasonic detection probe with a center frequency equal to the detection frequency to determine whether the part to be detected has the specific type of defect corresponding to the detection frequency; When it is detected that the inspected piece has a specific type of defect, the inspection is stopped.

9. The ultrasonic detection method according to claim 8, characterized in that: Perform reflection or penetration ultrasonic testing.

10. The ultrasonic detection method according to claim 8, characterized in that: When the sensitivity of the detected object exceeds When the reference sensitivity is detected as described in claim 5, the detection is stopped.

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