Microwave frequency scanning method for defect identification of fiber reinforced composite material

Abstract

The invention discloses a microwave frequency scanning method for defect identification of a fiber reinforced composite material, and the method comprises the following steps: P1, setting a Fermi antenna which is used for transmitting and receiving a microwave signal; p2, setting a vector network analyzer as a microwave source; and P3, analyzing the reflected microwave signal based on the Fermi antenna and the vector network analyzer, pre-determining the working frequency band of the fiber reinforced composite material, and carrying out debonding defect detection in the fiber reinforced composite material on the basis of the reflection coefficient S11. The microwave frequency scanning method for defect identification of the fiber reinforced composite material, disclosed by the invention, has the beneficial effects that a microwave nondestructive detection method is suitable for detecting dielectric materials such as the fiber reinforced composite material, and can accurately detect the defects such as debonding, holes, cracks, sand inclusion and the like in the fiber reinforced composite material; defect conditions are clearly reflected through the change of the S11 value.

Description

Technical Field

[0001] The invention belongs to the field of nondestructive testing of composite materials, and in particular relates to a microwave frequency scanning method for defect identification of fiber-reinforced composite materials. Background Art

[0002] The invention patent application with publication number CN111239166A and subject name is Microwave Detection Method for Defects of Carbon Fiber Wound Composite Material Gas Cylinders, and its IPC classification number is G01N22 / 02. Its technical solution discloses "The microwave detection method for defects of carbon fiber wound composite material gas cylinders includes the following steps: S1: preparation of gas cylinders, making gas cylinder samples of fiber wound composite materials with no defects in the cylinder body and one or more defects such as pores, cracks, delamination or debonding; S2: determining the optimal detection frequency, using the frequency scanning method to scan the defect-free cylinder body to determine the characteristic frequency of the cylinder body material, and using this frequency as the gas cylinder body The optimal detection frequency for defect detection; S3: At the optimal detection frequency, use a waveguide probe to scan and detect the gas cylinder with defects, and record the corresponding change in reflection coefficient according to the defect, and collect the change results of reflection coefficient to establish a conventional defect characteristic reflection coefficient database; S4: Determination of defect type, at the optimal detection frequency, use a waveguide probe to scan and detect the gas cylinder body to be inspected, observe the change in reflection coefficient and compare the reflection coefficient with the data in the reflection coefficient database to determine the type of defect; S5: Determination of defect location, when a defect is detected, record the location information of the waveguide probe at this time as the defect location".

[0003] It can be seen that the above invention patent application has disclosed one of the technical solutions for applying microwave detection to composite materials. However, the technical solution of the above invention patent application focuses on gas cylinders made of carbon fiber wrapped composite materials, that is, gas cylinders made by winding high-strength carbon fibers on metal or non-metallic inner shells. Compared with the fiber reinforced composite materials of the present application, the gas cylinders made of carbon fiber wrapped composite materials do not have the following characteristics of the fiber reinforced composite materials of the present application: the carbon fiber wrapped composite material gas cylinder is a high-pressure gas storage cylinder, which uses carbon fiber as a reinforcing material and is fixed on the inner shell of the gas cylinder by winding. The manufacturing process and material structure of this composite material are special. The fiber reinforced composite material of the present invention is a universal material form, which is composed of reinforcing fibers such as glass fiber, aramid fiber, carbon fiber, etc. and resin or other matrices. It can be made into profiles of various shapes and sizes, which are used to construct structural components or as reinforcing materials for other products, and has a very wide range of applications. Summary of the invention

[0004] The present invention aims at the state of the prior art, overcomes the above defects and provides a microwave frequency scanning method for defect identification of fiber reinforced composite materials.

[0005] The present invention adopts the following technical scheme, a microwave frequency scanning method for defect identification of fiber reinforced composite materials, comprising the following steps:

[0006] Step P1: Setting up a Fermi antenna for transmitting and receiving microwave signals;

[0007] Step P2: Setting up a vector network analyzer as a microwave source;

[0008] Step P3: Analyze the reflected microwave signal based on the Fermi antenna and vector network analyzer to predetermine the working frequency band of the fiber reinforced composite material and use the reflection coefficient S 11 The debonding defect detection in fiber reinforced composite materials is carried out as the basis.

[0009] As a preferred technical solution of the above technical solutions, the Fermi antenna is printed on a thin dielectric substrate with a low dielectric constant.

[0010] As a preferred technical solution of the above technical solutions, the Fermi antenna is provided with a curved tapered end so that a sinusoidal wave corrugation is loaded on the Fermi antenna.

[0011] As a preferred technical solution of the above technical solutions, the Fermi antenna includes a feeding structure, a plurality of tapered slot structures and a plurality of tapered slot structures, and the tapered slot structures and the tapered slot structures are adjacent to and spaced apart from each other.

[0012] The microwave frequency scanning method for defect identification of fiber-reinforced composite materials disclosed in the present invention has the following beneficial effects:

[0013] 1. Suitable for dielectric material testing: Microwave nondestructive testing method is suitable for testing dielectric materials such as fiber-reinforced composite materials.

[0014] 2. Superior antenna performance: Using Fermi antenna as a microwave probe has the characteristics of narrow beam, wide bandwidth, wide working bandwidth, stable working mode, and small size. The planar design is conducive to application in portable devices, and the sensitivity and resolution can be enhanced by loading specific structures.

[0015] 3. Effective defect detection: It can accurately detect defects such as debonding, holes, cracks, sand inclusions, etc. in fiber reinforced composite materials. 11 The change of value clearly reflects the defect situation. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] Figure 1 is the reflection coefficient S of the defect-free glass fiber reinforced composite plate 11 Graph showing the change with microwave frequency.

[0017] Figure 2 is the reflection coefficient S of a glass fiber reinforced composite plate with a 3 cm debonding defect11 Graph showing the change with microwave frequency.

[0018] Figure 3 is the reflection coefficient S of a carbon fiber reinforced composite plate with a 5 cm debonding defect 11 Graph showing the change with microwave frequency.

[0019] Figure 4 is the reflection coefficient S of the glass fiber reinforced composite plate containing holes and cracks 11 Graph showing the change with microwave frequency.

[0020] Figure 5 is the reflection coefficient S of the glass fiber reinforced composite plate containing sand inclusion defects 11 Graph showing the change with microwave frequency.

[0021] Figure 6 This is a schematic diagram of the structure of the Fermi antenna.

[0022] Explanation of the reference numerals: 1 - Fermi antenna; 2 - feeding structure; 3 - tapered slot structure; 4 - tapered slot structure. DETAILED DESCRIPTION

[0023] The present invention discloses a microwave frequency scanning method for defect identification of fiber reinforced composite materials. Figures 1 to 5 , the specific implementation modes of the present invention are further described.

[0024] Those skilled in the art should note that the “operating frequency band” and “operating frequency” that may be involved in various embodiments of the present invention are the same concept and are no longer distinguished.

[0025] Those skilled in the art should note that various embodiments of the present invention may involve a “reflection coefficient S 11 ” and “S 11 " are the same concept and are no longer distinguished.

[0026] See attached figure Figures 1 to 5 , Figures 1 to 5 The reflection coefficients S of different samples are shown respectively. 11 The degree of change with microwave frequency.

[0027] Example 1.

[0028] Preferably, the microwave frequency scanning method for defect identification of fiber reinforced composite materials comprises the following steps:

[0029] Step P1: Setting a Fermi antenna 1 for transmitting and receiving microwave signals;

[0030] Step P2: Setting up a vector network analyzer as a microwave source;

[0031] Step P3: Analyze the reflected microwave signal based on the Fermi antenna 1 and the vector network analyzer, predetermine the working frequency band of the fiber reinforced composite material, and use the reflection coefficient S 11 The debonding defect detection in fiber reinforced composite materials is carried out as the basis.

[0032] The Fermi antenna 1 is used as a microwave probe and is printed on a thin dielectric substrate with a low dielectric constant. As a planar end-fire antenna, the Fermi antenna 1 has the characteristics of narrow beam, wide bandwidth, stable working mode and small size. The planar design characteristics of the Fermi antenna 1 are conducive to the application of the Fermi antenna 1 in portable devices.

[0033] The Fermi antenna 1 is provided with a curved tapered end, so that a sinusoidal wave corrugation is loaded on the Fermi antenna 1 to flexibly control the surface waves flowing on the edge of the thin dielectric substrate. The smooth curve of the sinusoidal wave corrugation can reduce the radiation from the sharp edge of the thin dielectric substrate, thereby enhancing the sensitivity and resolution of the Fermi antenna 1.

[0034] See attached figure Figure 6 , wherein the Fermi antenna 1 includes a feeding structure 2, a plurality of tapered slot structures 3 and a plurality of tapered slot structures 4, and the tapered slot structures 3 and the tapered slot structures 4 are adjacent to and spaced apart from each other.

[0035] The following describes the test process and test results of the microwave frequency scanning method for defect identification of fiber-reinforced composite materials disclosed in this embodiment.

[0036] See attached figure Figure 1 , shows the reflection coefficient S obtained for a glass fiber reinforced composite material plate in the frequency range of 14 to 26 GHz 11 With the change of microwave frequency. Fermi antenna 1 is placed 0.3-2 cm away from the surface of the hydrogen storage tank, and the frequency is scanned from 5 to 26 GHz. At certain frequency points, S 11 The curve shows a valley. The frequency corresponding to the valley with the lowest valley value is the working frequency for testing fiber reinforced composite materials. The frequency corresponding to the lowest value of S11 is 13.88 GHz, so 13.88 GHz is used as the working frequency to test glass fiber reinforced composite panels.

[0037] See attached figure Figure 2 , showing the S of a glass fiber reinforced composite panel containing a 3 cm debonding defect under different conditions 11Changes with frequency. There is a debonding defect with a length of 3 cm in the glass fiber reinforced composite material plate, and the depth of the defect is about 8 mm. First, the Fermi antenna 1 connected to the vector network analyzer is placed at the defect-free position of the glass fiber reinforced composite material plate, with the antenna 1 cm away from the surface of the plate. The operating frequency is determined to be 14.25 GHz by frequency scanning; then the antenna is moved to the center and edge of the debonding defect respectively, and the frequency scan is performed in the frequency region near the operating frequency. At the defect-free position of the plate, S 11 The frequency curve shows a valley value at 14.25 GHz, and the corresponding S 11 The value is -36.3dB. When the antenna is moved to the debonding center, S 11 The valley value of the curve is -30.6dB, and the difference between the two valley values ​​is 5.7dB, which is easy to detect. 11 The valley value is -34.6dB. The debonding edge is the transition point between the normal area and the defect, which causes S 11 The values ​​are between the normal area and the debonding center. These results show that the debonding defect can be identified by microwave technology using Fermi antenna 1.

[0038] See attached figure Figure 3 , a carbon fiber reinforced composite plate containing a 5 cm debonding defect was used under different conditions S 11 Changes with frequency. There is a 5 cm long debonding defect in the carbon fiber reinforced composite material plate, and the depth of the defect is about 6 mm. First, the Fermi antenna 1 connected to the vector network analyzer is placed at the defect-free position of the carbon fiber reinforced composite material plate, with the antenna 0.5 cm away from the surface of the plate. The operating frequency is determined to be 17.30 GHz by frequency scanning; then the antenna is moved to the center and edge of the debonding defect respectively, and the frequency scan is performed in the frequency region near the operating frequency. At the defect-free position of the plate, S 11 The frequency curve shows a valley value at 17.30 GHz, and the corresponding S 11 The value is -49.5dB. When the antenna is moved to the debonding center, S 11 The valley value of the curve is -40.7dB, and the difference between the two valley values ​​is 8.8dB, which is easy to detect. 11 The valley value is -46.2dB. The debonding edge is the transition point between the normal area and the defect, which causes S 11 The values ​​are between the normal area and the debonding center. These results show that the debonding defect can be identified by microwave technology using Fermi antenna 1.

[0039] See attached figure Figure 4 , showing the reflection coefficient S of a glass fiber reinforced composite plate containing holes and cracks11 Changes with frequency. The glass fiber reinforced composite material plate contains holes and cracks. The diameter of the hole is 4 mm and the depth is 5 mm; the length of the crack is 5 mm and the depth is 5 mm. First, the Fermi antenna 1 connected to the vector network analyzer is placed at the defect-free position of the glass fiber reinforced composite material plate, with the antenna 0.8 cm away from the surface of the plate. The operating frequency is determined to be 14.50 GHz by the frequency scanning method; then the antenna is moved to the location of the hole and the crack respectively, and the frequency is scanned in the frequency region near the operating frequency. At the defect-free position of the plate, S 11 The frequency curve shows a valley value at 14.50 GHz, and the corresponding S 11 The value is -36.7dB. When the antenna is aimed at the hole defect, S 11 The valley value of the curve is -30.00dB, and the corresponding frequency is slightly changed to 14.48GHz. The difference between the two valley values ​​is 6.7dB, which is easy to detect. When the antenna is aimed at the location of the crack defect, S 11 The valley is -33.1 dB and the corresponding frequency is 14.50 GHz. The difference between the two valleys is 3.1 dB. These results show that holes and cracks can be detected and identified by microwave technology using Fermi antenna 1.

[0040] See attached figure Figure 5 , shows the reflection coefficient S of the glass fiber reinforced composite plate containing sand inclusion defects 11 Changes with frequency. There is a sand inclusion defect in the glass fiber reinforced composite material plate. The sand has a diameter of 4 mm and a depth of 4 mm. First, the Fermi antenna 1 connected to the vector network analyzer is placed at the defect-free position of the glass fiber reinforced composite material plate. The antenna is 1 cm away from the surface of the plate. The operating frequency is determined to be 14.50 GHz by frequency scanning. Then the antenna is moved to the position where the sand inclusion defect is located, and the frequency scan is performed in the frequency region near the operating frequency. At the defect-free position of the plate, S 11 The frequency curve shows a valley value at 14.50 GHz, and the corresponding S 11 The value is -36.6dB. When the antenna is aimed at the hole defect, S 11 The valley value of the curve is -40.80 dB, and the difference between the two valley values ​​is 4.2 dB, indicating that the sand inclusion defect can be detected by the microwave technology of Fermi antenna 1.

[0041] It is worth mentioning that the technical features such as the specific selection of the vector network analyzer involved in the patent application of this invention should be regarded as the prior art. The specific structure, working principle and possible control method and spatial layout method of these technical features can be selected according to the conventional selection in the field, and should not be regarded as the inventive point of the patent of this invention. The patent of this invention will not be further elaborated.

[0042] For those skilled in the art, it is still possible to modify the technical solutions described in the aforementioned embodiments, or to make equivalent substitutions for some of the technical features therein. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included in the protection scope of the present invention.

Claims

1. A microwave frequency scanning method for defect identification of fiber reinforced composite materials, characterized in that: The following steps are involved: Step P1: Setting up a Fermi antenna for transmitting and receiving microwave signals; Step P2: Setting up a vector network analyzer as a microwave source; Step P3: Analyze the reflected microwave signal based on the Fermi antenna and vector network analyzer to predetermine the working frequency band of the fiber reinforced composite material and use the reflection coefficient S 11 The debonding defect detection in fiber reinforced composite materials is carried out as the basis.

2. The microwave frequency scanning method for defect identification of fiber reinforced composite materials according to claim 1, characterized in that: The Fermi antenna is printed on a thin dielectric substrate with a low dielectric constant.

3. The microwave frequency scanning method for defect identification of fiber reinforced composite materials according to claim 1, characterized in that: The Fermi antenna is provided with a curved tapered end so that a sinusoidal wave corrugation is loaded on the Fermi antenna.

4. The microwave frequency scanning method for defect identification of fiber reinforced composite materials according to claim 1, characterized in that: The Fermi antenna comprises a feeding structure, a plurality of tapered slot structures and a plurality of tapered slot structures, wherein the tapered slot structures and the tapered slot structures are adjacent to and spaced apart from each other.

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