Composite material layered reference block and preparation method and detection method thereof

Abstract

The invention relates to a composite material layered reference block and a preparation method and a detection method thereof, the preparation method comprises the following steps: firstly, laying a circular pre-embedded defect between set layers of a composite material prepreg, and sequentially carrying out curing molding and demolding to obtain a first sample; eccentric drilling is carried out on the circular embedded defect in the first sample, and a second sample is obtained; and finally, processing an embedded defect size mark on the second sample to obtain the layered reference block of the composite material. According to the preparation method provided by the invention, a single-hole composite material layering reference block containing hole edge layering defects of various standard sizes can be prepared through eccentric drilling and processing of pre-embedded defect size marks, so that the requirements of calibration of different layering detection precision are met; by adopting the detection method of the composite material layered reference block, rapid, convenient and accurate calibration of ultrasonic detection equipment can be realized.

Description

Technical Field

[0001] The invention relates to the technical field of nondestructive testing, and in particular to a composite material layered comparison test block and a preparation method and a testing method thereof. Background Art

[0002] Composite materials are widely used in the aerospace field due to their advantages such as good designability, heat resistance, corrosion resistance and fatigue resistance. In order to meet assembly requirements, composite materials need to be drilled and then connected to two structural parts by riveting, etc. However, due to the presence of axial force in the drilling process and the shear stress on the hole structure during the equipment connection process, it is easy to produce delamination at the hole wall. The existence of delamination will cause stress concentration at the connection of composite structural parts, thereby reducing the strength of the structural connection and posing the risk of structural failure.

[0003] Therefore, it is necessary to conduct quantitative detection of composite material delamination. At present, the detection of composite material delamination usually adopts the ultrasonic method, which detects the delamination defects inside the composite material by receiving the defect echo of ultrasonic wave at the interface between the composite material and the air in the delamination or by comparing and analyzing the abnormal loss of the bottom wave of the received ultrasound at the delamination defect.

[0004] Composite material delamination defect comparison test blocks are a prerequisite for detecting the delamination of composite material structural parts. By comparing the test blocks, the test personnel can calibrate the equipment detection accuracy and determine the equipment detection parameters, thereby realizing the precise quantitative detection of structural parts delamination. At present, the existing methods for making composite material hole edge delamination comparison test blocks mainly include: (1) a method of artificially pre-embedding and then processing concentric through holes, specifically: embedding one or more circular artificial prefabricated defects in the pre-embedded test block, and then processing concentric through holes for the artificial prefabricated defects; (2) a method of processing hole edge step holes, specifically: first processing a through hole, and drilling step holes of the required delamination size at three different depths of the upper, middle and lower parts of the through hole; (3) a method of laser processing of the hole side wall, specifically: first cutting the hole structure, and then using a laser method to process the delamination inside the composite material through the hole side wall direction. Although the above methods can prepare composite material delamination defect comparison test blocks, there is a limitation that a single hole has only one delamination defect size. If the accuracy of the detection equipment needs to be graded and calibrated, multiple hole edge delamination comparison test blocks need to be made. For example, CN110196287A discloses a test block for analyzing the delamination defects of the hole edge of a composite workpiece. The simulated delamination of the test block is achieved by concentrically drilling holes in the circular film pre-embedded defects added during the composite molding stage. The delamination size of the single hole simulation is relatively simple. Another example is CN103529121A discloses a delamination defect simulation method for composite laminate machine-made hole edge pulse reflection method. This method starts from the upper surface of the composite material and concentrically digs grooves toward the lower surface, representing annular delamination. The delamination size of the single hole simulation is also relatively simple.

[0005] Therefore, providing a comparison test block that can simulate single-hole multi-size delamination defects is of great significance to improving the convenience of composite material delamination defect detection. Summary of the invention

[0006] In view of the above problems, the purpose of the present invention is to provide a composite material stratification comparison test block and a preparation method and a detection method thereof. Compared with the prior art, the preparation method provided by the present invention can prepare a composite material stratification comparison test block with a single hole and containing stratification defects of various standard sizes at the edge of the hole by eccentrically drilling a composite material sample with a built-in circular embedded defect and processing the embedded defect size mark, thereby meeting the requirements of different stratification detection accuracy calibration. The composite material stratification comparison test block detection method can realize fast, convenient and accurate calibration of ultrasonic detection equipment.

[0007] In order to achieve the purpose of the invention, the present invention adopts the following technical solutions:

[0008] In a first aspect, the present invention provides a method for preparing a composite material layered comparison test block, the preparation method comprising the following steps:

[0009] (1) laying a circular embedded defect between set layers of a composite material prepreg, and then sequentially performing curing molding and demolding to obtain a first sample;

[0010] (2) using a nondestructive testing method to determine the center position of the circular pre-embedded defect in the first sample obtained in step (1); then eccentrically drilling the circular pre-embedded defect to obtain a second sample;

[0011] (3) Using a nondestructive testing method to test the second sample obtained in step (2), and processing a pre-embedded defect size mark on the second sample according to the test data to obtain a composite material stratification comparison test block.

[0012] In the present invention, the first sample is a sample with a built-in circular pre-embedded defect. The present invention can manufacture multi-sized delamination defects around the hole structure by performing hole processing on the circular pre-embedded defect of the first sample at a position deviating from the center of the circular pre-embedded defect, i.e., eccentric drilling. Then, by processing the embedded defect size marks of various sizes, the preparation of composite material delamination comparison test blocks containing various standard sizes is finally realized. Compared with the existing comparison test blocks with simulated delamination and concentric hole structure, the single existing test block can only meet the calibration of one delamination size accuracy. If there are different detection accuracy requirements, different hole structure comparison test blocks need to be made and used. The present invention can meet the calibration requirements of different delamination detection accuracy only through one hole edge eccentric delamination, which significantly improves the convenience of detection.

[0013] In the present invention, the components of the composite material prepreg are not particularly limited, and may be any component used in the art for preparing composite material comparison test blocks, for example, may be a composite of carbon fiber and polymer.

[0014] In the present invention, the material of the circular pre-embedded defect is not particularly limited, and can be any material used for pre-embedded defects in the art, such as metal or plastic film. In the present invention, the setting depth of the circular pre-embedded defect can be selected as needed, and the circular pre-embedded defect can be laid in the corresponding set layer according to different depth requirements.

[0015] Preferably, the diameter of the circular embedded defect is denoted as R1, and the center of the circle is denoted as O1;

[0016] The eccentric drilling results in a circular through hole; the diameter of the circular through hole is denoted as R2, and the center of the circle is denoted as O2;

[0017] The distance between O1 and O2 is denoted as L o ;

[0018] The L o , R1 and R2 meet the following conditions: L o <R1+R2.

[0019] In the present invention, by controlling the condition L o <R1+R2, so that the contour circle of the circular embedded defect and the contour circle of the circular through hole have an overlapping area, that is, the positional relationship includes inclusion, inscription or intersection, so that a variety of delamination defects of different sizes can be manufactured.

[0020] Preferably, the embedded defect size mark includes a characteristic line segment and the length of the characteristic line segment;

[0021] The method for determining the embedded defect size mark is as follows: the remaining area of ​​the circular embedded defect after the eccentric drilling intersects with the straight line passing through the center of the circle O2, and a non-destructive testing method is used to confirm the endpoint position of the line segment intercepted by the remaining area of ​​the straight line; the endpoint positions are marked correspondingly on the upper surface of the second sample and connected as a characteristic line segment, and the length of the characteristic line segment is marked on the upper surface.

[0022] In the present invention, a characteristic line segment and the length of the characteristic line segment represent a delamination defect of a standard size. The present invention can further adjust the variation range of the standard size as required by controlling the circular through hole and the circular embedded defect.

[0023] Preferably, when the circular through hole and the circular pre-embedded defect satisfy R1>R2, and the contour circle of the circular through hole is located inside the contour circle of the circular pre-embedded defect, the length variation interval of the characteristic line segment is [L min1 , L max1];

[0024] The L min1 =R1-R2-L o ;

[0025] The L max1 =R1-R2+L o .

[0026] Preferably, when the contour circle of the circular through hole intersects the contour circle of the circular embedded defect, the length variation interval of the characteristic line segment is [0, L max2 ];

[0027] The L max2 =R1-R2+L o .

[0028] Preferably, the material of the composite material prepreg is the same as the material of the composite material prepreg used for the workpiece to be tested.

[0029] Preferably, the nondestructive testing method in step (2) and step (3) includes digital ray testing or ultrasonic testing, preferably digital ray testing.

[0030] In a second aspect, the present invention provides a composite material stratified comparison test block, wherein the composite material stratified comparison test block is obtained by the preparation method of the composite material stratified comparison test block according to the first aspect of the present invention.

[0031] The composite material stratification comparison test block provided by the present invention has a plurality of standard-sized hole edge stratification defects on the basis of a single hole, and can realize multi-level calibration of the accuracy of ultrasonic detection equipment by a single hole.

[0032] In a third aspect, the present invention provides a method for detecting a composite material stratification comparison test block, the detection method comprising using the composite material stratification comparison test block described in the second aspect of the present invention to perform precision calibration and correction on an ultrasonic detection device.

[0033] The detection method provided by the present invention adopts the composite material layered comparison test block, which is beneficial to improving the accuracy and convenience of the calibration of ultrasonic detection equipment.

[0034] Preferably, the accuracy calibration method includes: using ultrasonic testing equipment to test composite material layer comparison test blocks, if the ultrasonic equipment detects embedded defects, taking the minimum length of the detected characteristic line segment as the detection accuracy of the ultrasonic testing equipment.

[0035] Preferably, the correction method comprises: using ultrasonic testing equipment to detect characteristic line segments of specific length in the composite material stratification comparison test block, and debugging control parameters of the ultrasonic testing equipment until the detection result of the ultrasonic testing equipment is the specific length.

[0036] Compared with the prior art, the present invention has the following beneficial effects:

[0037] The preparation method provided by the present invention can prepare a composite material stratification comparison test block with a single hole and containing stratification defects of various standard sizes at the edge of the hole by eccentrically drilling a composite material sample with a built-in circular embedded defect and processing the embedded defect size mark, thereby meeting the requirements of different stratification detection accuracy calibrations. The composite material stratification comparison test block detection method can realize fast, convenient and accurate calibration of ultrasonic detection equipment. BRIEF DESCRIPTION OF THE DRAWINGS

[0038] Figure 1 is a schematic diagram of the positional relationship between the contour circle of the circular embedded defect and the contour circle of the circular through hole in the second sample of Example 1 of the present invention;

[0039] Figure 2 is a schematic diagram of the embedded defect size markings contained on the upper surface of the composite material layered comparison test block described in Example 1 of the present invention;

[0040] Figure 3 is a schematic structural diagram of a composite material layered comparison test block according to Example 1 of the present invention;

[0041] Figure 4 It is a schematic diagram of the detection results of the ultrasonic detection device during the precision calibration in Example 1 of the present invention;

[0042] Figure 5 is a schematic diagram of the positional relationship between the contour circle of the circular embedded defect and the contour circle of the circular through hole in the second sample of Example 2 of the present invention;

[0043] Figure 6 It is a schematic diagram of the positional relationship between the contour circle of the circular embedded defect and the contour circle of the circular through hole in the second sample in Example 3 of the present invention. DETAILED DESCRIPTION

[0044] The technical solution of the present invention is further described below by specific implementation methods. It should be understood by those skilled in the art that the embodiments are only to help understand the present invention and should not be regarded as specific limitations of the present invention.

[0045] Example 1

[0046] This embodiment provides a method for preparing a composite material layered comparison test block, the preparation method comprising the following steps:

[0047] (1) laying a circular pre-embedded defect between set layers of a composite material prepreg, wherein the diameter of the circular pre-embedded defect is denoted as R1 and the center of the circular pre-embedded defect is denoted as O1, and then sequentially performing curing molding and demolding to obtain a first sample;

[0048] (2) using digital radiographic detection to determine the center position of the circular pre-embedded defect in the first sample obtained in step (1); then eccentrically drilling the circular pre-embedded defect, that is, drilling a circular through hole in the circular pre-embedded defect at a position deviating from the center position of the circular pre-embedded defect, wherein the diameter of the circular through hole is recorded as R2, the center of the hole is recorded as O2, and the distance between O1 and O2 is recorded as L o , and obtain a second sample;

[0049] In the second sample, the positional relationship between the contour circle of the circular embedded defect and the contour circle of the circular through hole is shown in FIG. Figure 1 As shown, the circular embedded defect and the circular through hole are required to meet the condition: R1>R2, and the contour circle of the circular through hole is located inside the contour circle of the circular embedded defect;

[0050] (3) using digital radiographic testing to test the second sample obtained in step (2), and processing embedded defect size marks on the second sample according to the test data to obtain a composite material stratification comparison test block;

[0051] The method for determining the embedded defect size mark is as follows: the remaining area of ​​the circular embedded defect after the eccentric drilling intersects with the straight line passing through the center of the circle O2, and a non-destructive testing method is used to confirm the end point position of the line segment intercepted by the remaining area of ​​the straight line; the end point positions are marked on the upper surface of the second sample and connected as a characteristic line segment, and the length of the characteristic line segment is marked on the upper surface;

[0052] In this embodiment, a characteristic line segment and the length of the characteristic line segment represent a delamination defect of a standard size. In this embodiment, by controlling the circular through hole and the circular embedded defect, the variation range of the standard size can be further adjusted as needed. In this embodiment, the variation range of the standard size, i.e., the variation interval of the length of the characteristic line segment, is [L min1 , L max1 ];

[0053] The L min1 =R1-R2-L o ;

[0054] The L max1 =R1-R2+L o .

[0055] It can be seen from the above content that the preparation method of the composite material layered comparison test block and the composite material layered comparison test block provided in this embodiment can meet the standard size variation range of [R1-R2-L o , R1-R2+L o ] accuracy calibration requirements, when R1 = 6.675mm, R2 = 3.175mm, L o=2.5mm, the schematic diagram of the embedded defect size mark contained on the upper surface of the composite material layered comparison test block described in this embodiment is as shown in Figure 2 As shown, the structural schematic diagram of the composite material layered comparison test block is as follows Figure 3 shown.

[0056] The composite material layered comparison test block provided in this embodiment is used to calibrate the accuracy of the ultrasonic detection equipment. The method is as follows: the composite material layered comparison test block is detected by the ultrasonic detection equipment. If the ultrasonic detection equipment detects part of the embedded defects, that is, the area that the ultrasonic detection equipment can detect is as follows: Figure 4 As shown in A to H, the length of the minimum characteristic line segment in the range shown in A to H is taken as the detection accuracy of the ultrasonic detection equipment, that is, the detection accuracy is 2 mm.

[0057] The ultrasonic detection equipment is calibrated using the composite material stratification comparison test block provided in this embodiment. The method is: use the ultrasonic detection equipment to detect the embedded defect size mark of 1mm in the composite material stratification comparison test block, and adjust the control parameters of the ultrasonic detection equipment (such as gain, voltage or output power, etc.) until the detection result of the ultrasonic detection equipment is 1mm, then the detection result of the ultrasonic detection equipment is considered to be reliable.

[0058] Example 2

[0059] This embodiment provides a method for preparing a composite material layered comparison test block. The difference between the preparation method and the embodiment 1 is that in step (2), in the second test sample, the position relationship between the contour circle of the circular embedded defect and the contour circle of the circular through hole is shown in the schematic diagram. Figure 5 As shown, the circular embedded defect and the circular through hole are required to meet the condition: R1>R2, and the contour circle of the circular through hole intersects with the contour circle of the circular embedded defect.

[0060] This embodiment can adjust the range of the standard size in the composite material layer comparison test block by controlling the circular through hole and the circular embedded defect, that is, the length change interval of the characteristic line segment is [0, L max2 ], the L max2 =R1-R2+L o .

[0061] Example 3

[0062] This embodiment provides a method for preparing a composite material layered comparison test block. The difference between the preparation method and the embodiment 1 is that in step (2), in the second test sample, the position relationship between the contour circle of the circular embedded defect and the contour circle of the circular through hole is shown in the schematic diagram. Figure 6As shown, the circular embedded defect and the circular through hole are required to meet the condition: R1<R2, and the contour circle of the circular through hole intersects with the contour circle of the circular embedded defect.

[0063] This embodiment can adjust the range of the standard size in the composite material layer comparison test block by controlling the circular through hole and the circular embedded defect, that is, the length change interval of the characteristic line segment is [0, L max2 ], the L max2 =R1-R2+L o .

[0064] In summary, the preparation method provided by the present invention can prepare a composite material stratification comparison test block with a single hole and containing stratification defects of various standard sizes at the edge of the hole by eccentrically drilling a composite material sample with a built-in circular embedded defect and processing the embedded defect size mark, thereby meeting the requirements of different stratification detection accuracy calibrations. The detection method using the composite material stratification comparison test block can realize fast, convenient and accurate calibration of ultrasonic detection equipment.

[0065] The applicant declares that the above is only a specific implementation mode of the present invention, but the protection scope of the present invention is not limited thereto. Those skilled in the art should understand that any changes or substitutions that can be easily thought of by those skilled in the art within the technical scope disclosed by the present invention shall fall within the protection scope and disclosure scope of the present invention.

Claims

1. A method for preparing a composite material layered comparison test block, characterized in that: The preparation method comprises the following steps: (1) laying a circular embedded defect between set layers of a composite material prepreg, and then sequentially performing curing molding and demolding to obtain a first sample; (2) using a nondestructive testing method to determine the center position of the circular pre-embedded defect in the first sample obtained in step (1); then eccentrically drilling the circular pre-embedded defect to obtain a second sample; (3) Using a nondestructive testing method to test the second sample obtained in step (2), and processing a pre-embedded defect size mark on the second sample according to the test data to obtain a composite material stratification comparison test block.

2. The preparation method according to claim 1, characterized in that: The diameter of the circular embedded defect is denoted as R1, and the center of the circle is denoted as O1; The eccentric drilling results in a circular through hole; the diameter of the circular through hole is denoted as R2, and the center of the circle is denoted as O2; The distance between O1 and O2 is denoted as L o ; The L o , R1 and R2 meet the following conditions: L o <R1+R2.

3. The preparation method according to claim 2, characterized in that: The embedded defect size mark includes a characteristic line segment and the length of the characteristic line segment; The method for determining the embedded defect size mark is as follows: the remaining area of ​​the circular embedded defect after the eccentric drilling intersects with the straight line passing through the center of the circle O2, and a non-destructive testing method is used to confirm the endpoint position of the line segment intercepted by the remaining area of ​​the straight line; the endpoint positions are marked correspondingly on the upper surface of the second sample and connected as a characteristic line segment, and the length of the characteristic line segment is marked on the upper surface.

4. The preparation method according to claim 3, characterized in that: When the circular through hole and the circular embedded defect satisfy R1>R2, and the contour circle of the circular through hole is located inside the contour circle of the circular embedded defect, the length variation interval of the characteristic line segment is [L min1 , L max1 ]; The L min1 =R1-R2-L o ; The L max1 =R1-R2+L o .

5. The preparation method according to claim 3, characterized in that: When the contour circle of the circular through hole intersects the contour circle of the circular embedded defect, the length variation interval of the characteristic line segment is [0, L max2 ]; The L max2 =R1-R2+L o .

6. The preparation method according to any one of claims 1 to 5, characterized in that: The material of the composite material prepreg is the same as the material of the composite material prepreg used for the workpiece to be tested.

7. The preparation method according to any one of claims 1 to 6, characterized in that: The non-destructive testing method in step (2) and step (3) includes digital ray testing or ultrasonic testing, preferably digital ray testing.

8. A composite material layer comparison test block, characterized in that: The composite material layered comparison test block is obtained by the preparation method of the composite material layered comparison test block according to any one of claims 1 to 7.

9. A method for detecting a composite material layer comparison test block, characterized in that: The detection method comprises using the composite material layered comparison test block described in claim 8 to perform precision calibration and correction on the ultrasonic detection equipment.

10. The detection method according to claim 9, characterized in that: The accuracy calibration method comprises: using ultrasonic testing equipment to test a composite material layer comparison test block, if the ultrasonic testing equipment detects a pre-embedded defect, taking the minimum length of the detected characteristic line segment as the detection accuracy of the ultrasonic testing equipment; Preferably, the correction method comprises: using ultrasonic testing equipment to detect characteristic line segments of specific length in the composite material stratification comparison test block, and debugging control parameters of the ultrasonic testing equipment until the detection result of the ultrasonic testing equipment is the specific length.

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