Preparation method of surface crack-containing test block for nondestructive testing

Abstract

The invention relates to a preparation method of a surface crack-containing test block for nondestructive testing. The preparation method comprises the following steps: S1, generating a crack source: forming a through transverse seam in a test block base material by a linear cutting method or a fatigue loading method; s2, crack source processing: processing the transverse seam obtained in S1 to adjust at least one parameter of width, length and depth of the crack to reach a preset value. Compared with the prior art, the method has the advantages that precise machining of tiny defects is achieved, two crack source forming methods are provided, different requirements are met, the defects can be flexibly controlled and adjusted, and the like.

Description

Technical Field

[0001] This invention relates to the fields of nondestructive testing and instrument calibration technology, and in particular to a method for preparing a nondestructive testing specimen containing surface cracks. Background Technology

[0002] With societal development, the economic losses that may result from structural accidents are constantly increasing. To reduce damage and detect defects early, the precision requirements for non-destructive testing equipment such as ultrasonic flaw detectors are gradually increasing. However, the defects in current non-destructive testing blocks used to verify equipment precision and calibrate parameters are relatively large (e.g., the diameter of a circular hole is 2mm), which is not conducive to the verification and calibration of higher-precision testing equipment. A major reason for this situation is the difficulty in machining tiny defects in the test blocks; machining micron- or sub-millimeter-level cracks is technically very difficult.

[0003] Traditional methods use electrical discharge machining (EDM), but this requires specialized electrodes (0.05-0.08mm) for each machining operation, and these electrodes are consumables. Furthermore, during EDM, the extremely narrow discharge gap makes it difficult for electro-erosion products (debris) to escape, easily leading to secondary discharges and short circuits, resulting in unstable machining and decreased accuracy. This significantly increases the technical difficulty of this method, making it extremely costly, potentially more than 10 times more expensive.

[0004] CN202210119916.3 discloses a method for fabricating a standard test block for non-destructive testing of crack defects, including the following steps: Step 1: Prepare a steel plate of ordinary strength, cut it into a pair with V-shaped bevels, and prepare a suitable aluminum alloy strip; Step 2: Assemble the pair of steel plates with V-shaped bevels and perform root pass welding at the butt joint bevel position using CO2 gas shielded welding, and continue welding after the root pass welding is completed; Step 3: Gouge a groove in the weld at a predetermined position using carbon arc welding, place the aluminum alloy strip in the groove, and fill the groove with CO2 gas shielded welding. Part of the steel plate and aluminum alloy strip melt in the groove, and the weld is rapidly cooled to form a crack; Step 4: After the workpiece cools to room temperature, continue welding with CO2 gas shielded welding until a complete weld is formed. However, the dynamic process of the welding pool and the stress generated by rapid cooling are complex, and the actual crack size will still have deviations, resulting in low accuracy. The generated cracks are usually relatively large.

[0005] CN202110322287.X discloses a method for preparing a thermal fatigue crack simulation test block, belonging to the field of non-destructive testing test block preparation technology. First, a through-hole is machined in the center of the test block, and several crack-inducing tips are machined around the through-hole on one side of the test block. Then, thermal fatigue cracks are generated on the test block by repeated rapid heating to a high temperature followed by rapid cooling. Finally, the through-hole is enlarged, the crack-inducing tips are removed, and the test surface of the test block is polished until the roughness matches that of the workpiece being inspected, completing the preparation of the thermal fatigue crack simulation test block. However, the generated cracks are usually relatively large, and the realism of the crack morphology and the controllability and efficiency of the preparation process are poor. Summary of the Invention

[0006] The purpose of this invention is to overcome the shortcomings of the existing technology by providing a method for preparing a non-destructive testing block with surface cracks, achieving precise processing of minute defects, providing two methods for forming crack sources, adapting to different needs, and flexibly controlling and adjusting defects. The objective of this invention can be achieved through the following technical solutions: This invention provides a method for preparing a nondestructive testing specimen containing surface cracks, comprising the following steps: S1: Crack initiation: A continuous transverse crack is formed on the parent material of the specimen by wire cutting or fatigue loading. S2: Crack source processing: Process the transverse crack obtained in S1 to adjust at least one parameter of the crack width, length and depth to achieve a preset value.

[0007] Furthermore, in S1, when using the wire cutting method, a transverse wire cut is performed on the surface of the test block using a precise low-speed wire cutting method to form a transverse slit at the leading edge of a straight crack with a slit depth of no more than 0.3 mm and a slit width of no more than 0.14 mm. Furthermore, in S1, when using the fatigue loading method, the parent material of the test block is first processed into a CT specimen, and then a crack propagation test is carried out on the CT specimen (which can be carried out in accordance with the requirements of GB / T6398) until the crack length meets the requirements and a transverse seam with a forward-protruding crack front edge is formed. Furthermore, in S1, when using the fatigue loading method to process the inclined crack, the CT specimen containing the forward-convex transverse crack is subjected to inclined machining, and the excess material on the specimen is removed at a preset inclined angle. Furthermore, in S2, the method for adjusting the crack width includes: applying compressive stress perpendicular to the crack surface to the specimen containing transverse cracks, thereby narrowing the crack width through material yielding deformation. Furthermore, in S2, the method for adjusting the crack length includes: slotting from both ends of the transverse seam until the remaining seam length reaches the preset surface crack design length, and then filling the slotted openings by welding. Furthermore, in S2, after the repair welding, the surface of the test block is machined to remove the excess weld height.

[0008] Furthermore, in S2, the methods for adjusting the crack depth include: Measure the current depth h1 of the transverse seam; The surface of the test block containing the microcracks is machined to remove the thickness h1-h0, so that the crack depth on the test block surface becomes the preset design depth h0.

[0009] Furthermore, during or after the crack propagation test, the crack depth was measured using the compliance method recommended in BG / T6398, with a measurement accuracy of 0.1 mm.

[0010] Furthermore, in S1, the relevant state parameters of the crack source include crack inclination angle, crack depth, crack width, crack length, and crack front morphology (including straight cracks and forward-convex cracks).

[0011] The crack inclination angle ranges from 60° to 90°, the crack depth ranges from 0.3 mm to more than 0.3 mm, and the crack width ranges from 0.05 to 0.6 mm.

[0012] Compared with the prior art, the present invention has the following advantages: (1) Achieving precise processing of minute defects. This invention achieves precise control over the size of minute defects (depth ≥ 0.3 mm, width ≥ 0.05 mm) through precision wire cutting (directly processing micro-slits within 0.3 mm in depth and 0.14 mm in width) and subsequent finishing processes (such as grinding to compress depth and pressurizing to compress width). This makes it possible to calibrate high-precision ultrasonic flaw detectors.

[0013] (2) Two methods for forming crack initiation are provided to meet different needs. Compared with traditional electrical discharge machining and fatigue testing, wire cutting is a mature technology with relatively low cost, high processing efficiency, and easy to accurately control the initial geometric size of cracks. The fatigue loading method generates cracks through fatigue load propagation, and its micromorphology (convex leading edge) and generation mechanism are highly consistent with natural cracks in actual engineering structures. Using this "real crack" test block verification equipment can make the detection signal and performance evaluation closer to the actual working conditions, greatly improving the reliability and credibility of the verification results.

[0014] (3) It can flexibly control and adjust defects. Precisely control the crack depth: By adopting the method of "first accurately measuring (h1), then mechanically grinding (removing h1-h0)", the crack depth can be precisely controlled to the preset design depth h0. This method is simple, reliable and highly accurate. Flexibly adjust the crack width: It is proposed to apply compressive stress perpendicular to the crack surface to the specimen and use the plastic deformation of the material to "tighten" the crack, thereby reducing the crack width. This solves the problem that the initial width of the wire-cut crack may be too large and can simulate more subtle real defects. Effectively set the crack length and achieve "non-through": Through the process of "grooving at both ends, retaining in the middle, and welding to fill", a through crack can be easily transformed into a short surface crack of a specified length, while ensuring the integrity of the specimen. It can prepare cracks with complex shapes: Inclined cracks can be prepared by tilting the machine, which meets the verification requirements for detecting defects in different directions. Attached Figure Description

[0015] Figure 1 A schematic diagram of the relevant state parameters of the crack initiation; Figure 2 This is a schematic diagram of a CT specimen fabricated from the parent material of the test block when using a fatigue loading method. Figure 3 A schematic diagram of cutting a CT specimen with an angled crack during machining. Figure 4 A schematic diagram of the test block seam length cutting and welding when adjusting the crack length; Figure 5 This is a physical image of a test block used for non-destructive testing. Detailed Implementation

[0016] The present invention will now be described in detail with reference to the accompanying drawings and specific embodiments. Component models, material names, connection structures, control methods, algorithms, and other features not explicitly described in this technical solution are considered common technical features disclosed in the prior art.

[0017] Example 1 This embodiment provides a method for preparing a non-destructive testing block containing surface cracks, such as... Figure 1-5 As shown, it includes the following steps: S1: Crack initiation: A continuous transverse crack is formed on the parent material of the specimen by wire cutting or fatigue loading. S2: Crack source processing: Process the transverse crack obtained in S1 to adjust at least one parameter of the crack width, length and depth to achieve a preset value.

[0018] In a specific implementation, in S1, when using the wire cutting method, a transverse wire cut is performed on the surface of the test block using a precise low-speed wire cutting method to form a transverse slit at the leading edge of a straight crack with a slit depth of no more than 0.3 mm and a slit width of no more than 0.14 mm. In a specific implementation, in S1, when using the fatigue loading method, the parent material of the test block is first processed into a CT test piece, and then a crack propagation test is performed on the CT test piece (which can be carried out in accordance with the requirements of GB / T6398) until the crack length meets the requirements and a transverse seam with a forward-protruding crack front edge is formed. In a specific implementation, in S1, when the fatigue loading method is used to process the inclined crack, the CT specimen containing the forward convex transverse crack is subjected to inclined machining, and the excess material on the specimen is removed at a preset inclined angle. In a specific implementation, S2, the method for adjusting the crack width includes: applying compressive stress perpendicular to the crack surface to the test block containing the transverse crack, thereby narrowing the crack width through material yielding deformation. In a specific implementation, S2, the method for adjusting the crack length includes: slotting from both ends of the transverse seam until the remaining seam length reaches the preset surface crack design length, and then filling the slotted opening by welding. In a specific implementation, in step S2, after the repair welding, the surface of the test block is machined to remove the excess weld height.

[0019] In a specific implementation, S2, the method for adjusting the crack depth includes: Measure the current depth h1 of the transverse seam; The surface of the test block containing the microcracks is machined to remove the thickness h1-h0, so that the crack depth on the test block surface becomes the preset design depth h0.

[0020] In a specific implementation, the crack depth is measured using the compliance method recommended in BG / T6398 during or after the crack propagation test, with a measurement accuracy of 0.1 mm.

[0021] In a specific implementation, in S1, the relevant state parameters of the crack source include crack inclination angle, crack depth, crack width, crack length, and crack leading edge morphology (including two types: straight cracks and forward-convex cracks).

[0022] The crack inclination angle ranges from 60° to 90°, the crack depth ranges from 0.3 mm to more than 0.3 mm, and the crack width ranges from 0.05 to 0.6 mm.

[0023] Example 2 This embodiment provides a method for preparing a non-destructive testing block containing surface cracks, such as... Figure 1-5 As shown, it includes the following steps: S1: Crack initiation: A continuous transverse crack is formed on the parent material of the specimen through fatigue loading. S2: Crack source processing: The transverse crack obtained in S1 is processed to adjust at least one parameter among the crack width, length, and depth to achieve a preset value. In a specific implementation, the width of the test block is first set to 30mm, and then a CT test piece (width 144mm, length 150mm) can be designed according to the recommended values ​​for CT test piece specifications in GB / T6398.

[0024] In a specific implementation, a fatigue load of 2 to 20 tons is applied to the specimen, and the crack depth is simultaneously monitored using an extensometer mounted at the crack based on the compliance method (GB / T6398). The test is stopped when the effective crack depth reaches 3 mm, the CT specimen is removed, and the precise crack depth is re-determined by measuring with a ruler.

[0025] In a specific implementation, in S1, when the fatigue loading method is used to process the inclined crack, the CT specimen containing the forward convex transverse crack is subjected to inclined machining, and the excess material on the specimen is removed at a preset inclined angle. In a specific implementation, S2, the method for adjusting the crack width includes: applying compressive stress perpendicular to the crack surface to the test block containing the transverse crack, thereby narrowing the crack width through material yielding deformation. In a specific implementation, S2, the method for adjusting the crack length includes: slotting from both ends of the transverse seam until the remaining seam length reaches the preset surface crack design length, where the crack design length is 1mm, only retaining a 1mm section in the middle, and then filling the slotted opening with welding. In a specific implementation, in step S2, after the repair welding, the surface of the test block is machined to remove the excess weld height.

[0026] In a specific implementation, S2, the method for adjusting the crack depth includes: Measure the current depth h1 of the transverse seam; The surface of the test block containing microcracks is machined to remove thickness h1-h0, making the crack depth on the test block surface the preset design depth h0. The CT specimen is then machined to make the actual crack depth slightly larger than the design requirement by 1mm.

[0027] In a specific implementation, the crack depth is measured using the compliance method recommended in BG / T6398 during or after the crack propagation test, with a measurement accuracy of 0.1 mm.

[0028] In a specific implementation, in S1, the relevant state parameters of the crack initiation include crack inclination angle, crack depth, crack width, crack length, and crack leading edge morphology (including two types: straight cracks and forward-convex cracks). The crack inclination angle ranges from 60° to 90°, the crack depth ranges from 0.3 mm or more, and the crack width ranges from 0.05 mm to 0.6 mm.

[0029] Finally, other related operations are performed on the test block (such as polishing, pressing trademarks, etc.).

[0030] Components not described in detail in this embodiment are all existing components that can be purchased through public channels.

[0031] The above description of the embodiments is provided to enable those skilled in the art to understand and use the invention. It will be apparent to those skilled in the art that various modifications can be made to these embodiments, and the general principles described herein can be applied to other embodiments without inventive effort. Therefore, the present invention is not limited to the above embodiments, and any improvements and modifications made by those skilled in the art based on the disclosure of the present invention without departing from the scope of the invention should be within the protection scope of the present invention.

Claims

1. A method for preparing a nondestructive testing specimen containing surface cracks, characterized in that, Includes the following steps: S1: Crack initiation: A continuous transverse crack is formed on the parent material of the specimen by wire cutting or fatigue loading. S2: Crack source processing: Process the transverse crack obtained in S1 to adjust at least one parameter of the crack width, length and depth to achieve a preset value.

2. The method for preparing a nondestructive testing block with surface cracks according to claim 1, characterized in that, In S1, when using the wire cutting method, a transverse wire cut is performed on the surface of the test block using a precise low-speed wire feeding method to form a transverse slit at the leading edge of a straight crack with a slit depth reaching the set depth and a slit width not exceeding 0.14 mm.

3. The method for preparing a nondestructive testing block with surface cracks according to claim 1, characterized in that, In S1, when using the fatigue loading method, the parent material of the test block is first processed into a CT test piece, and then a crack propagation test is carried out on the CT test piece until the crack length meets the requirements and a transverse seam with a forward-convex crack front edge is formed.

4. The method for preparing a nondestructive testing block with surface cracks according to claim 3, characterized in that, In S1, when using the fatigue loading method to process the inclined crack, the CT specimen containing the forward-convex transverse crack is subjected to inclined machining, and the excess material on the specimen is removed at the preset inclined angle.

5. The method for preparing a nondestructive testing block with surface cracks according to claim 2, characterized in that, When using the wire cutting method, in S2, the methods for adjusting the crack width include: applying compressive stress perpendicular to the crack surface to the specimen containing transverse cracks, and narrowing the crack width through material yielding and compressive deformation.

6. The method for preparing a nondestructive testing block with surface cracks according to claim 1, characterized in that, In S2, adjusting the crack length includes changing the penetrating crack into a semi-buried crack and reducing the crack length. The steps are as follows: slotting from both ends of the transverse seam until the remaining seam length reaches the preset surface crack design length, and then filling the slotted opening with welding.

7. The method for preparing a nondestructive testing block containing surface cracks according to claim 6, characterized in that, In S2, after the repair welding, the surface of the test block is machined to remove the excess weld height.

8. The method for preparing a nondestructive testing block with surface cracks according to claim 1, characterized in that, In S2, methods for adjusting crack depth include: Measure the current depth h1 of the transverse seam; The surface of the test block containing the microcracks is machined to remove the thickness h1-h0, so that the crack depth on the test block surface becomes the preset design depth h0.

9. The method for preparing a nondestructive testing block with surface cracks according to claim 3, characterized in that, During or after the crack propagation test, the crack depth was measured using the compliance method with a measurement accuracy of 0.1 mm.

10. The method for preparing a nondestructive testing block with surface cracks according to claim 1, characterized in that, In S1, the relevant state parameters of the crack source include crack inclination angle, crack depth, crack width, crack length, and crack leading edge morphology.

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