Method for prefabricating stress corrosion crack of aircraft aluminum alloy structure sample piece containing fastener

Abstract

The invention relates to the field of airplane body structure maintenance, and particularly discloses a stress corrosion crack prefabricating method for an airplane aluminum alloy structure sample piece containing a fastener. Comprising the following steps: adhering an isolation adhesive tape to a position where a stress corrosion crack needs to be prefabricated on the surface of an aluminum alloy sample; fixing the aluminum alloy sample needing to prefabricate the stress corrosion crack and the base plate by using a fastener; anti-corrosion paint is sprayed on the assembled aluminum alloy sample and the base plate structure, and then the isolation adhesive tape is removed to expose a non-paint-spraying area; soaking the assembled aluminum alloy sample and the substrate structure in a container filled with a corrosion solution; and observing whether the crack prefabricating area on the aluminum alloy sample generates cracks or not. The position where the stress corrosion crack is generated is determined through adhesive tape and paint spraying, and control over the position and direction of the stress corrosion crack is achieved. And by adjusting the pre-tightening force of the fastener, the generation time of the stress corrosion crack is shortened.

Description

Technical Field

[0001] The invention relates to a prefabrication method, in particular to a stress corrosion crack prefabrication method for an aircraft aluminum alloy structure specimen containing fasteners, and belongs to the field of aircraft body structure maintenance. Background Art

[0002] The main structural material of domestic and foreign aircraft is aluminum alloy. Under the influence of structural assembly stress, service load and corrosive environment, aluminum alloy structures are prone to stress corrosion cracking around fastener holes, which reduces structural reliability. When conducting research on stress corrosion crack repair of aluminum alloy structures, it is necessary to prefabricate stress corrosion cracks on the specimens. Stress corrosion cracks are related to parameters such as sensitive materials, corrosive environment, and stress state. It is difficult to control the position, direction and length of cracks during crack prefabrication, resulting in poor consistency in the test results of the repaired specimens. At present, there are a large number of patents related to stress corrosion cracking in China, but they mainly focus on experimental monitoring of the initiation and propagation of stress corrosion cracks, and there are relatively few patents on the prefabrication of stress corrosion cracks in materials or specimens.

[0003] For example, Chinese patent CN201811459252.5 discloses a new method for preparing artificial stress corrosion cracks that are consistent with the real crack morphology. This method can prepare artificial crack specimens that are consistent with the stress corrosion cracks of the actual structure. However, this method is complicated to operate and involves multiple technologies and equipment, and cannot be used for the preparation of a large number of test specimens. Chinese patent CN202311114713.6 discloses a butt weld stress corrosion crack prefabrication device and its use method, which provides a method for prefabrication and monitoring of stress corrosion cracks in welds, but lacks effective control of the prefabrication position of the cracks. Chinese patent CN202310106736.6 discloses a constant load stress corrosion crack initiation test method, which is mainly used to monitor and measure the generation of stress corrosion cracks, and the device and use method are complex. Therefore, there is an urgent need to propose a new stress corrosion crack prefabrication method for aluminum alloy structures to solve the problem of difficulty in controlling the prefabrication position, direction and length of stress corrosion cracks in aluminum alloy specimens, and to achieve batch preparation of stress corrosion aluminum alloy specimens. Summary of the Invention

[0004] In view of the problems in the prior art, the present invention provides a method for prefabricating stress corrosion cracks of aircraft aluminum alloy structural specimens containing fasteners.

[0005] The purpose of the present invention can be achieved through the following technical solutions:

[0006] A method for prefabricating stress corrosion cracks of aircraft aluminum alloy structural specimens containing fasteners comprises the following steps:

[0007] Step 1: Paste isolation tape on the surface of the aluminum alloy specimen at the location where stress corrosion cracks need to be prefabricated;

[0008] Step 2: Use fasteners to fix the aluminum alloy specimen and substrate to which stress corrosion cracking needs to be prefabricated;

[0009] Step 3: Use a torque wrench to tighten the fasteners near the prefabricated stress crack on the aluminum alloy specimen to make the stress σ reach the stress corrosion threshold stress σ of the aluminum alloy specimen. th ;

[0010] Step 4: Spray anti-corrosion paint on the assembled aluminum alloy specimen and substrate structure, then remove the isolation tape to expose the unpainted area as a crack prefabrication area to control crack generation;

[0011] Step 5: Stick a scaled transparent tape next to the crack along the prefabricated direction of the unpainted area to observe the crack length;

[0012] Step 6: Immerse the assembled aluminum alloy specimen and substrate structure in a container filled with a corrosive solution to provide a corresponding corrosive environment for crack prefabrication;

[0013] Step 7: Take out the aluminum alloy specimen and the substrate structure every 8 minutes to observe whether cracks occur in the crack prefabrication area of ​​the aluminum alloy specimen; if cracks occur, observe the length of the cracks;

[0014] Step 8: When the crack reaches the expected length, remove the aluminum alloy sample and substrate structure, clean the residual corrosion solution on the surface of the aluminum alloy sample and dry it;

[0015] Step 9: Remove the anti-corrosion paint on the fasteners, substrate and the surface of the aluminum alloy specimen, thus completing the prefabrication of stress corrosion cracks of the aluminum alloy specimen.

[0016] Optionally, when the fastener is a bolt, the stress σ is expressed as Calculation shows that T is the torque of the torque wrench, K is the torque coefficient, usually 0.1-0.2, d1 is the nominal diameter of the bolt, d2 is the thread pitch diameter, and d3 is the diameter of the thread bottom after rounding.

[0017] Optionally, when the fasteners are rivets, the rivets at both ends of the crack should be stainless steel rivets, and the remaining fasteners should be aluminum alloy rivets.

[0018] Optionally, when the fastener is a rivet, the stress σ is expressed as Estimation is performed, where σ s is the rivet yield strength, b is the rivet flash width, and h is the rivet flash height.

[0019] Optionally, the corrosion solution is a 5% NaCl solution with a pH of 4.0 to 4.5 prepared from dilute sulfuric acid.

[0020] Optionally, the fastener is a bolt or a rivet.

[0021] Optionally, the anti-corrosion paint is QH-15 anti-corrosion epoxy primer.

[0022] Optionally, the width of the isolation tape is 2 mm, and the length of the tape can be selected according to the size of the crack to be prefabricated.

[0023] Optionally, the preset time in step 7 is 8 minutes.

[0024] Beneficial effects of the present invention:

[0025] By using tape and spray paint to determine the location of stress corrosion cracks, the location and direction of stress corrosion cracks can be controlled; by adjusting the preload force of the fasteners, the time it takes for stress corrosion cracks to occur can be shortened. This prefabrication method is convenient and effective, with simple operation, and the location, length and direction of stress corrosion cracks can be controlled.

[0026] The present invention realizes the control of the position and length of the prefabricated stress corrosion crack by setting the corrosion area and the local stress, and the method is simple and effective. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] To facilitate understanding by those skilled in the art, the present invention is further described below with reference to the accompanying drawings.

[0028] Figure 1 Schematic diagram of the aluminum alloy sample of the present invention in the corrosion solution.

[0029] In the figure: 1. Aluminum alloy specimen; 2. Substrate; 3. Fastener; 4. Isolation tape; 5. Stress corrosion cracking; 6. Graduated transparent tape; 7. Container; 8. Corrosive solution. DETAILED DESCRIPTION

[0030] The technical solutions of the present invention will be clearly and completely described below with reference to the embodiments. Obviously, the embodiments described are only some embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making any creative efforts shall fall within the scope of protection of the present invention.

[0031] Take the 5mm long stress corrosion crack of L-shaped 7B04-T6 aluminum alloy structural specimen containing fasteners as an example. Figure 1 The stress corrosion cracking prefabrication method is described as follows, which includes the following steps:

[0032] Step 1: Paste an isolation tape 4 on the surface of the aluminum alloy specimen 1 at the location where stress corrosion cracks are to be prefabricated. The isolation tape 4 can cover and shield the predetermined area, so that the area will not be sprayed when the anti-corrosion paint is subsequently sprayed, and can serve as a predetermined crack prefabrication area.

[0033] Step 2: Use fasteners 3 to fix the aluminum alloy specimen 1 and substrate 2 to which stress corrosion cracks are to be prefabricated. The fasteners 3 facilitate fixing the aluminum alloy specimen 1 and substrate 2, and facilitate control of stress in the crack prefabrication area of ​​the aluminum alloy specimen 1 during subsequent use.

[0034] Step 3: Use a torque wrench to tighten the fasteners 3 at both ends of the prefabricated stress corrosion crack on the aluminum alloy specimen 1 until the stress σ reaches the stress corrosion threshold stress σ of the aluminum alloy specimen 1. th By adjusting the preload force of the fastener 3, the time for stress corrosion cracking to occur can be shortened;

[0035] Step 4: spray anti-corrosion paint on the assembled aluminum alloy specimen 1 and substrate 2 structure, then remove the isolation tape 4 to expose the unpainted area, which serves as a crack prefabrication area for controlling the generation of cracks 5;

[0036] Step 5: Along the prefabricated direction of the crack 5 in the unpainted area, stick a scaled transparent tape 6 next to it to facilitate quick and accurate observation of the length of the crack 5;

[0037] Step 6: Immerse the assembled aluminum alloy sample 1 and substrate 2 structure in a container 7 filled with a corrosive solution 8 to provide a corresponding corrosive environment for prefabrication of the crack 5;

[0038] Step 7: Take out the aluminum alloy sample 1 and the substrate 2 structure every 8 minutes to observe whether crack 5 is generated in the crack prefabrication area of ​​the aluminum alloy sample 1; if crack 5 is generated, observe the length of crack 5;

[0039] Step 8: When the crack 5 reaches the expected length, the aluminum alloy sample 1 and the substrate 2 structure are removed, and the residual corrosion solution 8 on the surface of the aluminum alloy sample 1 is cleaned and dried;

[0040] Step 9: Remove the anti-corrosion paint on the surface of the fastener 3, the substrate 2 and the aluminum alloy sample 1, thereby completing the prefabrication of the stress corrosion crack of the aluminum alloy sample 1.

[0041] Specifically, the stress σ is expressed as Calculation shows that T is the torque of the torque wrench, K is the torque coefficient, usually 0.1-0.2, d1 is the nominal diameter of the bolt, d2 is the thread pitch diameter, and d3 is the diameter of the thread bottom after rounding.

[0042] Specifically, the etching solution 8 is a 5% NaCl solution prepared from dilute sulfuric acid with a pH of 4.0 to 4.5.

[0043] Specifically, the fastener 3 is a bolt or a rivet.

[0044] Specifically, when the fasteners are rivets, the rivets at both ends of the crack should be stainless steel rivets, and the other fasteners should be aluminum alloy rivets.

[0045] Specifically, when the fastener is a rivet, the stress σ is expressed as Estimation is performed, where σ s is the rivet yield strength, b is the rivet flash width, and h is the rivet flash height.

[0046] Specifically, the anticorrosive paint is QH-15 anticorrosive epoxy primer. QH-15 anticorrosive epoxy primer is used as the anticorrosive paint, which has good anticorrosive performance and low use cost.

[0047] Specifically, the isolation tape 4 has a width of 2 mm and a length of 6 mm.

[0048] The preferred embodiments of the present invention disclosed above are intended only to help illustrate the present invention. These preferred embodiments do not exhaustively describe all details, nor do they limit the present invention to the specific embodiments described. Obviously, many modifications and variations are possible based on the content of this specification. These embodiments are selected and described in detail in this specification to better explain the principles and practical applications of the present invention, thereby enabling those skilled in the art to better understand and utilize the present invention. The present invention is limited only by the claims and their full scope and equivalents.

Claims

1. A method for prefabricating stress corrosion cracks of aircraft aluminum alloy structural specimens containing fasteners, characterized in that: The following steps are involved: Step 1: Paste isolation tape on the surface of the aluminum alloy specimen at the location where stress corrosion cracks need to be prefabricated; Step 2: Use fasteners to fix the aluminum alloy specimen and substrate to which stress corrosion cracking needs to be prefabricated; Step 3: Use a torque wrench to tighten the fasteners near the prefabricated stress crack on the aluminum alloy specimen to make the stress σ reach the stress corrosion threshold stress σ of the aluminum alloy specimen. th ; Step 4: Spray anti-corrosion paint on the assembled aluminum alloy specimen and substrate structure, then remove the isolation tape to expose the unpainted area as a crack prefabrication area to control crack generation; Step 5: Stick a scaled transparent tape next to the crack along the prefabricated direction of the unpainted area; Step 6: Immerse the assembled aluminum alloy specimen and substrate structure in a container filled with a corrosive solution; Step 7: Take out the aluminum alloy sample and the substrate structure at predetermined intervals to observe whether cracks occur in the crack prefabrication area of ​​the aluminum alloy sample; if cracks occur, observe the length of the cracks; Step 8: When the crack reaches the expected length, remove the aluminum alloy sample and substrate structure, clean the residual corrosion solution on the surface of the aluminum alloy sample and dry it; Step 9: Remove the anti-corrosion paint on the fasteners, substrate and the surface of the aluminum alloy specimen, thus completing the prefabrication of stress corrosion cracks of the aluminum alloy specimen.

2. The method for prefabricating stress corrosion cracks of aircraft aluminum alloy structural specimens containing fasteners according to claim 1, characterized in that: The stress σ is expressed as Calculation shows that T is the torque of the torque wrench, K is the torque coefficient, d1 is the nominal diameter of the bolt, d2 is the pitch diameter of the thread, and d3 is the diameter of the thread bottom after rounding.

3. The method for prefabricating stress corrosion cracks of aircraft aluminum alloy structural specimens containing fasteners according to claim 1, characterized in that: The corrosion solution is a 5% NaCl solution prepared from dilute sulfuric acid with a pH of 4.0-4.

5.

4. The method for prefabricating stress corrosion cracks of aircraft aluminum alloy structural specimens containing fasteners according to claim 1, characterized in that: The fasteners are bolts or rivets.

5. The method for prefabricating stress corrosion cracks of aircraft aluminum alloy structural specimens containing fasteners according to claim 1, characterized in that: The anti-corrosion paint is QH-15 anti-corrosion epoxy primer.

6. The method for prefabricating stress corrosion cracks of aircraft aluminum alloy structural specimens containing fasteners according to claim 1, characterized in that: The width of the isolation tape is 2 mm.

7. The method for prefabricating stress corrosion cracks of aircraft aluminum alloy structural specimens containing fasteners according to claim 1, characterized in that: The preset time in step 7 is 8 minutes.

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