A portable device for measuring residual stress in an aluminum alloy product and a method of use

Abstract

The application provides a portable residual stress measuring device for an aluminum alloy product and a use method. First slider mechanism and second slider mechanism are installed on a steel ruler. The first slider mechanism comprises a first slider and a micrometer. The second slider mechanism comprises a second slider and a positioning rod. After the distance between the sample testing position and the first slider mechanism and the second slider mechanism is determined, the positions of the first slider mechanism and the second slider mechanism are fixed. The second slider mechanism is fixed on the sample, the sample deflection is measured through the first slider mechanism, and the residual stress is calculated through a formula after the thickness of the sample is measured.

Description

Technical Field

[0001] This invention belongs to the field of residual stress analysis of metallic materials, and particularly relates to a portable measuring device for residual stress in aluminum alloy products and its usage method. Background Technology

[0002] When a component is under load, if the stress in certain local areas exceeds the yield limit, these areas will undergo plastic deformation, while the rest of the component remains within the elastic deformation range. If the load is then removed, the plastically deformed parts cannot return to their original dimensions, which will inevitably hinder the recovery of the elastically deformed parts, thus causing internally interacting stresses. These stresses are called residual stresses.

[0003] During the production of aluminum alloy sheets, processes such as rolling, heat treatment, and pre-stretching are involved, resulting in residual stress within the sheet. This stress varies with the sheet thickness but remains generally balanced, allowing the sheet to maintain a certain dimensional shape. For sheet samples with residual stress, if a thin layer is removed from one of the extruded surfaces of the sample, the residual stress in the remaining sheet thickness will redistribute, causing the sample to undergo a certain degree of bending deformation to form a new equilibrium.

[0004] The principle of the layer-by-layer method for testing residual stress in plate samples is as follows: Using one rolled surface of the sheet metal sample as a reference plane, the other rolled surface opposite the reference plane is defined as the deflection surface. Thin layers of equal thickness are removed layer by layer from the deflection surface. The deformation deflection at the reference plane and the sample thickness are measured at the mid-length of the sample. Based on the material's Young's modulus, Poisson's ratio, and the sample's deformation deflection and thickness, the residual stress at different thicknesses of the sample and sheet metal is calculated using formulas established from the deflection model. The deflection method (also known as the peeling method) is used in the testing standards of Boeing and Airbus. Boeing's BMS7-323 standard uses the deflection method to test the processing deformation deflection of longitudinal samples of aerospace sheet metal, judging product acceptance based on the deflection value, without calculating the residual stress of the sample or sheet metal.

[0005] Currently, the layer-by-layer method for testing residual stress can only measure rectangular cross-section specimens of sheet metal. Typically, a blank is cut from the specimen, then the blank is machined into a layer-by-layer specimen, and finally, the specimen is placed on a fixed deflection measuring device to measure the deformation deflection. However, a problem arises when studying profiles, forgings, or other similar structural materials. The specimen also needs to be cut from the body before testing. But because the stress distribution in these specimens is uneven, some residual stress is released during the cutting process. Therefore, for these structural materials, the results obtained using the original layer-by-layer method cannot reflect the true residual stress of the material. Summary of the Invention

[0006] This invention addresses the problem that conventional layer-by-layer cutting methods for testing residual stress in rectangular cross-section specimens are ineffective for specimens with uneven stress distribution and where some residual stress is released during cutting, resulting in inaccurate measurement results. The invention provides a portable residual stress measuring device for aluminum alloy products. This device measures the deflection of the specimen before cutting from the blank, thus resolving the issue of inaccurate measurement results caused by changes in internal stress after sampling similar profiles.

[0007] To achieve the above objectives, the technical solution adopted by the present invention is as follows: A portable device for measuring residual stress in aluminum alloy products includes a ruler, a first slider mechanism, and a second slider mechanism. The ruler is horizontally positioned with graduations, the 0 mark being located in the center. The second slider mechanism is located on both sides of the first slider mechanism, and both mechanisms are movably connected to the ruler. The first slider mechanism includes a first slider and a dial indicator mounted on the first slider. The dial indicator includes a dial indicator body, a dial indicator screw, and a dial indicator probe. The dial indicator screw connects the probe to the body and controls the probe's up-and-down movement. The probe is perpendicular to the ground. The second slider mechanism includes a second slider and a positioning rod, which is perpendicular to the ground and positioned below the second slider.

[0008] Preferably, the first and second sliders are provided with recessed holes, and the ruler is provided with a sliding track that cooperates with the first and second sliders. The ruler passes through the recessed holes and connects the first and second sliders.

[0009] Preferably, the second slider mechanism further includes a counterweight; the counterweight is disposed on the front of the second slider, the recess is disposed on the rear side of the second slider, and the positioning rod is disposed between the recess and the counterweight.

[0010] Preferably, the first slider has a groove on its front side, and the dial indicator is installed in the groove.

[0011] Preferably, the first slider mechanism and the second slider mechanism further include a locking nut, which is installed on the first slider and the second slider.

[0012] Preferably, the ruler is provided with limit plates at both ends.

[0013] As a preferred option, its specific usage method is as follows: Step 1: Plan the position of the sample on the aluminum alloy product blank to be cut in advance, move the first slider mechanism to the 0 mark of the ruler, and align the dial indicator probe with the 0 mark; move the positions of the second slider mechanisms on both sides symmetrically to determine the distance between the centers of the bottom of the positioning rods on both sides; tighten the upper locking nuts of the first and second sliders to fix the positions of the first and second slider mechanisms. Step 2: Move the portable residual stress device to the sample location range; the point on the sample that aligns with the bottom of the dial indicator probe is the measurement point, and the position on the sample that aligns with the positioning rod is the positioning point; attach the positioning block to the blank to be cut, the positioning block is set in an "L" shape, and the positioning block is close to the side of the positioning rod. Step 3: Zero the reading of the dial indicator on the portable residual stress device, record it as ω(0)=0mm, test the sample thickness t(0), and remove the portable residual stress device; Step 4: Cut the sample from the blank to be cut and process it into a standard sample using the layer-by-layer cutting method; Step 5: Mill the surface of the sample that is far from the measurement point and the positioning point, and mill the same thickness each time; after milling, remove the sample from the milling machine; place the sample on the test platform with the measurement reference surface facing up, and use the portable residual stress measuring device to press the side of the positioning rod against the positioning block; after milling the first layer, the deflection of the sample is recorded as ω(1), and the thickness is t(1). Step 6: Repeat step 5, mill the i-th layer, denoted as ω(i) for deflection and t(i) for thickness; Step 7: Substitute the measured deflection and thickness values ​​of each layer into the following formula to calculate the residual stress of each layer: - In the formula, layer i-1 is the layer above the i-th layer being milled, i≥1, k≥1; k and i are both integers.

[0014] Compared with the prior art, the advantages and positive effects of the present invention are as follows: This invention integrates a residual stress measuring device into a single measuring ruler, resulting in a compact, lightweight, and easy-to-handle design. Furthermore, this invention allows for the measurement of sample deflection before the sample is cut from the blank. The combined use of positioning points, locking nuts, and positioning blocks solves the problem of inaccurate measurement results caused by changes in internal stress after sampling similar profiles. Attached Figure Description

[0015] To more clearly illustrate the technical solutions of the embodiments of the present invention, the drawings used in the following description of the embodiments will be briefly introduced. Obviously, the drawings described below are some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0016] Figure 1 This is a schematic diagram of the structure of a portable residual stress measuring device; Figure 2 This is the main view of the blank to be cut; Figure 3 This is a schematic diagram of the portable residual stress measuring device when the distance between the center points of the bottom ends of the positioning rods on both sides is 360mm, as shown in Example 1. Figure 4 Left view of the blank to be cut; Figure 5 This is a front view of the blank to be cut after the positioning baffle is installed in Example 1; Figure 6 This is a front view of the sample from Example 1; Figure 7 This is a line graph showing the variation of residual stress in each layer with thickness and location in Example 1; In the above figures, 1. Ruler; 2. First slider mechanism; 3. Second slider mechanism; 4. First slider; 401. Groove; 402. Small hole; 5. Dial indicator; 6. Dial indicator body; 7. Dial indicator probe; 8. Dial indicator screw; 9. Second slider; 10. Positioning rod; 11. Positioning point; 12. Measuring point; 13. Concave hole; 14. Sliding track; 15. Counterweight; 16. Locking nut; 17. Limiting plate; 18. Sample blank to be cut; 19. Measuring reference surface; 20. Milled surface; 21. Sample; 22. Positioning stop. Detailed Implementation

[0017] To better understand the above-mentioned objectives, features, and advantages of the present invention, the present invention will be further described below in conjunction with the accompanying drawings and embodiments. It should be noted that, unless otherwise specified, the embodiments and features described in these embodiments can be combined with each other.

[0018] Numerous specific details are set forth in the following description in order to provide a full understanding of the invention. However, the invention may also be practiced in other ways than those described herein, and therefore the invention is not limited to the specific embodiments disclosed in the following specification.

[0019] Example 1, as Figures 1-2As shown, this application aims to provide a portable measuring device and method for measuring residual stress in aluminum alloy products, which satisfies the requirement of measuring the deflection of the sample before it is cut from the sample to be cut, thus overcoming the defect in the prior art where the internal stress changes after sampling of aluminum alloy products, leading to inaccurate measurement results. To achieve the above objective, the portable measuring device for residual stress includes a ruler 1, which is horizontally set and has scale lines. The 0 scale line is located in the center of the ruler, and the scale values ​​increase from the 0 scale line to both sides. For easy observation, the scales on both sides are symmetrical and the unit is 0.5 mm. Specifically, the distance between the two sides at the same scale value is the scale value at the two sides. The above structure is a common existing structure, so it will not be described in detail in this embodiment.

[0020] like Figure 1 As shown, the portable residual stress measuring device also includes a first slider mechanism 2 and a second slider mechanism 3; the second slider mechanism 3 is disposed on both sides of the first slider mechanism 2, and the first slider mechanism 2 and the second slider mechanism 3 are movably connected to the ruler 1. The first slider mechanism 2 includes a first slider 4 and a dial indicator 5. The front of the first slider 4 is provided with a groove 401, and the dial indicator 5 is installed in the groove 401. A small hole 402 is dug in the bottom of the groove, and the small hole 402 is open from top to bottom. The dial indicator 5 includes a dial indicator body 6, a dial indicator probe 7 and a dial indicator screw 8. The dial indicator probe 7 passes through the small hole 402 and is set perpendicular to the ground. The dial indicator body 6 has a built-in gear mechanism. The dial indicator screw 8 and the dial indicator probe 7 extend into the dial indicator body 6 and are connected to the upper and lower sides of the gear mechanism. The gear mechanism converts the rotational motion of the dial indicator screw 8 into the linear motion of the dial indicator probe 7. At the same time, the rotational distance of the dial indicator screw 8 is reduced by the gear transmission in the gear mechanism and becomes the linear motion distance of the dial indicator probe 7. The reading displayed on the dial indicator body 6 reflects the actual movement distance of the dial indicator probe 7. The structure of the dial indicator 5 is a common existing structure. Only the working principle of the dial indicator 5 is introduced here, and it will not be described in detail in this embodiment. The second slider mechanism 3 includes a second slider 9 and a positioning rod 10; the positioning rod 10 is perpendicular to the ground, and is located below the second slider 9 and connected to the second slider 9; the center point of the bottom end of the positioning rods 10 on both sides is on the same straight line parallel to the ruler as the vertex of the bottom end of the dial indicator probe 7. like Figure 2 As shown, the portable measuring device for residual stress of aluminum alloy products provided in this application requires accurate positioning point 11 and measuring point 12 to ensure that the measuring positions are consistent. To enable the first slider mechanism 2 and the second slider mechanism 3 to move left and right on the ruler 1, the rear part of the side surface of the first slider 4 on the first slider mechanism 2 and the second slider 9 on the second slider mechanism 3 is provided with a recessed hole 13. The recessed hole 13 is open on both sides, and the ruler 1 passes through the recessed hole 13 to connect the first slider 4 and the second slider 9. The ruler 1 is provided with a sliding track 14 that cooperates with the first slider 4 and the second slider 9. The left and right sliding of the first slider mechanism 2 can realize the alignment of the dial indicator probe 7 with the sample measurement point 12, and the left and right sliding of the second slider mechanism 3 can realize the alignment of the positioning rod 10 with the sample positioning point 11. Furthermore, since the concave hole 13 is located at the rear of the first slider 4 and the second slider 9, and the ruler 1 passes through the concave hole 13, the portable measuring device for residual stress is difficult to maintain balance when the positioning rod 10 acts as a fulcrum. In order to keep the portable residual stress measuring device balanced, the second slider mechanism 3 also includes a counterweight 15. The counterweight 15 is set on the front of the second slider 9 and connected to the second slider 9. The positioning rod 10 is located between the concave hole 13 and the counterweight, so as to achieve the balance of the portable residual stress measuring device. This can reduce the wear of the sliding rail 14 on the first slider mechanism 2 and the second slider mechanism 3, and also reduce the impact of counterweight imbalance on the measurement results. During the use of the portable residual stress measuring device, it is necessary to determine the accurate measurement point. In order to prevent the measurement results from being inaccurate due to changes in the position of the first slider mechanism 2 and the second slider mechanism 3, the first slider mechanism 2 and the second slider mechanism 3 are also equipped with locking nuts 16. The locking nuts 16 are installed on the upper surface of the first slider 4 and the second slider 9. Tightening the locking nuts 16 can fix the position of the first slider mechanism 2 and the second slider mechanism 3 on the ruler 1. To prevent the first slider mechanism 2 and the second slider mechanism 3 from falling off during the transportation or use of the portable residual stress measuring device and causing damage to the instrument, limit plates 17 are also provided at both ends of the ruler 1.

[0021] like Figures 2-6 As shown in Example 1, a method for measuring residual stress in aluminum alloy products includes the following specific steps: Step 1: Select the aluminum alloy product to be cut into sample blank 18 used in this implementation, such as... Figure 2 , Figure 3As shown, the sample blank 18 to be cut is "T" shaped, with the raised surface being the measurement reference surface 19 and the non-raised bottom surface being the milling surface 20; the position of the sample 21 is planned in advance on one side of the raised reference surface 19; the first slider mechanism 2 is moved to the 0 mark position of the ruler 1, and the dial indicator probe 7 is aligned with the 0 mark; the positions of the second slider mechanisms 3 on both sides of the 0 mark are moved symmetrically to determine that the distance between the bottom centers of the two positioning rods 10 is 360mm, specifically, the positioning rods 10 on both sides of the 0 mark are aligned with the position of the scale value of 360 on the ruler 1; for ease of operation, the distance from the center point of the positioning rod 10 on the ground to the outer side of the second slider along the direction of the ruler 1 is 10mm, that is, the outer sides of the second sliders on both sides of the 0 mark are aligned with the position of the scale value of 380mm on the ruler 1; the upper locking nuts 16 of the first slider 4 and the second slider 9 are tightened to fix the positions of the first slider mechanism and the second slider mechanism. Step Two: As Figure 4 , Figure 5 As shown, the portable residual stress device is moved to the position range of the sample 21, and the dial indicator probe 7 and the positioning rod 10 are aligned with the measurement reference surface 19; the point on the sample 21 that is aligned with the bottom of the dial indicator probe 7 is the measurement point 12, and the position on the sample 21 that is aligned with the positioning rod 10 is the positioning point 11. The positioning block 22 is attached to the blank to be cut 18. The positioning block 22 is set in an "L" shape and is close to the side of the positioning rod 10. Step 3: Zero the reading of dial indicator 5 on the portable residual stress device, and record it as ω(0) = 0 mm. Test the sample thickness and record it as t(0) = 56.85 mm. Remove the portable residual stress device. Step Four: As Figure 6 As shown, the sample 21 is cut off from the blank 18 to be cut and processed into a standard sample 21 by the layer cutting method; Step 5: Mill the surface of the sample away from measuring point 12 and positioning point 11, with the same thickness each time; remove the sample from the milling machine after milling; place the sample on the test platform with the measurement reference surface facing up, and use a portable residual stress measuring device to press the side of the positioning rod 10 against the positioning block 22; measure the deflection of the sample after milling the first layer, which is 0.010 mm, and record it as ω(1); measure the thickness, which is 54.00 mm, and record it as t(1); Step 6: Repeat step 5, milling the (i-1)th layer, denoted as ω(i-1) and the thickness as t(i-1); milling the i-th layer, denoted as ω(i) and the thickness as t(i); Step 7: Substitute the measured deflection and thickness values ​​of each layer into the following formula to calculate the residual stress of each layer: - The i-1 layer is the layer above the i-th layer being milled, where 1 ≤ i, 1 ≤ k; k and i are both integers. Calculate the thickness of each layer, the total deflection of each layer, and the deflection of a single layer, and test its residual stress. The results of milling layers 0-10 are shown in Table 1: Table 1. Test results of layer thickness (0-10 layers), total deflection, single-layer deflection, and residual stress of the tested samples. As the milling thickness increases, the residual stress in each layer of the sample increases as follows: Figure 7 As shown.

[0022] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention in any other way. Any person skilled in the art may make changes or modifications to the above-disclosed technical content to create equivalent embodiments that can be applied to other fields. However, any simple modifications, equivalent changes, and modifications made to the above embodiments based on the technical essence of the present invention without departing from the scope of the present invention shall still fall within the protection scope of the present invention.

Claims

1. A method of using a portable measuring device for residual stress in aluminum alloy products, characterized in that, The device includes a ruler, a first slider mechanism, and a second slider mechanism. The ruler is horizontally positioned and has graduations, with the 0 mark at the center. The second slider mechanism is located on either side of the first slider mechanism, and both mechanisms are movably connected to the ruler. The first slider mechanism includes a first slider and a dial indicator mounted on the first slider. The dial indicator includes a dial indicator body, a dial indicator screw, and a dial indicator probe. The dial indicator screw connects the probe to the body and controls the probe's up-and-down movement. The probe is perpendicular to the ground. The second slider mechanism includes a second slider and a positioning rod, which is perpendicular to the ground and positioned below the second slider. The first and second sliders are provided with recessed holes, and the ruler is provided with a sliding track that cooperates with the first and second sliders. The ruler passes through the recessed holes and connects the first and second sliders. The second slider mechanism also includes a counterweight; the counterweight is disposed on the front of the second slider, the recess is disposed on the rear side of the second slider, and the positioning rod is disposed between the recess and the counterweight; The specific usage method of the portable measuring device for residual stress in aluminum alloy products is as follows: Step 1: Plan the position of the sample on the aluminum alloy product blank to be cut in advance, move the first slider mechanism to the 0 mark of the ruler, and align the dial indicator probe with the 0 mark; move the positions of the second slider mechanisms on both sides symmetrically to determine the distance between the centers of the bottom of the positioning rods on both sides; tighten the upper locking nuts of the first and second sliders to fix the positions of the first and second slider mechanisms. Step 2: Move the portable residual stress device to the sample location range; the point on the sample that aligns with the bottom of the dial indicator probe is the measurement point, and the position on the sample that aligns with the positioning rod is the positioning point; attach the positioning block to the blank to be cut, the positioning block is set in an "L" shape, and the positioning block is close to the side of the positioning rod. Step 3: Zero the reading of the dial indicator on the portable residual stress device, record it as ω(0)=0mm, test the sample thickness t(0), and remove the portable residual stress device; Step 4: Cut the sample from the blank to be cut and process it into a standard sample using the layer-by-layer cutting method; Step 5: Mill the surface of the sample that is far from the measurement point and the positioning point, and mill the same thickness each time; after milling, remove the sample from the milling machine; place the sample on the test platform with the measurement reference surface facing up, and use the portable residual stress measuring device to press the side of the positioning rod against the positioning block; after milling the first layer, the deflection of the sample is recorded as ω(1), and the thickness is t(1). Step 6: Repeat step 5, mill the i-th layer, denoted as ω(i) for deflection and t(i) for thickness; Step 7: Substitute the measured deflection and thickness values ​​of each layer into the following formula to calculate the residual stress of each layer: - ； In the formula, layer i-1 is the layer above the i-th layer being milled, i≥1, k≥1; k and i are both integers.

2. The method of using the portable measuring device for residual stress in aluminum alloy products according to claim 1, characterized in that, The first slider has a groove on its front side, and the dial indicator is installed in the groove.

3. The method of using the portable measuring device for residual stress in aluminum alloy products according to claim 1, characterized in that, The first slider mechanism and the second slider mechanism also include a locking nut, which is installed on the first slider and the second slider.

4. The method of using the portable measuring device for residual stress in aluminum alloy products according to claim 1, characterized in that, Limit plates are provided at both ends of the ruler.

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