A device and method for testing the distribution of residual stress in a plate

Abstract

The application discloses a kind of plate internal residual stress distribution testing device and testing method.Testing device includes base, support column, side limit block, deflection testing micrometer, wherein support column and side limit block position adjustable.Testing method is through along the thickness direction equal interval layer-by-layer milling processing sample, the cumulative deflection of remaining material after each milling is tested using testing device, and the residual stress under different thickness of sample is calculated to obtain.The application scientifically designs a kind of plate internal residual stress distribution testing device and testing method based on the deflection change of sample after layer-by-layer stripping, the deflection of plate sample after stripping can be accurately and reliably measured using testing device, the plate internal residual stress distribution can be calculated using testing method through the deflection change of sample after stripping, and the plate internal residual stress distribution testing of various plates has universal applicability, and can be widely applied to the rapid and accurate characterization of plate product residual stress under industrial conditions.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of residual stress testing, in particular to a device and method for testing the distribution of residual stress in a plate. BACKGROUND

[0002] Quenching heat treatment and other rapid cooling heat treatment is usually an important process in the preparation and processing of metal materials. For example, after solid solution heat treatment, aluminum alloy plates generally need to be quenched to obtain a supersaturated solid solution, so that the dispersed strengthening phase can be analyzed and precipitated during subsequent aging heat treatment to ensure the mechanical properties of the alloy. However, quenching treatment can cause a large temperature gradient in the plate, resulting in high residual stress. Although most of the residual stress can be eliminated by pre-deformation process after quenching, some residual stress still exists in the finished plate. The existence of residual stress can cause significant deformation during subsequent part processing, resulting in assembly failure or even cracking. Therefore, residual stress control and elimination of the plate is very important, which requires the support of residual stress testing methods.

[0003] Residual stress testing methods have been developed for a long time, and there are a large number of methods that can be used for plate residual stress testing. Among them, the layer peeling method is suitable for internal residual stress distribution testing and is commonly used by material production enterprises and aviation main machine manufacturers for residual stress testing. The traditional layer peeling method is to paste strain gauges on the sample peeling surface or back surface to capture the strain during the peeling process. However, the strain gauge testing accuracy is affected by multiple factors such as experimental temperature and paste quality, resulting in large errors in residual stress calculation results. SUMMARY

[0004] The purpose of the present application is to provide a device and method for testing the distribution of residual stress in a plate based on the deflection change of the sample after layer-by-layer peeling, which can realize fast and accurate testing of the distribution of residual stress in the plate and has practical value for actual industrial production.

[0005] In order to achieve the above purpose, the main technical solutions adopted by the present application include:

[0006] The present application provides a device for testing the distribution of residual stress in a plate, which has:

[0007] A base with a plurality of position mounting holes;

[0008] At least two support columns vertically installed on the base, the top ends of the at least two support columns forming a horizontal plane for placing a plate sample;

[0009] Side limit blocks vertically installed on the base for limiting the horizontal position of the plate sample;

[0010] A deflection testing micrometer, vertically installed on the base, with the pointer vertically upward, and the tip is intended to contact the center point of the bottom surface of the plate sample, for testing the deflection of the sample.

[0011] According to the present application, the position of the support column is adjustable, and the support distance l s Adjusting in the range of 200mm-600mm.

[0012] According to the present application, preferably, the support distance l s Adjusting in the range of 200mm-380mm.

[0013] According to the present application, the center point of the support plane formed by the support column coincides with the center point of the bottom surface of the sample.

[0014] According to the present application, the top ends of the three support columns form a horizontal plane for placing the sample.

[0015] According to the present application, the position of the side edge limiting block is adjustable, and can be applied to the testing of samples of different sizes: length range 200mm-1000mm, width range 30mm-100mm.

[0016] According to the present application, preferably, it can be applied to the testing of samples of different sizes: length range 200mm-600mm, width range 30mm-60mm.

[0017] According to the present application, the limiting line / surface contacted by the side edge limiting block and the sample is perpendicular to the base.

[0018] According to the present application, the accuracy of the deflection testing micrometer is 0.001mm.

[0019] According to the present application, the material elastic modulus of each component of the testing device is ≥100GPa.

[0020] Another aspect of the present application provides a plate internal residual stress distribution testing method, comprising the following steps:

[0021] (1) According to the size of the sample, determine the appropriate support distance l s Adjust the support column in the testing device, and adjust the position of the side edge limiting block according to the size of the sample;

[0022] (2) Test and record the initial thickness h0 of the sample, and place the sample on the support column, select the upper surface of the sample as the subsequent layer stripping processing surface, fix the lower surface unchanged, and the center point contacts the deflection testing micrometer pointer, and clear the micrometer;

[0023] (3) Use milling method to process the layer stripping processing surface of the sample with equal interval and layer by layer, after each layer is stripped, test the remaining thickness h nThen the sample is placed on the testing device according to step (2), and the reading of the micrometer is recorded as the cumulative deflection d n ;

[0024] (4) The residual stress σ of the sample at different thicknesses is calculated according to formula (1) n .

[0025]

[0026] Wherein, n is the number of stripping; l s is the support distance; E is the elastic modulus; h n is the thickness of the sample after the n-th stripping; d n is the cumulative deflection of the sample after the n-th stripping.

[0027] (5) The σ n calculated according to step (4) is used to draw the stress distribution curve at different thicknesses.

[0028] According to the application, in step (1), the suitable support distance is 0.5-0.95 times the length of the sample.

[0029] According to the application, the preferred suitable support distance is 0.8-0.95 times the length of the sample.

[0030] According to the application, between steps (1) and (2), the sample can also be processed with counter-sunk holes to facilitate clamping of the sample during milling.

[0031] According to the application, in step (3), the equal-interval layer-by-layer milling is continued until the sample is half the thickness.

[0032] According to the application, in step (3), after the equal-interval layer-by-layer milling to half the thickness of the sample, the equal-interval layer-by-layer milling is continued until the sample cannot be processed.

[0033] According to the application, in step (3), each stripping process first uses rough machining with a single feed amount ≤2mm, and then uses fine machining with a machining amount ≥0.25mm.

[0034] The application also provides a formula for calculating the residual stress distribution of a plate. By testing the residual stress of the length-direction sample and the width-direction sample of the plate, the long-direction partial stress and the width-direction partial stress

[0035]

[0036]

[0037] Wherein, is the test result of the length direction sample of the plate material, is the test result of the width direction sample of the plate material, and v is the Poisson ratio.

[0038] The beneficial effects of the present application are:

[0039] The test method for the internal residual stress distribution of the plate material of the present application innovatively uses a formula for calculating the residual stress by the deflection change of the sample after peeling, and the internal residual stress distribution result of the sample can be accurately calculated by the formula, and then the internal residual stress distribution result of the plate material is calculated. Compared with the traditional peeling residual stress test method for monitoring the strain of the sample by using the strain gauge, the method is simpler and more convenient, and is suitable for the rapid test and characterization of the residual stress of the industrialized metal plate material, and provides a method support for the residual stress regulation of the metal plate material under industrial conditions.

[0040] The test device of the present application can realize the accurate deflection test of the aluminum alloy sample after peeling by using the test device according to the innovative test method, and then calculate the residual stress by the deflection change of the sample after peeling. Different test parameters such as sample size and support distance can be set for samples of different specifications and grades (such as different plate thicknesses), so as to be used for the internal residual stress distribution test of various metal plate materials, and has universal applicability. Further, the test device fills the gap in the field of rapid and accurate characterization of the residual stress of the metal plate material product under industrial conditions. BRIEF DESCRIPTION OF DRAWINGS

[0041] Figure 1 is the peeling processing surface of the sample, the deflection test point and the peeling distribution schematic diagram.

[0042] Figure 2 is a schematic diagram of the sample placed on the test device.

[0043] Figure 3 is the comparison result of the stress distribution calculated by the test method and the stress distribution obtained by finite element simulation.

[0044] REFERENCE NUMERALS:

[0045] 1: peeling processing surface; 2: bottom center point; 3: thickness measurement position; 4: plate sample; 5: base; 6: deflection test micrometer; 7: support column; 8: side limit block. DETAILED DESCRIPTION

[0046] In order to better explain the present application, so as to be understood, the present application is described in detail by specific embodiments in combination with the drawings.

[0047] As Figure 2As shown, the testing device provided by the present invention includes a base 5, support columns 7, side limiting blocks 8, and a deflection test dial indicator 6. The base 5 has multiple pre-drilled mounting holes for mounting the support columns 7, side limiting blocks 8, and the deflection test dial indicator 6. At least two support columns 7 are vertically mounted on the base 5, with their top ends forming a horizontal plane for placing the plate sample 4. The side limiting blocks 8 are vertically mounted on the base 7 to define the horizontal position of the plate sample 4. The deflection test dial indicator 6 is vertically mounted on the base 7 with its pointer pointing vertically upwards and its tip intended to contact the center point of the bottom surface of the plate sample 4 for testing the deflection of the sample.

[0048] The test method for testing the internal residual stress distribution of a plate using this testing device includes the following steps:

[0049] (1) A sample was cut from a 60mm thick aluminum alloy sheet, with a length of 400mm and a width of 50mm. The sample was prepared using conventional solution-quenching, and the residual stress can be considered to be symmetrically distributed along the thickness direction. Therefore, half the thickness of the sample was milled, and the number of peeling layers was determined to be 10, with each milling layer being 3mm thick. See the schematic diagram. Figure 1 .

[0050] (2) First, test the initial thickness h0 of the sample at thickness measurement position 2; then, place the sample 4 on... Figure 2 On the support column 7 (the support distance is set to 0.9 times the sample length, i.e., 360mm), the upper surface is selected as the peeling surface 1. The side of the sample is pressed against the side limiting block 8, and the center point 3 of the sample bottom surface contacts the pointer of the deflection test dial gauge 6, and the dial gauge is zeroed. Then, the sample is placed on a milling machine to remove the first layer. After milling, the sample is placed on the testing device with the peeling surface 1 facing upwards, the side of the sample pressed against the side limiting block 8, and the center point 3 of the sample bottom surface contacting the pointer of the deflection test dial gauge 6. The dial gauge reading is recorded as the cumulative deflection d1, and the thickness h1 of the remaining sample is measured. This process is repeated until 10 milling operations are completed, and the cumulative deflections are recorded as d2 to d1. 10 The thicknesses are denoted as h2 to h3. 10 .

[0051] (3) The residual stress distribution inside the specimen is calculated based on the cumulative deflection and thickness test results. The specimen width is denoted as b, the original thickness is h0, and the support distance of the specimen on the deflection test platform after delamination is l. s The sample thickness before the nth peeling is h. n-1 The thickness of the sample after delamination is h. n The deflection change of the sample tested on the platform is d. n Generally, for a rectangular cross-section specimen with uniform stress distribution in the same horizontal plane, the midpoint along the length direction is where the deflection reaches its maximum value.

[0052] The physical meaning of the bending moment can be known from the first layer stress acting on the bending moment of the sample can be expressed as the product of force and force arm:

[0053]

[0054] Wherein, F1 is the average value of the first layer stress, r1 is the distance between the first layer and the neutral plane of the sample, for the stress symmetrically distributed along the thickness direction of the sample, r1 = 0.5h0, σ1 is the average stress of the sample in the first layer.

[0055] When the sample is stripped of the first layer, the first layer stress is completely released, the sample is deformed by bending to make the force and moment re-equilibrium, so the bending moment change ΔM1 is:

[0056]

[0057] According to the corresponding relationship between the maximum deflection of the sample and the bending moment, ΔM1 can also be expressed as:

[0058]

[0059] Wherein, E is the elastic modulus of the sample, I1 is the inertia moment of the cross section of the sample after stripping the first layer (also known as the area moment of inertia), for the rectangular cross section, its value is

[0060] Integrating equation (5) and equation (6), the average stress of the first layer of the sample can be obtained as:

[0061]

[0062] When the sample is stripped of the second layer, the sample occurs deflection d2 warping deformation when the required bending moment Is:

[0063]

[0064] Wherein, The bending moment There are four factors contributing to the generation of.

[0065] First, only the bending moment change

[0066]

[0067] Second, the bending moment change

[0068]

[0069] Third, the bending moment change The moment required to load the second layer specimen in the opposite direction on the basis of the deflection dl caused by the first layer stress release can be considered as:

[0070]

[0071] Where I = b - (h1-h2) Δh 3 / 12.

[0072] Fourthly, the first layer stress release causes the neutral layer position of the specimen to shift downward by (h0-h1) / 2, and the change value of the bending moment caused by the shift of the neutral layer position is

[0073]

[0074] Therefore, the bending moment change caused only by the second layer stress release is

[0075]

[0076] The average stress σ2 of the second layer of the specimen can be further obtained as:

[0077]

[0078] Similarly, when calculating the residual stress of the third layer, the above four factors also need to be considered, and the average stress σ3 of the third layer can be expressed as:

[0079]

[0080] Wherein, can be expressed as:

[0081]

[0082] In turn, the average stress σn of the nth layer can be expressed as: n

[0083]

[0084] Wherein, can be expressed as:

[0085]

[0086] The equation (18) is brought into the equation (17), and integration and simplification are performed to obtain the formula (1). According to the above method, the residual stress of the length direction specimen and the width direction specimen of the plate is tested, and the long direction component stress and the width direction component stress ​​​At this time, the stress distribution calculated is the stress distribution of one half thickness, and since the residual stress distribution of the sample is symmetrical along the thickness direction, the residual stress distribution of the other half thickness can be obtained by symmetrizing the calculated residual stress distribution of one half thickness along the center point of the thickness.

[0087] (4) In order to verify the accuracy of the calculation formula, the finite element software and the birth-death element technology are used to simulate the deformation behavior of the quenched plate after peeling, and the initial stress distribution and the stress distribution calculated by the formula are compared. The simulation process is as follows: ① A model with the same size as the actual plate is established, and the finite element model is established by using the real thermal physical parameters and the heat exchange condition, and the quenched residual stress distribution is obtained by simulation; ② The birth-death element technology is used to simulate the peeling method for the model with quenched residual stress distribution, and the peeling times and the thickness of each layer are consistent with the actual peeling process; ③ After the peeling is finished, the deflection change of the center point of the bottom surface of the sample model is output, the quenched residual stress distribution is calculated according to the derived formula, and is compared with the quenched residual stress distribution obtained by simulation. As shown in the stress distribution comparison of the deformation amount results obtained by the peeling method and the original stress distribution Figure 3 It can be seen that the calculation result is relatively accurate, which shows that the calculation formula of the present application can calculate the real residual stress distribution of the sample by collecting the deflection change.

[0088] The above only describes the preferred embodiments of the present application, and for those skilled in the art, according to the idea of the present application, the specific implementation manner and application range can be changed, and the content of the description should not be understood as the limitation of the present application.

Claims

1. A method of testing the distribution of residual stress inside a sheet material, characterized by, The method uses a testing device having: a base with a plurality of position mounting holes; at least two support columns vertically mounted on the base, the top ends of the at least two support columns forming a horizontal plane for placing the board sample; side edge limiting blocks vertically mounted on the base for limiting the horizontal position of the board sample; a deflection testing micrometer vertically mounted on the base, the pointer vertically upward, and the tip intended to contact the center point of the bottom surface of the board sample, for testing the deflection of the sample, the testing method comprising the following steps: (1) Determine the appropriate support distance according to the size of the plate sample l s 0.5~0.95 times the length of the sample to adjust the support column in the test device, and adjust the position of the side limit block according to the size of the sample; (2) Test and record the initial thickness of the sample h 0, and place the sample on the support column, select the upper surface of the sample as the subsequent delamination processing surface, fix the lower surface, and contact the center point of the sample with the deflection test micrometer pointer. (3) Milling the sample to remove layers of the surface at equal intervals, and after each layer is removed, test the remaining thickness of the sample h n Then, place the sample on the testing device according to step (2), and read the dial gauge value as the cumulative deflection d n ; (4) The residual stress of the sample at different thicknesses is calculated according to formula (1) ; （1） wherein, n is the number of delaminations; l s is the support distance; E is the modulus of elasticity; h n is the thickness of the sample after the n th delamination; d n is the cumulative deflection of the sample after the n th delamination; (5) the stress distribution curve calculated according to step (4) The stress distribution curve under different thicknesses is plotted.

2. The method of testing the residual stress distribution inside a plate according to claim 1, wherein The appropriate support distance is 0.8-0.95 times the length of the sample.

3. The method of testing the residual stress distribution inside a plate according to claim 1, wherein Between steps (1) and (2), the sample is also subjected to countersunk hole processing to facilitate clamping of the sample during milling.

4. The method of testing the residual stress distribution inside a plate according to claim 1, wherein In step (3), the sample is milled at equal intervals to half the thickness of the sample.

5. The method of testing the residual stress distribution inside a plate according to claim 1, wherein In step (3), after milling the sample at equal intervals to half the thickness, continue to mill at equal intervals until the sample cannot be processed.

6. The method of testing the residual stress distribution inside a plate according to claim 1, wherein In step (3), each layer of processing is first roughened, with a single feed amount ≤2mm, and then finished, with a processing amount ≥0.25mm.

7. The method of testing residual stress distribution in sheet material of claim 1 wherein, The position of the support column is adjustable, and the support distance can be realized l s Adjust in the range of 200mm~600mm.

8. The method of testing the residual stress distribution inside a plate according to claim 7, wherein The support distance l s Adjustable in the range 200 mm - 380 mm.

9. The method of testing residual stress distribution in a plate according to claim 1, wherein The center point of the support plane formed by the support columns coincides with the center point of the bottom surface of the sample.

10. The method of testing residual stress distribution in a plate according to claim 1, wherein The number of support columns is three.

11. The method of testing residual stress distribution in a plate according to claim 1, wherein The position of the side edge limiting block is adjustable, suitable for testing board samples with a length range of 200-1000mm and a width range of 30-100mm.

12. The method of testing the residual stress distribution inside a plate according to claim 11, wherein The position of the side edge limiting block is adjustable, suitable for testing board samples with a length range of 200-600mm and a width range of 30-60mm.

13. The method of testing residual stress distribution in a plate according to claim 1, wherein The limiting line / surface of the side edge limiting block in contact with the sample is perpendicular to the base.

14. The method of testing residual stress distribution in sheet material of claim 1, wherein, The accuracy of the deflection testing micrometer is 0.001mm.

15. The method of testing residual stress distribution in a plate according to claim 1, wherein The material elastic modulus of each component is ≥100GPa.

16. The method according to any one of claims 1 to 15, wherein the residual stress of the lengthwise and widthwise samples of the sheet material is measured, and the lengthwise and widthwise component stresses of the sheet material are calculated according to the following equations (2) and (3), respectively. σL = σx + σy (2) σW = σx - σy (3) （2） （3） wherein, the results of the tests for the length direction specimen of the plate material, the results of the tests for the width direction specimen of the plate material, v is the Poisson's ratio.

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