Thick plate composite residual stress detection method

Abstract

The invention discloses a thick plate composite residual stress detection method, and relates to the technical field of material residual stress detection. Comprising the following steps. The method comprises: 1, cutting a measurement sample; 2, clamping the sample from the upper end and the lower end of the left half side of the sample; 3, stress data are collected on the right half side of the sample according to a crack flexibility method, and the crack flexibility method residual stress of the sample in the thickness direction is calculated. And 4, calculating a first part stress on the left half side of the sample according to a contour method and contour deformation data of the first cutting surface, calculating a second part stress according to contour deformation data of the second cutting surface, and performing superposition to obtain contour method superposition correction residual stress of the sample in the thickness direction. And 5, uniformly arranging sampling points along the thickness direction of the sample, and determining final data according to a difference threshold value of the residual stress of the crack flexibility method and the residual stress of the contour method superposition correction at each sampling point. According to the invention, the technical problems of low material utilization rate, large repeated clamping error and incapability of self-checking error in the existing measurement technology can be solved.

Description

Technical Field

[0001] The present invention relates to the technical field of material residual stress detection, and specifically to a method for detecting the composite residual stress of thick plates. Background Art

[0002] Residual stress is the internal stress generated due to non-uniform deformation during the material processing, which directly affects the fatigue life and structural safety of components. The current mainstream detection methods include the crack compliance method and the contour method. The former calculates the stress by measuring the strain release after cutting, and the latter inversely calculates the stress distribution by analyzing the contour deformation of the cutting surface.

[0003] The crack compliance method requires semi-fixed clamping of the specimen, allowing strain release at the suspended end. It cuts layer by layer by wire cutting and collects strain data. However, only a single stress distribution curve along the thickness direction can be obtained by one cutting, and multiple cuttings are required, resulting in low utilization rate of the specimen.

[0004] The contour method requires full-fixed clamping of the specimen, scans the contour deformation after cutting, and inversely calculates the original stress in combination with the finite element. However, it is sensitive to the surface stress and is easily affected by the deviation of the cutting path. Summary of the Invention

[0005] The purpose of the present invention is to provide a method for detecting the composite residual stress of thick plates. By the co-directional cross-verification of the crack compliance method and the contour method, the systematic error of a single method is reduced. It is applicable to the measurement of the residual stress of metal thick plates and thick-wall welded structures, and can solve the technical problems of low material utilization rate, large error of multiple clamping, and inability to self-check the error in the existing measurement technology.

[0006] In order to achieve the above purpose, the present invention adopts the following technical solutions.

[0007] A method for detecting the composite residual stress of thick plates includes the following steps: S1. Cut a measurement specimen from the thick plate raw material. S2. Vertically clamp the specimen, and use the fixture to clamp the specimen from the upper and lower ends of the left half of the specimen. The right half of the specimen is in a free state. S3. Conduct the first cutting on the right half of the specimen. According to the crack compliance method, collect the stress data at the corresponding positions during the cutting process, and calculate the residual stress of the crack compliance method of the specimen along the thickness direction. S4. Conduct the second cutting on the left half of the specimen. According to the contour method, inversely calculate the first part of the stress released at the second cutting due to the first cutting based on the contour deformation data of the first cutting surface, and inversely calculate the second part of the stress released at the second cutting according to the contour deformation data of the second cutting surface. Superimpose the first part of the stress and the second part of the stress to obtain the superimposed and corrected residual stress of the contour method of the specimen along the thickness direction. S5. Uniformly set sampling points along the thickness direction of the specimen, and determine the final data according to the difference threshold between the residual stress by the crack compliance method and the residual stress by the contour method superposition correction at each sampling point.

[0008] Further, in S1, when intercepting the specimen, intercept it from the middle area of the thick plate raw material, and the length and width dimensions of the specimen are both greater than 2.5 times the thickness.

[0009] Further, in S2, the fixture includes two first cross beams and two pressing plates. The two first cross beams are arranged in parallel on the horizontal plane and are used to support the bottom of the left half of the specimen. The two pressing plates correspond to the two first cross beams respectively and are used to press the specimen on the first cross beam from the top of the left half of the specimen.

[0010] Further, the fixture also includes a second cross beam. The second cross beam and the first cross beam are arranged on the same horizontal plane and are used to support the bottom of the right half of the specimen to offset the self-weight of the right half of the specimen.

[0011] Further, in S3, for the first cutting, use a wire cutting machine to cut at the vertical midline of the specimen. The wire cutting wire feeds along the thickness direction of the specimen from one side of the specimen. A strain gauge is pasted on the back of the specimen at the cutting position to record strain data. During cutting, pause every 1 mm of cutting depth to record strain data. Stop recording data until 80% of the thickness is cut, and then cut off the remaining part at one time.

[0012] Further, the residual stress by the contour method superposition correction is the sum of the first part of the stress and the second part of the stress.

[0013] Further, in S4, keep the left half of the specimen in the fixed state after the first cutting in S3. For the second cutting, use a wire cutting machine to cut at the vertical midline of the left half of the specimen. The wire cutting wire feeds along the thickness direction of the specimen from one side of the left half of the specimen and cuts off at one time, and scan the contour deformation data of the two cutting surfaces for inverse calculation of the first part of the stress and the second part of the stress.

[0014] Further, select three paths along the thickness direction of the specimen at the corresponding positions on the scanned cutting surface, calculate the residual stress by the contour method superposition correction respectively, and take the average value of the three results to increase the accuracy of the data.

[0015] Further, in S5, sampling points are uniformly set at intervals of 1 mm along the thickness direction of the specimen. The calculation method of the difference threshold is , where is the residual stress by the crack compliance method along the thickness direction of the specimen, is the residual stress by the contour method superposition correction along the thickness direction of the specimen.

[0016] Further, when determining the final data, if the difference threshold Δσ(z) at all sampling points ≤ 10%, either the residual stress value obtained by the crack compliance method or the residual stress value obtained by the profile method with superposition correction can be adopted. if the difference threshold Δσ(z) of the sampling points within the area 3 mm from the specimen surface > 10%, the residual stress value obtained by the crack compliance method is adopted for the sampling points in this area. if the difference threshold Δσ(z) at locally discrete sampling points > 10% and the number is less than 10% of the total number of sampling points, it is regarded as a reasonable error, and the residual stress value obtained by the crack compliance method and the residual stress value obtained by the profile method with superposition correction are retained. if the difference threshold Δσ(z) at continuously multiple sampling points > 10% and the number is greater than 10% of the total number of sampling points, mark the abnormal area and trigger a retest.

[0017] After adopting the above technical solution, the present invention has the following beneficial effects: 1. By adopting cross-verification of two methods, the present invention reduces the measurement error and improves the comprehensiveness and reliability of the residual stress detection result; 2. The present invention can complete the stress tests of the two methods by using a single specimen, with high material utilization rate and reduced test cost; 3. The present invention can realize the tests of the two methods with only one clamping, avoiding the error caused by repeated clamping and saving time; 4. The present invention is adapted to a standard slow wire cutting machine tool and can be implemented without complex equipment modification. Brief Description of the Drawings

[0018] Figure 1 is a schematic flow chart of the method of the present invention.

[0019] Figure 2 is a schematic overall state diagram during the implementation of the present invention.

[0020] Figure 3 is a schematic flow chart for the present invention to determine the final result.

[0021] Figure 4 is a schematic diagram of the actual measurement result in the embodiment.

[0022] Brief Description of the Drawings: 1. Specimen, 21. First crossbeam, 22. Pressing plate, 23. Second crossbeam, 3. Strain gauge, 4. Wire cutting wire, 5. First cutting position, 6. Second cutting position. Detailed Embodiment

[0023] In order to make the objectives, technical solutions and advantages of the present invention more clear and understandable, the features and performance of a method for detecting the residual stress of thick plate composites in the present invention will be further described in detail below with reference to the accompanying drawings and embodiments.

[0024] Please refer to the attached Figures 1 to 3 , a method for detecting the residual stress of thick plate composites, comprising the following steps.

[0025] Step S1: Cut a measurement specimen 1 from the thick plate raw material. When cutting specimen 1, cut it from the middle area of the thick plate raw material, and the length and width dimensions of specimen 1 are both greater than 2.5 times the thickness. For example, if the thickness of specimen 1 is 20 mm, then the length and width of specimen 1 should both be greater than 50 mm.

[0026] Step S2: Vertically clamp specimen 1, and use a fixture to clamp specimen 1 from the upper and lower ends of the left half side of specimen 1, and the right half side of specimen 1 is in a free state. The fixture includes two first crossbeams 21 and two pressing plates 22. The two first crossbeams 21 are arranged in parallel on the horizontal plane and are used to support the bottom of the left half side of specimen 1. There is at least a 10-mm interval between the two first crossbeams 21.

[0027] The two pressing plates 22 correspond to the two first crossbeams 21 respectively and are used to press specimen 1 onto the first crossbeam 21 from the top of the left half side of specimen 1.

[0028] The fixture further includes a second crossbeam 23. The second crossbeam 23 is arranged on the same horizontal plane as the first crossbeam 21 and is used to support the bottom of the right half side of specimen 1 to offset the self-weight of the right half side of specimen 1. The position where the second crossbeam 23 contacts specimen 1 is coated with lubricating oil to enable specimen 1 to deform and release stress in the horizontal direction.

[0029] S3: Conduct a first cut on the right half side of specimen 1. According to the crack compliance method, collect the stress data at the corresponding positions during the cutting process, and calculate the residual stress of specimen 1 in the thickness direction by the crack compliance method . The cutting is performed using a slow wire cutting machine tool to improve the accuracy of the measurement results.

[0030] The first cut is performed using a wire cutting machine at the vertical center line of specimen 1. The wire cutting wire 4 feeds along the thickness direction of specimen 1 from one side of specimen 1. A strain gauge 3 is attached to the back of specimen 1 at the cutting position to record the strain data. During cutting, pause every 1 mm of cutting depth and record the strain data until 80% of the thickness is cut, then stop recording the data and cut off the remaining part at one time.

[0031] S4. Perform secondary cutting on the left half of specimen 1, maintaining the fixed state of the left half of specimen 1 after the first cutting in S3. The secondary cutting is carried out using a wire cutting machine at the vertical midline of the left half of specimen 1. The wire cutting wire feeds once along the thickness direction of specimen 1 from one side of the left half of specimen 1 and cuts through at once.

[0032] According to the contour method, scan the contour deformation data of the two cutting surfaces. For the first cutting surface, select the cutting surface close to the left half for scanning. For the secondary cutting surface, select any one surface for scanning.

[0033] Based on the contour deformation data of the first cutting surface, inversely calculate the first part of the stress released at the secondary cutting due to the first cutting , and based on the contour deformation data of the secondary cutting surface, inversely calculate the second part of the stress released at the secondary cutting , and superimpose the first part of the stress and the second part of the stress to obtain the contour method superimposed and corrected residual stress of specimen 1 along the thickness direction , and the contour method superimposed and corrected residual stress is the sum of the first part of the stress and the second part of the stress .

[0034] To improve the measurement accuracy, multiple paths along the thickness direction of specimen 1 can be selected at corresponding positions on the scanned cutting surface, and the contour method superimposed and corrected residual stress can be calculated separately , and the average value of multiple results is taken as the final contour method superimposed and corrected residual stress , which is used to increase the accuracy of the data. Preferably, in this scheme, three paths along the thickness direction of specimen 1 are selected, the contour method superimposed and corrected residual stress is calculated separately, and the average value of the three results is taken.

[0035] S5. Uniformly set sampling points along the thickness direction of specimen 1. Preferably, sampling points are uniformly set at intervals of 1 mm along the thickness direction of specimen 1.

[0036] Determine the final data according to the difference threshold between the crack compliance method residual stress and the contour method superimposed and corrected residual stress at each sampling point.

[0037] The calculation method of the difference threshold is , where is the crack compliance method residual stress of specimen 1 along the thickness direction, is the contour method superimposed and corrected residual stress of specimen 1 along the thickness direction.

[0038] When determining the final data, the following logic is adopted.

[0039] If the difference threshold Δσ(z) at all sampling points ≤ 10%, either the residual stress value obtained by the crack compliance method or the residual stress value corrected by the superposition of the profile method can be used.

[0040] If the difference threshold Δσ(z) of the sampling points within the area 3 mm from the surface of Specimen 1 > 10%, since the result of the profile method in the surface layer area is greatly affected by heat, the residual stress value obtained by the crack compliance method is used for the sampling points in this area.

[0041] If the difference threshold Δσ(z) at locally discrete sampling points > 10% and the number is less than 10% of the total number of sampling points, it is regarded as a reasonable error, and the residual stress value obtained by the crack compliance method and the residual stress value corrected by the superposition of the profile method are retained.

[0042] If the difference threshold Δσ(z) at continuously multiple sampling points > 10% and the number is greater than 10% of the total number of sampling points, mark the abnormal area and trigger a retest.

[0043] In specific implementation, the metal blank to be measured is a new type of 2050T84 aluminum alloy pre-stretched plate. Test Specimen 1 is a representative sample cut from this plate, and the size of Specimen 1 is 200 mm × 220 mm × 90 mm.

[0044] Clamp Specimen 1 according to the clamping method in this scheme. After clamping, simultaneously paste 2 strain gauges 3 at the strain measurement points, Figure 2 as shown. Use a JM3816D type static strain gauge to read the values of the 2 strain gauges 3 and perform arithmetic averaging.

[0045] At the first cutting position 5, use a Sodick ALN600Qs slow wire cutting machine for the first cutting. The cutting current is 3 A, the wire feeding speed is 3 m / s, the feeding speed is 5 mm / min, and deionized water is used for cooling.

[0046] Cut 1 mm deeper each time along the plate thickness direction. After reaching the predetermined depth, pause and read the value when the strain is stable. Repeat the cutting and reading process until cutting to 75 mm and then stop. The strain gauge is connected to a compensation block with the same material specification as Specimen 1 for temperature compensation.

[0047] After the crack compliance method cutting is completed, without loosening the clamping, re-thread the wire, and continue the profile method cutting test at the midline of the remaining specimen. The processing parameters are the same as those of the first cutting. After the secondary cutting is completed, use a Hexagon coordinate measuring machine to measure the profiles of the cutting surfaces of the two cuts, and the measurement lattice is 2 mm × 2 mm.

[0048] Based on the measurement data, the internal stress distribution of Specimen 1 is calculated respectively by using the stress calculation process of the standard crack compliance method and the contour method calculation method based on superposition correction proposed by the present invention.

[0049] In the contour method measurement, the midline of the cutting surface and two lines spaced 10 mm to the left and right of the midline are selected, a total of three paths, and the stress data is extracted and the average value is calculated as the contour method result.

[0050] The measurement data of the crack compliance method and the measurement data of the contour method are compared and analyzed, as Figure 4 shown. Using the difference threshold formula proposed by the present invention and the difference processing algorithm as Figure 3 shown, data cross-validation is carried out. Among the data from 0 to 90 mm in the thickness direction of Specimen 1, Δσ(z) > 10% at 8 discrete sampling points near z = 10 mm, z = 45 mm, and z = 80 mm, which is less than 10% of the total number of sampling points, is regarded as reasonable error, and the data results of both methods are retained.

[0051] It should be noted that the parts not described in detail in this solution are all prior arts. The above embodiments are only used to illustrate the present invention, but the present invention is not limited to the above embodiments. Any simple modification, equivalent change and modification made to the above embodiments according to the technical essence of the present invention shall fall within the protection scope of the present invention.

Claims

1. A method for detecting the residual stress of thick plate composite, characterized in that: It includes the following steps: S1. Cut a measurement specimen (1) from a thick plate raw material; S2. Vertically clamp the specimen (1), and use a fixture to clamp the specimen (1) from the upper and lower ends of the left half side of the specimen (1), and the right half side of the specimen (1) is in a free state; S3. Conduct the first cut on the right half side of the specimen (1). According to the crack compliance method, collect the stress data at the corresponding positions during the cutting process, and calculate the residual stress of the specimen (1) along the thickness direction by the crack compliance method; S4. Conduct the second cut on the left half side of the specimen (1). According to the contour method, inversely calculate the first part of the stress released at the second cut due to the first cut based on the contour deformation data of the first cut surface, and inversely calculate the second part of the stress released at the second cut according to the contour deformation data of the second cut surface. Superimpose the first part of the stress and the second part of the stress to obtain the superimposed and corrected residual stress of the specimen (1) along the thickness direction by the contour method; S5. Uniformly set sampling points along the thickness direction of the specimen (1), and determine the final data according to the difference threshold between the residual stress of the crack compliance method and the superimposed and corrected residual stress of the contour method at each sampling point.

2. The method for detecting the composite residual stress of thick plates according to claim 1, wherein: In S1, when cutting the specimen (1), cut it from the middle area of the thick plate raw material, and the length and width dimensions of the specimen (1) are both greater than 2.5 times the thickness.

3. The method for detecting the residual stress of thick plate composite as claimed in claim 1, wherein: In S2, the fixture includes two first cross beams (21) and two pressing plates (22). The two first cross beams (21) are arranged in parallel on the horizontal plane and are used to support the bottom of the left half side of the specimen (1). The two pressing plates (22) correspond to the two first cross beams (21) respectively and are used to press the specimen (1) on the first cross beam (21) from the top of the left half side of the specimen (1).

4. The method for detecting the residual stress of thick plate composite according to claim 3, wherein: The fixture further includes a second cross beam (23). The second cross beam (23) and the first cross beam (21) are arranged on the same horizontal plane and are used to support the bottom of the right half side of the specimen (1) to offset the self-weight of the right half side of the specimen (1).

5. The method for detecting the composite residual stress of thick plates according to claim 1, wherein: In S3, the first cut is carried out by a wire cutting machine at the vertical midline of the specimen (1). The wire cutting wire feeds along the thickness direction of the specimen (1) starting from one side of the specimen (1). A strain gauge (3) is attached to the back of the specimen (1) at the cutting position to record the strain data. During cutting, pause every 1 mm of cutting depth and record the strain data until 80% of the thickness is cut, then stop recording data and cut off the remaining part at one time.

6. The method for detecting the residual stress of thick plate composite according to claim 1, wherein: The superimposed and corrected residual stress by the contour method is the sum of the first part of the stress and the second part of the stress.

7. The method for detecting the composite residual stress of thick plates according to claim 1, wherein: In S4, keep the fixed state of the left half side of the specimen (1) after the first cut in S3. The second cut is carried out by a wire cutting machine at the vertical midline of the left half side of the specimen (1). The wire cutting wire feeds along the thickness direction of the specimen (1) once from one side of the left half side of the specimen (1) and cuts off at one time, and scan the contour deformation data of the two cut surfaces for inversely calculating the first part of the stress and the second part of the stress.

8. The method for detecting the composite residual stress of thick plates according to claim 6, wherein: Select three paths along the thickness direction of the specimen (1) at the corresponding positions on the scanned cut surface, calculate the superimposed and corrected residual stress by the contour method respectively, and take the average of the three results to increase the accuracy of the data.

9. A method for detecting the composite residual stress of thick plates according to claim 1, characterized in that: In S5, sampling points are uniformly set at intervals of 1 mm along the thickness direction of the specimen (1). The calculation method of the difference threshold is as follows: ， Among them, is the residual stress of the crack compliance method in the thickness direction of the specimen (1). The contour method superposition correction residual stress for the specimen (1) along the thickness direction.

10. A method for detecting the composite residual stress of thick plates according to claim 9, characterized in that: When determining the final data, if the difference threshold Δσ(z) at all sampling points ≤ 10%, either the residual stress value obtained by the crack compliance method or the residual stress value obtained by the superposition and correction of the contour method can be adopted, if the difference threshold Δσ(z) of the sampling points in the area within 3 mm from the surface of the specimen (1) > 10%, the residual stress value obtained by the crack compliance method is adopted for the sampling points in this area, if the difference threshold Δσ(z) at locally discrete sampling points > 10% and the number is less than 10% of the total number of sampling points, it is regarded as a reasonable error, and the residual stress value obtained by the crack compliance method and the residual stress value obtained by the superposition and correction of the contour method are retained, if the difference threshold Δσ(z) at continuously multiple sampling points > 10% and the number is greater than 10% of the total number of sampling points, the abnormal area is marked and retesting is triggered.

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