Method for detecting depth distribution of residual stress of material
By adjusting the grazing incidence angle of X-rays and analyzing multiple diffraction peak data, the shortcomings of X-ray methods in measuring the depth distribution of residual stress in materials were overcome, and non-destructive and accurate stress distribution measurement was achieved.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Patents(China)
- Current Assignee / Owner
- SOUTHWEAT UNIV OF SCI & TECH
- Filing Date
- 2023-03-23
- Publication Date
- 2026-05-12
AI Technical Summary
Existing X-ray methods for measuring residual stress in materials suffer from insufficient penetration depth, require electrochemical stripping which affects accuracy, and cannot accurately measure the stress distribution along the depth of the material.
X-ray diffraction was used to calculate the X-ray penetration depth by adjusting the grazing incidence angle. Combined with the analysis of multiple diffraction peak data, the residual stress distribution at different depths of the material was calculated to avoid electrochemical delamination.
It enables the detection of the depth distribution of residual stress in materials, avoiding the stress damage and accuracy impact of traditional methods, and is suitable for the accurate analysis of bulk and thin film samples.
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Figure CN116380949B_ABST
Abstract
Description
Technical Field
[0001] This invention belongs to the field of X-ray diffraction testing technology, and more specifically, this invention relates to a method for detecting the depth distribution of residual stress in materials. Background Technology
[0002] Residual stress in materials has a significant impact on their mechanical properties. Compressive stress is generally considered beneficial for improving the fatigue strength of components, while tensile stress can negatively affect components by potentially promoting crack initiation, stress corrosion, and reducing fatigue life. The study of residual stress has long been valued by both academia and industry. Researchers hope to understand the residual stress state of metallic components or coating materials and its impact on performance. Because predicting residual stress is difficult, accurate measurement of residual stress is crucial.
[0003] Methods for measuring residual stress mainly include the orifice relaxation method, mechanical extensometer method, ultrasonic method, X-ray method, neutron diffraction method, and resistance strain gauge method. X-ray detection of residual stress, as a non-destructive testing method, has been applied in production, scientific research and other fields.
[0004] Conventional X-ray residual stress detection methods have several problems. For example, the X-ray stress meter primarily used typically employs a Cr target, where the X-ray penetration depth of Cr-generated X-rays is lower than that of Cu-generated X-rays. The measured stress is the two-dimensional residual stress on the surface. To measure the stress distribution along a specific depth, electrochemical stripping is usually required. This not only deviates from the non-destructive testing principle of X-ray methods but also severely affects measurement accuracy due to stress relaxation or the introduction of new stresses during stripping. Furthermore, the measurement cycle is long, requiring stripping and measuring layer by layer, necessitating multiple loading and unloading of the specimen, which is time-consuming and labor-intensive. Summary of the Invention
[0005] One object of the present invention is to solve at least the above-mentioned problems and / or defects, and to provide at least the advantages described below.
[0006] To achieve these objectives and other advantages according to the present invention, a method for detecting the depth distribution of residual stress in a material is provided, comprising:
[0007] Step 1: Sample pretreatment;
[0008] Step 2: Collect the full X-ray diffraction spectrum of the sample to determine the diffraction crystal plane for residual stress testing;
[0009] Step 3: Collect X-ray stress maps at different depths of the sample, calculate the penetration depth of X-rays into the sample, and fit the relationship between the grazing incidence angle of X-rays and the penetration depth of X-rays into the sample.
[0010] Step 4: Based on the X-ray stress spectrum of the sample acquired in Step 3, the residual stress at different depths of the sample is calculated using the stress expression, and the functional relationship between the residual stress distribution of the sample and the X-ray penetration depth of the sample at different depths is determined.
[0011] Preferably, in step one, the specific method for sample pretreatment includes: cleaning the surface of the sample with anhydrous ethanol, placing the sample in the diffraction analysis sample cell, and ensuring that the surface to be tested of the sample is flush with the upper surface of the diffraction analysis sample cell by adding modeling clay or a pad on the back of the sample.
[0012] Preferably, the sample is a block sample or a thin film sample.
[0013] Preferably, in step two, the specific method for acquiring the full X-ray diffraction spectrum of the sample includes: placing the pretreated sample on the sample stage of an X-ray diffractometer equipped with a 1Der semiconductor array detector for sample data acquisition, using Cu Kα rays as the X-ray source, operating voltage 40kV, operating current 40mA, angle scanning range 10~150°, and step size 0.03°.
[0014] Preferably, in step two, when collecting the full X-ray diffraction spectrum of the sample, a full spectrum scan of the sample is performed first, and diffraction peaks of 5 to 7 crystal planes of the same phase are selected for subsequent stress measurement; under the premise of ensuring the independence of diffraction intensity and diffraction peaks, high-angle diffraction peaks with diffraction angle 2θ>70° should be selected as the test objects as much as possible.
[0015] Preferably, the specific method of step three includes: setting the scanning axis to 2Theta; setting the X-ray grazing incidence angle to 0.01~10° in the Omega setting, and setting the tilt axis to Omega; setting the scanning mode to continuous scanning; setting the scanning range of a single diffraction peak to 2~4°; setting the scanning step size to 0.03~0.05°; and setting the tilt angle. ψ The tilt range, in order to make the analysis 2 i ψ -sin 2 ψ Linear fitting of data points in coordinate systems is more statistically accurate, ensuring 5-7 different tilt angles; set sin 2 ψ Step size, ensure 2 i ψ -sin 2 ψ or d ψ -sin 2 ψ Data points in coordinates at sin 2 ψThe axes are evenly spaced, with a step size not exceeding 0.1, where 2 i ψ To change the tilt angle ψ The obtained diffraction angle d ψ For tilt angle ψ When the interplanar spacing is changed, the resulting interplanar spacing d Value; for the same sample depth, Cu Kα X-rays were used several times at different tilt angles. ψ Irradiate the sample and measure the corresponding diffraction angle 2. i ψ For different sample depths, different X-ray grazing incidence angles are selected, and the corresponding tilt angles are... ψ They are also different; when the X-ray grazing incident angle is... oh The penetration depth of X-rays into the sample is calculated using the following formula:
[0016]
[0017] In the formula, t The depth to which X-rays penetrate the sample. m It is the linear absorption coefficient of the sample to X-rays. oh This is the grazing incidence angle of the X-rays.
[0018] Preferably, in step three, the relationship between the grazing incidence angle of X-rays and the penetration depth of X-rays into the sample is fitted using the least squares method, and the fitted relationship between the grazing incidence angle of X-rays and the penetration depth into the sample is as follows: t =0.0459+4.49275 oh ,in t The depth to which X-rays penetrate the sample. oh This is the grazing incidence angle of the X-rays.
[0019] Preferably, the specific method of step four includes:
[0020] Assuming principal stress s 1 and s 2. Parallel to the sample surface, in the normal direction of the sample surface s When 3 = 0, the normal strain in the direction perpendicular to the surface is:
[0021]
[0022] In the formula, E It is the Young's modulus of the sample. n It is the Poisson's ratio of the sample; such as Figure 1 As shown, a coordinate system O- is constructed on the upper surface of the sample. XYZ , X , Y ,Z There are three coordinate axes, s 1. s 2 is parallel to the upper surface of the sample. x direction and y Principal stresses in the direction of s 3 is perpendicular to the upper surface of the sample. z The principal stresses in the direction are defined in a vertical plane ABCO constructed on the upper surface of the sample, where O is the origin of the coordinate system, OC is perpendicular to the upper surface of the sample, and OB is perpendicular to the upper surface of the sample. s 2 presentations ψ The included angle, OA direction is the angle between the sample and the upper surface of the sample, which is 90°. ψ The directions of OA and OA are respectively cos α cos β cos ψ ,in α , β , ψ These are OA direction and s 1. s 2. s The spatial angle between 3 and 4, then the normal strain in the OA direction. e ψ yes:
[0023] e ψ =e 1cos 2 α + e 2cos 2 β + e 3cos 2 ψ
[0024] set up s x and e x upper surface of the sample x Residual stress and strain in the direction of stress, according to Hooke's law and related formulas under plane stress:
[0025] e x =e 1cos 2 f + e 2cos 2 f
[0026] In the formula, e 1. e 2 is the strain parallel to the upper surface of the sample;
[0027] Based on the spatial relationship, we can derive:
[0028]
[0029] When the residual stress is constant s x and e 3 are all constants. e ψ It is an angle ψ The function, with respect to the above equation, sin 2 ψ Taking the derivative with respect to the variable, we have:
[0030]
[0031] At this point, the measurement of residual stress becomes e ψ and sin 2 ψ relation;
[0032] When there is no stress, if a beam of monochromatic X-rays is incident on the sample, the diffraction condition satisfies Bragg's equation:
[0033] 2d 0 sinth 0= nλ
[0034] In the formula, n For diffraction series, l The wavelength of the incident X-rays. d 0 represents the spacing between the diffraction crystal planes. i 0 is the angle of incidence;
[0035] If there is elastic strain inside the object, the interplanar spacing will change, Δd / d 0 represents the normal strain of this set of crystal planes. 2d 0 sinth 0= nλ
[0036] After differentiation, we get:
[0037]
[0038] If we consider the OA direction as the normal direction of the diffraction plane, then ψ It is the angle between this direction and the normal direction of the sample surface. i ψ The diffraction angle is under stress, and the linear strain in the OA direction is:
[0039]
[0040] Bundle and Substitution have to:
[0041]
[0042] make
[0043]
[0044]
[0045] but s x =KM;
[0046] Where K is a constant, and E is the Young's modulus of the sample. n It is the Poisson's ratio of the sample; once the sample being tested, the diffraction plane, and the X-ray wavelength are determined, the K value can be calculated; when calculating the M value, it is done at several different angles. ψ The X-rays are projected onto the upper surface of the sample, and the position of the diffraction is measured using an X-ray detector. i ψ And with 2 i ψ sin 2 ψ Plotting the graph yields a curve, the slope of which is M; by fixing the X-ray incident depth each time, a set of data can be obtained, based on... s x =KM can then be used to obtain the residual stress of samples at different depths;
[0047] Finally, the residual stress depth distribution curve of the test sample was plotted based on multiple residual stress data. The functional relationship between the residual stress distribution and different depths was determined using a nonlinear fitting mathematical method.
[0048] The present invention has at least the following beneficial effects:
[0049] (1) The detection method of the present invention is based on the analysis of multiple diffraction peak data, which can extract effective information from complex spectra and is suitable for the analysis of residual stress depth distribution in bulk and thin film samples.
[0050] (2) For specimens with large stress gradients in the subsurface region, the traditional sin 2 The ψ method is not suitable for determining the distribution of residual stress. This invention obtains X-ray diffraction data and residual stress information at different depths below the surface by adjusting the grazing angle of X-rays to achieve different X-ray penetration depths.
[0051] (3) This invention uses only one radiation source, without the need to peel off the surface layer of the specimen layer by layer, without damaging the sample, and without introducing new stress or changing the existing stress on the surface of the specimen, thus ensuring the measurement of intrinsic stress distribution results and overcoming the shortcomings of traditional X-ray stress detection methods that cannot truly and accurately reflect the depth distribution of residual stress in materials.
[0052] Other advantages, objectives and features of the present invention will become apparent in part from the following description, and in part from those skilled in the art through study and practice of the invention. Attached Figure Description
[0053] Figure 1 A schematic diagram for measuring residual stress using grazing-incidence X-ray diffraction;
[0054] Figure 2 The X-ray diffraction (XRD) spectrum of the aluminum sample is shown.
[0055] Figure 3 Grazing incidence angle of X-rays oh 2θ of a metallic aluminum sample measured at 0.5° ψ with sin 2 Relationship diagram of ψ;
[0056] Figure 4 Grazing incidence angle of X-rays oh 2θ of a metallic aluminum sample measured at 1.0° ψ with sin 2 Relationship diagram of ψ;
[0057] Figure 5 Grazing incidence angle of X-rays oh 2θ of a metallic aluminum sample measured at 2.0° ψ with sin 2 Relationship diagram of ψ;
[0058] Figure 6 Grazing incidence angle of X-rays oh 2θ of a metallic aluminum sample measured at 3.0° ψ with sin 2 Relationship diagram of ψ;
[0059] Figure 7 Grazing incidence angle of X-rays oh 2θ of a metallic aluminum sample measured at 4.0° ψ with sin 2 Relationship diagram of ψ;
[0060] Figure 8 Grazing incidence angle of X-rays oh 2θ of a metallic aluminum sample measured at 5.0° ψ with sin 2 Relationship diagram of ψ;
[0061] Figure 9 The graph shows the relationship between residual stress and the depth of X-ray penetration into a metallic aluminum sample.
[0062] Figure 10 The curve is a fitting function curve of residual stress versus the depth of X-ray penetration into the aluminum sample. Detailed Implementation
[0063] The present invention will now be described in further detail with reference to the accompanying drawings, so that those skilled in the art can implement it based on the description.
[0064] It should be understood that terms such as “having,” “comprising,” and “including” as used herein do not exclude the presence or addition of one or more other elements or combinations thereof. Example
[0065] This embodiment uses metallic aluminum as the test sample and provides a method for detecting the depth distribution of residual stress in a material, including the following steps:
[0066] Step 1: Sample pretreatment;
[0067] Step 2: Collect the full X-ray diffraction spectrum of the sample to determine the diffraction crystal plane for residual stress testing;
[0068] Step 3: Collect X-ray stress maps at different depths of the sample, calculate the penetration depth of X-rays into the sample, and fit the relationship between the grazing incidence angle of X-rays and the penetration depth of X-rays into the sample.
[0069] Step 4: Based on the X-ray stress spectrum of the sample acquired in Step 3, the residual stress at different depths of the sample is calculated using the stress expression, and the functional relationship between the residual stress distribution of the sample and the X-ray penetration depth of the sample at different depths is determined.
[0070] In the above technical solution, the specific method of sample pretreatment in step one includes: cleaning the stains on the sample surface with anhydrous ethanol, placing the sample in the diffraction analysis sample cell, and ensuring that the test surface of the sample is flush with the upper surface of the diffraction analysis sample cell by adding modeling clay or a pad on the back of the sample.
[0071] In the above technical solution, the sample is a block sample or a thin film sample.
[0072] In the above technical solution, the specific method for acquiring the full X-ray diffraction spectrum of the sample in step two includes: placing the pre-treated sample onto the sample stage of an X-ray diffractometer equipped with a 1Der semiconductor array detector for sample data acquisition, using Cu Kα rays as the X-ray source, an operating voltage of 40 kV, an operating current of 40 mA, an angle scanning range of 10~150°, and a step size of 0.03°. The obtained full X-ray diffraction spectrum of the aluminum sample is as follows: Figure 2 As shown.
[0073] In the above technical solution, in step two, when collecting the full X-ray diffraction spectrum of the sample, the full spectrum of the sample is first scanned, and the diffraction peaks of 5 to 7 crystal planes of the same phase are selected for subsequent stress measurement. Under the premise of ensuring the independence of diffraction intensity and diffraction peaks, high-angle diffraction peaks with diffraction angle 2θ>70° should be selected as the test object as much as possible.
[0074] In the above technical solution, the specific method of step three includes: setting the scanning axis to 2Theta; setting the X-ray grazing incidence angle to 0.01~10° in the Omega item, and setting the tilt axis to Omega; setting the scanning mode to continuous scanning; setting the scanning range of a single diffraction peak to 2~4°; setting the scanning step size to 0.03~0.05°; and setting the tilt angle. ψ The tilt range, in order to make the analysis 2 i ψ -sin 2 ψ Linear fitting of data points in coordinate systems is more statistically accurate, ensuring 5-7 different tilt angles; set sin 2 ψ Step size, ensure 2 i ψ -sin 2 ψ or d ψ -sin 2 ψ Data points in coordinates at sin 2 ψ The axes are evenly spaced, with a step size not exceeding 0.1, where 2 i ψ To change the tilt angle ψ The obtained diffraction angle d ψ For tilt angle ψ When the interplanar spacing is changed, the resulting interplanar spacing d Value; for the same sample depth, Cu Kα X-rays were used several times at different tilt angles. ψ Irradiate the sample and measure the corresponding diffraction angle 2. i ψFor different sample depths, different X-ray grazing incidence angles are selected, and the corresponding tilt angles are... ψ They are also different; when the X-ray grazing incident angle is... oh The penetration depth of X-rays into the sample is calculated using the following formula:
[0075]
[0076] In the formula, t The depth to which X-rays penetrate the sample. m It is the linear absorption coefficient of the sample to X-rays. oh Let be the grazing incidence angle of the X-rays. The depth of penetration into the sample was calculated for X-ray grazing incidence angles of 0.5°, 1°, 2°, 3°, 4°, 5°, 6°, 7°, and 10°, as shown in the table below:
[0077]
[0078] In the above technical solution, in step three, the relationship between the grazing incidence angle of X-rays and the penetration depth of X-rays into the sample is fitted using the least squares method. The relationship between the grazing incidence angle of X-rays and the penetration depth into the sample obtained by fitting the data from the nine sets in the table above is as follows: t =0.0459+4.49275 oh ,in t The depth to which X-rays penetrate the sample. oh This is the grazing incidence angle of the X-rays.
[0079] In the above technical solution, the specific method of step four includes:
[0080] Assuming principal stress s 1 and s 2. Parallel to the sample surface, in the normal direction of the sample surface s When 3 = 0, the normal strain in the direction perpendicular to the surface is:
[0081]
[0082] In the formula, E It is the Young's modulus of the sample. n It is the Poisson's ratio of the sample; such as Figure 1 As shown, a coordinate system O- is constructed on the upper surface of the sample. XYZ , X , Y , Z There are three coordinate axes, s 1. s 2 is parallel to the upper surface of the sample. x direction and y Principal stresses in the direction of s 3 is perpendicular to the upper surface of the sample.z The principal stresses in the direction are defined in a vertical plane ABCO constructed on the upper surface of the sample, where O is the origin of the coordinate system, OC is perpendicular to the upper surface of the sample, and OB is perpendicular to the upper surface of the sample. s 2 presentations ψ The included angle, OA direction is the angle between the sample and the upper surface of the sample, which is 90°. ψ The directions of OA and OA are respectively cos α cos β cos ψ ,in α , β , ψ These are OA direction and s 1. s 2. s The spatial angle between 3 and 4, then the normal strain in the OA direction. e ψ yes:
[0083] e ψ =e 1cos 2 α + e 2cos 2 β + e 3cos 2 ψ
[0084] set up s x and e x upper surface of the sample x Residual stress and strain in the direction of stress, according to Hooke's law and related formulas under plane stress:
[0085] e x =e 1cos 2 f + e 2cos 2 f
[0086] In the formula, e 1. e 2 is the strain parallel to the upper surface of the sample;
[0087] Based on the spatial relationship, we can derive:
[0088]
[0089] When the residual stress is constant s x and e 3 are all constants. e ψ It is an angle ψ The function, with respect to the above equation, sin 2 ψ Taking the derivative with respect to the variable, we have:
[0090]
[0091] At this point, the measurement of residual stress becomes e ψ and sin 2 ψ relation;
[0092] When there is no stress, if a beam of monochromatic X-rays is incident on the sample, the diffraction condition satisfies Bragg's equation:
[0093] 2d 0 sinth 0= nλ
[0094] In the formula, n For diffraction series, l The wavelength of the incident X-rays. d 0 represents the spacing between the diffraction crystal planes. i 0 is the angle of incidence;
[0095] If there is elastic strain inside the object, the interplanar spacing will change, Δd / d 0 represents the normal strain of this set of crystal planes. 2d 0 sinth 0= nλ
[0096] After differentiation, we get:
[0097]
[0098] If we consider the OA direction as the normal direction of the diffraction plane, then ψ It is the angle between this direction and the normal direction of the sample surface. i ψ The diffraction angle is under stress, and the linear strain in the OA direction is:
[0099]
[0100] Bundle and Substitution have to:
[0101]
[0102] make
[0103]
[0104]
[0105] but s x =KM;
[0106] Where K is a constant, E is the Young's modulus of the sample, and ν is the Poisson's ratio of the sample; once the sample being tested, the diffraction plane, and the X-ray wavelength are determined, the value of K can be calculated; when calculating the value of M, the X-rays are projected onto the upper surface of the sample at several different angles ψ, and the diffraction position is measured using an X-ray detector. ψ And with 2θ ψ sin 2 Plotting ψ yields a curve, the slope of which is M; under the condition that the X-ray grazing incident angle ω is 0.5°, 1.0°, 2.0°, 3.0°, 4.0°, and 5.0° respectively, according to 2θ ψ -sin 2 The relationship between ψ is obtained by plotting them separately. Figure 3-Figure 8 Based on the mathematical methods of linear fitting, we obtain... Figure 3-Figure 8 The slopes of the data are: 0.40831, 0.28964, 0.34476, 0.32845, 0.23228, and 0.14904. Meanwhile, according to... Each X-ray grazing incidence angle oh The corresponding X-ray incident depth can be obtained from all of them. t .
[0107] By fixing the X-ray incident depth each time, a set of data can be obtained, based on... s x =KM can then be used to obtain the residual stress of samples at different depths; Figure 9 and Figure 10 The residual stresses at different depths were -72.6 MPa, -51.5 MPa, -61.3 MPa, -58.4 MPa, -41.3 MPa, and -26.5 MPa, respectively, and the corresponding X-ray incident depths were 2.257 μm, 4.514 μm, 9.026 μm, 13.536 μm, 18.042 μm, and 22.542 μm, respectively.
[0108] Finally, based on multiple residual stress data, a residual stress depth distribution curve of the tested sample was plotted, resulting in... Figure 9 Based on the mathematical method of nonlinear fitting, the functional relationship between residual stress distribution and different depths is determined, and the results are obtained. Figure 10 , Figure 9 and Figure 10In the diagram, the horizontal axis represents the depth of the aluminum sample, and the vertical axis represents the stress magnitude; in this embodiment, the residual stress... s x Depth of X-ray penetration into the sample t The best-fit function is:
[0109]
[0110] The number of devices and processing scale described herein are for the purpose of simplifying the description of the invention. Applications, modifications, and variations of the invention will be readily apparent to those skilled in the art.
[0111] Although embodiments of the present invention have been disclosed above, they are not limited to the applications listed in the specification and embodiments. They can be applied to various fields suitable for the present invention. For those skilled in the art, other modifications can be easily made. Therefore, without departing from the general concept defined by the claims and their equivalents, the present invention is not limited to the specific details and illustrations shown and described herein.
Claims
1. A method of detecting the depth distribution of residual stress in a material, characterized by, Includes the following steps: Step 1: Sample pretreatment; Step 2: Collect the full X-ray diffraction spectrum of the sample to determine the diffraction crystal plane for residual stress testing; Step 3: Collect X-ray stress maps at different depths of the sample, calculate the penetration depth of X-rays into the sample, and fit the relationship between the grazing incidence angle of X-rays and the penetration depth of X-rays into the sample. Step 4: Based on the X-ray stress spectrum of the sample acquired in Step 3, the residual stress at different depths of the sample is calculated using the stress expression, and the functional relationship between the residual stress distribution of the sample and the X-ray penetration depth of the sample at different depths is determined. In step three, the relationship between the grazing incidence angle of X-rays and the penetration depth of X-rays into the sample is fitted using the least squares method. The fitted relationship between the grazing incidence angle of X-rays and the penetration depth of the sample is as follows: τ =0.0459+4.49275 ω ,in τ The depth to which X-rays penetrate the sample. ω This refers to the grazing incidence angle of the X-rays. Step four includes: Calculate the normal strain of the sample. Based on Hooke's law under plane stress and spatial relationships, obtain the normal strain of the sample and its relationship with sin. 2 ψ relational formula , ψ The tilt angle for X-ray scanning; When there is no stress, if a single monochromatic X-ray beam is incident on the sample, the diffraction condition satisfies the Bragg equation. Substituting the differentiated Bragg equation and the linear strain relationship along the X-ray scanning direction of the sample into the relationship between the normal strain and sin... 2 ψ From the relationship, the formula for calculating the residual stress of the sample is obtained; Finally, the residual stress depth distribution curve of the test sample was plotted based on multiple residual stress data; the functional relationship between the residual stress distribution and different depths was determined using a nonlinear fitting mathematical method.
2. The method for detecting the depth distribution of residual stress in materials as described in claim 1, characterized in that, In step one, the specific method of sample pretreatment includes: cleaning the stains on the sample surface with anhydrous ethanol, placing the sample in the diffraction analysis sample cell, and ensuring that the sample surface to be tested is flush with the upper surface of the diffraction analysis sample cell by adding modeling clay or a pad on the back of the sample.
3. The method for detecting the depth distribution of residual stress in materials as described in claim 2, characterized in that, The sample can be a block sample or a thin film sample.
4. The method for detecting the depth distribution of residual stress in materials as described in claim 1, characterized in that, In step two, the specific method for acquiring the full X-ray diffraction spectrum of the sample includes: placing the pre-treated sample on the sample stage of an X-ray diffractometer equipped with a 1Der semiconductor array detector for sample data acquisition, using Cu Kα rays as the X-ray source, operating voltage 40 kV, operating current 40 mA, angle scanning range 10~150°, and step size 0.03°.
5. The method for detecting the depth distribution of residual stress in a material as described in claim 1, characterized in that, In step two, when collecting the full X-ray diffraction spectrum of the sample, a full spectrum scan of the sample is performed first, and diffraction peaks of 5 to 7 crystal planes of the same phase are selected for subsequent stress measurement. Under the premise of ensuring the independence of diffraction intensity and diffraction peaks, high-angle diffraction peaks with diffraction angle 2θ > 70° should be selected as the test objects as much as possible.
6. The method for detecting the depth distribution of residual stress in a material as described in claim 1, characterized in that, The specific method for step three includes: setting the scanning axis to 2Theta; setting the X-ray grazing incidence angle to 0.01~10° in the Omega section, and setting the tilt axis to Omega; setting the scanning mode to continuous scanning; setting the scanning range of a single diffraction peak to 2~4°; setting the scanning step size to 0.03~0.05°; and setting the tilt angle. ψ The tilt range, in order to make the analysis 2 θ ψ -sin 2 ψ Linear fitting of data points in coordinate systems is more statistically accurate, ensuring 5-7 different tilt angles; set sin 2 ψ Step size, ensure 2 θ ψ -sin 2 ψ or d ψ -sin 2 ψ Data points in coordinates at sin 2 ψ The axes are evenly spaced, with a step size not exceeding 0.1, where 2 θ ψ To change the tilt angle ψ The obtained diffraction angle d ψ For tilt angle ψ When the interplanar spacing is changed, the resulting interplanar spacing d Value; for the same sample depth, Cu Kα X-rays were used several times at different tilt angles. ψ Irradiate the sample and measure the corresponding diffraction angle 2. θ ψ For different sample depths, different X-ray grazing incidence angles are selected, and the corresponding tilt angles are... ψ They are also different; when the X-ray grazing incident angle is... ω The penetration depth of X-rays into the sample is calculated using the following formula: In the formula, τ The depth to which X-rays penetrate the sample. μ It is the linear absorption coefficient of the sample to X-rays. ω This is the grazing incidence angle of the X-rays.
7. The method for detecting the depth distribution of residual stress in a material as described in claim 1, characterized in that, The specific methods for step four include: Assuming principal stress σ 1 and σ 2. Parallel to the sample surface, in the normal direction of the sample surface σ When 3 = 0, the normal strain in the direction perpendicular to the surface is: In the formula, E It is the Young's modulus of the sample. ν It is the Poisson's ratio of the sample; construct a coordinate system O- on the upper surface of the sample. XYZ , X , Y , Z There are three coordinate axes, σ 1. σ 2 is parallel to the upper surface of the sample. x direction and y Principal stresses in the direction of σ 3 is perpendicular to the upper surface of the sample. z The principal stresses in the direction are defined in a vertical plane ABCO constructed on the upper surface of the sample, where O is the origin of the coordinate system, OC is perpendicular to the upper surface of the sample, and OB is perpendicular to the upper surface of the sample. σ 2 presentations ψ The included angle, OA direction is the angle between the sample and the upper surface of the sample, which is 90°. ψ The directions of OA and OA are respectively cos α cos β cos ψ ,in α , β , ψ These are OA direction and σ 1. σ 2. σ The spatial angle between 3 and 4, then the normal strain in the OA direction. ε ψ yes: ε ψ = ε 1cos 2 α+ ε 2cos 2 β+ ε 1cos 2 ψ set up σ x and ε x upper surface of the sample x Residual stress and strain in the direction of stress, according to Hooke's law and related formulas under plane stress: ε x = ε 1cos 2 φ + ε 2sin 2 φ In the formula, ε 1. ε 2 is the strain parallel to the upper surface of the sample; Based on the spatial relationship, we can derive: When the residual stress is constant σ x and ε 3 are all constants. ε ψ It is an angle ψ The function, with respect to the above equation, sin 2 ψ Taking the derivative with respect to the variable, we have: At this point, the measurement of residual stress becomes ε ψ and sin 2 ψ relation; When there is no stress, if a beam of monochromatic X-rays is incident on the sample, the diffraction condition satisfies Bragg's equation: 2d 0 sinθ 0= nλ In the formula, n For diffraction series, λ The wavelength of the incident X-rays. d 0 represents the spacing between the diffraction crystal planes. θ 0 is the angle of incidence; If there is elastic strain inside the object, the interplanar spacing will change, Δd / d 0 represents the normal strain of this set of crystal planes. 2d 0 sinθ 0= nλ After differentiation, we get: If we consider the OA direction as the normal direction of the diffraction plane, then ψ It is the angle between this direction and the normal direction of the upper surface of the sample. θ ψ The diffraction angle is under stress, and the linear strain in the OA direction is: Bundle and Substitution have to: make but σ x =KM; Where K is a constant, and E is the Young's modulus of the sample. ν It is the Poisson's ratio of the sample; once the sample being tested, the diffraction plane, and the X-ray wavelength are determined, the K value can be calculated; when calculating the M value, it is done at several different angles. ψ The X-rays are projected onto the upper surface of the sample, and the position of the diffraction is measured using an X-ray detector. θ ψ And with 2 θ ψ sin 2 ψ Plotting the graph yields a curve, the slope of which is M; by fixing the X-ray incident depth each time, a set of data can be obtained, based on... σ x =KM can then be used to obtain the residual stress of samples at different depths; Finally, the residual stress depth distribution curve of the test sample was plotted based on multiple residual stress data; the functional relationship between the residual stress distribution and different depths was determined using a nonlinear fitting mathematical method.