Method and apparatus for measuring depth-resolved residual stress inside materials

Abstract

This application discloses a method and apparatus for measuring depth-resolved residual stress inside a material, relating to the field of residual stress measurement technology. The method includes: incident a beam of radiation onto a sample; setting a double-slit assembly along the propagation path of the diffraction signal to obtain a sampled diffraction beam based on a specific depth layer inside the sample; moving the double-slit assembly and / or a detector to receive the sampled diffraction beam, and recording the diffraction information of the received sampled diffraction beam; moving the sample and repeating the above steps to obtain a set of diffraction information received by the detector when the sample is at different positions; and obtaining the residual stress information inside the sample based on the set of diffraction information. This method aims to solve the problem of the lack of existing technologies capable of non-destructively and efficiently obtaining the three-dimensional residual stress distribution along the depth direction inside a material.

Description

Technical Field

[0001] This application relates to the field of residual stress measurement technology, and in particular to a method and apparatus for measuring depth-resolved residual stress inside a material. Background Technology

[0002] Residual stress is a self-balancing stress generated within a material during processing. Its distribution directly affects the fatigue life, stress corrosion resistance, and dimensional stability of engineering components. In the aerospace manufacturing field, cold extrusion strengthening is widely used to strengthen the connection holes of critical load-bearing components such as aircraft frame beams. However, improper control of process parameters can generate excessively high tensile residual stress around the holes, which can induce the initiation and propagation of microcracks, leading to premature component failure. Obtaining the three-dimensional residual stress distribution along the depth direction within the material is crucial for revealing crack initiation mechanisms, optimizing process parameters, and preventing quality accidents at their source.

[0003] Existing technologies lack a method that can obtain the three-dimensional residual stress distribution along the depth direction inside a material in a non-destructive, accurate, and efficient manner. Summary of the Invention

[0004] The main objective of this application is to provide a method and apparatus for measuring depth-resolved residual stress inside a material, aiming to solve the technical problem of lacking the ability to obtain the three-dimensional residual stress distribution along the depth direction inside a material in a non-destructive and efficient manner in the prior art.

[0005] To achieve the above objectives, in a first aspect, this application provides a method for measuring depth-resolved residual stress within a material, comprising: A beam of radiation is incident on the sample to be tested, generating a diffraction signal; A double slit group is set in the propagation path of the diffraction signal to obtain the sampled diffraction beam based on a specific depth layer inside the sample under test in the diffraction signal; Move the dual slit assembly and / or detector so that the sampled diffraction beam is received by the detector, and record the diffraction information of the sampled diffraction beam received by the detector; Move the sample to be tested and repeat the above steps to obtain the set of diffraction information received by the detector when the sample to be tested is in different positions. Based on the diffraction information set, the residual stress information inside the sample to be tested is obtained.

[0006] Optionally, the dual-slit group includes two slit plates that are spatially parallel and spaced apart. Each slit plate has an aperture. The geometric dimensions and spacing of the two apertures on the two slit plates together define a receiving angle, which is used to block the sampling diffraction beam in the diffraction signal based on a specific depth layer inside the sample under test.

[0007] Optionally, the receiving angle is obtained based on Bragg's law and the principle of ray tracing, according to the diffraction crystal plane of the sample to be tested, the energy of the rays, and the preset depth resolution, so that the volume of the sampling diffraction beam matches the stress gradient characteristic size inside the sample to be tested.

[0008] Optionally, before the step of incidenting a beam of radiation onto the sample to generate a diffraction signal, the method further includes: A stress-free standard sample is placed in the optical path of the X-ray, and the diffraction ring generated by the X-ray passing through the standard sample is obtained. The spatial position and orientation of the double slit group and the detector are iteratively adjusted until the deviation between the intensity distribution of the detected diffraction ring and the theoretical calculation value is less than a preset threshold. The transformation relationship between the measurement coordinate system and the diffraction physical coordinate system is then established.

[0009] Optionally, the preset threshold includes a diffraction ring roundness deviation of less than 0.1% and a diffraction ring diffraction intensity non-uniformity of less than 5%.

[0010] Optionally, the sample to be tested and the double slit assembly are each provided with a sample stage, and the sample stage is connected to a six-axis displacement system to drive the sample to be tested and the double slit assembly to move on three translation axes (X, Y, and Z) and three rotation axes, respectively.

[0011] Optionally, the step of obtaining residual stress information inside the sample under test based on the diffraction information set includes: By performing polar coordinate integration on the diffraction rings recorded at each sampling point in the diffraction information set, a diffraction pattern showing the distribution of diffraction intensity as a function of diffraction angle is obtained. The diffraction peaks in the diffraction pattern are fitted to obtain the diffraction angle values. The diffraction angle value is compared with the standard diffraction angle of the stress-free standard sample, and the lattice strain of the crystal plane corresponding to the sampling point is calculated according to Bragg's law. Based on the equations of elasticity, the lattice strain in at least six independent directions is converted into stress tensor components at the sampling point; Spatial interpolation is performed on the stress tensor of all sampling points to reconstruct the three-dimensional residual stress distribution inside the sample under test.

[0012] Secondly, this application provides an apparatus for measuring depth-resolved residual stress inside a material, comprising: A radiation source is used to emit a beam of radiation and direct it onto the sample to be tested, thereby generating a diffraction signal. The sample stage is connected to a six-axis displacement system for carrying and moving the sample to be tested; A dual-slit assembly is positioned between the sample to be tested and the detector. The dual-slit assembly includes two parallel slit plates. The sampling diffraction beam based on a specific depth layer inside the sample to be tested is obtained from the diffraction signal through the dual-slit assembly. A detector for receiving the diffraction signal; The control system, connected to the sample stage, the double slit assembly, and the detector, is used to coordinate and control the movement of the sample stage and signal acquisition. The data processing unit is used to obtain residual stress information inside the sample under test based on the diffraction information.

[0013] Optionally, the radiation source is a synchrotron radiation source, whose energy can be continuously or incrementally adjusted within a preset range; the detector is an energy-resolution two-dimensional detector.

[0014] Optionally, the control system is configured to control the X-ray source to output at least two beams of different energies at the same sampling point and trigger the detector to collect the diffraction signal of the corresponding energy.

[0015] The beneficial effects that this application can achieve are: This application proposes a method and apparatus for measuring depth-resolved residual stress within a material. By introducing a double-slit group into the diffraction path and utilizing the geometric constraints of the front and rear slits, a virtual sampling volume corresponding to a specific depth layer is defined in the diffraction space. This volume is uniquely determined by the receiving angle jointly determined by the incident beam cross-sectional area and the double-slit group, ensuring that the diffraction signal received by the detector originates only from this depth layer. This achieves precise resolution of the internal stress of the material along the depth direction at the physical level. This effect is directly brought about by the spatial filtering function of the double-slit group, eliminating the need for complex mathematical decoupling or destructive slicing, thus achieving non-destructive depth-resolved measurement. The diffraction information set can be used to inversely deduce the full tensor of lattice strain. Based on this set, a quantitative mapping relationship can be established between cold extrusion process parameters, such as extrusion amount, speed, die shape, and three-dimensional residual stress distribution, thereby achieving rational optimization of process parameters. For example, by comparing the differences in the three-dimensional stress field under different processes, the key stress threshold and dangerous area leading to crack initiation can be directly located, preventing part failure from the source. Attached Figure Description

[0016] Figure 1 This is a flowchart illustrating the method for measuring the depth-resolved residual stress inside a material according to an embodiment of this application. Figure 2 This is a schematic diagram of the structure of the device for measuring the depth-resolved residual stress inside a material according to an embodiment of this application; Figure 3 This is a schematic diagram illustrating the relationship between the double slit assembly and the ray in an embodiment of this application; Figure 4This is a schematic diagram of one of the slit plates in a double slit assembly according to an embodiment of this application; Figure 5 This is a schematic diagram of another slit plate in the double slit assembly according to an embodiment of this application; The numbers on the map are: 10 - X-ray source, 20 - front slit, 30 - sample to be tested, 40 - double slit assembly, 50 - detector, 60 - six-axis displacement system.

[0017] The realization of the purpose, functional features and advantages of this application will be further explained in conjunction with the embodiments and with reference to the accompanying drawings. Detailed Implementation

[0018] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0019] It should be noted that all directional indications (such as up, down, left, right, front, back, etc.) in the embodiments of the present invention are only used to explain the relative positional relationship and movement of each component in a certain specific posture (as shown in the figure). If the specific posture changes, the directional indication will also change accordingly.

[0020] In this invention, unless otherwise explicitly specified and limited, the terms "connection," "fixed," etc., should be interpreted broadly. For example, "fixed" can mean a fixed connection, a detachable connection, or an integral part; it can mean a mechanical connection or an electrical connection; it can mean a direct connection or an indirect connection through an intermediate medium; it can mean the internal communication of two components or the interaction between two components, unless otherwise explicitly limited. Those skilled in the art can understand the specific meaning of the above terms in this invention according to the specific circumstances.

[0021] Furthermore, if the embodiments of this invention involve descriptions such as "first" or "second," these descriptions are for descriptive purposes only and should not be construed as indicating or implying their relative importance or implicitly specifying the number of technical features indicated. Therefore, a feature defined with "first" or "second" may explicitly or implicitly include at least one of those features. Additionally, the meaning of "and / or" throughout the text includes three parallel solutions; for example, "A and / or B" includes solution A, solution B, or a solution where both A and B are satisfied simultaneously. Furthermore, the technical solutions of the various embodiments can be combined with each other, but this must be based on the ability of those skilled in the art to implement them. When the combination of technical solutions is contradictory or impossible to implement, it should be considered that such a combination of technical solutions does not exist and is not within the scope of protection claimed by this invention.

[0022] The labels in the figure are: 10-X-source, 20-front slit, 30-sample to be tested, 40-double slit group, 50-detector, 60-six-axis displacement system.

[0023] against Figure 3 In the image, the English meaning is: Beam size: The lateral dimension of the incident X-ray beam.

[0024] Aperture size: The opening size of the slit determines the actual width through which the light beam passes.

[0025] Effective aperture size: The effective aperture diameter of a ray.

[0026] Distance between plates: The distance between the two slit plates that make up a double slit group.

[0027] Plate stack thickness: The overall thickness of the slit plate affects the collimation of the beam.

[0028] Adjacent aperture distance: The center-to-center distance between adjacent slit plates.

[0029] Sample to plate distance: The distance between the sample to be tested and the slit plate.

[0030] Radial aperture distance from center: the distance from the center of the radial aperture.

[0031] Gauge length: In diffraction measurements, it refers to the measurement length defined along the direction of the incident beam.

[0032] Gauge volume: The volume of the sample that is irradiated and produces diffraction signals, defined by the incident beam cross section and the slit in front of the detector.

[0033] Example 1 Reference Figure 1 The first embodiment of this application provides a method for measuring depth-resolved residual stress inside a material, comprising: S10. A beam of radiation is incident on the sample to be tested, generating a diffraction signal.

[0034] Optionally, a synchrotron X-ray source or a high-energy laboratory X-ray source can be selected, and the X-ray energy can be adjusted to a preset value, such as 50 keV, using a monochromator. The incident beam is collimated into a rectangular spot by a focusing lens and a front slit, with an adjustable size, such as 100 μm horizontally × 100 μm vertically. This beam illuminates the sample under test at a fixed incident angle, and the crystal planes inside the sample that satisfy Bragg's law produce diffraction, forming a diffraction cone, which is recorded by a two-dimensional detector.

[0035] S20. A double slit group is set in the propagation path of the diffraction signal to obtain the sampled diffraction beam based on a specific depth layer inside the sample under test.

[0036] Optionally, the dual-slit assembly consists of two parallel and spaced-apart slit plates, each with a high-precision aperture, such as a rectangle or pinhole. The distance between the front and rear plates is designed according to the target depth resolution. Based on the principle of ray tracing, a receiving angle is defined by the geometry and spacing of the front and rear apertures. The expression for the receiving angle is: In the formula, Indicates the receiving angle, and L represents the distance between the two slit plates. This indicates the width of the aperture. Only diffracted beams originating from a specific depth layer within the sample under test, and whose exit angle falls within the receiving angle range, can simultaneously pass through both slits to reach the detector. The location of this specific depth layer is determined by the incident beam geometry, sample orientation, and the position of the slit assembly. By adjusting the spatial position of the slit assembly, diffraction signals from different depth layers can be selectively received, thereby achieving depth resolution.

[0037] S30. Move the double slit group and / or detector to allow the sampled diffraction beam to be received by the detector and record the diffraction information of the sampled diffraction beam received by the detector.

[0038] S40. Move the sample to be tested and repeat the above steps to obtain the set of diffraction information received by the detector when the sample to be tested is in different positions.

[0039] Specifically, the sample to be tested is mounted on a six-axis displacement system, which can control the movement of the sample along three translational axes (X, Y, and Z) and three rotational axes. Following a preset scanning path, for example, moving point-by-point along a direction perpendicular to the aperture wall, with the step size dynamically adjusted according to the stress gradient, the sample is sequentially moved to each sampling point. Steps S10-S30 are repeated at each sampling point to acquire and store a two-dimensional diffraction ring image of that point, forming a set of diffraction information covering the three-dimensional space inside the sample.

[0040] S50. Based on the diffraction information set, obtain the residual stress information inside the sample to be tested.

[0041] Example 2 Based on Example 1, this example provides a method for measuring depth-resolved residual stress inside a material, including: S10. A beam of radiation is incident on the sample to be tested, generating a diffraction signal.

[0042] Optionally, before the step of incidenting a beam of radiation onto the sample to generate a diffraction signal, the method further includes: A stress-free standard sample is placed in the optical path of the X-ray, and the diffraction rings generated by the X-ray passing through the standard sample are obtained. The spatial position and orientation of the double slit group and the detector are iteratively adjusted until the deviation between the intensity distribution of the detected diffraction rings and the theoretical calculation value is less than a preset threshold. The transformation relationship between the measurement coordinate system and the diffraction physical coordinate system is then established.

[0043] Specifically, before incident a beam of X-rays onto the sample to be tested, diffraction geometry calibration is required to ensure that the double-slit assembly is precisely aligned with the diffraction physical coordinate system. This includes placing a stress-free standard sample with known lattice parameters and diffraction angle in the optical path of the X-ray. Two-dimensional diffraction ring images generated from standard samples are acquired and defined as measured diffraction rings. Based on theoretically calculated standard diffraction rings, an objective function is constructed. ,in, The roundness deviation of the measured diffraction ring is defined as: (major axis length - minor axis length) / average radius. The intensity non-uniformity of the diffraction rings is defined as: (maximum intensity on the ring - minimum intensity) / average intensity. and For the weighting coefficients, satisfying In this embodiment, , The spatial position and attitude of the double-slit array, adjusted by translation in the X, Y, and Z directions and by rotation in the Rx and Ry directions, along with the detector position, are used as optimization variables. An iterative search is performed using the Nelder-Mead simplex method or gradient descent method. After each iteration, the diffraction rings are re-acquired and calculated. Value, until The value is less than the preset threshold. At this point, the position parameters of the double-slit assembly and the detector are recorded to establish a precise transformation relationship between the measurement coordinate system and the diffraction physical coordinate system, ensuring that the definition of the sampling volume is accurate and reliable in subsequent measurements.

[0044] S20. A double slit group is set in the propagation path of the diffraction signal to obtain the sampled diffraction beam based on a specific depth layer inside the sample under test.

[0045] Optionally, the dual-slit assembly includes two slit plates that are spatially parallel and spaced apart. Each slit plate has an aperture. The geometric dimensions and spacing of the two apertures on the two slit plates together define a receiving angle, which is used to block the sampled diffraction beam in the diffraction signal based on a specific depth layer inside the sample under test.

[0046] Optionally, based on the diffraction crystal plane of the sample under test, the energy of the rays, and the preset depth resolution, the receiving angle is obtained according to Bragg's law and the principle of ray tracing, so that the volume of the sampling diffraction beam matches the stress gradient characteristic size inside the sample under test.

[0047] Specifically, Bragg's law is the foundation of X-ray crystallography. It describes why strong diffraction peaks are produced at specific angles when X-rays strike a crystal. X-rays are electromagnetic waves with very short wavelengths, comparable to the interatomic distance. When they strike a crystal, the regularly arranged atoms in the crystal are actually scattered by the electron cloud, becoming secondary wave sources. These secondary waves interfere with each other. Ray tracing is a core tool of geometrical optics, based on Fermat's principle that light propagates along the path where the optical path reaches its extreme value. It ignores the wave nature of light, i.e., ignores interference and diffraction effects, provided that the size of the optical element is much larger than the wavelength of light. A series of rays emitted from an object are calculated, and by analyzing their refraction / reflection paths through the lens, the image point where they converge can be found. By tracing thousands of rays, aberrations, image blur, field of view, focal length, etc., can be evaluated. In other words, only diffracted beams originating from a specific depth layer and whose exit angle falls within the receiving angle range can simultaneously pass through both slits to reach the detector; diffracted beams along other paths are absorbed by the slit plates.

[0048] The specific process for determining the receiving angle α is as follows: Based on the target diffraction crystal plane of the sample to be tested, its interplanar spacing d is a known constant; the X-ray energy E corresponds to the wavelength... The diffraction angle of this crystal plane can be calculated using Bragg's law. : Where d is the interplanar spacing, The wavelength of the ray. Based on the preset depth resolution. That is, the spatial resolution along the X-ray incident direction, based on the principle of ray tracing to determine the receiving angle α and The geometric relationship. For a parallel incident beam, the length of the sampling volume along the depth direction. The following approximate relationships exist between the receiving angle α, the incident beam width b, and the diffraction geometry: Based on the relationship between the receiving angle α and the geometric parameters of the double-slit group, The spacing L between the front and rear slit plates and the aperture opening width w are determined. To ensure sufficient signal strength, the selection of w and L needs to strike a balance between depth resolution and diffraction intensity. Finally, it is verified whether the determined sampling volume corresponds to the stress gradient characteristic size inside the sample under test. Matching, stress gradient feature size Defined as the minimum distance at which residual stress undergoes a significant spatial change, it can be estimated in advance through finite element pre-analysis or material microstructure characteristics, such as grain size and precipitate distribution. The matching condition is: to In other words, the depth resolution should be at least 1 / 3 to 1 / 5 of the stress gradient feature size to ensure that the details of the stress gradient can be resolved. If this condition is not met, α, that is, w and L, need to be adjusted and recalculated until the matching condition is met.

[0049] Optionally, the preset thresholds include a diffraction ring roundness deviation of less than 0.1% and a diffraction ring intensity non-uniformity of less than 5%.

[0050] Optionally, the sample to be tested and the double slit assembly are each provided with a sample stage, and the sample stage is connected to a six-axis displacement system to drive the sample to be tested and the double slit assembly to move on the three translation axes X, Y, and Z and the three rotation axes respectively.

[0051] Optionally, the six-axis displacement system includes three translation axes and three rotation axes. The three translation axes are defined as the X-axis (horizontal direction, parallel to the incident beam direction or defined as needed), the Y-axis (horizontal direction, perpendicular to the X-axis), and the Z-axis (vertical direction). Each translation axis is equipped with a high-precision linear motor and closed-loop feedback with a linear encoder. The three rotation axes are defined as the Rx-axis (rotating around the X-axis), the Ry-axis (rotating around the Y-axis), and the Rz-axis (rotating around the Z-axis). Each rotation axis is equipped with a high-precision rotary motor and an angle encoder.

[0052] For the sample stage containing the sample to be tested, the six-axis displacement system is used to: sequentially move different positions on the sample into the measurement area through X, Y, and Z axis motion, achieving three-dimensional gridded scanning. By rotating Rx or Ry, different angles are created between the sample surface normal and the diffraction crystal plane normal. to satisfy This method involves acquiring multi-angle strain data required for measurement. By rotating Rz, the azimuth angle φ of the measurement direction within the sample plane is changed to obtain stress components in different directions.

[0053] For the sample stage containing the double-slit assembly, the six-axis displacement system is used to: precisely move the double-slit assembly to its calibrated zero position via X, Y, and Z-axis translation, ensuring the centers of the front and rear slits coincide with the axis of the diffraction cone; and fine-tune the orientation of the double-slit assembly via Rx and Ry rotation, ensuring it is perpendicular to the exit direction of the diffraction beam and avoiding reception angle distortion caused by tilting. The two six-axis displacement systems are managed collaboratively by the same control system, enabling either linked or independent movement. During measurement, the position and orientation of the double-slit assembly are typically fixed, remaining unchanged after calibration, with three-dimensional scanning completed only by moving the sample under test; however, during calibration, both systems can move to find the optimal alignment position.

[0054] S30. Move the double slit group and / or detector to allow the sampled diffraction beam to be received by the detector and record the diffraction information of the sampled diffraction beam received by the detector.

[0055] Specifically, based on the coordinate transformation relationship established in step S10, the double-slit assembly and detector are moved to the calibrated zero position. For each sampling point on the sample under test, the detector exposes and records a two-dimensional diffraction ring image, which is the diffraction information for that point. The diffraction information includes raw data such as the intensity distribution and geometric morphology of the diffraction rings.

[0056] S40. Move the sample to be tested and repeat the above steps to obtain the set of diffraction information received by the detector when the sample to be tested is in different positions.

[0057] Specifically, the sample to be tested is mounted on a six-axis high-precision displacement system. This system can control the sample's movement along three translational axes (X, Y, and Z) and three rotational axes, with a repeatability accuracy better than ±1 μm. According to a preset scanning path, for example, a 2 mm scan is performed along the X direction perpendicular to the hole wall, with a step size of 20 μm in areas with high stress gradients near the hole and 100 μm in areas far from the hole; the entire thickness is scanned along the Y direction with a step size of 200 μm, moving the sample sequentially to each sampling point. S10-S30 is repeated at each sampling point to acquire and store a two-dimensional diffraction ring image of that point, forming a set of diffraction information covering the three-dimensional space inside the sample.

[0058] S50. Based on the diffraction information set, obtain the residual stress information inside the sample to be tested.

[0059] Optionally, the step of obtaining residual stress information inside the sample under test based on the diffraction information set includes: S501. Perform polar coordinate integration on the diffraction rings recorded at each sampling point in the diffraction information set to obtain the diffraction pattern of diffraction intensity as a function of diffraction angle. Specifically, for the two-dimensional diffraction ring image at each sampling point, a polar coordinate system is established with the geometric center of the diffraction ring as the pole. The image is divided into M sectors along the azimuth angle, for example, M=72, i.e., one sector every 5. The pixel intensity within each sector is integrated radially to obtain a one-dimensional spectrum of diffraction intensity as a function of the diffraction angle. The integration formula is: ,in, The diffraction angle, The azimuth angle is represented by r, and the polar radius r is related to the diffraction angle. There is a linear relationship. (k is obtained from the detector's geometric calibration). Represents the intensity value of a pixel in polar coordinates. The one-dimensional spectral line obtained after integration represents the azimuth angle. The intensity varies with the diffraction angle. The purpose of polar coordinate integration on the diffraction rings is to reduce the dimensionality of the two-dimensional data, which facilitates subsequent peak position fitting; at the same time, the signal-to-noise ratio is improved through integration.

[0060] S502. Fit the peak positions of the diffraction peaks in the diffraction pattern to obtain the diffraction angle values. Specifically, the expression for Gaussian peak fitting is:

[0061] In the formula, This indicates the variation of diffraction intensity with the diffraction angle. This represents the background intensity, which is a constant. Peak height is represented by subtracting the background intensity from the peak intensity. Indicates the peak position, which is the parameter to be fitted. The peak width is represented by the standard deviation, reflecting the degree of peak broadening. Diffraction peaks are typically approximated by Gaussian lines and are used to fit experimentally measured diffraction peaks to accurately determine their positions.

[0062] The peak position with sub-pixel accuracy is obtained by nonlinear least squares fitting. This is the basis of strain calculation.

[0063] S503. Compare the diffraction angle value with the standard diffraction angle of the stress-free standard sample, and calculate the lattice strain of the crystal plane corresponding to the sampling point according to Bragg's law. Specifically, the Bragg equation is: In the formula, d represents the interplanar spacing, which depends on the crystal structure of the material. The angle is the Bragg angle, which is the angle between the incident X-ray and the crystal plane, and n is the diffraction order, usually taken as 1. The wavelength is X-ray. The diffraction angle is measured at 2... This allows us to infer changes in interplanar spacing and thus calculate lattice strain. It describes the conditions under which X-rays diffract in a crystal. When X-rays are grazing at an angle... When incident on a crystal plane with a spacing of d, if the optical path difference is equal to an integer multiple of the wavelength, constructive interference occurs, resulting in diffraction.

[0064] The fitted diffraction angle In step S10 In comparison, lattice strain is calculated using the differential form of Bragg's law. Its expression is:

[0065] This formula originates from the differential form of Bragg's law, and relates to the Bragg equation. Taking the differential of both sides, we get ,get ,in, That is, lattice strain , Because in experiments, 2 is usually measured. Therefore Substituting, we get: However, more precisely, it is important to note the use of... Difference, This is a value in radians. The formula already includes a conversion factor from angle to radians. In the formula, It is the lattice strain, which is dimensionless; The Bragg angle is the angle under stress-free conditions, which is measured from a standard sample. This is the measured diffraction angle; This is the standard diffraction angle without stress.

[0066] S504. Based on the equation of elasticity, the lattice strain in at least six independent directions is converted into the stress tensor components of the sampling point. Specifically, adopt The method involves tilting the sample at different angles. The strain measured below In relation to stress components, for a plane stress state, we have:

[0067] In the formula, In the sample coordinate system, the azimuth angle is used to represent the coordinates. (Within the sample plane) and tilt angle Strain measured in the direction of (angle deviating from the normal to the sample surface); For elastic modulus, Poisson's ratio, Azimuth Normal stress in the direction, The angle of inclination of the sample to be tested is the angle between the normal of the diffraction crystal plane and the normal of the sample surface. and These are the principal stresses in the plane. This is determined by measuring at least three different... Angles, such as 0°, 10°, 15° and 20° ,by Perform linear fitting for the independent variable, using the slope Seeking , by intercept Seeking To obtain the full stress tensor, six independent components are needed. , , , , and Then it is necessary to have multiple Repeat the above measurements in the direction of change, and solve the system of equations using the generalized Hooke's law of elasticity. This involves measuring multiple... The slope of the strain at the angle is obtained by linear fitting, and then the result is calculated. , S505. Spatial interpolation is performed on the stress tensor of all sampling points to reconstruct the three-dimensional residual stress distribution inside the sample under test.

[0068] Optionally, the stress tensor components of all sampling points, such as , , , , and As discrete spatial point data, Kriging interpolation or cubic spline interpolation methods are used to generate a continuous three-dimensional stress field distribution. Anisotropy is considered during the interpolation process, and the interpolation node density is appropriately increased in directions with large stress gradients, such as the direction perpendicular to the hole wall. The final output is a visualization of the three-dimensional residual stress inside the sample under test, including stress isosurface cloud maps and arbitrary cross-sectional slices, which are used to quantitatively analyze stress concentration areas, gradient variation characteristics, and their correlation with failure modes such as crack initiation.

[0069] Example 3 Based on Example 1, this example provides a device for measuring depth-resolved residual stress inside a material, comprising: The X-ray source 10 is used to emit a beam of X-rays and incident it onto the sample 30 to generate a diffraction signal. In this embodiment, the X-ray source is an oscillator.

[0070] The sample stage is connected to a six-axis displacement system 60, which is used to carry and move the sample 30 to be tested. The dual slit group 40 is disposed between the sample to be tested 30 and the detector 50. The dual slit group 40 includes two parallel slit plates. The sampling diffraction beam based on a specific depth layer inside the sample to be tested 30 is obtained through the dual slit group 40. Detector 50 is used to receive diffraction signals; The control system, connected to the sample stage, the double slit assembly 40 and the detector 50, is used to coordinate and control the movement of the sample stage and signal acquisition. The data processing unit is used to obtain residual stress information inside the sample 30 under test based on diffraction information.

[0071] Optionally, the radiation source 10 is a synchrotron radiation source, whose energy can be continuously or incrementally adjusted within a preset range; the detector is an energy-resolved two-dimensional detector.

[0072] Specifically, the X-ray source 10 employs a synchrotron radiation source and is equipped with a dual-crystal monochromator or a multilayer monochromator, allowing the output X-ray energy E to be continuously scanned or stepped within a preset range. The energy adjustment range is selected based on the absorption edge and diffraction crystal plane of the material under test. For example, for aluminum alloy materials, it is typically set to 20keV ≤ E ≤ 100keV, corresponding to a wavelength range of 0.062nm ≥ λ ≥ 0.0124nm.

[0073] Optionally, the control system is configured to control the X-ray source to output at least two beams of different energies at the same sampling point and trigger the detector to collect the diffraction signal of the corresponding energy.

[0074] Specifically, the control system works in conjunction with the monochromator, shutter, and energy-resolved detector of the synchrotron radiation source, and is configured to perform a multi-energy rapid acquisition mode at the same sampling point. By keeping the sample stationary at a sampling position, the energy of the incident X-rays is rapidly switched, and diffraction signals are acquired at each energy, thereby obtaining diffraction information from multiple depth layers at that point at once. This avoids positioning errors introduced by sample movement and significantly improves data acquisition efficiency.

[0075] The above are merely preferred embodiments of this application and do not limit the patent scope of this application. Any equivalent structural or procedural transformations made using the content of this application's specification and drawings, or direct or indirect applications in other related technical fields, are similarly included within the patent protection scope of this application.

Claims

1. A method for measuring depth-resolved residual stress inside a material, characterized in that, include: A beam of radiation is incident on the sample to be tested, generating a diffraction signal; A double slit group is set in the propagation path of the diffraction signal to obtain the sampled diffraction beam based on a specific depth layer inside the sample under test in the diffraction signal; Move the dual slit assembly and / or detector so that the sampled diffraction beam is received by the detector, and record the diffraction information of the sampled diffraction beam received by the detector; Move the sample to be tested and repeat the above steps to obtain the set of diffraction information received by the detector when the sample to be tested is in different positions. Based on the diffraction information set, the residual stress information inside the sample to be tested is obtained.

2. The method for measuring depth-resolved residual stress inside a material as described in claim 1, characterized in that, The dual-slit assembly includes two slit plates that are spatially parallel and spaced apart. Each slit plate has an aperture. The geometric dimensions and spacing of the two apertures on the two slit plates together define a receiving angle, which is used to block the sampling diffraction beam in the diffraction signal based on a specific depth layer inside the sample under test.

3. The method for measuring depth-resolved residual stress inside a material as described in claim 2, characterized in that, Based on the diffraction crystal planes of the sample under test, the energy of the rays, and the preset depth resolution, the receiving angle is obtained according to Bragg's law and the principle of ray tracing, so that the volume of the sampling diffraction beam matches the stress gradient characteristic size inside the sample under test.

4. The method for measuring depth-resolved residual stress inside a material as described in claim 1, characterized in that, Before the step of incidenting a beam of radiation onto the sample to generate a diffraction signal, the procedure also includes: A stress-free standard sample is placed in the optical path of the X-ray, and the diffraction ring generated by the X-ray passing through the standard sample is obtained. The spatial position and orientation of the double slit group and the detector are iteratively adjusted until the deviation between the intensity distribution of the detected diffraction ring and the theoretical calculation value is less than a preset threshold. The transformation relationship between the measurement coordinate system and the diffraction physical coordinate system is then established.

5. The method for measuring depth-resolved residual stress inside a material as described in claim 4, characterized in that, The preset thresholds include a diffraction ring roundness deviation of less than 0.1% and a diffraction ring intensity non-uniformity of less than 5%.

6. The method for measuring depth-resolved residual stress inside a material as described in claim 1, characterized in that, The sample to be tested and the double slit assembly are each provided with a sample stage. The sample stage is connected to a six-axis displacement system, which can drive the sample to be tested and the double slit assembly to move on three translation axes (X, Y, and Z) and three rotation axes, respectively.

7. The method for measuring depth-resolved residual stress inside a material as described in claim 1, characterized in that, The step of obtaining residual stress information inside the sample under test based on the diffraction information set includes: By performing polar coordinate integration on the diffraction rings recorded at each sampling point in the diffraction information set, a diffraction pattern showing the distribution of diffraction intensity as a function of diffraction angle is obtained. The diffraction peaks in the diffraction pattern are fitted to obtain the diffraction angle values. The diffraction angle value is compared with the standard diffraction angle of the stress-free standard sample, and the lattice strain of the crystal plane corresponding to the sampling point is calculated according to Bragg's law. Based on the equations of elasticity, the lattice strain in at least six independent directions is converted into stress tensor components at the sampling point; Spatial interpolation is performed on the stress tensor of all sampling points to reconstruct the three-dimensional residual stress distribution inside the sample under test.

8. An apparatus for measuring depth-resolved residual stress within a material, characterized in that, include: A radiation source is used to emit a beam of radiation and direct it onto the sample to be tested, thereby generating a diffraction signal. The sample stage is connected to a six-axis displacement system for carrying and moving the sample to be tested; A dual-slit assembly is positioned between the sample to be tested and the detector. The dual-slit assembly includes two parallel slit plates. The sampling diffraction beam based on a specific depth layer inside the sample to be tested is obtained from the diffraction signal through the dual-slit assembly. A detector for receiving the diffraction signal; The control system, connected to the sample stage, the double slit assembly, and the detector, is used to coordinate and control the movement of the sample stage and signal acquisition. The data processing unit is used to obtain residual stress information inside the sample under test based on the diffraction information.

9. The apparatus for measuring depth-resolved residual stress within a material as described in claim 8, characterized in that, The radiation source is a synchrotron radiation source, and its energy can be continuously or incrementally adjusted within a preset range; the detector is an energy-resolution two-dimensional detector.

10. The apparatus for measuring depth-resolved residual stress within a material as described in claim 8, characterized in that, The control system is configured to control the X-ray source to output at least two beams of different energies at the same sampling point and trigger the detector to collect the diffraction signal of the corresponding energy.

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