A method and system for detecting residual stress of a blind hole based on optical fiber distributed sensing, and a storage medium

Abstract

The application discloses a kind of residual stress detection method, system and storage medium based on optical fiber distributed sensing blind hole method, belong to residual stress test and optical fiber sensing technical field.The method first establishes the strain release coefficient database under different hole depth and radial position by finite element analysis, and constructs the continuous correction factor function model about dimensionless hole depth and radial position for correcting the difference between blind hole and through hole.Implementation, distributed fiber optic sensor is laid on the surface of workpiece and blind hole is drilled, and the release strain data of multiple angles and multiple radial positions before and after drilling are collected.The measured data is substituted into the theoretical strain model corrected by the correction factor, and the residual stress parameters are obtained by least square optimization inversion.The application does not need to rely on sample calibration, and the measurement accuracy and applicability of blind hole method in actual engineering are significantly improved by accurate matching of full-field strain data and theoretical model.

Description

Technical Field

[0001] This invention belongs to the field of residual stress testing and fiber optic sensing technology, specifically relating to a blind-hole method, system, and storage medium for residual stress detection based on fiber optic distributed sensing. Background Technology

[0002] Among existing residual stress detection methods, the blind hole method, as a semi-destructive mechanical release method, is widely used due to its simple equipment and strong on-site operability. Traditional blind hole methods typically require calibration tests on dedicated specimens of the same material and with consistent hole diameters to obtain the stress release characteristics around the hole. However, even after annealing, the calibration specimens may still retain unknown residual stresses, and the elastic properties, microstructure, and processing technology of the specimens are difficult to completely match those of the actual component being tested. Therefore, the release coefficient obtained through this type of calibration inevitably contains deviations, which accumulate and are transmitted during subsequent stress inversion, affecting the reliability of the measurement results.

[0003] Meanwhile, the release coefficients given in the current ASTM standard (ASTM International. Standard Test Method for Determining Residual Stresses by the Hole-Drilling Strain-Gage Method: ASTM E837-25[S]. West Conshohocken, PA: ASTM International, 2025.) are mainly based on specific hole depths and measuring point locations. When the drilling depth changes or the measuring point shifts, the existing tables cannot be directly applied and often need to be recalibrated, which limits the engineering applicability of the blind hole method under complex working conditions (Li Chunhui, Zhang Congyi, Li Rongfeng, et al. Calibration and plastic correction of residual stress and strain release coefficients of 5083 aluminum alloy[J]. Physical and Chemical Testing - Physical Section, 2025, 61(09):21-25.).

[0004] To address the aforementioned shortcomings, this invention constructs a depth-dependent release coefficient correction factor function model based on the evolution law of radial strain release during blind hole drilling. This allows the hole depth ratio and radial position to participate in the characterization as continuous variables, eliminating the need for additional sample calibration. Furthermore, this invention introduces distributed fiber optic strain monitoring technology into the blind hole testing process. Utilizing its high spatial resolution, it acquires full-field strain release information around the hole, achieving precise matching with the constructed correction model. This enables high-precision inversion of residual stress based on full-field strain data, significantly improving the applicability and measurement accuracy of the blind hole method in practical engineering. Summary of the Invention

[0005] The purpose of this invention is to provide a method, system, and storage medium for detecting residual stress in blind holes based on fiber optic distributed sensing. This addresses the problems of traditional blind hole methods that rely on calibrated samples to obtain the release coefficient, but the material properties of the samples are difficult to match with those of actual components; and the fact that ASTM standards only provide some discrete hole depths and measurement point conditions.

[0006] The objective of this invention is achieved through the following technical solution:

[0007] The blind hole method for residual stress detection based on fiber optic distributed sensing includes the following steps:

[0008] Step 1: Construct a blind hole finite element analysis model and calculate different dimensionless hole depths. With dimensionless radial position Establish a discrete release coefficient dataset based on the corresponding stress release coefficients A and B;

[0009] Step 2: Based on the discrete release coefficient dataset, according to the stress release coefficients A and B and the release coefficient corresponding to the through-hole theory. and This yields a discrete dimensionless correction factor that evolves only with the hole depth and radial position. and Dataset;

[0010] Step 3: Fiber optic sensing paths are laid out on the surface of the workpiece to be tested. Blind holes are drilled along the geometric center of the laid out paths, and measured release strain data are collected at multiple angles and radial positions before and after drilling.

[0011] Step 4: Based on the bivariate correction function and the through-hole theoretical solution, construct the blind hole release strain correction model;

[0012] Step 5: The measured release strain data and the theoretical strain data calculated by the blind hole release strain correction model are inverted using the least squares optimization method to obtain the combination of residual stress parameters of the workpiece.

[0013] Furthermore, the dimensionless hole depth in step 1 The ratio of hole depth h to blind hole diameter d; dimensionless radial position. The ratio of the distance r from the measuring point to the center of the blind hole to the radius a of the blind hole is used. Based on Kirsch stress-strain theory, the actual stress release coefficients A and B under the corresponding hole depth conditions are calculated according to the strain distribution in different angular directions obtained by finite element solution. The discrete release coefficient database containing a large number of data samples is obtained by traversing the combinations of hole depth and radial position.

[0014] Furthermore, the dimensionless correction factor in step 2 and for,

[0015]

[0016] Furthermore, the bivariate release coefficient depth correction factor model is as follows:

[0017]

[0018] Among them, the first item The dominant stress relief term; the second term This is a correction term for the bottom-of-hole effect. For convergence rate coefficients, The bottom constraint strength coefficient is denoted by . This is the constraint attenuation coefficient.

[0019] parameter , , The variation law of radial position can be expressed in power function form:

[0020]

[0021]

[0022]

[0023] in, These represent the hole edge effect intensity, The spatial decay exponent, These are the baseline values.

[0024] Furthermore, in step 3, a drill bit equipped with a centering guide device is used to drill a blind hole at the geometric center of the optical fiber petal-shaped laying path. An optical fiber sensing system is used to collect the radial release strain of the laying path before and after drilling, according to different angle directions. and discrete radial position Measurement points were selected to generate measured release strain data consisting of multiple radial release strain curves. Simultaneously, a temperature-compensating fiber unaffected by mechanical stress is arranged in the vicinity of the fiber arrangement to eliminate spurious strain caused by drilling thermal effects.

[0025] Furthermore, the blind hole release strain correction model in step 4 is as follows:

[0026]

[0027] Where E is the workpiece's elastic modulus. and These are the maximum principal stress and the minimum principal stress, respectively. The angle between the radial stress and the principal stress. For radial strain.

[0028] Furthermore, in step 5, the combination of residual stress parameters is calculated using the blind hole release strain correction model. At the measurement point Theoretical release strain at the location The calculation formula is:

[0029] .

[0030] Furthermore, step 5 uses a least-squares optimization algorithm to invert the combination of residual stress parameters by minimizing the following objective function J:

[0031]

[0032] in, Angle quantity, This represents the number of measurement points.

[0033] A computer system includes a memory, a processor, and a computer program stored in the memory, wherein the processor executes the computer program to implement the steps of a blind-hole method for residual stress detection based on fiber optic distributed sensing.

[0034] A computer-readable storage medium having a computer program stored thereon, which, when executed by a processor, implements the steps of a blind-hole method for residual stress detection based on fiber optic distributed sensing.

[0035] The beneficial effects of this invention are as follows:

[0036] 1. Traditional blind hole methods require calibration specimens to obtain the release coefficient. However, even after annealing, the specimens may still retain unknown residual stress, and the material properties and processing conditions are difficult to match with the actual workpiece, resulting in inherent errors in the calibration results that are transmitted to stress inversion. This invention directly constructs a blind hole release coefficient model through theoretical analysis and finite element fitting, eliminating the need for specimen calibration experiments and avoiding the influence of calibration deviations from the outset.

[0037] 2. Current ASTM standards only provide release coefficients corresponding to discrete hole depths and measuring point locations, failing to cover complex situations such as multiple hole depths and multiple measuring distances. This invention proposes a continuous correction factor function based on dimensionless hole depth and radial position, which can generate release coefficients under arbitrary working conditions, achieving an accurate description of the three-dimensional stress release behavior of blind holes.

[0038] 3. This invention introduces distributed optical fiber sensing into the blind hole method test to obtain the continuous strain release curve around the hole. This curve is then fitted with the proposed modified theoretical model across the entire field to directly solve for the residual stress and direction. Compared to traditional data processing methods that rely on three-point or a small number of discrete measurements, this invention utilizes full-field data to improve the accuracy, stability, and noise resistance of the inversion results. Attached Figure Description

[0039] Figure 1 This is a flowchart of the present invention;

[0040] Figure 2 This is a schematic diagram of a distributed optical fiber layout;

[0041] Figure 3 The graph shows the fitting effect of the two-dimensional function curve of the correction factor;

[0042] Figure 4 A comparison diagram of the maximum principal stress obtained by using the present invention and by directly using Kirsch theory at different hole depths;

[0043] Figure 5 A comparison diagram of the minimum principal stress obtained by using the present invention and by directly using Kirsch theory at different hole depths;

[0044] Figure 6 A comparison diagram of the maximum principal stress and x-axis angle obtained by using the present invention and by directly using Kirsch theory for different hole depths. Detailed Implementation

[0045] The present invention will now be further described with reference to the accompanying drawings.

[0046] This invention establishes a continuously corrected factor function model of the blind hole depth release law, directly generating release coefficients applicable to different working conditions. Combined with the full-field strain around the hole acquired by distributed optical fibers, it achieves high-precision inversion of residual stress without material calibration, thereby improving the accuracy, stability, and engineering applicability of residual stress testing. The specific steps are as follows:

[0047] Step 1: Select workpiece material parameters and hole diameter, and construct a three-dimensional blind hole finite element analysis model; define the dimensionless hole depth. Define the dimensionless radial position as the ratio of hole depth h to blind hole diameter d. This is the ratio of the distance *r* from the measuring point to the center of the blind hole to the radius *a* of the blind hole. Multiple combinations of different hole depths and radial positions are set and used as parameterized inputs for the finite element solution.

[0048] Step 2: Based on Kirsch's stress-strain theory in elasticity, and according to the strain distribution in different angular directions obtained from the finite element method, the actual stress release coefficients A and B under the corresponding hole depth conditions are calculated. By traversing all combinations of hole depth and radial position, a discrete release coefficient database containing a large number of data samples is obtained.

[0049] Step 3: Compare the actual release coefficients A and B obtained from the finite element back calculation with the release coefficients under the theoretical state of the through-hole. and Dividing the result yields a dimensionless correction factor that evolves only with the hole depth and radial position. and :

[0050]

[0051] Among them, the corresponding coefficients of the through-hole theoretical solution , It can be represented as

[0052]

[0053] in, Let be the Poisson's ratio of the workpiece, a be the radius of the blind hole, and r be the radius of the measuring point.

[0054] This forms only with and The relevant correction factor discrete sample dataset.

[0055] Step 4: Construct a bivariate release coefficient depth correction factor model that includes a saturation control term and an overshoot correction term. and further parameters , , The variation law of radial position can be expressed in power function form:

[0056]

[0057]

[0058]

[0059] Among them, the first term of the depth correction factor model The dominant stress relief term; the second term This is a correction term for the bottom-of-hole effect. For convergence rate coefficients, The bottom constraint strength coefficient is denoted by . The attenuation coefficient is a constraint. These represent the hole edge effect intensity, The spatial decay exponent, These are the baseline values.

[0060] A nonlinear least squares fitting method is used, incorporating the discrete sample dataset of the correction factor obtained in step 3 into the fitting solution, thereby obtaining a smooth two-dimensional correction function. .

[0061] Step 5: Modify the function and Substituting into the theoretical solution expression for through holes, we obtain the complete corrected expression for radial strain relief in blind holes:

[0062]

[0063] in, and Here, E represents the release coefficient corresponding to the through-hole theoretical solution, and E represents the workpiece's elastic modulus. and These are the maximum principal stress and the minimum principal stress, respectively. The angle between the radial stress and the principal stress. For radial strain.

[0064] Step 6: Drill a blind hole at the geometric center of the fiber optic petal-shaped layout path using a drill bit equipped with a centering guide. Collect radial release strain data of the layout path before and after drilling using a fiber optic sensing system, according to different angle directions. and discrete radial position Measurement points were selected to form an observation dataset consisting of multiple radial release strain curves. Simultaneously, a section of temperature-compensating fiber, unaffected by mechanical stress, is placed in the vicinity of the fiber arrangement to eliminate spurious strain caused by drilling thermal effects.

[0065] Step 7: Assuming arbitrary combinations of residual stresses Under these conditions, the hole depth ratio and radial ratio are substituted into the modified theoretical expression constructed in step 5 to calculate the theoretical release strain value at each measurement point:

[0066]

[0067] The predictive model response values ​​containing multi-directional and multi-distance measurement information are obtained.

[0068] Step 8: Construct a residual function using the difference between the measured strain and the theoretically predicted strain, and form an overdetermined system of equations at all measurement angles and radial sampling points:

[0069]

[0070] And construct the objective function:

[0071]

[0072] in, Angle quantity, This represents the number of measurement points.

[0073] The objective function is solved using the least squares method. Through iterative search, the objective function is minimized, thus obtaining a set of parameters that best matches the measured full curve. , and .

[0074] In this embodiment of the invention, optical frequency domain reflection technology is selected as the distributed optical fiber sensing scheme, with selected parameters of spatial resolution of 1 mm and strain resolution of 1 µε.

[0075] Furthermore, a single-mode optical fiber is arranged as the sensing fiber on the surface of the workpiece to be measured. For example... Figure 2 As shown, the optical fiber forms a radial, petal-shaped path along the workpiece surface, consisting of multiple radial measuring segments and connecting arc-shaped loops. The extensions of the radial measuring segments all point towards the predetermined drill hole center, while the fiber body curves around the center near the center to avoid the drill hole area. Preferably, there are 3 to 6 radial measuring segments, with an angular interval of 45° between adjacent segments, and each radial measuring segment has an effective measuring length of 5 to 15 mm. The optical fiber is bonded to the workpiece surface using epoxy resin adhesive, preferably with an adhesive layer thickness of less than 0.2 mm, to ensure effective strain transfer to the fiber while avoiding the introduction of significant additional stiffness. After the fiber is cured, both ends are connected to the sensing arm interface of the optical frequency domain reflection system.

[0076] Before drilling, the optical frequency domain reflection system was activated to acquire data with a strain resolution better than 1µε and a spatial resolution better than 1mm. The strain distribution data can be obtained by calculation, where The center wavelength of the laser. Where L is the effective refractive index of the optical fiber, and L is the relevant window length. This represents the phase change of the Rayleigh scattering echo.

[0077] Furthermore, blind hole drilling is performed on the workpiece in the central area enclosed by the petal-shaped optical fiber. A miniature electric spindle drilling device is preferably used, with the drill bit diameter set to 1–3 mm as needed, and the drilling axis perpendicular to the workpiece surface. A staged feed method is adopted, with each stage having a hole depth of 0.05–0.2 mm, and the maximum hole depth not exceeding 30% of the workpiece thickness. After drilling is completed and stabilized, the optical frequency domain reflection system is immediately triggered to acquire data according to the same settings, obtaining strain distribution data at that hole depth.

[0078] Furthermore, based on the geometric coordinates of the petal-shaped optical fiber on the workpiece surface, the fiber strain data is mapped to a polar coordinate system with the borehole center as the origin, reconstructing multiple radial release strain curves distributed along different angular directions. , where radial coordinates The value range is set to 2-5 times the radius of the blind hole.

[0079] Furthermore, assuming arbitrary combinations of residual stresses... Under these conditions, the hole depth ratio and radial ratio are substituted into the modified theoretical expression constructed in this invention to calculate the theoretical release strain value at each measurement point:

[0080]

[0081] like Figure 3 The discrete points shown are the original discrete data obtained from finite element inverse calculation, and the surface is the continuous expression obtained by fitting the bivariate correction factor function proposed in this invention.

[0082] function parameter , , The specific expression is:

[0083]

[0084]

[0085]

[0086] function parameter , , The specific expression is:

[0087]

[0088]

[0089]

[0090] Furthermore, a residual function is constructed using the difference between the measured strain and the theoretically predicted strain, forming an overdetermined set of equations at all measurement angles and radial sampling points:

[0091]

[0092] And construct the objective function:

[0093]

[0094] The objective function is solved using the least squares method. Through iterative search, the objective function is minimized, thus obtaining a set of parameters that best matches the measured full curve. , and This allows us to obtain the magnitude and principal direction of the residual principal stress on the surface of the workpiece under test, enabling the inversion of residual stress in blind holes based on fiber optic distributed sensing.

[0095] To verify the accuracy of the blind hole method for residual stress detection based on fiber optic distributed sensing proposed in this invention, this embodiment constructs a test model with a known stress state: a uniaxial tensile load is applied, with a theoretical maximum principal stress of 100 MPa and a minimum principal stress of 0 MPa, and the principal stress direction coincides with the x-axis. The traditional through-hole method theoretical formula and the modified theoretical expression constructed in this invention are used to test different normalized drilling depths. The strain data is used for inversion calculation.

[0096] like Figure 4 As shown, with increasing drilling depth, the maximum principal stress calculated by the traditional through-hole method decreases from... The pressure at 0.1 gradually increased from 19.64 MPa to... The stress at 0.6 is 94.42 MPa. This indicates that the traditional through-hole method suffers from a severe depth effect error when dealing with blind hole problems, significantly underestimating the actual stress in shallow holes, and the calculation results are highly unstable and dependent on the drilling depth. After correction by the depth correction factor of this invention, the calculated maximum principal stress remains highly stable throughout the entire drilling depth range, with minimal fluctuations around 100 MPa. This demonstrates that this invention effectively eliminates the influence of drilling depth on the accuracy of stress inversion and can accurately restore the true stress magnitude.

[0097] like Figure 5 As shown, the theoretical calculation results of the traditional through-hole method fluctuate greatly between 6.29 MPa and 20.28 MPa, and always show a large positive error. After applying the method of the present invention, the calculated value of the minimum principal stress is stable within -4.21 to 0.29 MPa throughout the entire depth range.

[0098] like Figure 6 As shown, the theoretical solution values ​​obtained by the traditional through-hole method and the solution values ​​obtained by this invention show little difference in the calculation of the direction angle, both fluctuating within a small range of -1° to 1°. This indicates that although both methods are relatively accurate in direction determination, this invention, while incorporating stress amplitude correction, still maintains high precision in stress direction determination without introducing additional phase errors.

[0099] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A method for detecting residual stress using a blind aperture method based on fiber optic distributed sensing, characterized in that: Includes the following steps: Step 1: Construct a blind hole finite element analysis model and calculate different dimensionless hole depths. With dimensionless radial position Establish a discrete release coefficient dataset based on the corresponding stress release coefficients A and B; Step 2: Based on the discrete release coefficient dataset, according to the stress release coefficients A and B and the release coefficient corresponding to the through-hole theory. and This yields a discrete dimensionless correction factor that evolves only with the hole depth and radial position. and Dataset; Step 3: Fiber optic sensing paths are laid out on the surface of the workpiece to be tested. Blind holes are drilled along the geometric center of the laid out paths, and measured release strain data are collected at multiple angles and radial positions before and after drilling. Step 4: Based on the bivariate correction function and the through-hole theoretical solution, construct the blind hole release strain correction model; Step 5: The measured release strain data and the theoretical strain data calculated by the blind hole release strain correction model are inverted using the least squares optimization method to obtain the combination of residual stress parameters of the workpiece.

2. The method for detecting residual stress using a blind aperture method based on fiber optic distributed sensing according to claim 1, characterized in that: dimensionless hole depth in step 1 The ratio of hole depth h to blind hole diameter d; dimensionless radial position. The ratio of the distance r from the measuring point to the center of the blind hole to the radius a of the blind hole is used. Based on Kirsch stress-strain theory, the actual stress release coefficients A and B under the corresponding hole depth conditions are calculated according to the strain distribution in different angular directions obtained by finite element solution. The discrete release coefficient database containing a large number of data samples is obtained by traversing the combinations of hole depth and radial position.

3. The method for detecting residual stress using a blind aperture method based on fiber optic distributed sensing according to claim 2, characterized in that: The dimensionless correction factor in step 2 and for, 4. The blind-hole method for residual stress detection based on fiber optic distributed sensing according to claim 3, characterized in that: The bivariate release coefficient depth correction factor model is as follows: Among them, the first item The dominant stress relief term; the second term This is a correction term for the bottom-of-hole effect. For convergence rate coefficients, The bottom constraint strength coefficient is denoted by . This is the constraint attenuation coefficient. parameter , , The variation law of radial position can be expressed in power function form: in, These represent the hole edge effect intensity, The spatial decay exponent, These are the baseline values.

5. The method for detecting residual stress using a blind aperture method based on fiber optic distributed sensing according to claim 1, characterized in that, In step 3, a drill bit equipped with a centering guide device is used to drill a blind hole at the geometric center of the fiber optic petal-shaped layout path. The radial release strain of the layout path before and after drilling is collected using a fiber optic sensing system, according to different angle directions. and discrete radial position Measurement points were selected to generate measured release strain data consisting of multiple radial release strain curves. Simultaneously, a temperature-compensating fiber unaffected by mechanical stress is arranged in the vicinity of the fiber arrangement to eliminate spurious strain caused by drilling thermal effects.

6. The method for detecting residual stress using a blind aperture method based on fiber optic distributed sensing according to claim 1, characterized in that, The blind hole release strain correction model in step 4 is as follows: Where E is the workpiece's elastic modulus. and These are the maximum principal stress and the minimum principal stress, respectively. The angle between the radial stress and the principal stress. For radial strain.

7. A method for detecting residual stress using a blind aperture method based on fiber optic distributed sensing according to claim 1 or 6, characterized in that, In step 5, the combination of residual stress parameters is calculated using the blind hole release strain correction model. At the measurement point Theoretical release strain at the location The calculation formula is: 。 8. The method for detecting residual stress using a blind aperture method based on fiber optic distributed sensing according to claim 7, characterized in that, Step 5 uses a least-squares optimization algorithm to invert the combination of residual stress parameters by minimizing the following objective function J: in, Angle quantity, This represents the number of measurement points.

9. A computer system comprising a memory, a processor, and a computer program stored in the memory, characterized in that: The processor executes the computer program to implement the steps of the method according to any one of claims 1 to 8.

10. A computer-readable storage medium having a computer program stored thereon, characterized in that: When executed by a processor, the computer program implements the steps of the method according to any one of claims 1 to 8.

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