Method for measuring residual stress of tc4 titanium alloy linear friction welding joint by contour method

Abstract

The application discloses a profile method for measuring residual stress of a TC4 titanium alloy linear friction welding joint, and specifically implements the following steps: step 1: a TC4 titanium alloy welding sample is prepared by using linear friction welding, and welding process parameters are determined; step 2: the welding sample is cut by using a slow wire cutting method; step 3: high-precision three-coordinate measuring instruments are used to obtain profile coordinate data of a cutting surface; step 4: original data are sequentially processed by using Matlab; step 5: a finite element model is established in Abaqus, and node coordinates are extracted in batches by using a Python script; step 6: processed measurement profile data are matched with finite element node coordinates; and step 7: a Z-direction deformation load is automatically applied to the finite element model by using a Python script, constraints are applied, and calculation is submitted, and residual stress is solved by inversion. By means of partition variable step length measurement, standardized data processing and full automation stress inversion, the application significantly improves measurement precision and stability.

Description

Technical Field

[0001] This invention belongs to the technical field of welding residual stress measurement methods, specifically relating to a contour method for measuring residual stress in TC4 titanium alloy linear friction welded joints. Background Technology

[0002] TC4 titanium alloy possesses advantages such as high specific strength, excellent corrosion resistance, and stable high-temperature mechanical properties, making it widely used in aero-engines and main load-bearing structural components of airframes. Linear friction welding, as a solid-state joining technology, offers advantages such as high welding precision, dense joint structure, and absence of molten pool defects, making it an ideal method for manufacturing integral TC4 titanium alloy components.

[0003] The evolution of non-uniform temperature and stress fields during welding can lead to stress concentration in the weld and heat-affected zone, resulting in residual stress that directly affects the dimensional stability, fatigue life, and fracture safety of components. Therefore, accurate and high-resolution measurement of post-weld residual stress is crucial.

[0004] Traditional residual stress measurement methods, such as X-ray diffraction, borehole drilling, and neutron diffraction, generally suffer from limitations in measurement depth, insufficient spatial resolution, and high equipment costs. The profilometry method, a full-field, high-precision residual stress testing method based on stress release and finite element inversion, obtains the complete residual stress distribution inside the sample by releasing cross-sectional stress through wire cutting, performing high-precision profilometry, and combining it with finite element inversion for solution.

[0005] Currently, several contour method-related technologies exist for residual stress testing, including: Chinese invention patent CN120525866A, which focuses on workpiece shaping and dual-coordinate system measurement to achieve contour data acquisition, does not cover TC4 titanium alloy linear friction welding heads, nor does it mention partitioned variable step size measurement and automated stress inversion processes. Chinese invention patent CN110487464A improves contour measurement accuracy through multi-coordinate system correction, but has not yet conducted testing on welded joints and has not achieved complete residual stress inversion calculation. Chinese invention patent CN110261022A uses three-dimensional optical scanning and two vertical cuts to obtain multi-directional residual stress; its stress inversion relies on manual input of displacement boundaries and step-by-step superposition calculation. Chinese invention patent CN121199128A, which focuses on additive manufacturing components and heat treatment processes, only provides a general description of the conventional steps of the contour method, without disclosing specific cutting parameters, measurement step sizes, data processing rules, and fully automated stress inversion methods. Summary of the Invention

[0006] The purpose of this invention is to provide a contour method for measuring the residual stress of TC4 titanium alloy linear friction welded joints, which can achieve high-resolution and high-stability measurement of the residual stress of TC4 titanium alloy linear friction welded joints.

[0007] The technical solution adopted in this invention is a contour method for measuring the residual stress of TC4 titanium alloy linear friction welded joints, which is implemented according to the following steps: Step 1: Prepare TC4 titanium alloy welded samples using linear friction welding and determine the welding process parameters; Step 2: Cut the welding sample using a slow wire cutting method; Step 3: Use a high-precision coordinate measuring machine to obtain the contour coordinate data of the cutting surface; Step 4: Process the raw data sequentially using Matlab; Step 5: Build a finite element model in Abaqus and extract node coordinates in batches using a Python script; Step 6: Match the processed measurement contour data with the finite element node coordinates; Step 7: Automatically apply Z-direction deformation load to the finite element model using a Python script, apply constraints, submit the calculation, and invert the solution to obtain the residual stress.

[0008] The invention is further characterized by: In step 1, the process parameters for linear friction welding of TC4 titanium alloy are: friction pressure 50 MPa, welding temperature 948~962 ℃, actual shrinkage after upsetting 6.34~7.53 mm, and welding time 3~5 s.

[0009] In step 2, a BA8 slow wire EDM cutting device is used, with an electrode wire diameter of 0.25 mm, a cutting medium of deionized water with a conductivity of approximately 10 µS / cm, a wire feed speed of 8 m / min, and a wire tension of 1.4 kgf.

[0010] In step 3, a high-precision coordinate measuring machine is used to collect coordinate data in the range of ±20 mm from the weld center with a step size of 0.25 mm × 1 mm, and in the remaining area with a step size of 0.5 mm × 1 mm.

[0011] In step 4, data processing includes coordinate system calibration, outlier cleaning, regular mesh generation, and Gaussian smoothing for noise reduction. The criterion for outliers is that the measured data deviates from the mean by more than 15%.

[0012] In step 5, the material properties consistent with TC4 titanium alloy are used in the finite element modeling, and the mesh density is set to match the measurement step size.

[0013] In step 5, the finite element model has dimensions of 100 mm × 9 mm × 25 mm, the material has a Young's modulus of 110 GPa, a Poisson's ratio of 0.34, a mesh seeding size of 0.25 mm in the X direction, and 1 mm in the other directions.

[0014] In step 7, the finite element analysis adopts a constraint-separated loading method: the stress surface of the model is set to be completely fixed, the XY direction displacement of the stress surface is constrained, and only the Z-direction degree of freedom is released; based on the automatically matched node-profile correspondence, the Z-direction deformation load is applied to the whole at once through a Python script to complete the residual stress inversion and obtain the S33 stress distribution.

[0015] The beneficial effects of this invention are as follows: The contour method for measuring residual stress in TC4 titanium alloy linear friction welded joints significantly improves the accuracy of contour measurement, data stability, and reliability of stress inversion by employing partitioned variable step size measurement in the weld area, four-step standardized data processing in Matlab, automatic outlier removal rule of 15%, regular mesh reconstruction and Gaussian smoothing noise reduction, and a constraint separation inversion method that automatically matches nodes and applies Z-direction deformation load at one time through Python script. This greatly reduces manual intervention and achieves high-resolution and high-repeatability characterization of residual stress. Attached Figure Description

[0016] Figure 1 This is a schematic flowchart of the contour method for measuring residual stress in the TC4 titanium alloy linear friction welded joint of the present invention. Figure 2 This is a schematic diagram illustrating the measurement principle of the contour method for measuring residual stress in the TC4 titanium alloy linear friction welded joint of the present invention. Figure 3 This is a schematic diagram of the three-coordinate measurement area and step size division in the contour method for measuring residual stress in the TC4 titanium alloy linear friction welded joint of the present invention. Figure 4 This is the S33 stress cloud diagram obtained in Example 1 of the contour method for measuring residual stress in the TC4 titanium alloy linear friction welded joint of the present invention. Detailed Implementation

[0017] The present invention will now be described in detail with reference to the accompanying drawings and specific embodiments.

[0018] The present invention relates to a contour method for measuring residual stress in TC4 titanium alloy linear friction welded joints, such as... Figure 1-2 As shown, please follow these steps: Step 1: Prepare TC4 titanium alloy welded samples using linear friction welding and determine the welding process parameters; The process parameters for linear friction welding of TC4 titanium alloy are: friction pressure 50 MPa, welding temperature 948~962 ℃, actual shrinkage after upsetting 6.34~7.53 mm, and welding time 3~5 s; Step 2: Cut the welded sample using a slow wire cutting method to release residual stress in the cross-section; The BA8 slow wire EDM cutting equipment was used, with an electrode wire diameter of 0.25 mm, a cutting medium of deionized water with a conductivity of approximately 10 µS / cm, a wire feed speed of 8 m / min, and a wire tension of 1.4 kgf. Step 3: Use a high-precision coordinate measuring machine to obtain the contour coordinate data of the cutting surface; A high-precision coordinate measuring machine was used to collect coordinate data in the range of ±20 mm from the weld center with a step size of 0.25 mm × 1 mm, and in the remaining area with a step size of 0.5 mm × 1 mm. Step 4: Process the raw data sequentially using Matlab; Data processing includes coordinate system calibration, outlier cleaning, regular mesh generation, and Gaussian smoothing for noise reduction. The criteria for outlier determination is: the deviation of the measured data from the mean exceeds 15%. Step 5: Build a finite element model in Abaqus and extract node coordinates in batches using a Python script; The material properties were consistent with those of TC4 titanium alloy when using finite element modeling, and the mesh density was set to match the measurement step size. The finite element model has dimensions of 100 mm × 9 mm × 25 mm, a Young's modulus of 110 GPa, a Poisson's ratio of 0.34, a mesh seeding size of 0.25 mm in the X direction, and 1 mm in the other directions. Step 6: Match the processed measurement contour data with the finite element node coordinates to obtain the node ID and Z-direction deformation; Step 7: Automatically apply Z-axis deformation load to the finite element model using a Python script, apply constraints, submit the calculation, and invert the solution to obtain the residual stress; The finite element analysis adopts a constraint-separated loading method: the stress surface of the model is set to be completely fixed, the XY direction displacement of the stress surface is constrained, and only the Z-direction degree of freedom is released; based on the automatically matched node-profile correspondence, the Z-direction deformation load is applied to the whole at once through a Python script to complete the residual stress inversion and obtain the S33 stress distribution.

[0019] Example 1 The contour method for measuring residual stress in TC4 titanium alloy linear friction welded joints is implemented according to the following steps: Step 1: Prepare TC4 titanium alloy welded specimens using linear friction welding. The welding parameters are: friction pressure 50 MPa, welding temperature 948 ℃, upsetting shrinkage 6.34 mm, and welding time 3 s. Step 2: Cut using a BA8 slow wire EDM machine with an electrode wire diameter of 0.25 mm, deionized water as the cooling medium, conductivity of 10 µS / cm, wire feed speed of 8 m / min, and wire tension of 1.4 kgf to release residual stress in the cross section.

[0020] Step 3: Use a high-precision coordinate measuring machine to collect contour data. Within ±20 mm of the weld seam, use a step size of 0.25 mm (L) × 1 mm (H), and for the remaining areas, use a step size of 0.5 mm (L) × 1 mm (H) to obtain the original three-dimensional coordinate data. The coordinate measuring area and step size division are as follows: Figure 3 As shown; Step 4: Save the data as a CSV file and perform the following processing in Matlab in sequence: coordinate system calibration to unify the measurement benchmark; outlier cleaning to remove outliers that deviate from the mean by more than 15%; regular grid generation to normalize the discrete points into a uniform grid; Gaussian smoothing to reduce noise and improve the accuracy of contour measurement. Step 5: In Abaqus, establish a finite element model with the geometric center as the origin. The model size is 100 mm (X) × 9 mm (Y) × 25 mm (Z). Assign material properties: Young's modulus 110 GPa, Poisson's ratio 0.34. Create a static general analysis step and enable geometric nonlinearity. Mesh the model: 0.25 mm mesh size in the X direction and 1 mm mesh size in the other directions. Generate an odb file, create a set of nodes for the stress surface, and use a Python script to extract the node coordinates in batches and output them as a CSV file. Step 6: Match the measured contour data with the finite element node coordinates using Matlab, delete redundant data, and retain the node ID and Z-direction deformation data; Step 7: Set model constraints: Apply full constraints to the stress surface, fixing the XY displacement of the stress surface; use a Python script to read the matching file and automatically apply Z-direction deformation loads to the corresponding nodes. Submit the calculation to obtain the S33 stress contour map. The results are as follows: Figure 4 As shown.

[0021] Example 2 The contour method for measuring residual stress in TC4 titanium alloy linear friction welded joints is implemented according to the following steps: Step 1: Prepare TC4 titanium alloy welded specimens using linear friction welding. The welding parameters are: friction pressure 50 MPa, welding temperature 962 ℃, upsetting shrinkage 7.53 mm, and welding time 5 s. Step 2: Cut using a BA8 slow wire EDM machine with an electrode wire diameter of 0.25 mm, deionized water as the cooling medium, conductivity of 10 µS / cm, wire feed speed of 8 m / min, and wire tension of 1.4 kgf to release residual stress in the cross section. Step 3: Use a high-precision coordinate measuring machine to collect contour data. Within ±20 mm of the weld, use a step size of 0.25 mm (L) × 1 mm (H), and in other areas, use a step size of 0.5 mm (L) × 1 mm (H) to obtain the original three-dimensional coordinate data. Step 4: Save the data as a CSV file and perform the following processing in Matlab in sequence: coordinate system calibration to unify the measurement benchmark; outlier cleaning to remove outliers that deviate from the mean by more than 15%; regular grid generation to normalize the discrete points into a uniform grid; Gaussian smoothing to reduce noise and improve the accuracy of contour measurement. Step 5: In Abaqus, establish a finite element model with the geometric center as the origin. The model size is 100 mm (X) × 9 mm (Y) × 25 mm (Z). Assign material properties: Young's modulus 110 GPa, Poisson's ratio 0.34. Create a static general analysis step and enable geometric nonlinearity. Mesh the model: 0.25 mm mesh size in the X direction and 1 mm mesh size in the other directions. Generate an odb file, create a set of nodes for the stress surface, and use a Python script to extract the node coordinates in batches and output them as a CSV file. Step 6: Match the measured contour data with the finite element node coordinates using Matlab, delete redundant data, and retain the node ID and Z-direction deformation data; Step 7: Set model constraints: Apply full constraints to the stress surface, fixing the XY direction displacement of the stress surface; use a Python script to read the matching file and automatically apply Z-direction deformation loads to the corresponding nodes. Submit the calculation to obtain the S33 stress contour map.

[0022] Example 3 The contour method for measuring residual stress in TC4 titanium alloy linear friction welded joints is implemented according to the following steps: Step 1: Prepare TC4 titanium alloy welded specimens using linear friction welding. The welding parameters are: friction pressure 50 MPa, welding temperature 955 ℃, upsetting shrinkage 6.94 mm, and welding time 4 s. Step 2: Cut using a BA8 slow wire EDM machine with an electrode wire diameter of 0.25 mm, deionized water as the cooling medium, conductivity of 10 µS / cm, wire feed speed of 8 m / min, and wire tension of 1.4 kgf to release residual stress in the cross section. Step 3: Use a high-precision coordinate measuring machine to collect contour data. Within ±20 mm of the weld, use a step size of 0.25 mm (L) × 1 mm (H), and in other areas, use a step size of 0.5 mm (L) × 1 mm (H) to obtain the original three-dimensional coordinate data. Step 4: Save the data as a CSV file and perform the following processing in Matlab in sequence: coordinate system calibration to unify the measurement benchmark; outlier cleaning to remove outliers that deviate from the mean by more than 15%; regular grid generation to normalize the discrete points into a uniform grid; Gaussian smoothing to reduce noise and improve the accuracy of contour measurement. Step 5: In Abaqus, establish a finite element model with the geometric center as the origin. The model size is 100 mm (X) × 9 mm (Y) × 25 mm (Z). Assign material properties: Young's modulus 110 GPa, Poisson's ratio 0.34. Create a static general analysis step and enable geometric nonlinearity. Mesh the model: 0.25 mm mesh size in the X direction and 1 mm mesh size in the other directions. Generate an odb file, create a set of nodes for the stress surface, and use a Python script to extract the node coordinates in batches and output them as a CSV file. Step 6: Match the measured contour data with the finite element node coordinates using Matlab, delete redundant data, and retain the node ID and Z-direction deformation data; Step 7: Set model constraints: Apply full constraints to the stress surface, fixing the XY direction displacement of the stress surface; use a Python script to read the matching file and automatically apply Z-direction deformation loads to the corresponding nodes. Submit the calculation to obtain the S33 stress contour map.

[0023] Example 4 The contour method for measuring residual stress in TC4 titanium alloy linear friction welded joints is implemented according to the following steps: Step 1: Prepare TC4 titanium alloy welded specimens using linear friction welding. The welding parameters are: friction pressure 50 MPa, welding temperature 951 ℃, upsetting shrinkage 6.64 mm, and welding time 3.5 s. Step 2: Cut using a BA8 slow wire EDM machine with an electrode wire diameter of 0.25 mm, deionized water as the cooling medium, conductivity of 10 µS / cm, wire feed speed of 8 m / min, and wire tension of 1.4 kgf to release residual stress in the cross section. Step 3: Use a high-precision coordinate measuring machine to collect contour data. Within ±20 mm of the weld, use a step size of 0.25 mm (L) × 1 mm (H), and in other areas, use a step size of 0.5 mm (L) × 1 mm (H) to obtain the original three-dimensional coordinate data. Step 4: Save the data as a CSV file and perform the following processing in Matlab in sequence: coordinate system calibration to unify the measurement benchmark; outlier cleaning to remove outliers that deviate from the mean by more than 15%; regular grid generation to normalize the discrete points into a uniform grid; Gaussian smoothing to reduce noise and improve the accuracy of contour measurement. Step 5: In Abaqus, establish a finite element model with the geometric center as the origin. The model size is 100 mm (X) × 9 mm (Y) × 25 mm (Z). Assign material properties: Young's modulus 110 GPa, Poisson's ratio 0.34. Create a static general analysis step and enable geometric nonlinearity. Mesh the model: 0.25 mm mesh size in the X direction and 1 mm mesh size in the other directions. Generate an odb file, create a set of nodes for the stress surface, and use a Python script to extract the node coordinates in batches and output them as a CSV file. Step 6: Match the measured contour data with the finite element node coordinates using Matlab, delete redundant data, and retain the node ID and Z-direction deformation data; Step 7: Set model constraints: Apply full constraints to the stress surface, fixing the XY direction displacement of the stress surface; use a Python script to read the matching file and automatically apply Z-direction deformation loads to the corresponding nodes. Submit the calculation to obtain the S33 stress contour map.

[0024] Example 5 The contour method for measuring residual stress in TC4 titanium alloy linear friction welded joints is implemented according to the following steps: Step 1: Prepare TC4 titanium alloy welded specimens using linear friction welding. The welding parameters are: friction pressure 50 MPa, welding temperature 954 ℃, upsetting shrinkage 6.82 mm, and welding time 3.8 s. Step 2: Cut using a BA8 slow wire EDM machine with an electrode wire diameter of 0.25 mm, deionized water as the cooling medium, conductivity of 10 µS / cm, wire feed speed of 8 m / min, and wire tension of 1.4 kgf to release residual stress in the cross section. Step 3: Use a high-precision coordinate measuring machine to collect contour data. Within ±20 mm of the weld, use a step size of 0.25 mm (L) × 1 mm (H), and in other areas, use a step size of 0.5 mm (L) × 1 mm (H) to obtain the original three-dimensional coordinate data. Step 4: Save the data as a CSV file and perform the following processing in Matlab in sequence: coordinate system calibration to unify the measurement benchmark; outlier cleaning to remove outliers that deviate from the mean by more than 15%; regular grid generation to normalize the discrete points into a uniform grid; Gaussian smoothing to reduce noise and improve the accuracy of contour measurement. Step 5: In Abaqus, establish a finite element model with the geometric center as the origin. The model size is 100 mm (X) × 9 mm (Y) × 25 mm (Z). Assign material properties: Young's modulus 110 GPa, Poisson's ratio 0.34. Create a static general analysis step and enable geometric nonlinearity. Mesh the model: 0.25 mm mesh size in the X direction and 1 mm mesh size in the other directions. Generate an odb file, create a set of nodes for the stress surface, and use a Python script to extract the node coordinates in batches and output them as a CSV file. Step 6: Match the measured contour data with the finite element node coordinates using Matlab, delete redundant data, and retain the node ID and Z-direction deformation data; Step 7: Set model constraints: Apply full constraints to the stress surfaces, fixing their XY direction displacements. Use a Python script to read the matching file and automatically apply Z-direction deformation loads to the corresponding nodes. Submit the calculation to obtain the S33 stress contour map.

[0025] Example 6 The contour method for measuring residual stress in TC4 titanium alloy linear friction welded joints is implemented according to the following steps: Step 1: Prepare TC4 titanium alloy welded specimens using linear friction welding. The welding parameters are: friction pressure 50 MPa, welding temperature 959 ℃, upsetting shrinkage 7.23 mm, and welding time 4.5 s. Step 2: Cut using a BA8 slow wire EDM machine with an electrode wire diameter of 0.25 mm, deionized water as the cooling medium, conductivity of 10 µS / cm, wire feed speed of 8 m / min, and wire tension of 1.4 kgf to release residual stress in the cross section. Step 3: Use a high-precision coordinate measuring machine to collect contour data. Within ±20 mm of the weld, use a step size of 0.25 mm (L) × 1 mm (H), and in other areas, use a step size of 0.5 mm (L) × 1 mm (H) to obtain the original three-dimensional coordinate data. Step 4: Save the data as a CSV file and perform the following processing in Matlab in sequence: coordinate system calibration to unify the measurement benchmark; outlier cleaning to remove outliers that deviate from the mean by more than 15%; regular grid generation to normalize the discrete points into a uniform grid; Gaussian smoothing to reduce noise and improve the accuracy of contour measurement. Step 5: In Abaqus, establish a finite element model with the geometric center as the origin. The model size is 100 mm (X) × 9 mm (Y) × 25 mm (Z). Assign material properties: Young's modulus 110 GPa, Poisson's ratio 0.34. Create a static general analysis step and enable geometric nonlinearity. Mesh the model: 0.25 mm mesh size in the X direction and 1 mm mesh size in the other directions. Generate an odb file, create a set of nodes for the stress surface, and use a Python script to extract the node coordinates in batches and output them as a CSV file. Step 6: Match the measured contour data with the finite element node coordinates using Matlab, delete redundant data, and retain the node ID and Z-direction deformation data; Step 7: Set model constraints: Apply full constraints to the stress surface, fixing the XY direction displacement of the stress surface; use a Python script to read the matching file and automatically apply Z-direction deformation loads to the corresponding nodes. Submit the calculation to obtain the S33 stress contour map.

[0026] The present invention provides a contour method for measuring residual stress in TC4 titanium alloy linear friction welded joints. By optimizing the entire process strategy of slow wire cutting, high-precision three-coordinate measurement, automated Matlab data processing, finite element modeling and Python script deformation loading, the method achieves high-resolution, high-stability and high-automation measurement of residual stress in TC4 titanium alloy linear friction welded joints, solving the problems of insufficient measurement accuracy, poor stability and excessive manual intervention in the prior art.

Claims

1. A contour method for measuring residual stress in TC4 titanium alloy linear friction welded joints, characterized in that, The specific steps are as follows: Step 1: Prepare TC4 titanium alloy welding samples using linear friction welding and determine welding process parameters; Step 2: Cut the welding sample using a slow wire cutting method; Step 3: Use a high-precision coordinate measuring machine to obtain the contour coordinate data of the cutting surface; Step 4: Process the raw data sequentially using Matlab; Step 5: Build a finite element model in Abaqus and extract node coordinates in batches using a Python script; Step 6: Match the processed measurement contour data with the finite element node coordinates; Step 7: Automatically apply Z-direction deformation load to the finite element model using a Python script, apply constraints, submit the calculation, and invert the solution to obtain the residual stress.

2. The contour method for measuring residual stress in TC4 titanium alloy linear friction welded joints according to claim 1, characterized in that, In step 1, the process parameters for linear friction welding of TC4 titanium alloy are: friction pressure 50 MPa, welding temperature 948~962 ℃, actual shrinkage after upsetting 6.34~7.53 mm, and welding time 3~5 s.

3. The contour method for measuring residual stress in TC4 titanium alloy linear friction welded joints according to claim 1, characterized in that, In step 2, a BA8 slow wire cutting device is used, with an electrode wire diameter of 0.25 mm, a cutting medium of deionized water with a conductivity of approximately 10 µS / cm, a wire feed speed of 8 m / min, and a wire tension of 1.4 kgf.

4. The contour method for measuring residual stress in TC4 titanium alloy linear friction welded joints according to claim 1, characterized in that, In step 3, a high-precision coordinate measuring machine is used to collect coordinate data in the range of ±20 mm from the center of the weld with a step size of 0.25 mm × 1 mm, and in the remaining area with a step size of 0.5 mm × 1 mm.

5. The contour method for measuring residual stress in TC4 titanium alloy linear friction welded joints according to claim 1, characterized in that, In step 4, data processing includes coordinate system calibration, outlier cleaning, regular mesh generation, and Gaussian smoothing for noise reduction. The criterion for outliers is that the measured data deviates from the mean by more than 15%.

6. The contour method for measuring residual stress in TC4 titanium alloy linear friction welded joints according to claim 1, characterized in that, In step 5, the material properties that match those of TC4 titanium alloy are used in the finite element modeling, and the mesh density is set to match the measurement step size.

7. The contour method for measuring residual stress in TC4 titanium alloy linear friction welded joints according to claim 1, characterized in that, In step 5, the finite element model has dimensions of 100 mm × 9 mm × 25 mm, the material has a Young's modulus of 110 GPa, a Poisson's ratio of 0.34, a mesh seeding size of 0.25 mm in the X direction, and 1 mm in the other directions.

8. The contour method for measuring residual stress in TC4 titanium alloy linear friction welded joints according to claim 1, characterized in that, In step 7, the finite element analysis adopts a constraint-separated loading method: the stress surface of the model is set to be completely fixed, the XY direction displacement of the stress surface is constrained, and only the Z-direction degree of freedom is released; based on the automatically matched node-contour correspondence, the Z-direction deformation load is applied to the whole at once through a Python script to complete the residual stress inversion and obtain the S33 stress distribution.

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