Method for establishing initial residual stress field of blank based on ultrasonic method

Abstract

The application discloses a method for establishing a blank initial residual stress field based on an ultrasonic method, which comprises the following steps: slicing a measured part according to a detection depth, and then performing grid division on each slice; measuring residual stress values at grid node positions of each slice by using the ultrasonic method; performing interpolation fitting on residual stress values of each node on x-direction grid lines and y-direction grid lines, and calculating residual stresses in x-direction and y-direction on the grid lines; calculating an equivalent residual stress cloud diagram of the whole slice according to stress values on the grid lines; and finally, drawing the equivalent residual stress cloud diagram of each slice, and drawing a three-dimensional equivalent residual stress cloud diagram of the whole part according to different depths. The application can obtain residual stress distribution conditions in the depth gradient direction of the measured part, and provides data support for studying the influence mechanism of residual stress on machining deformation.

Description

Technical Field

[0001] This invention relates to the field of residual stress field detection and modeling technology in machining, specifically to a method for establishing the initial residual stress field of a blank based on ultrasonic method. Background Technology

[0002] The machining of thin-walled parts is characterized by large material removal and low overall stiffness, making them highly susceptible to deformation after machining. This results in high machining costs, long processing times, and significant difficulty, making it challenging to achieve the required machining accuracy. Currently, it is generally believed that the evolution of residual stress within the material is the main factor affecting the overall deformation of the part, and the initial residual stress field state of the blank plays a crucial role in the evolution of the residual stress field during machining. Therefore, to effectively predict and control the machining deformation of thin-walled parts, it is necessary to obtain the initial residual stress field distribution state of the part, establish a three-dimensional residual stress field distribution model, and based on this, study methods for predicting and controlling machining deformation.

[0003] Currently, there are two widely used methods for initial residual stress field modeling. The first method uses the blind hole method or X-ray diffraction to detect the stress value at a point on the blank part, then removes the surface of the blank part, and measures the residual stress value at a point on the new surface. This process is repeated to obtain the residual stress value at a point at different depth gradients, and then a two-dimensional curve showing the change of residual stress value with increasing depth is plotted. The second method uses ultrasonic waves to obtain residual stress values ​​at different depths by adjusting the ultrasonic frequency, and then also plots a two-dimensional curve showing the change of residual stress value with increasing depth. The first method requires damaging the blank material to obtain data, resulting in a long testing time and a cumbersome process. The second method is non-destructive testing and can obtain residual stress values ​​at different depths. However, both of these modeling methods equate the detected residual stress value to the residual stress value of the entire plane, and characterize the residual stress field by plotting a two-dimensional curve. This residual stress field model has serious limitations and is difficult to express the overall three-dimensional residual stress field distribution of the tested object.

[0004] The invention disclosed in CN112307574B presents a method for quantifying stress concentration areas in pressure-bearing pipe fittings. It transforms the stress results from finite element analysis (FEM) calculations into three-dimensional images using appropriate image processing software. Image processing methods are then used to extract the stress concentration feature areas of the fittings, providing a more visual and concrete representation compared to traditional stress analysis. Furthermore, mathematical methods are used to quantify these feature areas, accurately obtaining their location, size, and stress distribution. By extracting and quantifying these stress feature areas, the invention can precisely analyze their location, size, and stress distribution. This provides guidance and reference for the inspection range and lifespan assessment of pressure-bearing pipe fittings. However, the technical problem this invention aims to solve is the inadequacy of existing methods for analyzing stress concentration in pressure-bearing pipe fittings using FEM calculations. It does not address the overall construction of the initial residual stress field of the blank. Additionally, the invention requires the construction of a finite element model, which is a significant workload for blanks with varied or irregular shapes.

[0005] Therefore, it is particularly important for this invention to study a three-dimensional initial residual stress field modeling method based on ultrasonic methods. Summary of the Invention

[0006] This invention addresses the problem that existing residual stress field models are insufficient to characterize the overall three-dimensional residual stress field state of a part. It provides a method for establishing the initial residual stress field of a blank based on ultrasonic testing. The method involves determining the residual stress detection locations by slicing and meshing the object under test. Ultrasonic testing is used to obtain the stress values ​​in the x and y directions along the transverse and longitudinal directions of the mesh nodes on a slice plane. These values ​​are then interpolated. The equivalent stress values ​​are calculated using the von Mises stress calculation formula. A script written in Python is then used to plot the stress distribution cloud map of the interpolated plane based on the equivalent stress at the interpolation points. Finally, the stress values ​​and their distribution cloud maps on each slice plane are obtained through this method, thereby establishing an overall three-dimensional residual stress field distribution model for the blank part.

[0007] To achieve the above-mentioned technical objectives, the technical solution adopted by the present invention is as follows:

[0008] A method for establishing the initial residual stress field of a blank based on ultrasonic method, the process of establishing the initial residual stress field of a blank based on ultrasonic method includes the following steps:

[0009] Step 1: Slice the workpiece to be tested along the depth direction using the ultrasonic detection depth as a reference, and divide the surface of the sliced ​​workpiece into a grid.

[0010] Step 2: Place the wedge and ultrasonic probe on the surface of the sliced ​​workpiece, and use the ultrasonic method to obtain the residual stress values ​​in the x and y directions at the mesh intersection nodes;

[0011] Step 3: Interpolate the residual stress values ​​of the nodes on the horizontal and vertical grid lines respectively, and fit the points generated after interpolation to obtain the residual stress distribution on the grid lines;

[0012] Step 4: After calculating the stress values ​​in the x and y directions on the horizontal and vertical grid lines to obtain the Mies stress values, draw the residual stress field distribution cloud map of the current sheet body;

[0013] Step 5: Repeat steps 2 to 4 above to draw the residual stress field distribution cloud map of each sheet, and finally obtain the three-dimensional residual stress field of the entire workpiece under test.

[0014] Step 1 further includes:

[0015] Set the Z-axis as the depth direction of the workpiece being measured, and establish a spatial coordinate system for the workpiece; move along the Z-axis with numerical values ​​Z... d To establish a plane for the interval, the workpiece to be measured is cut into n slices S. i , i=1,2,…,n,Z d The value is obtained from the ultrasonic frequency, and the calculation formula is as follows:

[0016] Z d = α s ×f -0.96

[0017] Where, α s f is the penetration depth correction factor; f is the center frequency of the ultrasonic probe;

[0018] Using the minimum propagation path value of the ultrasonic wave as the grid size, on sheet S... i Divide the grid into sections, with the grid lines parallel to the x-axis and y-axis, respectively.

[0019] In step 2, the geometry of the wedge is related to the material of the object being measured and the material of the wedge. The angle θ of the wedge's inclined plane is calculated using the following formula. m :

[0020] θ m = sin -1 (V) m / V w )

[0021] Among them, V m V is the speed at which ultrasound propagates in the wedge. w The speed at which ultrasound waves propagate in the object being measured.

[0022] Step 2 further includes:

[0023] An ultrasonic probe is positioned on both sides of the grid node along the x-direction, and the measured residual stress result is equivalent to the residual stress value Rs in the x-direction at the node. x Rotate the ultrasonic probe 90° to measure the residual stress value Rs in the y-direction of the grid nodes. y Obtain the slice S i Rs of each node x and Rs y .

[0024] Step 3 further includes:

[0025] Using cubic spline curves to measure Rs of nodes on all grid lines parallel to the x-axis x and Rs y Perform interpolation, and then calculate Rs for nodes on all grid lines parallel to the y-axis. x and Rs y Perform interpolation; for all Rs on the grid lines in the x and y directions x Values ​​are saved to matrix M x Rs on all grid lines in the x and y directions y Values ​​are saved to matrix M y .

[0026] Step 4 further includes:

[0027] Write a Python script to calculate M according to the following formula. x and M y Calculations are performed to obtain the Mises stress σ at each node. mises and σ of all nodes mises Data saved to matrix M mises The calculation formula is as follows:

[0028]

[0029] The obtained M mises The matrix data is plotted as a contour map with color gradient fill, representing the current sheet S. i The residual stress field distribution cloud map.

[0030] Step 5 further includes:

[0031] After drawing the residual stress field contour maps of all sheet bodies, the residual stress field contour maps of all sheet bodies are plotted using Z-axis methods. d The residual stress field of the measured object is plotted at intervals on a three-dimensional coordinate axis to obtain a three-dimensional residual stress field characterization.

[0032] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0033] Compared with existing initial residual stress models for blanks, the method for establishing the initial residual stress field of a blank based on ultrasonic methods in this invention considers the distribution of residual stress at various points on a plane with different depth gradients. By slicing the object under test and dividing it into meshes to determine the detection positions, and after obtaining the stress at each node on the surface of each slice, a stress distribution cloud map of each slice's plane is drawn, ultimately obtaining a three-dimensional residual stress field distribution model of the object under test. This invention provides a modeling method for the residual stress field of thin-walled parts, providing a theoretical basis and technical support for obtaining accurate three-dimensional residual stress field distribution of blank parts and effectively predicting and controlling machining deformation. Attached Figure Description

[0034] Figure 1 This is a flowchart of the method for establishing the initial residual stress field of a blank based on the ultrasonic method of the present invention;

[0035] Figure 2 This is a schematic diagram of the slice and mesh division of the measured physics in an embodiment of the present invention;

[0036] Figure 3 This is a schematic diagram of an ultrasonic residual stress measurement system.

[0037] Figure 4 This is a schematic diagram of residual stress measurement at the nodes of the first layer sheet.

[0038] Figure 5 A schematic diagram of the residual stress interpolation curves in the x and y directions on the first layer of the sheet;

[0039] Figure 6 The stress contour diagrams for the first layer sheet are shown in the x and y directions and the Mises stress contour diagram.

[0040] Figure 7 A three-dimensional schematic diagram of the three-prestressed field is drawn from the Mies stress cloud diagram of each sheet. Detailed Implementation

[0041] The embodiments of the present invention will be described in further detail below with reference to the accompanying drawings.

[0042] See Figure 1 The present invention provides a method for establishing the initial residual stress field of a blank based on ultrasonic method, comprising the following steps:

[0043] Step 1: Construct an ultrasonic testing device for residual stress. The ultrasonic testing device for residual stress includes: an ultrasonic probe, an ultrasonic plate, a wedge, and cables.

[0044] Step 2: Slice the object to be tested along the depth direction using the ultrasonic detection depth as a reference;

[0045] Step 3: Divide the surface of the sliced ​​object into a mesh, and use the ultrasonic method to obtain the residual stress values ​​in the x and y directions at the mesh intersection nodes;

[0046] Step 4: Interpolate the residual stress values ​​of the nodes on the horizontal and vertical grid lines respectively, and fit the points generated after interpolation to obtain the residual stress distribution on the grid lines;

[0047] Step 5: After calculating the stress values ​​in the x and y directions on the horizontal and vertical grid lines to obtain the Mies stress values, draw the residual stress field distribution cloud map of the current sheet body;

[0048] Step 6: Repeat steps 3-5 above to draw the residual stress field distribution cloud map of each sheet, and finally obtain the three-dimensional residual stress field of the entire object under test.

[0049] Figure 2 This is a schematic diagram of the slice and mesh generation of the physical object being tested in this embodiment of the invention. In practical applications, since the object has already been sliced, there are no requirements regarding the shape of the blank; theoretically, the method of this invention can be applied to blanks of any shape. The ultrasonic testing equipment in this embodiment is as follows: Figure 3 As shown, it consists of a Mistras ultrasonic board, cables, and an Olympus ultrasonic probe. The procedure for measuring residual stress using the ultrasonic method is as follows: The board emits a pulse voltage, which is transmitted to the ultrasonic probe via the cable. The ultrasonic probe emits ultrasonic waves that enter wedge 1 at the first critical angle. When the ultrasonic wave reaches the interface between wedge 1 and the object being measured, it is refracted. The resulting critically refracted longitudinal wave (LCR wave) propagates parallel to the surface of the object being measured. When the LCR wave reaches wedge 2, it is refracted again, and finally, the ultrasonic signal is received by the receiving probe and transmitted back to the board via the cable. The entire detection process is as follows: Figure 3 As shown.

[0050] In step 1, the wedge material in this embodiment is plexiglass, and the material being tested is titanium alloy (grade: TA15). The propagation speed of ultrasound in the plexiglass is V. m =2700m / s, propagation speed V in titanium alloy w =5900m / s, according to the formula θ m =sin -1 (V) m / V w The first critical incident angle θ is calculated. m It is 26°.

[0051] In step 2, the object being measured is a thin-walled, skinned blank part. The geometric model of the object is sliced ​​at intervals of x mm, where x is determined according to formula Z. d = α s ×f -0.96The ultrasonic detection depth gradient was calculated. The α value of the titanium alloy was obtained through querying. s =5.598. After calculation at a frequency f=10MHz, the detection depth Z... d =0.5mm; when the frequency f=5MHz, the detection depth Zd=1mm; when the frequency f=2.5MHz, the detection depth Z d =2mm. The blank is oriented in a Z-shape... d Slice at intervals, such as Figure 2 As shown. The surface of the sliced ​​body is divided into a grid with a grid size of 10×10.

[0052] In step 3, the effective area for ultrasonic testing is placed at the grid nodes, and the test results are equivalent to the stress values ​​at the nodes.

[0053] In step 4, a Python script is used to write a program that uses cubic spline curves to measure the Rs of nodes on all grid lines parallel to the x-axis. x and Rs y Perform interpolation, and then calculate Rs for nodes on all grid lines parallel to the y-axis. x and Rs y Perform interpolation. Calculate the Rs values ​​along all grid lines in the x and y directions. x Values ​​are saved to matrix M x Rs on all grid lines in the x and y directions y Values ​​are saved to matrix M y ,like Figure 4 As shown.

[0054] In step 5, write a Python script to calculate M according to the following formula. x and M y Calculations are performed to obtain the Mises stress σ at each node. mises and σ of all nodes mises Data saved to matrix M mises The calculation formula is as follows:

[0055]

[0056] The obtained M mises The matrix data is plotted as a contour map with color gradient fill, representing the current sheet S. i The residual stress field distribution cloud map, the results are as follows Figure 5 As shown.

[0057] In step 6, the residual stress field data of all the obtained sheet bodies are saved to a three-dimensional matrix, and the residual stress field contour maps of all sheet bodies are plotted using Z-axis methods. d The residual stress field of the measured object is plotted at intervals on a three-dimensional coordinate axis, ultimately obtaining a three-dimensional characterization of the residual stress field. Figure 6 As shown. Figure 7 A three-dimensional schematic diagram of the three-prestressed field is drawn from the Mies stress cloud diagram of each sheet.

[0058] Those skilled in the art will understand that embodiments of this application can be provided as methods, systems, or computer program products. Therefore, this application can take the form of a completely hardware embodiment, a completely software embodiment, or an embodiment combining software and hardware aspects. Furthermore, this application can take the form of a computer program product implemented on one or more computer-usable storage media (including but not limited to disk storage, CD-ROM, optical storage, etc.) containing computer-usable program code. The solutions in the embodiments of this application can be implemented in various computer languages, such as the object-oriented programming language Java and the interpreted scripting language JavaScript.

[0059] This application is described with reference to flowchart illustrations and / or block diagrams of methods, apparatus (systems), and computer program products according to embodiments of this application. It will be understood that each block of the flowchart illustrations and / or block diagrams, and combinations of blocks in the flowchart illustrations and / or block diagrams, can be implemented by computer program instructions. These computer program instructions can be provided to a processor of a general-purpose computer, special-purpose computer, embedded processor, or other programmable data processing apparatus to produce a machine, such that the instructions, which execute via the processor of the computer or other programmable data processing apparatus, produce instructions for implementing the flowchart... Figure 1 One or more processes and / or boxes Figure 1 A device that provides the functions specified in one or more boxes.

[0060] These computer program instructions may also be stored in a computer-readable storage medium that can direct a computer or other programmable data processing device to function in a particular manner, such that the instructions stored in the computer-readable storage medium produce an article of manufacture including instruction means, which are implemented in a process Figure 1 One or more processes and / or boxes Figure 1 The function specified in one or more boxes.

[0061] These computer program instructions may also be loaded onto a computer or other programmable data processing equipment, causing a series of operational steps to be executed on the computer or other programmable equipment to produce a computer-implemented process, thereby providing instructions that run on the computer or other programmable equipment for implementing the process. Figure 1 One or more processes and / or boxes Figure 1 The steps of the function specified in one or more boxes.

[0062] Although preferred embodiments of this application have been described, those skilled in the art, upon learning the basic inventive concept, can make other changes and modifications to these embodiments. Therefore, the appended claims are intended to be interpreted as including the preferred embodiments as well as all changes and modifications falling within the scope of this application.

[0063] Obviously, those skilled in the art can make various modifications and variations to this application without departing from the spirit and scope of this application. Therefore, if such modifications and variations fall within the scope of the claims of this application and their equivalents, this application also intends to include such modifications and variations.

Claims

1. A method for establishing the initial residual stress field of a blank based on ultrasonic method, characterized in that, The process of establishing the initial residual stress field of the blank based on the ultrasonic method includes the following steps: Step 1: Slice the workpiece to be tested along the depth direction using the ultrasonic detection depth as a reference, and divide the surface of the sliced ​​workpiece into a grid. Step 2: Place the wedge and ultrasonic probe on the surface of the sliced ​​workpiece, and use the ultrasonic method to obtain the residual stress values ​​Rs in the x and y directions at the mesh intersection nodes. x and Rs y ; Step 3: Interpolate the residual stress values ​​of the nodes on the horizontal and vertical grid lines respectively, and fit the points generated after interpolation to obtain the residual stress distribution on the grid lines; Step 4: After calculating the stress values ​​in the x and y directions on the horizontal and vertical grid lines to obtain the Mies stress values, draw the residual stress field distribution cloud map of the current sheet body; Step 5: Repeat steps 2 to 4 above to draw the residual stress field distribution cloud map of each sheet, and finally obtain the three-dimensional residual stress field of the entire workpiece under test. Step 3 further includes: Using cubic spline curves to measure Rs of nodes on all grid lines parallel to the x-axis x and Rs y Perform interpolation, and then calculate Rs for nodes on all grid lines parallel to the y-axis. x and Rs y Perform interpolation; for all Rs on the grid lines in the x and y directions x Values ​​are saved to matrix M x Rs on all grid lines in the x and y directions y Values ​​are saved to matrix M y ; Step 4 further includes: Write a Python script to calculate M according to the following formula. x and M y Calculations are performed to obtain the Mises stress σ at each node. mises and σ of all nodes mises Data saved to matrix M mises The calculation formula is as follows: ； The obtained M mises The matrix data is plotted as a contour map with color gradient fill, representing the current sheet S. i The residual stress field distribution cloud map.

2. The method for establishing the initial residual stress field of a blank based on ultrasonic method according to claim 1, characterized in that, Step 1 further includes: Set the Z-axis as the depth direction of the workpiece being measured, and establish a spatial coordinate system for the workpiece; move along the Z-axis with numerical values ​​Z... d To establish a plane for the interval, the workpiece to be measured is cut into n slices S. i , i=1,2,…,n,Z d The formula is as follows: It is calculated using the ultrasonic frequency and penetration depth correction factor. WITH d = α s ×f -0.96 ; Where, α s f is the penetration depth correction factor; f is the center frequency of the ultrasonic probe; Using the minimum propagation path value of the ultrasonic wave as the grid size, on sheet S... i Divide the grid into sections, with the grid lines parallel to the x-axis and y-axis, respectively.

3. The method for establishing the initial residual stress field of a blank based on ultrasonic method according to claim 1, characterized in that, In step 2, the geometry of the wedge is related to the material of the object being measured and the material of the wedge. The angle θ of the wedge's inclined plane is calculated using the following formula. m : θ m = sin -1 (V) m / V w ); Among them, V m V is the speed at which ultrasound propagates in the wedge. w The speed at which ultrasound waves propagate in the object being measured.

4. The method for establishing the initial residual stress field of a blank based on ultrasonic method according to claim 1, characterized in that, Step 2 further includes: An ultrasonic probe is positioned on both sides of the grid node along the x-direction, and the measured residual stress result is equivalent to the residual stress value Rs in the x-direction at the node. x Rotate the ultrasonic probe 90° to measure the residual stress value Rs in the y-direction of the grid nodes. y Obtain the slice S i Rs of each node x and Rs y .

5. The method for establishing the initial residual stress field of a blank based on ultrasonic method according to claim 2, characterized in that, Step 5 further includes: After drawing the residual stress field contour maps of all sheet bodies, the residual stress field contour maps of all sheet bodies are plotted using Z-axis methods. d The residual stress field of the measured object is plotted at intervals on a three-dimensional coordinate axis to obtain a three-dimensional residual stress field characterization.

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