Visual measurement visualization method for sheet metal part strain

Abstract

The invention relates to the technical field of data visualization based on visual measurement, in particular to a visual measurement visualization method for sheet metal part strain. Visualization of visual measurement strain of the sheet metal part is realized by adopting a VTK-based visualization technology, and the method comprises the following steps: firstly, obtaining full-field strain data of the sheet metal part by adopting a full-field strain non-contact measurement system, and storing the full-field strain data as a JSON format file; secondly, the full-field strain data is visualized based on the JSON format file, a three-dimensional visualization platform is built, and a full-field cloud picture of the sheet metal part is generated; and finally, according to the three-dimensional visualization platform and the full-field cloud picture, establishing an interaction function module of the visualization platform, and realizing visual multi-dimensional analysis of the strain law of the sheet metal part. The invention provides a data display mode with interactivity, which is helpful for users to more accurately analyze and observe the distribution and variation trend of the strain.

Description

Technical Field

[0001] The present invention relates to the technical field of data visualization based on visual measurement, and in particular to a visual measurement visualization method for sheet metal part strain. Background Art

[0002] Strain is a key structural parameter when evaluating the mechanical properties of materials. Accurate strain measurement is crucial for sheet metal forming performance analysis, because the accuracy of strain measurement directly affects the validity of the analysis results. Although strain measurement technology has made significant progress, it still faces many challenges in practical applications.

[0003] With the development of industrial cameras and image processing technology, non-contact strain measurement has gradually matured, providing a solid foundation for vision-based strain measurement. Modern non-contact measurement technology can obtain more comprehensive strain data on the surface and inside of the structure through computer vision systems, combined with visual sensors, image acquisition systems and image processing systems. This method overcomes the limitations of traditional contact measurement and has the advantages of non-contact, fast speed and anti-interference. However, in scientific research and engineering applications, these measurement technologies will generate a large amount of complex data, which are usually abstract, discrete and complex, and difficult to understand and process directly.

[0004] When processing and visualizing massive strain data, existing visualization technologies lack specificity, which leads to challenges for users in analyzing and understanding the data. Especially in the strain measurement of complex sheet metal parts and other structural parts, existing methods may not be able to effectively display the spatial distribution and change trend of strain data. Therefore, how to improve the accuracy and interactivity of data visualization, especially in the three-dimensional spatial analysis and dynamic change display of strain data, is still an important issue facing current technology.

[0005] In order to overcome these challenges, it is necessary to use appropriate measurement techniques and improve existing data visualization methods to improve the accuracy of strain measurement and the efficiency of data analysis. At the same time, the friendliness and ease of use of the user interface must also be considered so that non-professional users can also effectively complete interactive operations. Summary of the invention

[0006] The purpose of the present invention is to study the visualization technology in the field of scientific computing visualization. Based on the VTK platform, strain data is obtained by computer vision measurement methods. Then, combined with the surface shape of the sheet metal and the changes in the internal and external structures, the strain data is visualized to grasp the full-field distribution of the strain in multiple dimensions, and provide direct guidance for engineering and technical personnel to analyze the dynamic process of object force distribution and strain change development. The goal is to achieve three-dimensional visualization of strain data and full-field cloud map display with color coloring, so that engineering and technical personnel can grasp the overall and local force, deformation and strain distribution of the measured object through visual data presentation, which can better improve work efficiency and accuracy, and also help promote the development and innovation of the field of scientific computing visualization.

[0007] The present invention provides a visual measurement visualization method for sheet metal part strain, which specifically comprises the following steps:

[0008] Step 1: Using a full-field strain non-contact measurement system to obtain full-field strain data of the sheet metal part, and saving the full-field strain data as a JSON format file;

[0009] Step 2: Visualize the full-field strain data based on the JSON format file, build a three-dimensional visualization platform, and generate a full-field cloud map of the sheet metal part;

[0010] Step 3: Establish an interactive function module of the visualization platform based on the three-dimensional visualization platform and the full-field cloud map.

[0011] Furthermore, the full-field strain non-contact measurement system includes a computer installed with full-field strain non-contact measurement software, dual cameras, a light source and a tripod.

[0012] Furthermore, the full-field strain non-contact measurement system is used, and the deformation process of the sheet metal part is continuously photographed using the dual camera to obtain a deformation image sequence, and the deformation image sequence is analyzed to obtain the extreme points of the image correlation function of the reference image and the deformation image, and the parameters of the shape function are obtained, and the matching points are obtained according to the extreme points of the correlation function and the parameters; the sheet metal part is three-dimensionally reconstructed according to the matching points, and the three-dimensional reconstruction adopts triangulation, and the process of obtaining the three-dimensional coordinates is as follows:

[0013] The left side of the dual camera is the left camera, and the right side is the right camera; the optical center of the left camera and the left point P cl The connected ray is aP cl , right camera optical center and right point P cr The connected ray is bR r2l P cr +t r2l ; where a and b represent the parameters of the two rays, Rr2l is the rotation matrix, t r2l is the translation vector; w is the common vertical vector, and the specific calculation formula of the common vertical vector is:

[0014] w=P cl ×R r2l P cr ; (1)

[0015] According to the formula aP cl -bR r2l P cr +cW=t r2l , obtain a, b and c, and obtain the three-dimensional coordinates as:

[0016]

[0017] Wherein, P is a three-dimensional coordinate; the full-field three-dimensional coordinate points of the sheet metal part are generated to obtain the full-field strain distribution information of the sheet metal part.

[0018] Furthermore, based on the full-field strain information of the sheet metal part, the full-field strain distribution data of the sheet metal part is obtained according to the finite strain theory in solid mechanics, and the full-field strain distribution data includes:

[0019] Get the vectors V1, V2, V1' and V'2 as follows:

[0020]

[0021] Among them, (x0, y0, z0), (x1, y1, z1) and (x2, y2, z2) are the coordinates of the triangular mesh before deformation; (x'0, y'0, z'0), (x'1, y'1, z'1) and (x'2, y'2, z'2) are the coordinates of the triangular mesh after deformation; after the local coordinate system is established with (x0, y0) and (x'0, y'0) as the origin, the formula for calculating the triangular mesh coordinates in the local coordinate system is:

[0022]

[0023] Among them, (X1, Y1), (X2, Y2), (X'1, Y1') and (X'2, Y'2) are the coordinates of the triangular mesh in the local coordinate system; according to the finite strain theory, we can get:

[0024] C=F T F; (5)

[0025] Where C is the Cauchy-Green tensor; F is the in-plane gradient tensor; the relationship between the Cauchy-Green tensor C and the Green-Lagrange strain is:

[0026] C=I+2E; (6)

[0027] Where I is the unit matrix; E is the Green-Lagrange strain, and the components of the Green-Lagrange strain E are:

[0028]

[0029] Among them, C 11 is the tensile stress tensor along the X-axis; C 12 is the shear stress tensor along the Y direction in the X plane; C 22 is the tensile stress tensor along the Y direction; E 11 is the tensile strain along the X-axis; E 12 is the shear strain along the Y direction in the X plane, and E 12 >0;E 22 is the tensile strain along the Y-axis;

[0030] From the geometric relationship, the specific calculation formula of the horizontal coordinate of the center of the Mohr circle is:

[0031]

[0032] Among them, E average is the abscissa of the center of the Mohr circle; R is the radius of the center of the Mohr circle; the maximum and minimum values ​​of the Green-Lagrange strain are:

[0033]

[0034] Among them, E max is the maximum value of Green-Lagrange strain; E min is the minimum value of Green-Lagrange strain; according to the Cauchy-Green tensor, tensile ratio and true strain, the maximum principal strain and the minimum principal strain are obtained, and the specific formula is expressed as:

[0035]

[0036] Among them, l is the length after deformation; l0 is the original length; ε major is the maximum principal strain; ε minor is the minimum principal strain; according to the Mohr circle, the azimuth of the principal strain is:

[0037] θ=tan -1 (2E 12 / (E 11 -E 22 )) / 2; (11)

[0038] where θ is the azimuth of the principal strain.

[0039] Furthermore, the maximum principal strain, the minimum principal strain, the azimuth of the principal strain, the three-dimensional coordinates of the triangular mesh nodes and the topological relationship between the triangular mesh nodes in the measured image of the sheet metal part are written into the file management module of the full-field non-contact measurement system, and three data objects are designed and saved as JSON format files, specifically:

[0040] (1) storing the three-dimensional coordinates of the triangular mesh nodes on the image of the sheet metal object to be measured as the JSON format file through the 3DReconstruction object; wherein the 3DReconstruction object includes a series of arrays, the first row represents the number of the triangular mesh node, and the second, third, and fourth rows represent the X, Y, and Z three-dimensional coordinates of the triangular mesh node respectively;

[0041] (2) storing the topological relationship between the triangular mesh nodes in the image of the sheet metal part under test as the JSON format file through the GridTriangleID object; wherein the GridTriangleID object is composed of a plurality of arrays, and the three numbers in each array correspond to the node numbers in the 3DReconstruction object, and are used to represent the triangular mesh formed by these nodes;

[0042] (3) The strain values ​​of the triangular mesh nodes in the sheet metal object image are stored as the JSON format file through the Strain object; wherein the Strain object is composed of a plurality of arrays, and each array group records the triangular mesh node number, the maximum principal strain and the minimum principal strain of the node in the deformation stage.

[0043] Furthermore, the full-field strain data is visualized based on the JSON format file, a three-dimensional visualization platform is built, and a full-field cloud map of the sheet metal part is generated; the acquisition process of the full-field cloud map includes:

[0044] Firstly, a three-dimensional visualization platform is constructed based on the VTK function library, wherein the operating system and the VTK rendering engine are connected through the vtkRenderWindow class function in the VTK function library, and the scene objects, including object entities, lights and cameras, are rendered using the vtkRenderer class function in the VTK function library. Then, the user input and interactive response are processed through the vtkRenderWindowInteractor class function. Then, the three-dimensional coordinates of the grid points in all deformation stages, the strain data and the topological relationship of the triangular grid points are read from the JSON format file, a color bar is created according to the maximum and minimum values ​​in the strain data, and a visualization image of the strain distribution is generated. Finally, the three-dimensional coordinates of the grid points of the sheet metal part, the strain data and the topological relationship of the triangular grid points are combined with the renderer and the rendering window to obtain the full-field cloud map of the sheet metal part.

[0045] Furthermore, based on the full-field cloud map, an interactive function of the display component is established, specifically:

[0046] (1) First, define the mapping relationship between color and strain data values, using the vtkLookupTable class function in the VTK function library; then use the vtkScalarBarActor class function in the VTK function library to create a scalar bar, and configure the color, quantity and text string of its label and title, and then associate it with the vtkLookupTable class function in the VTK function library; then add the scalar bar to the rendering window, and position and orient it, and configure the interaction component between the vtkScalarBarActor class function in the VTK function library and the rendering window; finally, the scalar bar display of the sheet metal part is obtained in the visualization window;

[0047] (2) First, draw a balloon pop-up window instance through the vtkBalloonRepresentation class function in the VTK function library, and use the member function to set the pop-up window to the right of the cursor position; then specify the balloon pop-up window instance by defining the vtkBalloonWidget class function object in the VTK function library, and use the member function to set the interactive object entity of the pop-up window and the text content displayed; finally, when the cursor stays on the 3D reconstructed entity of the sheet metal part for more than the set time, the balloon pop-up window component is displayed.

[0048] Furthermore, based on the full-field cloud map, the interactive functions of the functional components are established, specifically:

[0049] (1) First, create a finite plane that can be oriented and positioned, generate an implicit function, obtain plane information through the GetPlane member function in the VTK function library, and query polygon output through the GetPolyData member function in the VTK function library; then, use the GetPlane member function to set the size, color and plane line width of the plane vertex, and display the intersection line of the cutting plane and the object entity; finally, obtain the cutting plane component of the sheet metal part, which includes the control handles of the four corner vertices, a normal vector and the cutting plane itself;

[0050] (2) First, the class pointer is used to obtain the mouse click position according to the set picking tolerance, obtain the ID of the current picked unit, and identify it when the mouse hovers over the object entity; then, an object is defined to store the selected unit ID and declare the data type and content to be extracted, and the input data is set. The data set, edge visibility, edge line width and color are set through the member object. In the main function, the static pointer of the class is set to interactive mode, and then associated with the rendering window to complete the unit picking function; then, a double loop is used to traverse the unit vertices, the inner loop traverses the vertices on the unit, and the outer loop obtains the unit where the mouse is clicked, and performs strain interpolation calculation; finally, the strain value of the mouse click position is calculated, and the strain value of the pick point on the sheet metal part is obtained in the output window.

[0051] Compared with the prior art, the present invention has the following beneficial effects:

[0052] 1. This invention provides a more accurate three-dimensional strain data display method through VTK-based visualization technology. It can clearly display the strain distribution and change trend of sheet metal parts, allowing users to understand strain data more intuitively and reduce analysis deviations caused by misunderstanding or improper processing of data.

[0053] 2. The present invention introduces an interactive visualization function, which allows users to dynamically adjust the viewing angle, zoom and rotate the data view in three-dimensional space, so as to conveniently analyze the local characteristics and global trends of strain data. This interactivity greatly improves the efficiency of data analysis, helping users to quickly locate problem areas and make corresponding decisions.

[0054] 3. Aiming at the processing requirements of massive complex strain data, the present invention solves the problems of complex data processing and poor display effect in the prior art through an improved visualization method. It can effectively integrate and display a large amount of discrete strain data, and provide clear strain information through scalar bars, balloon pop-up windows, strain output on cutting lines, strain unit picking, and strain output of picking units, which is particularly suitable for strain measurement and analysis of complex sheet metal parts and structural parts. BRIEF DESCRIPTION OF THE DRAWINGS

[0055] Figure 1 A sheet metal part strain visualization flow chart proposed in an embodiment of the present invention;

[0056] Figure 2 The full-field strain cloud diagram display of the sheet metal part proposed in the embodiment of the present invention;

[0057] Figure 3 This is a diagram showing the effect of implementing the scalar bar proposed in the embodiment of the present invention;

[0058] Figure 4 This is a diagram showing the effect of implementing the balloon pop-up window component proposed in the embodiment of the present invention;

[0059] Figure 5 This is a diagram showing the effect of the cutting plane component proposed in the embodiment of the present invention;

[0060] Figure 6 This is a diagram showing the effect of the cutting line proposed in the embodiment of the present invention;

[0061] Figure 7 This is a diagram showing the effect of implementing the strain output of the strain unit pick-up point proposed in the embodiment of the present invention;

[0062] Figure 8 This is a strain output effect diagram of the cutting line passing through the unit and point proposed in the embodiment of the present application. DETAILED DESCRIPTION

[0063] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0064] The purpose of the present invention is to study the visualization technology direction in the field of scientific computing visualization. Based on the VTK library function, the sheet metal strain data is obtained by a full-field non-contact strain measurement method. After that, the data is visualized in combination with the surface shape of the object and the changes in the internal and external structures, so as to grasp the full-field distribution of the strain in multiple dimensions, and provide direct guidance for engineering and technical personnel to analyze the dynamic process of object force distribution and strain change development. The goal is to achieve three-dimensional visualization of strain data and full-field cloud map display with color coloring, so that engineering and technical personnel can grasp the overall and local force, deformation and strain distribution of the measured object through visual data presentation, which can better improve work efficiency and accuracy, and also help promote the development and innovation of the field of scientific computing visualization. In order to illustrate the feasibility of the present invention, it will be described below from the following examples.

[0065] Example

[0066] In the embodiment of the present application, a visual measurement visualization method for sheet metal strain is used. The specific implementation process is as follows: Figure 1 As shown in the figure, firstly, the full-field strain non-contact measurement system is used to obtain the full-field strain distribution and full-field strain data of the sheet metal; secondly, the full-field strain data is visualized based on the VTK function library, a three-dimensional visualization platform is built, and a full-field cloud map of the sheet metal is generated; finally, based on the three-dimensional visualization platform and the full-field cloud map, an interactive function module of the visualization platform is established to realize an intuitive multi-dimensional analysis of the strain law of the sheet metal. Through this method, the full-field strain distribution of the sheet metal can be intuitively displayed, and through the three-dimensional visualization platform and the interactive function module, a multi-dimensional analysis of the strain law of the sheet metal can be realized, which significantly improves the accuracy and efficiency of strain measurement and analysis.

[0067] Furthermore, the specific implementation process of the embodiment of the present application is as follows:

[0068] The full-field strain non-contact measurement system comprises a computer equipped with full-field strain non-contact measurement software, a dual camera, a light source and a tripod.

[0069] In the embodiment of the present application, there is no need to install any contact sensors on the sheet metal being measured to avoid interference with the measurement results; the strain and displacement of the entire surface of the object can be measured simultaneously to provide comprehensive data; modern full-field measurement systems provide high spatial resolution and measurement accuracy, and can accurately analyze the mechanical properties of sheet metal.

[0070] The full-field strain non-contact measurement system is adopted, and the deformation process of the sheet metal part is continuously photographed using the dual camera to obtain a deformation image sequence, and the deformation image sequence is analyzed to obtain the extreme value points of the image cross-correlation function of the reference image and the deformation image, and the parameters of the shape function are obtained, and the matching points are obtained according to the extreme value points of the correlation function and the parameters; the sheet metal part is three-dimensionally reconstructed according to the matching points, and the three-dimensional reconstruction adopts triangulation method, and the process of obtaining the three-dimensional coordinates is as follows:

[0071] The left side of the dual camera is the left camera, and the right side is the right camera; the optical center of the left camera and the left point P cl The connected ray is aP cl , right camera optical center and right point P cr The connected ray is bR r2l P cr +t r2l ; where a and b represent the parameters of the two rays, R r2l is the rotation matrix, t r2l is the translation vector; w is the common vertical vector, and the specific calculation formula of the common vertical vector is:

[0072] w=P cl ×R r2l P cr ; (12)

[0073] According to the formula aP cl -bR r2l P cr +cW=t r2l , obtain a, b and c, and obtain the three-dimensional coordinates as:

[0074]

[0075] Wherein, P is a three-dimensional coordinate; the full-field three-dimensional coordinate points of the sheet metal part are generated to obtain the full-field strain distribution information of the sheet metal part.

[0076] In the embodiments of the present application, triangulation is based on geometric principles and is easy to implement. Compared with some other three-dimensional reconstruction methods, triangulation does not require a complicated camera calibration process. In addition, the use of multiple perspectives can provide data redundancy, which helps to improve the robustness and accuracy of reconstruction.

[0077] Based on the full-field strain information of the sheet metal part, the full-field strain distribution data of the sheet metal part is obtained according to the finite strain theory in solid mechanics. The full-field strain distribution data includes:

[0078] Get the vectors V1, V2, V1' and V'2 as follows:

[0079]

[0080] Among them, (x0, y0, z0), (x1, y1, z1) and (x2, y2, z2) are the coordinates of the triangular mesh before deformation; (x'0, y'0, z'0), (x'1, y'1, z'1) and (x'2, y'2, z'2) are the coordinates of the triangular mesh after deformation; after the local coordinate system is established with (x0, y0) and (x'0, y'0) as the origin, the formula for calculating the triangular mesh coordinates in the local coordinate system is:

[0081]

[0082] Among them, (X1, Y1), (X2, Y2), (X'1, Y1') and (X'2, Y'2) are the coordinates of the triangular mesh in the local coordinate system; according to the finite strain theory, we can get:

[0083] C=F T F; (16)

[0084] Where C is the Cauchy-Green tensor; F is the in-plane gradient tensor; the relationship between the Cauchy-Green tensor C and the Green-Lagrange strain is:

[0085] C=I+2E; (17)

[0086] Where I is the unit matrix; E is the Green-Lagrange strain, and the components of the Green-Lagrange strain E are:

[0087]

[0088] Among them, C 11 is the tensile stress tensor along the X-axis; C 12 is the shear stress tensor along the Y direction in the X plane; C 22 is the tensile stress tensor along the Y direction; E 11 is the tensile strain along the X-axis; E 12 is the shear strain along the Y direction in the X plane, and E 12 >0;E 22 is the tensile strain along the Y-axis;

[0089] From the geometric relationship, the specific calculation formula of the horizontal coordinate of the center of the Mohr circle is:

[0090]

[0091] Among them, E average is the abscissa of the center of the Mohr circle; R is the radius of the center of the Mohr circle; the maximum and minimum values ​​of the Green-Lagrange strain are:

[0092]

[0093] Among them, E max is the maximum value of Green-Lagrange strain; E min is the minimum value of Green-Lagrange strain; according to the Cauchy-Green tensor, tensile ratio and true strain, the maximum principal strain and the minimum principal strain are obtained, and the specific formula is expressed as:

[0094]

[0095] Among them, l is the length after deformation; l0 is the original length; ε major is the maximum principal strain; ε minor is the minimum principal strain; according to the Mohr circle, the azimuth of the principal strain is:

[0096] θ=tan -1 (2E 12 / (E 11 -E 22 )) / 2; (22)

[0097] where θ is the azimuth of the principal strain.

[0098] In the embodiments of the present application, Lagrangian strain intuitively reflects the physical changes of the material during the deformation process; the initial state of the material is taken into account; Lagrangian strain is a standard widely accepted and used in the engineering field; in addition, Lagrangian strain retains the historical information of the material during the deformation process.

[0099] Furthermore, the maximum principal strain, the minimum principal strain, the azimuth of the principal strain, the three-dimensional coordinates of the triangular mesh nodes and the topological relationship between the triangular mesh nodes in the measured image of the sheet metal part are written into the file management module of the full-field non-contact measurement system, and three data objects are designed and saved as JSON format files, specifically:

[0100] (1) storing the three-dimensional coordinates of the triangular mesh nodes on the image of the sheet metal object to be measured as the JSON format file through the 3DReconstruction object; wherein the 3DReconstruction object includes a series of arrays, the first row represents the number of the triangular mesh node, and the second, third, and fourth rows represent the X, Y, and Z three-dimensional coordinates of the triangular mesh node respectively;

[0101] (2) storing the topological relationship between the triangular mesh nodes in the image of the sheet metal part under test as the JSON format file through the GridTriangleID object; wherein the GridTriangleID object is composed of a plurality of arrays, and the three numbers in each array correspond to the node numbers in the 3DReconstruction object, and are used to represent the triangular mesh formed by these nodes;

[0102] (3) The strain values ​​of the triangular mesh nodes in the sheet metal object image are stored as the JSON format file through the Strain object; wherein the Strain object is composed of multiple arrays, each array recording the triangular mesh node number, the maximum principal strain and the minimum principal strain of the node in the deformation stage, such as Figure 2 shown.

[0103] In the embodiment of the present application, the JSON format file is a lightweight data exchange format. Since it adopts an editing format different from that of the programming language, data storage is more intuitive and convenient, which is beneficial for programmers to read and greatly improves network transmission efficiency; saving in the format facilitates more intuitive and efficient processing and analysis.

[0104] Furthermore, the full-field strain data is visualized based on the JSON format file, a three-dimensional visualization platform is built, and a full-field cloud map of the sheet metal part is generated; the acquisition process of the full-field cloud map includes:

[0105] Firstly, a three-dimensional visualization platform is constructed based on the VTK function library, wherein the operating system and the VTK rendering engine are connected through the vtkRenderWindow class function in the VTK function library, and the scene objects, including object entities, lights and cameras, are rendered using the vtkRenderer class function in the VTK function library. Then, the user input and interactive response are processed through the vtkRenderWindowInteractor class function. Then, the three-dimensional coordinates of the grid points in all deformation stages, the strain data and the topological relationship of the triangular grid points are read from the JSON format file, a color bar is created according to the maximum and minimum values ​​in the strain data, and a visualization image of the strain distribution is generated. Finally, the three-dimensional coordinates of the grid points of the sheet metal part, the strain data and the topological relationship of the triangular grid points are combined with the renderer and the rendering window to obtain the full-field cloud map of the sheet metal part.

[0106] In the embodiment of the present application, a more accurate three-dimensional strain data display method is provided through VTK-based visualization technology. It can clearly display the strain distribution and change trend of sheet metal parts, allowing users to understand strain data more intuitively and reduce analysis deviations caused by misunderstanding or improper processing of data.

[0107] Furthermore, based on the full-field cloud map, an interactive function of the display component is established, specifically:

[0108] (1) First, define the mapping relationship between color and strain data values, using the vtkLookupTable class function in the VTK function library; then use the vtkScalarBarActor class function in the VTK function library to create a scalar bar, and configure the color, quantity, and text string of its label and title, and then associate it with the vtkLookupTable class function in the VTK function library; then add the scalar bar to the rendering window, and position and orient it, and configure the interaction component between the vtkScalarBarActor class function in the VTK function library and the rendering window; finally, the scalar bar display of the sheet metal part is obtained in the visualization window, as shown in FIG. Figure 3 As shown;

[0109] (2) First, draw a balloon pop-up window instance through the vtkBalloonRepresentation class function in the VTK function library, and use the member function to set the pop-up window to the right of the cursor position; then, specify the balloon pop-up window instance by defining the vtkBalloonWidget class function object in the VTK function library, and use the member function to set the interactive object entity of the pop-up window and the text content displayed; finally, when the cursor stays on the 3D reconstructed entity of the sheet metal part for more than the set time, the balloon pop-up window component is displayed, such as Figure 4 shown.

[0110] In the embodiment of the present application, the present invention adopts a balloon pop-up widget, and relevant text pops up when the mouse hovers over the target instance, but is not displayed in other areas. This design not only enhances interactivity, but also provides corresponding annotation text for different target instances. In addition, in order to more intuitively associate color and strain size, the present invention also introduces a scalar bar, which allows users to more clearly understand the distribution and size of strain.

[0111] Furthermore, based on the full-field cloud map, the interactive functions of the functional components are established, specifically:

[0112] (1) First, create a finite plane that can be oriented and positioned, generate an implicit function, obtain plane information through the GetPlane member function in the VTK function library, and query polygon output through the GetPolyData member function in the VTK function library; then, use the GetPlane member function to set the size, color and plane line width of the plane vertex, and display the intersection line of the cutting plane and the object entity; finally, obtain the cutting plane component of the sheet metal part, which includes the control handles of the four corner vertices, a normal vector and the cutting plane itself, as shown in Figure 5 and Figure 6 As shown;

[0113] (2) First, use the class pointer to obtain the mouse click position according to the set picking tolerance, obtain the ID of the current picking unit, and identify it when the mouse hovers over the object entity; then, define the object to store the selected unit ID and declare the data type and content to be extracted, and set the input data. Through the member object, complete the setting of the data set, edge visibility, edge line width and color. In the main function, set the static pointer of the class to interactive mode, and then associate it with the rendering window to complete the unit picking function, such as Figure 7 As shown; then, through a double loop to traverse the unit vertices, the inner loop traverses the vertices on the unit, the outer loop obtains the unit where the mouse is clicked, and performs strain interpolation calculation; finally, the strain value of the mouse click position is calculated, and the strain value of the pick-up point on the sheet metal part is obtained in the output window, as shown Figure 8 shown.

[0114] In the embodiment of the present application, a display function of the intersection line of the cutting plane and the object entity is provided, which enables the user to observe the interactive part of the cutting plane and the sheet metal more intuitively. Through multi-dimensional strain display, in addition to the strain output of the cutting component to the unit and point on the cutting line, the present invention also obtains the strain value of any point on the sheet metal, realizing a more comprehensive and in-depth strain analysis, which helps to more accurately understand the mechanical behavior and performance characteristics of the sheet metal.

[0115] The above is only a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the principle of the present invention. These improvements and modifications should also be regarded as the scope of protection of the present invention.

Claims

1. A visual measurement visualization method for sheet metal strain, characterized in that: include: Step 1: Use a full-field strain non-contact measurement system to obtain full-field strain data of the sheet metal part, and save the full-field strain data into a JSON format file by designing three data objects; Step 2: Visualize the full-field strain data based on the JSON format file, build a three-dimensional visualization platform, and generate a full-field cloud map of the sheet metal part; Step 3: Establish an interactive function module of the visualization platform based on the three-dimensional visualization platform and the full-field cloud map.

2. A visual measurement visualization method for sheet metal strain according to claim 1, characterized in that: The full-field strain non-contact measurement system comprises a computer installed with full-field strain non-contact measurement software, a dual camera, a light source and a tripod.

3. A visual measurement and visualization method for sheet metal strain according to claim 2, characterized in that: The full-field strain non-contact measurement system is adopted, and the deformation process of the sheet metal part is continuously photographed using the dual camera to obtain a deformation image sequence, and the deformation image sequence is analyzed to obtain the extreme value points of the image cross-correlation function of the reference image and the deformation image, and the parameters of the shape function are obtained, and the matching points are obtained according to the extreme value points of the cross-correlation function and the parameters; the sheet metal part is three-dimensionally reconstructed according to the matching points, and the three-dimensional reconstruction adopts triangulation method, and the process of obtaining the three-dimensional coordinates is as follows: The left side of the dual camera is the left camera, and the right side is the right camera; the optical center of the left camera and the left point P cl The connected ray is aP cl , right camera optical center and right point P cr The connected ray is bR r2l P cr +t r2l ; Among them, a and b represent the parameters of the two rays, R r2l is the rotation matrix, t r2l is the translation vector; w is the common vertical vector, and the specific calculation formula of the common vertical vector is: w=P cl ×R r2l P cr ; (1) According to the formula aP cl -bR r2l P cr +cW=t r2l , obtain a, b and c, and obtain the three-dimensional coordinates as: Wherein, P is a three-dimensional coordinate; the full-field three-dimensional coordinate points of the sheet metal part are generated to obtain the full-field strain distribution information of the sheet metal part.

4. A visual measurement and visualization method for sheet metal strain according to claim 3, characterized in that: Based on the full-field strain information of the sheet metal part, the full-field strain distribution data of the sheet metal part is obtained according to the finite strain theory in solid mechanics. The full-field strain distribution data includes: Get the vectors V1, V2, V1' and V2' as follows: Among them, (x0, y0, z0), (x1, y1, z1) and (x2, y2, z2) are the coordinates of the triangular mesh before deformation; (x'0, y'0, z'0), (x1', y1', z1') and (x'2, y'2, z'2) are the coordinates of the triangular mesh after deformation; after the local coordinate system is established with (x0, y0) and (x'0, y'0) as the origin, the formula for calculating the triangular mesh coordinates in the local coordinate system is: Among them, (X1, Y1), (X2, Y2), (X1', Y1') and (X'2, Y2') are the coordinates of the triangular mesh in the local coordinate system; according to the finite strain theory, we can get: C=F T F; (5) Where C is the Cauchy-Green tensor; F is the in-plane gradient tensor; the relationship between the Cauchy-Green tensor C and the Green-Lagrange strain is: C=I+2E; (6) Where I is the unit matrix; E is the Green-Lagrange strain, and the components of the Green-Lagrange strain E are: Among them, C 11 is the tensile stress tensor along the X-axis; C 12 is the shear stress tensor along the Y direction in the X plane; C 22 is the tensile stress tensor along the Y direction; E 11 is the tensile strain along the X-axis; E 12 is the shear strain along the Y direction in the X plane, and E 12 >0;E 22 is the tensile strain along the Y-axis; From the geometric relationship, the specific calculation formula of the horizontal coordinate of the center of the Mohr circle is: Among them, E average is the abscissa of the center of the Mohr circle; R is the radius of the center of the Mohr circle; the maximum and minimum values ​​of the Green-Lagrange strain are: Among them, E max is the maximum value of Green-Lagrange strain; E min is the minimum value of Green-Lagrange strain; according to the Cauchy-Green tensor, tensile ratio and true strain, the maximum principal strain and the minimum principal strain are obtained, and the specific formula is expressed as: Among them, l is the length after deformation; l0 is the original length; ε major is the maximum principal strain; ε minor is the minimum principal strain; according to the Mohr circle, the azimuth of the principal strain is: θ=time -1 (2E 12 / (TEACHER 11 -TEACHER 22 )) / 2; (11) where θ is the azimuth of the principal strain.

5. A visual measurement visualization method for sheet metal strain according to claim 4, characterized in that: The maximum principal strain, the minimum principal strain, the azimuth of the principal strain, the three-dimensional coordinates of the triangular mesh nodes and the topological relationship between the triangular mesh nodes in the measured image of the sheet metal part are written into the file management module of the full-field non-contact measurement system, and three data objects are designed to be saved as JSON format files, specifically: (1) storing the three-dimensional coordinates of the triangular mesh nodes on the image of the sheet metal object to be measured as the JSON format file through the 3DReconstruction object; wherein the 3DReconstruction object includes a series of arrays, the first row represents the number of the triangular mesh node, and the second, third, and fourth rows represent the X, Y, and Z three-dimensional coordinates of the triangular mesh node respectively; (2) storing the topological relationship between the triangular mesh nodes in the image of the sheet metal part under test as the JSON format file through the GridTriangleID object; wherein the GridTriangleID object is composed of a plurality of arrays, and the three numbers in each array correspond to the node numbers in the 3DReconstruction object, and are used to represent the triangular mesh formed by these nodes; (3) The strain values ​​of the triangular mesh nodes in the sheet metal object image are stored as the JSON format file through the Strain object; wherein the Strain object is composed of a plurality of arrays, and each array group records the triangular mesh node number, the maximum principal strain and the minimum principal strain of the node in the deformation stage.

6. The visual measurement and visualization method for sheet metal strain according to claim 1, characterized in that: Visualize the full-field strain data based on the JSON format file, build a three-dimensional visualization platform, and generate a full-field cloud map of the sheet metal part; The process of obtaining the full-field cloud image includes: Firstly, a three-dimensional visualization platform is constructed based on the VTK function library, wherein the operating system and the VTK rendering engine are connected through the vtkRenderWindow class function in the VTK function library, and the scene objects, including object entities, lights and cameras, are rendered using the vtkRenderer class function in the VTK function library. Then, the user input and interactive response are processed through the vtkRenderWindowInteractor class function. Then, the three-dimensional coordinates of the grid points in all deformation stages, the strain data and the topological relationship of the triangular grid points are read from the JSON format file, a color bar is created according to the maximum and minimum values ​​in the strain data, and a visualization image of the strain distribution is generated. Finally, the three-dimensional coordinates of the grid points of the sheet metal part, the strain data and the topological relationship of the triangular grid points are combined with the renderer and the rendering window to obtain the full-field cloud map of the sheet metal part.

7. The visual measurement and visualization method for sheet metal strain according to claim 1, characterized in that: Based on the full-scene cloud map, the interactive functions of the display component are established, specifically: (1) First, define the mapping relationship between color and strain data values, using the vtkLookupTable class function in the VTK function library; then use the vtkScalarBarActor class function in the VTK function library to create a scalar bar, and configure the color, quantity and text string of its label and title, and then associate it with the vtkLookupTable class function in the VTK function library; then add the scalar bar to the rendering window, and position and orient it, and configure the interaction component between the vtkScalarBarActor class function in the VTK function library and the rendering window; finally, the scalar bar display of the sheet metal part is obtained in the visualization window; (2) First, draw a balloon pop-up window instance through the vtkBalloonRepresentation class function in the VTK function library, and use the member function to set the pop-up window to the right of the cursor position; then specify the balloon pop-up window instance by defining the vtkBalloonWidget class function object in the VTK function library, and use the member function to set the interactive object entity of the pop-up window and the text content displayed; finally, when the cursor stays on the 3D reconstructed entity of the sheet metal part for more than the set time, the balloon pop-up window component is displayed.

8. The method for visual measurement and visualization of sheet metal strain according to claim 7, characterized in that: Based on the full-field cloud map, the functional component interaction function is established, specifically: (1) First, create a finite plane that can be oriented and positioned, generate an implicit function, obtain plane information through the GetPlane member function in the VTK function library, and query polygon output through the GetPolyData member function in the VTK function library; then, use the GetPlane member function to set the size, color and plane line width of the plane vertex, and display the intersection line of the cutting plane and the object entity; finally, obtain the cutting plane component of the sheet metal part, which includes the control handles of the four corner vertices, a normal vector and the cutting plane itself; (2) First, the class pointer is used to obtain the mouse click position according to the set picking tolerance, obtain the ID of the current picked unit, and identify it when the mouse hovers over the object entity; then, an object is defined to store the selected unit ID and declare the data type and content to be extracted, and the input data is set. The data set, edge visibility, edge line width and color are set through the member object. In the main function, the static pointer of the class is set to interactive mode, and then associated with the rendering window to complete the unit picking function; then, a double loop is used to traverse the unit vertices, the inner loop traverses the vertices on the unit, and the outer loop obtains the unit where the mouse is clicked, and performs strain interpolation calculation; finally, the strain value of the mouse click position is calculated, and the strain value of the pick point on the sheet metal part is obtained in the output window.

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