Method for testing the wrinkle resistance of a sheet

Abstract

The embodiment of the application provides a method for testing the wrinkle resistance of a plate, which comprises: preparing a sample corresponding to the plate to be tested according to the shape of a stamping die and the wrinkle mechanism of the plate; simultaneously performing a tensile test and online strain measurement on the sample, and carrying out strain analysis by taking a photograph of the initial state of the sample as an analysis reference surface; and determining the corresponding relationship between the wrinkle height and the strain size and the critical strain value of the wrinkle based on the strain analysis result. The technical scheme of the embodiment of the application can simply and effectively and accurately test the wrinkle height of the plate after being stretched or stamped, so as to realize the evaluation of the wrinkle resistance of the plate.

Description

Technical Field

[0001] This application relates to the field of sheet metal testing technology, and more specifically, to a method for testing the wrinkle resistance of sheet metal. Background Technology

[0002] Stamping wrinkling is a common problem in sheet metal stamping. With the increasing demands for vehicle body design and lightweighting, stamped parts have become more complex, and material thinning makes wrinkling more frequent. Slight wrinkling affects the surface quality and dimensional accuracy of stamped parts, while severe wrinkling can cause the sheet metal to fail to pass through the die-punch gap, leading to cracking and even die wear, reducing its service life. Currently, the most widely used method is the diagonal tensile test (YBT) for square sheets. However, this test method does not consider the contact between the sheet metal and the die during forming, and can only provide a limited understanding of the sheet metal's wrinkle resistance, making it insufficiently accurate. Summary of the Invention

[0003] The embodiments of this application provide a method for testing the wrinkle resistance of sheet metal, which can at least to a certain extent simply, effectively and accurately test the wrinkle height of sheet metal after stretching or stamping, thereby achieving the evaluation of the wrinkle resistance of sheet metal.

[0004] Other features and advantages of this application will become apparent from the following detailed description, or may be learned in part from practice of this application.

[0005] According to one aspect of the embodiments of this application, a method for testing the wrinkle resistance of sheet metal is provided. The method includes: preparing a sample corresponding to the sheet metal to be tested according to the shape of the stamping die and the wrinkling mechanism of the sheet metal; simultaneously performing a tensile test and online strain measurement on the sample, and conducting strain analysis using an initial state photograph of the sample as an analytical reference surface; and determining the correspondence between wrinkling height and strain magnitude and the critical strain value for wrinkling based on the strain analysis results.

[0006] In some embodiments of this application, the step of preparing a sample corresponding to the sheet metal to be tested based on the shape of the stamping die and the wrinkling mechanism of the sheet metal includes: determining the sample shape based on the shape of the stamping die and the wrinkling mechanism of the sheet metal; preparing an initial sample corresponding to the sheet metal to be tested based on the sample shape; and performing single-sided inkjet printing of speckle patterns on the initial sample to prepare a sample corresponding to the sheet metal to be tested.

[0007] In some embodiments of this application, based on the foregoing scheme, the step of single-sided spraying speckle on the initial sample includes: cleaning the surface of the initial sample; spraying a white paint film onto one side of the initial sample; and spraying black speckle onto the initial sample after the paint film dries.

[0008] In some embodiments of this application, the step of simultaneously performing tensile testing and online strain measurement on the specimen, and using an initial state photograph of the specimen as an analytical reference surface for strain analysis, includes: simultaneously performing tensile testing and online strain measurement on the specimen, using an initial state photograph of the specimen as an analytical reference surface for strain analysis, and obtaining a strain contour map of the specimen; creating a cross-sectional line on the strain contour map, obtaining the displacement of each feature point on the cross-sectional line along the upward direction of the main cylinder of the stamping equipment, and generating a cross-sectional line displacement curve; generating a relative displacement curve between each feature point on the cross-sectional line and the analytical reference surface based on the effective displacement of the main cylinder of the stamping equipment and the cross-sectional line displacement curve; and obtaining the strain data corresponding to each feature point on the relative displacement curve on the strain contour map to complete the strain analysis.

[0009] In some embodiments of this application, based on the foregoing scheme, generating the relative displacement curve between each feature point of the cross-section line and the analysis reference surface according to the effective displacement of the main cylinder of the stamping equipment and the cross-section line displacement curve includes: calculating the difference between each feature point of the cross-section line and the effective displacement of the main cylinder according to the effective displacement of the main cylinder of the stamping equipment and the cross-section line displacement curve, and using the difference as the relative displacement value between each feature point of the cross-section line and the analysis reference surface; generating the relative displacement curve between each feature point of the cross-section line and the analysis reference surface according to each relative displacement value.

[0010] In some embodiments of this application, based on the foregoing scheme, determining the correspondence between wrinkling height and strain magnitude based on strain analysis results includes: based on strain analysis results, obtaining feature points whose absolute values ​​of all relative displacement values ​​are greater than or equal to preset displacement values, as wrinkling feature points; obtaining the strain values ​​corresponding to the wrinkling feature points to determine the correspondence between wrinkling height and strain magnitude.

[0011] In some embodiments of this application, based on the aforementioned scheme, determining the critical strain value for wrinkling based on strain analysis results includes: obtaining the relative displacement value corresponding to the peak feature point or trough feature point in the relative displacement curve based on the strain analysis results; if there is a relative displacement value whose absolute value is greater than or equal to a preset displacement value, then the strain value corresponding to the peak feature point or trough feature point is obtained as the critical strain value for wrinkling.

[0012] In some embodiments of this application, the optimized specimen is stretched to different heights using a forming testing machine. An online strain monitoring system is used to measure and analyze the strain stages, obtaining the critical strain at which the material becomes unstable and the wrinkle height after instability and wrinkling, thus enabling the testing of the material's wrinkle resistance. Online strain analysis provides data support for research on stamping wrinkling by obtaining the strain distribution and stress conditions at different forming stages of the material.

[0013] It should be understood that the above general description and the following detailed description are exemplary and explanatory only, and do not limit this application. Attached Figure Description

[0014] The accompanying drawings, which are incorporated in and form part of this specification, illustrate embodiments consistent with this application and, together with the description, serve to explain the principles of this application. It is obvious that the drawings described below are merely some embodiments of this application, and those skilled in the art can obtain other drawings based on these drawings without any inventive effort. In the drawings:

[0015] Figure 1 A flowchart is shown for a method of testing the wrinkle resistance of a sheet material according to an embodiment of this application;

[0016] Figure 2 A simplified structural diagram of an initial sample according to an embodiment of this application is shown;

[0017] Figure 3 A simplified shape diagram of a stamping die according to an embodiment of this application is shown;

[0018] Figure 4 The sample after being sprayed with black speckles according to one embodiment of this application is shown;

[0019] Figure 5 A flowchart is shown for a method of testing the wrinkle resistance of a sheet material according to an embodiment of this application;

[0020] Figure 6 A strain contour plot is shown in one embodiment according to this application;

[0021] Figure 7 The cross-sectional line displacement curve is shown in one embodiment according to this application;

[0022] Figure 8 The relative displacement curve according to one embodiment of this application is shown;

[0023] Figure 9 The strain contour plot of the DC06 steel sample is shown.

[0024] Figure 10The cross-sectional linear displacement curve of the DC06 steel sample is shown;

[0025] Figure 11 The relative displacement curves of the DC06 steel sample are shown. Detailed Implementation

[0026] Exemplary embodiments will now be described more fully with reference to the accompanying drawings. However, these exemplary embodiments can be implemented in many forms and should not be construed as limited to the examples set forth herein; rather, these embodiments are provided to make this application more comprehensive and complete, and to fully convey the concept of the exemplary embodiments to those skilled in the art.

[0027] Furthermore, the described features, structures, or characteristics can be combined in any suitable manner in one or more embodiments. Numerous specific details are provided in the following description to give a thorough understanding of embodiments of this application. However, those skilled in the art will recognize that the technical solutions of this application can be practiced without one or more of the specific details, or other methods, components, apparatuses, steps, etc., can be employed. In other instances, well-known methods, apparatuses, implementations, or operations are not shown or described in detail to avoid obscuring various aspects of this application.

[0028] The flowcharts shown in the accompanying drawings are merely illustrative and do not necessarily include all content and operations / steps, nor do they necessarily have to be performed in the described order. For example, some operations / steps can be broken down, while others can be combined or partially combined; therefore, the actual execution order may change depending on the specific circumstances.

[0029] It should be noted that "multiple" in this article refers to two or more. "And / or" describes the relationship between related objects, indicating that three relationships can exist. For example, A and / or B can represent: A alone, A and B simultaneously, or B alone. The character " / " generally indicates that the preceding and following related objects have an "or" relationship.

[0030] Please see Figure 1 .

[0031] Figure 1 A flowchart illustrating a method for testing the wrinkle resistance of sheet metal according to an embodiment of this application is shown, as follows: Figure 1 As shown, the test method for the wrinkle resistance of this board includes at least steps S101 to S103, which are described in detail below:

[0032] Step S101: Prepare a sample corresponding to the sheet material to be tested based on the shape of the stamping die and the wrinkling mechanism of the sheet material.

[0033] Step S102: Simultaneously perform tensile testing and online strain measurement on the specimen, and conduct strain analysis using the initial state photograph of the specimen as the analysis reference surface.

[0034] Step S103: Based on the strain analysis results, determine the correspondence between wrinkling height and strain magnitude and the critical strain value for wrinkling.

[0035] In this application, a forming testing machine is used to tensile the optimized specimen to different heights. An online strain monitoring system is used to measure and analyze the strain stages, obtaining the critical strain at which the material becomes unstable and the wrinkle height after instability and wrinkling, thus enabling the testing of the material's wrinkle resistance. Online strain analysis provides data support for research on stamping wrinkling by obtaining the strain distribution and stress conditions at different forming stages of the material.

[0036] In this application, the method for preparing a sample corresponding to the sheet metal to be tested based on the shape of the stamping die and the wrinkling mechanism of the sheet metal may include: determining the sample shape based on the shape of the stamping die and the wrinkling mechanism of the sheet metal; preparing an initial sample corresponding to the sheet metal to be tested based on the sample shape; and performing single-sided inkjet printing of speckle patterns on the initial sample to prepare the initial sample corresponding to the sheet metal to be tested.

[0037] For example, please see Figure 2 , Figure 2 A simplified structural diagram of an initial sample according to an embodiment of this application is shown, as follows: Figure 2 As shown, the middle part of the initial sample 201 can be circular with a diameter of 80 mm, serving as the main stress area. The rectangular extensions on both sides serve as positioning areas or secondary stress areas, with a width of 50 mm, which is smaller than the diameter of the circle.

[0038] For example, please see Figure 3 , Figure 3 A simplified diagram of a stamping die shape according to an embodiment of this application is shown. An initial sample is placed on top of the stamping die, and stamping is performed from bottom to top.

[0039] In this application, for subsequent online strain measurement, speckle printing is required on the sample to provide positioning points for online strain measurement.

[0040] In this application, the step of printing speckle patterns on one side of the initial sample includes: cleaning the surface of the initial sample; spraying a white paint film onto one side of the initial sample; and spraying black speckle patterns onto the initial sample after the paint film has dried.

[0041] In this application, the surface of the initial sample is first cleaned with alcohol to remove surface oil stains. Then, a white paint film can be sprayed on one side of the initial sample. After the paint film dries, black speckle is sprayed on. The speckle should be small, uniform, and dense to ensure measurement accuracy.

[0042] For example, please see Figure 4 , Figure 4 A sample after being sprayed with black speckles according to one embodiment of this application is shown.

[0043] Please see Figure 5 .

[0044] Figure 5 A flowchart illustrating a method for testing the wrinkle resistance of sheet metal according to an embodiment of this application is shown. The method of simultaneously performing tensile tests and online strain measurements on the sample, and conducting strain analysis using an initial state photograph of the sample as an analytical reference surface, may include steps S501-S504:

[0045] Step S501: Simultaneously perform tensile testing and online strain measurement on the sample, and conduct strain analysis using the initial state photograph of the sample as the analysis reference surface to obtain the strain cloud map of the sample.

[0046] Step S502: Create a cross-section line on the strain cloud diagram, obtain the displacement of each feature point on the cross-section line along the upward direction of the main cylinder of the stamping equipment, and generate a cross-section line displacement curve.

[0047] Step S503: Based on the effective displacement of the main cylinder of the stamping equipment and the displacement curve of the cross-section line, generate the relative displacement curve between each feature point of the cross-section line and the analysis reference surface;

[0048] Step S504: Obtain the strain data corresponding to each feature point on the relative displacement curve in the strain cloud diagram to complete the strain analysis.

[0049] In this application, a three-dimensional digital speckle dynamic strain measurement and analysis system can be used for online strain measurement. This system is an optical non-contact three-dimensional deformation and strain measurement system. It employs Digital Image Correlation (DIC) combined with binocular stereo vision technology. Two high-speed cameras are used to acquire speckle images of the object at various deformation stages in real time, calculating the overall strain and deformation. This data is used to analyze, calculate, and record deformation data. The measurement results are displayed graphically for better understanding and analysis of the tested material's properties. The system identifies digital images of the object's surface structure, calculates coordinates for image pixels, and the first image represents the undeformed state. Continuous images are acquired during or after the deformation of the object. The system compares the digital images and calculates the displacement and deformation of the object's texture features. This system is particularly suitable for measuring three-dimensional deformation under static and dynamic loads, and for analyzing the deformation and strain of actual components.

[0050] In this application, the molding process of the sample is photographed using an online measurement system, and strain analysis is carried out at each molding stage of the sample to obtain strain cloud maps.

[0051] For example, please see Figure 6 , Figure 6 A strain contour plot according to one embodiment of this application is shown. Figure 6 As shown, different colors in the strain cloud diagram can represent different strain intensities. This allows us to visually see the changes in strain intensity during the stamping or stretching of the sample, and also to determine where the maximum strain occurs.

[0052] In this application, a cross-sectional line can be created at the middle of the specimen along the vertical tensile direction to obtain the displacement d of each point on the cross-section along the Z-axis (i.e., the upward direction of the master cylinder) at different forming stages. z1 A cross-sectional displacement curve is generated, which can characterize the warping profile of the cross section after plastic deformation of the specimen.

[0053] For example, please see Figure 7 , Figure 7 This invention illustrates a cross-sectional line displacement curve according to one embodiment of the present application, wherein the abscissa can be derived from the position information of feature points along the cross-sectional line, and the ordinate is the cross-sectional line displacement d corresponding to each feature point. z1 .

[0054] In this application, the method for generating relative displacement curves between each feature point of the cross-section line and the analysis reference surface based on the effective displacement of the main cylinder of the stamping equipment and the cross-section line displacement curve may include: calculating the difference between each feature point of the cross-section line and the effective displacement of the main cylinder based on the effective displacement of the main cylinder of the stamping equipment and the cross-section line displacement curve, and using the difference as the relative displacement value between each feature point of the cross-section line and the analysis reference surface; and generating relative displacement curves between each feature point of the cross-section line and the analysis reference surface based on each relative displacement value.

[0055] In this application, the effective displacement of the master cylinder can be obtained. The effective displacement of the master cylinder refers to the displacement of the master cylinder after the stamping head of the stamping equipment is in close contact with the sample. Ignoring wrinkling of the sample, the effective displacement of the master cylinder is the displacement of the cross-section line along the vertical direction, and the total displacement d of the cross-section line is... z1 With the displacement d of the main cylinder z0 Difference Δd z This is the relative displacement Δd between the measurement point and the analytical reference surface. z =d z1 -d z0 Δd zThe wrinkling displacement height of each point on the cross-sectional curve relative to the analysis reference surface is given. The X-axis is defined by the original characteristic point data of the cross-sectional curve, and Δd is... z Generate relative displacement curves between each feature point of the cross-section line and the analysis reference surface for the Y-axis.

[0056] For example, please see Figure 8 , Figure 8 A relative displacement curve according to an embodiment of this application is shown.

[0057] In this application, based on the strain analysis results, feature points whose absolute values ​​of all relative displacement values ​​are greater than or equal to preset displacement values ​​can be obtained as wrinkling feature points; the strain values ​​corresponding to the wrinkling feature points can be obtained to determine the correspondence between wrinkling height and strain magnitude.

[0058] In this application, the relative displacement value corresponding to the peak feature point or trough feature point in the relative displacement curve can also be obtained based on the strain analysis results.

[0059] If, among the relative displacement values ​​corresponding to the crest feature point or the trough feature point, there exists an absolute value of a relative displacement value that is greater than or equal to a preset displacement value, then the strain value corresponding to the crest feature point or the trough feature point is obtained as the wrinkling critical strain value.

[0060] In this application, based on the empirical value for judging stamping defects in parts, a preset displacement value of 0.2mm can be used. Therefore, when Δd zmax When Δd = 0.2 mm, it can be determined that the sample is wrinkling and unstable. Therefore, when Δd zmax When the strain is 0.2 mm, the strain in the center region of the sample is the critical wrinkling strain value of the tested steel grade.

[0061] To enable those skilled in the art to gain a deeper understanding of the technical solutions provided in this application, an embodiment will be described below.

[0062] Using DC06 steel as an example, the diagonal tensile wrinkle resistance performance was evaluated, and the critical strain value for wrinkle instability of the part was obtained. Please refer to [link / reference]. Figure 9 , Figure 9 The strain contour plot of the DC06 steel sample is shown. Figure 9 Section line 901 has been identified, and the next step will be to analyze section line 901 as the main object of analysis.

[0063] Please refer to the following. Figure 10 and Figure 11 , Figure 10 The cross-sectional linear displacement curves of the DC06 steel sample are shown. Figure 11 The relative displacement curves of the DC06 steel sample are shown.

[0064] The experiment showed that when the main cylinder stroke height was 16mm, this DC06 steel exhibited wrinkling instability, and at this time the critical principal and secondary strains in the middle of the sample were 7% and -7%, respectively.

[0065] Other embodiments of this application will readily occur to those skilled in the art upon consideration of the specification and practice of the embodiments disclosed herein. This application is intended to cover any variations, uses, or adaptations of this application that follow the general principles of this application and include common knowledge or customary techniques in the art not disclosed herein.

[0066] It should be understood that this application is not limited to the precise structure described above and shown in the accompanying drawings, and various modifications and changes can be made without departing from its scope. The scope of this application is limited only by the appended claims.

Claims

1. A method for testing the wrinkle resistance of sheet metal, characterized in that, The method includes: Based on the shape of the stamping die and the wrinkling mechanism of the sheet metal, prepare the corresponding sample of the sheet metal to be tested; Tensile tests and online strain measurements were performed on the specimen simultaneously, and strain analysis was carried out using the initial state photograph of the specimen as the analytical reference surface. Based on the strain analysis results, the correspondence between wrinkling height and strain magnitude and the critical strain value for wrinkling are determined. The process of simultaneously performing tensile tests and online strain measurements on the specimen, and using the initial state photograph of the specimen as an analytical reference surface for strain analysis, includes: Tensile tests and online strain measurements were performed on the specimen simultaneously. Strain analysis was carried out using the initial state photograph of the specimen as the analysis reference surface to obtain the strain cloud map of the specimen. A cross-sectional line is created on the strain cloud diagram, and the displacement of each feature point on the cross-sectional line along the upward direction of the main cylinder of the stamping equipment is obtained to generate a cross-sectional line displacement curve. Based on the effective displacement of the main cylinder of the stamping equipment and the displacement curve of the cross-section line, a relative displacement curve between each feature point of the cross-section line and the analysis reference surface is generated. Obtain the strain data corresponding to each feature point on the relative displacement curve in the strain cloud map to complete the strain analysis; The step of generating relative displacement curves between each feature point of the cross-section and the analysis reference surface based on the effective displacement of the main cylinder of the stamping equipment and the displacement curve of the cross-section includes: Based on the effective displacement of the main cylinder of the stamping equipment and the displacement curve of the cross-section line, the difference between each feature point of the cross-section line and the effective displacement of the main cylinder is calculated, and the difference is used as the relative displacement value between each feature point of the cross-section line and the analysis reference surface. The relative displacement value is the wrinkling displacement height of each point on the cross-sectional curve relative to the analysis reference surface; Based on each relative displacement value, a relative displacement curve between each feature point of the cross-section line and the analysis reference surface is generated; The effective displacement of the main cylinder refers to the displacement of the main cylinder after the stamping head of the stamping equipment is in close contact with the sample. Ignoring the wrinkling of the sample, the effective displacement of the main cylinder is the displacement of the cross-section line along the vertical direction.

2. The method according to claim 1, characterized in that, The preparation of a sample corresponding to the sheet metal to be tested, based on the shape of the stamping die and the wrinkling mechanism of the sheet metal, includes: The sample shape is determined based on the shape of the stamping die and the wrinkling mechanism of the sheet metal; Based on the shape of the sample, prepare an initial sample corresponding to the plate to be tested; The initial sample is subjected to single-sided speckle printing to prepare a sample corresponding to the plate to be tested.

3. The method according to claim 2, characterized in that, The process of applying speckle printing to the initial sample on one side includes: Clean the surface of the initial sample; A white paint film is sprayed onto one side of the initial sample, and after the paint film dries, black speckled paint is sprayed onto the initial sample.

4. The method according to claim 1, characterized in that, The determination of the correspondence between wrinkle height and strain magnitude based on strain analysis results includes: Based on the strain analysis results, feature points whose absolute values ​​of all relative displacements are greater than or equal to preset displacement values ​​are obtained and used as wrinkling feature points. Obtain the strain value corresponding to the wrinkling feature point to determine the correspondence between wrinkling height and strain magnitude.

5. The method according to claim 1, characterized in that, The determination of the critical strain value for wrinkling based on strain analysis results includes: Based on the strain analysis results, the relative displacement values ​​corresponding to the peak or trough feature points in the relative displacement curve are obtained. If, among the relative displacement values ​​corresponding to the crest feature point or the trough feature point, there exists an absolute value of a relative displacement value that is greater than or equal to a preset displacement value, then the strain value corresponding to the crest feature point or the trough feature point is obtained as the wrinkling critical strain value.

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