Method, system and device for calculating limit point cold bending strain of ultra-high strength automobile steel plate

Abstract

The application discloses a kind of ultra-high strength automobile steel plate limit tip cold bending strain calculation method, system and equipment, and it is related to the field of automobile.Based on the relationship between the strain and bending angle provided by the application, the fracture strain under the limit tip cold bending working condition can be predicted according to the measured cold bending angle, so as to quantitatively evaluate the bending resistance of the material according to the cold bending angle-strain relationship.Further, the cold bending angle-strain relationship calculated by the method of the application can be input into the finite element simulation model, and directly used for the fracture toughness evaluation of parts and the CAE analysis of the whole vehicle.The relationship between the strain and bending angle provided by the application only needs to be substituted by the pressing displacement, sheet thickness and cold bending angle to solve the critical fracture strain of the material, that is, through the simple and easy-to-measure cold bending angle parameter, the complex limit tip cold bending fracture strain parameter is obtained, which solves the problem of difficult fracture strain measurement and reduces the equipment investment and time cost of actual production.

Description

Technical Field

[0001] This invention relates to the field of automotive technology, and in particular to a method, system, and equipment for calculating the ultimate cold bending strain of ultra-high strength automotive steel sheets. Background Technology

[0002] With the continuous improvement of automotive collision safety standards, the application of advanced high-strength steel and ultra-high-strength steel in automotive lightweight design is increasing, achieving weight reduction of components and realizing lightweighting effects. During a car collision, structural components will bend or even fold. How to evaluate the bending fracture performance of ultra-high-strength steel used in automobiles is a widespread need. According to the "Specification for Testing and Evaluation of Ultimate Cold Bending Performance of Steel Sheets for Automobiles", for high-strength steel with a tensile strength ≥780MPa, the industry currently uses the ultimate cold bending angle (also known as the bending angle) to evaluate bending resistance. In traditional methods, the sheet metal is deformed within a very small radius until fracture occurs in the ultimate cold bending test. The strain gradient along the thickness direction is relatively large. When fracture occurs, the cold bending angle is easy to measure. Therefore, bending fracture performance is often evaluated by only one cold bending angle value, but accurate measurement of fracture strain is difficult. The experimental method primarily yields load-displacement curves, providing only the maximum load and the cold bending angle at fracture. This data can only evaluate material quality and can be used as empirical values. It cannot directly measure the relationship between the cold bending angle and strain, nor can it quantitatively assess the material's bending resistance, nor can it directly provide input parameters for CAE (Computer Aided Engineering). Further testing with extreme cold bending strain requires an additional set of tooling and extreme cold bending fracture strain testing equipment, as well as the manufacture and processing of plates of varying thicknesses, resulting in significant equipment costs and time investment. Summary of the Invention

[0003] To address the problems mentioned in the background art, the present invention provides a method, system, and device for calculating the ultimate cold bending strain of ultra-high strength automotive steel sheets, so as to obtain the complex ultimate cold bending fracture strain parameters through simple and easily measurable cold bending angle parameters, and quantitatively evaluate the bending resistance of the material.

[0004] To achieve the above objectives, the present invention provides the following solution:

[0005] On one hand, this invention provides a method for calculating the ultimate cold bending strain of ultra-high strength automotive steel sheets, including:

[0006] Material tests were conducted on sheet metal with a strength higher than 780 MPa for automotive structural components to obtain the measured value of the sheet metal's bending angle.

[0007] Establish the shape function of the outer surface of the board, and obtain the curvature of the shape function by combining the curvature formula. Further establish the relationship between the curvature of the shape function and the bending angle during the bending process of the board by geometric relationships.

[0008] Based on the bending strain-curvature formula in mechanics of materials, and combined with the established relationship between the curvature of the shape function and the bending angle, the relationship between strain and bending angle is obtained.

[0009] The strain value of the plate is calculated by substituting the measured bending angle of the plate into the relationship between strain and bending angle.

[0010] Optionally, the material testing of the sheet metal for automotive structural components with a strength higher than 780 MPa to obtain the measured value of the sheet metal's bending angle specifically includes:

[0011] Material tests were conducted on sheet metal for automotive structural components with a strength exceeding 780 MPa, and the test process parameters were recorded. These parameters included the diameter of the support rollers, the spacing between the support rollers, the radius of the indenter tip, the sheet metal thickness, and the indenter's downward stroke.

[0012] Based on the test process parameters, and using the formula The measured bending angle of the plate was calculated; where α 测 The measured bending angle is represented by p = d / 2 + L / 2; d is the diameter of the support roller; L is the distance between the support rollers; c = d / 2 + r + t0; r is the radius of the pressure head tip; t0 is the thickness of the sheet material. S represents the downward stroke of the pressure head.

[0013] Optionally, the step of establishing the shape function of the outer surface of the sheet metal, obtaining the curvature of the shape function using the curvature formula, and further establishing the relationship between the curvature of the shape function and the bending angle during the bending process of the sheet metal using geometric relationships specifically includes:

[0014] Establish the shape function of the outer surface of the sheet material as y = -acos(bx), and combine it with the curvature formula. The curvature of the shape function K = ab is obtained. 2 Where 'a' represents the pressure displacement of the sheet metal; OB is the intercept of the material with the positive x-axis;

[0015] Establishing the geometric relationships during the bending process of the sheet metal. Where α represents the bending angle of the sheet material;

[0016] Simultaneous equation of shape function curvature k = ab 2 and geometric relationships The relationship between the curvature of the shape function and the bending angle is obtained.

[0017] Optionally, the relationship between strain and bending angle is obtained by combining the bending strain-curvature formula in mechanics of materials with the established relationship between the curvature of the shape function and the bending angle, specifically including:

[0018] Based on the bending strain-curvature formula ε=kt in mechanics of materials, where t is the thickness from the strain neutral plane to the outer surface, and combined with the established relationship between the shape function curvature and the bending angle... Substituting the values, we obtain the relationship between strain ε and bending angle α.

[0019] On the other hand, the present invention also provides a system for calculating the ultimate cold bending strain of ultra-high strength automotive steel sheets, comprising:

[0020] The material testing module is used to perform material testing on sheet metal with a strength higher than 780MPa for automotive structural components, and to obtain the measured value of the bending angle of the sheet metal.

[0021] The module for establishing the relationship between the curvature of the shape function and the bending angle during the bending process of the sheet material is used to establish the shape function of the outer surface of the sheet material. The curvature of the shape function is obtained by combining the curvature formula, and the relationship between the curvature of the shape function and the bending angle during the bending process of the sheet material is further established by geometric relationships.

[0022] The strain-bending angle relationship establishment module is used to obtain the relationship between strain and bending angle based on the bending strain-curvature formula in mechanics of materials and the established relationship between shape function curvature and bending angle.

[0023] The strain value calculation module is used to substitute the measured bending angle of the plate into the relationship between strain and bending angle to calculate the strain value of the plate.

[0024] On the other hand, the present invention also provides an electronic device, including a memory, a processor, and a computer program stored in the memory and executable on the processor, wherein the processor executes the computer program to implement the method for calculating the ultimate cold bending strain of ultra-high strength automotive steel sheet.

[0025] Optionally, the memory is a non-transitory computer-readable storage medium.

[0026] According to specific embodiments provided by the present invention, the present invention discloses the following technical effects:

[0027] For assessing the fracture performance of components and the entire vehicle in collisions, the strain-bending angle relationship provided by this invention can be used to predict the fracture strain under extreme cold bending conditions based on the measured cold bending angle. Furthermore, the bending resistance of materials can be quantitatively assessed based on the cold bending angle-strain relationship, solving the problem of judging material toughness using empirical values. The cold bending angle-strain relationship parameters calculated by this invention can be input into a finite element simulation model for direct use in component fracture toughness assessment and vehicle CAE analysis. For extreme cold bending experiments, based on the strain-bending angle relationship provided by this invention, the critical fracture strain of the material can be solved simply by substituting the downward displacement, plate thickness, and cold bending angle. That is, the complex extreme cold bending fracture strain parameters can be obtained using the simple and easily measurable cold bending angle parameter, solving the problem of difficult fracture strain measurement and reducing equipment investment and time costs in actual production. Attached Figure Description

[0028] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0029] Figure 1 A flowchart illustrating a method for calculating the ultimate cold bending strain of ultra-high strength automotive steel sheet provided by the present invention;

[0030] Figure 2 This is a schematic diagram of the bending angle test process;

[0031] Figure 3 This is a schematic diagram of the variables involved in the bending angle test process;

[0032] Figure 4 This is a schematic diagram illustrating the shape changes during the bending process of the sheet metal.

[0033] Figure 5 This is a schematic diagram of the neutral surface;

[0034] Figure 6 This is a schematic diagram of the geometric relationship during the bending process of the sheet metal.

[0035] Figure 7 This is a schematic diagram of the ultimate cold bending load-displacement curve;

[0036] Figure 8 This is a schematic diagram showing the folding of sheet metal parts during the collision.

[0037] Figure 9 This is a schematic diagram of the MMC fracture model;

[0038] Figure 10 A schematic diagram of the cold bending finite element simulation model established for the example;

[0039] Figure 11 This is a schematic diagram showing the strain results of the unit elements output from the finite element simulation model.

[0040] Figure 12 This is a schematic diagram of the bending angle-strain relationship curves for HS1500 steel of different thicknesses; where Figure 12 (a) Figure 12 (b) Figure 12 (c) Figure 12 (d) Schematic diagrams of bending angle-strain relationship curves for HS1500 steel with thicknesses of 1.2mm, 1.6mm, 2.0mm, and 2.5mm, respectively;

[0041] Figure 13 This is a schematic diagram of the bending angle-strain relationship curves for DP780 steel of different thicknesses; where Figure 13 (a) Figure 13 (b) Figure 13 (c) Figure 13 (d) Schematic diagrams of bending angle-strain relationship curves for DP780 steel with thicknesses of 1.2mm, 1.6mm, 2.0mm, and 2.5mm, respectively;

[0042] Figure 14 This is a schematic diagram of the bending angle-strain relationship curves for DH780 steel of different thicknesses; where Figure 14 (a) Figure 14 (b) Figure 14 (c) Figure 14 (d) Schematic diagrams of bending angle-strain relationship curves for DH780 steel with thicknesses of 1.2mm, 1.6mm, 2.0mm, and 2.5mm, respectively. Detailed Implementation

[0043] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0044] The purpose of this invention is to provide a method, system, and device for calculating the ultimate cold bending strain of ultra-high strength automotive steel sheets, so as to obtain the complex ultimate cold bending fracture strain parameters through simple and easy-to-measure cold bending angle parameters, and quantitatively evaluate the bending resistance of the material.

[0045] To make the above-mentioned objects, features and advantages of the present invention more apparent and understandable, the present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments.

[0046] Figure 1 A flowchart illustrating the method for calculating the ultimate cold bending strain of ultra-high strength automotive steel sheet provided by this invention is available in the attached diagram. Figure 1 A method for calculating the ultimate cold bending strain of ultra-high strength automotive steel sheet, comprising:

[0047] Step 1: Conduct material testing on sheet metal with a strength higher than 780MPa for automotive structural components to obtain the measured value of the sheet metal's bending angle.

[0048] Plates with a strength of not less than 780 MPa were selected for use in automotive structural components. The materials were tested according to T / CSAE154-2020 "Test Method for Ultimate Cold Bending Performance of Ultra-High Strength Automotive Steel Plates". The testing process is as follows: Figure 2 As shown, the indenter is connected to a mechanical sensor to transmit force values ​​in real time. The indenter continuously presses down on the plate until the peak load reaches 10% or visible cracks appear, at which point the test is terminated. The bending angle α of the plate is calculated according to the following formula (1):

[0049]

[0050] The value of α calculated according to equation (1) will then be used as the measured value of the bending angle α. 测 The variables in the above formula are shown in the figure. Figure 3 The specifications are as follows: d is the diameter of the support roller; L is the distance between the two support rollers; r is the radius of the pressure head tip; t0 is the thickness of the sheet material; and S is the pressure head's downward stroke. Intermediate parameters: p = d / 2 + L / 2; c = d / 2 + r + t0;

[0051] Step 2: Establish the shape function of the outer surface of the board, and obtain the curvature of the shape function by combining the curvature formula. Then, establish the relationship between the curvature of the shape function and the bending angle during the bending process of the board by geometric relationships.

[0052] As the sheet material comes into contact with the pressure head and is continuously pressed down, its contact surface is pressed from a flat plane into an arc with continuously increasing curvature, and the entire sheet material exhibits a constantly changing curve, such as... Figure 4 As shown. Let the shape of the outer surface of the sheet material follow a function:

[0053] y = -scos(bx) (2)

[0054] In the formula, a is the pressing displacement of the sheet metal; b is π / 2 divided by the intercept OB between the sheet metal and the positive x-axis, i.e. In practical applications, in addition to the trigonometric cosine function used in equation (2), the surface shape function of the plate can also be established by using the Taylor expansion of the cosine function, the sine function and its Taylor expansion to achieve an approximate effect.

[0055] The formula for the curvature of the part of the sheet metal in contact with the pressure head is:

[0056]

[0057] The curvature of the shape function can be further obtained from equation (2):

[0058] K = ab 2 (4)

[0059] The strain at the contact point between the sheet metal and the pressure head is:

[0060]

[0061] In the formula, such as Figure 5 As shown, t is the radial distance from the strain neutral surface to the desired surface (in this embodiment, the curved surface of the outer surface of the plate), which is approximately taken as half the plate thickness. ρ is the radius of curvature of the curved surface of the plate. K is the curvature of the curved surface, and the bending strain-curvature formula applies:

[0062] ε = ab 2 t=Kt (6)

[0063] Figure 6 This represents the geometric relationship during the bending process of the sheet metal. According to equation (2), OA = a. Then approximately:

[0064]

[0065] Therefore, we can conclude that:

[0066]

[0067] Substituting equation (8) into equation (4), we can obtain the relationship between the curvature of the shape function and the bending angle:

[0068]

[0069] Step 3: Based on the bending strain-curvature formula in mechanics of materials, and combined with the established relationship between the curvature of the shape function and the bending angle, the relationship between strain and bending angle is obtained.

[0070] Combining equations (6) and (9), we obtain the relationship between strain ε and bending angle α:

[0071]

[0072] Step 4: Substitute the measured bending angle of the plate into the relationship between strain and bending angle to calculate the strain value of the plate.

[0073] The measured value of the bending angle α obtained in step 1 测 Substituting the value of α into equation (10), the strain value ε of the plate can be calculated. Similarly, if the strain value ε is known, it can also be substituted into equation (10) to obtain the bending angle α.

[0074] During automotive collisions, thin-plate parts often exhibit bending fractures. Their fracture modes or stress triaxiality differ significantly from those observed in conventional tensile testing. Since the fracture performance of automotive sheet metal is primarily evaluated through tensile properties, this field employs the German Association of the Automotive Industry (VDA) standard 238-100 "Plate bending test for metallic materials" and the China Society of Automotive Engineers (T / CSAE) standard T / CSAE154-2020 "Test Method for Ultimate Cold Bending Performance of Ultra-High Strength Automotive Steel Sheets" to evaluate the collision fracture toughness of structural components, particularly structural sheet metal. Both standards involve pressing the sheet metal down with a very small radius indenter and calculating the bending angle when the peak load is reduced to 10% to assess the sheet metal's fracture performance. This bending angle can only be used to evaluate the material's quality and cannot serve as effective input data for simulation analysis; it lacks physical meaning and can only be used as empirical data. The method of this invention, based on the testing methods of the above two standards and related mathematical and physical methods, yields the relationship between the bending angle and the critical fracture strain (10). This relationship can be directly used to evaluate the material's collision toughness and can also be directly applied to CAE analysis of whole-vehicle collisions.

[0075] Impact toughness generally refers to a material's resistance to the forces that cause it to undergo plastic deformation and fracture during an impact. Materials with better toughness have a higher elongation at break and a lower likelihood of brittle fracture; in other words, they absorb more energy during plastic deformation before fracture. For materials of the same thickness and specifications, a larger cold bending angle results in greater deformation before fracture and better impact toughness. However, this process only qualitatively determines material toughness; how to quantitatively determine the quality of a material remains a problem to be solved.

[0076] The load-displacement curves obtained from the extreme cold bending test are as follows: Figure 7 As shown, when the cold bending angle is determined empirically in the experiment, the timing of stopping the loading needs to be controlled according to the magnitude of the load. For example... Figure 7The four methods shown are: 5% earlier than the maximum force, stopping loading at the maximum force, stopping loading when the maximum force decreases by 5%, and stopping loading when the maximum force decreases by 15%. This existing method can quantitatively determine the impact toughness of a material, but it relies heavily on experience. Secondly, the obtained data is a force-displacement curve, which cannot provide strain information. Strain information can be obtained using an additional DIC (digital image correlation) system, but the data obtained by DIC is also related to the empirical value. Therefore, a mathematical formula that can quantitatively describe the relationship between the cold bending angle and strain information is extremely necessary. According to the strain-bending angle relationship (10) provided by this invention, the fracture strain under extreme cold bending conditions can be predicted based on the measured cold bending angle, and the bending resistance of the material can be quantitatively evaluated based on the cold bending angle-strain relationship, thus solving the problem of judging the toughness of a material using empirical values.

[0077] During a collision, the possible forms of damage to the parts are as follows: Figure 8 As shown, parts may be subjected to loads under complex stress states. The cold bending angle data obtained solely from extreme cold bending tests cannot assess whether the part will fracture. For example, with materials exhibiting good plasticity, even if folding occurs, fracture may not be observed. The magnitude of the ultimate bending angle is determined by the ultimate fracture strain under the material's plane strain state. For instance, in extreme cold bending tests, for the same material with the same critical fracture strain, different thicknesses may result in a measured cold bending angle that is either too small or too large when the material reaches its fracture strain. In vehicle collision CAE simulation analysis, the evaluation of whether fracture has occurred is usually determined by both the material's fracture strain and the stress state. When using fracture models such as MMC (Modified Mohr Coulomb) for simulation, fracture strain data under different stress states are required. Figure 9 The data (shown by the midpoint) is used to fit the critical fracture surface. Different cold bending fracture strain data (different vertical coordinates of the midpoint at the same horizontal coordinate) affect the height of the fracture model curve, thus affecting the simulation accuracy. Further substituting this fracture model into the finite element method (FEA) for calculation can identify the parts of the system that may fracture. Therefore, CAE needs to obtain fracture strain. Traditional experimental measurements only have cold bending angle data, which is insufficient for CAE fracture simulation. However, fracture strain can be easily obtained using the method of this invention, thus directly providing input parameters for CAE.

[0078] Based on the method provided by this invention, this invention also provides a system for calculating the ultimate cold bending strain of ultra-high strength automotive steel sheets, comprising:

[0079] The material testing module is used to perform material testing on sheet metal with a strength higher than 780MPa for automotive structural components, and to obtain the measured value of the bending angle of the sheet metal.

[0080] The module for establishing the relationship between the curvature of the shape function and the bending angle during the bending process of the sheet material is used to establish the shape function of the outer surface of the sheet material. The curvature of the shape function is obtained by combining the curvature formula, and the relationship between the curvature of the shape function and the bending angle during the bending process of the sheet material is further established by geometric relationships.

[0081] The strain-bending angle relationship establishment module is used to obtain the relationship between strain and bending angle based on the bending strain-curvature formula in mechanics of materials and the established relationship between shape function curvature and bending angle.

[0082] The strain value calculation module is used to substitute the measured bending angle of the plate into the relationship between strain and bending angle to calculate the strain value of the plate.

[0083] The following specific embodiments verify the effectiveness of the method of the present invention. This embodiment uses automotive structural steel DP780 with thicknesses of 1.2mm, 1.6mm, 2.0mm, and 2.5mm; HS1500 with thicknesses of 1.2mm, 1.6mm, 2.0mm, and 2.5mm; and DH780 with thicknesses of 1.2mm, 1.6mm, 2.0mm, and 2.5mm as examples. Bending angle tests are performed on each, and finite element models are established to simulate the strain on the outer surface of the sheet metal during the pressing process. The fracture strain is predicted using the method of the present invention, verifying the effectiveness and accuracy of the proposed method.

[0084] Finite element model establishment process:

[0085] Based on the actual dimensions of the tooling and the test conditions of VDA238-100, a finite element simulation model was established as follows: Figure 10 As shown, the pressure head and support rollers are set to rigid, while the sheet material is elastic. The mesh at the contact point between the pressure head and the sheet material is refined. The distance L between the two roller surfaces is 2t0 + 0.5 mm, where t0 is the sheet thickness. A uniform 5-layer unit is used in the sheet thickness direction. The maximum downward displacement is 12 mm. The output results are the downward displacement of the pressure head, the bending angle of the sheet material, and the maximum strain in the X direction of the two middle units on the outer surface of the sheet material. Figure 11 As shown.

[0086] The finite element simulation values ​​of bending strain of HS1500 hot-formed steel with a strength of 1500MPa at different thicknesses were compared with the calculated values ​​in this embodiment. The displacement α and corresponding bending angle α output in real time from the finite element models with thicknesses of 1.2mm, 1.6mm, 2.0mm, and 2.5mm were substituted into formula (10) to calculate the strain value ε, which was then compared with the maximum strain value in the X direction of the two middle elements on the outer surface output by the finite element model. Figure 12 As shown.

[0087] Similarly, the bending angle-strain relationship curves for DP780 with thicknesses of 1.2mm, 1.6mm, 2.0mm, and 2.5mm are obtained for example. Figure 13As shown; the bending angle-strain relationship curves of DH780 with thicknesses of 1.2mm, 1.6mm, 2.0mm, and 2.5mm are compared. Figure 14 As shown.

[0088] By comparison Figure 12 , Figure 13 and Figure 14 As can be seen from the curves, the cold bending angle-strain relationship of various grades and thicknesses of high-strength automotive steel calculated and predicted by the method of the present invention has the same overall trend as the cold bending angle-strain relationship output by the simulation model, and the error of the predicted strain value is small, which proves the effectiveness of the method of the present invention.

[0089] Furthermore, the present invention also provides an electronic device, which may include: a processor, a communication interface, a memory, and a communication bus. The processor, communication interface, and memory communicate with each other via the communication bus. The processor can call a computer program stored in the memory to execute the aforementioned method for calculating the ultimate cold bending strain of ultra-high strength automotive steel sheets.

[0090] Furthermore, when the computer program in the aforementioned memory is implemented as a software functional unit and sold or used as an independent product, it can be stored in a non-transitory computer-readable storage medium. Based on this understanding, the technical solution of the present invention, in essence, or the part that contributes to the prior art, or a part of the technical solution, can be embodied in the form of a software product. This computer software product is stored in a storage medium and includes several instructions to cause a computer device (which may be a personal computer, server, or network device, etc.) to execute all or part of the steps of the methods described in the various embodiments of the present invention. The aforementioned storage medium includes various media capable of storing program code, such as USB flash drives, portable hard drives, read-only memory, random access memory, magnetic disks, or optical disks.

[0091] The various embodiments in this specification are described in a progressive manner, with each embodiment focusing on its differences from other embodiments. Similar or identical parts between embodiments can be referred to interchangeably. For the systems disclosed in the embodiments, since they correspond to the methods disclosed in the embodiments, the descriptions are relatively simple; relevant parts can be referred to the method section.

[0092] This document uses specific examples to illustrate the principles and implementation methods of the present invention. The descriptions of the above embodiments are only for the purpose of helping to understand the method and core ideas of the present invention. Furthermore, those skilled in the art will recognize that, based on the ideas of the present invention, there will be changes in the specific implementation methods and application scope. Therefore, the content of this specification should not be construed as a limitation of the present invention.

Claims

1. A method for calculating the ultimate cold bending strain of ultra-high strength automotive steel sheet, characterized in that, include: Material testing was conducted on sheet metal with a strength exceeding 780 MPa for automotive structural components, obtaining measured values ​​of the sheet metal's bending angle, specifically including: Material tests were conducted on sheet metal for automotive structural components with a strength exceeding 780 MPa, and the test process parameters were recorded. These parameters included the diameter of the support rollers, the spacing between the support rollers, the radius of the indenter tip, the sheet metal thickness, and the indenter's downward stroke. Based on the test process parameters, and using the formula The measured value of the bending angle of the plate was calculated; where This represents the measured value of the bending angle; d is the diameter of the support roller; To support the roller spacing; r is the radius of the indenter tip; t0 is the thickness of the sheet metal. S represents the downward stroke of the pressure head; Establish the shape function of the outer surface of the board, and obtain the curvature of the shape function by combining the curvature formula. Further establish the relationship between the curvature of the shape function and the bending angle during the bending process of the board by geometric relationships. Based on the bending strain-curvature formula in mechanics of materials, and combined with the established relationship between the curvature of the shape function and the bending angle, the relationship between strain and bending angle is obtained. The strain value of the plate is calculated by substituting the measured bending angle of the plate into the relationship between strain and bending angle.

2. The method for calculating the ultimate cold bending strain of ultra-high strength automotive steel sheet according to claim 1, characterized in that, The process of establishing the shape function of the outer surface of the sheet metal, obtaining the curvature of the shape function using the curvature formula, and further establishing the relationship between the curvature of the shape function and the bending angle during the bending process of the sheet metal using geometric relationships specifically includes: Establish the shape function of the outer surface of the sheet material Combined with curvature formula Find the curvature of the shape function in a This refers to the displacement of the sheet metal under pressure. ; OB The intercept of the plate material with the positive x-axis; Establishing the geometric relationships during the bending process of the sheet metal. ;in Indicates the bending angle of the sheet material; Simultaneous shape function curvature and geometric relationships The relationship between the curvature of the shape function and the bending angle is obtained. .

3. The method for calculating the ultimate cold bending strain of ultra-high strength automotive steel sheet according to claim 2, characterized in that, Based on the bending strain-curvature formula in mechanics of materials, and combined with the established relationship between shape function curvature and bending angle, the relationship between strain and bending angle is obtained, specifically including: According to the bending strain-curvature formula in mechanics of materials , t The thickness from the strain neutral surface to the outer surface is determined by the established relationship between the curvature of the shape function and the bending angle. Substituting the values ​​yields the strain. With bending angle Relationship .

4. A system for calculating the ultimate cold bending strain of ultra-high strength automotive steel sheets, characterized in that, include: The materials testing module is used to perform material testing on sheet metal with a strength higher than 780MPa for automotive structural components, obtaining the measured value of the sheet metal's bending angle. Specifically, it includes: Material tests were conducted on sheet metal for automotive structural components with a strength exceeding 780 MPa, and the test process parameters were recorded. These parameters included the diameter of the support rollers, the spacing between the support rollers, the radius of the indenter tip, the sheet metal thickness, and the indenter's downward stroke. Based on the test process parameters, and using the formula The measured value of the bending angle of the plate was calculated; where This represents the measured value of the bending angle; d is the diameter of the support roller; To support the roller spacing; r is the radius of the indenter tip; t0 is the thickness of the sheet metal. S represents the downward stroke of the pressure head; The module for establishing the relationship between the curvature of the shape function and the bending angle during the bending process of the sheet material is used to establish the shape function of the outer surface of the sheet material. The curvature of the shape function is obtained by combining the curvature formula, and the relationship between the curvature of the shape function and the bending angle during the bending process of the sheet material is further established by geometric relationships. The strain-bending angle relationship establishment module is used to obtain the relationship between strain and bending angle based on the bending strain-curvature formula in mechanics of materials and the established relationship between shape function curvature and bending angle. The strain value calculation module is used to substitute the measured bending angle of the plate into the relationship between strain and bending angle to calculate the strain value of the plate.

5. An electronic device comprising a memory, a processor, and a computer program stored in the memory and executable on the processor, characterized in that, When the processor executes the computer program, it implements the method for calculating the ultimate cold bending strain of ultra-high strength automotive steel sheet as described in any one of claims 1 to 3.

6. The electronic device according to claim 5, characterized in that, The memory is a non-transitory computer-readable storage medium.

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