Method for evaluating wrinkle resistance of bimetallic clad plate

Abstract

The application provides an evaluation method for wrinkle resistance of a bimetal composite plate, which comprises the following steps: S1, preparing a plurality of bimetal composite plate test pieces, and obtaining wrinkle morphology characteristics of the plurality of bimetal composite plate test pieces; S2, based on the wrinkle morphology characteristics, obtaining wrinkle quantity and wrinkle height, and preliminarily determining the wrinkle resistance of the composite plate by using a qualitative analysis method; and S3, by using a quantitative analysis method, comparing the absolute value of the slope of the critical wrinkle strain line based on the critical wrinkle strain line, and further evaluating the wrinkle resistance of the bimetal composite plate. The application establishes the critical wrinkle strain line based on the wrinkle morphology characteristics and the strain data, and qualitatively and quantitatively analyzes and evaluates the wrinkle resistance of the composite plate, which can accurately evaluate the wrinkle resistance of the bimetal composite plate, is simple and convenient to operate, has high work efficiency, is intuitive in process, has high reliability of results, can be popularized and applied in engineering practice, and provides a new technical scheme for accurate evaluation of the wrinkle resistance of the metal composite plate.

Description

Technical Field

[0001] This application relates to the field of sheet metal plastic processing technology, and in particular to a method for evaluating the wrinkle resistance of bimetallic composite plates. Background Technology

[0002] With the development of high-tech fields such as aerospace, military, rail transportation, and energy electronics, new requirements have been placed on material properties. Traditional metallic materials are struggling to meet the demands of modern development, and metal composites have become an effective way for many materials to achieve functionalization and high performance. Against this backdrop, metal matrix composites have emerged. These advanced materials combine the unique properties of both metals and reinforcements, creating limitless possibilities for further development in high-tech fields. Thanks to the efforts of scholars both domestically and internationally, significant progress has been made in the preparation and application of metal matrix composites. However, bimetallic composite plates still face the problem of plastic instability in engineering practice, and there is a lack of effective evaluation indicators and assessment methods for the wrinkle resistance of bimetallic composite plates, making it difficult to meet the requirements of industrial production. Summary of the Invention

[0003] To overcome the shortcomings of existing technologies, this invention provides a method for evaluating the wrinkle resistance of bimetallic composite plates. This method can evaluate the wrinkle resistance of composite plates based on morphological characteristics and critical wrinkling strain lines. The method can accurately evaluate the wrinkle resistance of bimetallic composite plates. The whole method is simple to operate, highly practical, and has high reliability. It can be promoted and applied in engineering practice, providing a new technical solution for the accurate evaluation of the wrinkle resistance of bimetallic composite plates.

[0004] This invention provides a method for evaluating the wrinkle resistance of bimetallic composite plates, which includes the following steps: S1. Prepare multiple composite plate specimens and obtain the wrinkle morphology characteristics of multiple composite plate specimens; S2. Based on the wrinkle morphology characteristics, obtain the number and height of wrinkles, and use qualitative analysis to preliminarily determine the wrinkle resistance of the composite board. This includes the following sub-steps: S21. First, determine the number of wrinkles in different specimens. If the number of wrinkles in different specimens is the same, proceed to step S22. If the number of wrinkles in different specimens is different, the more wrinkles a specimen has, the worse its wrinkle resistance is. S22. When the number of wrinkles in different specimens is the same, the wrinkle height of different specimens is judged: the larger the wrinkle height of a specimen, the worse the wrinkle resistance of the specimen. S3. Using quantitative analysis methods, based on the critical wrinkling strain line, the absolute values ​​of the slopes of the critical wrinkling strain lines are compared to further evaluate the wrinkle resistance of the composite board. This includes the following sub-steps: S31. Determine the location of the stress neutral layer in the bimetallic composite plate, which includes the following sub-steps: S311. Divide the bimetallic composite plate specimen into equal thickness intervals along the thickness direction. The specimen is divided into layers, with one integration point set on each layer. The in-plane normal stress values ​​of each layer's integration point are extracted along the direction perpendicular to the ridges during the entire deformation process. The in-plane normal stress values ​​at any two adjacent integration points at the same moment are compared. The specimen thickness is recorded as... Let the positions of the two adjacent integration points closest to the stress neutral layer along the thickness direction of the bimetallic composite plate be respectively. and ,in ; S312. When the two nearest adjacent integration points to the stress neutral layer are both located in a certain metal layer and the following conditions are met, the stress neutral layer is determined to be located in the metal layer where the two integration points are located:

[0005] In the formula, , These represent the in-plane normal stresses at the two adjacent integration points closest to the stress neutral layer in the direction perpendicular to the ridge; S313. When the two adjacent integration points closest to the stress neutral layer are located in the metal layer and the metallurgical bonding layer respectively, the stress neutral layer is determined to be the metal layer where one of the integration points is located. S32. Determine the critical wrinkling moment of the bimetallic composite plate, including the following sub-steps: S321. Divide the metal layer containing the stress neutral layer into equal parts along the thickness direction. Layer, in which It is an odd number, and Each layer is sequentially denoted as , ... , , ... , One integration point is set sequentially on each isolayer, and the first and second principal strains of each integration point are extracted during the entire deformation process. One analysis step is set throughout the entire deformation process, including steps 0, 1, 2... , , ...... At that moment, among which ,Depend on and The bifurcation time of the strain path, jointly determined by the integration points on two sets of symmetrical integration layers, satisfies the following condition:

[0006] In the formula, express and The integration points set on the equal strata are at the th The value of the above expression is first satisfied at time t, i.e., the first time. The time is the bifurcation time of the strain path determined by the two layers, denoted as . ; express The integration point on the same layer is at the th The first principal strain value corresponding to the given moment; express The integration point on the same layer is at the th The first principal strain value corresponding to the given moment; express The integration point on the same layer is at the th The second principal strain value corresponding to the given moment; express The integration point on the same layer is at the th The second principal strain value corresponding to the given moment; S322, and There are two sets of symmetrical integration layers. , Calculate in sequence and , and , and ...... and The strain path bifurcation times determined by the integration points on the same stratum are denoted as follows: , , ...... Based on the calculation results, the bifurcation time of the strain path in the metal layer containing the stress neutral layer is determined. As shown in the following formula:

[0007] In the formula, This indicates the bifurcation point of the strain path in the metal layer containing the stress-neutral layer. Take the integer part; , , ...... Total A number; S323. Based on the bifurcation time of the strain path in the metal layer where the stress neutral layer is located. Determine the critical wrinkling moment of the integral bimetallic composite panel The specific formula is as follows:

[0008] In the formula: This indicates the critical wrinkling moment of the overall bimetallic composite panel; Indicates the moment when the strain path of the metal layer containing the stress neutral layer bifurcates; S33. Extract the critical wrinkling strain values ​​of different metal layers at the critical wrinkling moment, and generate a critical wrinkling strain line based on the critical wrinkling strain value. Compare the absolute values ​​of the slopes of the critical wrinkling strain lines to evaluate the wrinkle resistance of the composite plate. The larger the absolute value of the slope of the critical wrinkling strain line, the worse the wrinkle resistance.

[0009] Preferably, the bimetallic composite plate includes a first metal layer, a second metal layer, and a metallurgical bonding layer at the junction of the first metal layer and the second metal layer.

[0010] Preferably, step S31 further includes step S314: verifying the accuracy of the determined stress neutral layer. If the stress neutral layer meets the following judgment conditions, the selected stress neutral layer is determined to be the final stress neutral layer; otherwise, return to step S311 to redetermine the position of the stress neutral layer. The judgment conditions are specifically stated as follows: Let the theoretical offset of the stress-neutral layer relative to the geometrically neutral layer at the time of wrinkling be... The thickness of the first metal layer is The thickness of the second metal layer is In any cross-section At this location, the stress on the upper surface of the first metal layer is The stress on the lower surface of the second metal layer is The stress-neutral layer should satisfy the following formula:

[0011] Let the simulated offset of the stress neutral layer relative to the geometric neutral layer be . Theoretical offset With simulated offset The following formula should be satisfied between them: .

[0012] Preferably, the wrinkle morphology characteristics of the composite plate specimen in step S1 are obtained through a finite element simulation model. The input data of the finite element simulation model includes the thickness and hardness of each metal layer and the metallurgical bonding layer, as well as the stress-strain relationship of each metal layer.

[0013] Preferably, the method for determining the thickness and hardness of each metal layer and the metallurgical bonding layer is as follows: the distribution of hardness along the thickness direction is obtained by using a microhardness test, and the thickness and hardness of the first metal layer, the metallurgical bonding layer and the second metal layer of the composite plate are determined.

[0014] Preferably, in step S313, if two adjacent integration points are both located in the metallurgical bonding layer, then the stress neutral layer is determined to be located in the metallurgical bonding layer.

[0015] Preferably, the specific method for obtaining the number of wrinkles and the height of wrinkles based on wrinkle morphology features in step S2 is as follows: extract the wrinkle morphology features from the simulation results of the finite element simulation model. The wrinkle morphology features include the thickness displacement cloud map and the thickness displacement change curve along the predetermined path. Analyze the number of wrinkles and the height of wrinkles through the thickness displacement cloud map and the thickness displacement change curve along the predetermined path.

[0016] Preferably, the specific method for analyzing the number and height of wrinkles using the thickness displacement cloud map and the thickness displacement variation curve along a predetermined path is as follows: taking the line connecting the points where the maximum wrinkle height is located in the thickness displacement cloud map of the simulation results as the geometric path, outputting the thickness displacement variation curve along the selected geometric path, with the horizontal axis of the thickness displacement variation curve representing the geometric distance of the specimen and the vertical axis representing the wrinkle height, thereby obtaining the accurate number and height of wrinkles.

[0017] Compared with the prior art, the beneficial effects of the present invention are as follows: (1) Based on the influence of morphological characteristics and critical wrinkling strain line on the wrinkle resistance of composite board, this method proposes two different criteria to evaluate the wrinkle resistance of composite board from two different perspectives: qualitative analysis and quantitative analysis. Different composite boards can choose one or two of them. On the basis of rapid qualitative analysis, quantitative analysis with higher accuracy is added. The two complement each other, and the whole evaluation process is scientific and efficient with high accuracy.

[0018] (2) By establishing a wrinkle morphology feature map related to wrinkle resistance, the present invention expresses the differences in wrinkle resistance performance through data and graphics. The acquisition of wrinkle resistance performance is more intuitive and visible, and has an intuitive guiding role in the prediction of wrinkle resistance performance and industrial application. The overall method is simple to operate, highly practical, and conducive to its promotion and application in engineering practice.

[0019] (3) The present invention obtains the hardness and stress-strain data of bimetallic composite plate through material performance test, and establishes a finite element simulation model based on tensile wrinkling test, and compares the wrinkling morphology of the two to verify the accuracy of finite element simulation; based on the wrinkle morphology characteristics and the critical wrinkling strain line based on strain data, the anti-wrinkle performance of composite plate is evaluated. Only the thickness and hardness of each metal layer and metallurgical bonding layer and the stress-strain relationship of each metal layer are needed to obtain the wrinkling morphology characteristic map, which provides a basis for quantitative and qualitative analysis. No additional complex test is required, which reduces a lot of time and material waste.

[0020] (4) This invention finds the stress-neutral layer through a specific method, thereby determining the critical wrinkling time based on the location of the stress-neutral layer, obtaining the critical wrinkling strain line based on the critical wrinkling time, and evaluating the wrinkle resistance of the composite metal plate by the slope of the critical wrinkling strain line. A new wrinkle resistance evaluation method is proposed. Furthermore, a verification process is set up in the process of finding the stress-neutral layer, which can ensure that the location of the stress-neutral layer is accurate, providing a basis for subsequent accurate evaluation, avoiding inaccurate results due to operational errors, and further improving the reliability of the entire evaluation method. Attached Figure Description

[0021] 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.

[0022] Figure 1 This is a simplified flowchart of the method for evaluating the wrinkle resistance of the bimetallic composite laminate of the present invention. Figure 2 This is a schematic diagram of the copper-aluminum composite plate under uniaxial tensile stress according to an embodiment of the present invention. Figure 3a -c represents the actual stress-strain curves of each layer of the copper-aluminum composite plate in this embodiment of the invention. Figure 4 The following are assembly drawings and actual drawings of the tensile wrinkling test mold according to an embodiment of the present invention; Figure 5 This is a simplified flowchart of the tensile wrinkling test process according to an embodiment of the present invention; Figure 6 A flowchart is established for the composite layup rapid modeling method of this invention. Figure 7a -c is a diagram showing the thickness displacement development process of wedges of different sizes along the path in embodiments of the present invention; Figure 8a-c represents the thickness displacement cloud diagram of specimens of different sizes in the embodiments of the present invention; Figure 9a -e represents the wrinkling morphology feature diagram of copper-aluminum composite plates with different thickness ratios in the embodiments of the present invention; Figure 10a -c is a feature diagram of the wrinkling morphology of the composite plate with different wedge angles of the wedge-shaped part in the embodiment of the present invention; Figure 11a This is a thickness displacement cloud diagram of a copper-aluminum composite plate with a copper content of 15% according to an embodiment of the present invention. Figure 11b -d represents the critical wrinkling strain line on different ridges of the copper-aluminum composite plate with a copper content of 15% in the embodiment of the present invention. Figure 12a -c represents the critical wrinkling strain line of the copper-aluminum composite plate under different thickness ratios in the embodiments of the present invention. Detailed Implementation

[0023] 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.

[0024] like Figures 1 to 12a As shown in -c, the purpose of this invention is to provide a method for evaluating the wrinkle resistance of bimetallic composite plates. Through finite element simulation technology, a qualitative analysis method is adopted, based on wrinkle morphology characteristics, using the number and height of wrinkles as indicators to determine the wrinkle resistance of the composite plate; a quantitative analysis method is adopted, based on the critical wrinkle initiation strain line, comparing the absolute values ​​of the slopes of the critical wrinkle initiation strain line to achieve an accurate evaluation of the wrinkle resistance of the composite plate.

[0025] This invention provides a method for evaluating the wrinkle resistance of bimetallic composite plates, which includes the following steps: S1. Obtain the material parameters of the composite plate, conduct a tensile wrinkling test on the wedge-shaped part under the normal clearance constraint boundary condition, and establish a finite element simulation model. This includes the following sub-steps: S11. Obtain composite plate material parameters: Composite plate material parameters include the hardness of each metal layer, the thickness of each metal layer, and the actual stress-strain curve of each metal layer.

[0026] S12. Based on the composite plate material parameters obtained in step S11, conduct a tensile wrinkling test on the wedge-shaped part, and establish a finite element simulation model based on the experimental results.

[0027] S2. Using qualitative analysis based on wrinkle morphology characteristics, the wrinkle resistance of the composite board is preliminarily determined, specifically including the following sub-steps: S21. First, determine the number of wrinkles in different specimens. If the number of wrinkles in different specimens is the same, proceed to step S22. If the number of wrinkles in different specimens is different, the more wrinkles a specimen has, the worse its wrinkle resistance is.

[0028] S22. When the number of wrinkles in different specimens is the same, the wrinkle height of different specimens is judged: the larger the wrinkle height of a specimen, the worse the wrinkle resistance of the specimen.

[0029] S3. Using quantitative analysis methods, based on the critical wrinkling strain line, the absolute values ​​of the slopes of the critical wrinkling strain lines are compared to further evaluate the wrinkle resistance of the composite board. This includes the following sub-steps: S31. Determine the location of the stress neutral layer in the bimetallic composite plate, specifically including the following sub-steps: S311. Divide the bimetallic composite plate specimen into equal thickness intervals along the thickness direction. The specimen is divided into layers, with one integration point set on each layer. The in-plane normal stress values ​​of each layer's integration point are extracted along the direction perpendicular to the ridges during the entire deformation process. The in-plane normal stress values ​​at any two adjacent integration points at the same moment are compared. The specimen thickness is recorded as... Let the positions of the two adjacent integration points closest to the stress neutral layer along the thickness direction of the bimetallic composite plate be respectively. and ,in .

[0030] S312. When the two nearest adjacent integration points to the stress neutral layer are both located in a certain metal layer and the following conditions are met, the stress neutral layer is determined to be located in the metal layer where the two integration points are located:

[0031] In the formula, , These represent the in-plane normal stresses at the two adjacent integration points closest to the stress neutral layer in the direction perpendicular to the ridge.

[0032] S313. When the two adjacent integration points closest to the stress neutral layer are located in the metal layer and the metallurgical bonding layer respectively, the stress neutral layer is determined to be the metal layer where one of the integration points is located.

[0033] Under normal circumstances, due to the relatively small thickness of the metallurgical bonding layer, it is almost impossible for two adjacent integration points to both be located within the metallurgical bonding layer. In an extreme case, if two adjacent integration points are both located within the metallurgical bonding layer in step S313, then the stress neutral layer is determined to be located within the metallurgical bonding layer. In actual production, this situation almost never occurs.

[0034] After determining the location of the stress neutral layer, in order to ensure that the location of the stress neutral layer is accurate, it is necessary to verify the accuracy of the determined stress neutral layer location to avoid errors in finding the location of the stress neutral layer due to operational mistakes.

[0035] If the stress neutral layer meets the following criteria, the selected stress neutral layer is determined to be the final stress neutral layer; otherwise, return to step S311 to redetermine the position of the stress neutral layer. The specific criteria are as follows: Let the theoretical offset of the stress-neutral layer relative to the geometrically neutral layer at the time of wrinkling be... The thickness of the first metal layer is The thickness of the second metal layer is In any cross-section At this location, the stress on the upper surface of the first metal layer is The stress on the lower surface of the second metal layer is The stress-neutral layer should satisfy the following formula:

[0036] Let the simulated offset of the stress neutral layer relative to the geometric neutral layer be . Theoretical offset With simulated offset The following formula should be satisfied between them: .

[0037] S32. Determine the critical wrinkling moment of the bimetallic composite plate, including the following sub-steps: S321. Divide the metal layer containing the stress neutral layer into equal parts along the thickness direction. Layer, in which It is an odd number, and Each layer is sequentially denoted as , ... , , ... , One integration point is set sequentially on each isolayer, and the first and second principal strains of each integration point are extracted during the entire deformation process. One analysis step is set throughout the entire deformation process, including steps 0, 1, 2... , , ...... At that moment, among which ,Depend on and The bifurcation time of the strain path, jointly determined by the integration points on two sets of symmetrical integration layers, satisfies the following condition:

[0038] In the formula, express and The integration points set on the equal strata are at the th The value of the above expression is first satisfied at time t, i.e., the first time. The time is the bifurcation time of the strain path determined by the two layers, denoted as . ; express The integration point on the same stratum is at the th The first principal strain value corresponding to the given moment; express The integration point on the same stratum is at the th The first principal strain value corresponding to the given moment; express The integration point on the same stratum is at the th The second principal strain value corresponding to the given moment; express The integration point on the same stratum is at the th The second principal strain value corresponding to the time.

[0039] S322, and There are two sets of symmetrical integration layers. , Calculate in sequence , ... , , ... , The strain path bifurcation times determined by the integration points on the same stratum are denoted as follows: , , ...... Based on the calculation results, the bifurcation time of the strain path in the metal layer containing the stress neutral layer is determined. As shown in the following formula:

[0040] In the formula, This indicates the bifurcation point of the strain path in the metal layer containing the stress-neutral layer. Take the integer part; , , ...... Total A number.

[0041] S323. Based on the bifurcation time of the strain path in the metal layer where the stress neutral layer is located. Determine the critical wrinkling moment of the integral bimetallic composite panel The specific formula is as follows:

[0042] In the formula: This indicates the critical wrinkling moment of the overall bimetallic composite panel; This indicates the moment when the strain path of the metal layer containing the stress-neutral layer bifurcates.

[0043] S33. The bifurcation moment of the strain path of the metal layer where the stress neutral layer is located is taken as the critical wrinkling moment of the whole composite plate. The critical wrinkling strain values ​​of different metal layers at the critical wrinkling moment are extracted. The critical wrinkling strain line is generated by fitting based on the critical wrinkling strain value. The absolute value of the slope of the critical wrinkling strain line is compared to evaluate the wrinkle resistance of the composite plate. The larger the absolute value of the slope of the critical wrinkling strain line, the worse the wrinkle resistance.

[0044] 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.

[0045] This embodiment uses a copper-aluminum composite plate, taking a wedge-shaped specimen as an example. The process of this embodiment is as follows: obtain the material parameters of the composite plate, design a tensile wrinkling test of the wedge-shaped specimen under the normal gap constraint boundary condition, establish a finite element model, and compare the test and numerical simulation results to verify the accuracy of the numerical simulation; use qualitative and quantitative analysis methods, based on the wrinkle morphology characteristics and the critical wrinkling strain line, to determine the wrinkle resistance of the composite plate.

[0046] Specifically, it includes the following steps: S1. Obtain the material parameters of the composite plate, conduct a tensile wrinkling test on the wedge-shaped part under the normal gap constraint boundary condition, and establish a finite element simulation model.

[0047] The material parameters of the composite plate include: each metal layer, the thickness and hardness of each metal layer, and the true stress-strain curve of each metal layer. These parameters are obtained as follows: taking the copper-aluminum composite plate as the research object, the stress-strain relationship curve of the entire composite plate is obtained through uniaxial tensile testing. The distribution of hardness along the thickness direction is obtained using microhardness testing, thereby determining the thickness and hardness of the copper layer, the intermediate metallurgical bonding layer, and the aluminum layer of the copper-aluminum composite plate. The stress-strain relationship of each metal layer of the copper-aluminum composite plate is calculated using the mixing principle, providing material properties for the numerical simulation of wrinkling and instability of the copper-aluminum composite plate.

[0048] The stress-strain relationship of each metal layer in a copper-aluminum composite panel is obtained as follows: Figure 2The diagram shows a copper-aluminum composite plate under uniaxial tensile stress in the thickness direction. The stress-strain relationship between the layers is calculated based on the stress conditions shown in the diagram. The calculation process is as follows: In the tensile integral specimen of copper-aluminum composite plate, the total load F satisfies the equation: (1) in, , , , These represent the actual stresses of the overall composite material, the copper layer, the copper-aluminum bonding layer, and the aluminum layer, respectively. , , , These are the cross-sectional areas of the overall composite material, the copper layer, the copper-aluminum bonding layer, and the aluminum layer, respectively, and the relationship between their cross-sectional areas is as follows: (2) Based on the relationship between microhardness and stress in metallic materials, the stress and microhardness of each heterogeneous layer in a heterogeneous metal layered composite plate satisfy the following equation: (3) in, , , These represent the hardness of the aluminum layer, copper layer, and copper-aluminum bonding layer, respectively.

[0049] If we set the ratio in equation (3) to a constant k, then equation (3) can be transformed into: (4) (5) (6) Substituting equations (4), (5), and (6) into equation (1), we get: (7) (8) (9) (10) Assuming that the strain in the tensile direction of each heterogeneous layer of the composite plate remains consistent, the strain of the overall composite material and each heterogeneous layer satisfies the following equation: (11) Based on the overall stress-strain relationship of the composite plate obtained in the experiment and the theoretical calculations (8), (9), and (10), the stress-strain relationships of the copper layer, the intermediate metallurgical layer, and the aluminum layer can be obtained, and stress-strain curves can be prepared. Figure 3a-c is shown. The constitutive equations for each layer of material are shown in Table 1.

[0050] Table 1. Constitutive Equation Parameters for Layered Materials

[0051] Specifically, the tensile wrinkling test is explained in detail using a wedge-shaped component as an example: Among them, the mold assembly and actual mold of the tensile wrinkling test are as follows: Figure 4 As shown, the side of the wedge 1 can slide within the support groove formed between the two support sliders 2. The installation of the wedge 1 in different deformation zones can be adapted by adjusting the angle between the two support sliders 2. A clamp 3 is placed at the support block to restrict the normal movement of the specimen on both sides. The normal direction of the wedge 1 is constrained by a transparent acrylic plate 4, which is transparent to facilitate the measurement of specimen strain data during the experiment. It is connected by three rows of bolts 5 at the top, and the bolts 5 are fixed by nuts 8 and fasteners 9. The gap between the two acrylic plates is controlled by a slender strip 6 located above the bolt holes of the acrylic plate. The gap distance can be adjusted by changing strips of different thicknesses. Since the acrylic plate is not fixedly constrained in the normal direction, it will tilt as the specimen buckles. In order to maintain the consistency of the constraint gap in the deformation zone of the specimen, a normal constraint buckle 7 is designed to fix the buckle 7 on both sides of the wedge angle without obstructing the position of the specimen, thus restricting the tilting behavior of the acrylic plate.

[0052] Figure 5 The process of the tensile wrinkling test is illustrated. First, the pre-fabricated wedge is prepared using electrical discharge machining (EDM), and its beveled cut surface needs to be sanded until it is smooth to the touch. Second, the wedge is painted to create speckle patterns that are easily recognizable by the DIC (Differentiated Injection Control) system. Then, a system calibration process is performed, processing the speckle group images and the calibration plate group images. Next, parameters are set, and a tensile test is conducted to complete the deformation acquisition. Finally, the acquired image data is processed accordingly.

[0053] Specifically, the finite element simulation model establishment method in this embodiment is as follows: Based on the tensile wrinkling test of the wedge-shaped part, the simulation model is established by using ABAQUS software with continuous shell elements and the Composite layup rapid modeling method; the material parameters are set in the attribute module, and the material parameters of each layer of the composite plate obtained from the above experimental and theoretical calculations are input sequentially; the layer thickness, material selection, layup direction, and number of integration points of each layer of the composite plate are set; the mesh is generated, and the SC8R mesh type is selected; the analysis step of the Buckle-dynamic finite element algorithm using continuous shell elements with initial defects is set. The flowchart of the establishment process is as follows: Figure 6 As shown.

[0054] Methods to verify the accuracy of finite element simulations: Extract the thickness displacement development path of wedges of different sizes along the path, such as... Figure 7a As shown in -c, the thickness displacement variation curves of the measurement path at different times are compared to the consistency between the simulation results and the experiment of the wrinkle derivation process. Thickness displacement contour maps are extracted from the experimental and simulation results, as shown below. Figure 8a As shown in -c, further comparisons are made to prove that the simulation can accurately reflect the real results of the experiment.

[0055] exist Figure 7a -c and Figure 8a In -c, For thickness, The vertical distance of the deformation zone. For the wedge angle of the wedge-shaped part, This represents the percentage of copper layer.

[0056] S2. Qualitative analysis was used to make a preliminary judgment on the wrinkle resistance of the composite board based on the wrinkle morphology characteristics.

[0057] The wrinkling morphology features mainly consist of a thickness displacement contour map and a thickness displacement variation curve along the path. The specific extraction method is as follows: Based on different working conditions and the specific characteristics of the specimen, the line connecting the points with the maximum wrinkle height in the thickness displacement contour map of the simulation results is taken as the geometric path. A thickness displacement variation curve along the selected geometric path is then output, with the horizontal axis representing the geometric distance of the specimen and the vertical axis representing the wrinkle height. This allows for the accurate acquisition of the number and height of wrinkles. Furthermore, the thickness displacement contour map can be directly output after the numerical simulation is completed.

[0058] S21. First, determine the number of wrinkles in different specimens. If the number of wrinkles is the same in different specimens, proceed to step S22; if the number of wrinkles is different in different specimens, the more wrinkles a specimen has, the worse its wrinkle resistance. For the tensile wrinkling model of a wedge-shaped part under normal constraint boundary conditions, based on the wrinkle formation characteristics, from... Figure 7a The thickness displacement development diagram along the path for wedges of different sizes shows the overall wrinkle generation process: wrinkles always originate in the middle of the wedge. Due to the constraints of the normal boundary conditions, when the wrinkles reach the height of the normal gap constraint, their growth in the height direction stops, and they gradually extend to both sides to generate new wrinkles. Therefore, when other external conditions remain unchanged, the more wrinkles on the sheet, the earlier the first wrinkle in the middle is generated, that is, the earlier the overall critical moment of the wedge, and the worse its wrinkle resistance. When the number of wrinkles is the same, the higher the wrinkle height, the stronger the overall instability of the wedge, and the weaker its wrinkle resistance.

[0059] S22. When the number of wrinkles in different specimens is the same, the wrinkle height of different specimens is judged: the larger the wrinkle height of a specimen, the worse the wrinkle resistance of the specimen.

[0060] For wedge-shaped specimens, their wrinkle resistance can also be judged by the wedge angle. When the wrinkle height of different specimens is equal, the wedge angle of the wedge-shaped specimens of different specimens is judged: the larger the wedge angle value of the wedge-shaped specimen, the worse the wrinkle resistance of the specimen.

[0061] Example 1 Taking copper-aluminum composite panels with copper layer proportions of 10%, 15%, 30%, 65%, and 80% as examples, this study explores the influence of the composite panel thickness ratio on its anti-wrinkle performance based on wrinkle morphology characteristics.

[0062] like Figure 9a -e shows the wrinkling morphology characteristics of copper-aluminum composite panels with different thickness ratios. Based on numerical simulation results, wrinkling morphology characteristics of copper-aluminum composite panels with different thickness ratios were established. By comparing the differences in wrinkling morphology characteristics, the following conclusions were drawn: The wrinkle resistance of bimetallic composite panels lies between that of base metal (which accounts for a larger proportion) and cladding metal (which accounts for a smaller proportion) single-layer panels. When the base metal in the composite panel is a metal with relatively low hardness, the overall wrinkle resistance of the composite panel is close to that of the base metal. Furthermore, within a certain range, increasing the proportion of cladding metal (increasing the proportion of harder metal) increases the number of wrinkles in the composite panel, or, at a certain number, increases the wrinkle height, thus reducing the wrinkle resistance.

[0063] Example 2 Taking copper-aluminum composite plates with wedge angles of 45°, 55°, and 75° as examples, this study verifies the influence of specimen geometric dimensions, represented by different wedge angles, on wrinkle resistance based on wrinkle morphology characteristics.

[0064] like Figure 10a The wrinkling morphology characteristics of composite plates with different wedge angles (-c) show that, under the same downward displacement and normal clearance, the wrinkle height remains basically consistent at approximately 2.5 mm as the wedge angle changes. The difference lies in the number of wrinkles. At a wedge angle of 45°, there are 5 wrinkles; at 55°, there are 4; and at 75°, there are 3. According to the evaluation index for wrinkle resistance, the more wrinkles a plate has, the worse its wrinkle resistance. Therefore, under the same conditions, the wedge with a 45° angle has the worst wrinkle resistance, followed by the 55° angle, and the 75° angle has the strongest wrinkle resistance.

[0065] Therefore, as can be seen from this embodiment, the change in the wedge angle will affect the wrinkle resistance of the specimen. Within a certain range, the larger the wedge angle, the fewer the wrinkles and the stronger the wrinkle resistance.

[0066] S3. To more accurately evaluate the wrinkle resistance of the composite board, a quantitative analysis method is further adopted. Based on the critical wrinkle initiation strain line, the absolute values ​​of the slopes of the critical wrinkle initiation strain lines are compared to further evaluate the wrinkle resistance of the composite board. This includes the following sub-steps: S31. Determine the location of the stress neutral layer in the bimetallic composite plate, specifically including the following sub-steps: S311. Divide the bimetallic composite plate specimen into k layers with equal thickness intervals along the thickness direction. Set one integration point on each layer. Extract the in-plane normal stress data of each layer's integration point during the entire deformation process in the direction perpendicular to the ridges. Compare the in-plane normal stress values ​​at any two adjacent integration points at the same time. Record the specimen thickness as... Let the positions of the two adjacent integration points closest to the stress neutral layer along the thickness direction of the bimetallic composite plate be denoted as . and ( ).

[0067] S312. When the two nearest adjacent integration points to the stress neutral layer are both located in the metal layer and the following conditions are met, the stress neutral layer is determined to be located in the metal layer where the two integration points are located:

[0068] In the formula, , These represent the in-plane normal stresses at the two adjacent integration points closest to the stress neutral layer in the direction perpendicular to the ridge.

[0069] S313. When the two adjacent integration points closest to the stress neutral layer are located in the metal layer and the metallurgical bonding layer respectively, it is determined that the stress neutral layer is in the metal layer.

[0070] In this embodiment, the two adjacent integration points closest to the stress neutral layer are both located in the metal layer, and the stress neutral layer is located in the metal layer where the two integration points are located. After verification, the position of the stress neutral layer is accurate.

[0071] S32. Determine the critical wrinkling moment of the bimetallic composite plate, including the following sub-steps: S321. Divide the metal layer containing the stress neutral layer into equal parts along the thickness direction. Layer, in which It is an odd number, and Each layer is sequentially denoted as , ... , , ... , One integration point is set sequentially on each isolayer, and the first and second principal strains of each integration point are extracted during the entire deformation process. One analysis step is set throughout the entire deformation process, including steps 0, 1, 2... , , ...... At any moment ( ),Depend on and The bifurcation time of the strain path, jointly determined by the integration points on two sets of symmetrical integration layers, satisfies the following condition:

[0072] In the formula, express and The integration points set on the equal strata are at the th The value of the above expression is first satisfied at time t, i.e., the first time. The time is the bifurcation time of the strain path determined by these two layers, denoted as . If there are still integration points that satisfy the above equation, then the buckling stage has already begun, rather than the critical buckling moment. express The integration point on the same layer is at the th The first principal strain value corresponding to the given moment; express The integration point on the same layer is at the th The first principal strain value corresponding to the given moment; express The second principal strain value corresponding to the integration point on the stratified layer at time r; express The second principal strain value corresponding to the integration point on the stratified layer at time r.

[0073] S322, and There are two sets of symmetrical integration layers. , Calculate in sequence and , and , and ...... and The bifurcation time determined by the integration points on the same layer is denoted as . , , ...... Based on the calculation results, the bifurcation time of the strain path in the metal layer containing the stress neutral layer is determined, as shown in the following formula:

[0074] In the formula, This indicates the bifurcation point of the strain path in the metal layer containing the stress-neutral layer. Take the integer part; , , ...... There are a total A number, that is for Quantity, equal .

[0075] S323. Based on the bifurcation time of the strain path in the metal layer where the stress neutral layer is located. Determine the critical wrinkling moment of the integral bimetallic composite panel The details are as follows:

[0076] In the formula: This indicates the critical wrinkling moment of the overall bimetallic composite panel; Indicates the moment when the strain path of the metal layer containing the stress neutral layer bifurcates; S32. Based on the fitting of the critical wrinkling strain value, a critical wrinkling strain line is generated. The absolute values ​​of the slopes of the critical wrinkling strain lines are compared to evaluate the wrinkle resistance of the composite board.

[0077] The specific method for determining the wrinkle resistance of composite plates based on the critical wrinkling strain line in this embodiment is as follows: Figure 11b The critical wrinkling strain lines on different ridges of a copper-aluminum composite plate with a copper content of 15% are shown in the figure. The example is a copper-aluminum composite plate with a copper layer content of 15%, an overall thickness of 1 mm, and a wedge deformation zone height of 48 mm.

[0078] Based on the order of wrinkle formation, the different wrinkle ridges are named path a, path b, and path c, with path a forming first and path c forming last. For different wrinkles, the later the critical wrinkling moment, the stronger the wrinkle resistance. Therefore, the wrinkle resistance performance of different parts of the wedge can be ranked as follows: path c > path b > path a. Figure 11b As can be seen from -d, the critical wrinkling strain values ​​of the copper and aluminum layers are different at different paths, but they are linearly distributed and have high fitting accuracy.

[0079] The slope of the critical wrinkling strain line at path a is -0.491, the slope of the critical wrinkling strain line at path b is -0.474, and the slope of the critical wrinkling strain line at path c is -0.436. The order of their absolute slope values ​​is as follows: Based on the known development sequence of wrinkles, the wrinkle resistance of different parts of the wedge-shaped component is ranked as follows: path c > path b > path a. The smaller the absolute value of the slope of the critical wrinkle initiation strain line, the stronger the wrinkle resistance of the sheet material.

[0080] Specifically, qualitative and quantitative analyses of the wrinkle resistance criteria for composite panels are used, and the two are compared and verified to achieve an accurate assessment of the wrinkle resistance performance of the composite panels. The specific implementation details are as follows: Taking copper-aluminum composite panels with copper layer proportions of 10%, 15%, and 30% as examples, this will be explained. Figure 12a The critical wrinkling strain lines of copper-aluminum composite plates with different thickness ratios are shown in Figure -c. The critical wrinkling strain values ​​for different thickness ratios can all be fitted to a straight line approximately passing through the origin. On the same wrinkle ridge, the ratio of the first principal strain to the second principal strain is approximately equal. The difference lies in the slope of the critical wrinkling strain lines for different thickness ratios. Observation reveals that... It can be seen that the copper-aluminum composite plate with a copper layer content of 10% has the strongest wrinkle resistance, while the copper-aluminum composite plate with a copper layer content of 30% has the weakest wrinkle resistance. This conclusion is consistent with the results of wrinkle resistance performance judgment based on wrinkle morphology, further proving that there is a correlation between the critical wrinkle initiation strain line and wrinkle resistance; the smaller the absolute value of the slope of the critical wrinkle initiation strain line, the stronger the wrinkle resistance.

[0081] The embodiments in this specification employ a wedge-shaped tensile wrinkling test with complex boundary conditions during the forming process. This test can reflect the wrinkling behavior under the mold's covering during actual forming. Furthermore, the wedge-shaped tensile test can clearly reflect the characteristics of sheet metal instability in terms of wrinkle morphology and wrinkle quantity. It is more applicable to specimens with simpler boundary conditions during forming and has significant guiding significance for composite panel forming.

[0082] The embodiments described above are merely preferred embodiments of the present invention and are not intended to limit the scope of the present invention. Various modifications and improvements made by those skilled in the art to the technical solutions of the present invention without departing from the spirit of the present invention should fall within the protection scope defined by the claims of the present invention.

Claims

1. A method for evaluating the wrinkle resistance of bimetallic composite plates, characterized in that: It includes the following steps: S1. Prepare multiple bimetallic composite plate specimens and obtain the wrinkle morphology characteristics of multiple bimetallic composite plate specimens; S2. Based on the wrinkle morphology characteristics, obtain the number and height of wrinkles, and use qualitative analysis to preliminarily determine the wrinkle resistance of the composite board. This includes the following sub-steps: S21. First, determine the number of wrinkles in different specimens. If the number of wrinkles in different specimens is the same, proceed to step S22. If the number of wrinkles in different specimens is different, the more wrinkles a specimen has, the worse its wrinkle resistance is. S22. When the number of wrinkles in different specimens is the same, the wrinkle height of different specimens is judged: the larger the wrinkle height of a specimen, the worse the wrinkle resistance of the specimen. S3. Using quantitative analysis based on the critical wrinkling strain line, the absolute values ​​of the slopes of the critical wrinkling strain line are compared to further evaluate the wrinkle resistance of the bimetallic composite plate. This includes the following sub-steps: S31. Determine the location of the stress neutral layer in the bimetallic composite plate, which includes the following sub-steps: S311. Divide the bimetallic composite plate specimen into equal thickness intervals along the thickness direction. The specimen is divided into layers, with one integration point set on each layer. The in-plane normal stress values ​​of each layer's integration point are extracted along the direction perpendicular to the ridges during the entire deformation process. The in-plane normal stress values ​​at any two adjacent integration points at the same moment are compared. The specimen thickness is recorded as... Let the positions of the two adjacent integration points closest to the stress neutral layer along the thickness direction of the bimetallic composite plate be respectively. and ,in ; S312. When the two nearest adjacent integration points to the stress neutral layer are both located in a certain metal layer and the following conditions are met, the stress neutral layer is determined to be located in the metal layer where the two integration points are located: In the formula, , These represent the in-plane normal stresses at the two adjacent integration points closest to the stress neutral layer in the direction perpendicular to the ridge; S313. When the two adjacent integration points closest to the stress neutral layer are located in the metal layer and the metallurgical bonding layer respectively, the stress neutral layer is determined to be the metal layer where one of the integration points is located. S314. Verify the accuracy of the determined stress neutral layer. If the stress neutral layer meets the following judgment conditions, the selected stress neutral layer is determined as the final stress neutral layer; otherwise, return to step S311 to redetermine the position of the stress neutral layer. The judgment conditions are specifically stated as follows: Let the theoretical offset of the stress-neutral layer relative to the geometrically neutral layer at the time of wrinkling be... The thickness of the first metal layer is The thickness of the second metal layer is In any cross-section At this location, the stress on the upper surface of the first metal layer is The stress on the lower surface of the second metal layer is The stress-neutral layer should satisfy the following formula: Let the simulated offset of the stress neutral layer relative to the geometric neutral layer be . Theoretical offset With simulated offset The following formula should be satisfied between them: ； S32. Determine the critical wrinkling moment of the bimetallic composite plate, including the following sub-steps: S321. Divide the metal layer containing the stress neutral layer into v layers along the thickness direction, where v is an odd number, and Each layer is sequentially denoted as , ... , , ... , One integration point is set sequentially on each isolayer, and the first and second principal strains of each integration point are extracted during the entire deformation process. One analysis step is set throughout the entire deformation process, including steps 0, 1, 2... , , ...... At that moment, among which ,Depend on and The bifurcation time of the strain path, jointly determined by the integration points on two sets of symmetrical integration layers, satisfies the following condition: In the formula, express and The integration points set on the equal strata are at the th The value of the above expression is first satisfied at time t, i.e., the first time. The time is the bifurcation time of the strain path determined by the two layers, denoted as . ; express The integration point on the same stratum is at the th The first principal strain value corresponding to the given moment; express The integration point on the same stratum is at the th The first principal strain value corresponding to the given moment; express The integration point on the same stratum is at the th The second principal strain value corresponding to the given moment; express The integration point on the same stratum is at the th The second principal strain value corresponding to the given moment; S322, and There are two sets of symmetrical integration layers. , Calculate in sequence and , and , and ...... and The strain path bifurcation times determined by the integration points on the same stratum are denoted as follows: , , ...... Based on the calculation results, the bifurcation time T of the strain path in the metal layer containing the stress neutral layer is determined as follows: In the formula, This indicates the bifurcation point of the strain path in the metal layer containing the stress-neutral layer. Take the integer part; , , ...... Total A number; S323. Based on the bifurcation time of the strain path in the metal layer where the stress neutral layer is located. Determine the critical wrinkling moment of the integral bimetallic composite panel The specific formula is as follows: In the formula: This indicates the critical wrinkling moment of the overall bimetallic composite panel; Indicates the moment when the strain path of the metal layer containing the stress neutral layer bifurcates; S33. Extract the critical wrinkling strain values ​​of different metal layers at the critical wrinkling moment, and generate a critical wrinkling strain line based on the critical wrinkling strain value. Compare the absolute values ​​of the slopes of the critical wrinkling strain lines to evaluate the wrinkle resistance of the composite plate. The larger the absolute value of the slope of the critical wrinkling strain line, the worse the wrinkle resistance.

2. The method for evaluating the wrinkle resistance of bimetallic composite plates according to claim 1, characterized in that: The bimetallic composite plate includes a first metal layer, a second metal layer, and a metallurgical bonding layer at the junction of the first metal layer and the second metal layer.

3. The method for evaluating the wrinkle resistance of bimetallic composite plates according to claim 1, characterized in that: In step S1, the wrinkle morphology characteristics of the composite plate specimen are obtained through a finite element simulation model. The input data of the finite element simulation model includes the thickness and hardness of each metal layer and the metallurgical bonding layer, as well as the stress-strain relationship of each metal layer and the metallurgical bonding layer.

4. The method for evaluating the wrinkle resistance of bimetallic composite plates according to claim 3, characterized in that: The methods for determining the thickness and hardness of each metal layer and the metallurgical bonding layer are as follows: The distribution of hardness along the thickness direction is obtained by using microhardness testing to determine the thickness and hardness of the first metal layer, the metallurgical bonding layer and the second metal layer of the composite plate.

5. The method for evaluating the wrinkle resistance of bimetallic composite plates according to claim 1, characterized in that: In step S313, if two adjacent integration points are both located in the metallurgical bonding layer, then the stress neutral layer is determined to be located in the metallurgical bonding layer.

6. The method for evaluating the wrinkle resistance of bimetallic composite plates according to claim 1, characterized in that: The specific method for obtaining the number and height of wrinkles based on wrinkle morphology features in step S2 is as follows: The wrinkle morphology features in the simulation results of the finite element model are extracted. The wrinkle morphology features include the thickness displacement cloud map and the thickness displacement variation curve along the predetermined path. The number and height of wrinkles are analyzed by the thickness displacement cloud map and the thickness displacement variation curve along the predetermined path.

7. The method for evaluating the wrinkle resistance of bimetallic composite plates according to claim 6, characterized in that: The specific method for analyzing the number and height of wrinkles using thickness displacement cloud maps and thickness displacement variation curves along a predetermined path is as follows: The line connecting the points where the maximum wrinkle height is located in the thickness displacement cloud map of the simulation results is taken as the geometric path. The thickness displacement variation curve along the selected geometric path is output. The horizontal axis of the thickness displacement variation curve is the geometric distance of the specimen, and the vertical axis is the wrinkle height, thus obtaining the accurate number and height of wrinkles.

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