Apparatus and method for electromagnetic force driven biaxial tensile test of sheet

Abstract

The present application belongs to the technical field of plate tensile test, and particularly relates to a device and method for electromagnetic force driven biaxial tensile limit test of thin plate, which comprises a base plate, an asymmetrically shaped coil arranged on the top of the base plate, a power supply unit electrically connected with the asymmetrically shaped coil, and a strain measurement system, wherein a detachably connected pressing plate is arranged on the base plate, the pressing plate is provided with hole one and hole two, and the hole one and the hole two are both located above the speckle area of the sample; the area where a part of the asymmetrically shaped coil is located is the center measurement area, and the area where the other part is located is the bulging deformation area; the strain measurement system comprises a movable strain shooting camera and / or a movable stress shooting camera; the hole one is used for the light source of the strain shooting camera and / or the stress shooting camera to pass through so as to measure the strain, and the hole two corresponds to the bulging deformation area; the implementation of more high-speed complex loading ratio is met, and the limit test of the sample multiple strain path is realized.

Description

Technical Field

[0001] This invention belongs to the field of sheet metal tensile testing technology, specifically relating to a device and method for performing biaxial tensile limit testing on thin sheets driven by electromagnetic force. Background Technology

[0002] Lightweight alloys, primarily aluminum alloys, are widely used in aerospace, transportation, and other fields due to their excellent properties. Under current development trends, higher demands are being placed on processing technology and forming performance. High-speed forming technology is poised for significant development due to its ability to improve the forming performance of aluminum alloys. Therefore, constructing high-speed constitutive models to comprehensively characterize and test the mechanical properties of materials under high-speed loading is crucial.

[0003] Meanwhile, the high cost and long cycle of a single test restrict the development of high-speed testing equipment. The limited range of dynamic testing equipment and strain paths restricts the evaluation of material forming properties under high-speed and complex processes. Achieving tensile limits for multiaxial test specimens is a current technical challenge in the field of high-speed testing. Summary of the Invention

[0004] The technical problem to be solved by the present invention is to provide an apparatus and method for biaxial tensile limit testing of thin plates driven by electromagnetic force, which can meet the requirements of more high-speed and complex loading ratios and realize the limit test of multiple strain paths of the specimen.

[0005] This invention provides a device for performing biaxial tensile limit testing on a thin plate using electromagnetic force, comprising: A substrate, on which a detachably connected pressure plate is provided, the pressure plate having a hole one and a hole two, both of which are located above the sample bulging area and speckle area; An asymmetric loop coil is disposed on the top of the substrate. A portion of the asymmetric loop coil is located in the central measurement area, and the other portion is located in the expansion deformation area. The power supply unit electrically connected to the asymmetric loop coil; and A strain measurement system, comprising a movable strain imaging camera and / or a movable stress imaging camera; the first aperture corresponds to the bulging deformation zone, and the second aperture is for the light source of the strain imaging camera and / or stress imaging camera to pass through for strain measurement.

[0006] Optionally, the asymmetric loop coil is a two-turn coil.

[0007] Optionally, the device further includes a positive and negative electrode busbar rigidly connected to the bottom of the substrate, the positive and negative electrode busbar being electrically connected to the power supply unit, and the asymmetric loop coil being electrically connected to the positive and negative electrode busbar.

[0008] Optionally, the substrate is provided with multiple positioning marks for precise positioning of the sample, which facilitates the realization of various extreme loading ratios.

[0009] Optionally, the first hole is a square hole, and the second hole is a wedge-shaped hole.

[0010] Optionally, the asymmetric loop coil is embedded within the substrate; or The asymmetric loop coil is disposed within the base, which is embedded within the substrate and fixed by screws.

[0011] Optionally, the strain measurement system further includes a planar drive mechanism and a mounting bracket. The planar drive mechanism is mounted on a tripod and located above the pressure plate, and the strain imaging camera and / or stress imaging camera are mounted on the planar drive mechanism.

[0012] Optionally, the power supply unit includes a charging circuit and a discharging circuit. The charging circuit boosts and rectifies the electrical energy and stores it in the discharging circuit, which provides power to the asymmetric loop coil.

[0013] This invention also provides a method for testing the biaxial tensile limit of a thin metal sheet driven by electromagnetic force, comprising the following steps: S1. Prepare a standard biaxial tensile specimen and spray speckle pattern onto the shooting area; S2. Fix the sample between the substrate and the pressure plate; S3. Design test schemes. In order to construct the high-speed forming limit diagram, several test schemes with loading ratios of 1:1, 1:2, 1:4, 3:4, 4:3, 4:1 and 2:1 were carried out. By translating the sample placed in the discharge test area up and down, different lever arm lengths were obtained. Different loading ratios were achieved by the difference in plastic strain wave propagation. The S4 strain imaging camera and / or stress imaging camera will be translated and adjusted in different loading ratio tests, and further fine-tuned to ensure that the field of view is directly facing the central speckle area and to ensure image clarity. S5. The power supply unit discharges to the asymmetric loop coil, which generates an electromagnetic force that acts on the sample. The sample expands rapidly in the sample area under the influence of the electromagnetic force. At the same time, the strain measurement system records the deformation process that occurs in the speckle area of ​​the tensile sample. S6. The strain measurement system transmits the captured photos to the strain data analysis device, which processes the experimental data to obtain the engineering strain in the central region of the specimen during the tensile process. S7. Using the above-mentioned sample, coil tooling, and forming limit measurement scheme, the high-speed forming limit of the material is realized by using different biaxial loading ratios, and a high-speed forming limit diagram is constructed.

[0014] Optionally, the central region of the sample is thinned in a fan shape, and speckled coating is sprayed onto this central region.

[0015] The beneficial effects of this invention are that the device for biaxial tensile limit testing of thin plates driven by electromagnetic force provided by this invention utilizes the electromagnetic force generated by the energization of an asymmetric loop coil to drive the sample to expand at high speed in the expansion deformation zone. Due to the clamping and limiting effect of the substrate and the pressure plate, the part of the sample located in the central measurement area undergoes planar tensile motion. The biaxial tensile test and strain path change of the sample are realized through the asymmetric loop coil. Furthermore, the strain measurement system monitors and analyzes the data of the tensile process in real time to obtain the engineering strain of the central measurement area of ​​the sample during the tensile process. By cooperating with the substrate and the pressure plate, and by adjusting the position of the sample on the substrate, the limit test of the sample under various loading ratios can be realized, which meets the evaluation of material forming performance under high-speed and complex processes. Attached Figure Description

[0016] Figure 1 A partial three-dimensional structural schematic diagram of the device provided by the present invention; Figure 2 A schematic diagram of the working principle of the device provided by the present invention; Figure 3 This is a schematic diagram showing the placement of samples at different loading ratios provided by the present invention.

[0017] In the figure: 10, substrate; 11, pressure plate; 111, hole one; 112, hole two; 12, screw; 20, asymmetric loop coil; 31, charging circuit; 32, discharging circuit; 40, strain measurement system; 41, strain imaging camera; 42, stress imaging camera; 43, planar drive mechanism; 5, sample. Detailed Implementation

[0018] like Figure 1-3 As shown, the present invention provides an apparatus for biaxial tensile limit testing of a thin plate driven by electromagnetic force, comprising: a substrate 10, an asymmetric loop coil 20 disposed on the top of the substrate 10, a power supply unit electrically connected to the asymmetric loop coil 20, and a strain measurement system 40. A detachably connected pressure plate 11 is disposed on the substrate 10. The pressure plate 11 has a first hole 111 and a second hole 112, which are located above the bulging area and speckle area of ​​the sample 5. The working area of ​​the asymmetric loop coil 20 is the bulging deformation area, which is transmitted by plastic stress waves and acts on the central area. The strain measurement system 40 includes a movable strain imaging camera 41 and / or a movable stress imaging camera 42. The first hole 111 corresponds to the bulging deformation area, and the second hole 112 is used for the light source of the strain imaging camera 41 and / or the stress imaging camera 42 to pass through for strain measurement.

[0019] Compared with the prior art, the device for biaxial tensile limit testing of thin plates driven by electromagnetic force provided by the present invention utilizes the electromagnetic force generated by the energization of the asymmetric loop coil 20 to drive the sample 5 to expand at high speed in the expansion deformation zone. Due to the clamping and limiting effect of the substrate 10 and the pressure plate 11, the sample 5 is located in the central measurement area and undergoes planar tensile motion. The asymmetric loop coil 20 realizes the biaxial strain path stretching of the sample 5, and the strain measurement system 40 monitors and analyzes the data of the stretching process in real time to obtain the engineering strain of the central measurement area of ​​the sample 5 during the stretching process. By cooperating with the substrate 10 and the pressure plate 11, and by adjusting the position of the sample 5 on the substrate 10, the sample 5 can be subjected to multi-load ratio limit testing, which meets the evaluation of material forming performance under high-speed and complex processes.

[0020] In one embodiment, the asymmetric loop coil 20 is a two-turn coil. Specifically, the coil is divided into a test area (high-speed expansion area) and a non-test area. The test area consists of two narrow, side-by-side coils. A toroidal double-turn coil design is adopted, with a 3mm distance between the two working coils to improve discharge concentration and efficiency. The test area has a narrower coil width, while the non-test area has a wider width; this design reduces coil resistance and improves overall efficiency. The width of a single coil in the test area is 4mm, while the coil width in the non-test area ranges from 25mm to 60mm based on the overall arrangement.

[0021] In this embodiment, the device also includes positive and negative electrode busbars rigidly connected to the bottom of the substrate 10. The positive and negative electrode busbars are electrically connected to the power supply unit, and the asymmetric loop coil 20 is electrically connected to the positive and negative electrode busbars. Specifically, there are fastening screws below the busbar access points. The positive and negative electrode busbars are fastened to the pressure plate 11 by these 12 screws. This upper and lower gap arrangement can ensure the safety of the discharge circuit, avoid arcing, and ensure the normal operation of the entire device during the discharge process.

[0022] In this embodiment, the substrate 10 is provided with multiple positioning marks for precise positioning of the sample 5, which facilitates the realization of various extreme loading ratios. Specifically, the multiple positioning marks are distributed in a planar coordinate system within the corresponding asymmetric loop 20 area on the substrate 10. The positioning marks can be formed by opening layer holes on the substrate 10 or by laser marking. At least two positioning marks are a pair, so multiple pairs of positioning marks indicate extreme test loading ratios of 1:1, 1:2, 1:4, 3:4, 4:3, 4:1, and 2:1 on the substrate 10.

[0023] In this embodiment, hole 111 is a square hole, and hole 112 is a wedge-shaped hole. The wedge-shaped hole 112 is located above the center of the sample 5. The center of the sample 5 is a key part of the test. Under high-speed test conditions, the light source is easily affected by the high-speed shock wave. In order to avoid affecting the light, a wedge-shaped hole is used to allow the light to be better guided into the center of the sample 5, so as to obtain the real-time strain and forming limit of the central region under high-speed loading conditions.

[0024] In one embodiment, the asymmetric loop coil 20 is embedded in the substrate 10. Specifically, corresponding guide grooves and through holes (not shown in the figure) are formed on the surface of the substrate 10 according to the designed shape of the asymmetric loop coil 20. The asymmetric loop coil 20 is fixed in the guide groove, and the two ends of the asymmetric loop coil 20 pass through the through holes and are respectively connected to the positive and negative terminals of the positive and negative poles. In this way, the number of components can be reduced and the cost can be reduced.

[0025] In another embodiment, the asymmetric loop coil 20 is disposed within a base, which is embedded in the substrate 10 and fixed by screws 12. Specifically, a groove (not shown) is machined in the middle of the substrate 10, and corresponding through holes (not shown) are formed. Corresponding guide grooves and through holes (not shown) are formed on the surface of the base according to the designed shape of the asymmetric loop coil 20. The asymmetric loop coil 20 is fixed in the guide groove, and the base is embedded in the groove of the substrate 10 and fixed by bolts. The two ends of the asymmetric loop coil 20 pass through the through holes on the base and the substrate 10 and are respectively connected to the positive and negative terminals of the positive and negative poles. In this way, bases with coils of various shapes are prepared in advance to match the poles and meet more testing requirements.

[0026] Of course, the groove can penetrate the substrate 10, and the edge of the groove forms a stepped structure for mounting the base and fixing it with bolts, so the positive and negative electrode lines can be fastened to the base with bolts.

[0027] In this embodiment, the strain measurement system 40 further includes a planar drive mechanism 43 and a mounting bracket. The planar drive mechanism 43 is mounted on a tripod and located above the pressure plate 11. The strain imaging camera 41 and / or the stress imaging camera 42 are mounted on the planar drive mechanism 43.

[0028] Specifically, the mounting frame can be a gantry frame, and the planar drive mechanism 43 is located above the pressure plate 11. The planar drive mechanism 43 consists of two stacked motor screws, and the driving directions of the two motor screws are perpendicular to each other. The motor screw closest to the pressure plate 11 is connected to a mounting plate, and the mounting plate is equipped with corresponding guide rails. The strain imaging camera 41 and / or stress imaging camera 42 are rigidly connected to the side of the mounting plate facing the pressure plate 11, thereby realizing the planar position adjustment of the strain imaging camera 41 and stress imaging camera 42 to more accurately record the tensile deformation process of the sample 5.

[0029] The power supply unit includes a charging circuit 31 and a discharging circuit 32. The charging circuit 31 boosts and rectifies the electrical energy, then stores it in the discharging circuit 32, which provides power to the asymmetric loop coil 20. The main components of the charging circuit 31 are capacitors. Several capacitors are connected in parallel and embedded in the electromagnetic pulse host to complete the charging process. Then, the multiple capacitors discharge synchronously, and the pulse current flows into the coil tool instantaneously, generating a strong electromagnetic force to complete the process.

[0030] This invention provides a method for testing the biaxial tensile limit of thin metal plates driven by electromagnetic force, comprising the following steps: S1. Prepare a standard biaxial tensile specimen 5 and spray speckle pattern on the shooting area; S2. Fix the sample 5 between the substrate 10 and the pressure plate 11; S3. Design experimental schemes: To construct a high-speed forming limit diagram, several experimental schemes were conducted with biaxial loading ratios of x:y = 1:1, 1:2, 1:4, 3:4, 4:3, 4:1, and 2:1. By translating the sample 5 placed in the discharge test area vertically, different lever arm lengths were obtained. Different loading ratios were achieved through the differences in plastic strain wave propagation. Specifically, the vertical translation of sample 5 was carried out within a narrow coil segment with high concentration. Different loading ratios were achieved by the length ratio of the lever arm ends of sample 5. Among them, a 1:1 loading ratio can be achieved after electromagnetic discharge, that is, a biaxial tensile strain path can be obtained. Similarly, when the lever arm length ratio is 1:2, 1:4, 2:1, or 4:1, the material will undergo a high-speed deformation process from biaxial to plane strain.

[0031] The S4 strain imaging camera 41 and / or stress imaging camera 42 will be translated and adjusted in different loading ratio tests, and further fine-tuned to ensure that the field of view is directly facing the central speckle area and to ensure that the image is clear. S5. The power supply unit discharges to the asymmetric loop coil 20. The asymmetric loop coil 20 generates an electromagnetic force that acts on the sample 5. The sample 5 is affected by the electromagnetic force and expands rapidly in the sample 5 region. At the same time, the strain measurement system 40 records the deformation process that occurs in the speckle region of the tensile sample 5. S6. The strain measurement system 40 transmits the captured photos to the strain data analysis device, which processes the experimental data to obtain the engineering strain of the central region of the specimen 5 during the tensile process. S7. Using the above-mentioned sample 5, coil tooling, and forming limit measurement scheme, the material high-speed forming limit is realized by using different biaxial loading ratios, and a high-speed forming limit diagram is constructed.

[0032] Optionally, the central region of the sample 5 is thinned in a fan shape, and a speckle pattern is sprayed onto this central region. Extensive prior experiments have demonstrated that the fan-shaped thinning shape concentrates strain in the central region, facilitating strain acquisition using a high-speed DIC (Digital Interference Catalyst) and ensuring that fracture occurs at the central location, enabling the entire measurement system to accurately capture the forming limit. Furthermore, due to the small size of the central region, a speckle pattern is used to ensure effective identification of the strain measurement data.

[0033] Those skilled in the art should understand that the discussion of any of the above embodiments is merely exemplary and is not intended to imply that the scope of protection of this application is limited to these examples; within the framework of this application, the technical features of the above embodiments or different embodiments can also be combined, the steps can be implemented in any order, and there are many other variations of different aspects of one or more embodiments of this application as described above, which are not provided in detail for the sake of brevity.

[0034] One or more embodiments in this application are intended to cover all such substitutions, modifications, and variations that fall within the broad scope of this application. Therefore, any omissions, modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of one or more embodiments in this application should be included within the protection scope of this application.

Claims

1. A method for biaxial tensile limit testing of a thin plate driven by electromagnetic force, characterized in that, The device is used to perform biaxial tensile limit testing on thin plates using electromagnetic force. The device includes: The substrate (10) is provided with a detachably connected pressure plate (11), the pressure plate (11) is provided with a hole one (111) and a hole two (112), the hole one (111) and the hole two (112) are respectively located above the bulging deformation area and the central speckle area of ​​the sample (5); An asymmetric loop coil (20) is disposed on the top of the substrate (10), the asymmetric loop coil (20) acts on the bulging deformation area; a power supply unit is electrically connected to the asymmetric loop coil (20); And a strain measurement system (40), the strain measurement system (40) including a movable strain imaging camera (41) and / or a movable stress imaging camera (42); the first hole (111) corresponds to the bulging deformation area, the second hole (112) corresponds to the central measurement area, and the light source of the strain imaging camera (41) and / or the stress imaging camera (42) passes through for strain measurement; The testing method includes the following steps: S1. Prepare a standard biaxial tensile specimen (5) and spray speckle pattern on the shooting area; S2. Fix the sample (5) between the substrate (10) and the pressure plate (11); S3. Design test schemes. In order to construct the high-speed forming limit diagram, carry out several test schemes with loading ratios of 1:1, 1:2, 1:4, 3:4, 4:3, 4:1 and 2:

1. The pair of adjacent arms of the sample (5) are located in the test area of ​​the asymmetric loop coil (20). By translating the sample (5) placed in the discharge test area up and down, the up and down translation of the sample (5) is kept in the narrow coil segment with strong concentration. Different lever arm lengths are obtained. Different loading ratios are achieved through the difference in plastic strain wave transmission. S4. The strain imaging camera (41) and / or stress imaging camera (42) will be translated and adjusted in different loading ratio tests, and the strain imaging camera (41) and / or stress imaging camera (42) will be further fine-tuned so that the field of view is directly facing the central speckle area and the image is clear. S5. The power supply unit discharges to the asymmetric loop coil (20), and the asymmetric loop coil (20) generates electromagnetic force to act on the sample (5). The sample (5) is affected by the electromagnetic force and expands rapidly in the sample (5) area. At the same time, the strain measurement system (40) records the deformation process that occurs in the speckle area of ​​the tensile sample (5). S6. The strain measurement system (40) transmits the captured photos to the strain data analysis device. The strain data analysis device processes the experimental data to obtain the engineering strain of the central region of the specimen (5) during the tensile process. S7. Using the above-mentioned sample (5), coil tooling, and forming limit measurement scheme, the material high-speed forming limit is realized by using different biaxial loading ratios, and a high-speed forming limit diagram is constructed.

2. The method for biaxial tensile limit testing of a thin plate driven by electromagnetic force according to claim 1, characterized in that, The asymmetric loop coil (20) is a two-turn coil.

3. The method for biaxial tensile limit testing of a thin plate driven by electromagnetic force according to claim 1, characterized in that, It also includes a positive and negative electrode busbar rigidly connected to the bottom of the substrate (10), the positive and negative electrode busbar being electrically connected to the power supply unit, and the asymmetric loop coil (20) being electrically connected to the positive and negative electrode busbar.

4. The method for biaxial tensile limit testing of a thin plate driven by electromagnetic force according to claim 1, characterized in that, The substrate (10) is provided with multiple positioning marks for precise positioning of the sample (5), which facilitates the realization of various extreme loading ratios.

5. The method for biaxial tensile limit testing of a thin plate driven by electromagnetic force according to claim 1, characterized in that, Hole 1 (111) is a square hole, and hole 2 (112) is a wedge-shaped hole.

6. The method for biaxial tensile limit testing of a thin plate driven by electromagnetic force according to any one of claims 1-5, characterized in that, The asymmetric loop coil (20) is embedded in the substrate (10); or The asymmetric loop coil (20) is disposed in the base, which is embedded in the substrate (10) and fixed by screws (12).

7. The method for biaxial tensile limit testing of a thin plate driven by electromagnetic force according to any one of claims 1-5, characterized in that, The strain measurement system (40) further includes a planar drive mechanism (43), which is mounted on a tripod and located above the pressure plate (11). The strain imaging camera (41) and / or stress imaging camera (42) are mounted on the planar drive mechanism (43).

8. The method for performing biaxial tensile limit testing on a thin plate driven by electromagnetic force according to any one of claims 1-5, characterized in that, The power supply unit includes a charging circuit (31) and a discharging circuit (32). The charging circuit (31) boosts and rectifies the electrical energy and stores it in the discharging circuit (32). The discharging circuit (32) provides power to the asymmetric loop coil (20).

9. The method for biaxial tensile limit testing of a thin plate driven by electromagnetic force according to claim 1, characterized in that, The sample (5) is thinned in a fan shape in the central region and a speckled coating is sprayed in the central region.

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