Metal sheet high-temperature two-way stretching test system and method based on current heating

Abstract

The invention discloses a metal sheet high-temperature two-way tensile testing system and method based on current heating, and relates to the field of metal stretching, and the testing system comprises a cross-shaped test piece, a clamp, a two-way tensile testing machine, a heating mechanism and a DIC strain measurement mechanism. The cross-shaped test piece comprises a central area, a connecting arm and a clamping end; the clamp comprises a clamping main body, a clamping block, a conductive block and an insulating part; the two-way tensile testing machine comprises a clamping head and a tensile control part; the heating mechanism comprises a direct-current heating power supply, an infrared thermal imaging thermodetector and a temperature control part; the direct-current heating power supply adopts a single-channel time sequence switching pulse or a one-main two-time positive electrode rotation pulse output electrifying heating mode; the DIC strain measurement mechanism comprises a lighting device, a CCD camera, real-time shooting software and strain field calculation software. According to the test system and method, the heating efficiency of the high-temperature two-way tensile test and the temperature uniformity of the central area of the cross-shaped test piece can be remarkably improved, and the temperature and strain characterization range of the two-way tensile test of the metal sheet is expanded.

Description

Technical Field

[0001] This specification relates to the field of metal tensile technology, and in particular to a high-temperature biaxial tensile testing system and method for thin metal sheets based on electric current heating. Background Technology

[0002] The description in this section provides only background information relevant to the disclosure in this specification and does not constitute prior art.

[0003] With the automotive, aerospace, and other industries moving towards lightweighting and precision, the performance requirements for various metal parts are becoming increasingly specialized, and their shapes and structures are becoming increasingly complex. Thin metal sheets have poor formability at room temperature, while traditional hot forming processes are inefficient and costly, failing to meet the high-efficiency and high-precision requirements of modern industry. Therefore, there is an urgent need to develop new hot forming processes to improve the formability of thin metal sheets. Scientific forming processes require accurate material constitutive models as guidance. Research on advanced constitutive models for thin metal sheets requires key data support from stress-strain responses under different loading ratios (Fx:Fy, where Fx is the load in the X direction and Fy is the load in the Y direction, with their directions perpendicular to each other). Biaxial tensile testing using cruciform specimens is the preferred method for obtaining this data because it offers numerous advantages, including frictionless operation, absence of out-of-plane stress, and ease of controlling the loading ratio, effectively characterizing the yielding behavior of thin sheets under biaxial stress.

[0004] However, the mechanical behavior of metallic materials at high temperatures differs significantly from that at room temperature, making it impossible to directly use room-temperature biaxial tensile data for the study and calibration of high-temperature constitutive models. Traditional solutions often employ a constant-temperature chamber to heat the entire specimen for high-temperature testing, but this method suffers from low heating efficiency, limited temperature limits, and a high risk of overheating and premature failure at the specimen's clamping ends. While induction heating can achieve rapid temperature rise, the extremely high current required to heat the sample to a high temperature during biaxial tensile testing generates strong electromagnetic interference, affecting the accuracy of deformation measurements in thin metal sheets. Therefore, there is an urgent need to develop a new method that can both efficiently heat the specimen and effectively expand the temperature and strain characterization range of biaxial tensile tests on thin metal sheets.

[0005] Patent document CN103398905B (A Method for Localized Heating Forming Limit Test) discloses a method for localized heating forming limit test, mainly using a biaxial tensile test as an example. It uses a laser to scan and heat the central region of the cross-shaped specimen along a fixed trajectory, causing the main deformation zone to soften and fracture first, thus improving the efficiency of high-temperature biaxial tensile testing. However, due to the highly concentrated energy of the laser beam, the temperature at the laser spot is high, making it difficult to achieve a truly uniform and stable temperature field in the central region of the cross-shaped specimen, even with beam scanning or oscillation. Furthermore, this laser scanning heating method requires a complex optical path scanning system, precise motion control, and a real-time temperature feedback system, significantly increasing the complexity, cost, and maintenance difficulty of the experimental system.

[0006] Patent document CN111385932A (Electromagnetic induction heating coil and heating device for isothermal biaxial tensile testing) proposes an electromagnetic induction heating coil for isothermal biaxial tensile testing. It achieves precise local heating of the central area of ​​the cross-shaped specimen through the square end face of the coil head, realizing a relatively uniform temperature field in the main deformation zone. However, when electromagnetic induction heating of thin metal sheets to high temperatures, the required high frequency and large current easily generate a strong alternating electromagnetic field, which in turn produces electromagnetic forces that affect the deformation of the thin metal sheet, limiting the temperature range that the biaxial tensile test can characterize and the reliability of the data.

[0007] It should be noted that the above introduction to the technical background is only for the purpose of providing a clear and complete explanation of the technical solutions in this specification and facilitating understanding by those skilled in the art. The fact that these solutions have been described in the background section of this specification should not be construed as meaning that the aforementioned technical solutions are known to those skilled in the art. Summary of the Invention

[0008] In view of the shortcomings of the prior art, one object of this specification is to provide a high-temperature biaxial tensile testing system and method for metal thin plates based on current heating, which can significantly improve the heating efficiency of existing high-temperature biaxial tensile tests, the temperature uniformity of the central region of the cross specimen, and expand the temperature and strain characterization range of metal thin plate biaxial tensile tests.

[0009] To achieve the above objectives, this specification provides a high-temperature biaxial tensile testing system for thin metal sheets based on current heating, comprising: A cross-shaped specimen includes a central region and four connecting arms connected to the periphery of the central region, with a clamping end connected to the end of each connecting arm away from the central region; the central region has opposing first and second surfaces, the second surface being sprayed with black speckles. A clamp for holding a cross-shaped specimen; the clamp includes a clamping body, a clamping block, a conductive block and an insulating part, the clamping body and the clamping block press the clamping end together, and the conductive block is connected to the clamping end; A biaxial tensile testing machine includes a clamping head and a tensile control unit. The end of the clamping body away from the clamping end is fixedly connected to the clamping head through the insulating part. The tensile control unit is electrically connected to the clamping head and is used to set the loading program of the clamping head. The heating mechanism includes a DC heating power supply, an infrared thermal imaging thermometer, and a temperature control unit. The DC heating power supply uses a single-path timing-switching pulse or a main-two-positive-electrode rotation pulse output heating method. The infrared thermal imaging thermometer includes a temperature output interface and a temperature measuring lens, with the temperature measuring lens facing the first surface. The temperature control unit is connected to the conductive block via a first cable and to the DC heating power supply via a second cable. The temperature control unit is connected to the temperature output interface. The DIC strain measurement mechanism includes an illumination device, two CCD cameras, real-time imaging software, and strain field calculation software. The illumination device faces the second surface. The lenses of the two CCD cameras face the second surface together at a predetermined angle. The real-time imaging software is electrically connected to the CCD cameras and is used to record the deformation process of the central region. The strain field calculation software is electrically connected to the real-time imaging software and is used to perform strain calculation on the deformation process.

[0010] In a preferred embodiment, the connecting arm is provided with a slit; the clamping end is provided with a plurality of first positioning holes; the clamping body is provided with a plurality of second positioning holes; the clamping block is provided with a plurality of third positioning holes; the first positioning holes, the second positioning holes and the third positioning holes correspond one to one, and the first positioning hole is located between the second positioning hole and the third positioning hole.

[0011] In a preferred embodiment, the clamping body has a first clamping surface, the clamping block has a second clamping surface, the conductive block has an energized surface, the first clamping surface is in contact with one side of the clamping end, and the second clamping surface and the energized surface are in contact with the other side of the clamping end.

[0012] In a preferred embodiment, the clamping block has a mounting hole; the conductive block has a connecting portion that passes through and protrudes from the mounting hole; the portion of the connecting portion protruding from the mounting hole has a connecting hole, which is connected and fixed to the first cable.

[0013] In a preferred embodiment, the end of the clamping body that is fixedly connected to the clamping head is the tail end; the insulating part includes two insulating pads that are respectively attached to the two opposite sides of the tail end.

[0014] In a preferred embodiment, the tail end is provided with a plurality of fourth positioning holes, the clamping head is provided with a plurality of fifth positioning holes, and the insulating pad is provided with a plurality of sixth positioning holes. The fourth positioning holes, fifth positioning holes, and sixth positioning holes correspond one-to-one, and the fourth positioning hole is located between two sixth positioning holes, and the sixth positioning hole is located between the fourth positioning hole and the fifth positioning hole.

[0015] In a preferred embodiment, the insulating part includes a plurality of insulating rings, each insulating ring having an outer ring surface and an inner ring surface. The outer ring surface is fitted with the fourth positioning hole and the sixth positioning hole. The size of the inner ring surface is the same as the size of the fifth positioning hole. The biaxial tensile testing machine also includes a positioning pin, which passes through the fifth positioning hole, the inner ring surface, and the fifth positioning hole in sequence to fix the clamp to the clamping head.

[0016] This application also provides a high-temperature biaxial tensile testing method for thin metal sheets based on electric current heating. The testing method is performed using the testing system described in any of the above embodiments, and includes the following steps: Step S10: Prepare the cross-shaped specimen; Step S20: Install the fixture and connect the cross specimen to the fixture; Step S30: Set the heating mechanism; Step S40: Construct the DIC strain measurement mechanism; Step S50: Set up the biaxial tensile testing machine and perform a tensile test on the cross specimen.

[0017] In a preferred embodiment, the four clamping ends of the cross-shaped specimen are respectively a first clamping end, a second clamping end, a third clamping end, and a fourth clamping end arranged counterclockwise along the circumference; in step S30, when the DC heating power supply adopts a single-path timing switching pulse output energizing heating mode, the first clamping end and the third clamping end are respectively connected to the positive and negative terminals of a pair of electrodes, and the second clamping end and the fourth clamping end are respectively connected to the positive and negative terminals of another pair of electrodes; only one pair of electrodes is energized to form a circuit within one pulse moment, while the other pair of electrodes is in an open circuit state; the circuits of the two pairs of electrodes are time-switched according to a predetermined frequency.

[0018] In a preferred embodiment, the four clamping ends of the cross-shaped specimen are respectively a first clamping end, a second clamping end, a third clamping end, and a fourth clamping end arranged counterclockwise along the circumference; in step S30, when the DC heating power supply adopts a main two-phase positive electrode rotation pulse output heating mode, at the first pulse moment, the first clamping end is connected to the main positive electrode, the second clamping end and the fourth clamping end are respectively connected to the secondary positive electrode, and the potential of the secondary positive electrode is half of the potential of the main positive electrode; the third clamping end is connected to the negative electrode; at each subsequent pulse moment, the electrode potential arrangement of the previous pulse moment is rotated by 90°. Beneficial effects

[0019] The high-temperature biaxial tensile testing system for thin metal sheets based on current heating provided in this embodiment can significantly improve the heating efficiency and temperature uniformity of the central region of the cross-shaped specimen in existing high-temperature biaxial tensile tests, and expand the temperature and strain characterization range of biaxial tensile tests for thin metal sheets. Specifically, it has the following advantages: 1. A DC heating power supply is used to heat the cross-shaped specimen for high-temperature biaxial tensile testing. Non-contact heating avoids affecting the tensile strength of the specimen, is fast, efficient, easy to control, and can achieve a wider range of test temperature characterization. 2. The DC heating power supply in this application adopts a single-path timing switching pulse or a main two positive pole rotation pulse output power-on heating method, which realizes a uniform heating temperature field in the central area of ​​the specimen. The temperature in the central area is the highest, while the temperature of the four connecting arms is lower than that in the central area. This is conducive to failure occurring in the central area of ​​the specimen, thereby expanding the strain characterization range. 3. The clamp for the cross-shaped specimen designed in this invention is insulated and heat-resistant, can be installed accurately and can completely transfer the tensile load of the biaxial tensile testing machine without the need for complex modifications to the original equipment. Furthermore, based on the same design principle, the application range of the heating mechanism can be extended to high-temperature uniaxial tensile testing.

[0020] Specific embodiments of the present invention are disclosed in detail with reference to the following description and accompanying drawings, indicating how the principles of the invention can be employed. It should be understood that the embodiments of the present invention are not limited in scope as a result.

[0021] Features described and / or illustrated for one embodiment may be used in the same or similar manner in one or more other embodiments, combined with features in other embodiments, or substituted for features in other embodiments.

[0022] It should be emphasized that the term "including / comprises" as used herein refers to the presence of a feature, whole, step, or component, but does not exclude the presence or addition of one or more other features, wholes, steps, or components. Attached Figure Description

[0023] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art 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.

[0024] Figure 1 This is a schematic diagram of the structure of a cross-shaped specimen provided in this embodiment; Figure 2 This is a schematic diagram of the structure of a clamp provided in this embodiment; Figure 3 for Figure 2 A schematic diagram of the exploded structure; Figure 4 for Figure 2 A partial diagram of the exploded structure from another perspective; Figure 5 This is a physical image of the clamping head of a biaxial tensile testing machine provided in this embodiment; Figure 6 A schematic diagram of the energization of the cross-shaped specimen provided in Example 1 when a single-path timing switching pulse is used; Figure 7 The pulse timing diagram for the DC heating power supply provided in Example 1 when using a single-path timing switching pulse; wherein, Figure 7 (a) shows the pulse timing diagram of the first clamping end. Figure 7 (b) shows the pulse timing diagram of the second clamping end; Figure 8 (a) is the current distribution diagram of the finite element simulation when using single-path timing-switching pulse heating in Example 1; Figure 8 (b) is a temperature distribution diagram from a finite element simulation of single-path timing-switching pulse heating in Example 1; Figure 9 This is a temperature distribution cloud map of the central region when the target temperature is 650°C in Example 1; Figure 10 This is a temperature curve of the central region in the X / Y direction (i.e., horizontal / vertical) when the target temperature is 650℃ in Example 1; Figure 11 The image shows an infrared thermal imaging thermometer and a cross-shaped specimen provided in Example 1. Figure 12 This is a physical diagram of a heating mechanism provided in Example 1; Figure 13 A physical image of a biaxial tensile testing machine provided in Example 1; Figure 14The image shows a physical diagram of a DIC strain measurement mechanism provided in Example 1. Figure 15 This is a temperature distribution diagram of the central region of the cross-shaped specimen during the high-temperature biaxial tensile test in Example 1; Figure 16 This is a historical temperature change diagram of the central region of the cross-shaped specimen during the high-temperature biaxial tensile test in Example 1; Figure 17 The stress-strain data and fitting curves for the target region of the biaxial tensile test cruciform specimen at 650℃ in Example 1 are shown. Figure 18 This is a schematic diagram of the energization of the cross-shaped specimen provided in Example 2 when a main two-stage positive electrode rotation pulse is applied. Figure 19 The pulse timing diagram for the DC heating power supply provided in Example 2 using a main two-stage positive electrode rotation pulse; wherein, Figure 19 (a) shows the pulse timing diagram of the first clamping end. Figure 19 (b) shows the pulse timing diagram of the second clamping end. Figure 19 (c) shows the pulse timing diagram of the third clamping end. Figure 19 (d) shows the pulse timing diagram of the fourth clamping end; Figure 20 (a) is the current distribution diagram of the finite element simulation when a main double positive electrode rotating pulse heating is used in Example 2; Figure 20 (b) is a temperature distribution diagram from a finite element simulation of heating using a primary and secondary positive electrode rotating pulse in Example 2.

[0025] Explanation of reference numerals in the attached figures: 1. Cross-shaped specimen; 11. Central region; 111. First surface; 112. Second surface; 12. Connecting arm; 121. Slit; 13. Clamping end; 131. First positioning hole; 141. First clamping end; 142. Second clamping end; 143. Third clamping end; 144. Fourth clamping end; 2. Fixture; 21. Clamping body; 211. Second positioning hole; 212. First clamping surface; 213. Tail end; 214. Fourth positioning hole; 22. Clamping block; 221. Third positioning hole; 222. Second clamping surface; 223. Mounting hole; 23. Conductive block; 231. Current-carrying surface; 232. Connecting part; 233. Connecting hole; 24. Insulating part; 241. Insulating gasket; 242. Sixth positioning hole; 243. Insulating ring; 244. Outer ring surface; 245. Inner ring surface; 3. Biaxial tensile testing machine; 31. Clamping head; 311. Fifth positioning hole; 312. Mounting port; 32. Tensile control unit; 4. Heating mechanism; 41. DC heating power supply; 42. Infrared thermal imaging thermometer; 421. Temperature output interface; 43. Temperature control unit; 431. Control panel; 5. DIC strain measurement mechanism; 511. White light lamp for illumination; 512. Blue light flashlight; 52. CCD camera; 53. Real-time shooting software. Detailed Implementation

[0026] To enable those skilled in the art to better understand the technical solutions of this invention, the technical solutions of the embodiments of this invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this invention, and not all embodiments. Based on the embodiments of this invention, all other embodiments obtained by those skilled in the art without creative effort should fall within the scope of protection of this invention.

[0027] It should be noted that when an element is referred to as being "set on" another element, it can be directly on the other element or may be interposed with another element. When an element is referred to as being "connected to" another element, it can be directly connected to the other element or may be interposed with another element. The terms "vertical," "horizontal," "left," "right," and similar expressions used herein are for illustrative purposes only and do not represent the only possible implementations.

[0028] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains. The terminology used herein in the description of the invention is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention. The term "and / or" as used herein includes any and all combinations of one or more of the associated listed items.

[0029] Please see Figures 1 to 20 This application provides a high-temperature biaxial tensile testing system for thin metal sheets based on current heating, comprising: a cross specimen 1, a clamp 2, a biaxial tensile testing machine 3, a heating mechanism 4, and a DIC (Digital Image Correlation) strain measurement mechanism.

[0030] Among them, such as Figure 1As shown, the cross-shaped specimen 1 includes a central region 11 and four connecting arms 12 connected to the periphery of the central region 11. A clamping end 13 is connected to one end of each connecting arm 12 away from the central region 11. The central region 11 has opposing first surfaces 111 and second surfaces 112, the second surface 112 being sprayed with black speckles. The cross-shaped specimen 1 is made of metal. The thickness of the cross-shaped specimen 1 is 0.1mm-1.5mm, and its shape and dimensions may conform to the requirements of standard GB / T 36024-2018 or ASTM E3459-24. The first surface 111 is sprayed with high-temperature resistant white paint or other coatings to ensure stable infrared emissivity during temperature measurement during heating. The second surface 112 is sprayed with high-temperature resistant white primer and black speckles for the DIC strain measurement mechanism 5 to record the deformation process of the cross-shaped specimen 1.

[0031] Specifically, the four clamping ends 13 of the cross specimen 1 are the first clamping end 141, the second clamping end 142, the third clamping end 143, and the fourth clamping end 144, which are arranged counterclockwise along the circumference.

[0032] like Figure 2 , Figure 3 and Figure 4 As shown, the clamp 2 is used to clamp the cross-shaped specimen 1. The clamp 2 includes a clamping body 21, a clamping block 22, a conductive block 23, and an insulating part 24. The clamping body 21 and the clamping block 22 press the clamping end 13 together, and the conductive block 23 is connected to the clamping end 13. The clamp 2 can conduct current to the cross-shaped specimen 1 through the conductive block 23 to heat the cross-shaped specimen 1, and has a heat-resistant effect. The included angle allows the cross-shaped specimen 1 to be installed accurately and can transmit tensile load, and can install the cross-shaped specimen 1 onto the clamping head 31 of the biaxial tensile testing machine 3. The clamp 2 can clamp and fix the four clamping ends 13 of the cross-shaped specimen 1, ensuring the correctness of the clamping position, that is, the center lines of the cross-shaped specimen 1 in two directions coincide with the center lines of the four clamping heads 31 of the biaxial tensile testing machine 3. The two directions in this application refer to the mutually perpendicular X direction and Y direction, that is, the perpendicular transverse and longitudinal directions.

[0033] like Figure 5 and Figure 13 As shown, the biaxial tensile testing machine 3 includes a clamping head 31 and a tensile control unit 32. The end of the clamping body 21 furthest from the clamping end 13 is fixedly connected to the clamping head 31 via an insulating part 24. The tensile control unit 32 is electrically connected to the clamping head 31 and is used to set the loading program of the clamping head 31. Specifically, the computer control software of the tensile control unit 32 sets the test loading program settings such as the loading ratio and loading rate in both directions of the biaxial tensile testing machine 3 during the test, so as to realize biaxial tensile testing of thin metal sheets with different strain paths.

[0034] like Figure 11 and Figure 12As shown, the heating mechanism 4 includes a DC heating power supply 41, an infrared thermal imaging thermometer 42, and a temperature control unit 43. The DC heating power supply 41 employs a single-path sequential switching pulse or a main-two-positive-pole rotation pulse output heating method, enabling uniform heating of the central region 11 of the cross-shaped specimen 1 and control of power output parameters such as output voltage. The temperature control unit 43 further regulates the output of the DC heating power supply 41, allowing for the setting of constant voltage / constant temperature output mode, power-on switching frequency, target heating temperature, and temperature feedback control PID parameters. The temperature control unit 43 may include a control panel 431 for setting various parameters. The infrared thermal imaging thermometer 42 includes a temperature output interface 421 and a temperature measuring lens, with the lens facing the first surface 111. The temperature control unit 43 is connected to the conductive block 23 via a first cable and to the DC heating power supply 41 via a second cable. The temperature control unit 43 is connected to the temperature output interface 421.

[0035] For cross-shaped specimens 1 of different materials, thicknesses, and sizes, the required input electrical energy for heating varies. Before the test, the output voltage, power switching frequency, and other heating power parameters should be roughly determined using the constant voltage output mode of the temperature control unit 43 to ensure that the temperature can be heated to the target temperature or above. During the test, the temperature control unit 43 is switched to the constant temperature output mode, and the target heating temperature is set to carry out the subsequent test.

[0036] like Figure 13 and Figure 14 As shown, the DIC strain measurement mechanism 5 includes an illumination device, two CCD cameras 52, real-time imaging software 53, and strain field calculation software. The illumination device faces the second surface 112. The lenses of the two CCD cameras 52 are both facing the second surface 112 at a predetermined angle. The illumination device ensures that the real-time captured image is bright and clear, and it does not affect the temperature measurement of the infrared thermal imaging thermometer 42 on the first surface 111. The real-time imaging software 53 is electrically connected to the CCD cameras 52 and is used to record the deformation process of the central region 11. The real-time imaging software 53 can set the shooting interval and the total shooting time. The strain field calculation software is electrically connected to the real-time imaging software 53 and is used to calculate the strain during the deformation process.

[0037] During the test, the test loading program of the biaxial tensile testing machine 3 should be set first, the photo interval and total duration of the real-time shooting software 53 should be adjusted, the target heating temperature in the constant temperature output mode should be set in the temperature control unit 43, the DC heating power supply 41 should be turned on to heat the central area 11 of the cross specimen 1, and the infrared thermal imaging thermometer 42 should start recording the temperature change history of the central area 11 during the test. After the target heating temperature is reached, the test loading program and the real-time shooting program of the biaxial tensile testing machine 3 should start simultaneously. The test is completed when the cross specimen 1 fractures and fails, or when the test is interrupted for other reasons, the test loading program, the real-time shooting program, the infrared thermal imaging thermometer 42 and the DC heating power supply 41 of the biaxial tensile testing machine 3 should be stopped at the same time to end the test. Subsequently, the strain calculation of the deformation process of the central area 11 of the cross specimen 1 recorded by the real-time shooting software 53 should be performed using strain field calculation software.

[0038] The high-temperature biaxial tensile testing system for thin metal sheets based on current heating provided in this embodiment can significantly improve the heating efficiency and temperature uniformity of the central region 11 of the cross specimen 1 in existing high-temperature biaxial tensile tests, and expand the temperature and strain characterization range of biaxial tensile tests for thin metal sheets. Specifically, it has the following advantages: 1. A DC heating power supply 41 is used to heat the cross specimen 1 for high-temperature biaxial tensile testing. Non-contact heating avoids affecting the tensile strength of the specimen, is fast, efficient, easy to control, and can achieve a wider range of test temperature characterization. 2. The DC heating power supply 41 in this application adopts a single-path timing switching pulse or a main two positive pole rotation pulse output power-on heating mode, which realizes a uniform heating temperature field in the central region 11 of the specimen. The temperature in the central region 11 is the highest, and the temperature of the four connecting arms 12 is lower than that in the central region 11. This is conducive to failure occurring in the central region 11 of the specimen, thereby expanding the strain characterization range. 3. The clamp 2 of the cross specimen 1 designed in this invention is insulated and heat-resistant, can be installed accurately and can completely transfer the tensile load of the biaxial tensile testing machine 3 without the need for complex modifications to the original equipment. Furthermore, based on the same design principle, the application scope of the heating mechanism 4 can be extended to high-temperature uniaxial tensile testing.

[0039] In this embodiment, when performing a high-temperature biaxial tensile test with current heating, the clamp 2 should not only ensure accurate installation of the specimen and transfer the tensile load of the biaxial tensile testing machine 3, but also be able to conduct the current to the central area 11 of the cross specimen 1, while preventing the current from flowing to the metal clamping head 31 of the biaxial tensile testing machine 3 which is also conductive, and have a certain heat resistance.

[0040] like Figure 1As shown, the connecting arm 12 has a slit 121 for heat dissipation. The clamping end 13 has multiple first positioning holes 131, the clamping body 21 has multiple second positioning holes 211, and the clamping block 22 has multiple third positioning holes 221. The first positioning holes 131, second positioning holes 211, and third positioning holes 221 correspond one-to-one, and the first positioning hole 131 is located between the second positioning hole 211 and the third positioning hole 221. Through the cooperation of these three positioning holes, the cross specimen 1 and the clamp 2 can be accurately installed and fixed.

[0041] like Figure 3 and Figure 4 As shown, the clamping body 21 has a first clamping surface 212, the clamping block 22 has a second clamping surface 222, and the conductive block 23 has a current-carrying surface 231. The first clamping surface 212 is in contact with one side of the clamping end 13, and the second clamping surface 222 and the current-carrying surface 231 are in contact with the other side of the clamping end 13, so that current can flow from the conductive block 23 to the clamping end 13, and then flow through the central region 11.

[0042] Specifically, the clamping block 22 has a mounting hole 223. The conductive block 23 has a connecting portion 232, which passes through and protrudes from the mounting hole 223. The portion of the connecting portion 232 protruding from the mounting hole 223 has a connecting hole 233, which is connected and fixed to the first cable. The size of the connecting portion 232 is smaller than the size of the conductive surface 231. The mounting hole 223 can be a stepped hole, consisting of two parts of different sizes, which can achieve limiting contact between the conductive block 23 and the clamping block 22. Through the shape design of the clamping block 22 and the conductive block 23, not only is the conductive block 23 fixed to the clamping body 21, but also the conductive block 23 is in fixed contact with the cross specimen 1.

[0043] In this embodiment, the end of the clamping body 21 that is fixedly connected to the clamping head 31 is defined as the tail end 213. The insulating part 24 includes two insulating pads 241, which are respectively attached to the two opposite sides of the tail end 213 to insulate the clamping body 21 and the clamping head 31 from each other.

[0044] Specifically, the tail end 213 is provided with multiple fourth positioning holes 214, the clamping head 31 is provided with multiple fifth positioning holes 311, and the insulating pad 241 is provided with multiple sixth positioning holes 242. The fourth positioning holes 214, the fifth positioning holes 311 and the sixth positioning holes 242 correspond one-to-one, and the fourth positioning hole 214 is located between two sixth positioning holes 242, and the sixth positioning hole 242 is located between the fourth positioning hole 214 and the fifth positioning hole 311. Through the cooperation of these three positioning holes, the clamp 2 and the clamping head 31 can be accurately installed and fixed.

[0045] Furthermore, the insulating part 24 includes multiple insulating rings 243, each including an outer ring surface 244 and an inner ring surface 245. The outer ring surface 244 is in contact with the fourth positioning hole 214 and the sixth positioning hole 242. The inner ring surface 245 has the same dimensions as the fifth positioning hole 311. The biaxial tensile testing machine 3 also includes a positioning pin, which passes sequentially through the fifth positioning hole 311, the inner ring surface 245, and the fifth positioning hole 311 to fix the clamp 2 to the clamping head 31. By setting the insulating rings 243 and the insulating gaskets 241, the clamping body 21 and the clamping head 31 can be effectively insulated from each other.

[0046] In this embodiment, the main body of the clamp 2 can support other components and transmit the tensile load of the biaxial tensile testing machine 3. The clamping block 22 can be secured by bolts to the clamping end 13 of the cross specimen 1 to ensure assembly. The conductive block 23 is connected to the output cable (i.e., the first cable) of the temperature control unit 43 to conduct current to heat the cross specimen 1. The insulating gasket 241 and the insulating ring 243 isolate the current flow to the metal clamping head 31 of the biaxial tensile testing machine 3. Specifically, the first clamping surface 212 of the clamping body 21 contacts one side of the clamping end 13 of the cross specimen 1, the second clamping surface 222 of the clamping block 22 and the energized surface 231 of the conductive block 23 contact the other side of the clamping end 13 of the cross specimen 1, the conductive block 23 is installed in the mounting hole 223 of the clamping block 22, and the third positioning hole 221, the first positioning hole 131 and the second positioning hole 211 are connected by bolts. The nut is tightened to ensure reliable installation and accurate positioning of the cross specimen 1.

[0047] Two insulating pads 241 are installed on both sides of the tail end 213 of the clamping body 21. The insulating ring 243 is installed by engaging the fourth positioning hole 214 and the sixth positioning hole 242 of the clamping body 21 through the outer ring surface 244. After the insulating pads 241 and the insulating ring 243 are installed, the tail end 213 of the clamping body 21 is inserted into the mounting port 312 of the clamping head 31. The fifth positioning hole 311 is connected to the inner hole surface by the positioning pin to ensure the accurate installation position of the fixture 2. Each of the four clamping heads 31 on the biaxial tensile testing machine 3 needs to be equipped with a fixture 2. After connecting and fixing the four clamping ends 13 of the cross specimen 1, the cross specimen 1 is clamped. Finally, the output cable of the temperature control unit 43 is connected and fixed to the connection hole 233 of the conductive block 23.

[0048] Based on the same concept, this invention also provides a method for high-temperature biaxial tensile testing of thin metal sheets based on current heating, as described in the following embodiments. Since the principle behind this method and the technical effects it achieves are similar to the aforementioned high-temperature biaxial tensile testing system for thin metal sheets based on current heating, the implementation of this method can refer to the implementation of the aforementioned high-temperature biaxial tensile testing system for thin metal sheets based on current heating; repeated details will not be elaborated further.

[0049] One embodiment of the present invention also provides a high-temperature biaxial tensile testing method for thin metal sheets based on current heating, wherein the testing method employs the testing system described in any of the above embodiments. The testing method includes the following steps: Step S10: Prepare cross-shaped specimen 1; Step S20: Install clamp 2 and connect cross specimen 1 to clamp 2; Step S30: Set the heating mechanism 4; Step S40: Construct the DIC strain measurement mechanism 5; Step S50: Set up the biaxial tensile testing machine 3 and perform a tensile test on the cross specimen 1.

[0050] In this embodiment, the method implementation corresponds to the system implementation and can solve the technical problems solved by the system implementation, thereby achieving the technical effects of the system implementation. The specific details will not be elaborated here.

[0051] In step S10, industrial pure titanium with a thickness of 0.1 mm and a titanium content higher than 99.5% produced by a Japanese steel mill can be selected as the substrate for the cross specimen 1. The industrial pure titanium is a titanium substrate with an α-phase microstructure obtained by cold rolling followed by annealing heat treatment. The substrate is then processed into the cross specimen 1 using laser cutting or wire cutting, with the shape shown below. Figure 1 As shown. The central area 11 of the cross specimen 1 is the main heating target area and the strain occurrence area. The first positioning hole 131 of the clamping end 13 is used for bolt connection. The width of the slit 121 on the connecting arm 12 should not exceed 0.2 mm.

[0052] Specifically, the total length and total width of the cross specimen 1 are both 108mm, the width of the connecting arm 12 is 15mm, the length of the clamping end 13 is 38mm and the width is 23mm, the diameter of the first positioning hole 131 is 5.6mm, and each clamping end 13 is provided with three first positioning holes 131 that are evenly spaced along the length of the clamping end 13, with a distance of 12mm between two adjacent first positioning holes 131.

[0053] In Example 1, in step S30, when the DC heating power supply 41 adopts a single-path timing switching pulse output power-on heating mode, its electrode arrangement and pulse timing are as follows: Figure 6 and Figure 7 The first clamping end 141 and the third clamping end 143 are respectively connected to the positive and negative terminals of a pair of electrodes, and the second clamping end 142 and the fourth clamping end 144 are respectively connected to the positive and negative terminals of another pair of electrodes. Only one pair of electrodes is energized to form a circuit within a single pulse moment, while the other pair of electrodes remains open. The circuits of the two pairs of electrodes are switched sequentially according to a predetermined frequency.

[0054] This electric heating method was verified through finite element simulation using Abaqus software. The switching frequency was set to 5Hz in the simulation. Figure 8 (a) It can be seen that under this energized heating method, only one path has a uniform current flowing through it at the same pulse moment, which effectively controls the current flow direction. Figure 8 (b) The temperature distribution cloud map shows that under this electric heating method, the temperature distribution in the central region 11 of the cross-shaped specimen 1 is relatively uniform and higher than that of the connecting arm 12, indicating a relatively ideal heating effect. Taking a target temperature of 650℃ as an example, the temperature distribution cloud map of the central region 11 of the cross-shaped specimen 1 at this temperature is shown below. Figure 9 Temperature curves in the X and Y directions of the central region 11 of the cross-shaped specimen 1 were extracted. Figure 10 Within the selected target area (the area where uniform strain occurs and is extracted), the temperature difference is only ±8.05℃, with an error of 1.12%.

[0055] In this embodiment, the high-temperature resistant white paint or other coating used on the infrared temperature measuring surface (i.e., the first surface 111) of the cross-shaped specimen 1 is a high-temperature resistant boron nitride spray. The lens of the infrared thermal imaging thermometer 42 should be directly facing the side of the cross-shaped specimen 1 with the boron nitride spray sprayed on the center area 11. After temperature calibration, the infrared emissivity of this spray coating is 0.98. The real-time temperature of the infrared thermal imaging thermometer 42 is input to the temperature control unit 43 through the temperature output interface 421. The target temperature is set to 650℃ and the switching frequency is set to 2kHz on the control panel 431 of the temperature control unit 43. The temperature control unit 43 will adjust the output of the DC heating power supply 41 according to the real-time temperature feedback to heat the cross-shaped specimen 1 to the target temperature. For specific equipment, see [link to equipment description]. Figure 11 and Figure 12 .

[0056] In Example 1, for step S40, the high-temperature resistant white primer used on the strain measurement surface (i.e., the second surface 112) of the cross specimen 1 is high-temperature resistant silver paint, and the black speckle is made by spraying iron oxide powder. The two CCD cameras 52 of the DIC strain measurement mechanism 5 are positioned at a certain angle towards the side of the cross specimen 11 sprayed with high-temperature resistant silver paint and black iron oxide speckle. White light lamps 511 on both sides construct the illumination field of the central area 11, and a blue light flashlight 512 is added directly below to supplement the illumination, making the image bright and clear when the CCD camera 52 captures the image. The light sources of the above lighting equipment should be far away from the lens window of the infrared thermal imaging thermometer 42 to avoid affecting the temperature measurement on the other side of the cross specimen 1. For specific experimental equipment setup, see [link to specific setup instructions]. Figure 13 and Figure 14 .

[0057] After the CCD camera 52 and lighting equipment are set up, the shooting program is set in the real-time shooting software 53. In this embodiment, segmented shooting is set. The first segment shooting interval is 333ms and the shooting time is 90s. The second segment shooting interval is 500ms and the shooting time is set to be extremely long. The software shooting is manually stopped when the cross specimen 1 breaks and fails.

[0058] In step S50, the test loading program of the biaxial tensile testing machine 3 is set, the control mode is tensile force control, and two-stage equal biaxial loading (i.e., the loads in the X and Y directions are the same during loading) is performed. The first stage loading time is 90s, and the termination load is set to 80% of the yield strength obtained by the uniaxial tensile test of 0.1mm industrial pure titanium TA1 with the same substrate as the substrate in this embodiment at 650℃. The termination load of the second stage loading is the upper limit of the tensile force of the tensile machine. At the same time, a failure detection program is added when the tensile force sensor suddenly drops, that is, the test loading program is stopped when the cross specimen 1 breaks due to tensile stress.

[0059] After completing the above settings, turn on the output switch of the DC heating power supply 41 and the infrared thermal imaging thermometer 42 starts recording the temperature change of the central area 11 of the cross specimen 1 during the test. After reaching the target temperature of 650℃, the test loading program and real-time shooting program of the biaxial tensile testing machine 3 start simultaneously, recording the tensile force in four directions of the cross specimen 1 and the deformation process of the central area 11 during the test. When the cross specimen 1 breaks and fails, the test loading program, the DIC real-time shooting program, the infrared thermal imaging thermometer 42 and the DC heating power supply 41 are stopped, and the test is completed.

[0060] Historical data on temperature distribution and temperature changes in the central region 11 of the cross-shaped specimen 1, recorded by the infrared thermal imaging thermometer 42 during the experiment, can be found in [link to relevant documentation]. Figure 15 and Figure 16 Experiments show that when the target temperature of the cross specimen 1 is 650℃ under single-channel time-switched pulse current heating, the temperature difference in the target area remains within ±10℃ during the actual heating process, with an error of 1.54%. Due to the presence of the temperature control unit 43, the material temperature consistency is well maintained during the material deformation process. Strain calculations were performed on the deformation process of the central region 11 of the cross specimen 1 recorded by the real-time imaging software 53 using DIC strain field calculation software. The stress-strain data of the target area obtained through data processing is shown in [the figure]. Figure 17 The strains in both the X and Y directions can reach close to 0.07, indicating that the method of the present invention can complete the calibration of the high-temperature yield behavior of metal sheets and can characterize a large strain range.

[0061] This application also provides an embodiment 2. In this embodiment, the design of the cross specimen 1 substrate, the fixture 2, the biaxial tensile testing machine 3, the DIC strain measurement mechanism 5, and the heating mechanism 4 are the same as in embodiment 1. The heating mode of the DC heating power supply 41 is changed to one main and two positive electrode rotation pulses. Finite element simulation verifies that this method can also achieve the same heating effect in the central region 11 of the cross specimen 1 as in embodiment 1.

[0062] In Example 2, when the DC heating power supply 41 adopts a primary and secondary positive electrode rotation pulse output heating method in step S30, its electrode arrangement and pulse timing are as follows: Figure 18 and Figure 19 At the first pulse moment, the first clamping end 141 is connected to the main positive electrode, and the second clamping end 142 and the fourth clamping end 144 are respectively connected to the secondary positive electrodes, with the potential of the secondary positive electrode being half of the potential of the main positive electrode. The third clamping end 143 is connected to the negative electrode. At each subsequent pulse moment, the electrode potential arrangement of the previous pulse moment is rotated by 90°.

[0063] This electric heating method was verified through finite element simulation using Abaqus software. The rotation frequency of the potential arrangement in the simulation was set to 5Hz. Figure 20 (a) It can be seen that under this energized heating method, only one direction has a uniform current flowing through at the same pulse moment, which effectively controls the current flow direction. Figure 20 (b) The temperature distribution cloud map shows that the temperature distribution in the central region 11 of the cross specimen 1 is relatively uniform and higher than that of the cross arm under this electric heating method, which can achieve the same ideal heating effect as the single-path timing switching pulse in Example 1.

[0064] It should be noted that in the description of this specification, the terms "first," "second," etc., are used only for descriptive purposes and to distinguish similar objects; there is no order between them, nor should they be construed as indicating or implying relative importance. Furthermore, in the description of this specification, unless otherwise stated, "a plurality of" means two or more.

[0065] Any numerical values ​​cited herein include all values ​​ranging from a lower limit to an upper limit, increasing by one unit, with at least two units between any lower and any higher value. For example, if the quantity of a component or the value of a process variable (e.g., temperature, pressure, time, etc.) is described as being from 1 to 90, preferably from 20 to 80, more preferably from 30 to 70, the purpose is to illustrate that values ​​such as 15 to 85, 22 to 68, 43 to 51, 30 to 32 are also explicitly listed in this specification. For values ​​less than 1, a unit is appropriately considered to be 0.0001, 0.001, 0.01, 0.1, etc. These are merely examples intended for explicit expression, and it can be assumed that all possible combinations of values ​​listed between the minimum and maximum values ​​are explicitly described in this specification in a similar manner.

[0066] Unless otherwise stated, all ranges include the endpoints and all numbers between them. The terms "approximately" or "about" used with ranges apply to both endpoints of the range. Thus, "approximately 20 to 30" is intended to cover "approximately 20 to approximately 30," including at least the specified endpoints.

[0067] All articles and references disclosed herein, including patent applications and publications, are incorporated herein by reference for various purposes. The term “substantially constitutes…” used to describe a combination should include the identified elements, components, parts, or steps, as well as other elements, components, parts, or steps that do not substantially affect the essential novelty of the combination. The use of the terms “comprising” or “including” to describe combinations of elements, components, parts, or steps herein also contemplates embodiments substantially constituted by such elements, components, parts, or steps. The use of the term “may” herein is intended to indicate that any described attribute included by “may” is optional.

[0068] Multiple elements, components, parts, or steps can be provided by a single integrated element, component, part, or step. Alternatively, a single integrated element, component, part, or step can be divided into multiple separate elements, components, parts, or steps. The use of "a" or "an" to describe an element, component, part, or step does not imply the exclusion of other elements, components, parts, or steps.

[0069] It should be understood that the above description is for illustrative purposes and not for limitation. Many embodiments and applications beyond the provided examples will be apparent to those skilled in the art upon reading the above description. Therefore, the scope of this teaching should not be determined by reference to the above description, but rather by reference to the appended claims and the full scope of their equivalents. For purposes of completeness, all articles and references, including patent applications and publications, are incorporated herein by reference. The omission of any aspect of the subject matter disclosed herein in the preceding claims is not intended as a waiver of that subject matter, nor should it be construed as an indication that the inventors have not considered that subject matter as part of the disclosed inventive subject matter.

Claims

1. A high-temperature biaxial tensile testing system for thin metal sheets based on electric current heating, characterized in that, include: A cross-shaped specimen includes a central region and four connecting arms connected to the periphery of the central region, with a clamping end connected to the end of each connecting arm away from the central region; the central region has opposing first and second surfaces, the second surface being sprayed with black speckles. A clamp for holding a cross-shaped specimen; the clamp includes a clamping body, a clamping block, a conductive block and an insulating part, the clamping body and the clamping block press the clamping end together, and the conductive block is connected to the clamping end; A biaxial tensile testing machine includes a clamping head and a tensile control unit. The end of the clamping body away from the clamping end is fixedly connected to the clamping head through the insulating part. The tensile control unit is electrically connected to the clamping head and is used to set the loading program of the clamping head. The heating mechanism includes a DC heating power supply, an infrared thermal imaging thermometer, and a temperature control unit. The DC heating power supply uses a single-path timing-switching pulse or a main-two-positive-electrode rotation pulse output heating method. The infrared thermal imaging thermometer includes a temperature output interface and a temperature measuring lens, with the temperature measuring lens facing the first surface. The temperature control unit is connected to the conductive block via a first cable and to the DC heating power supply via a second cable. The temperature control unit is connected to the temperature output interface. The DIC strain measurement mechanism includes an illumination device, two CCD cameras, real-time imaging software, and strain field calculation software. The illumination device faces the second surface. The lenses of the two CCD cameras face the second surface together at a predetermined angle. The real-time imaging software is electrically connected to the CCD cameras and is used to record the deformation process of the central region. The strain field calculation software is electrically connected to the real-time imaging software and is used to perform strain calculation on the deformation process.

2. The high-temperature biaxial tensile testing system for thin metal sheets based on current heating according to claim 1, characterized in that, The connecting arm has a slit; the clamping end has multiple first positioning holes; the clamping body has multiple second positioning holes; the clamping block has multiple third positioning holes; the first positioning hole, the second positioning hole and the third positioning hole correspond one-to-one, and the first positioning hole is located between the second positioning hole and the third positioning hole.

3. The high-temperature biaxial tensile testing system for thin metal sheets based on current heating according to claim 1, characterized in that, The clamping body has a first clamping surface, and the clamping block has a second clamping surface; the conductive block has an energized surface; the first clamping surface is in contact with one side of the clamping end, and the second clamping surface and the energized surface are in contact with the other side of the clamping end.

4. The high-temperature biaxial tensile testing system for thin metal sheets based on current heating according to claim 1, characterized in that, The clamping block has a mounting hole; the conductive block has a connecting part that passes through and protrudes from the mounting hole; the portion of the connecting part that protrudes from the mounting hole has a connecting hole that is connected and fixed to the first cable.

5. The high-temperature biaxial tensile testing system for thin metal sheets based on current heating according to claim 1, characterized in that, The end of the clamping body that is fixedly connected to the clamping head is the tail end; the insulating part includes two insulating pads that are respectively attached to the two opposite sides of the tail end.

6. The high-temperature biaxial tensile testing system for thin metal sheets based on current heating according to claim 5, characterized in that, The tail end is provided with multiple fourth positioning holes, the clamping head is provided with multiple fifth positioning holes, and the insulating pad is provided with multiple sixth positioning holes. The fourth positioning holes, fifth positioning holes, and sixth positioning holes correspond one-to-one, and the fourth positioning hole is located between two sixth positioning holes, and the sixth positioning hole is located between the fourth positioning hole and the fifth positioning hole.

7. The high-temperature biaxial tensile testing system for thin metal sheets based on current heating according to claim 6, characterized in that, The insulating part includes multiple insulating rings, each insulating ring having an outer ring surface and an inner ring surface. The outer ring surface fits into the fourth positioning hole and the sixth positioning hole. The size of the inner ring surface is the same as the size of the fifth positioning hole. The biaxial tensile testing machine also includes a positioning pin, which passes through the fifth positioning hole, the inner ring surface, and the fifth positioning hole in sequence to fix the clamp to the clamping head.

8. A method for high-temperature biaxial tensile testing of thin metal sheets based on electric current heating, characterized in that, The testing method is performed using the testing system described in any one of claims 1 to 7, and the testing method includes the following steps: Step S10: Prepare the cross-shaped specimen; Step S20: Install the fixture and connect the cross specimen to the fixture; Step S30: Set the heating mechanism; Step S40: Construct the DIC strain measurement mechanism; Step S50: Set up the biaxial tensile testing machine and perform a tensile test on the cross specimen.

9. The method for high-temperature biaxial tensile testing of thin metal sheets based on current heating according to claim 8, characterized in that, The four clamping ends of the cross-shaped specimen are respectively the first clamping end, the second clamping end, the third clamping end, and the fourth clamping end arranged counterclockwise along the circumference; in step S30, when the DC heating power supply adopts the output power-on heating mode of single-path timing switching pulse, the first clamping end and the third clamping end are respectively connected to the positive and negative terminals of a pair of electrodes, and the second clamping end and the fourth clamping end are respectively connected to the positive and negative terminals of another pair of electrodes; only one pair of electrodes is energized to form a circuit within one pulse moment, while the other pair of electrodes is in an open circuit state; the circuits of the two pairs of electrodes are time-switched according to a predetermined frequency.

10. The method for high-temperature biaxial tensile testing of thin metal sheets based on current heating according to claim 8, characterized in that, The four clamping ends of the cross-shaped specimen are respectively the first clamping end, the second clamping end, the third clamping end, and the fourth clamping end arranged counterclockwise along the circumference. In step S30, when the DC heating power supply adopts a main two-phase positive electrode rotation pulse output heating mode, at the first pulse moment, the first clamping end is connected to the main positive electrode, and the second and fourth clamping ends are respectively connected to the secondary positive electrodes, the potential of the secondary positive electrode being half of the potential of the main positive electrode; the third clamping end is connected to the negative electrode; at each subsequent pulse moment, the electrode potential arrangement of the previous pulse moment is rotated by 90°.

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