Electrically-assisted biaxial tensile test device and method

Abstract

The invention provides an electrically-assisted biaxial tensile testing device and method, belongs to the technical field of material mechanical property characterization testing, and aims to solve the technical problem that the current direction is single when a tensile testing device in the prior art is used for electrically-assisted tensile testing. The electrically-assisted biaxial tensile test device comprises a test platform, the four stretching assemblies are arranged on the test platform, are connected with four stretching ends of the cross-shaped stretching sample and are used for stretching the cross-shaped stretching sample; the power supply is arranged on the test platform; the first single-pole four-throw switch is connected with the positive pole of the power supply and the four stretching assemblies, the second single-pole four-throw switch is connected with the negative pole of the power supply and the four stretching assemblies, the first control device is connected with the first single-pole four-throw switch, and the second control device is connected with the second single-pole four-throw switch. By arranging the two single-pole four-throw switches, the direction of current flowing through the cross-shaped tensile sample can be changed, so that the mechanical properties of the cross-shaped tensile sample in different current directions are obtained.

Description

Technical Field

[0001] The invention belongs to the technical field of material mechanical property characterization testing, and specifically relates to an electrically assisted biaxial tensile testing device and method. Background Art

[0002] In the fields of aerospace, transportation, etc., more high-strength materials (ultra-high-strength steel, composite materials and high-strength aluminum alloys, etc.) are used in complex components. As the strength of the material increases, the difficulty of its manufacturing process also increases, and the defects generated during the forming process become more difficult to control. Therefore, it is necessary to explore and improve the forming potential of difficult-to-deform materials. Metal materials have an electroplastic effect of increased plasticity and reduced deformation resistance when electrically assisted loading is applied. The electrically assisted forming process developed in combination with traditional plastic processing technology can greatly improve the material forming limit and forming quality.

[0003] Under the action of electric current, materials usually show the phenomenon of increased plasticity and reduced flow stress, which is called electroplastic effect. It mainly includes Joule heating effect and "non-thermal effect". "Non-thermal effect" is also called "pure electroplastic effect". There is still some controversy about the influence of "non-thermal effect" in existing research. In the current research context, accurately measuring the influence of pure electroplastic effect on materials is still a key technical challenge.

[0004] The electrically assisted tensile deformation process of metal materials is a complex deformation process of electric-thermal-mechanical coupling, involving the coupling of electromagnetic field, temperature field, deformation field and force field. At the same time, the electroplastic mechanism is complex due to the influence of multiple electrical, thermal and mechanical factors such as material properties, current parameters, temperature and strain distribution. Therefore, how to optimize and design reliable and accurate electroplastic effect test characterization test methods is the premise for exploring the electroplastic mechanism and developing the electrically assisted forming process.

[0005] In the current technical field, due to the limitations of test conditions and methods, most devices mainly use uniaxial stretching to stretch specimens under electrically assisted loading conditions. At the same time, the complex influence of current direction on material deformation behavior is not considered. The test conditions are limited and the test results are not ideal. Summary of the invention

[0006] The present invention aims to solve or improve the technical problem of a single current direction in a tensile testing device in the prior art during an electric-assisted tensile testing.

[0007] A first aspect of the present invention is to provide an electrically assisted biaxial tensile testing device.

[0008] A second aspect of the present invention is to provide an electrically assisted biaxial tensile testing method.

[0009] The electric-assisted biaxial tensile test device provided by the present invention comprises: a test platform; four tensile components, which are arranged on the test platform and connected to the four tensile ends of a cross tensile specimen, and are used to stretch the cross tensile specimen; a power supply, which is arranged on the test platform; a first single-pole four-throw switch, which is connected to the positive pole of the power supply and the four tensile components, and the four tensile components include a first tensile component, a second tensile component, a third tensile component and a fourth tensile component, and the first single-pole four-throw switch can be in a first position to electrically connect the positive pole of the power supply to the first tensile component, the first single-pole four-throw switch can be in a second position to electrically connect the positive pole of the power supply to the second tensile component, the first single-pole four-throw switch can be in a third position to electrically connect the positive pole of the power supply to the third tensile component, and the first single-pole four-throw switch can be in a fourth position to electrically connect the positive pole of the power supply to the fourth tensile component; a first control device, which is connected to the first single-pole four-throw switch and is used to control the single-pole four-throw switch to be in the first position, the second position, the third position or the fourth position; the second single-pole four-throw switch A single-pole four-throw switch is connected to the negative pole of the power supply and the four stretching components. The second single-pole four-throw switch can be in the fifth position to electrically connect the negative pole of the power supply to the first stretching component. The second single-pole four-throw switch can be in the sixth position to electrically connect the negative pole of the power supply to the second stretching component. The second single-pole four-throw switch can be in the seventh position to electrically connect the negative pole of the power supply to the third stretching component. The second single-pole four-throw switch can be in the eighth position to electrically connect the negative pole of the power supply to the fourth stretching component. A second control device is connected to the second single-pole four-throw switch and is used to control the second single-pole four-throw switch to be in the fifth position, the sixth position, the seventh position or the eighth position. An image acquisition device is provided on the test platform to acquire image information of the cross-stretching specimen during the stretching process. A temperature sensor is provided on the test platform to acquire the temperature of the cross-stretching specimen. An air-cooling spray device is provided on the test platform and is connected to the temperature sensor to spray cooling gas onto the cross-stretching specimen when the temperature of the cross-stretching specimen is greater than the temperature threshold.

[0010] The electrically assisted biaxial tensile test device provided by the present invention can accurately obtain the mechanical properties of the cross tensile specimen under electrically assisted loading conditions, that is, the mechanical properties of the cross tensile specimen under different currents can be understood, and the influence of different current characteristics on the plastic deformation process of the material can be evaluated. In addition, by setting two single-pole four-throw switches, the direction of the current flowing through the cross tensile specimen can be changed, so as to measure the tensile properties of the cross tensile specimen under different current directions, which is particularly suitable for metal rolled plates with strong anisotropy. It can be understood that strong anisotropy, that is, the mechanical properties in the rolling direction and the vertical rolling direction are quite different. For such materials, the influence of loading current in different directions on their tensile properties is relatively large, and conventional biaxial tensile test devices do not take into account the influence of current direction on the deformation behavior of the material, so their measurement effect is poor. The present invention can change the direction of the current flowing through the cross tensile specimen by setting two single-pole four-throw switches, so as to measure the mechanical properties of the cross tensile specimen under various current directions, and can deeply understand the mechanical behavior of the material. In addition, the electrically assisted biaxial tensile testing device of the present invention is also particularly suitable for tailor-welded plates, such as cross-welded plates such as body frame parts and door outer panels. The difference between the weld direction and the current direction has a greater impact on the deformation behavior of the tailor-welded plates. Therefore, the present invention can adjust different current directions, thereby capturing the mechanical properties of the tailor-welded plates under different current directions.

[0011] In addition, since the cross-tensile specimen will generate Joule heat during the process of power-on, the present invention is also provided with an air-cooling spray device, which can spray cooling gas onto the cross-tensile specimen to achieve temperature control when the temperature of the cross-tensile specimen is greater than the temperature threshold. The temperature threshold can be set independently, for example, 25°C. In this way, when the temperature of the cross-tensile specimen is higher than the temperature threshold during the power-on process, the air-cooling spray device can spray cooling gas onto the cross-tensile specimen, so that the temperature of the cross-tensile specimen is maintained at the set temperature, which can reduce the influence of the Joule heat effect caused by power-on on the performance of the specimen, thereby studying the influence of the pure electroplastic effect on the deformation behavior of the material.

[0012] It should be noted that, since the present invention needs to form a current conducting loop, the stretching component should be made of a material with conductive properties.

[0013] In some technical solutions, the power supply can be a direct current power supply or a low-frequency pulse power supply, and the influence of different current characteristics on the electroplastic effect of the material can be evaluated by changing the parameters of the power supply, such as the current magnitude, pulse frequency and duty cycle. When direct current passes through the material, the continuous flow of current may cause a stable thermal effect inside the material, while the intermittent low-frequency pulse current can reduce the accumulation of heat, thereby reducing the heat-affected zone.

[0014] In some technical solutions, optionally, the electrically assisted biaxial tensile testing device further includes a gas compressor connected to a temperature sensor and an air-cooled injection device. The gas compressor can adjust the operating power of the gas compressor according to the temperature of the cross-tensile specimen, thereby controlling the rate at which the air-cooled injection device injects cooling gas to maintain the specimen at a set temperature. The cooling gas can be compressed air, low-temperature nitrogen, etc. When the temperature of the cross-tensile specimen is higher than the temperature threshold, the gas compressor starts to compress the cooling gas, and discharges it from the air-cooled injection device and injects it onto the surface of the cross-tensile specimen to cool the cross-tensile specimen.

[0015] In some technical solutions, optionally, a temperature sensor can be in contact with the cross-tension specimen.

[0016] In this technical solution, the temperature sensor can contact the cross-tensile specimen. Since the air-cooled jet device is arranged above the cross-tensile specimen to cool the upper surface of the cross-tensile specimen, the temperature sensor can contact the lower surface of the cross-tensile specimen. This can improve the measurement accuracy, avoid the influence of the cooling gas sprayed by the air-cooled jet device on the temperature sensor, and avoid the influence of other heating elements in the system on the temperature sensor. Compared with infrared temperature sensors, the accuracy is high. Of course, considering the simple layout, the temperature sensor can also adopt a non-contact infrared temperature sensor, so that its design position is more diversified, such as being set on a test platform.

[0017] In some technical schemes, optionally, the electrically-assisted biaxial tensile testing device also includes: a bracket, arranged on the test platform; a driving device, arranged on the bracket; a top plate, connected to the driving device, and the driving device can drive the top plate to perform lifting movements; four trapezoidal blocks, connected to the top plate, and the four trapezoidal blocks are arranged corresponding to four tensile components, wherein, when the driving device drives the top plate to descend, each trapezoidal block can contact the corresponding tensile component and make the tensile component move in a direction away from the cross-tensile specimen to stretch the cross-tensile specimen.

[0018] In this technical solution, four trapezoidal blocks are correspondingly arranged above four tensile assemblies, so that when the driving device drives the top plate to descend, each trapezoidal block can contact the corresponding tensile assembly and make the tensile assembly move away from the cross tensile specimen, so that the four tensile assemblies stretch the cross tensile specimen at the same time. The driving device can be a universal testing machine.

[0019] In some technical solutions, the four trapezoidal blocks can be optionally identical, which is equivalent to the same tensile force of the four tensile components on the cross tensile specimen. Of course, the four trapezoidal blocks can also be different. When the four trapezoidal blocks are different, biaxial tensile tests with multiple ratios such as 1:4, 2:4, 3:4, 4:4, etc. can be achieved by replacing trapezoidal blocks with different angles, so that the tensile ratio can be easily adjusted according to different test requirements.

[0020] In some technical solutions, optionally, a connection hole is provided on the top plate, and an insertion portion is provided on each trapezoidal block, and the insertion portion can be inserted into the connection hole, so as to fix the trapezoidal block on the top plate. Optionally, there are multiple connection holes, and the insertion portion of each trapezoidal block can be inserted into different connection holes to adjust the position of the trapezoidal block on the top plate to adapt to cross tensile specimens of various sizes, and can perform stretching for tensile specimens of different sizes.

[0021] In some technical schemes, optionally, the stretching assembly includes: a stretching frame, the stretching frame includes an avoidance space; a rolling wheel, the rolling wheel is arranged on the stretching frame; a clamp, connected to the stretching frame, and used to clamp the cross tensile specimen; wherein, during the descending process of the top plate, the trapezoidal block can pass through the avoidance space and contact the rolling wheel to squeeze the stretching frame to move away from the cross tensile specimen, so as to drive the clamp to stretch the cross tensile specimen.

[0022] In this technical solution, when the trapezoidal block descends along with the top plate, the trapezoidal block gradually goes deeper into the avoidance space of the fixed frame. During this process, the inclined edge of the trapezoidal block inevitably contacts the rolling wheel. When the rolling wheel slides on the inclined edge of the trapezoidal block, it bears the pressure from the trapezoidal block and also converts this force into an outward tensile force, so that the tensile frame is pulled, thereby achieving precise stretching of the cross tensile specimen. By providing a rolling wheel, the present invention can avoid direct contact between the trapezoidal block and the tensile frame, convert sliding friction into rolling friction, and reduce power loss.

[0023] In some technical solutions, optionally, the stretching assembly also includes two force transmission columns and a tension sensor. The tension sensor is arranged between the force transmission columns at both ends, one of the force transmission columns is connected to the stretching frame, and the other of the force transmission columns is connected to the clamp. The tension sensor of the present invention has high sensitivity and accuracy, and can accurately measure and record the stress borne by the cross-tensile specimen during the stretching process.

[0024] In some technical solutions, optionally, the rolling wheel is made of materials with excellent insulation properties, such as rubber, nylon, etc. These materials can effectively prevent the conduction of electric current, not only ensuring the safety of the cross-tensile specimen, but also providing good mechanical properties and wear resistance.

[0025] In some technical solutions, optionally, the surface of the trapezoidal block in contact with the rolling wheel is provided with a track groove, and this structure can effectively guide the rolling wheel to maintain a correct track and avoid errors caused by deviation of the rolling wheel.

[0026] In some technical solutions, optionally, the wire connecting the power source and the stretching frame can be a high-conductivity copper wire.

[0027] In some technical solutions, optionally, a fixing hole is provided on the clamp, and a connecting hole is provided on the cross tensile specimen, and a locking piece can be inserted into the fixing hole and the connecting hole to ensure that the clamp accurately clamps the cross tensile specimen and does not fall off the clamp.

[0028] In some technical schemes, optionally, the electrically-assisted biaxial tensile testing device also includes four support components, each support component is used to support a stretching frame, and the support components include: a support column, which is arranged on the test platform, and a longitudinal slide groove is provided on the support column; a support block, which is fixedly arranged on the support column, and a transverse slide groove is provided on the support block, and the stretching frame is slidably arranged in the transverse slide groove; a guide wheel, which is slidably arranged on the longitudinal slide groove and is correspondingly arranged below the trapezoidal block; wherein, during the descent of the trapezoidal block, it can abut against the corresponding guide wheel to guide the trapezoidal block through the guide wheel.

[0029] In this technical solution, the guide wheel is arranged below the trapezoidal block, so that during the descent of the trapezoidal block, it can contact the corresponding two guide wheels, that is, the trapezoidal block can be engaged with the inner side of the two guide wheels, so that the trapezoidal block can move downward together with the guide wheels, so that the two guide wheels can guide the trapezoidal block, thereby improving the force transmission efficiency and avoiding the deviation of the movement trajectory of the trapezoidal block. In addition, a transverse slide groove is also arranged on the support block, so that the transverse slide groove can guide the stretching frame in the transverse direction, that is, the guiding direction of the transverse slide groove is the direction in which the stretching frame moves away from the cross tensile specimen, so that the sliding direction of the stretching frame can be ensured, thereby improving the stretching efficiency.

[0030] In some technical schemes, optionally, the electrically-assisted biaxial tensile testing device also includes: a fixed column, which is arranged on the testing platform; a support rod, which is connected to the fixed column, the support rod can be lifted and lowered relative to the fixed column, and the fixed column can be rotated relative to the testing platform, and the image acquisition device is arranged on the support rod.

[0031] In this technical solution, the support rod can move up and down relative to the fixed column, and the fixed column can rotate relative to the test platform. The image acquisition device is arranged on the support rod. Such a design is equivalent to the image acquisition device being able to move up and down and also being able to rotate. The lifting movement is for testing different types of cross-tensile specimens. Understandably, for cross-tensile specimens with smaller specifications, it is necessary to increase the height of the image acquisition device, so that the image information of the cross-tensile specimen can be obtained more clearly and the measurement accuracy can be improved. For cross-tensile specimens with larger specifications, it is necessary to lower the height of the image acquisition device to ensure that the image acquisition device can obtain all the image information of the cross-tensile specimen and ensure the measurement accuracy. The rotation movement is to change the image acquisition angle of the image acquisition device, so that the image information of the cross-tensile specimen can be obtained from multiple angles, which is better for the later deformation feature analysis.

[0032] Furthermore, in order to realize the lifting and lowering movement or rotation of the support rod relative to the fixed column, a variety of connection methods can be adopted. For example, the fixed column is an outer cylinder, the support rod is an inner cylinder, and the outer cylinder is sleeved outside the inner cylinder, so that the inner cylinder can perform lifting and lowering movement and rotation relative to the outer cylinder. At the same time, multiple rows of longitudinal locking holes are arranged in the longitudinal direction of the outer cylinder, and multiple rows of circumferential locking holes are arranged in the circumference of the outer cylinder, and a locking piece is arranged on the inner cylinder. When the locking piece of the inner cylinder is connected to the longitudinal locking holes of different heights, the height of the inner cylinder relative to the outer cylinder can be adjusted. When the locking piece of the inner cylinder is connected to different circumferential locking holes, the rotation angle of the inner cylinder relative to the outer cylinder can be adjusted.

[0033] In some technical solutions, optionally, the cross tensile specimen includes a metal plate, a tailor-welded plate, a multi-metal composite plate or a plate of different thickness.

[0034] In this technical solution, since the weld seam is provided on the tailor-welded plate, the influence of the current in different directions on the tensile mechanical properties of the tailor-welded plate can be analyzed by adjusting the direction of the current. The multi-metal composite plate, for example, can be a copper-aluminum composite plate. In this way, the current first passes through copper or aluminum, and the influence on the mechanical properties of the tensile specimen is also different. Therefore, the influence of the current in different directions on the mechanical properties of the tensile specimen can also be analyzed. In addition, the cross tensile specimen can also be a differential thickness plate, that is, the thickness of the differential thickness plate varies along a certain direction. Of course, for the tailor-welded plate, the thickness of the two plates can also be different. Therefore, for this type of tensile specimen, the influence of the current in different directions on the mechanical properties of the tensile specimen can be analyzed by changing the direction of the current. In addition, the cross tensile specimen of the present invention is not limited to tailor-welded plates, multi-metal composite plates or differential thickness plates. As long as the cross tensile specimen has a greater impact on the mechanical properties of the tensile specimen when changing different current directions, it can be used.

[0035] In some technical solutions, optionally, the electrically-assisted biaxial tensile testing device also includes: a circuit breaker, which is arranged between the power supply and the first single-pole four-throw switch, or between the power supply and the second single-pole four-throw switch, and the circuit breaker can automatically disconnect when the current is greater than a threshold value.

[0036] In this technical solution, a circuit breaker is set between the power supply and the first single-pole four-throw switch or between the power supply and the second single-pole four-throw switch. In this way, when the current in the loop is greater than the threshold, it indicates that there is a short circuit in the loop. At this time, the circuit breaker can be automatically disconnected, thereby ensuring the safety of the device.

[0037] In some technical solutions, optionally, the outer surfaces of the stretching frame, force transmission column and clamp can be insulated. For example, a layer of insulating coating is provided on the outer surfaces of the stretching frame, force transmission column and clamp. Specifically, physical vapor deposition or chemical vapor deposition can be used to plate an alumina ceramic coating or a ceramic polymer coating on the outer surfaces of the stretching frame, force transmission column and clamp, so as to avoid the problem of electric shock caused by the conductive conduction of the stretching frame, force transmission column and clamp exposed to the outside during the power-on process.

[0038] The technical solution of the second aspect of the present invention provides a testing method for an electrically assisted biaxial tensile testing device, comprising: controlling a first single-pole four-throw switch to be in a first position through a first control device so that the positive pole of the power supply is electrically connected to the first tensile component; controlling a second single-pole four-throw switch to be in a seventh position through a second control device so that the negative pole of the power supply is electrically connected to the third tensile component to form a first closed loop; after the current in the first closed loop is turned on for a preset period of time, obtaining the temperature of the cross tensile specimen collected by the temperature sensor; when the temperature of the cross tensile specimen is greater than the preset temperature, controlling the air-cooling spray device to spray cooling gas onto the surface of the cross tensile specimen, and stopping the spraying when the temperature of the cross tensile specimen is equal to the preset temperature; controlling the four tensile components The components are used to stretch the four stretching ends of the cross-stretching specimen respectively, and the first image information of the cross-stretching specimen during the stretching process is obtained through the image acquisition device; the first single-pole four-throw switch is controlled to be in the second position through the first control device, so that the positive pole of the power supply is electrically connected to the second stretching component; the second single-pole four-throw switch is controlled to be in the eighth position through the second control device, so that the negative pole of the power supply is electrically connected to the fourth stretching component to form a second closed loop; the four stretching components are controlled to stretch the four stretching ends of the cross-stretching specimen respectively, and the second image information of the cross-stretching specimen during the stretching process is obtained through the image acquisition device; based on the first image information, the second image information and the stress data, the influence of different current directions on the mechanical properties of the specimen is analyzed. Among them, the stress data is also the data collected by the tension sensor.

[0039] The beneficial effects of the present invention are as follows: the electrically assisted biaxial tensile testing device of the present invention can quantify the pure electroplastic effect, the device has a simple structure, the cross tensile specimen is easy to disassemble, and it has good practicability. It can be widely used in cross tensile specimens of various sizes, ensuring the efficiency and accuracy of the test. The rolling wheel and the guide wheel are made of insulating material, which can ensure the safety of the test. The trapezoidal block adopts a detachable design, and the trapezoidal blocks in different positions and angles can be replaced, thereby adapting to cross tensile specimens of various sizes, and biaxial stretching of different proportions can also be achieved. The power supply can be a DC power supply or a low-frequency pulse power supply, so as to evaluate the influence of different current characteristics on the electroplastic effect. The air-cooled injection device can release cooling gas to keep the cross tensile specimen at room temperature, so as to study the influence of the pure electroplastic effect on the deformation behavior of the material, especially being able to decouple the influence of the current direction on the electroplastic effect.

[0040] Additional aspects and advantages of the present invention will become apparent in the following description or may be learned through practice of the present invention. BRIEF DESCRIPTION OF THE DRAWINGS

[0041] According to the above aspects and advantages, embodiments are described in conjunction with the following drawings, so that the features of the present invention are distinct and easy to understand, wherein:

[0042] Figure 1 An exploded view of an electrically assisted biaxial tensile testing device according to an embodiment of the present invention;

[0043] Figure 2 A structural diagram of a single-pole four-throw switch portion of an electrically assisted biaxial tensile testing device according to an embodiment of the present invention;

[0044] Figure 3 A structural diagram of a support assembly portion of an electrically assisted biaxial tensile testing device according to an embodiment of the present invention;

[0045] Figure 4 This is one of the structural schematic diagrams of the electrically assisted biaxial tensile testing device according to an embodiment of the present invention;

[0046] Figure 5 This is a second structural schematic diagram of the electrically assisted biaxial tensile testing device according to an embodiment of the present invention;

[0047] Figure 6 This is a third structural schematic diagram of the electrically assisted biaxial tensile testing device according to an embodiment of the present invention;

[0048] Figure 7 It is a schematic structural diagram of a cross tensile specimen according to an embodiment of the present invention;

[0049] Figure 8 This is a fourth structural schematic diagram of the electrically assisted biaxial tensile testing device according to an embodiment of the present invention;

[0050] Fig. 9 This is a fifth structural schematic diagram of the electrically assisted biaxial tensile testing device according to an embodiment of the present invention;

[0051] Fig.10 A force decomposition principle diagram of an electrically assisted biaxial tensile testing device according to an embodiment of the present invention;

[0052] Fig.11 This is the sixth structural schematic diagram of the electrically assisted biaxial tensile testing device according to an embodiment of the present invention.

[0053] in, Figures 1 to 11 The corresponding relationship between the reference numerals and component names in the figure is:

[0054] 1Electrically assisted biaxial tensile testing device, 11testing platform, 12tensile assembly, 121first tensile assembly, 122second tensile assembly, 123third tensile assembly, 124fourth tensile assembly, 1251tensile frame, 1252rolling wheel, 1253clamp, 1254avoidance space, 1255force transmission column, 1256tensile sensor, 13cross tensile specimen, 132weld, 14power supply, 15current guide control device, 152 a single-pole four-throw switch, 156 a second single-pole four-throw switch, 162 an image acquisition device, 164 a temperature sensor, 166 an air-cooled injection device, 168 a light source, 174 a fixing column, 176 a support rod, 178 a circuit breaker, 182 a bracket, 184 a driving device, 186 a top plate, 187 a connecting hole, 188 a trapezoidal block, 189 a hanging column, 19 a supporting assembly, 192 a supporting column, 194 a supporting block, 195 a horizontal slide groove, 196 a guide wheel. DETAILED DESCRIPTION

[0055] In order to more clearly understand the above aspects, features and advantages of the embodiments of the present invention, the embodiments of the present invention are further described in detail below in conjunction with the accompanying drawings and specific implementation methods. It should be noted that the embodiments of the present application and the features in the embodiments can be combined with each other without conflict.

[0056] In the following description, many specific details are set forth to facilitate a full understanding of the embodiments according to the present invention. However, the embodiments according to the present invention may also be implemented in other ways different from those described herein. Therefore, the protection scope of the embodiments according to the present invention is not limited to the specific embodiments disclosed below.

[0057] like Figure 1 , Figure 2 , Figure 4 , Figure 5 and Fig.11As shown, the electric-assisted biaxial tensile test device 1 provided in this embodiment includes a test platform 11, four tensile components 12 are arranged on the test platform 11, and are connected to the four tensile ends of the cross tensile specimen 13, so as to stretch the cross tensile specimen 13; a power supply 14 is arranged on the test platform 11; a current guiding control device 15 includes a first single-pole four-throw switch 152, a second single-pole four-throw switch 156, a first control device and a second control device, the first single-pole four-throw switch 152 is connected to the positive electrode of the power supply 14 and the four tensile components 12, and the four tensile components 12 include a first tensile component 121, a second tensile component 122, and a third tensile component 12 3 and the fourth stretching component 124, the first single-pole four-throw switch 152 can be in a first position to electrically connect the positive electrode of the power supply 14 to the first stretching component 121, the first single-pole four-throw switch 152 can be in a second position to electrically connect the positive electrode of the power supply 14 to the second stretching component 122, the first single-pole four-throw switch 152 can be in a third position to electrically connect the positive electrode of the power supply 14 to the third stretching component 123, and the first single-pole four-throw switch 152 can be in a fourth position to electrically connect the positive electrode of the power supply 14 to the fourth stretching component 124; the first control device is connected to the first single-pole four-throw switch 152, and is used to control the single-pole four-throw switch The switch is in the first position, the second position, the third position or the fourth position; the second single-pole four-throw switch 156 is connected to the negative pole of the power supply 14 and the four tensile components 12, the second single-pole four-throw switch 156 can be in the fifth position to electrically connect the negative pole of the power supply 14 to the first tensile component 121, the second single-pole four-throw switch 156 can be in the sixth position to electrically connect the negative pole of the power supply 14 to the second tensile component 122, the second single-pole four-throw switch 156 can be in the seventh position to electrically connect the negative pole of the power supply 14 to the third tensile component 123, the second single-pole four-throw switch 156 can be in the eighth position to electrically connect the negative pole of the power supply 14 to the first tensile component 121, the second single-pole four-throw switch 156 can be in the eighth position to electrically connect the negative pole of the power supply 14 to the second tensile component 122. The four tensile components 124 are electrically connected; the second control device is connected to the second single-pole four-throw switch 156, and is used to control the second single-pole four-throw switch 156 to be in the fifth position, the sixth position, the seventh position or the eighth position; the image acquisition device 162 is arranged on the test platform 11, and is used to obtain image information of the cross tensile specimen 13 during the stretching process; the temperature sensor 164 is arranged on the test platform 11, and is used to obtain the temperature of the cross tensile specimen 13; the air-cooling injection device 166 is arranged on the test platform 11, and is electrically connected to the temperature sensor 164, and is used to inject cooling gas onto the cross tensile specimen 13 when the temperature of the cross tensile specimen 13 is greater than the temperature threshold.

[0058] The electrically assisted biaxial tensile test device 1 provided by the present invention can accurately obtain the mechanical properties of the cross tensile specimen 13 under electrically assisted loading conditions, that is, the mechanical properties of the cross tensile specimen 13 under different currents can be understood, and the influence of different current characteristics on the plastic deformation process of the material can be evaluated. In addition, by setting two single-pole four-throw switches, the direction of the current flowing through the cross tensile specimen 13 can be changed, so as to measure the tensile properties of the cross tensile specimen 13 under different current directions, which is particularly suitable for metal rolled plates with strong anisotropy. It can be understood that strong anisotropy can be understood as a large difference in mechanical properties between the rolling direction and the vertical rolling direction. For such a material, the influence of loading current in different directions on its tensile properties is large, and conventional biaxial tensile test devices do not take into account the influence of current direction on the deformation behavior of the material, so its measurement effect is poor. The present invention changes the direction of the current flowing through the cross tensile specimen 13 by setting two single-pole four-throw switches, so that the mechanical properties of the cross tensile specimen 13 under various current directions can be measured, and the mechanical behavior of the material can be deeply understood. In addition, the electrically assisted biaxial tensile testing device 1 of the present invention is also particularly suitable for tailor-welded plates, such as cross-welded plates such as body frame parts and door outer panels. The difference between the weld direction and the current direction has a greater impact on the deformation behavior of the tailor-welded plates. Therefore, the present invention can adjust different current directions, so that the mechanical properties of the tailor-welded plates under different current directions can be understood.

[0059] In addition, since the cross tensile specimen 13 generates Joule heat during the process of electrification, the present invention is further provided with an air-cooling injection device 166, which is arranged above the cross tensile specimen 13 and can spray cooling gas onto the cross tensile specimen 13 when the temperature of the cross tensile specimen 13 is greater than the temperature threshold. The temperature threshold can be 22°C to 28°C, for example, 25°C. In this way, when the temperature of the cross tensile specimen 13 is higher than the temperature threshold during the electrification process, the air-cooling injection device 166 can spray cooling gas onto the cross tensile specimen 13, thereby maintaining the temperature of the cross tensile specimen 13 at room temperature, which can reduce the influence of the Joule heat effect caused by electrification on the performance of the specimen, thereby studying the influence of the pure electroplastic effect on the deformation behavior of the material.

[0060] It should be noted that, since the present invention needs to form a conductive loop, the stretching element 12 should be made of a material with conductive properties.

[0061] In some technical solutions, the power source 14 may be a direct current power source 14 or a low-frequency pulse power source 14. The effects of different current characteristics on the electroplastic effect of the material may be evaluated by changing the parameters of the power source 14, such as the current magnitude, pulse frequency, and duty cycle. When a direct current passes through a material, the continuous flow of the current may cause a stable thermal effect to be generated inside the material, while when a low-frequency pulse current acts on the material intermittently, the accumulation of heat may be reduced, thereby reducing the heat-affected zone.

[0062] In some technical solutions, optionally, the electrically assisted biaxial tensile testing device 1 also includes a gas compressor connected to the temperature sensor 164 and the air-cooling injection device 166. The gas compressor can adjust the operating power of the gas compressor according to the temperature of the cross-tensile specimen 13, and then control the rate at which the air-cooling injection device 166 injects cooling gas to maintain the specimen at a set temperature. The cooling gas can be compressed air, low-temperature nitrogen, etc. When the temperature of the cross-tensile specimen 13 is higher than the temperature threshold, the gas compressor starts to compress the cooling gas, and discharges it from the air-cooling injection device 166, and injects it on the surface of the cross-tensile specimen 13 to cool the cross-tensile specimen 13.

[0063] In some technical solutions, optionally, the temperature sensor 164 can be in contact with the cross tensile specimen 13 .

[0064] In this technical solution, the temperature sensor 164 can be arranged on the test platform 11 through a bracket (not shown), so that the temperature sensor 164 can contact with the cross tensile specimen 13. Since the air-cooling spray device 166 is arranged above the cross tensile specimen 13 to cool the upper surface of the cross tensile specimen 13, the temperature sensor 164 can contact with the lower surface of the cross tensile specimen 13, which can improve the accuracy of the measurement, avoid the influence of the cooling gas sprayed by the air-cooling spray device 166 on the temperature sensor 164, and avoid the influence of other heating elements in the system on the temperature sensor 164. Compared with non-contact sensors such as infrared temperature sensors, the accuracy is high. Of course, considering the simple layout, the temperature sensor 164 can also adopt a non-contact infrared temperature sensor 164, so that its design position is more diverse, such as being arranged on the test platform 11.

[0065] In some technical solutions, optionally, as Figure 1 and Figure 8 As shown, the electrically assisted biaxial tensile testing device 1 also includes: a bracket 182, which is arranged on the test platform 11; a driving device 184, which is arranged on the bracket 182; a top plate 186, which is connected to the driving device 184, and the driving device 184 can drive the top plate 186 to perform lifting movements; four trapezoidal blocks 188, which are connected to the top plate 186, and the four trapezoidal blocks 188 are arranged corresponding to the four tensile components 12, wherein, when the driving device 184 drives the top plate 186 to descend, each trapezoidal block 188 can contact the corresponding tensile component 12 and make the tensile component 12 move in a direction away from the cross tensile specimen 13 to stretch the cross tensile specimen 13.

[0066] In this technical solution, four trapezoidal blocks 188 are correspondingly arranged above four tensile assemblies 12, so that when the driving device 184 drives the top plate 186 to descend, each trapezoidal block 188 can contact the corresponding tensile assembly 12 and make the tensile assembly 12 move away from the cross tensile specimen 13, so that the four tensile assemblies 12 can stretch the cross tensile specimen 13 at the same time. The driving device 184 can be a universal testing machine.

[0067] In some technical solutions, the four trapezoidal blocks 188 can be completely identical, which is equivalent to the four tensile components 12 exerting the same tensile force on the cross tensile specimen 13. Of course, the four trapezoidal blocks 188 can also be different. When the four trapezoidal blocks 188 are different, biaxial tensile tests with various ratios such as 1:4, 2:4, 3:4, and 4:4 can be achieved by replacing the trapezoidal blocks 188 with different angles, so that the tensile ratio can be easily adjusted according to different test requirements.

[0068] In some technical solutions, optionally, as Figure 1 As shown, a connection hole 187 is provided on the top plate 186, and an insertion portion (not shown) is provided on each trapezoidal block 188, and the insertion portion can be inserted into the connection hole 187, so as to fix the trapezoidal block 188 on the top plate 186. Optionally, there are multiple connection holes 187, and the insertion portion of each trapezoidal block 188 can be inserted into different connection holes 187 to adjust the position of the trapezoidal block 188 on the top plate 186 to adapt to cross tensile specimens 13 of various sizes, and can perform tensile tests for cross tensile specimens 13 of different sizes. Of course, in another embodiment, four slideways can also be provided on the top plate 186, and then sliding portions are provided on the four trapezoidal blocks 188, and the sliding portion on each trapezoidal block 188 can slide in the corresponding slideway, so as to adjust the position of the trapezoidal block 188 on the top plate 186, so as to adapt to cross tensile specimens 13 of different sizes.

[0069] In some technical solutions, optionally, as Figure 1 and Figure 5 As shown, the stretching assembly 12 includes: a stretching frame 1251, the stretching frame 1251 includes an avoidance space 1254; a rolling wheel 1252, the rolling wheel is arranged on the stretching frame 1251; a clamp 1253, connected to the stretching frame 1251, and used to clamp the cross tensile specimen 13; wherein, during the descending process of the top plate 186, the trapezoidal block 188 can pass through the avoidance space 1254 and contact with the rolling wheel 1252, so as to squeeze the stretching frame 1251 to move away from the cross tensile specimen 13, so as to drive the clamp 1253 to stretch the cross tensile specimen 13.

[0070] In this technical solution, when the trapezoidal block 188 descends along with the top plate 186, the trapezoidal block 188 gradually penetrates into the avoidance space 1254 of the fixed frame. During this process, the hypotenuse of the trapezoidal block 188 inevitably contacts the rolling wheel 1252. When the rolling wheel 1252 slides on the hypotenuse of the trapezoidal block 188, it bears the pressure from the trapezoidal block 188 and also converts this force into an outward tensile force, so that the tensile frame 1251 is pulled, thereby achieving precise stretching of the cross tensile specimen 13. By providing the rolling wheel 1252, the present invention can avoid direct contact between the trapezoidal block 188 and the tensile frame 1251, convert sliding friction into rolling friction, and reduce power loss.

[0071] In some technical solutions, optionally, as Figure 5 As shown, the stretching assembly 12 also includes two force transmission columns 1255 and a tension sensor 1256. The tension sensor 1256 is arranged between the force transmission columns 1255 at both ends, wherein one force transmission column 1255 is connected to the stretching frame 1251, and the other force transmission column 1255 is connected to the clamp 1253. The tension sensor 1256 of the present invention has high sensitivity and accuracy, and can accurately measure and record the stress borne by the cross tensile specimen 13 during the stretching process.

[0072] In some technical solutions, optionally, the rolling wheel 1252 is made of a material with excellent insulation properties, such as rubber, nylon, etc. These materials can effectively prevent the conduction of current, not only ensuring the safety of the cross tensile specimen 13, but also providing good mechanical properties and wear resistance.

[0073] In some technical solutions, optionally, the surface of the trapezoidal block 188 that contacts the rolling wheel 1252 is provided with a track groove (not shown). This structure can effectively guide the rolling wheel 1252 to maintain the correct track and avoid errors caused by deviation of the rolling wheel 1252.

[0074] In some technical solutions, optionally, the wire connecting the power source 14 and the stretching frame 1251 can be a high-conductivity copper wire.

[0075] In some technical solutions, optionally, as Figure 7 As shown, a fixing hole is provided on the clamp 1253, and a connecting hole 187 is provided on the cross tensile specimen 13. The fixing hole and the connecting hole 187 can be inserted through a locking piece, thereby ensuring that the clamp 1253 accurately clamps the cross tensile specimen 13 and will not fall off the clamp 1253.

[0076] In some technical solutions, such as Figure 1 , Figure 3 and Figure 6As shown, optionally, the electrically assisted biaxial tensile testing device 1 also includes four support assemblies 19, each support assembly 19 is used to support a stretching frame 1251, and the support assembly 19 includes: a support column 192, which is arranged on the test platform 11, and a longitudinal slide groove (not shown in the figure) is arranged on the support column 192; a support block 194, which is fixedly arranged on the support column 192, and a transverse slide groove 195 is arranged on the support block 194, and the stretching frame 1251 is slidably arranged in the transverse slide groove 195; a guide wheel 196, which is slidably arranged on the longitudinal slide groove and is correspondingly arranged below the trapezoidal block 188; wherein, during the descent process of the trapezoidal block 188, it can abut against the corresponding guide wheel 196 to guide the trapezoidal block 188 through the guide wheel 196.

[0077] In this technical solution, the guide wheel 196 is arranged below the trapezoidal block 188, so that the trapezoidal block 188 can abut against the corresponding two guide wheels 196 during the descent process, that is, the trapezoidal block 188 can be engaged with the inner side of the two guide wheels 196, so that the trapezoidal block 188 can move downward together with the guide wheels 196, so that the two guide wheels 196 can guide the trapezoidal block 188, thereby improving the force transmission efficiency and avoiding the deviation of the movement trajectory of the trapezoidal block 188. In addition, a transverse slide groove 195 is also arranged on the support block 194, so that the transverse slide groove 195 can guide the stretching frame 1251 in the transverse direction, that is, the guiding direction of the transverse slide groove 195 is the direction in which the stretching frame 1251 moves away from the cross tensile specimen 13, so that the sliding direction of the stretching frame 1251 can be ensured, thereby improving the stretching efficiency.

[0078] In some technical solutions, optionally, as Fig. 9 As shown, the electrically assisted biaxial tensile testing device 1 also includes: a fixed column 174, which is arranged on the testing platform 11; a support rod 176, which is connected to the fixed column 174, and the support rod 176 can be lifted and lowered relative to the fixed column 174, and the fixed column 174 can be rotated relative to the testing platform 11, and the image acquisition device 162 is arranged on the support rod 176.

[0079] In this technical solution, the support rod 176 can do lifting motion relative to the fixed column 174, and the fixed column 174 can rotate relative to the test platform 11. The image acquisition device 162 is arranged on the support rod 176. Such a design is equivalent to the image acquisition device 162 being able to do lifting motion and also rotating. The lifting motion is for testing different types of cross tensile specimens 13. It is understandable that for the cross tensile specimens 13 with smaller specifications, it is necessary to increase the height of the image acquisition device 162, so that the image information of the cross tensile specimen 13 can be obtained more clearly and the measurement accuracy can be improved. For the cross tensile specimens 13 with larger specifications, it is necessary to lower the height of the image acquisition device 162 to ensure that the image acquisition device 162 can obtain all the image information of the cross tensile specimen 13 and ensure the measurement accuracy. The rotation motion is to change the image acquisition angle of the image acquisition device 162, so that the image information of the cross tensile specimen 13 can be obtained from multiple angles, which is better for the later analysis effect.

[0080] Furthermore, in order to realize the lifting and lowering movement or rotation of the support rod 176 relative to the fixed column 174, a variety of connection methods can be adopted, for example, the fixed column 174 is an outer cylinder, the support rod 176 is an inner cylinder, and the outer cylinder is sleeved outside the inner cylinder, so that the inner cylinder can perform lifting and lowering movement and rotation relative to the outer cylinder, and at the same time, multiple rows of longitudinal locking holes are provided in the longitudinal direction of the outer cylinder, multiple rows of circumferential locking holes are provided in the circumference of the outer cylinder, and a locking piece is provided on the inner cylinder, so that when the locking piece of the inner cylinder is connected with the longitudinal locking holes of different heights, the height of the inner cylinder relative to the outer cylinder can be adjusted, and when the locking piece of the inner cylinder is connected with different circumferential locking holes, the rotation angle of the inner cylinder relative to the outer cylinder can be adjusted. Alternatively, a rotating motor is provided to connect with the fixed column 174, and the fixed column 174 is driven to rotate on the test platform 11 by the rotating motor.

[0081] In some technical solutions, optionally, the cross tensile specimen 13 includes a metal plate, a tailor-welded plate, a multi-metal composite plate or a plate of different thickness.

[0082] In this technical solution, if Figure 7As shown, since the weld 132 is provided on the tailor-welded plate, the influence of the current in different directions on the tensile mechanical properties of the tailor-welded plate can be analyzed by adjusting the direction of the current. The multi-metal composite plate, for example, can be a copper-aluminum composite plate. In this way, the current first passes through copper or aluminum, and the influence on the mechanical properties of the tensile specimen is also different. Therefore, the influence of the current in different directions on the mechanical properties of the cross tensile specimen 13 can also be analyzed. In addition, the cross tensile specimen can also be a differential thickness plate, that is, the thickness of the differential thickness plate varies along a certain direction. Of course, for the tailor-welded plate, the thickness of the two plates can also be different. Therefore, for this type of tensile specimen, the influence of the current in different directions on the mechanical properties of the tensile specimen can be analyzed by changing the direction of the current. In addition, the cross tensile specimen of the present invention is not limited to tailor-welded plates, multi-metal composite plates or differential thickness plates. As long as the cross tensile specimen has a greater influence on the mechanical properties of the tensile specimen when changing different current directions, it can be used. Among them, the metal sheet can be a metal sheet that is difficult to deform.

[0083] In some technical solutions, optionally, as Figure 2 As shown, the electrically assisted biaxial tensile testing device 1 also includes: a circuit breaker 178, which is arranged between the power supply 14 and the first single-pole four-throw switch 152, or between the power supply 14 and the second single-pole four-throw switch 156. The circuit breaker 178 can automatically disconnect when the current is greater than a threshold.

[0084] In this technical solution, a circuit breaker 178 is provided between the power supply 14 and the first single-pole four-throw switch 152 or between the power supply 14 and the second single-pole four-throw switch 156. Thus, when the current in the loop is greater than the threshold value, it indicates that there is a short circuit in the loop. At this time, the circuit breaker 178 can be automatically disconnected, thereby ensuring the safety of the device.

[0085] In some technical solutions, optionally, the outer surfaces of the stretching frame 1251, the force transmission column 1255 and the clamp 1253 can be insulated. For example, a layer of insulating coating is provided on the outer surfaces of the stretching frame 1251, the force transmission column 1255 and the clamp 1253. Specifically, physical vapor deposition or chemical vapor deposition can be used to plate an alumina ceramic coating or a ceramic polymer coating on the outer surfaces of the stretching frame 1251, the force transmission column 1255 and the clamp 1253, so as to avoid the problem of electric shock caused by the conductive conduction of the stretching frame 1251, the force transmission column 1255 and the clamp 1253 exposed to the outside during the power-on process.

[0086] The beneficial effects of the present invention are as follows: the electrically assisted biaxial tensile testing device 1 of the present invention can quantify the pure electroplastic effect, the device has a simple structure, the cross tensile specimen 13 is easy to disassemble, and the device has good practicability. It can be widely applied to cross tensile specimens 13 of various sizes, ensuring the efficiency and accuracy of the test. The rolling wheel 1252 and the guide wheel 196 are made of insulating material, which can ensure the safety of the test. The trapezoidal block 188 adopts a detachable design, and the trapezoidal blocks 188 of different positions and angles can be replaced, thereby adapting to cross tensile specimens 13 of various sizes, and biaxial stretching of different proportions can also be achieved. The power supply 14 can be a DC power supply 14 or a low-frequency pulse power supply 14, so as to evaluate the influence of different current characteristics on the electroplastic effect. The air-cooled injection device 166 can release cooling gas to keep the cross tensile specimen 13 at room temperature, so as to study the influence of the pure electroplastic effect on the deformation behavior of the material.

[0087] Another embodiment of the present invention provides a testing method for an electrically assisted biaxial tensile testing device 1, comprising: controlling a first single-pole four-throw switch 152 to be in a first position by a first control device, so that the positive electrode of the power supply 14 is electrically connected to the first tensile component 121; controlling a second single-pole four-throw switch 156 to be in a seventh position by a second control device, so that the negative electrode of the power supply 14 is electrically connected to the third tensile component 123, so as to form a first closed loop; after the current in the first closed loop is turned on for a preset time, obtaining the temperature of the cross tensile specimen 13 collected by the temperature sensor 164; when the temperature of the cross tensile specimen 13 is greater than the preset temperature, controlling the air-cooling spray device 166 to spray cooling gas onto the surface of the cross tensile specimen 13, and stopping the spraying when the temperature of the cross tensile specimen 13 is equal to the preset temperature; controlling the four tensile components 12 to respectively pull The four stretching ends of the cross tensile specimen 13 are stretched, and the first image information of the cross tensile specimen 13 during the stretching process is obtained through the image acquisition device 162; the first single-pole four-throw switch 152 is controlled by the first control device to be in the second position, so that the positive electrode of the power supply 14 is electrically connected to the second stretching component 122; the second single-pole four-throw switch 156 is controlled by the second control device to be in the eighth position, so that the negative electrode of the power supply 14 is electrically connected to the fourth stretching component 124 to form a second closed loop; the four stretching components 12 are controlled to stretch the four stretching ends of the cross tensile specimen 13 respectively, and the second image information of the cross tensile specimen 13 during the stretching process is obtained through the image acquisition device 162; based on the first image information, the second image information and the stress data, the influence of different current directions on the mechanical properties of the cross tensile specimen 13 is analyzed. Among them, the stress data is also the data collected by the tension sensor 1256.

[0088] like Figure 1As shown, another embodiment of the present invention provides an electrically assisted biaxial tensile testing device 1 including a movable top plate mechanism, a biaxial tensile specimen loading mechanism, a strain detection mechanism, a pressure base mechanism, a temperature control mechanism, and an electrically assisted mechanism. The movable top plate mechanism is composed of a driving device 184 (e.g., a universal testing machine), a hanging column 189, a top plate 186, a trapezoidal block 188, and a positioning pin; the strain detection mechanism is a non-contact full-field strain measurement system (DIC), which is composed of a control and analysis system, an image acquisition device 162 (e.g., a high-definition camera), and a light source 168. The high-definition camera and the light source 168 are fixed on the test platform 11 and are used to measure the strain data of the cross tensile specimen; the biaxial tensile specimen loading mechanism is composed of a clamp 1253, a force transmission column 1255, a tension sensor 1256, a tensile frame 1251, and a rolling wheel 1252. The fixture 1253 is connected to the force transmission column 1255. Similarly, the cylindrical tension sensor 1256 is connected to the two sections of the force transmission column 1255. The fixture 1253 is clamped at one end of the cross tensile specimen. The end of the force transmission column 1255 is tightly connected to the stretching frame 1251 by welding to form a complete and reliable structure. Under the action of the movable top plate mechanism, the universal testing machine drives the top plate 186 to move through the hanging column 189 above the top plate 186, so that it moves smoothly at a set constant speed. When the trapezoidal block 188 descends together with the top plate 186, the trapezoidal block 188 gradually penetrates into the interior of the stretching frame 1251, and its volume passing through the stretching frame 1251 increases accordingly. In this process, the hypotenuse of the trapezoidal block 188 inevitably contacts the rolling wheel 1252. When the rolling wheel 1252 slides on the hypotenuse of the trapezoidal block 188, it not only bears the pressure from the trapezoidal block 188, but also converts this force into an outward tensile force. It is this tensile force that causes the stretching frame 1251 to move outward while being pulled. Since the force transmission column 1255 is connected to the stretching frame 1251 by welding, the force transmission column 1255 also moves outward and drives the clamp 1253, thereby driving the cross tensile specimen 13 to perform biaxial stretching.

[0089] During the stretching process, Fig.10 As shown, it is assumed that the trapezoidal block 188 is subjected to a downward pressure F from the testing machine, and the inclination angle of the trapezoidal block 188 is θ. According to the principle of mechanical decomposition, the force F can be decomposed into two components, that is, the force perpendicular to the hypotenuse on the rolling wheel 1252 is Fcosθ. Further, the component force perpendicular to the hypotenuse can be further decomposed, including a horizontal rightward force of Fcosθsinθ, which is the direct force for stretching the sample.

[0090] Assuming that the tensile strength of the cross tensile specimen 13 is σ, the thickness and width of the tensile arm are a and b respectively, the cross-sectional area is a×b. From this, the strength limit F of the specimen arm can be calculated. b , that is, F b=σ×a×b. Based on the known conditions, we can deduce F b =Fcosθsinθ. Based on this result, we can further determine the value of F: F=σ×a×b / cosθsinθ. Through such mechanical analysis, we can simply estimate the tonnage of the required testing machine, and then select the appropriate testing machine according to the specimens of different materials to ensure the energy saving and reliability of the test.

[0091] The temperature control mechanism is composed of an air-cooled injection device 166, a gas compressor, and a temperature sensor 164 (for example, an infrared temperature sensor 164). The air-cooled injection device 166 is fixed on the top plate 186, and the infrared temperature sensor 164 is fixed on the bottom plate. The signal is transmitted to the PID controller. The gas compressor is used to receive the signal of the PID controller and then control the gas rate. The temperature of the sample is adaptively controlled by this mechanism. The electric auxiliary mechanism is composed of a power supply 14 and a current guide control device 15. The positive and negative poles of the power supply 14 are connected to the current guide control device 15, and four wires are led to the stretching frame 1251. The current guide control device 15 includes a first single-pole four-throw switch 152 and a second single-pole four-throw switch 156. The two single-pole four-throw switches are used to accurately control the output direction of the high-frequency current or the low-frequency pulse current, and then the current acts on the tensile specimen. By applying current, the cross tensile specimen 13 can be induced to produce an electroplastic effect, thereby promoting plastic deformation of the cross tensile specimen 13, significantly improving the deformation capacity of the material.

[0092] Optionally, the rolling wheel 1252 and the guide wheel 196 are made of insulating material, which can ensure the safety of the test.

[0093] Optionally, the trapezoidal block 188 and the top plate 186 are connected by pins, which is not only easy to disassemble, but also allows the trapezoidal blocks 188 to be replaced at different positions and angles, thereby adapting to specimens of various sizes and realizing biaxial tensile specimens of different proportions.

[0094] Optionally, track grooves are designed on both sides of the trapezoidal block 188. This structure effectively guides the rolling wheel 1252 to maintain the correct track and avoids errors caused by deviation of the rolling wheel 1252.

[0095] Optionally, the tension sensor 1256 is connected to the two force transmission columns 1255, which has high sensitivity and accuracy and can accurately measure and record the stress borne by the tensile specimen during the stretching process.

[0096] Optionally, the clamp 1253 may be an existing device or the device disclosed in the present invention. The clamp 1253 has fixing holes distributed at positions corresponding to the tensile specimen, so as to accurately clamp the specimen.

[0097] Optionally, the wire connecting the pulse power supply 14 and the fixing frame is a high-conductivity copper wire, which ensures efficient transmission of current.

[0098] Optionally, a single-pole four-throw switch is used to precisely control the current direction of a high-frequency current or a low-frequency pulse current, so that the influence of different current directions on the pure electroplastic effect can be studied.

[0099] Optionally, the temperature control mechanism can adaptively adjust the operating power of the gas compressor by setting the temperature, thereby controlling the rate at which the air-cooling injection device 166 injects cooling gas to maintain the cross-tensile specimen 13 at the set temperature.

[0100] Optionally, the cross tensile specimen 13 is cooled by spraying cooling gas. The cooling gas may be room temperature air, low temperature nitrogen, etc. It is recommended to select an environmentally friendly and easily available resource.

[0101] Optionally, under the action of direct current or low-frequency pulse current, the cross tensile specimen 13 usually produces an electroplastic effect, which mainly includes Joule heating effect and pure electroplastic effect. The cross tensile specimen 13 is kept at room temperature by air cooling to eliminate the influence of Joule heating effect on the material, so as to study the influence of pure electroplastic effect on the deformation behavior of the material.

[0102] This embodiment provides an electrically assisted biaxial tensile test method, which specifically includes the following steps:

[0103] Step 1: To ensure the accuracy of the cross tensile specimen 13, select a suitable testing machine tonnage according to the material and estimated performance of the cross tensile specimen 13, first disconnect the power supply 14 of the test platform 11 to ensure that the test platform 11 maintains a constant level during the test, and then obtain reliable data.

[0104] Step 2: Place the cross tensile specimen 13 on the fixture 1253 , fasten the fixture 1253 and the cross tensile specimen 13 with bolts to ensure the stability of the cross tensile specimen 13 , and stably place the tensile frame 1251 connected to the force transmission column 1255 on the support block 194 .

[0105] Step 3: Assemble the movable top plate mechanism, select the trapezoidal block 188 with a suitable angle according to the biaxial stretching ratio required for the test, and according to the size of the cross-tensile specimen 13, the trapezoidal block 188 is accurately positioned to the appropriate position of the top plate 186 through the positioning pins, thereby preparing for the performance test.

[0106] Step 4: operate the strain measurement mechanism, start the high-definition camera and light source 168 fixed on the test platform 11 , and ensure that the high-definition camera is located directly below the cross tensile specimen 13 .

[0107] Step 5: Run the temperature control mechanism, start the infrared temperature sensor 164 fixed on the test platform 11, which can accurately track the temperature change of the cross tensile specimen 13 during the stretching process, and start the air cooling injection device 166 fixed on the top plate 186 to ensure that it is located directly above the cross tensile specimen 13.

[0108] Step 6: Connect the positive and negative electrodes of the power source 14 to the current guide control device 15, and lead four wires to the stretching frame 1251, and set the current movement direction according to the test requirements.

[0109] Step 7: Turn on the pulse power supply 14 and the power supply 14, turn on the PID controller and the control analysis system, and set the pulse current process parameters and the sample holding temperature.

[0110] Step 8: Turn on the gas compressor to ensure that the temperature of the sample is stably maintained at the set value. The gas compressor adjusts the air-cooling injection device 166 according to the feedback result of the infrared temperature sensor 164. By accurately controlling the injection of cooling gas, the sample temperature can be effectively regulated.

[0111] Step 9: After the temperature of the cross tensile specimen 13 is stabilized, the tensile rate of the testing machine is set and the test is started. The universal testing machine can drive the top plate 186 to move downward at the set speed, and the trapezoidal block 188 is lowered together with the top plate 186. During this process, the hypotenuse of the trapezoidal block 188 inevitably contacts the rolling wheel 1252, and the rolling wheel 1252 slides on the hypotenuse of the trapezoidal block 188, thereby causing the tensile frame 1251 to be pulled and move outward, driving the force transmission column 1255, so that the cross tensile specimen 13 is subjected to biaxial stretching.

[0112] Step 10: After the test is completed, disconnect all power supplies 14 of the test platform 11, raise the movable top plate mechanism to a suitable position, loosen the bolts of the fixture 1253, and then take out the cross tensile specimen 13.

[0113] The electrically assisted biaxial tensile testing device of the present invention can also realize ordinary electrically assisted tensile testing. When conducting ordinary electrically assisted biaxial tensile testing on a specimen, the gas compressor can be turned off to prevent the air-cooled injection device 166 from releasing cooling gas, thereby causing deviations in the test results.

[0114] In the embodiments according to the present invention, the terms "first", "second", and "third" are only used for description and cannot be understood as indicating or implying relative importance; the term "plurality" refers to two or more, unless otherwise clearly defined. The terms "installed", "connected", "connected", "fixed" and the like should be understood in a broad sense. For example, "connected" can be a fixed connection, a detachable connection, or an integral connection; "connected" can be a direct connection or an indirect connection through an intermediate medium. For those of ordinary skill in the art, the specific meanings of the above terms in the embodiments according to the present invention can be understood according to specific circumstances.

[0115] In addition, although each operation is described in a specific order, this should be understood as requiring such operation to be performed in a specific order or in a sequential order, or requiring that all illustrated operations should be performed to obtain desired results. Under certain circumstances, multitasking and parallel processing may be advantageous. Similarly, although some specific implementation details are included in the above discussion, these should not be interpreted as limiting the scope of the present invention. Some features described in the context of a separate embodiment can also be implemented in a single implementation in combination. On the contrary, the various features described in the context of a single implementation can also be implemented in multiple implementations individually or in any suitable sub-combination mode.

[0116] Although the subject matter has been described in the language of specific structural features and / or method logical actions, it should be understood that the subject matter defined in the appended claims is not necessarily limited to the specific features or actions described above. On the contrary, the specific features and actions described above are merely example forms of implementing the claims.

[0117] The above are only preferred embodiments according to the embodiments of the present invention, and are not intended to limit the embodiments of the present invention. For those skilled in the art, various modifications and changes may be made according to the embodiments of the present invention. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the embodiments of the present invention shall be included in the protection scope of the embodiments of the present invention.

Claims

1. An electrically assisted biaxial tensile testing device, characterized in that: include: Test platform; Four stretching components, arranged on the test platform and connected to four stretching ends of the cross tensile specimen, for stretching the cross tensile specimen; A power supply, provided on the test platform; a first single-pole four-throw switch connected to the positive electrode of the power supply and the four tensile components, the four tensile components including a first tensile component, a second tensile component, a third tensile component and a fourth tensile component, the first single-pole four-throw switch can be in a first position to electrically connect the positive electrode of the power supply to the first tensile component, the first single-pole four-throw switch can be in a second position to electrically connect the positive electrode of the power supply to the second tensile component, the first single-pole four-throw switch can be in a third position to electrically connect the positive electrode of the power supply to the third tensile component, and the first single-pole four-throw switch can be in a fourth position to electrically connect the positive electrode of the power supply to the fourth tensile component; a first control device, connected to the first single-pole four-throw switch, and configured to control the single-pole four-throw switch to be in the first position, the second position, the third position, or the fourth position; a second single-pole four-throw switch connected to the negative pole of the power supply and the four tension components, the second single-pole four-throw switch can be in a fifth position to electrically connect the negative pole of the power supply to the first tension component, the second single-pole four-throw switch can be in a sixth position to electrically connect the negative pole of the power supply to the second tension component, the second single-pole four-throw switch can be in a seventh position to electrically connect the negative pole of the power supply to the third tension component, and the second single-pole four-throw switch can be in an eighth position to electrically connect the negative pole of the power supply to the fourth tension component; a second control device, connected to the second single-pole four-throw switch, and configured to control the second single-pole four-throw switch to be in the fifth position, the sixth position, the seventh position, or the eighth position; An image acquisition device, provided on the test platform, for acquiring image information of the cross tensile specimen during the stretching process; A temperature sensor, provided on the test platform, for obtaining the temperature of the cross tensile specimen; The air-cooling spray device is arranged on the test platform and connected to the temperature sensor, and is used for spraying cooling gas onto the cross tensile specimen when the temperature of the cross tensile specimen is greater than a temperature threshold.

2. The electrically assisted biaxial tensile testing device according to claim 1, characterized in that: The temperature sensor can be in contact with the cross tensile specimen.

3. The electrically assisted biaxial tensile testing device according to claim 1, characterized in that: Also includes: A bracket, arranged on the test platform; A driving device, arranged on the support; A top plate connected to the driving device, wherein the driving device can drive the top plate to move up and down; Four trapezoidal blocks are connected to the top plate, and the four trapezoidal blocks are arranged corresponding to the four tensile assemblies, wherein when the driving device drives the top plate to descend, each of the trapezoidal blocks can contact the corresponding tensile assembly and make the tensile assembly move in a direction away from the cross tensile specimen to stretch the cross tensile specimen.

4. The electrically assisted biaxial tensile testing device according to claim 3, characterized in that: The stretching assembly comprises: A stretching frame, the stretching frame including an escape space; A rolling wheel, which is arranged on the stretching frame; A clamp, connected to the tensile frame, for clamping the cross tensile specimen; Wherein, during the descending process of the top plate, the trapezoidal block can pass through the avoidance space and contact the rolling wheel to squeeze the stretching frame to move away from the cross tensile specimen, so as to drive the fixture to stretch the cross tensile specimen.

5. The electrically assisted biaxial tensile testing device according to claim 4, characterized in that: It also includes four support assemblies, each of which is used to support one of the stretching frames, and the support assemblies include: A support column, arranged on the test platform, wherein a longitudinal slide groove is arranged on the support column; A support block, fixedly arranged on the support column, the support block is provided with a transverse slide groove, and the stretching frame is slidably arranged in the transverse slide groove; A guide wheel, slidably disposed on the longitudinal slide groove and correspondingly disposed below the trapezoidal block; Wherein, during the descending process of the trapezoidal block, it can abut against the corresponding guide wheel so as to guide the trapezoidal block through the guide wheel.

6. The electrically assisted biaxial tensile testing device according to claim 1, characterized in that: Also includes: A fixed column, arranged on the test platform; A support rod is connected to the fixed column. The support rod can move up and down relative to the fixed column, and the fixed column can rotate relative to the test platform. The image acquisition device is arranged on the support rod.

7. The electrically assisted biaxial tensile testing device according to claim 1, characterized in that: The cross tensile test specimen comprises a metal plate, a tailor-welded plate, a multi-metal composite plate or a plate of different thickness.

8. The electrically assisted biaxial tensile testing device according to claim 1, characterized in that: Also includes: A circuit breaker is provided between the power supply and the first single-pole four-throw switch, or between the power supply and the second single-pole four-throw switch, and the circuit breaker can automatically disconnect when the current is greater than a threshold value.

9. A testing method for the electrically assisted biaxial tensile testing device according to any one of claims 1 to 8, characterized in that: include: Controlling the first single-pole four-throw switch to be in the first position by the first control device so that the positive electrode of the power supply is electrically connected to the first stretching assembly; Controlling the second single-pole four-throw switch to be in the seventh position through the second control device, so that the negative electrode of the power supply is electrically connected to the third stretching assembly to form a first closed loop; After the current in the first closed loop is conducted for a preset time, obtaining the temperature of the cross tensile specimen collected by the temperature sensor; When the temperature of the cross tensile specimen is greater than a preset temperature, controlling the air cooling spray device to spray cooling gas onto the surface of the cross tensile specimen, and stopping the spraying when the temperature of the cross tensile specimen is equal to the preset temperature; Controlling the four stretching assemblies to stretch the four stretching ends of the cross tensile specimen respectively, and obtaining first image information of the cross tensile specimen during the stretching process through the image acquisition device; Controlling the first single-pole four-throw switch to the second position by the first control device so that the positive electrode of the power supply is electrically connected to the second stretching assembly; Controlling the second single-pole four-throw switch to be in the eighth position through the second control device, so that the negative electrode of the power supply is electrically connected to the fourth stretching assembly to form a second closed loop; Controlling the four stretching assemblies to stretch the four stretching ends of the cross tensile specimen respectively, and obtaining second image information of the cross tensile specimen during the stretching process through the image acquisition device; Based on the first image information, the second image information and the stress data, the influence of different current directions on the mechanical properties of the sample is analyzed.

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