Electrically-assisted tension and compression cyclic loading device and test method for ultrathin titanium plate

Abstract

The invention discloses an ultra-thin titanium plate electric auxiliary tension and compression cyclic loading device and a test method, the device comprises two outer side samples used in cooperation with an ultra-thin titanium plate sample, the two outer side samples are fixed on the two sides of the ultra-thin titanium plate sample, the two outer side samples and the ultra-thin titanium plate sample form a composite tension and compression sample, the ends of the ultra-thin titanium plate sample extend out of the ends of the outer side samples, and the outer side samples are fixed on the two sides of the ultra-thin titanium plate sample. The two sides of the composite tension and compression sample are fixed through the clamping assemblies and then are applied with lateral force; the two pairs of electric auxiliary clamps are clamped at the two ends of the composite tension and compression sample respectively, each pair of electric auxiliary clamps comprises two oppositely-arranged chucks, the clamping faces of the chucks are provided with conductive structures, the conductive structures are connected with an external power source, and when the composite tension and compression sample is clamped on the chucks, the conductive structures make contact with the composite tension and compression sample. The chuck is connected with the loading end part of the universal testing machine, and the ultrathin titanium plate sample can be prevented from being distorted and deformed in the testing process.

Description

Technical Field

[0001] The present invention relates to the technical field of electro-assisted tensile-compression testing, and particularly to an electro-assisted tensile-compression cyclic loading device and testing method for ultra-thin titanium plates. Background Art

[0002] With the demands for lightweight and high performance in industries such as aerospace, transportation, and automotive manufacturing, titanium and its alloys with high specific strength are widely used. However, at room temperature, titanium has poor plasticity, high deformation resistance, and a high yield-elastic ratio, which severely limits the application of ultra-thin titanium plates.

[0003] In response to the problem of poor formability of titanium at room temperature, the electro-assisted forming process has emerged. However, during the electro-assisted forming process, the deformation behavior of ultra-thin titanium plates is complex. During the stamping process, the fillet undergoes complex deformation loading paths such as loading-unloading, reverse loading, and cyclic loading, which are difficult to characterize by electro-assisted uniaxial tensile tests. Usually, an electro-assisted tensile-compression cyclic loading test device is used to test ultra-thin titanium plates to characterize the mechanical behavior of ultra-thin titanium plates under complex loading paths under the action of current. Currently, the thin plate tensile-compression test device mainly prevents the ultra-thin titanium plate specimen located between two clamping plates from buckling and losing stability during the compression process by applying lateral forces to the left and right clamping plates, and applies tensile-compression loads to the upper and lower ends of the ultra-thin titanium plate through the clamps of a universal testing machine to achieve the tensile-compression process of the specimen. However, the test process is often affected by wrinkling and deformation of the specimen, making it difficult to ensure that the ultra-thin titanium plate does not twist and deform only through the clamping plates and specimen clamps due to the extremely thin thickness of the ultra-thin titanium plate. Also, in existing electro-assisted tensile-compression tests, an electric field is mainly applied by designing special specimens with wire interfaces, and the connection between the wire and the ultra-thin specimen is prone to kinking. Summary of the Invention

[0004] In order to solve the above technical problems, the present invention provides an electro-assisted tensile-compression cyclic loading device and testing method for ultra-thin titanium plates, which can avoid the twisting and deformation of ultra-thin titanium plate specimens during the test process.

[0005] In the first aspect of the present invention, an electro-assisted tension-compression cyclic loading device for ultra-thin titanium plates is provided, comprising: two outer specimens used in cooperation with the ultra-thin titanium plate specimen, the two outer specimens are fixed on both sides of the ultra-thin titanium plate specimen, and the three form a composite tension-compression specimen. The ends of the ultra-thin titanium plate specimen extend out of the ends of the outer specimens. After the two sides of the composite tension-compression specimen are fixed by a clamping assembly, a lateral force is applied to it. Two pairs of electro-assisted clamps are respectively clamped at both ends of the composite tension-compression specimen. Each pair of electro-assisted clamps includes two oppositely arranged chucks. The clamping surface of the chuck has a conductive structure, and the conductive structure is connected to an external power supply. When the composite tension-compression specimen is clamped on the chuck, the conductive structure contacts the composite tension-compression specimen to transfer current through the conductive structure to the composite tension-compression specimen for heating it. The chuck is connected to the loading end of a universal testing machine. The composite tension-compression specimen should ensure a moderate thickness. If it is too thin, it is still prone to distortion during the compression process. If it is too thick, the specimen is not easy to be clamped. At the same time, the two outer specimens are fixed on both sides of the ultra-thin titanium plate specimen to form a composite tension-compression specimen structure, which can also ensure the uniform transmission of force.

[0006] Optionally, the resistivity of the outer specimen is 10 12 Ω·m - 10 17 Ω·m. When the resistivity is within the range of 10 12 Ω·m - 10 17 Ω·m, it can be considered insulated, and the current has basically no influence on the outer specimen.

[0007] Optionally, the conductive structure includes a conductive sheet and a connecting sheet connected as a whole. Both the conductive sheet and the connecting sheet are made of conductive materials. The conductive sheet is located on the clamping surface of the chuck. One side of it in contact with the composite tension-compression specimen has serrations, and a through groove is also opened on the conductive sheet. The end of the outer specimen is placed in the through groove, the ultra-thin titanium plate specimen contacts the conductive sheet, and the connecting sheet is connected to the external power supply. The conductive sheet is responsible for transferring current and heating the ultra-thin titanium plate specimen, and the connecting sheet is connected to the external power supply and is responsible for transferring the current of the external power supply to the conductive sheet.

[0008] Optionally, the upper and lower clamps of the universal testing machine respectively clamp two pairs of electro-assisted clamps. The chuck also has a positioning post and a fixing groove. The positioning post cooperates with the positioning groove of the universal testing machine, and the loading head of the universal testing machine is clamped in the fixing groove, so as to quickly complete the connection and alignment with the universal testing machine, accurately position the relative position of the electro-assisted clamp and the clamp of the universal testing machine, and ensure the centering and stability during the loading process.

[0009] Optionally, the thickness of the outer specimen is 0.5 mm - 0.7 mm, and the material is one of glass fiber composite material, polyether ether ketone, or carbon fiber - glass fiber composite material, or other composite materials with good insulation, high temperature resistance and elongation can also be used.

[0010] Optionally, the outer specimen and the ultra-thin titanium plate specimen are adhesively fixed by epoxy resin. The layer thickness of the epoxy resin is 0.02 mm - 0.05 mm. Selecting a layer thickness within this range can neglect the tensile and compressive forces on the resin layer, facilitating subsequent calculations.

[0011] Optionally, the clamping assembly includes: two insulating gaskets symmetrically arranged on both sides of the composite tensile-compressive specimen, each insulating gasket includes a first insulating sheet and a second insulating sheet stacked along the extension direction of the ultra-thin titanium plate specimen, and two clamping plates symmetrically arranged outside the two insulating gaskets. A lateral force adjusting assembly is connected to the outside of the clamping plates. Each clamping plate includes a first clamping plate and a second clamping plate stacked. The first clamping plate is fixedly connected to the corresponding first insulating sheet, and the second clamping plate is fixedly connected to the corresponding second insulating sheet. Between the first insulating sheet and the second insulating sheet, and between the first clamping plate and the second clamping plate, they are each slidably connected by multiple straight rods, so that the first insulating sheet and the second insulating sheet, and the first clamping plate and the second clamping plate move synchronously along the extension direction of the ultra-thin titanium plate specimen. The insulating gasket is used to isolate the current, and the clamping plate is used to transmit the lateral force.

[0012] Optionally, between the first insulating sheet and the second insulating sheet, and between the first clamping plate and the second clamping plate, they are also each connected by a comb-like structure. The comb-like structure ensures that all sections of the composite tensile-compressive specimen can be constrained by the lateral force when it is stretched and then compressed.

[0013] Optionally, the lateral force adjusting assembly includes: two inner plates, two outer plates and a spring. The two inner plates are respectively placed outside the corresponding clamping plates, and the two outer plates are respectively placed outside the corresponding inner plates. Sliding holes are provided on the inner plates and the outer plates along the extension direction of the ultra-thin titanium plate specimen. The screw passes through the sliding holes in sequence and is fixed to the clamping plate and the insulating gasket. A spring adjusting block is rotatably connected to one of the outer plates. One end of the spring is fixedly connected to the spring adjusting block, and the other end is fixedly connected to the corresponding inner plate. By rotating the spring adjusting block, the compression force of the spring is adjusted, thereby adjusting the lateral force applied to one side of the inner plate. In this way, only the spring adjusting block and the spring are arranged on one side for convenient adjustment, and the lateral force can be collected by a force sensor on the other side.

[0014] The second aspect of the present invention provides a test method based on the above ultra-thin titanium plate electro-assisted tensile-compressive cyclic loading device, including the following steps: Step 1: Prepare a composite tensile-compressive specimen, and fix the outer specimens on both sides of the ultra-thin titanium plate specimen to form a composite tensile-compressive specimen; Step 2: Clamp the prepared composite tensile-compressive specimen to a universal testing machine by an electro-assisted fixture, and apply lateral forces to the composite tensile-compressive specimen on both sides through the clamping assembly for fixation; Step 3: Set the parameters required for the tensile-compressive test and conduct the tensile-compressive test; Step 4: Observe whether buckling occurs in the ultra-thin titanium plate specimen. If buckling occurs, adjust the lateral force, and then repeat Steps 1 - 4 until buckling does not occur in the ultra-thin titanium plate specimen, and obtain the corresponding lateral force when buckling does not occur. Step 5: Fix the remaining composite tension-compression specimens using the corresponding lateral force when buckling does not occur, conduct tension-compression tests, obtain experimental data, and use the experimental data to obtain stress-strain curves.

[0015] The technical solution provided by the embodiment of the present invention has the following advantages compared with the prior art: An electro-assisted tension-compression cyclic loading device and test method for ultra-thin titanium plates provided by an embodiment of the present invention are used for the test of thin plate compression with a thickness less than 1 mm. By fixing two outer specimens on both sides of the original ultra-thin titanium plate specimen to form a composite tension-compression specimen as a whole, the thickness of the specimen is increased, thus avoiding instability buckling during the compression process. At the same time, two pairs of electro-assisted clamps clamp the composite tension-compression specimen, and the conductive structures on each chuck of the electro-assisted clamps are directly connected to the composite tension-compression specimen to heat it. By connecting the composite tension-compression specimen and the electro-assisted clamps to form a whole to replace the original ultra-thin titanium plate specimen, the setting of wire interfaces on the specimen is avoided, and further distortion of the specimen is avoided, solving the problem of wrinkling of ultra-thin plates under compressive loads, ensuring the smooth progress of the test. Then, connect the chuck and the loading end of the universal testing machine, which can be used to characterize the mechanical behavior of ultra-thin titanium plates under complex loading paths in the case of current, providing theoretical support for the electro-assisted forming process. Description of the Drawings

[0016] Figure 1 is a schematic structural diagram of an electro-assisted tension-compression cyclic loading device for ultra-thin titanium plates provided by an embodiment of the present invention; Figure 2 is an exploded structural diagram of an electro-assisted tension-compression cyclic loading device for ultra-thin titanium plates provided by an embodiment of the present invention; Figure 3 is a schematic structural diagram of the first orientation of the composite tension-compression specimen provided by an embodiment of the present invention; Figure 4 is a schematic structural diagram of the chuck provided by an embodiment of the present invention; Figure 5 is a schematic structural diagram of the first insulating sheet and the second insulating sheet provided by an embodiment of the present invention; Figure 6 is a schematic structural diagram of the first clamping plate and the second clamping plate provided by an embodiment of the present invention; Figure 7 is a schematic structural diagram of the second orientation of the composite tension-compression specimen provided by an embodiment of the present invention; Figure 8 is Figure 7 a partially enlarged schematic diagram of the structure at position G in

[0017] Description of the reference numerals: 1. Outer specimen; 2. Ultra-thin titanium plate specimen; 3. First insulating sheet; 4. Second insulating sheet; 5. Spring; 6. Spring adjusting block; 7. Force sensor; 8. Outer plate; 9. Inner plate; 10. Straight rod; 11. Chuck; 12. First clamping plate; 13. Second clamping plate; 14. Thermocouple; 15. Conductive structure; 150. Conductive sheet; 151. Connecting sheet; 152. Through groove; 16. Positioning post; 17. Fixed groove; 18. Insulating layer. Detailed implementation manners

[0018] The following describes in detail a specific implementation manner of the present invention with reference to the accompanying drawings. It should be understood that the protection scope of the present invention is not limited by the specific implementation manner.

[0019] In the description of the present invention, it should be understood that the terms "center", "longitudinal", "transverse", "length", "width", "thickness", "upper", "lower", "front", "rear", "left", "right", "vertical", "horizontal", "top", "bottom", "inner", "outer", "axial", "radial", "circumferential", etc. indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are only for facilitating the description of the technical solutions of the present invention and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation. Therefore, it should not be construed as a limitation to the present invention.

[0020] When the existing electro-assisted tension-compression cyclic loading test device conducts a test on an ultra-thin titanium plate, the ultra-thin titanium plate will undergo buckling deformation. For example, because the thickness of the ultra-thin titanium plate is too thin, it is difficult for the pressure to be transmitted from both ends of the specimen to the gauge section during the compression process, and the transition area between the clamping section and the gauge section is prone to distortion. It is difficult to ensure that the ultra-thin titanium plate does not undergo distortion deformation only through the clamping plate and the specimen fixture. Another example is that the existing electro-assisted tension-compression test mainly applies an electric field by designing a special specimen with a wire interface, and the connection between the wire and the ultra-thin specimen is prone to kinking, thus affecting the test.

[0021] Therefore, the embodiment of the present invention provides an electro-assisted tension-compression cyclic loading device and test method for an ultra-thin titanium plate, which can avoid the ultra-thin titanium plate specimen from undergoing distortion deformation during the test.

[0022] The following illustrates the present invention through several specific embodiments. To keep the following description of the embodiments of the present invention clear and concise, the detailed description of known functions and known components may be omitted. When any component of the embodiments of the present invention appears in more than one drawing, the component may be denoted by the same reference numeral in each drawing.

[0023] Refer to Figure 1 、Figure 2 and Figure 3 , Figure 1 FIG. Figure 1 is a schematic structural diagram of an electro-assisted tension-compression cyclic loading device for an ultra-thin titanium plate provided by an embodiment of the present invention, Figure 2 FIG. Figure 2 is a schematic packaging structure diagram of an electro-assisted tension-compression cyclic loading device for an ultra-thin titanium plate provided by an embodiment of the present invention, Figure 3 FIG. Figure 3 is a schematic structural diagram of the first orientation of a composite tension-compression specimen provided by an embodiment of the present invention. As shown in FIGS. Figure 1 , Figure 2 and Figure 3 , an electro-assisted tension-compression cyclic loading device for an ultra-thin titanium plate provided by an embodiment of the present invention includes: two outer specimens 1 used in cooperation with an ultra-thin titanium plate specimen 2 and two pairs of electro-assisted clamps. The two outer specimens 1 are fixed on both sides of the ultra-thin titanium plate specimen 2, and the three form a composite tension-compression specimen. It should be understood that the composite tension-compression specimen should ensure a moderate thickness. If it is too thin, it is still easy to twist during the compression process. If it is too thick, the specimen is not easy to be clamped. At the same time, the two outer specimens 1 are fixed on both sides of the ultra-thin titanium plate specimen 2 to form a composite tension-compression specimen structure, which can also ensure the uniform transmission of force. The ends of the ultra-thin titanium plate specimen 2 extend out of the ends of the outer specimens 1 to ensure contact between the ultra-thin titanium plate specimen 2 and the conductive structure 15, ensuring that current accurately enters the ultra-thin titanium plate specimen 2. Lateral forces are applied to both sides of the composite tension-compression specimen after it is fixed by a clamping assembly. The clamping assembly fixes the composite tension-compression specimen to ensure that it does not undergo torsional buckling during the loading process. Mechanical clamping, hydraulic clamping or pneumatic clamping can be used, and the specific choice depends on the test requirements. The two pairs of electro-assisted clamps are respectively clamped at both ends of the composite tension-compression specimen. Each pair of electro-assisted clamps includes two relatively arranged chucks 11. The clamping surfaces of the chucks 11 have conductive structures 15. The conductive structures 15 usually use highly conductive materials such as copper or silver to ensure efficient current transmission and reduce energy loss. The conductive structure can be designed as multi-point contact or surface contact to optimize current distribution and heating uniformity. The conductive structure 15 is connected to an external power supply. When the composite tension-compression specimen is clamped on the chucks 11, the conductive structure 15 contacts the composite tension-compression specimen to transfer current through the conductive structure 15 to the composite tension-compression specimen for heating. The external power supply provides the required current, and the current magnitude is adjustable to adapt to different heating requirements. The current magnitude and heating time are adjusted through a control system to ensure that the composite tension-compression specimen is tested at a set temperature. The chucks 11 are connected to the loading ends of a universal testing machine, and tensile and compressive forces are applied through the universal testing machine. The universal testing machine can accurately control the loading speed, cycle number, and the current magnitude is controlled through an external power supply to meet different test conditions and achieve electro-thermal coupled loading.

[0024] ​​​​​​An electro-assisted tension-compression cyclic loading device for ultra-thin titanium plates provided by an embodiment of the present invention is used for the test of compressing thin plates with a thickness less than 1 mm. By fixing two outer specimens on both sides of the original ultra-thin titanium plate specimen to form a composite tension-compression specimen as a whole, the thickness of the specimen is increased, thus avoiding instability buckling during the compression process. At the same time, two pairs of electro-assisted clamps clamp the composite tension-compression specimen, and the conductive structures on each chuck of the electro-assisted clamps are directly connected to the composite tension-compression specimen to heat it. By connecting the composite tension-compression specimen with the electro-assisted clamps to form a whole, the original ultra-thin titanium plate specimen is replaced, avoiding the setting of wire interfaces on the specimen, further avoiding the twisting deformation of the specimen, solving the problem of wrinkling of the ultra-thin plate under the action of compressive load, ensuring the smooth progress of the test, and then connecting the chuck with the loading end of the universal testing machine, which can be used to characterize the mechanical behavior of the ultra-thin titanium plate under complex loading paths under the condition of current, providing theoretical support for the electro-assisted forming process.

[0025] Specifically, in the embodiment of the present invention, the resistivity of the outer specimen 1 is 10 12 Ω·m - 10 17 Ω·m. When the resistivity of the outer specimen 1 is 10 12 Ω·m - 10 17 Ω·m, it can be considered that it is insulated and the current has basically no influence on the outer specimen 1. In this way, when the chuck 11 clamps the composite tension-compression specimen, there is no need to repeatedly adjust the position of the composite tension-compression specimen, as long as it is ensured that the ultra-thin titanium plate specimen 2 contacts the conductive structure 15, and it is okay whether the outer specimen 1 contacts the conductive structure 15 or not. In this way, there is no need to separately measure the mechanical properties of the outer specimen 1 and the force-bearing situation during the tension-compression process when there is current.

[0026] Refer to Figure 4 , Figure 4 which is the structural schematic diagram of the chuck provided by the embodiment of the present invention. As Figure 4 shown, the conductive structure 15 includes a conductive sheet 150 and a connecting sheet 151 that are connected as a whole. Both the conductive sheet 150 and the connecting sheet 151 are made of conductive materials, such as copper. The conductive sheet 150 is located on the clamping surface of the chuck 11, and the side in contact with the composite tension-compression specimen has serrations. A through groove 152 is also provided on the conductive sheet 150. The end of the outer specimen 1 is placed in the through groove 152, and the ultra-thin titanium plate specimen 2 contacts the conductive sheet 150. The conductive sheet 150 is responsible for transmitting current and heating the ultra-thin titanium plate specimen 2. The connecting sheet 151 is connected to an external power supply and is responsible for transmitting the current of the external power supply to the conductive sheet 150.

[0027] A through groove 152 is also provided on the conductive sheet 150. The end of the outer specimen 1 is placed in the through groove 152, thereby increasing the thickness clamped by the chuck 11, increasing the clamping force of the chuck 11 on the combined tension and compression specimen, preventing the combined tension and compression specimen from sliding, and at the same time ensuring that the current is directly transmitted to the ultra-thin titanium plate specimen 2. The conductive sheet 150 is located on the clamping surface of the chuck 11, and the side thereof in contact with the combined tension and compression specimen has serrations, which can increase the contact area and friction force, prevent the combined tension and compression specimen from sliding, and at the same time optimize the current distribution. When the chuck 11 clamps the combined tension and compression specimen, the serrated structure of the conductive sheet 150 is in close contact with the combined tension and compression specimen, ensuring uniform current transmission and heating of the ultra-thin titanium plate specimen 2.

[0028] Refer again to Figure 4 , the upper and lower clamps of the universal testing machine respectively clamp two pairs of electro-assisted clamps. The chuck 11 also has a positioning post 16 and a fixing groove 17. The positioning post 16 cooperates with the positioning groove of the universal testing machine, so as to achieve the purpose of quickly connecting and aligning with the universal testing machine, accurately positioning the relative position of the electro-assisted clamp and the clamp of the universal testing machine, and ensuring the centering and stability during the loading process. The loading head of the universal testing machine is clamped in the fixing groove 17, and the force can be accurately transmitted to the combined tension and compression specimen through the loading head. It should be noted that the chuck 11 also has an insulating layer 18. The insulating layer 18 is located under the conductive sheet 150, and peek polyetheretherketone insulating material is selected. The main part of the chuck 11 is made of iron, which has high strength and ensures that the electro-assisted clamp will not be damaged under repeated use.

[0029] In this embodiment, the thickness of the outer specimen 1 is 0.5 mm - 0.7 mm, and the material can be one of glass fiber composite material, polyetheretherketone, carbon fiber - glass fiber composite material or other composite materials with good insulation, high temperature resistance and elongation. After the outer specimens 1 are clamped on both sides of the ultra-thin titanium plate specimen 2, the thickness should be appropriate. If the specimen is too thin, it is easy to twist during the compression process; if the specimen is too thick, it is not easy to be clamped. When glass fiber is selected, it is because it has a large resistivity and a large elastic limit, and it is generally elastically deformed in the tension and compression test, which is convenient for calculating the force during the tension and compression process, but the elongation at break is small, and it can be used for the tension and compression cyclic loading test with small strain. Polyetheretherketone has good elongation, can be used for the tension and compression cyclic loading under high strain, and has good strength and hardness, ensuring the smooth progress of the test.

[0030] In this embodiment, the outer specimen 1 and the ultra-thin titanium plate specimen 2 are adhesively fixed by epoxy resin. The layer thickness of the epoxy resin is 0.02 mm - 0.05 mm. If the layer thickness of the epoxy resin is too thick, it will affect the stress calculation of the ultra-thin titanium plate specimen 2 during the stretching and compression processes. Selecting the layer thickness in the range of 0.02 mm - 0.05 mm can ignore the tensile and compressive forces received by the resin layer, which is convenient for subsequent calculation.

[0031] Refer toFigure 5 and Figure 6 , Figure 5 FIG. is a schematic structural diagram of a first insulating sheet and a second insulating sheet provided by an embodiment of the present invention, Figure 6 FIG. is a schematic structural diagram of a first clamping plate and a second clamping plate provided by an embodiment of the present invention. As shown in Figure 5 and Figure 6 , in the embodiment of the present invention, the clamping assembly includes: two insulating gaskets symmetrically arranged on both sides of the composite tensile-compressive specimen; each insulating gasket includes a first insulating sheet and a second insulating sheet stacked along the extending direction of the ultra-thin titanium plate specimen; two clamping plates symmetrically arranged on the outer sides of the two insulating gaskets, and a lateral force adjusting assembly is connected to the outer sides of the clamping plates to adjust the clamping force of the clamping plates and the insulating gaskets on the composite tensile-compressive specimen; each clamping plate includes a stacked first clamping plate and a second clamping plate, the first clamping plate is fixedly connected to the corresponding first insulating sheet, and the second clamping plate is fixedly connected to the corresponding second insulating sheet; between the first insulating sheet and the second insulating sheet, and between the first clamping plate and the second clamping plate, they are each slidably connected by a plurality of straight rods, so that the first insulating sheet and the second insulating sheet, and the first clamping plate and the second clamping plate move synchronously along the extending direction of the ultra-thin titanium plate specimen. In this embodiment, the insulating gasket is used to isolate the current. Since the melting point of the insulating material is generally relatively low, between 200°C and 300°C, the softening of the insulating gasket caused by the increase in the specimen temperature during the electro-assisted process cannot well transmit the lateral force. Therefore, a clamping plate is further arranged on the outer layer of the insulating gasket, and the clamping plate is used to transmit the lateral force. The through grooves opened at the same positions of the insulating gasket and the clamping plate can facilitate the DIC measurement of the strain.

[0032] The first insulating sheet and the second insulating sheet are connected to the first clamping plate and the second clamping plate by bolts and can move freely in the direction perpendicular to the clamping plate through the first clamping plate and the second clamping plate to realize the tensile-compressive cyclic loading process. To prevent the upper and lower misalignment of the clamping plate and the insulating gasket, straight rods exist between the first insulating sheet and the second insulating sheet, and between the first clamping plate and the second clamping plate, which play a role of centering and guiding. And the clamping plates and the insulating gaskets on the left and right sides of the specimen are symmetrically distributed to prevent the specimen from being distorted in the comb-shaped areas of the insulating gasket and the clamping plate.

[0033] Specifically, between the first insulating sheet and the second insulating sheet, and between the first clamping plate and the second clamping plate, they are each further connected by a comb-shaped structure. The comb-shaped structure ensures that all sections can be subjected to the constraint of the lateral force when the composite tensile-compressive specimen is stretched and then compressed. While realizing the movement through the comb-shaped structure in the non-gauge section, the anti-buckling ability of the device is not reduced, further avoiding its buckling deformation, and the tensile-compressive cyclic loading of the ultra-thin titanium plate specimen can be realized.

[0034] Refer to again Figure 2, in this embodiment, the lateral force adjustment assembly includes: two inner plates 9, two outer plates 8 and a spring 5. The two inner plates 9 are respectively placed on the outer sides of the corresponding clamping plates, and the two outer plates 8 are respectively placed on the outer sides of the corresponding inner plates 9. Slide holes extending along the extension direction of the ultra-thin titanium plate specimen 2 are provided on both the inner plates 9 and the outer plates 8. The screw passes through the slide holes in sequence and is fixed to the clamping plate and the insulating gasket. A spring adjustment block 6 is rotatably connected to one of the outer plates 8. One end of the spring 5 is fixedly connected to the spring adjustment block 6, and the other end is fixedly connected to the corresponding inner plate 9. By rotating the spring adjustment block 6, the compression amount of the spring 5 is adjusted, thereby adjusting the lateral force applied to one side of the inner plate 9.

[0035] The spring adjustment block 6 can freely rotate the spring 5 at the outer plate 8. When the spring adjustment block 6 rotates downward, the spring 5 is compressed. At the same time, the bolt at the outer plate 8 is adjusted so that the outer plate 8 is closely attached to the spring adjustment block 6, so that the lateral force is transmitted from the inner plate 9 to both sides of the composite tensile-compressive specimen through the spring 5. In this way, it is convenient to adjust by only setting the spring adjustment block 6 and the spring 5 on one side. The lateral force on the other side can be collected by the force sensor 7.

[0036] The second aspect of the present invention provides a test method based on the above ultra-thin titanium plate electro-assisted tensile-compressive cyclic loading device, including the following steps: Step 1: Prepare a composite tensile-compressive specimen, and fix the outer specimens 1 on both sides of the ultra-thin titanium plate specimen 2 to form a composite tensile-compressive specimen; Step 2: Clamp the prepared composite tensile-compressive specimen to a universal testing machine through an electro-assisted fixture, and apply lateral force to the composite tensile-compressive specimen through the clamping assembly on both sides for fixation; Step 3: Set the parameters required for the tensile-compressive test and conduct the tensile-compressive test; Step 4: Observe whether the ultra-thin titanium plate specimen 2 buckles. If buckling occurs, adjust the lateral force, and then repeat steps 1-step 4 until the ultra-thin titanium plate specimen 2 does not buckle, and obtain the corresponding lateral force when no buckling occurs; Step 5: Fix the remaining composite tensile-compressive specimens with the corresponding lateral force when no buckling occurs, conduct the tensile-compressive test, obtain experimental data, and obtain the stress-strain curve using the experimental data.

[0037] The specific implementation method is as follows: 1) Prepare a composite tensile-compressive specimen. The outer specimens 1 with a thickness of 0.5 mm to 0.7 mm are adhered to both sides of the ultra-thin titanium plate specimen 2 through epoxy resin. The thickness of the epoxy resin layer is about 0.05 mm. After bonding, the specimen is cured to ensure that the outer specimen 1 is closely attached to the ultra-thin titanium specimen 2 to form a composite tensile-compressive specimen; 2) Spray speckles in the thickness direction of the prepared composite tensile-compressive specimen for DIC strain measurement; 3) Clamp the prepared composite tensile-compressive specimen to the universal testing machine with an electric-assisted fixture. Apply a lubricant with a thickness of about 0.1 mm on both the gauge sections and the periphery of the composite tensile-compressive specimen to ensure sufficient lubrication and reduce the friction between the composite tensile-compressive specimen and the insulating backing plate. Then, install the first clamping plate 12, the second clamping plate 13, the straight rod 10, the spring 5, the spring adjusting block 6, the outer plate 8, the inner plate 9, and the force sensor 7 in sequence, and separate the first clamping plate 12 and the second clamping plate 13 by a certain distance for compression. After installation, connect the force sensor 7 in the device to the computer to obtain the lateral force F applied to the composite tensile-compressive specimen c ; 4) Adjust the spring adjusting block 6 to clamp the composite tensile-compressive specimen, and record the screwing-in amount x; 5) Set the parameters required for the tensile-compressive test and conduct the tensile-compressive test; 6) Observe whether the ultra-thin titanium plate specimen 2 buckles. If buckling occurs, remove the buckled composite tensile-compressive specimen, adjust the screwing-in amount x in step 4 to 1.5 times that of the previous time, and repeat steps 1 - 6 until the ultra-thin titanium plate specimen 2 does not buckle, and then continue with the following steps; 7) If no buckling occurs, record the current screwing-in amount x, take a new composite tensile-compressive specimen for reinstallation and adjust the screwing-in amount to x, and start the following steps; 8) Set the current parameters and test conditions, start the power supply, and the current is transmitted to the composite tensile-compressive specimen through the electric-assisted fixture. Heat the ultra-thin titanium plate specimen 2 to the predetermined temperature, and monitor the temperature through the thermocouple 14, refer to Figure 7 and Figure 8 ; 9) Start the universal testing machine to conduct the tensile-compressive cyclic loading test; 10) After the test is completed, adjust the spring adjusting block 6 to relax the clamping plates and remove the composite tensile-compressive specimen; 11) Calculate the force F received by the ultra-thin titanium plate specimen 2 during the tensile-compressive process through the data measured by the universal testing machine and the force sensor 7 Ti =F A -F f -F gf , where F A is the force received by the composite tensile-compressive specimen, F f is the frictional force, and F gf is the force received by the outer specimen 1 during the tensile-compressive process; 12) The frictional force is equal to the lateral force multiplied by the friction coefficient, that is, F f =2F c *μ, where μ can be measured through an electric-assisted friction coefficient test; 13) If the outer specimen 1 is always in the elastic state during the deformation process, F gf can be obtained through the elastic modulus E gfCalculated from the stress and strain, if the outer specimen 1 enters the plastic stage during the deformation process, since the outer specimen 1 is not affected by the current during the insulation electric-assisted process, the force F on it during the tension and compression process can be obtained through the thin plate tension and compression test. gf ; 14) Obtain the force magnitudes of each part of the specimen during the tension and compression process, and then through the formula F Ti =F A -F f -F gf The magnitude of the force F on the ultra-thin titanium plate specimen 2 during the tension and compression process can be calculated. Ti ; 15) Through the F Ti value and the strain measured by DIC, the stress-strain curve during the electro-assisted tension-compression cyclic loading process of the ultra-thin titanium plate can be calculated.

[0038] The above are only several specific embodiments of the present invention. However, the embodiments of the present invention are not limited thereto, and any changes that can be thought of by those skilled in the art should fall within the protection scope of the present invention.

Claims

1. An electro-assisted tensile and compressive cyclic loading device for ultra-thin titanium plates, characterized in that, Comprising: Two outer specimens (1) used in conjunction with an ultra-thin titanium plate specimen (2), the two outer specimens (1) being fixed to both sides of the ultra-thin titanium plate specimen (2), and the three forming a composite tensile-compressive specimen. The ends of the ultra-thin titanium plate specimen (2) extend beyond the ends of the outer specimens (1). Lateral forces are applied to the two sides of the composite tensile-compressive specimen after it is fixed by a clamping assembly. Two pairs of electric-assisted clamps, respectively clamped at both ends of the composite tensile-compressive specimen. Each pair of electric-assisted clamps includes two oppositely arranged chucks (11). The clamping surfaces of the chucks (11) have conductive structures (15). The conductive structures (15) are connected to an external power source. When the composite tensile-compressive specimen is clamped on the chucks (11), the conductive structures (15) contact the composite tensile-compressive specimen to transfer current through the conductive structures (15) to the composite tensile-compressive specimen for heating it. The chucks (11) are connected to the loading ends of a universal testing machine.

2. The electro-assisted tensile and compressive cyclic loading device for ultra-thin titanium plates according to claim 1, characterized in that, The resistivity of the outer specimen (1) is 10 12 Ω·m - 10 17 Ω·m.

3. The electro-assisted tensile and compressive cyclic loading device for ultra-thin titanium plates according to claim 1, characterized in that, The conductive structure (15) includes a conductive sheet (150) and a connecting sheet (151) connected as a whole. Both the conductive sheet (150) and the connecting sheet (151) are made of conductive materials. The conductive sheet (150) is located on the clamping surface of the chuck (11). The side of the conductive sheet (150) that contacts the composite tensile-compressive specimen has serrations. A through groove (152) is also provided on the conductive sheet (150). The end of the outer specimen (1) is placed in the through groove (152). The ultra-thin titanium plate specimen (2) contacts the conductive sheet (150). The connecting sheet (151) is connected to an external power source.

4. The electro-assisted tensile and compressive cyclic loading device for ultra-thin titanium plates according to claim 1, characterized in that, The upper and lower clamps of the universal testing machine correspondingly clamp the two pairs of electric-assisted clamps. The chucks (11) also have positioning posts (16) and fixing grooves (17). The positioning posts (16) cooperate with the positioning grooves of the universal testing machine. The loading head of the universal testing machine is clamped in the fixing grooves (17).

5. The electro-assisted tensile and compressive cyclic loading device for ultra-thin titanium plates according to claim 1, characterized in that, The thickness of the outer specimen (1) is 0.5 mm - 0.7 mm, and the material is one of glass fiber composite material, polyetheretherketone, or carbon fiber - glass fiber composite material.

6. The electro-assisted tensile and compressive cyclic loading device for ultra-thin titanium plates according to claim 5, characterized in that, The outer specimen (1) and the ultra-thin titanium plate specimen (2) are adhesively fixed by epoxy resin. The layer thickness of the epoxy resin is 0.02 mm - 0.05 mm.

7. The electro-assisted tensile and compressive cyclic loading device for ultra-thin titanium plates according to claim 1, characterized in that, The clamping assembly includes: Two insulating gaskets symmetrically arranged at the center on both sides of the composite tensile-compressive specimen. Each insulating gasket includes a first insulating sheet (3) and a second insulating sheet (4) stacked along the extending direction of the ultra-thin titanium plate specimen (2). Two clamping plates symmetrically arranged at the outer sides of two insulating gaskets in a central symmetry manner. A lateral force adjusting component is connected to the outer sides of the clamping plates. Each clamping plate includes a first clamping plate (12) and a second clamping plate (13) stacked together. The first clamping plate (12) is fixedly connected to the corresponding first insulating sheet (3), and the second clamping plate (13) is fixedly connected to the corresponding second insulating sheet (4). Between the first insulating sheet (3) and the second insulating sheet (4), and between the first clamping plate (12) and the second clamping plate (13), they are slidably connected through a plurality of straight rods (10) respectively, so that the first insulating sheet (3) and the second insulating sheet (4), and the first clamping plate (12) and the second clamping plate (13) move synchronously along the extension direction of the ultra-thin titanium plate specimen (2).

8. The electro-assisted tensile and compressive cyclic loading device for ultra-thin titanium plates according to claim 7, characterized in that, Between the first insulating sheet (3) and the second insulating sheet (4), and between the first clamping plate (12) and the second clamping plate (13), they are also connected through a comb-shaped structure respectively.

9. The electro-assisted tensile and compressive cyclic loading device for ultra-thin titanium plates according to claim 7, characterized in that, The lateral force adjusting component includes: Two inner plates (9) respectively placed on the outer sides of the corresponding clamping plates; Two outer plates (8) respectively placed on the outer sides of the corresponding inner plates (9). Slide holes are formed in both the inner plates (9) and the outer plates (8) along the extension direction of the ultra-thin titanium plate specimen (2). A screw sequentially passes through the slide holes and then is fixed to the clamping plate and the insulating gasket. A spring adjusting block (6) is rotatably connected to one of the outer plates (8); A spring (5) with one end fixedly connected to the spring adjusting block (6) and the other end fixedly connected to the corresponding inner plate (9).

10. A test method based on the electro-assisted tensile and compressive cyclic loading device for ultra-thin titanium plates according to any one of claims 1-9, characterized in that, It includes the following steps: Step 1: Prepare a composite tensile-compressive specimen. Fix the outer specimens (1) on both sides of the ultra-thin titanium plate specimen (2) to form a composite tensile-compressive specimen; Step 2: Clamp the prepared composite tensile-compressive specimen onto a universal testing machine through an electro-assisted fixture, and apply lateral forces to the composite tensile-compressive specimen through the clamping components on both sides for fixation; Step 3: Set the parameters required for the tensile-compressive test and conduct the tensile-compressive test; Step 4: Observe whether the ultra-thin titanium plate specimen (2) buckles. If buckling occurs, adjust the lateral force, and then repeat Steps 1 - 4 until the ultra-thin titanium plate specimen (2) does not buckle, and obtain the corresponding lateral force when no buckling occurs; Step 5: Fix the remaining composite tensile-compressive specimens with the corresponding lateral force when no buckling occurs, conduct the tensile-compressive test, obtain experimental data, and obtain the stress-strain curve using the experimental data.

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