Multi-field coupling metal plate uniaxial tension experiment device and experiment method

Abstract

The invention discloses a multi-field coupling metal plate uniaxial tension experimental device and experimental method, and belongs to the technical field of material science and engineering, the multi-field coupling metal plate uniaxial tension experimental device comprises a fixed support system connected with a material testing machine, an energy conversion system, an integrated loading system and a clamping system; wherein the energy conversion system is in transmission connection with the integrated loading system and is used for converting electric energy into ultrasonic mechanical vibration and transmitting the ultrasonic mechanical vibration to a test piece, and a contact part and a connecting part of the clamping system and the test piece are made of an insulating heat-insulating material; and the spatial layout of the fixed supporting system, the integrated loading system and the clamping system is matched with the non-contact full-field strain measurement equipment. According to the invention, ultrasonic vibration-electricity-heat-force four-field coupling mechanical property testing and stress relaxation behavior research can be realized, the system is simple in structure and convenient to operate, and the influence of ultrasonic vibration on the mechanical behavior of the metal material can be explored.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of material science and engineering technology, and particularly relates to a multi-field coupling metal sheet uniaxial tensile test device and a test method. BACKGROUND

[0002] As a core structural unit, metal sheet plays an irreplaceable role in the manufacturing of key products such as aerospace engine blades, automotive chassis components, offshore platform support components, medical device implants, etc. The high-precision forming technology of metal sheet is a key indicator for measuring the overall level of manufacturing industry. However, the springback phenomenon has always been the core bottleneck restricting the forming precision of metal sheet. During the forming process, the residual stress generated inside the material will cause shape deviation after unloading, which seriously affects the dimensional accuracy of the product.

[0003] To solve the springback problem, the traditional process mainly adopts passive adaptation methods such as optimizing the loading path or compensating the die surface. However, for hard metal materials with large springback, such methods often have limitations: when the load is too low, springback cannot be effectively controlled, and when the load is too high, new forming defects such as excessive thinning and cross-section distortion of the material are easily caused. The subsequent development of hot stretch bending process utilizes the softening effect of materials at high temperature to reduce springback, but this process not only puts strict requirements on the high-temperature resistance of the equipment, but also has prominent problems such as high energy consumption, complex process flow, and easy oxidation of materials.

[0004] In recent years, as a new physical field assisted forming method, the ultrasonic vibration assisted machining technology has shown significant advantages in improving the plasticity of metal materials and prolonging the service life due to its unique volume effect, surface effect and residual effect. This technology can effectively improve the material processing performance by generating ultrasonic softening effect in the material through high-frequency vibration energy, but most existing researches focus on the material behavior analysis under single ultrasonic field or simple stress state, and lack of special experimental equipment for systematically studying the mechanical properties of metal sheet (especially the stress relaxation behavior in the tensile process) under the coupling effect of ultrasonic vibration field, electric field, temperature field and mechanical load field.

[0005] Meanwhile, the existing high-temperature uniaxial tensile experimental device still has many technical shortcomings: firstly, the compatibility with non-contact full-field strain measurement technology (such as digital image correlation method DIC) is poor - the transmission parts, clamps or support structures of the device easily block the shooting field of view, and the strong light, heat radiation or air flow disturbance generated by the heating system will cause the image clarity to decrease and the gray value to drift, thereby affecting the displacement and strain calculation accuracy; secondly, the temperature control precision is insufficient - the furnace heating has the problem of uneven temperature field, the infrared heating is greatly affected by the surface characteristics of the test sample, the electromagnetic induction heating is easy to have temperature overshoot, and the single-point temperature measurement method cannot monitor the global temperature distribution of the test piece in real time; thirdly, the clamping stability is poor in the high-temperature ultrasonic environment - the traditional clamping materials are conductive and thermal, which not only causes energy loss, but also may cause short circuit risk, and the clamping structure is easy to cause the test piece to deviate or loosen under high-frequency vibration; fourthly, the structure is complex and heavy, and the closed cavity design not only is inconvenient to operate, but also further limits the flexibility of multi-field coupling test.

[0006] The above technical defects result in that the softening / hardening mechanism of the material under multi-field coupling cannot be revealed in depth, it is difficult to establish a high-precision material constitutive model, and thus the development of metal sheet forming springback precision prediction and active control technology is restricted. Therefore, it is an urgent need in the field of material science and engineering to develop a uniaxial tensile experimental device and method which can realize four-field synergistic coupling, adapt to non-contact measurement, control temperature accurately and clamp stably. SUMMARY

[0007] In order to solve the problems that the existing high-temperature uniaxial tensile experimental device has obvious technical shortcomings in space layout, motion control, measurement compatibility and temperature control, the present application provides a multi-field coupled metal sheet uniaxial tensile experimental device and experimental method, which can realize ultrasonic vibration-electric-thermal-force four-field coupled mechanical property test and stress relaxation behavior research, and has simple system structure, convenient operation and can explore the influence of ultrasonic vibration on the mechanical behavior of metal materials.

[0008] The technical scheme adopted by the multi-field coupled metal sheet uniaxial tensile experimental device and experimental method of the present application is as follows: A multi-field coupled metal sheet uniaxial tensile experimental device, comprising a fixed support system connected with a material testing machine, an energy conversion system, an integrated loading system and a clamping system; wherein the energy conversion system is in transmission connection with the integrated loading system, for converting electric energy into ultrasonic mechanical vibration and transmitting it to the test piece, the contact part and connecting part of the test piece with the clamping system are made of insulating and heat insulating materials, and the space layout of the fixed support system, the integrated loading system and the clamping system is adapted to the non-contact full-field strain measurement equipment.

[0009] A further improvement of the technical solution of the present invention is that the energy conversion system includes an ultrasonic generator and a transducer; wherein the output power of the ultrasonic generator is 2000W and the working frequency is 20KHz, and the transducer is a piezoelectric ceramic transducer, which is used to convert ultrasonic frequency electrical oscillation signals into ultrasonic frequency mechanical vibrations.

[0010] A further improvement of the technical solution of the present invention is that: the integrated loading system includes a stepped integrated amplitude transformer, one end of which is detachably connected to the transducer through a threaded hole, and the other end of which is fixedly connected to the clamping system, for amplifying the amplitude of the mechanical vibration generated by the transducer and transmitting it to the specimen along the axial direction.

[0011] A further improvement of the technical solution of the present invention is that the integrated amplitude transformer is clamped and fixed in the fixed support system by two sets of flanges and bolts and nuts.

[0012] A further improvement of the technical solution of the present invention is that: the insulating and heat-insulating material is alumina, and the clamping system includes a wedge-shaped chuck and multiple fastening bolts; wherein, the contact surface between the wedge-shaped chuck and the specimen is provided with an anti-slip structure, and the multiple fastening bolts are evenly distributed circumferentially.

[0013] A further improvement of the technical solution of the present invention is that: the two ends of the specimen are provided with electrical terminals, which are electrically connected to an external power source.

[0014] A further improvement of the technical solution of the present invention is that: the fixed support system includes an upper support unit and a lower fixing unit; wherein, the upper support unit is detachably connected to the crossbeam of the material testing machine by means of pins and fastening nuts, and applies tensile load by means of crossbeam displacement; the lower fixing unit is fixed to the platform of the material testing machine by means of pins and fastening nuts, and includes support rods and multiple sets of flanges.

[0015] A method for uniaxial tensile testing of multi-field coupled metal sheets, using the above-mentioned experimental apparatus, includes the following steps: S1. Equipment preparation: Debug the ultrasonic generator and complete the impedance matching between the transducer and the integrated amplitude transformer; check the connection tightness of the fixed support system, and calibrate the material testing machine and the non-contact full-field strain measurement equipment. S2. Processing and testing specimens: In accordance with GB / T228.2010 standard, the specimens are dumbbell-shaped metal sheets processed by wire cutting. The clamping section and the working section of the specimen are smoothly connected by a transition arc, and the two ends are extended to provide electrical terminals. The surface of the specimens is then polished, cleaned, and treated with speckled spray coating. S3. Specimen Installation and Preheating: Insert both ends of the specimen into the clamping system of the upper support unit and the wedge chuck of the integrated amplitude transformer, respectively, and tighten them with fastening bolts; connect the specimen's electrical terminals to the heating power supply, start the heating system, preheat the specimen to the target temperature and keep it at that temperature; S4. Coupled tensile test: Divide the specimens into groups of 3-5. One group is subjected to a conventional high-temperature uniaxial tensile test, while the other group is subjected to an ultrasonic vibration-assisted high-temperature uniaxial tensile test using an ultrasonic generator. Simultaneously, start the material testing machine and non-contact full-field strain measurement equipment to collect tensile force, displacement and strain data. S5. Stress relaxation test: Two sets of specimens were selected, and ultrasonic vibration-assisted stress relaxation test and stress relaxation test without ultrasonic vibration were performed respectively. The specimens were stretched to the preset pre-strain and then fixed at the position of the crossbeam. The stress change was continuously monitored until the relaxation limit was reached. S6. Data Processing: Calculate engineering stress and strain based on the collected data, and plot the actual stress-strain curve; analyze the influence of ultrasonic vibration on the rheological stress of the material, determine the stress drop peak and corresponding strain; fit the stress relaxation curve, and explore the relaxation time and relaxation limit under different conditions.

[0016] The technological advancements achieved by this invention due to the adoption of the above technical solutions are as follows: This invention achieves the coupling of ultrasonic vibration field, electric field, temperature field and mechanical load field through the coordinated design of energy conversion system, integrated loading system and clamping system. It can simulate the real stress and environmental state of metal sheet in complex forming process, and provides a dedicated experimental platform for studying the softening mechanism, mechanical behavior and stress relaxation characteristics of materials under multi-field coupling. It solves the problem that existing equipment cannot systematically carry out multi-field coupling tests.

[0017] The experimental device of this invention adopts an open spatial layout without a closed cavity design. The arrangement of the clamping system and support structure avoids the measurement field of view of the working section of the specimen. Moreover, the electric heating method avoids the strong light and airflow interference generated by traditional heating systems, ensuring that non-contact full-field strain measurement equipment (such as DIC) can clearly acquire images of the specimen surface, improve the accuracy of displacement and strain measurement, and provide a reliable data foundation for subsequent stress-strain analysis. Attached Figure Description

[0018] Figure 1 This is a schematic diagram of the structure of a multi-field coupled uniaxial tensile testing device for metal sheets according to the present invention.

[0019] In the attached diagram: 1. Crossbeam; 2. Upper fastening nut; 3. First base; 4. Upper M8 bolt; 5. Upper clamping system; 6. M6 alumina bolt; 7. Upper wedge chuck; 8. Specimen; 9. Integrated amplitude transformer; 10. Lower M8 bolt; 11. First pin; 12. First flange; 13. M5 bolt; 14. M10 bolt; 15. Second flange; 16. Third flange; 17. Support rod; 18. Transducer; 19. Second base; 20. Second pin; 21. Lower fastening nut; 22. Testing machine platform; 23. Lower wedge chuck. Detailed Implementation

[0020] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to specific embodiments and accompanying drawings. In the following description, descriptions of well-known structures and technologies are omitted to avoid unnecessarily obscuring the concept of this invention.

[0021] Example 1 like Figure 1 As shown, this embodiment provides a multi-field coupled uniaxial tensile testing device for metal sheets, including a fixed support system, an energy conversion system, an integrated loading system, and a clamping system connected to a material testing machine.

[0022] The fixed support system includes an upper support unit and a lower fixed unit. The upper support unit consists of an upper clamp mounting base, a first pin 11, an upper fastening nut 2, a first base 3, and an upper clamping system 5. The first base 3 is detachably connected to the crossbeam 1 of the Inspekt Table universal testing machine via the first pin 11 and the upper fastening nut 2. The vertical displacement of the crossbeam 1 can directly apply tensile loads. The first base 3 is detachably connected to the upper clamping system 5 via an upper M8 bolt 4 and a first flange 12. The lower fixing unit includes a second base 19, a support rod 17, a second flange 15, and a third flange 16. The support rod 17 is designed with a height of 225mm. This dimension is determined based on the half-wavelength requirements of the specimen 8 and the fixture head, the position of the ultrasonic transducer node section, and the flange installation position to ensure no energy loss during ultrasonic vibration transmission. The second base 19 is fixed to the material testing machine platform 22 by the second pin 20 and the lower fastening nut 21. The two ends of the support rod 17 are connected to the third flange 16 and the second base 19 by M10 bolts 14, respectively. The second flange 15 is fixed to the third flange 16 by the lower M8 bolts 10 and cooperates with the integrated amplitude transformer 9 to achieve the fixation of the integrated loading system.

[0023] The energy conversion system consists of an ultrasonic generator and a piezoelectric ceramic transducer 18. The ultrasonic generator is the core device that provides ultrasonic electrical energy to the ultrasonic transducer 18. Its core function is to convert alternating current into ultrasonic frequency electrical power and output it, providing the energy required for the vibration of the specimen 8 during ultrasonic vibration and tensile testing. Its main components include an oscillator, a voltage amplifier, a power amplifier, and an output transformer, among which the oscillator is the core component of the entire system. To ensure the frequency of the ultrasonic generator remains stable, impedance matching between the generator and the transducer 18 is necessary.

[0024] The commonly used ultrasonic generator in unidirectional tensile testing is the H66MC, with a rated power supply voltage of 220V, an input frequency of 50Hz, an output power of no less than 250W, and an adjustable frequency range of 18kHz to 22kHz. Practical application shows that while this model of ultrasonic generator has stable performance, it suffers from low output power, making it difficult to accurately simulate actual working conditions and thus limiting the reference value of the obtained test data.

[0025] The ultrasonic generator in this application is custom-designed and has no specific model number. Its purpose is to simulate the operating environment to the greatest extent possible. It features a 220V voltage, a 20kHz frequency, and a 2000W output power, with a non-adjustable frequency. It boasts high forward power, small size, low cost, and high intelligence, and can display the oscillation frequency. In this embodiment, the generator and transducer 18 are matched to maximize generator efficiency and the integrated amplitude transformer 9's amplitude. Through testing, the ultrasonic generator's output power in this embodiment has met the corresponding technical specifications. The generator's output impedance should match the transducer 18's impedance. During testing, there was almost no resonant frequency drift, and the amplitude remained essentially constant, meeting the simulation requirements of the operating environment, and the test data is highly reliable. One end of the piezoelectric ceramic transducer 18 is connected to the integrated amplitude transformer 9 via a threaded hole, and the other end is electrically connected to the ultrasonic generator via an electrical signal output line, capable of converting ultrasonic frequency electrical oscillation signals into ultrasonic frequency mechanical vibrations with an amplitude of 4µm~5µm.

[0026] The integrated loading system employs a stepped integrated amplitude transformer 9, whose length is designed according to the half-wavelength of the ultrasound. One end is threadedly connected to the piezoelectric ceramic transducer 18, and the other end is fixedly assembled to the upper wedge-shaped clamp 7 via M5 bolts 13. The function of the integrated amplitude transformer 9 is to amplify the amplitude of the mechanical vibration generated by the transducer 18 to 10~20µm to achieve the best ultrasonic softening effect. Simultaneously, it acts as a mechanical impedance converter, ensuring that ultrasonic energy is efficiently transferred from the transducer 18 to the specimen 8. The integrated amplitude transformer 9 is clamped and fixed between the second flange 15 and the third flange 16 with bolts and nuts, ensuring structural stability during vibration without displacement or loosening.

[0027] The ultrasonic integrated amplitude transformer 9, also known as an ultrasonic speed transformer, ultrasonic amplifier, or ultrasonic energy concentrator, is one of the key components of an ultrasonic vibration system. Its expansion and contraction under high-frequency electrical oscillation is very small. Even under resonance conditions, the maximum amplitude directly obtainable from the transducer 18 is only 4-5 μm. However, to achieve the most significant ultrasonic vibration stretching effect, the tool's amplitude must be at least 10-20 μm. This necessitates adding an amplitude amplification section between the transducer 18 and the machining tool, namely the integrated amplitude transformer 9. The integrated amplitude transformer 9 has two main functions: first, to amplify the displacement or velocity amplitude of mechanical vibration, or to concentrate energy on a smaller radiation surface, i.e., energy concentration; second, to act as a mechanical impedance converter, enabling more efficient transmission of ultrasonic energy from the ultrasonic transducer 18 to the load. Since the material tested in this application is solid, a certain static pressure is required during operation, especially during ultrasonic machining, where the machining tool continuously wears down, resulting in significant load variations. Therefore, the integrated amplitude transformer 9 requires not only a sufficiently large amplification factor but also high operational stability and sufficient bending stiffness. Thus, a stepped amplitude transformer is adopted.

[0028] The clamping system includes an upper wedge chuck 7, a lower wedge chuck 23, M6 alumina bolts 6, and multiple fastening bolts. The upper wedge chuck 7 is installed in the upper clamping system 5 of the upper support unit, and the lower wedge chuck 23 is fixedly connected to the integrated amplitude transformer 9. The working surface of the chuck in contact with the specimen 8 is provided with anti-slip texture to increase the clamping friction. The chuck body and the connecting M6 bolts in contact with the specimen 8 are all made of alumina material, which has excellent insulation and heat insulation properties. This can prevent current leakage during electric heating and reduce temperature loss, ensuring the temperature uniformity of the specimen 8. The multiple fastening bolts are evenly distributed along the circumference of the chuck. The preload adjustment ensures that the specimen 8 is firmly clamped for a long time in high temperature and ultrasonic vibration environment without relative slippage.

[0029] In this embodiment, the spatial layout of the fixed support system, integrated loading system, and clamping system is adapted to the non-contact full-field strain measurement equipment. The non-contact full-field strain measurement equipment adopts a three-dimensional displacement strain gauge (DIC). The spatial layout of this embodiment is specifically designed for this equipment: the upper support unit, lower fixed unit, and clamping system all avoid the gauge length and parallel section of the specimen 8, without any obstructing structures. Furthermore, the electric heating method does not generate strong light, thermal radiation, or airflow disturbance, ensuring that the DIC camera can clearly acquire speckle images of the specimen 8 surface. The heating system is connected to an external adjustable power supply through the electrical terminals at both ends of the specimen 8. The specimen 8 is heated using the current heating effect. The power supply output voltage is adjustable, thereby controlling the temperature of the specimen 8 within the range of 300-800℃. The temperature of the gauge length section of the specimen 8 is monitored in real time by distributed thermocouples to ensure that the temperature fluctuation is controlled within ±10℃ and the temperature gradient is less than 5℃ / mm.

[0030] Example 2 This embodiment provides a method for uniaxial tensile testing of multi-field coupled metal sheets. This embodiment mainly focuses on tensile testing of TC4 titanium alloy, which is commonly used in aerospace engine systems, structural components, fuel systems, control systems, and sensor piping. It has a normal operating temperature range of -253 to 600°C, good weldability, and excellent fracture toughness. TC4 titanium alloy belongs to the α+β type titanium alloy, characterized by high specific strength, excellent corrosion resistance, a tensile strength of over 950 MPa at room temperature, a yield strength ≥900 MPa, an elongation after fracture greater than 10%, and a density of only 4.4~4.5 g / cm³. TC4 titanium alloy is suitable for manufacturing key load-bearing components in the aerospace field, such as aircraft engine compressor blades, turbine disks, fuselage frames, landing gear door components, rocket body connecting rings, and satellite supports. In hot-rolled or forged states, it is used to manufacture various mechanical structural parts that withstand complex stresses and require lightweight construction. In the marine engineering field, it is used to manufacture ship propellers, seawater pipelines, offshore platform support arms, and underwater probe housings. In the field of medical devices, it is often used to manufacture components that are implanted in the human body for a long time, such as artificial hip joint prostheses, femoral condyles of the knee joint, dental implants, and intramedullary nails for orthopedic surgery. In the high-end automotive industry, it is used to manufacture precision parts such as engine valves, chassis suspension control arms, and lightweight drive shafts. Therefore, it is of research significance to conduct uniaxial tensile tests on TC4 titanium alloy.

[0031] This embodiment mainly focuses on the study of stress-strain curves obtained from uniaxial tensile tests to reveal the variation law of various performance parameters of metal sheets under ultrasonic vibration, obtain σ−ε curves to analyze mechanical properties, and use finite element software ABAQUS and data processing software Origin to analyze the mechanical law of stress relaxation.

[0032] S1. Prepare an ultrasonic generator: Based on the material to be tested and the environmental parameters of the material's intended use, select an ultrasonic source with a power supply voltage of 220V, a frequency of 20KHz, an output power of 2000W, and a non-adjustable frequency.

[0033] S2. Processing Test Specimen 8: In accordance with the requirements of GB / T228.2010 Metals - Tensile Testing - Part 1 - Room Temperature Test Method, specimen 8 is processed from a metal sheet using wire cutting into a dumbbell-shaped specimen that is wider at both ends and narrower in the middle, with a smooth transition arc connecting the clamping section and the working section. A section extends from each end as an electrical terminal. The gauge length of specimen 8 is 16 mm, and the length of the parallel section is 23 mm. One end of specimen 8 is mounted in the upper clamping system 5, and the other end is mounted on the integrated amplitude transformer 9 with a chuck.

[0034] The shape of specimen 8 is not limited to a dumbbell shape that is thicker at both ends and thinner in the middle. It can be processed into other required shapes, as long as the tensile force does not affect the vibration effect of the ultrasonic vibration tensile device and does not affect the setting of the electrical connection terminal. At the same time, the ultrasonic vibration tensile device should not affect the tensile effect of specimen 8. When performing a uniaxial tensile test on specimen 8, the output frequency of the ultrasonic generator is 20KHz.

[0035] Surface treatment of specimen 8 is required. The experiment requires full-field strain measurement or in-situ observation of DIC. The surface of dumbbell-shaped specimen 8 needs to be polished and etched. Use 400#, 800# and 1200# sandpaper to grind the surface of specimen 8 in sequence to remove the oxide layer and scratches, and then wipe it clean with alcohol. Spray DIC special speckle coating on the surface of specimen 8 to ensure that the speckle distribution is uniform and the contrast is high. After the coating is dry, it is ready for use.

[0036] S3. Perform ultrasonic vibration-electric-thermal-mechanical four-field coupled mechanical property test on specimen 8: Divide specimen 8 into groups of 3-5 specimens each. Assemble one end of specimen 8 in the upper clamping system 5, and load the other end onto the integrated amplitude transformer 9 with a clamp below. Start the ultrasonic generator and perform 3 sets of conventional high-temperature uniaxial tensile tests and ultrasonic vibration-assisted high-temperature uniaxial tensile tests. Test data are obtained using the built-in software of the Inspekt Table universal testing machine and the Newtop three-dimensional displacement-strain meter (DIC).

[0037] The test temperature was 550℃, and the test loading rate was 0.96 mm / min. A Newtop three-dimensional displacement-strain measuring instrument was required for the ultrasonic vibration tensile test; therefore, a uniformly distributed, high-contrast speckle pattern had to be sprayed onto the surface.

[0038] Because it is a high-temperature experiment, stress relaxation will proceed faster than at room temperature. Moreover, the strength of the material will decrease at high temperatures, and the stress when stretched to the set strain will also decrease. In order to more intuitively analyze the influence of ultrasonic vibration on stress relaxation behavior, a 10% pre-strain loading was selected to ensure that the stress at the beginning of the stress relaxation experiment is high enough, and that the time for stress relaxation to reach a certain stable stress value in the second stage is moderate, avoiding an experiment that is too long or too short.

[0039] S4. Based on the uniaxial tensile test, a comparative experiment on stress relaxation with and without long-wave ultrasonic vibration was conducted. One end of the specimen 8 was assembled in the upper clamping system 5, and the other end was mounted on the integrated amplitude transformer 9 with a clamp below. Three sets of specimens 8 were selected for stress relaxation tests with and without long-wave ultrasonic vibration. Three sets of tests were conducted to select a suitable curve.

[0040] S5. Stress-strain analysis: Based on the experiment, the stress-strain curves of specimen 8 under conventional high-temperature uniaxial tension and short-wave ultrasonic vibration-assisted high-temperature uniaxial tension were obtained. The tensile force was measured by the Inspekt Table universal testing machine, and the displacement was measured by the Xintuo three-dimensional displacement-strain measuring instrument (DIC). The engineering strain and engineering stress were calculated, and the true stress-strain curve was obtained.

[0041] The ultrasonic vibration-assisted uniaxial tensile mechanical property test mainly tests the acoustic softening effect and examines the role of ultrasonic vibration in the thermal tensile process, primarily the decrease in rheological stress and the change in rheological stress after the ultrasonic vibration is removed. The ultrasonic vibration is applied by selecting a strain point (pre-strain) in the range between the yield strength and the tensile strength, and vibration is applied at this point to observe the change in rheological stress. At this point, the rheological stress will undergo a change process, decreasing sharply and then gradually increasing. The goal is to find the peak value of stress decrease and the corresponding strain under these conditions (temperature, amplitude, pre-strain) in order to find suitable parameters for subsequent stress relaxation.

[0042] By establishing a model, modal analysis of the assembly of specimen 8 and integrated amplitude transformer 9 was performed using the finite element analysis software ABAQUS. The resonant frequency of the assembly was found to be 20 kHz. The stress distribution of specimen 8 under ultrasonic vibration tension was simulated by computer, and a clear stress-strain distribution diagram of specimen 8 was obtained. By comparing and analyzing the simulation results of specimen 8 under normal tension, it was confirmed that ultrasound does indeed change the constitutive relationship of the material.

[0043] During the experiment, scanning electron microscopy revealed that the fracture surfaces under normal tensile conditions and ultrasonic tensile conditions were significantly different. The ultrasonic tensile fracture surface exhibited more obvious plastic fracture characteristics than the normal tensile fracture surface. The presence of plastic fracture characteristics indicates that the material does indeed exhibit a "softening" phenomenon, which is consistent with the changes in the mechanical properties of the material under ultrasonic tensile action. Combined with the analysis of the tensile fracture morphology characteristics, it was concluded that TC4 titanium alloy exhibits a significant acoustic softening effect under ultrasonic vibration tensile action.

[0044] S6. Stress Relaxation Behavior Analysis: Using the stress-strain curves obtained in the above steps, stress relaxation experiments are conducted. During the stress relaxation process, the position of the upper beam 1 no longer changes. Under ultrasonic vibration and thermal environment, the stress decreases, manifested as a reduction in the tension on the upper beam 1. The relaxation time under different conditions is studied, with the standard being the stress reaching the relaxation limit, to explore the specific value of the relaxation limit.

[0045] In the above embodiments, a multi-field coupled uniaxial tensile testing device and method for metal sheets are provided. This invention, through the coordinated design of an energy conversion system, an integrated loading system, and a clamping system, achieves the coupling of ultrasonic vibration field, electric field, temperature field, and mechanical load field. It can simulate the actual stress and environmental conditions of metal sheets during complex forming processes, providing a dedicated experimental platform for studying the softening mechanism, mechanical behavior, and stress relaxation characteristics of materials under multi-field coupling. This solves the problem that existing equipment cannot systematically conduct multi-field coupling tests. The experimental device of this invention adopts an open spatial layout without enclosed cavities. The arrangement of the clamping system and support structure avoids the measurement field of view of the working section of the specimen. Furthermore, the electric heating method avoids the strong light and airflow interference generated by traditional heating systems, ensuring that non-contact full-field strain measurement equipment (such as DIC) can clearly acquire images of the specimen surface, improving the accuracy of displacement and strain measurements and providing a reliable data foundation for subsequent stress-strain analysis.

[0046] The embodiments described above are merely preferred embodiments of the present invention and are not intended to limit the concept and scope of the present invention. Various modifications and improvements made to the technical solutions of the present invention by those skilled in the art without departing from the inventive concept should fall within the protection scope of the present invention. All technical contents for which protection is sought in this invention are fully described in the claims.

Claims

1. A multi-field coupled sheet metal uniaxial tensile test device, characterized in that: The experimental device comprises a fixed support system connected with a material testing machine, an energy conversion system, an integrated loading system and a clamping system; the energy conversion system is in transmission connection with the integrated loading system, and is used for converting electric energy into ultrasonic mechanical vibration and transmitting the ultrasonic mechanical vibration to a test piece (8); the contact part and the connecting part of the test piece (8) with the clamping system are made of insulating and heat-insulating materials; and the spatial layout of the fixed support system, the integrated loading system and the clamping system is matched with a non-contact full-field strain measurement device.

2. The multi-field coupled metal sheet uniaxial tensile test device according to claim 1, characterized in that: The energy conversion system comprises an ultrasonic generator and a transducer (18); the output power of the ultrasonic generator is 2000W, and the working frequency is 20KHz; and the transducer (18) is a piezoelectric ceramic transducer (18) used for converting ultrasonic frequency electric oscillation signals into ultrasonic frequency mechanical vibration.

3. The multi-field coupled metal sheet uniaxial tensile test device according to claim 1, characterized in that: The integrated loading system comprises a stepped integrated amplitude transformer (9); one end of the integrated amplitude transformer (9) is detachably connected with the transducer (18) through a threaded hole; the other end of the integrated amplitude transformer (9) is fixedly connected with the clamping system; and the integrated amplitude transformer (9) is used for amplifying the mechanical vibration generated by the transducer (18) in amplitude and transmitting the mechanical vibration to the test piece (8) along an axial direction.

4. The multi-field coupled sheet metal uniaxial tensile test device according to claim 3, characterized in that: The integrated amplitude transformer (9) is clamped and fixed in the fixed support system through two groups of flanges and bolts and nuts.

5. The multi-field coupled sheet metal uniaxial tensile test device of claim 1, wherein: The insulating and heat-insulating material is alumina, and the clamping system comprises a wedge-shaped chuck and multiple fastening bolts; the contact surface of the wedge-shaped chuck with the test piece (8) is provided with an anti-skid structure; and the multiple fastening bolts are uniformly distributed in a circumferential direction.

6. The multi-field coupled sheet metal uniaxial tensile test device of claim 1, wherein: The test piece (8) is provided with an electric connection end at each end thereof, and the electric connection end is electrically connected with an external power supply.

7. The multi-field coupled sheet metal uniaxial tensile test device of claim 1, wherein: The fixed support system comprises an upper support unit and a lower fixing unit; the upper support unit is detachably connected with a beam (1) of the material testing machine through a pin and a fastening nut, and a tensile load is applied through displacement of the beam (1); the lower fixing unit is fixed with a platform (22) of the material testing machine through a pin and a fastening nut, and comprises a support rod (17) and multiple groups of flanges.

8. A method of multi-field coupled sheet metal uniaxial tension experiment, characterized in that, The experimental device of any one of claims 1-7 comprises the following steps: S1, device preparation: adjusting the ultrasonic generator, completing impedance matching of the transducer (18) and the integrated amplitude transformer (9), checking the connection fastening of the fixed support system, and calibrating the material testing machine and the non-contact full-field strain measurement device; S2, processing a test piece (8): according to the GB / T228.2010 standard, a wire-cutting processing metal plate is processed into a dumbbell-shaped test piece (8); a clamping section and a working section of the test piece (8) are smoothly connected through a transition arc; and an electric connection end is provided at each end of the test piece (8); and the surface of the test piece (8) is polished, cleaned and treated by speckle spraying; S3, test piece (8) installation and preheating: the two ends of the test piece (8) are respectively loaded into the clamping system of the upper support unit and the wedge-shaped chuck of the integrated amplitude transformer (9) and locked by fastening bolts; the electric connection end of the test piece (8) is connected with a heating power supply; and the heating system is started to preheat the test piece (8) to a target temperature and keep the temperature. S4, coupling tensile test: the test piece (8) is grouped, each group has 3-5, one group carries out conventional high temperature uniaxial tensile test, another group starts ultrasonic generator to carry out ultrasonic vibration assisted high temperature uniaxial tensile test; the material testing machine and the non-contact full-field strain measurement device are started simultaneously, and the tension, displacement and strain data are collected; S5, stress relaxation experiment: select two groups of test pieces (8), respectively, carry out ultrasonic vibration assisted stress relaxation experiment and stress relaxation experiment without ultrasonic vibration, stretch the test piece (8) to the preset pre-strain, then fix the position of the cross beam (1), continuously monitor the stress change until the relaxation limit is reached; S6, data processing: calculate the engineering stress and engineering strain according to the collected data, draw the true stress-strain curve; analyze the influence of ultrasonic vibration on the rheological stress of the material, determine the stress drop peak value and the corresponding strain; fit the stress relaxation curve, and explore the relaxation time and relaxation limit under different conditions.

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