Biaxial creep testing device and testing method for large-size titanium alloy used in ocean engineering

Abstract

The application relates to the technical field of material testing equipment, in particular to a biaxial creep testing device and method for large-size titanium alloy in marine engineering, which comprises a support frame, two groups of pressure applying components, a first hydraulic control system, a second hydraulic control system and an air compressor, wherein the first hydraulic cylinder and the second hydraulic cylinder are symmetrically fixed on the support frame along the X direction, and the third hydraulic cylinder and the fourth hydraulic cylinder are symmetrically fixed on the support frame along the Y direction; two groups of pressure applying components distributed along the X direction and the Y direction are arranged, biaxial tensile creep testing or biaxial pressure creep testing can be simultaneously carried out, the hydraulic system is used for applying pressure to the sample to be tested, the pressure is stable, and the pressure can be applied for a long time, the mechanical extensometer and the laser displacement meter are used for recording independent strains in four directions during the experiment process, and the strain gauge array is additionally arranged at the center of the sample to be tested, so that the overall coordinated deformation of the sample to be tested is analyzed, and the testing accuracy is improved.

Description

Technical Field

[0001] This invention relates to the field of creep testing technology, and more specifically to a biaxial creep testing device and method for large-size titanium alloys used in marine engineering. Background Technology

[0002] As countries continue to explore the deep sea, the requirements for related materials, including various structural materials and advanced buoyancy materials, for equipment such as deep-sea space stations and deep-sea submersibles are gradually increasing. Titanium alloy, as a low-density, high-strength, and corrosion-resistant metal material, is the first choice for the construction of large pressure-resistant structures in deep-sea environments.

[0003] Unlike traditional operating environments, in deep-sea conditions, thick-walled structural components are subjected to prolonged hydrostatic pressure from the surrounding seawater. Stress analysis of deep-sea pressure-resistant structures reveals that the pressure hull is subjected to triaxial compressive stress. The compressive stress perpendicular to the hull direction originates from hydrostatic pressure and is relatively low, negligible. The biaxial compressive stress within the plane is substantial, sometimes exceeding the yield strength of the hull material, leading to structural deformation or even instability. Therefore, studying the creep behavior of titanium alloys used in large deep-sea pressure-resistant structures under biaxial compressive stress conditions and establishing a compression creep failure model for titanium alloys under deep-sea conditions has significant scientific and engineering application value.

[0004] Currently, traditional test specimens are relatively small, such as bars in national standards, with diameters ranging from a few millimeters to tens of millimeters. This limits the applicable force, primarily resulting in uniaxial tensile stress. Large structures operating in the deep sea, however, endure multidimensional compressive stresses. For primary construction materials like titanium alloys, prolonged deep-sea operation leads to compressive creep deformation. When dealing with titanium alloys used in large pressure-resistant structures for marine engineering, their anisotropic nature results in significant differences in strain distribution and strain rate variations across different stress directions, making traditional methods and systems unsuitable.

[0005] Furthermore, in order to evaluate the material deformation behavior of large deep-sea engineering equipment in the deep sea for a long time (usually more than 1,000 hours), the testing time for large titanium alloy materials usually needs to be hundreds to thousands of hours. However, the traditional system that relies on screws or weights to apply pressure is only suitable for tensile testing of small bars because the force transmission structure is made of high-strength steel, which deforms and becomes unstable under long-term high pressure. For the application of multi-directional compression, the existing equipment cannot meet the pressure consistency of the pressure test process for thousands of hours, and cannot carry out biaxial creep tests under high stress. Therefore, there is an urgent need for a biaxial creep testing device and method for large-size titanium alloys in marine engineering to solve the above problems. Summary of the Invention

[0006] This invention proposes a biaxial creep testing device for large-size titanium alloys used in marine engineering, comprising:

[0007] The support frame is defined with its width direction as the X-direction and its length direction as the Y-direction.

[0008] Two sets of pressure-applying components: the first set of pressure-applying components includes a first hydraulic cylinder and a second hydraulic cylinder, and the second set of pressure-applying components includes a third hydraulic cylinder and a fourth hydraulic cylinder.

[0009] A first hydraulic control system controls the first hydraulic cylinder and the second hydraulic cylinder to operate simultaneously.

[0010] The second hydraulic control system controls the third and fourth hydraulic cylinders to operate simultaneously.

[0011] An air compressor is connected to the first hydraulic control system and the second hydraulic control system;

[0012] A constant pressure pump is connected to the first hydraulic control system and the second hydraulic control system;

[0013] A strain gauge array is attached to the surface of the sample to be tested and used to detect the regional strain characteristics of the sample.

[0014] The first hydraulic control system and the second hydraulic control system each include a pneumatic pressurization mode and a hydraulic pressurization mode. In the pneumatic pressurization mode, the air compressor pressurizes the first hydraulic control system and the second hydraulic control system, causing the first hydraulic cylinder, the second hydraulic cylinder, the third hydraulic cylinder and the fourth hydraulic cylinder to come into contact with the surface of the sample to be tested. In the hydraulic pressurization mode, the constant pressure pump pressurizes the first hydraulic control system and the second hydraulic control system, causing the first hydraulic cylinder, the second hydraulic cylinder, the third hydraulic cylinder and the fourth hydraulic cylinder to apply a predetermined pressure to the surface of the sample to be tested.

[0015] The first hydraulic cylinder and the second hydraulic cylinder are symmetrically fixed on the support frame along the X direction, and the third hydraulic cylinder and the fourth hydraulic cylinder are symmetrically fixed on the support frame along the Y direction. The first hydraulic cylinder and the second hydraulic cylinder are used to apply creep pressure in the X-axis direction to the sample to be tested, and the third hydraulic cylinder and the fourth hydraulic cylinder are used to apply creep pressure in the Y-axis direction to the sample to be tested.

[0016] The intersection of the axis of the first hydraulic cylinder and the axis of the third hydraulic cylinder is located at the center of the support frame;

[0017] The support frame is equipped with four sets of detection sensors, which respectively detect the movement of the piston rods of the first hydraulic cylinder, the second hydraulic cylinder, the third hydraulic cylinder and the fourth hydraulic cylinder. The detection sensors are electrically connected to a computer.

[0018] Preferably, the first hydraulic cylinder, the second hydraulic cylinder, the third hydraulic cylinder and the fourth hydraulic cylinder each include a cylinder body and a piston rod, the piston end of the piston rod slides in the cylinder body, and the cylinder body is provided with a first cavity and a second cavity, the first cavity and the second cavity are respectively located on both sides of the piston end of the piston rod;

[0019] The hydraulic control system is configured to pump liquid into the first cavity or the second cavity, causing the piston rod to reciprocate along the axis to stretch or compress the sample to be tested. A pressure head is fixed at the end of the piston rod away from the piston.

[0020] The constant pressure pump includes a first constant pressure pump and a second constant pressure pump.

[0021] Preferably, the first hydraulic control system includes a first liquid storage tank, a first gas valve, a second liquid storage tank, and a second gas valve. The output end of the first liquid storage tank is connected to the second cavity of the first hydraulic cylinder and the second hydraulic cylinder through a first hydraulic output pipe. A first hydraulic control valve is provided on the first hydraulic output pipe.

[0022] The output end of the second liquid storage tank is connected to the first cavity of the first hydraulic cylinder and the second hydraulic cylinder through a second hydraulic output pipe, and a second hydraulic control valve is provided on the second hydraulic output pipe;

[0023] The first output end of the first constant pressure pump is connected to the first hydraulic output pipe, and the second output end of the first constant pressure pump is connected to the second hydraulic output pipe;

[0024] The air inlet of the first liquid storage tank is connected to the output of the air compressor through a first air supply pipe, and the first air supply pipe is equipped with a first gas valve. The air inlet of the second liquid storage tank is connected to the output of the air compressor through a second air supply pipe, and the second air supply pipe is equipped with a second gas valve.

[0025] Preferably, a first pressure control transmitter is provided between the first output end of the first constant pressure pump and the first hydraulic output pipe to control the hydraulic pressure applied to the first hydraulic output pipe;

[0026] A second pressure control transmitter is provided between the second output end of the first constant pressure pump and the second hydraulic output pipe to control the hydraulic pressure applied to the second hydraulic output pipe;

[0027] The first constant pressure pump is equipped with a first pressure sensor for detecting the output pressure, and the first pressure sensor is electrically connected to the computer.

[0028] Preferably, a third hydraulic control valve is provided at the connection between the first hydraulic cylinder and the first hydraulic output pipe to control whether the first hydraulic output pipe is connected to the first hydraulic cylinder. When the detection sensor detects that the first hydraulic cylinder has a compression displacement, the third hydraulic control valve opens, so that the pressure in the first hydraulic cylinder is repressurized to the preset pressure.

[0029] A fourth hydraulic control valve is provided at the connection between the second hydraulic cylinder and the first hydraulic output pipe, which is used to control whether the first hydraulic output pipe is connected to the second hydraulic cylinder. When the detection sensor detects that the second hydraulic cylinder has a compression displacement, the fourth hydraulic control valve opens, so that the pressure in the second hydraulic cylinder is repressurized to the preset pressure.

[0030] A ninth hydraulic control valve is provided at the connection between the first hydraulic cylinder and the second hydraulic output pipe to control whether the second hydraulic output pipe is connected to the first hydraulic cylinder. When the detection sensor detects that the first hydraulic cylinder has a tensile displacement, the ninth hydraulic control valve opens, so that the tension applied to the sample by the first hydraulic cylinder is repressurized to the preset tension.

[0031] A tenth hydraulic control valve is provided at the connection between the second hydraulic cylinder and the second hydraulic output pipe to control whether the second hydraulic cylinder is connected to the second hydraulic output pipe. When the detection sensor detects that the second hydraulic cylinder has a tensile displacement, the tenth hydraulic control valve opens, so that the tension applied to the sample to be tested by the second hydraulic cylinder is repressurized to the preset tension.

[0032] Preferably, the second hydraulic control system includes a third liquid storage tank, a third gas valve, a fourth liquid storage tank, and a fourth gas valve. The output end of the third liquid storage tank is connected to the second cavity of the third hydraulic cylinder and the fourth hydraulic cylinder through a third hydraulic output pipe. A fifth hydraulic control valve is provided on the third hydraulic output pipe.

[0033] The output end of the fourth liquid storage tank is connected to the third hydraulic cylinder and the first cavity of the fourth hydraulic cylinder through the fourth hydraulic output pipe, and the fourth hydraulic output pipe is equipped with a sixth hydraulic control valve.

[0034] The first output end of the second constant pressure pump is connected to the third hydraulic output pipe, and the second output end of the second constant pressure pump is connected to the fourth hydraulic output pipe;

[0035] The air inlet of the third liquid storage tank is connected to the output of the air compressor through a third air supply pipe, and the third air supply pipe is equipped with the third gas valve. The air inlet of the fourth liquid storage tank is connected to the output of the air compressor through a fourth air supply pipe, and the fourth air supply pipe is equipped with the fourth gas valve.

[0036] Preferably, a third pressure control transmitter is provided between the first output end of the second constant pressure pump and the third hydraulic output pipe to control the hydraulic pressure applied to the third hydraulic output pipe;

[0037] A fourth pressure control transmitter is provided between the second output end of the second constant pressure pump and the fourth hydraulic output pipe to control the hydraulic pressure applied to the fourth hydraulic output pipe;

[0038] The second constant pressure pump is equipped with a second pressure sensor for detecting the output pressure, and the second pressure sensor is electrically connected to the computer.

[0039] Preferably, an eighth hydraulic control valve is provided at the connection between the third hydraulic cylinder and the third hydraulic output pipe to control whether the third hydraulic output pipe is connected to the third hydraulic cylinder. When the detection sensor detects that the third hydraulic cylinder has a compression displacement, the eighth hydraulic control valve opens to repressurize the pressure in the third hydraulic cylinder to the preset pressure.

[0040] A seventh hydraulic control valve is provided at the connection between the fourth hydraulic cylinder and the third hydraulic output pipe. This valve is used to control whether the third hydraulic output pipe is connected to the fourth hydraulic cylinder. When the detection sensor detects that the fourth hydraulic cylinder has a displacement in the compression direction, the seventh hydraulic control valve opens, so that the pressure in the fourth hydraulic cylinder is repressurized to the preset pressure.

[0041] A twelfth hydraulic control valve is provided at the connection between the third hydraulic cylinder and the fourth hydraulic output pipe to control whether the fourth hydraulic output pipe is connected to the third hydraulic cylinder. When the detection sensor detects that the third hydraulic cylinder has a tensile displacement, the twelfth hydraulic control valve opens, so that the tension applied to the sample to be tested by the third hydraulic cylinder is repressurized to the preset tension.

[0042] An eleventh hydraulic control valve is provided at the connection between the fourth hydraulic cylinder and the fourth hydraulic output pipe. This valve is used to control whether the fourth hydraulic output pipe is connected to the fourth hydraulic cylinder. When the detection sensor detects that the fourth hydraulic cylinder has a tensile displacement, the eleventh hydraulic control valve opens, causing the fourth hydraulic cylinder to repressurize the tension applied to the sample to be tested to the preset tension.

[0043] Preferably, each set of the detection sensors includes a mechanical extensometer and a laser displacement meter, which are mounted on the support frame and located on both sides of the piston rod to detect the displacement distance of the piston rod.

[0044] The test method for the biaxial creep testing device for large-size titanium alloys used in marine engineering, as described above, includes the following steps:

[0045] S1. Sample clamping: The sample to be tested is placed at the center of the support frame. The air compressor provides power to the first hydraulic control system and the second hydraulic control system, so that the first hydraulic cylinder, the second hydraulic cylinder, the third hydraulic cylinder and the fourth hydraulic cylinder stably clamp the sample to be tested from the X and Y directions, and fix the sample to be tested to the piston rod.

[0046] S2. After clamping, the air compressor is turned off. During the pressure creep test, the first and second hydraulic cylinders synchronously adjust the pressure through the first constant pressure pump to ensure that the pressure applied to the sample by the first and second hydraulic cylinders reaches the specified value and is stabilized. The second and third hydraulic cylinders synchronously adjust the pressure through the second constant pressure pump to ensure that the pressure applied to the sample by the second and third hydraulic cylinders reaches the specified value and is stabilized. At this time, the sample is subjected to biaxial pressure in the X and Y directions. The pressure of the sample under biaxial pressure is measured. During the tensile creep test, the first hydraulic cylinder and the second hydraulic cylinder synchronously adjust the tensile force through the first constant pressure pump to make the tensile force applied by the first hydraulic cylinder and the second hydraulic cylinder to the sample under test reach the specified value and stabilize the tensile force. The second hydraulic cylinder and the third hydraulic cylinder synchronously adjust the tensile force through the second constant pressure pump to make the tensile force applied by the second hydraulic cylinder and the third hydraulic cylinder to the sample under test reach the specified value and stabilize the tensile force. At this time, the sample under test is subjected to biaxial tensile force in the X and Y directions, and the creep of the sample under test under biaxial tensile force is measured.

[0047] S3. Creep detection: The piston rods of the first hydraulic cylinder, the second hydraulic cylinder, the third hydraulic cylinder and the fourth hydraulic cylinder are all detected by corresponding detection sensors to detect the movement distance of the piston rods, and the detection information is transmitted to the computer for comparison and calculation to finally obtain the creep data of the sample to be tested;

[0048] S4. Sample removal: Turn off the first and second constant pressure pumps, and provide power to the first and second hydraulic control systems through the air compressor, so that the first, second, third, and fourth hydraulic cylinders release the pressure on the sample to be tested, and then remove the sample to be tested.

[0049] Preferably, in step S2 above, during the pressure creep test, after the pressures of the first and second hydraulic cylinders are stable, the third and fourth hydraulic control valves are closed. When the creep of the sample to be tested on one side of the first hydraulic cylinder causes a decrease in pressure, the mechanical extensometer and laser displacement gauge at the corresponding positions detect the movement of the piston rod at that location, and then control the third hydraulic control valve to open. The first constant pressure pump pressurizes the first hydraulic cylinder to a specified pressure. After the pressure stabilizes, the third hydraulic control valve closes. When the creep of the sample to be tested on one side of the second hydraulic cylinder causes a decrease in pressure, the mechanical extensometer and laser displacement gauge at the corresponding positions detect the movement of the piston rod at that location, and then control the fourth hydraulic control valve to open. The first constant pressure pump pressurizes the second hydraulic cylinder to a specified pressure. After the pressure stabilizes, the fourth hydraulic control valve closes. When the control valves are closed and the tensile creep test is conducted, after the tensile forces of the first and second hydraulic cylinders stabilize, the ninth and tenth hydraulic control valves are closed. When the creep of the sample to be tested on one side of the first hydraulic cylinder causes a decrease in tensile force, the mechanical extensometer and laser displacement gauge at the corresponding positions detect the movement of the piston rod at that location, and then control the ninth hydraulic control valve to open. The first constant pressure pump pressurizes the first hydraulic cylinder to the specified tensile force. After the tensile force stabilizes, the ninth hydraulic control valve closes. When the creep of the sample to be tested on one side of the second hydraulic cylinder causes a decrease in tensile force, the mechanical extensometer and laser displacement gauge at the corresponding positions detect the movement of the piston rod at that location, and then control the tenth hydraulic control valve to open. The first constant pressure pump pressurizes the second hydraulic cylinder to the specified tensile force. After the tensile force stabilizes, the tenth hydraulic control valve closes.

[0050] Preferably, in step S2 above, during the pressure creep test, after the pressures of the third and fourth hydraulic cylinders are stable, the seventh and eighth hydraulic control valves are closed. When the pressure decreases due to creep of the sample to be tested on one side of the third hydraulic cylinder, the mechanical extensometer and laser displacement gauge at the corresponding positions detect the movement of the piston rod at that location, and then control the eighth hydraulic control valve to open. The second constant pressure pump pressurizes the third hydraulic cylinder to the specified pressure. After the pressure stabilizes, the eighth hydraulic control valve closes. When the pressure decreases due to creep of the sample to be tested on one side of the fourth hydraulic cylinder, the mechanical extensometer and laser displacement gauge at the corresponding positions detect the movement of the piston rod at that location, and then control the seventh hydraulic control valve to open. The second constant pressure pump pressurizes the fourth hydraulic cylinder to the specified pressure. After the pressure stabilizes, the seventh hydraulic control valve closes. When the valves are closed and the tensile creep test is conducted, after the tensile forces of the third and fourth hydraulic cylinders stabilize, the twelfth and eleventh hydraulic control valves are closed. When the creep of the sample to be tested on one side of the third hydraulic cylinder causes a decrease in tensile force, the mechanical extensometer and laser displacement gauge at the corresponding positions detect the movement of the piston rod at that location, and then control the twelfth hydraulic control valve to open. The second constant pressure pump pressurizes the third hydraulic cylinder to the specified tensile force. After the tensile force stabilizes, the twelfth hydraulic control valve closes. When the creep of the sample to be tested on one side of the fourth hydraulic cylinder causes a decrease in tensile force, the mechanical extensometer and laser displacement gauge at the corresponding positions detect the movement of the piston rod at that location, and then control the eleventh hydraulic control valve to open. The second constant pressure pump pressurizes the fourth hydraulic cylinder to the specified tensile force. After the tensile force stabilizes, the eleventh hydraulic control valve closes.

[0051] The significant advantages of the biaxial creep testing device for large-size titanium alloys in marine engineering proposed in this invention, especially its application to creep testing of anisotropic titanium alloy components in large deep-sea pressure-resistant structures, are as follows:

[0052] By setting up two sets of pressure-applying components, the first set of pressure-applying components, including the first and second hydraulic cylinders, are symmetrically arranged in the X-axis, while the second set of pressure-applying components, including the third and fourth hydraulic cylinders, are symmetrically arranged in the Y-axis. The first and second hydraulic cylinders apply creep pressure or tension along the X-axis to both sides of the sample under test, while the third and fourth hydraulic cylinders apply creep pressure or tension along the Y-axis to both sides of the sample under test. This allows for simultaneous biaxial pressure or tensile creep testing. Furthermore, the hydraulic system applies tension / compression to the sample under test, ensuring stable tension / compression and enabling prolonged application of tension / compression, resulting in more accurate test results. During the experiment, a mechanical extensometer and a laser displacement meter are used to record the independent strain in four directions. By adding a strain gauge array at the center of the sample under test, the overall coordinated deformation of the sample under test is analyzed, further improving the accuracy of the test. Attached Figure Description

[0053] The accompanying drawings are not intended to be drawn to scale. In the drawings, each identical or nearly identical component shown in the various figures may be denoted by the same reference numeral. For clarity, not every component is labeled in each figure. Embodiments of various aspects of the invention will now be described by way of example and with reference to the accompanying drawings.

[0054] Figure 1 This is a schematic diagram of the biaxial creep testing device for large-size titanium alloys used in marine engineering, as shown in this invention.

[0055] Figure 2 This is a schematic diagram of the hydraulic cylinder structure of the biaxial creep testing device for large-size titanium alloys in marine engineering, as shown in this invention.

[0056] Figure 3 This is a schematic diagram of the first hydraulic control system structure of the biaxial creep testing device for large-size titanium alloys in marine engineering, as shown in this invention.

[0057] Figure 4 This is a schematic diagram of the second hydraulic control system of the biaxial creep testing device for large-size titanium alloys in marine engineering, as shown in this invention.

[0058] Figure 5 This is a schematic diagram of the structure of the sample to be tested according to the present invention.

[0059] The meanings of the reference numerals in the figure are as follows:

[0060] 10. Support frame; 11. Mechanical extensometer; 12. Laser displacement gauge; 20. Pressing component; 21. First hydraulic cylinder; 22. Second hydraulic cylinder; 23. Third hydraulic cylinder; 24. Fourth hydraulic cylinder; 201. Cylinder body; 202. Piston rod; 203. First cavity; 204. Second cavity; 205. Pressure head; 206. Connecting threaded sleeve; 30. First hydraulic control system; 31. First constant pressure pump; 311. First pressure control transmitter; 312. Second pressure control transmitter; 313. First pressure sensor; 32. First liquid storage tank; 321. First hydraulic output pipe; 322. First hydraulic control valve; 323. First gas supply pipe; 33. First gas valve; 34. Second liquid storage tank; 341. Second hydraulic output pipe; 342. Second hydraulic control valve; 343. Second gas supply pipe; 35. 36. Second gas valve; 37. Third hydraulic control valve; 38. Fourth hydraulic control valve; 39. Ninth hydraulic control valve; 30. Tenth hydraulic control valve; 41. Second hydraulic control system; 42. Second constant pressure pump; 43. Third pressure control transmitter; 44. Fourth pressure control transmitter; 45. Second pressure sensor; 46. Third liquid storage tank; 47. Third hydraulic output pipe; 48. Fifth hydraulic control valve; 49. Third gas supply pipe; 40. Fourth liquid storage tank; 41. Fourth hydraulic output pipe; 41. Sixth hydraulic control valve; 42. Fourth gas supply pipe; 43. Fourth gas valve; 44. Seventh hydraulic control valve; 45. Eighth hydraulic control valve; 46. Eleventh hydraulic control valve; 47. Twelfth hydraulic control valve; 50. Air compressor; 61. Computer. Detailed Implementation

[0061] To better understand the technical content of the present invention, specific embodiments are described below in conjunction with the accompanying drawings.

[0062] Existing testing equipment is typically designed for tensile creep tests on thin-diameter bars, which is unsuitable for the large titanium alloy parts used in marine engineering as described in this application. From the perspective of the test object, the titanium alloy used in large deep-sea pressure-resistant structures is anisotropic, with significant strain differences in various characteristic regions, which differs greatly from traditional methods. From the perspective of testing time, the test requires thousands of hours. Under high stress loading conditions, the stress loading system of ordinary threaded screws deforms under continuous pressure loading, leading to instability in the pressure loading. The purpose of this test is multi-directional compressive stress, requiring high consistency and tolerance in the pressure application.

[0063] Based on the above, this application aims to apply hydraulic pressure and first use air pressure to bring the pressure loading structure into contact with the surface of the part to be tested, ensuring the same initial stress and facilitating the alignment of the part. Furthermore, the pressure loading system is equipped with constant pressure feedback and control to ensure the consistency of pressure in each test stage. At the same time, the hydraulic pressurization (pressure rise) and pressure leakage (air leakage) processes are also very slow, which can ensure the stability of pressure loading and reduce pressure deviation under long-term pressure loading environment.

[0064] Biaxial creep testing device for large-size titanium alloys used in marine engineering

[0065] Combination Figures 1-5 As shown, the present invention provides a biaxial creep testing device for large-size titanium alloys in marine engineering. It is mainly used for creep testing of anisotropic titanium alloy components of large deep-sea pressure-resistant structures. The device includes a support frame 10, two sets of pressure-applying components 20, a first hydraulic control system 30, a second hydraulic control system 40, and an air compressor 50.

[0066] Define the width direction of the support frame 10 as the X direction and the length direction of the support frame 10 as the Y direction.

[0067] The first set of pressure-applying components 20 includes a first hydraulic cylinder 21 and a second hydraulic cylinder 22. The second set of pressure-applying components 20 includes a third hydraulic cylinder 23 and a fourth hydraulic cylinder 24, and the test sample is cross-shaped.

[0068] The first hydraulic control system 30 controls the first hydraulic cylinder 21 and the second hydraulic cylinder 22 to operate simultaneously, and the second hydraulic control system 40 controls the third hydraulic cylinder 23 and the fourth hydraulic cylinder 24 to operate simultaneously.

[0069] Hydraulic control system pressurization mode

[0070] Referring to the illustrated examples, both the first hydraulic control system 30 and the second hydraulic control system 40 of the present invention can be configured to operate in pneumatic pressurization mode and hydraulic pressurization mode.

[0071] In the pneumatic pressurization mode, the air compressor 50 pressurizes the first hydraulic control system 30 and the second hydraulic control system 40, causing the first hydraulic cylinder 21, the second hydraulic cylinder 22, the third hydraulic cylinder 23 and the fourth hydraulic cylinder 24 to come into contact with the surface of the sample to be tested.

[0072] In the hydraulic pressurization mode, the constant pressure pump pressurizes the first hydraulic control system 30 and the second hydraulic control system 40, so that the first hydraulic cylinder 21, the second hydraulic cylinder 22, the third hydraulic cylinder 23 and the fourth hydraulic cylinder 24 apply a predetermined pressure to the surface of the sample to be tested. The first hydraulic cylinder 21 and the second hydraulic cylinder 22 are symmetrically fixed on the support frame 10 along the X direction, and the third hydraulic cylinder 23 and the fourth hydraulic cylinder 24 are symmetrically fixed on the support frame 10 along the Y direction. The intersection of the axes of the two sets of pressure-applying components 20 is located at the center of the support frame 10. The sample to be tested can be subjected to precise biaxial pressure in the X and Y directions. The creep of the sample under biaxial pressure is observed. The X and Y directions are pressured by the two sets of hydraulic cylinders. The pressure is stable and can provide a maximum compressive stress of 1300MPa and an experimental duration of up to 1500 hours, which is sufficient to provide a long steady-state creep duration for room temperature creep experiments.

[0073] Monitoring of deformation during creep testing

[0074] Furthermore, the support frame 10 is equipped with four sets of detection sensors, which are located at the output ends of the four pressure-applying components 20 respectively, and are used to detect the movement of the output ends of the pressure-applying components 20 in real time. The detection sensors are electrically connected to the computer 60. Each set of detection sensors includes a mechanical extensometer 11 and a laser displacement meter 12. The mechanical extensometer 11 and the laser displacement meter 12 are mounted on the support frame 10 and located on both sides of the piston rod 202, and are used to detect the displacement distance of the piston rod 202. They can record the independent strain in four directions in a timely manner.

[0075] Furthermore, a strain gauge array is set at the center of the sample to be tested. Optionally, the strain gauges are placed on the surface of the sample in a rectangular or circular array to analyze the overall coordinated deformation of the sample and further improve the accuracy of the test.

[0076] Specifically, by measuring strain data, the stress deviatoric tensor of anisotropic alloys can be accurately calibrated, and the deformation compatibility of metal alloys in different directions under different stress levels can be precisely described.

[0077] Arrangement of hydraulic cylinders

[0078] Combination Figure 2 As shown, the first hydraulic cylinder 21, the second hydraulic cylinder 22, the third hydraulic cylinder 23, and the fourth hydraulic cylinder 24 all include a cylinder body 201 and a piston rod 202. The piston end of the piston rod 202 slides inside the cylinder body 201. The cylinder body 201 has a first cavity 203 and a second cavity 204 inside. The first cavity 203 and the second cavity 204 are located on both sides of the piston end of the piston rod 202, respectively. Liquid is pumped into the first cavity 203 or the second cavity 204, causing the piston rod 202 to reciprocate along the axis to stretch or compress the sample to be tested. The constant pressure pump includes a first constant pressure pump 31 and a second constant pressure pump 41.

[0079] Furthermore, a pressure head 205 is fixed to the end of the piston rod 202 away from the piston end. The piston rod 202 contacts the sample to be tested through the pressure head 205 and applies pressure to it. The pressure head 205 is made of high-strength mold steel. After the pressure head 205 wears out, it can be directly replaced to avoid wear on the piston rod 202.

[0080] In an optional embodiment, a connecting sleeve 206 is threaded onto the pressure head 205. The piston rod 202, the pressure head 205, and the connecting sleeve 206 are on the same axis, so that the pressure is applied perpendicularly to the sample to be tested. During the tensile creep test, the sample to be tested has a thread corresponding to the connecting sleeve 206. After the pressure head 205 contacts and presses against the sample to be tested, the connecting sleeve 206 is screwed out to one side of the sample to be tested, so that one end of the connecting sleeve 206 is threadedly connected to the sample to be tested, thereby fixing the sample to be tested.

[0081] First hydraulic control system

[0082] Combination Figure 3 As shown, the first hydraulic control system 30 includes a first liquid storage tank 32, a first gas valve 33, a second liquid storage tank 34, and a second gas valve 35. The output end of the first liquid storage tank 32 is connected to the second cavity 204 of the first hydraulic cylinder 21 and the second hydraulic cylinder 22 through a first hydraulic output pipe 321. A first hydraulic control valve 322 is provided on the first hydraulic output pipe 321. By opening the first hydraulic control valve 322, the liquid medium stored in the first liquid storage tank 32 is driven by air pressure and transported to the second cavity 204 of the first hydraulic cylinder 21 and the second hydraulic cylinder 22 through the first hydraulic output pipe 321. At this time, under the hydraulic push, the piston rod 202 moves towards the sample to be tested and clamps the sample to be tested along the X direction.

[0083] The output end of the second liquid storage tank 34 is connected to the first cavity 203 of the first hydraulic cylinder 21 and the second hydraulic cylinder 22 through the second hydraulic output pipe 341. The second hydraulic output pipe 341 is equipped with a second hydraulic control valve 342. By opening the second hydraulic control valve 342, the liquid medium stored in the second liquid storage tank 34 is transported to the first cavity 203 of the first hydraulic cylinder 21 and the second hydraulic cylinder 22. At this time, under the action of liquid pressure, the piston rod 202 moves away from the sample to be tested, leaving enough space to install the sample to be tested.

[0084] The first output end of the first constant pressure pump 31 is connected to the first hydraulic output pipe 321. When performing a pressure creep test on the sample to be tested, after the first hydraulic cylinder 21 and the second hydraulic cylinder 22 stably clamp the sample to be tested, the first constant pressure pump 31 simultaneously adjusts the hydraulic pressure inside the second cavity 204 of the first hydraulic cylinder 21 and the second hydraulic cylinder 22, so that the pressure exerted by the piston rod 202 on the sample to be tested reaches the specified pressure. The second output end of the first constant pressure pump 31 is connected to the second hydraulic output pipe 341. When performing a tensile creep test on the sample to be tested, the first constant pressure pump 31 simultaneously adjusts the hydraulic pressure inside the first cavity 203 of the first hydraulic cylinder 21 and the second hydraulic cylinder 22, so that the tensile force of the piston rod 202 on the sample to be tested reaches the specified tensile force.

[0085] Pneumatic pressurization mode

[0086] Furthermore, the air inlet of the first liquid storage tank 32 is connected to the output of the air compressor 50 through the first air supply pipe 323, and the first air supply pipe 323 is equipped with a first gas valve 33. The air inlet of the second liquid storage tank 34 is connected to the output of the air compressor 50 through the second air supply pipe 343, and the second air supply pipe 343 is equipped with a second gas valve 35. When clamping or removing the sample to be tested, the air compressor 50 applies air pressure to the first liquid storage tank 32 or the second liquid storage tank 34, causing the liquid medium stored in the first liquid storage tank 32 and the second liquid storage tank 34 to be output outward, thereby quickly controlling the piston rod 202 to clamp the sample to be tested or move away from the sample to be tested.

[0087] Hydraulic pressurization mode

[0088] Furthermore, a first pressure control transmitter 311 is provided between the first output end of the first constant pressure pump 31 and the first hydraulic output pipe 321 to control the hydraulic pressure applied to the first hydraulic output pipe 321. A second pressure control transmitter 312 is provided between the second output end of the first constant pressure pump 31 and the second hydraulic output pipe 341 to control the hydraulic pressure applied to the second hydraulic output pipe 341. The first constant pressure pump 31 is provided with a first pressure sensor 313 for detecting the output pressure. The first pressure sensor 313 is electrically connected to the computer 60. The first constant pressure pump 31 controls the pressure transmission in the first hydraulic output pipe 321 in real time through the first pressure control transmitter 311. The first constant pressure pump 31 controls the pressure transmission in the second hydraulic output pipe 341 in real time through the second pressure control transmitter 312. The first pressure sensor 313 detects the pressure output of the first constant pressure pump 31 in real time and transmits the signal to the computer 60 in real time.

[0089] Pressure mode during creep

[0090] Combination Figure 3As shown, a third hydraulic control valve 36 is provided at the connection between the first hydraulic cylinder 21 and the first hydraulic output pipe 321, and a fourth hydraulic control valve 37 is provided at the connection between the second hydraulic cylinder 22 and the first hydraulic output pipe 321. During the pressure creep test, when the first hydraulic cylinder 21 and the second hydraulic cylinder 22 are in a pressure-stabilized state and pressure is applied to the sample to be tested, the third hydraulic control valve 36 and the fourth hydraulic control valve 37 are in a closed state. When the sample to be tested creeps on one side of the first hydraulic cylinder 21, causing the pressure to decrease, the mechanical extensometer 11 and the laser displacement gauge 12 at the corresponding positions detect this. The piston rod 202 moves, and then the third hydraulic control valve 36 is opened. The first constant pressure pump 31 pressurizes the first hydraulic cylinder 21 to the specified pressure. After the pressure stabilizes, the third hydraulic control valve 36 closes. When the pressure decreases due to the creep of the sample to be tested on one side of the second hydraulic cylinder 22, the mechanical extensometer 11 and the laser displacement meter 12 at the corresponding positions detect the movement of the piston rod 202 at that position. Then the fourth hydraulic control valve 37 is opened, and the first constant pressure pump 31 pressurizes the second hydraulic cylinder 22 to the specified pressure. After the pressure stabilizes, the fourth hydraulic control valve 37 closes.

[0091] In this way, the first hydraulic cylinder 21 and the second hydraulic cylinder 22 will not pressurize synchronously to push the sample under test towards the creeping side, so the position of the sample under test remains accurate and the test accuracy is improved.

[0092] Furthermore, a ninth hydraulic control valve 38 is provided at the connection between the first hydraulic cylinder 21 and the second hydraulic output pipe 341, and a tenth hydraulic control valve 39 is provided at the connection between the second hydraulic cylinder 22 and the second hydraulic output pipe 341. During tensile creep testing, when the tensile force of the first hydraulic cylinder 21 and the second hydraulic cylinder 22 is in a stable state, the ninth hydraulic control valve 38 and the tenth hydraulic control valve 39 are in a closed state. When the creep of the sample to be tested on the side of the first hydraulic cylinder 21 causes the tensile force to decrease, the mechanical extensometer 11 and the laser displacement meter 12 at the corresponding positions detect this. The piston rod 202 moves, and then the ninth hydraulic control valve 38 is opened. The first constant pressure pump 31 pressurizes the first hydraulic cylinder 21 to the specified tension. After the tension stabilizes, the ninth hydraulic control valve 38 closes. When the sample to be tested on one side of the second hydraulic cylinder 22 creeps and the tension decreases, the mechanical extensometer 11 and laser displacement meter 12 at the corresponding positions detect the movement of the piston rod 202 at that point. Then the tenth hydraulic control valve 39 is opened, and the first constant pressure pump 31 pressurizes the second hydraulic cylinder 22 to the specified tension. After the tension stabilizes, the tenth hydraulic control valve 39 closes.

[0093] In this way, the first hydraulic cylinder 21 and the second hydraulic cylinder 22 will not pressurize synchronously to push the sample under test towards the creeping side, so the position of the sample under test remains accurate and the test accuracy is improved.

[0094] Second hydraulic control system

[0095] Combination Figure 4 As shown, the second hydraulic control system 40 includes a third liquid storage tank 42, a third gas valve 43, a fourth liquid storage tank 44, and a fourth gas valve 45. The output end of the third liquid storage tank 42 is connected to the second cavity 204 of the third hydraulic cylinder 23 and the fourth hydraulic cylinder 24 through a third hydraulic output pipe 421. A fifth hydraulic control valve 422 is provided on the third hydraulic output pipe 421. By opening the fifth hydraulic control valve 422, the liquid medium stored in the third liquid storage tank 42 is transported to the second cavity 204 of the third hydraulic cylinder 23 and the fourth hydraulic cylinder 24 through the third hydraulic output pipe 421. At this time, under the push of hydraulic pressure, the piston rod 202 moves towards the sample to be tested and clamps the sample to be tested along the Y direction.

[0096] The output end of the fourth liquid storage tank 44 is connected to the first cavity 203 of the third hydraulic cylinder 23 and the fourth hydraulic cylinder 24 through the fourth hydraulic output pipe 441. The fourth hydraulic output pipe 441 is equipped with a sixth hydraulic control valve 442. By opening the sixth hydraulic control valve 442, the liquid medium stored in the fourth liquid storage tank 44 is transported to the first cavity 203 of the third hydraulic cylinder 23 and the fourth hydraulic cylinder 24. At this time, under the action of liquid pressure, the piston rod 202 moves away from the sample to be tested.

[0097] The first output end of the second constant pressure pump 41 is connected to the third hydraulic output pipe 421. When performing a pressure creep test on the sample to be tested, after the third hydraulic cylinder 23 and the fourth hydraulic cylinder 24 stably clamp the sample to be tested, the second constant pressure pump 41 simultaneously adjusts the hydraulic pressure inside the second cavity 204 of the third hydraulic cylinder 23 and the fourth hydraulic cylinder 24, so that the pressure exerted by the piston rod 202 on the sample to be tested reaches the specified pressure. The second output end of the second constant pressure pump 41 is connected to the fourth hydraulic output pipe 441. When performing a tensile creep test on the sample to be tested, the second constant pressure pump 41 simultaneously adjusts the hydraulic pressure inside the first cavity 203 of the third hydraulic cylinder 23 and the fourth hydraulic cylinder 24, so that the piston rod 202 moves away from the sample to be tested, so that the tensile force of the piston rod 202 on the sample to be tested reaches the specified tensile force.

[0098] Pneumatic pressurization mode

[0099] Furthermore, the air inlet of the third liquid storage tank 42 is connected to the output of the air compressor 50 through the third air supply pipe 423, and the third air supply pipe 423 is equipped with a third gas valve 43. The air inlet of the fourth liquid storage tank 44 is connected to the output of the air compressor 50 through the fourth air supply pipe 443, and the fourth air supply pipe 443 is equipped with a fourth gas valve 45. When clamping or removing the sample to be tested, the air compressor 50 applies air pressure to the third liquid storage tank 42 or the fourth liquid storage tank 44, causing the liquid medium stored in the third liquid storage tank 42 and the fourth liquid storage tank 44 to be output outward, thereby controlling the piston rod 202 to quickly clamp or move away from the sample to be tested.

[0100] Hydraulic pressurization mode

[0101] Furthermore, a third pressure control transmitter 411 is provided between the first output end of the second constant pressure pump 41 and the third hydraulic output pipe 421 to control the hydraulic pressure applied to the third hydraulic output pipe 421. A fourth pressure control transmitter 412 is provided between the second output end of the second constant pressure pump 41 and the fourth hydraulic output pipe 441 to control the hydraulic pressure applied to the fourth hydraulic output pipe 441. A second pressure sensor 413 for detecting the output pressure is provided on the second constant pressure pump 41. The second pressure sensor 413 is electrically connected to the computer 60. The second constant pressure pump 41 controls the pressure transmission in the third hydraulic output pipe 421 in real time through the third pressure control transmitter 411. The second constant pressure pump 41 controls the pressure transmission in the fourth hydraulic output pipe 441 in real time through the fourth pressure control transmitter 412. The second pressure sensor 413 detects the pressure output of the second constant pressure pump 41 in real time and transmits the signal to the computer 60 in real time.

[0102] Pressure mode during creep

[0103] Combination Figure 4 As shown, an eighth hydraulic control valve 47 is provided at the connection between the third hydraulic cylinder 23 and the third hydraulic output pipe 421, and a seventh hydraulic control valve 46 is provided at the connection between the fourth hydraulic cylinder 24 and the third hydraulic output pipe 421. During the pressure creep test, when the third hydraulic cylinder 23 and the fourth hydraulic cylinder 24 are in a pressure-stabilizing state and pressure is applied to the sample to be tested, the seventh hydraulic control valve 46 and the eighth hydraulic control valve 47 are in a closed state. When the sample to be tested on the third hydraulic cylinder 23 undergoes creep, causing the pressure to decrease, the mechanical extensometer 11 and the laser displacement gauge 12 at the corresponding positions detect this. The piston rod 202 moves, and then the eighth hydraulic control valve 47 is opened. The second constant pressure pump 41 pressurizes the third hydraulic cylinder 23 to the specified pressure. After the pressure stabilizes, the eighth hydraulic control valve 47 closes. When the pressure decreases due to the creep of the sample to be tested on one side of the fourth hydraulic cylinder 24, the mechanical extensometer 11 and the laser displacement meter 12 at the corresponding positions detect the movement of the piston rod 202 at that position. Then the seventh hydraulic control valve 46 is opened, and the second constant pressure pump 41 pressurizes the fourth hydraulic cylinder 24 to the specified pressure. After the pressure stabilizes, the seventh hydraulic control valve 46 closes.

[0104] In this way, the third hydraulic cylinder 23 and the fourth hydraulic cylinder 24 will not pressurize synchronously to push the sample to the creep side, so the position of the sample remains accurate and the test accuracy is improved.

[0105] Furthermore, a twelfth hydraulic control valve 49 is provided at the connection between the third hydraulic cylinder 23 and the fourth hydraulic output pipe 441, and an eleventh hydraulic control valve 48 is provided at the connection between the fourth hydraulic cylinder 24 and the fourth hydraulic output pipe 441. During tensile creep testing, when the tensile force of the third hydraulic cylinder 23 and the fourth hydraulic cylinder 24 is in a stable state, the eleventh hydraulic control valve 48 and the twelfth hydraulic control valve 49 are in a closed state. When the creep of the sample to be tested on the side of the third hydraulic cylinder 23 causes the tensile force to decrease, the mechanical extensometer 11 and the laser displacement gauge 12 at the corresponding positions detect this. The piston rod 202 moves, and then the twelfth hydraulic control valve 49 is opened. The second constant pressure pump 41 pressurizes the third hydraulic cylinder 23 to the specified tension. After the tension stabilizes, the twelfth hydraulic control valve 49 closes. When the sample to be tested on one side of the fourth hydraulic cylinder 24 creeps and causes the tension to decrease, the mechanical extensometer 11 and laser displacement meter 12 at the corresponding positions detect the movement of the piston rod 202 at that position. Then the eleventh hydraulic control valve 48 is opened, and the second constant pressure pump 41 pressurizes the fourth hydraulic cylinder 24 to the specified tension. After the tension stabilizes, the eleventh hydraulic control valve 48 closes.

[0106] In this way, the third hydraulic cylinder 23 and the fourth hydraulic cylinder 24 will not pressurize synchronously to push the sample to the creep side, so the position of the sample remains accurate and the test accuracy is improved.

[0107] [Biaxial Creep Testing Method]

[0108] In the embodiments of the present invention, we will describe in more detail the creep testing process of the biaxial creep testing device for anisotropic titanium alloy components of large deep-sea pressure-resistant structures, in conjunction with the biaxial creep testing device of the above embodiments.

[0109] S1. Sample clamping: Place the sample to be tested at the center of the support frame 10, then turn on the air compressor 50, the first gas valve 33, and the first hydraulic control valve 322. The air compressor 50 injects gas into the first liquid storage tank 32 through the first gas supply pipe 323. Under the action of air pressure, the liquid medium stored inside the first liquid storage tank 32 is simultaneously transported to the second cavity 204 of the first hydraulic cylinder 21 and the second hydraulic cylinder 22 through the first hydraulic output pipe 321, so that the piston rods 202 of the first hydraulic cylinder 21 and the second hydraulic cylinder 22 move synchronously towards the sample to be tested until the sample is stably clamped in the X direction. Then, the third gas valve 43 and the fifth hydraulic control valve 422 are opened. The air compressor 50 injects gas into the third liquid storage tank 42 through the third air supply pipe 423. Under the action of air pressure, the liquid medium stored in the third liquid storage tank 42 is simultaneously transported to the second cavity 204 of the third hydraulic cylinder 23 and the fourth hydraulic cylinder 24 through the third hydraulic output pipe 421, so that the piston rods 202 of the third hydraulic cylinder 23 and the fourth hydraulic cylinder 24 move synchronously towards the side of the sample to be tested until the sample to be tested is stably clamped along the Y direction. At this time, the sample to be tested is stably clamped in both the X and Y directions. Then, the sample to be tested is fixed to the piston rod 202.

[0110] In this method, a strain gauge array is placed at the center of the sample to be tested. In an optional embodiment, the strain gauges are placed on the surface of the sample in a rectangular or circular array to analyze the overall coordinated deformation of the sample, thereby further improving the accuracy of the test.

[0111] Specifically, by measuring strain data, the stress deviatoric tensor of anisotropic alloys can be accurately calibrated, and the deformation compatibility of metal alloys in different directions under different stress levels can be precisely described.

[0112] S2. Creep Test: After the sample to be tested is stably clamped, during the pressure creep test, close the first gas valve 33 and the third gas valve 43, then close the first hydraulic control valve 322 and the fifth hydraulic control valve 422 to eliminate the influence of the air compressor 50 on the first hydraulic output pipe 321 and the third hydraulic output pipe 421. Turn on the first constant pressure pump 31 to adjust the pressure applied to the sample in the X direction by the first hydraulic cylinder 21 and the second hydraulic cylinder 22. After reaching the specified pressure and stabilizing, put the first hydraulic cylinder 21 and the second hydraulic cylinder 22 into a pressure-stabilized state. Turn on the second constant pressure pump 41 to adjust the pressure applied to the sample in the Y direction by the third hydraulic cylinder 23 and the fourth hydraulic cylinder 24. After reaching the specified pressure and stabilizing, put the third hydraulic cylinder 23 and the fourth hydraulic cylinder 24 into a pressure-stabilized state. At this time, the sample to be tested is subjected to pressure in the X and Y directions. Biaxial pressure is used to measure the creep of the sample under biaxial pressure. During the tensile creep test, the second gas valve 35, the second hydraulic control valve 342, the fourth gas valve 45, and the sixth hydraulic control valve 442 are closed to eliminate the influence of the air compressor 50 on the second hydraulic output pipe 341 and the fourth hydraulic output pipe 441. The first hydraulic cylinder 21 and the second hydraulic cylinder 22 are synchronously adjusted by the first constant pressure pump 31 to make the tensile force applied to the sample by the first hydraulic cylinder 21 and the second hydraulic cylinder 22 reach the specified value and stabilize the tensile force. The second hydraulic cylinder 22 and the third hydraulic cylinder 23 are synchronously adjusted by the second constant pressure pump 41 to make the tensile force applied to the sample by the second hydraulic cylinder 22 and the third hydraulic cylinder 23 reach the specified value and stabilize the tensile force. At this time, the sample under test is subjected to biaxial tensile force in the X and Y directions, and the creep of the sample under test is measured.

[0113] S3. Creep detection: The piston rods 202 of the first hydraulic cylinder 21, the second hydraulic cylinder 22, the third hydraulic cylinder 23 and the fourth hydraulic cylinder 24 are all detected simultaneously by the corresponding mechanical extensometer 11 and laser displacement meter 12. The mechanical extensometer 11 and the laser displacement meter 12 simultaneously detect the movement distance of the piston rods 202 and transmit the detection information to the computer 60 for comparison and calculation, and finally obtain the creep data of the sample to be tested.

[0114] S4. Sample Disassembly: After the pressure creep test is completed, open the first hydraulic control valve 322 and the fifth hydraulic control valve 422, then open the second gas valve 35, the second hydraulic control valve 342, the fourth gas valve 45, and the sixth hydraulic control valve 442; finally, turn on the air compressor 50. The air compressor 50 injects gas into the second liquid storage tank 34 through the second air supply pipe 343. Under the action of air pressure, the liquid medium stored in the second liquid storage tank 34 is transported to the first cavity 203 of the first hydraulic cylinder 21 and the second hydraulic cylinder 22 through the second hydraulic output pipe 341, causing the piston rod 202 of the first hydraulic cylinder 21 and the second hydraulic cylinder 22 to slide away from the sample to be tested. The liquid medium flows back to the first storage tank 32 via the first hydraulic output pipe 321. The air compressor 50 injects gas into the fourth storage tank 44 via the fourth air supply pipe 443. Under the action of air pressure, the liquid medium stored in the second storage tank 34 is transported to the first cavity 203 of the third hydraulic cylinder 23 and the fourth hydraulic cylinder 24 via the fourth hydraulic output pipe 441, causing the piston rod 202 of the third hydraulic cylinder 23 and the fourth hydraulic cylinder 24 to slide away from the sample to be tested. The liquid medium in the second cavity 204 flows back to the third storage tank 42 via the third hydraulic output pipe 421. At this time, the sample to be tested can be removed. After the tensile creep test is completed, the sample to be tested and the piston rod 202 can be directly disassembled.

[0115] Combination Figure 3 As shown, in step S1 above, the third hydraulic control valve 36 and the fourth hydraulic control valve 37 are in the open state. Step S2 above includes pressure creep test and tensile creep test:

[0116] Pressure creep test: After the pressure of the first hydraulic cylinder 21 and the second hydraulic cylinder 22 is stable, the third hydraulic control valve 36 and the fourth hydraulic control valve 37 are closed.

[0117] When the pressure decreases due to the creep of the sample to be tested on one side of the first hydraulic cylinder 21, the mechanical extensometer 11 and the laser displacement meter 12 at the corresponding positions detect the movement of the piston rod 202 at that location. The computer 60 controls the third hydraulic control valve 36 to open, and the first constant pressure pump 31 pressurizes the first hydraulic cylinder 21 to the specified pressure. After the pressure stabilizes, the third hydraulic control valve 36 closes.

[0118] When the pressure decreases due to the creep of the sample to be tested on one side of the second hydraulic cylinder 22, the mechanical extensometer 11 and the laser displacement meter 12 at the corresponding positions detect the movement of the piston rod 202 at that point. The computer 60 controls the fourth hydraulic control valve 37 to open, and the first constant pressure pump 31 pressurizes the second hydraulic cylinder 22 to the specified pressure. After the pressure stabilizes, the fourth hydraulic control valve 37 closes.

[0119] Tensile creep test: When the tension of the first hydraulic cylinder 21 and the second hydraulic cylinder 22 is stable, the ninth hydraulic control valve 38 and the tenth hydraulic control valve 39 are closed. When the creep of the test sample on one side of the first hydraulic cylinder 21 causes the tension to decrease, the mechanical extensometer 11 and the laser displacement meter 12 at the corresponding positions detect the movement of the piston rod 202 at that point. The computer 60 controls the ninth hydraulic control valve 38 to open, and the first constant pressure pump 31 pressurizes the first hydraulic cylinder 21 to the specified tension. After the tension stabilizes, the ninth hydraulic control valve 38 closes.

[0120] When the sample under test on one side of the second hydraulic cylinder 22 creeps and the tension decreases, the mechanical extensometer 11 and the laser displacement meter 12 at the corresponding positions detect the movement of the piston rod 202 at that point, and then control the tenth hydraulic control valve 39 to open. The first constant pressure pump 31 pressurizes the second hydraulic cylinder 22 to the specified tension. After the tension stabilizes, the tenth hydraulic control valve 39 closes.

[0121] Combination Figure 4 As shown, in step S1 above, the seventh hydraulic control valve 46 and the eighth hydraulic control valve 47 are in the open state. In step S2 above, pressure creep test and tensile creep test are included.

[0122] Pressure creep test: When the pressure of the third hydraulic cylinder 23 and the fourth hydraulic cylinder 24 is stable, the seventh hydraulic control valve 46 and the eighth hydraulic control valve 47 are closed.

[0123] When the pressure decreases due to the creep of the sample to be tested on one side of the third hydraulic cylinder 23, the mechanical extensometer 11 and the laser displacement meter 12 at the corresponding positions detect the movement of the piston rod 202 at that location. The computer 60 controls the eighth hydraulic control valve 47 to open, and the second constant pressure pump 41 pressurizes the third hydraulic cylinder 23 to the specified pressure. After the pressure stabilizes, the eighth hydraulic control valve 47 closes.

[0124] When the pressure decreases due to the creep of the sample to be tested on one side of the fourth hydraulic cylinder 24, the mechanical extensometer 11 and the laser displacement meter 12 at the corresponding positions detect the movement of the piston rod 202 at that location. The computer 60 controls the seventh hydraulic control valve 46 to open, and the second constant pressure pump 41 pressurizes the fourth hydraulic cylinder 24 to the specified pressure. After the pressure stabilizes, the seventh hydraulic control valve 46 closes.

[0125] Tensile creep test: When the tension of the third hydraulic cylinder 23 and the fourth hydraulic cylinder 24 is stable, the twelfth hydraulic control valve 49 and the eleventh hydraulic control valve 48 are closed. When the creep of the test sample on the side of the third hydraulic cylinder 23 causes the tension to decrease, the mechanical extensometer 11 and the laser displacement meter 12 at the corresponding positions detect the movement of the piston rod 202 at that point. The computer 60 controls the twelfth hydraulic control valve 49 to open, and the second constant pressure pump 41 pressurizes the third hydraulic cylinder 23 to the specified tension. After the tension stabilizes, the twelfth hydraulic control valve 49 closes.

[0126] When the sample under test on one side of the fourth hydraulic cylinder 24 creeps and the tension decreases, the mechanical extensometer 11 and the laser displacement meter 12 at the corresponding positions detect the movement of the piston rod 202 at that point. The computer 60 controls the eleventh hydraulic control valve 48 to open, and the second constant pressure pump 41 pressurizes the fourth hydraulic cylinder 24 to the specified tension. After the tension stabilizes, the eleventh hydraulic control valve 48 closes.

[0127] In conjunction with the above embodiments, by setting up two sets of pressure-applying components 20, wherein the first set of pressure-applying components 20 includes a first hydraulic cylinder 21 and a second hydraulic cylinder 22 arranged symmetrically in the X direction, and the second set of pressure-applying components 20 includes a third hydraulic cylinder 23 and a fourth hydraulic cylinder 24 arranged symmetrically in the Y direction, the first hydraulic cylinder 21 and the second hydraulic cylinder 22 apply creep pressure or tension to both sides of the sample to be tested along the X direction, and the third hydraulic cylinder 23 and the fourth hydraulic cylinder 24 apply creep pressure or tension to both sides of the sample to be tested along the Y direction, which can simultaneously perform biaxial tensile / compression creep tests, and the use of a hydraulic system to apply tensile / compression to the sample to be tested results in a stable tensile / compression and can apply tensile / compression for a long time, resulting in more accurate test results.

[0128] Meanwhile, the experiment used a mechanical extensometer 11 and a laser displacement meter 12 to record the independent strain in four directions. By adding a strain gauge array at the center of the sample, the overall coordinated deformation of the sample was analyzed, which improved the accuracy of the creep test and comprehensively characterized the various creep states of the anisotropic titanium alloy components of the large deep-sea pressure-resistant structure.

[0129] While the present invention has been disclosed above with reference to preferred embodiments, it is not intended to limit the invention. Those skilled in the art can make various modifications and refinements without departing from the spirit and scope of the invention. Therefore, the scope of protection of the present invention shall be determined by the claims.

Claims

1. A biaxial creep testing device for large-size titanium alloys used in marine engineering, characterized in that, include: Support frame (10), the width direction of the support frame (10) is defined as the X direction, and the length direction of the support frame (10) is defined as the Y direction; Two sets of pressure-applying components (20), the first set of pressure-applying components includes a first hydraulic cylinder (21) and a second hydraulic cylinder (22), and the second set of pressure-applying components includes a third hydraulic cylinder (23) and a fourth hydraulic cylinder (24); A first hydraulic control system (30) controls the first hydraulic cylinder (21) and the second hydraulic cylinder (22) to operate simultaneously; The second hydraulic control system (40) controls the third hydraulic cylinder (23) and the fourth hydraulic cylinder (24) to operate simultaneously; An air compressor (50) is connected to the first hydraulic control system (30) and the second hydraulic control system (40); A constant pressure pump is connected to the first hydraulic control system (30) and the second hydraulic control system (40); A strain gauge array is attached to the surface of the sample to be tested and used to detect the regional strain characteristics of the sample. The first hydraulic control system (30) and the second hydraulic control system (40) both include a pneumatic pressurization mode and a hydraulic pressurization mode. In the pneumatic pressurization mode, the air compressor (50) pressurizes the first hydraulic control system (30) and the second hydraulic control system (40) so that the first hydraulic cylinder (21), the second hydraulic cylinder (22), the third hydraulic cylinder (23) and the fourth hydraulic cylinder (24) come into contact with the surface of the sample to be tested. In the hydraulic pressurization mode, the constant pressure pump pressurizes the first hydraulic control system (30) and the second hydraulic control system (40) so that the first hydraulic cylinder (21), the second hydraulic cylinder (22), the third hydraulic cylinder (23) and the fourth hydraulic cylinder (24) apply a predetermined pressure to the surface of the sample to be tested. The first hydraulic cylinder (21) and the second hydraulic cylinder (22) are symmetrically fixed on the support frame (10) along the X direction, and the third hydraulic cylinder (23) and the fourth hydraulic cylinder (24) are symmetrically fixed on the support frame (10) along the Y direction. The first hydraulic cylinder (21) and the second hydraulic cylinder (22) are used to apply creep pressure in the X-axis direction to the sample to be tested, and the third hydraulic cylinder (23) and the fourth hydraulic cylinder (24) are used to apply creep pressure in the Y-axis direction to the sample to be tested. The intersection of the axis of the first hydraulic cylinder (21) and the axis of the third hydraulic cylinder (23) is located at the center of the support frame (10); the support frame (10) is provided with four sets of detection sensors to detect the movement of the piston rods (202) of the first hydraulic cylinder (21), the second hydraulic cylinder (22), the third hydraulic cylinder (23) and the fourth hydraulic cylinder (24), respectively; the detection sensors are electrically connected to the computer (60); The first hydraulic cylinder (21), the second hydraulic cylinder (22), the third hydraulic cylinder (23) and the fourth hydraulic cylinder (24) each include a cylinder body (201) and a piston rod (202). The piston end of the piston rod (202) slides inside the cylinder body (201). The cylinder body (201) is provided with a first cavity (203) and a second cavity (204). The first cavity (203) and the second cavity (204) are located on both sides of the piston end of the piston rod (202). The first hydraulic control system (30) includes a first liquid storage tank (32), a first gas valve (33), a second liquid storage tank (34), and a second gas valve (35). The output end of the first liquid storage tank (32) is connected to the second cavity (204) of the first hydraulic cylinder (21) and the second hydraulic cylinder (22) through a first hydraulic output pipe (321). A first hydraulic control valve (322) is provided on the first hydraulic output pipe (321). The second hydraulic control system (40) includes a third reservoir (42), a third gas valve (43), a fourth reservoir (44), and a fourth gas valve (45). The output end of the third reservoir (42) is connected to the second cavity (204) of the third hydraulic cylinder (23) and the fourth hydraulic cylinder (24) through a third hydraulic output pipe (421). A fifth hydraulic control valve (422) is provided on the third hydraulic output pipe (421). Each set of detection sensors includes a mechanical extensometer (11) and a laser displacement meter (12).

2. The biaxial creep testing device for large-size titanium alloys in marine engineering according to claim 1, characterized in that, The hydraulic control system is configured to pump liquid into the first cavity (203) or the second cavity (204) to cause the piston rod (202) to reciprocate along the axis to stretch or compress the sample to be tested. A pressure head (205) is fixed at the end of the piston rod (202) away from the piston. The constant pressure pump includes a first constant pressure pump (31) and a second constant pressure pump (41).

3. The biaxial creep testing device for large-size titanium alloys in marine engineering according to claim 2, characterized in that, The output end of the second liquid storage tank (34) is connected to the first cavity (203) of the first hydraulic cylinder (21) and the second hydraulic cylinder (22) through the second hydraulic output pipe (341), and the second hydraulic control valve (342) is provided on the second hydraulic output pipe (341); The first output end of the first constant pressure pump (31) is connected to the first hydraulic output pipe (321), and the second output end of the first constant pressure pump (31) is connected to the second hydraulic output pipe (341). The air inlet of the first liquid storage tank (32) is connected to the output of the air compressor (50) through the first air supply pipe (323), and the first gas valve (33) is provided on the first air supply pipe (323). The air inlet of the second liquid storage tank (34) is connected to the output of the air compressor (50) through the second air supply pipe (343), and the second gas valve (35) is provided on the second air supply pipe (343).

4. The biaxial creep testing device for large-size titanium alloys in marine engineering according to claim 3, characterized in that, A first pressure control transmitter (311) is provided between the first output end of the first constant pressure pump (31) and the first hydraulic output pipe (321) to control the hydraulic pressure applied to the first hydraulic output pipe (321); A second pressure control transmitter (312) is provided between the second output end of the first constant pressure pump (31) and the second hydraulic output pipe (341) to control the hydraulic pressure applied to the second hydraulic output pipe (341); The first constant pressure pump (31) is equipped with a first pressure sensor (313) for detecting the output pressure, and the first pressure sensor (313) is electrically connected to the computer (60).

5. The biaxial creep testing device for large-size titanium alloys in marine engineering according to claim 3, characterized in that, A third hydraulic control valve (36) is provided at the connection between the first hydraulic cylinder (21) and the first hydraulic output pipe (321) to control whether the first hydraulic output pipe (321) is connected to the first hydraulic cylinder (21). When the detection sensor detects that the first hydraulic cylinder (21) has a compression direction displacement, the third hydraulic control valve (36) opens, so that the pressure in the first hydraulic cylinder (21) is repressurized to the preset pressure. A fourth hydraulic control valve (37) is provided at the connection between the second hydraulic cylinder (22) and the first hydraulic output pipe (321) to control whether the first hydraulic output pipe (321) is connected to the second hydraulic cylinder (22). When the detection sensor detects that the second hydraulic cylinder (22) has a compression direction displacement, the fourth hydraulic control valve (37) opens, so that the pressure in the second hydraulic cylinder (22) is repressurized to the preset pressure. A ninth hydraulic control valve (38) is provided at the connection between the first hydraulic cylinder (21) and the second hydraulic output pipe (341) to control whether the second hydraulic output pipe (341) is connected to the first hydraulic cylinder (21). When the detection sensor detects that the first hydraulic cylinder (21) has a tensile displacement, the ninth hydraulic control valve (38) opens, so that the first hydraulic cylinder (21) repressurizes the tension applied to the sample to be tested to the preset tension. A tenth hydraulic control valve (39) is provided at the connection between the second hydraulic cylinder (22) and the second hydraulic output pipe (341) to control whether the second hydraulic cylinder (22) is connected to the second hydraulic output pipe (341). When the detection sensor detects that the second hydraulic cylinder (22) has a tensile displacement, the tenth hydraulic control valve (39) opens, so that the second hydraulic cylinder (22) repressurizes the tension applied to the sample to be tested to the preset tension.

6. The biaxial creep testing device for large-size titanium alloys in marine engineering according to claim 2, characterized in that, The output end of the fourth liquid storage tank (44) is connected to the first cavity (203) of the third hydraulic cylinder (23) and the fourth hydraulic cylinder (24) through the fourth hydraulic output pipe (441). The fourth hydraulic output pipe (441) is provided with a sixth hydraulic control valve (442). The first output end of the second constant pressure pump (41) is connected to the third hydraulic output pipe (421), and the second output end of the second constant pressure pump (41) is connected to the fourth hydraulic output pipe (441). The air inlet of the third liquid storage tank (42) is connected to the output of the air compressor (50) through the third air supply pipe (423), and the third air supply pipe (423) is equipped with the third gas valve (43). The air inlet of the fourth liquid storage tank (44) is connected to the output of the air compressor (50) through the fourth air supply pipe (443), and the fourth air supply pipe (443) is equipped with the fourth gas valve (45).

7. The biaxial creep testing device for large-size titanium alloys in marine engineering according to claim 6, characterized in that, A third pressure control transmitter (411) is provided between the first output end of the second constant pressure pump (41) and the third hydraulic output pipe (421) for controlling the hydraulic pressure applied to the third hydraulic output pipe (421); A fourth pressure control transmitter (412) is provided between the second output end of the second constant pressure pump (41) and the fourth hydraulic output pipe (441) for controlling the hydraulic pressure applied to the fourth hydraulic output pipe (441); The second constant pressure pump (41) is equipped with a second pressure sensor (413) for detecting the output pressure, and the second pressure sensor (413) is electrically connected to the computer (60).

8. The biaxial creep testing device for large-size titanium alloys in marine engineering according to claim 6, characterized in that, An eighth hydraulic control valve (47) is provided at the connection between the third hydraulic cylinder (23) and the third hydraulic output pipe (421) to control whether the third hydraulic output pipe (421) is connected to the third hydraulic cylinder (23). When the detection sensor detects that the third hydraulic cylinder (23) has a displacement in the compression direction, the eighth hydraulic control valve (47) opens, so that the pressure in the third hydraulic cylinder (23) is repressurized to the preset pressure. A seventh hydraulic control valve (46) is provided at the connection between the fourth hydraulic cylinder (24) and the third hydraulic output pipe (421) to control whether the third hydraulic output pipe (421) is connected to the fourth hydraulic cylinder (24). When the detection sensor detects that the fourth hydraulic cylinder (24) has a displacement in the compression direction, the seventh hydraulic control valve (46) opens, so that the pressure in the fourth hydraulic cylinder (24) is repressurized to the preset pressure. A twelfth hydraulic control valve (49) is provided at the connection between the third hydraulic cylinder (23) and the fourth hydraulic output pipe (441) to control whether the fourth hydraulic output pipe (441) is connected to the third hydraulic cylinder (23). When the detection sensor detects that the third hydraulic cylinder (23) has a tensile displacement, the twelfth hydraulic control valve (49) opens, so that the third hydraulic cylinder (23) repressurizes the tension applied to the sample to be tested to the preset tension. An eleventh hydraulic control valve (48) is provided at the connection between the fourth hydraulic cylinder (24) and the fourth hydraulic output pipe (441) to control whether the fourth hydraulic output pipe (441) is connected to the fourth hydraulic cylinder (24). When the detection sensor detects that the fourth hydraulic cylinder (24) has a tensile displacement, the eleventh hydraulic control valve (48) opens, so that the fourth hydraulic cylinder (24) repressurizes the tension applied to the sample to be tested to the preset tension.

9. The biaxial creep testing device for large-size titanium alloys in marine engineering according to claim 2, characterized in that, The mechanical extensometer (11) and the laser displacement meter (12) are mounted on the support frame (10) and located on both sides of the piston rod (202) to detect the displacement distance of the piston rod (202).

10. A biaxial creep testing method for large-size titanium alloys used in marine engineering, characterized in that, The biaxial creep testing apparatus for large-size titanium alloys in marine engineering according to any one of claims 1-9 includes the following steps: S1. Sample clamping: The sample to be tested is placed at the center of the support frame (10). Power is supplied to the first hydraulic control system (30) and the second hydraulic control system (40) by the air compressor (50). The first hydraulic control system (30) and the second hydraulic control system (40) are in pneumatic pressurization mode, so that the first hydraulic cylinder (21), the second hydraulic cylinder (22), the third hydraulic cylinder (23) and the fourth hydraulic cylinder (24) stably clamp the sample to be tested from the X and Y directions, and fix the sample to be tested to the piston rod (202). S2, Creep Test: After clamping is completed, the air compressor (50) is turned off, and the first hydraulic control system (30) and the second hydraulic control system (40) are in hydraulic pressurization mode; During the pressure creep test, the first hydraulic cylinder (21) and the second hydraulic cylinder (22) adjust the pressure synchronously through the first constant pressure pump (31) so that the pressure applied to the sample by the first hydraulic cylinder (21) and the second hydraulic cylinder (22) reaches the specified value and the pressure is stabilized. The second hydraulic cylinder (22) and the third hydraulic cylinder (23) adjust the pressure synchronously through the second constant pressure pump (41) so that the pressure applied to the sample by the second hydraulic cylinder (22) and the third hydraulic cylinder (23) reaches the specified value and the pressure is stabilized. At this time, the sample is subjected to biaxial pressure in the X and Y directions, and the creep of the sample under the action of biaxial pressure is measured. During the tensile creep test, the first hydraulic cylinder (21) and the second hydraulic cylinder (22) synchronously adjust the tensile force through the first constant pressure pump (31) so that the tensile force applied by the first hydraulic cylinder (21) and the second hydraulic cylinder (22) to the sample under test reaches the specified value and the tensile force is stabilized. The second hydraulic cylinder (22) and the third hydraulic cylinder (23) synchronously adjust the tensile force through the second constant pressure pump (41) so that the tensile force applied by the second hydraulic cylinder (22) and the third hydraulic cylinder (23) to the sample under test reaches the specified value and the tensile force is stabilized. At this time, the sample under test is subjected to biaxial tensile force in the X and Y directions, and the creep of the sample under test under biaxial tensile force is measured. S3. Creep detection: The piston rods (202) of the first hydraulic cylinder (21), the second hydraulic cylinder (22), the third hydraulic cylinder (23) and the fourth hydraulic cylinder (24) all detect the movement distance of the piston rods (202) through corresponding detection sensors, and transmit the detection information to the computer (60) for comparison and calculation, and finally obtain the creep data of the sample to be tested. S4. Sample removal: Turn off the first constant pressure pump (31) and the second constant pressure pump (41), and provide power to the first hydraulic control system (30) and the second hydraulic control system (40) through the air compressor (50) so that the first hydraulic cylinder (21), the second hydraulic cylinder (22), the third hydraulic cylinder (23) and the fourth hydraulic cylinder (24) release the pressure on the sample to be tested, and then remove the sample to be tested.

11. The testing method for large-size titanium alloys used in marine engineering according to claim 10, characterized in that: Step S2 above includes pressure creep test and tensile creep test: Pressure creep test: After the pressure of the first hydraulic cylinder (21) and the second hydraulic cylinder (22) reaches a stable state, The third hydraulic control valve (36) and the fourth hydraulic control valve (37) are in the closed state; When the pressure decreases due to creep of the sample to be tested on one side of the first hydraulic cylinder (21), the mechanical extensometer (11) and the laser displacement meter (12) at the corresponding positions detect the movement of the piston rod (202) at that location. The computer (60) controls the third hydraulic control valve (36) to open, and the first constant pressure pump (31) pressurizes the first hydraulic cylinder (21) to the specified pressure. After the pressure stabilizes, the third hydraulic control valve (36) closes. When the pressure decreases due to creep of the sample to be tested on one side of the second hydraulic cylinder (22), the mechanical extensometer (11) and the laser displacement meter (12) at the corresponding positions detect the movement of the piston rod (202) at that location. The computer (60) controls the fourth hydraulic control valve (37) to open, and the first constant pressure pump (31) pressurizes the second hydraulic cylinder (22) to the specified pressure. After the pressure stabilizes, the fourth hydraulic control valve (37) closes. Tensile creep test: When the tension of the first hydraulic cylinder (21) and the second hydraulic cylinder (22) is in a stable state, The ninth hydraulic control valve (38) and the tenth hydraulic control valve (39) are in the closed state when the first hydraulic cylinder (21) is in the closed state. When the creep of the sample to be tested on one side causes the tensile force to decrease, the mechanical extensometer (11) and the laser displacement meter (12) at the corresponding positions detect the movement of the piston rod (202) at that location. The computer (60) controls the ninth hydraulic control valve (38) to open, and the first constant pressure pump (31) pressurizes the first hydraulic cylinder (21) to the specified tensile force. After the tensile force stabilizes, the ninth hydraulic control valve (38) closes. When the sample under test creeps on one side of the second hydraulic cylinder (22), causing the tension to decrease, the mechanical extensometer (11) and the laser displacement meter (12) at the corresponding positions detect the movement of the piston rod (202) at that location, and then control the tenth hydraulic control valve (39) to open. The first constant pressure pump (31) pressurizes the second hydraulic cylinder (22) to the specified tension. After the tension stabilizes, the tenth hydraulic control valve (39) closes.

12. The testing method for large-size titanium alloys used in marine engineering according to claim 10, characterized in that: Step S2 above includes pressure creep test and tensile creep test; Pressure creep test: After the pressure of the third hydraulic cylinder (23) and the fourth hydraulic cylinder (24) reaches a stable state, The seventh hydraulic control valve (46) and the eighth hydraulic control valve (47) are in the closed state; When the pressure decreases due to creep of the sample to be tested on one side of the third hydraulic cylinder (23), the mechanical extensometer (11) and the laser displacement meter (12) at the corresponding positions detect the movement of the piston rod (202) at that location. The computer (60) controls the eighth hydraulic control valve (47) to open, and the second constant pressure pump (41) pressurizes the third hydraulic cylinder (23) to the specified pressure. After the pressure stabilizes, the eighth hydraulic control valve (47) closes. When the pressure decreases due to creep of the sample to be tested on one side of the fourth hydraulic cylinder (24), the mechanical extensometer (11) and the laser displacement meter (12) at the corresponding positions detect the movement of the piston rod (202) at that location. The computer (60) controls the seventh hydraulic control valve (46) to open, and the second constant pressure pump (41) pressurizes the fourth hydraulic cylinder (24) to the specified pressure. After the pressure stabilizes, the seventh hydraulic control valve (46) closes. Tensile creep test: When the tension of the third hydraulic cylinder (23) and the fourth hydraulic cylinder (24) is in a stable state, the twelfth hydraulic control valve (49) and the eleventh hydraulic control valve (48) are in the closed state. When the third hydraulic cylinder (23) When the creep of the sample to be tested on one side causes the tensile force to decrease, the mechanical extensometer (11) and the laser displacement meter (12) at the corresponding positions detect the movement of the piston rod (202) at that location. The computer (60) controls the twelfth hydraulic control valve (49) to open, and the second constant pressure pump (41) pressurizes the third hydraulic cylinder (23) to the specified tensile force. After the tensile force stabilizes, the twelfth hydraulic control valve (49) closes. When the sample under test creeps on one side of the fourth hydraulic cylinder (24), causing the tension to decrease, the mechanical extensometer (11) and the laser displacement meter (12) at the corresponding positions detect the movement of the piston rod (202) at that location. The computer (60) controls the eleventh hydraulic control valve (48) to open, and the second constant pressure pump (41) pressurizes the fourth hydraulic cylinder (24) to the specified tension. After the tension stabilizes, the eleventh hydraulic control valve (48) closes.

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