Tensile fixture system for biaxial creep test and method for implementing biaxial creep
By designing a combined structure of outer clamp, inner clamp, and sliding ring, and combining it with high-temperature alloy materials, the problems of clamping force attenuation and sealing failure under high temperature and high pressure conditions were solved. This enabled accurate multiaxial creep performance evaluation of high temperature and high pressure thin-walled materials, improving the utilization rate and economy of the equipment.
Patent Information
- Application Number
- CN202511914721.8
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2025-12-18
- Publication Date
- 2026-03-13
AI Technical Summary
Existing clamping systems struggle to apply internal pressure and axial load stably and accurately under high temperature and high pressure conditions, resulting in problems such as clamping force attenuation, sealing failure, sample eccentricity, and inaccurate deformation measurement, which affect the evaluation of multiaxial creep performance of high temperature and high pressure thin-walled materials.
A biaxial creep test tensile clamp system was designed, which adopts a combination structure of outer clamp, inner clamp and sliding ring, combined with high temperature alloy material to achieve clamping reliability, centering and high temperature stability. The load transfer symmetry is ensured by threaded connection and automatic adjustment of sliding ring, and gas flow channel is equipped for internal pressure loading.
It achieves stable clamping force and reliable sealing under high temperature and high pressure environment, reduces measurement error, provides accurate biaxial creep performance evaluation, is suitable for samples of different shapes and sizes, and improves equipment utilization and economy.
Smart Images
Figure CN121655989A_ABST
Abstract
Description
Technical Field
[0001] This invention relates to the field of high-temperature material mechanical property testing technology, and in particular to a biaxial creep test tensile fixture system and a method for implementing biaxial creep. Background Technology
[0002] In industrial fields such as petrochemicals, nuclear power, and supercritical power generation, tubular components operating under high temperature and high pressure environments often simultaneously bear internal medium pressure and external mechanically or thermally induced axial tensile loads. The failure modes of these thin-walled components during long-term service often stem from multiaxial creep damage caused by the interaction of internal pressure and tensile stress. Therefore, accurately assessing the high-temperature creep performance of thin-walled materials under biaxial stress is crucial for ensuring safe equipment operation and predicting equipment lifespan. However, the key challenge in conducting such tests lies in developing a specialized clamping system capable of stably and accurately applying internal pressure and axial loads simultaneously, while maintaining clamping and sealing reliability over long periods in high-temperature environments.
[0003] Currently, widely used uniaxial creep testing machines cannot simulate actual multiaxial stress states. Furthermore, the clamping systems of the few existing biaxial testing devices still have significant limitations when used for internal compression-tensile tests on thin-walled shell specimens: First, thin-walled specimens have low stiffness and are extremely sensitive to neutrality. The structural design fails to adequately consider the differences in material thermal expansion behavior caused by high temperatures, leading to incoordination between clamping components, resulting in clamping force attenuation, sealing failure, or specimen eccentricity. Second, the lack of efficient and reliable thermal compensation and self-alignment mechanisms makes it difficult to maintain coaxiality under axial tension and internal compression loading at high temperatures, and the introduction of additional bending stress is severe. The reliability of test data is significantly reduced; thirdly, high-pressure sealing structures are often incompatible with high-temperature environments, and commonly used sealing materials are prone to aging, creep, or strength degradation at high temperatures, leading to media leakage or difficulty in maintaining pressure during the test; fourthly, existing fixtures are usually not integrated with deformation measurement systems, making it difficult to obtain the local deformation response of the specimen under biaxial load in real time and directly, which limits in-depth research on creep mechanisms; fifthly, there is insufficient research on the selection of fixture materials suitable for high-temperature environments and their long-term performance evolution, and the oxidation, creep, and fatigue behavior of materials at high temperatures directly affect the service life of the fixture and the safety of the test.
[0004] To address the aforementioned technical bottlenecks, this invention provides a fixture system specifically designed for high-temperature internal pressure-tensile biaxial creep endurance testing of thin-walled shell specimens. This system focuses on innovations in thermo-mechanical coupling design, high-temperature sealing, automatic self-alignment, integrated deformation measurement, and material selection. It aims to solve key problems related to specimen clamping, alignment, sealing, and long-term stable operation under high-temperature and high-pressure environments, providing a reliable fixture technology foundation for accurately evaluating the creep performance of materials under multiaxial stress states. Summary of the Invention
[0005] The present invention aims to solve the technical problems that easily occur during the testing of thin-walled shell samples under high temperature and high pressure environments, such as clamping force attenuation, sealing failure, or sample eccentricity.
[0006] To achieve the above objectives, according to one aspect of the invention, a biaxial creep testing tensile clamp system is provided, characterized in that it comprises two sets of clamp assemblies arranged opposite to each other and symmetrically for connection to a biaxial creep testing machine; each clamp assembly comprises: an outer clamp, one end of which is provided with an external thread for connection to a testing machine pull rod, and the outer clamp has a clamping hole for clamping the outer wall of a tubular specimen; an inner clamp, which is partially disposed inside the outer clamp, and the inner clamp has a cylindrical clamping surface that abuts against and clamps the inner wall of the tubular specimen; the inner clamp has a gas flow channel extending into the interior of the tubular specimen; and a sliding ring, which is sleeved on the outside of the inner clamp and can slide freely along its axial direction, for automatically adjusting during loading to ensure the alignment of the tubular specimen.
[0007] As a preferred embodiment of the above technical solution, the inner clamp is arranged axially as a cylindrical section, a clamp connecting section, an air inlet section, and a pull rod connecting section; the cylindrical section has a cylindrical clamping surface, the clamp connecting section is connected to the outer clamp, the air inlet of the gas flow channel is opened on the air inlet section, and the pull rod connecting section has an external thread for engaging with the high-temperature pull rod thread.
[0008] As a preferred embodiment of the above technical solution, the outer clamp is further provided with a mating hole, the clamping hole communicates with the mating hole, and the mating hole is provided with an internal thread; the inner clamp is provided with an external thread that matches the internal thread of the mating hole, and the external thread is provided on the clamp connecting section.
[0009] As a preferred embodiment of the above technical solution, the gas flow channel includes a radial air inlet section for connecting the pressurizing device and an axial extension section communicating with the interior of the tubular sample; the radial air inlet section is arranged perpendicularly to the axial extension section, and the axial extension section is arranged coaxially with the central axis of the inner clamp.
[0010] As a preferred embodiment of the above technical solution, a transitional guide cone hole is provided between the mating hole and the clamping hole, and a guide cone surface adapted to the guide cone hole is provided on the outer end face of the sliding ring.
[0011] As a preferred embodiment of the above technical solution, the sliding ring is provided with a gap notch.
[0012] As a preferred embodiment of the above technical solution, the outer wall of the outer clamp has two symmetrical clamping planes in the middle.
[0013] As a preferred embodiment of the above technical solution, the clamp assembly is made of a high-temperature resistant alloy material.
[0014] A method for implementing biaxial creep testing, using the biaxial creep test tensile fixture system described in any of the above-mentioned technical solutions, the method comprising the following steps:
[0015] S1: Insert both ends of the tubular sample into the inner clamps of the two clamp assemblies located at the upper and lower positions respectively;
[0016] S2: Tightly fit the outer clamp with the inner clamp to complete the sample clamping;
[0017] S3: Pressurizing medium is introduced into the tubular sample through the gas channel to apply the required internal pressure;
[0018] S4: Install the high-temperature environment device and heat up to the set test temperature;
[0019] S5: After the temperature stabilizes, apply axial tensile force and internal pressure to the tubular specimen simultaneously using a testing machine to conduct a biaxial creep or endurance test.
[0020] In summary, the present invention has the following advantages:
[0021] 1. By employing a combination structure of an outer clamp, an inner clamp, and a sliding ring, the clamping system of claim 1 achieves a balance between clamping reliability, centering, and high-temperature stability. The threaded connection provides a stable clamping force, and the free sliding characteristic of the sliding ring can automatically compensate for deviations caused by machining errors or thermal expansion, ensuring that the load is transmitted along the sample axis and significantly reducing measurement errors caused by eccentric loading.
[0022] 2. Furthermore, the clamp material of the present invention is a high-temperature alloy, which has good high-temperature strength and creep resistance, and can work stably for a long time in a high-temperature environment;
[0023] 3. Furthermore, the present invention features a compact structure that perfectly matches the biaxial creep testing machine. The overall height of the fixture is reasonable, allowing the entire testing process to be completed within the machine's stroke range without interference.
[0024] 4. Furthermore, the present invention has a wide range of applications. It can be used not only for standard tubular specimens, but also for specimens of different shapes and sizes by changing the clamping components. The modular design of the clamp allows users to configure it flexibly according to specific test requirements, which greatly improves the utilization rate and economy of the equipment.
[0025] Further or other beneficial effects will be discussed in the embodiments. Attached Figure Description
[0026] Figure 1 This is a schematic diagram of the fixture system structure of the present invention;
[0027] Figure 2 This is a full sectional view of the outer clamp of the present invention;
[0028] Figure 3 This is a top view of the inner clamp of the present invention;
[0029] Figure 4 This is a schematic diagram of the full cross-section of the inner clamp of the present invention;
[0030] Figure 5 This is a left view of the sliding ring of the present invention;
[0031] Figure 6 This is a front view of the sliding ring of the present invention;
[0032] Among them, 1-outer clamp, 11-clamping hole, 12-fitting hole, 13-guide cone hole, 14-clampable plane, 2-inner clamp, 21-cylindrical section, 22-clamp connecting section, 23-air inlet section, 24-pull rod connecting section, 25-gas flow channel, 251-radial air inlet section, 252-axial extension section, 3-sliding ring, 31-guide cone surface, 32-gap notch, 4-tubular sample. Detailed Implementation
[0033] The directional terms such as up, down, left, right, front, back, front, back, top, and bottom mentioned or possibly used in this specification are defined relative to the construction shown in the accompanying drawings. The terms "inner" and "outer" refer to directions toward or away from the geometric center of a specific component, respectively. These are relative concepts and may therefore vary depending on their location and usage. Therefore, these or other directional terms should not be interpreted as restrictive.
[0034] The present invention will be further explained below with reference to the embodiments:
[0035] Example 1:
[0036] A biaxial creep testing tensile fixture system, specifically applicable to biaxial creep testing of thin-walled shell specimens, is particularly suitable for simulating multiaxial stress states under the combined action of internal pressure and axial tension. (Refer to...) Figure 1 It includes two sets of clamp assemblies with identical structures and symmetrical arrangement. The two sets of clamp assemblies are used to clamp the two ends of the tubular specimen 4 and are connected to the upper and lower pull rods of the biaxial creep testing machine. Each clamp assembly includes an outer clamp 1, an inner clamp 2, and a sliding ring 3.
[0037] The outer collet 1 is typically made of a high-temperature resistant alloy material. In this embodiment, K465 nickel-based high-temperature alloy is preferred to ensure good fatigue resistance, oxidation resistance, and corrosion resistance under high-temperature environments. (Refer to...) Figure 2 and Figure 3 One end of the outer chuck 1 is machined with an external thread for reliable connection with the pull rod of the testing machine. The outer chuck 1 also has a clamping hole 11 for holding the outer wall of the tubular sample 4. To facilitate connection with the inner chuck 2, the outer chuck 1 also has a mating hole 12 communicating with the clamping hole 11, and the mating hole 12 is machined with an internal thread. Between the clamping hole 11 and the mating hole 12, there is a transitional guide cone hole 13. Furthermore, for ease of installation and operation, the middle outer wall of the outer chuck 1 typically has two symmetrical clamping surfaces 14 for clamping or loosening operations using tools such as wrenches.
[0038] Reference Figure 4 The inner clamp 2 is located inside the outer clamp 1 and can be divided into four functional sections along the axial direction: a cylindrical section 21, a clamp connecting section 22, an air inlet section 23, and a tie rod connecting section 24. The outer surface of the cylindrical section 21 is a precision-machined cylindrical surface, serving as a cylindrical clamping surface that directly contacts and clamps the inner wall of the tubular sample 4. The outer wall of the clamp connecting section 22 is machined with external threads for engaging with the internal threads in the mating hole 12 of the outer clamp 1, thereby fixing the inner clamp 2 inside the outer clamp 1. The side wall of the air inlet section 23 has an air inlet for a gas flow channel 25. The tie rod connecting section 24 is machined with external threads for connecting with the high-temperature tie rod or connecting sleeve of the testing machine to transmit axial loads. The inner clamp 2 has a through gas flow channel 25 machined inside, which includes a radial air inlet section 251 and an axial extension section 252. The radial air inlet section 251 is used to connect the pipeline of the external pressurization device, while the axial extension section 252 communicates with the internal cavity of the tubular specimen 4, thereby allowing pressurized media such as gas or liquid to be introduced into the specimen to simulate internal pressure load. The axial extension section 252 is preferably coaxially arranged with the central axis of the inner clamp 2 to ensure the symmetry of pressure application.
[0039] Reference Figure 5 and Figure 6 The sliding ring 3 is fitted around the cylindrical section 21 of the inner clamp 2 and can slide freely along its axial direction. The outer end face of the sliding ring 3 is machined with a guide cone surface 31, which matches the guide cone hole 13 inside the outer clamp 1. During loading, the sliding ring 3 can automatically fine-tune its position. The cooperation between its guide cone surface 31 and the guide cone hole 13 helps correct any minor eccentricities that may exist in the tubular specimen 4, ensuring that the axial tensile load is uniformly transmitted along the specimen axis and reducing additional bending stress. This self-centering design is crucial for obtaining reliable biaxial creep data. To prevent jamming due to thermal expansion or deformation, the sliding ring 3 typically has a gap notch 32, giving it a certain elastic deformation capacity.
[0040] The main steps for using this biaxial creep testing tensile fixture system are as follows:
[0041] S1: Insert both ends of the tubular sample 4 into the cylindrical sections of the inner clamps 2 of the upper and lower clamp assemblies respectively.
[0042] S2: Screw the outer collet 1 into the collet connecting section 22 of the inner collet 2 so that the two are tightly fitted by threads.
[0043] During this process, the guide cone surface 31 of the sliding ring 3 interacts with the guide cone hole 13 of the outer clamp 1, automatically adjusting the position of the tubular sample 4 to achieve initial alignment.
[0044] S3: Connect the pressurization system through the air inlet of the gas flow channel 25 of the inner clamp 2, and introduce a pressurization medium such as inert gas into the tubular sample 4 to apply the circumferential stress internal pressure required for the test.
[0045] S4: Install a high-temperature environment device, such as a resistance furnace, and heat the entire fixture-sample system to the predetermined test temperature.
[0046] S5: After the temperature stabilizes, apply axial tension to the upper and lower tie rods using a biaxial creep testing machine, while maintaining or adjusting the internal pressure of the tubular specimen 4, and then begin the biaxial creep or endurance test.
[0047] Example 2:
[0048] This embodiment uses a nickel-based superalloy tubular specimen as an example to demonstrate the biaxial creep performance test of the fixture system under high temperature and high stress conditions. The specimen specifications are an outer diameter of 8 mm, an inner diameter of 6 mm, and a gauge length of 50 mm. The test setting temperature is 850℃, the target axial stress is 300 MPa, and the internal pressure is 15 MPa.
[0049] The specific operating steps are as follows: First, insert both ends of the sample into the inner clamps 2 of the upper and lower clamp assemblies, respectively. Then, use a torque wrench to tighten the connecting threads between the outer clamp 1 and the inner clamp 2 with a torque of 50 Nm to ensure that the sample is firmly clamped and an effective seal is formed at the interface. Next, install the gas-filled high-temperature furnace, set the furnace temperature to 850℃, and start heating. Throughout the heating process and subsequent tests, continuously introduce high-purity argon gas into the furnace as a protective atmosphere. After the furnace temperature stabilizes at 850℃, apply an axial tensile force to the sample to a stress level of 300 MPa through the testing machine control system, and simultaneously apply a pressure of 15 MPa to the inside of the sample through an external pressurization system. The biaxial creep test then begins.
[0050] During the 500-hour test, the axial deformation of the specimen was measured non-contactly using a video extensometer, while a light curtain micrometer monitored the change in specimen diameter in real time. The test continued until the specimen fractured, and the system automatically recorded the fracture time and total deformation. Post-test inspection showed that the fixture system maintained stable load transfer and excellent sealing performance at 850℃, and the axial deformation and diameter change data were recorded completely and accurately, meeting the requirements for biaxial creep testing under high-parameter conditions.
[0051] Example 3:
[0052] This embodiment uses a stainless steel tubular specimen to further illustrate the applicability and durability of the fixture system in long-term endurance testing. The specimen specifications are: outer diameter 10 mm, inner diameter 8 mm, gauge length 60 mm. The test conditions are set as follows: temperature 600℃, axial stress 200 MPa, and internal pressure 10 MPa.
[0053] The sample clamping procedure was the same as in Example 1. After 2000 hours of continuous testing, the sample did not break, and the test was automatically paused. A careful inspection of the fixture system revealed that the threaded connection between the outer clamp 1 and the inner clamp 2 remained firm, with no signs of loosening; no obvious oxidation or structural deformation was observed in key areas, and the gas flow channel had good sealing performance. This demonstrates that the fixture system, made of high-temperature resistant alloy material and with optimized structural design, can withstand long-term high-temperature and high-pressure environments and possesses the reliability for long-term, long-term testing.
[0054] Although preferred embodiments of the invention have been described, those skilled in the art, upon learning the basic inventive concept, can make other changes and modifications to these embodiments. Therefore, the appended claims are intended to be interpreted as including both the preferred embodiments and all changes and modifications falling within the scope of the invention.
[0055] Obviously, those skilled in the art can make various modifications and variations to this invention without departing from its spirit and scope. Therefore, if these modifications and variations fall within the scope of the claims of this invention and their equivalents, this invention also intends to include these modifications and variations.
Claims
1. A biaxial creep testing tensile clamp system, characterized in that, It includes two sets of opposing and symmetrically arranged clamp assemblies for connection to a biaxial creep testing machine; each clamp assembly includes: The outer clamp (1) has an external thread at one end for connecting with the test machine pull rod, and the outer clamp (1) has a clamping hole (11) for clamping the outer wall of the tubular sample (4). An inner clamp (2) is partially disposed inside the outer clamp (1). The inner clamp (2) is provided with a cylindrical clamping surface that abuts against and clamps the inner wall of the tubular sample (4). A gas flow channel (25) is provided inside the inner clamp (2) that extends into the tubular sample (4). A sliding ring (3), which is sleeved on the outside of the inner clamp (2) and can slide freely along its axial direction, is used to automatically adjust during loading to ensure the alignment of the tubular sample (4).
2. The biaxial creep testing tensile fixture system according to claim 1, characterized in that, The inner clamp (2) is arranged in sequence along the axial direction as a cylindrical section (21), a clamp connecting section (22), an air inlet section (23), and a pull rod connecting section (24); the cylindrical section (21) is provided with a cylindrical clamping surface; the clamp connecting section (22) is connected to the outer clamp (1); the air inlet of the gas flow channel (25) is opened on the air inlet section (23); and the pull rod connecting section (24) is provided with an external thread for engaging with the high-temperature pull rod thread.
3. A biaxial creep testing tensile fixture system according to claim 2, characterized in that, The outer clamp (1) is also provided with a mating hole (12), the clamping hole (11) is connected to the mating hole (12), and the mating hole (12) is provided with an internal thread; the inner clamp (2) is provided with an external thread that matches the internal thread of the mating hole (12), and the external thread is provided on the clamp connecting section (22).
4. The biaxial creep testing tensile fixture system according to claim 1, characterized in that, The gas flow channel (25) includes a radial air inlet section (251) for connecting the pressurizing device and an axial extension section (252) communicating with the interior of the tubular sample (4); the radial air inlet section (251) is arranged perpendicularly to the axial extension section (252), and the axial extension section (252) is arranged coaxially with the central axis of the inner clamp (2).
5. A biaxial creep testing tensile fixture system according to claim 3, characterized in that, A transitional guide cone hole (13) is provided between the mating hole (12) and the clamping hole (11), and a guide cone surface (31) adapted to the guide cone hole (13) is provided on the outer end face of the sliding ring (3).
6. A biaxial creep testing tensile fixture system according to claim 1, characterized in that, The sliding ring (3) has a gap notch (32).
7. A biaxial creep testing tensile fixture system according to claim 1, characterized in that, The outer wall of the outer clamp (1) has two symmetrical clamping planes (14).
8. A biaxial creep testing tensile fixture system according to claim 1, characterized in that, The clamp assembly is made of high-temperature resistant alloy material.
9. A method for implementing biaxial creep, characterized in that, Using the biaxial creep testing tensile fixture system as described in any one of claims 1 to 8, the method comprises the following steps: S1: Insert both ends of the tubular sample (4) into the inner clamps (2) of the two clamp assemblies located at the upper and lower positions respectively; S2: Tightly fit the outer clamp (1) and the inner clamp (2) to complete the sample clamping; S3: Pressurized medium is introduced into the tubular sample (4) through the gas channel (25) to apply the required internal pressure; S4: Install the high-temperature environment device and heat up to the set test temperature; S5: After the temperature stabilizes, apply axial tension and internal pressure to the tubular specimen (4) simultaneously using a testing machine to conduct a biaxial creep or endurance test.