A clamping device and testing system for metal pipe fatigue test

Abstract

This utility model provides a clamping device for fatigue testing of metal pipes, comprising: an inner clamp detachably disposed on the inner wall of the first end of the pipe body, for providing support and fixation from inside the pipe body, the inner clamp including a bushing and a mandrel; and an outer clamp detachably disposed on the outer wall of the first end of the pipe body, for applying pressure from outside the pipe body to fix the pipe body, the outer clamp including a support cover, a locking ring, and multiple locking blocks. Through the synergistic effect of the inner clamp supporting and fixing the pipe body inside the pipe body and the outer clamp locking it outside the pipe body, a stable clamping of the pipe body is achieved. The overall structure is simple and can realize fatigue testing of pipes of different specifications. This utility model also relates to a testing system for fatigue testing of metal pipes.

Description

Technical Field

[0001] This utility model relates to the field of pipe fatigue testing technology, specifically to a clamping device and testing system for metal pipe fatigue testing. Background Technology

[0002] In the field of materials mechanical property testing, fatigue performance testing of metal pipes is crucial for evaluating their comprehensive mechanical properties, especially in complex operating conditions such as those simulating nuclear reactor heat transfer tubes. Nuclear reactor heat transfer tubes operate in harsh environments, facing not only high temperatures of 300-400°C and strong corrosion, but also multiaxial cyclic stresses generated by coolant flow-induced vibrations, thermal cycling, and mechanical vibrations. Among these, rotational bending fatigue loads can easily induce microcracks on the tube surface or at defects. Over time, these cracks propagate, leading to fatigue failure and severely impacting the life prediction and safety assessment of the heat transfer tube. Furthermore, axial tensile and compressive fatigue is another common form of fatigue faced by tubes in actual operating conditions. Under the influence of thermal expansion and contraction, mechanical tension, or compression, the tubes are subjected to cyclic axial tensile and compressive stresses, which can also lead to fatigue damage.

[0003] Currently, existing clamping devices for fixing pipes in fatigue tests have many problems. For example, mechanical connection involves machining threads on the clamping section of the pipe before screwing it onto the testing machine. While this method is relatively simple to operate, machining threads can cause stress concentration on the pipe wall and even geometric distortion, making the test results unable to accurately reflect the true performance of the pipe. Hydraulic clamping methods involve first inserting a custom-made plug into the inner cavity of the pipe end to enhance radial stiffness, then placing a high-friction coefficient gasket on the outer surface of the pipe, and finally clamping it using a hydraulically driven fixture. However, this method is prone to deformation and damage to the pipe surface, and the clamping effect varies greatly from test to test, resulting in poor repeatability and hindering the acquisition of stable and reliable test data.

[0004] Existing clamping devices, such as those in patent publication CN104390856A, employ a combined approach of mandrel-mandrel inner clamping and outer clamp-locking nut outer clamping. While this improves clamping force and reduces stress concentration, the device's complex structure leads to high assembly and maintenance costs. Furthermore, its compatibility with pipe dimensions is limited, and the adjustable size range is not clearly defined, making it difficult to meet diverse pipe testing needs in practical applications. Another example is patent publication CN116858654A, which utilizes an internally expanding clamping design combined with a tapered sliding mandrel and a tensioning slider to achieve uniform force application within the steel pipe's inner bore, offering advantages in reducing assembly stress and improving test repeatability. However, the applicability of this device is strictly limited by the inner diameter of the steel pipe, resulting in insufficient adaptability to steel pipes with different inner diameters. Moreover, the lack of effective clamping force protection measures around the pipe poses a risk of pipe deformation during testing, affecting the accuracy and reliability of the test results. For example, the clamping devices with patent publication numbers CN101526451A and CN203101173U optimize stress distribution through elastic or adjustable clamping structures, which can improve clamping stability and test repeatability in high-temperature or high-speed scenarios. However, these two patented technologies rely on the precision of material processing. If the material processing precision is not up to standard, deformation of the clamping components can easily occur, leading to insufficient coaxiality and affecting the accuracy of the test. In addition, they also have shortcomings in reliability verification, failing to fully guarantee the reliability of test results under various complex working conditions. Therefore, how to develop a device that can adapt to various fatigue conditions and has stable and reliable clamping performance is an urgent problem to be solved. Utility Model Content

[0005] To address the problems existing in the prior art, the first objective of this utility model is to provide a clamping device for fatigue testing of metal pipes. Through the coordinated action of the inner clamp supporting and fixing inside the pipe and the outer clamp locking outside the pipe, a stable clamping of the pipe is achieved. The overall structure is simple and can realize fatigue testing of pipes of different specifications.

[0006] The second objective of this invention is to provide a testing system for fatigue testing of metal pipes, including the aforementioned clamping device, which can be used to test the rotational bending fatigue and axial tensile and compressive fatigue of metal pipes.

[0007] To achieve the above objectives, the present invention adopts the following technical solution:

[0008] A clamping device for fatigue testing of metal pipes includes: an inner clamp detachably disposed on the inner wall of a first end of a pipe body for providing support and fixation from inside the pipe body; the inner clamp includes a bushing and a mandrel; the bushing extends from the first end of the pipe body to its inner wall, and a first through hole is formed in the axial direction inside the bushing, through which the mandrel is engaged with the bushing; and an outer clamp detachably disposed on the outer wall of the first end of the pipe body for applying pressure from outside the pipe body to clamp the pipe body; the outer clamp includes a support cover, a locking ring, and a plurality of clamping blocks; the support cover is engaged with the outer wall of the first end of the pipe body and detachably connected to one end of the mandrel; the locking ring is engaged with the outer wall of the support cover; one end of each of the plurality of clamping blocks is detachably disposed between the locking ring and the support cover, and the other end abuts against the outer wall of the pipe body to form a clamping force on the pipe body.

[0009] According to one example, one end of the bushing is provided with a flange that abuts against the first end of the tube body.

[0010] According to one example, the mandrel includes a frustum and a connecting rod arranged in series, the frustum being engaged within a first through hole, and the connecting rod extending axially from an end face of the frustum, one end of which is detachably located in a second through hole formed on the top of the support cover.

[0011] According to one example, the first through hole and the frustum both have trapezoidal cross sections and fit together.

[0012] According to one example, the outer wall of the connecting rod is threaded, and a nut engages with the thread to fix one end of the connecting rod in the second through hole.

[0013] According to one example, the outer wall of the support cover has a plurality of slots formed along its circumferential direction, and one end of the card block is detachably embedded in the slot for circumferential positioning of the card block.

[0014] According to one example, the inner wall of the locking ring is formed with a first thread, and the outer wall of the locking block is formed with a second thread that mates with the first thread.

[0015] According to one example, an annular groove is formed on the outer side wall of the support cover, and an annular boss that mates with the annular groove is formed on the inner side wall of the locking ring.

[0016] According to one example, the inner wall of the locking ring, the outer wall of the support cover, and the outer wall of the locking block are all inclined at a certain angle toward the central axis of the tube along the length of the tube, and their inclination angles are matched with each other.

[0017] A testing system for fatigue testing of metal pipes includes: a clamping device as described above, the clamping device being mounted on a fixed support; a pipe body, a first end of which is detachably mounted in the clamping device; and a power input device, the power input device being detachably disposed at a second end of the pipe body for applying rotational force or axial tensile or compressive force to the pipe body.

[0018] This utility model has the following advantages:

[0019] The clamping device of this invention is simple to operate and reliably fixed. First, the mandrel is installed into the bushing, then the assembled inner clamp is placed into the pipe body. The flange of the bushing provides precise positioning, laying the foundation for the subsequent installation of the outer clamp. During the installation of the outer clamp, the rotation of the locking ring plays a crucial role. It not only ensures the bushing is tightly against the inner wall of the pipe, providing strong support for the pipe body, but also drives the clamping blocks to tightly adhere to the outer wall of the pipe body, completing the stable locking of the outer clamp onto the pipe body. From the perspective of clamping effect, the rotation of the locking ring drives the clamping blocks to hold the pipe body, effectively avoiding stress concentration. This is crucial for accurately testing the fatigue performance of the pipe material, ensuring the authenticity and reliability of the test results. Simultaneously, the slot design of the support cover ensures that multiple clamping blocks are evenly distributed circumferentially, guaranteeing the coaxiality of the clamping device and allowing for uniform stress distribution across the pipe during testing, improving the stability and accuracy of the test. The clamping block structure is simple and can be adjusted according to the pipe size specifications, quickly adapting to different pipe materials and improving efficiency. Moreover, the card block is not easily deformed during the test, has a long service life, reduces the trouble and cost of frequent component replacement, and further improves the economy and efficiency of the overall test. Attached Figure Description

[0020] Figure 1 This is a three-dimensional structural diagram of the clamping device of this utility model.

[0021] Figure 2 This is a three-dimensional sectional view of the clamping device of this utility model.

[0022] Figure 3 This is a cross-sectional view of the clamping device of this utility model.

[0023] Figure 4 This is an exploded perspective view of the clamping device of this utility model.

[0024] Figure 5 This is a partial perspective sectional view of the clamping device of this utility model.

[0025] Wherein, A is the clamping device, 1 is the inner clamp, 101 is the bushing, 101a is the first through hole, 101b is the flange, 102 is the mandrel, 102a is the frustum, 102b is the connecting rod, 102b1 is the thread, 2 is the outer clamp, 201 is the support cover, 201a is the second through hole, 201b is the slot, 201c is the annular groove, 202 is the locking ring, 202a is the first thread, 202b is the annular boss, 203 is the locking block, 203a is the second thread, 204 is the nut, and 3 is the tube body. Detailed Implementation

[0026] The present invention will now be described in further detail with reference to the accompanying drawings and specific embodiments.

[0027] Reference Figure 1-5 The illustration shows an embodiment of the clamping device A, which mainly includes an inner clamp 1 and an outer clamp 2 that clamp the inner and outer walls of the tube body 3, respectively. These clamps cooperate to hold the first end of the tube body 3. The inner clamp 1 is fixedly supported inside the tube body 3, while the outer clamp 2 is locked outside the tube body 3. This coordinated internal and external clamping method achieves stable clamping of the tube body 3, effectively meeting the fatigue testing requirements of tubes of different specifications. The tube body 3 has a hollow cylindrical structure; for example, in the field of nuclear reactor heat transfer tube material testing, titanium alloy tubes can be used as the test object.

[0028] Reference Figure 2-4 The function of the inner clamp 1 is to provide support and fixation from the inside of the tube body 3. It is detachably set on the inner side wall of the first end of the tube body 3. The inner clamp 1 mainly includes a bushing 101 and a spindle 102.

[0029] The bushing 101 is cylindrical, with its outer diameter approximately the same as the inner diameter of the tube 3. This allows the bushing 101 to fit tightly against the inner wall of the tube 3, providing stable support. One end of the bushing 101 has a flange 101b, which is annular and has a diameter approximately the same as the outer diameter of the tube 3. During installation, the flange 101b abuts against the first end of the tube 3, positioning the bushing 101 within the tube 3 and effectively preventing axial movement of the bushing 101 within the tube 3.

[0030] The bushing 101 has a first through hole 101a inside along the axial direction, which extends through both ends of the bushing 101. The cross-section of the first through hole 101a is trapezoidal, meaning that the opening diameters at its two ends are different. In this embodiment, the opening diameter of the first through hole 101a at one end near the first end of the tube body 3 is smaller than the opening diameter at the other end.

[0031] The mandrel 102 includes a frustum 102a and a connecting rod 102b arranged in series. The frustum 102a is engaged within the first through hole 101a. The cross-section of the frustum 102a is also trapezoidal, and the diameter of one end face of the frustum 102a near the first end of the tube 3 is smaller than the diameter of the other end face, so that the frustum 102a and the first through hole 101a are mutually adapted to form a snap-fit ​​structure. The connecting rod 102b extends axially from the end face of the frustum 102a and is detachably connected to the outer clamp 2.

[0032] Next, refer to Figure 1-5 The outer clamp 2 is mainly used to apply pressure from the outside of the tube body 3 to clamp the tube body 3. It includes a support cover 201, a locking ring 202 and multiple locking blocks 203 to ensure a stable clamping of the tube body 3.

[0033] The support cover 201 is snapped onto the outer wall of the first end of the tube body 3 and is detachably connected to one end of the mandrel 102 for connection and positioning. One end of the connecting rod 102b of the mandrel 102 is detachably located in the second through hole 201a at the top of the support cover 201. The outer wall of the connecting rod 102b is threaded 102b1 and is fixed by cooperating with a nut 204. The nut 204 is located on the upper surface of the support cover 201 and corresponds to the second through hole 201a. When the nut 204 is tightened, the mandrel 102 and the support cover 201 are tightly connected, making the inner clamp 1 and the outer clamp 2 an organic whole, working together on the tube body 3.

[0034] The outer wall of the support cover 201 is provided with multiple slots 201b along the circumferential direction. The slots 201b are used to circumferentially position the locking blocks 203. In this embodiment, there are three slots 201b, which are evenly distributed on the outer wall of the support cover 201. Correspondingly, there are also three locking blocks 203. One end of each locking block 203 is detachably embedded in the slot 201b. In this way, the circumferential position of the locking block 203 is determined, preventing it from rotating or shifting during operation. Of course, in actual application scenarios, the number of locking blocks 203 and slots 201b can be flexibly configured according to different pipe specifications, test requirements, and clamping force requirements, such as four, five, or six.

[0035] The locking ring 202 is engaged with the outer wall of the support cover 201 to clamp the outer clamp 2. The inner wall of the locking ring 202 is provided with a first thread 202a, while the outer wall of the clamping block 203 is provided with a matching second thread 203a. When the locking ring 202 is rotated, the clamping block 203 will move radially due to the interaction of the threads, thereby achieving the clamping or loosening operation on the outer wall of the tube body 3.

[0036] An annular groove 201c is provided on the outer side wall of the support cover 201, and an annular boss 202b is formed on the inner side wall of the locking ring 202 to cooperate with it. The annular boss 202b can be embedded in the annular groove 201c. This can limit the axial movement of the locking ring 202 on the support cover 201, and can also enhance the integrity and stability of the entire outer clamp 2 structure to a certain extent, ensuring that the outer clamp 2 can continuously and stably apply clamping force to the tube 3 during the test.

[0037] In an embodiment not shown, the locking ring 202 includes two arc-shaped segments that together form a circular structure. One end of each arc-shaped segment is hinged together, allowing the two segments to rotate relative to each other around the hinge point, thus opening and closing the locking ring 202. The other ends of the two arc-shaped segments are detachably connected, facilitating their installation on the outside of the support cover 201. The detachable connection can be achieved through snap-fitting, bolting, etc. For example, with snap-fitting, one arc-shaped segment has a buckle seat with a rectangular snap-fit ​​groove at its end, while the other arc-shaped segment has an elastic buckle consisting of an elastic arm and a buckle head. When brought close together, the buckle head engages in the snap-fit ​​groove to achieve snap-fitting. With bolting, one arc-shaped segment has a first hole seat with an internally threaded hole at its end, and the other arc-shaped segment has a corresponding second hole seat with an internally threaded hole at its end. After mating, a bolt is inserted, and a nut is tightened for connection. Loosening the nut and unscrewing the bolt allows for separation. This design improves the ease of installing the locking ring 202 onto the outside of the support cover 201. Operators can open or close the locking ring 202 and fit it onto the support cover 201 according to actual needs.

[0038] Continue to refer to Figure 1-5 The inner wall of the locking ring 202, the outer wall of the support cover 201, and the outer wall of the locking block 203 are all inclined at a certain angle along the length of the tube body 3 toward the central axis of the tube body 3, and their inclination angles are matched with each other.

[0039] The inner wall of the locking ring 202 is inclined at a certain angle towards the central axis of the tube 3 along its length. This angle allows the locking ring 202 to apply a force in a specific direction to the locking block 203 when it rotates, guiding the locking block 203 to move along a specific trajectory, thereby achieving a better clamping effect on the tube 3. The outer wall of the support cover 201 is inclined at a certain angle towards the central axis of the tube 3 along its length. Its inclined outer wall corresponds to the inclination angle of the locking ring 202, ensuring that the locking ring 202 can fit tightly against the outer wall of the support cover 201 after installation. The outer wall of the locking block 203 is inclined at a certain angle towards the central axis of the tube 3 along its length. The inclination angle of the locking block 203 cooperates with the inclination angles of the locking ring 202 and the support cover 201. When the locking ring 202 rotates, the locking block 203 can apply a clamping force evenly to the outer wall of the tube 3 under the action of the locking ring 202 and the support cover 201.

[0040] The inclination angles of the inner wall of the locking ring 202, the outer wall of the support cover 201, and the outer wall of the clamping block 203 are all 10-30 degrees. This ensures that the clamping block 203 applies force evenly when the locking ring 202 rotates, avoiding localized stress concentration. For example, the inclination angle of the inner wall of the locking ring 202 is 10 degrees, the inclination angle of the outer wall of the support cover 201 matches this, and the inclination angle of the outer wall of the clamping block 203 is also 10 degrees. In actual operation, when the locking ring 202 rotates, the force applied to the clamping block 203 by its inner wall is transmitted along the inclination direction, causing the clamping block 203 to smoothly approach the central axis of the tube body 3. Furthermore, due to the coordinated inclination angles of the three components, multiple clamping blocks 203 can synchronously and evenly press against the tube body 3, ensuring a uniform distribution of clamping force and improving clamping stability.

[0041] In an embodiment not shown, a testing system for fatigue testing of metal pipes is also provided, mainly including clamping devices A, a pipe body 3, and a power input device to achieve fatigue testing of the metal pipe. Clamping devices A are respectively installed at both ends of the pipe body 3. The power input device can be driven by electric drive, hydraulic drive, or pneumatic drive, etc. When performing a rotational bending fatigue test, there are two power input devices, each installed on one of the two clamping devices A. Taking electric drive as an example, the motor acts as a power source to drive the transmission mechanism, which converts the rotational motion generated by the motor into rotational torque and bending force, thereby applying rotational bending loads to both ends of the pipe body 3. Alternatively, when performing an axial tensile-compression fatigue test, there is one power input device. One clamping device A is detachably installed on a fixed base, which provides support and fixation for the clamping device A. The power input device is detachably mounted on the other clamping device A. Taking electric drive as an example, if axial tension or pressure is to be applied, the rotational motion of the motor can be converted into linear motion through components such as a screw and nut mechanism or a hydraulic cylinder, thereby applying axial tension or pressure to one end of the tube body 3 to achieve axial fatigue testing of the tube body.

[0042] In an embodiment not shown, a heating chamber is also provided outside the tube body 3. The heating chamber contains a heater that can maintain the internal temperature above 350 degrees Celsius to simulate the temperature conditions of the tube body 3 under actual high-temperature service environment, thereby conducting relevant tests and making the test results closer to the performance of the tube body under real working conditions.

[0043] The above embodiments are preferred embodiments of the present invention, but the embodiments of the present invention are not limited to the above embodiments. Any changes, modifications, substitutions, combinations, or simplifications made without departing from the spirit and principle of the present invention should be considered equivalent substitutions and are included within the protection scope of the present invention. The embodiments described in this disclosure are intended as non-limiting examples, and other embodiments may take various and alternative forms. Furthermore, the drawings are not necessarily to scale and may present simplified expressions of various features of the present disclosure, including, for example, specific dimensions, orientations, positions, and shapes. Details associated with such features will be determined in part by the intended application and usage environment of the described embodiments.

[0044] The detailed description and accompanying drawings are supporting and descriptive of this teaching, but the scope of this teaching is defined only by the claims. While the best mode and some other embodiments for carrying out this teaching have been described in detail, various alternative designs and embodiments exist for practicing the teaching as defined in the appended claims. Furthermore, this disclosure expressly includes combinations and sub-combinations of the elements and features set forth above and below.

Claims

1. A clamping device for fatigue testing of metal pipes, characterized in that, include: An inner clamp is detachably disposed on the inner sidewall of the first end of the tube body for providing support and fixation from inside the tube body. The inner clamp includes a bushing and a mandrel. The bushing extends from the first end of the tube body to its inner sidewall. A first through hole is formed in the axial direction inside the bushing. The mandrel is engaged with the bushing through the first through hole. An external clamp is detachably disposed on the outer side wall of the first end of the tube body for applying pressure from the outside of the tube body to clamp the tube body. The external clamp includes a support cover, a locking ring, and a plurality of clamping blocks. The support cover is snapped onto the outer side wall of the first end of the tube body and is detachably connected to one end of the mandrel. The locking ring is snapped onto the outer side wall of the support cover. One end of each of the plurality of clamping blocks is detachably disposed between the locking ring and the support cover, and the other end abuts against the outer side wall of the tube body to form a clamping force on the tube body.

2. The clamping device according to claim 1, characterized in that, One end of the bushing is provided with a flange, which abuts against the first end of the tube body.

3. The clamping device according to claim 1, characterized in that, The mandrel includes a frustum and a connecting rod arranged in series. The frustum is engaged in the first through hole, and the connecting rod extends axially from the end face of the frustum, with one end detachably located in the second through hole formed on the top of the support cover.

4. The clamping device according to claim 3, characterized in that, The first through hole and the frustum both have trapezoidal cross sections and fit together.

5. The clamping device according to claim 3, characterized in that, The outer wall of the connecting rod is threaded, and a nut engages with the thread to fix one end of the connecting rod in the second through hole.

6. The clamping device according to claim 1, characterized in that, The outer wall of the support cover has multiple slots formed along its circumferential direction. One end of the card block is detachably embedded in the slot for circumferential positioning of the card block.

7. The clamping device according to claim 1, characterized in that, The inner wall of the locking ring is formed with a first thread, and the outer wall of the locking block is formed with a second thread that mates with the first thread.

8. The clamping device according to claim 1, characterized in that, An annular groove is formed on the outer side wall of the support cover, and an annular boss that mates with the annular groove is formed on the inner side wall of the locking ring.

9. The clamping device according to claim 1, characterized in that, The inner wall of the locking ring, the outer wall of the support cover, and the outer wall of the locking block are all inclined at a certain angle along the length of the tube towards the central axis of the tube, and their inclination angles are coordinated with each other.

10. A testing system for fatigue testing of metal pipes, characterized in that, include: The clamping device according to any one of claims 1 to 9; The tube body, with the clamping device detachably installed at both ends of the tube body; A power input device is detachably mounted on one of the two clamping devices for applying rotational bending loads to both ends of the tube; or the power input device is detachably mounted on one of the clamping devices, and the other clamping device is detachably mounted on a fixed base for applying axial tensile and compressive loads to one end of the tube.

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