Pipe end positioning fixture for pipe drop hammer impact test

Abstract

The application discloses a pipe end positioning clamp for pipeline drop hammer impact test, and particularly relates to the technical field of pipeline impact test, which comprises a base, two clamping units, two groups of elastic members and two locking members, the two clamping units are symmetrically and slidably arranged on the base and can be switched between a clamping state of approaching each other and a releasing state of moving away from each other; in the clamping state, the two clamping units clamp and position two end portions of the pipeline respectively; in the releasing state, the two clamping units move away from each other along the axial direction of the pipeline and completely separate from the pipe end. Through cooperation of the elastic members and the locking members, the clamping units are instantly bounced away and completely separated from the pipe end when the hammer head falls to a preset trigger position, so that no additional constraint is generated on the pipe end at the moment of impact, the pipeline impact response purely reflects the structural performance of the pipeline itself, and the physical meaning of the test result is clear.

Description

Technical Field

[0001] This invention relates to the field of pipeline impact testing technology, specifically to a pipe end positioning fixture for pipeline drop hammer impact testing. Background Technology

[0002] The drop hammer impact test evaluates the impact resistance of pipe materials by releasing a drop hammer of a specified mass to impact the middle of the pipe specimen. The accuracy of the test results is highly dependent on whether the boundary conditions at the pipe end are clearly defined and controllable. Ideally, the pipe is precisely positioned before impact, and there are no additional constraints on the pipe end at the moment of impact, so that the measured response purely reflects the performance of the pipe itself.

[0003] Currently, the commonly used pipe end support device is an integral support V-groove, such as... Figure 12 As shown, the test pipe is placed directly into the V-shaped notch, relying on gravity and contact with the tank wall for support and positioning. This scheme has a simple structure, but it has the following problems.

[0004] Regarding positioning accuracy, the pipe is placed on the V-groove solely by gravity, lacking reliable axial and circumferential positioning benchmarks. The alignment of the impact point with the center line of the drop hammer relies entirely on the operator's visual inspection and feel, resulting in poor consistency in the impact point positions of samples from the same batch and large data dispersion. In terms of dynamic behavior, the pipe experiences severe vibration and bending deformation upon impact. The pipe end undergoes uncontrollable movements within the V-groove, such as bouncing upwards and sliding along the sidewall. Boundary conditions change randomly between contact and disengagement, introducing nonlinear disturbances that are difficult to quantify. When the pipe end bounces back, it may also experience secondary impacts with the sidewall or bottom of the V-groove, causing additional damage to non-impact areas and masking the true damage mode of the pipe from a single impact. Furthermore, the complex dynamic contact process provided by the rigid V-groove is neither equivalent to an ideal free boundary nor represents the elastic constraint conditions in engineering. The physical meaning of the test results is ambiguous, making it difficult to establish a reliable correlation with the design model.

[0005] To address the positioning issue, some experiments have employed mechanical grippers to rigidly clamp the pipe ends. However, if the clamping is maintained during impact, the gripper itself becomes an additional constraint, absorbing energy and restricting the pipe's free deformation, thus distorting the results. Therefore, existing pipe end clamps generally face a contradiction: improving positioning accuracy requires applying mechanical constraints, but the constraint at the moment of impact inevitably interferes with the pipe's free response, making it impossible to simultaneously achieve reliable positioning and non-interference during impact. Summary of the Invention

[0006] The technical problem this invention aims to solve is as follows: Existing integral support V-grooves rely solely on the pipe's gravity and contact with the groove wall for support and positioning. The pipe lacks reliable axial and circumferential positioning benchmarks, and the accuracy of impact point alignment depends on operator experience, resulting in large data dispersion within the same batch of samples. At the moment of impact, the pipe end undergoes uncontrollable movements such as bounce and slippage within the V-groove, with boundary conditions randomly changing between contact and disengagement, introducing nonlinear interference that is difficult to quantify. Furthermore, the pipe end experiences a secondary impact with the V-groove during its bounce and fall, causing additional damage and masking the true damage mode of the pipe under a single impact. While rigid clamping with mechanical grippers improves positioning accuracy, the gripper itself becomes an additional constraint during impact, absorbing energy and restricting the pipe's free deformation, similarly distorting the test results. Therefore, existing pipe end clamps generally face a contradiction: improving positioning accuracy requires applying mechanical constraints, but these constraints at the moment of impact inevitably interfere with the pipe's free response, making it impossible to simultaneously achieve reliable positioning and interference-free impact.

[0007] To solve the above-mentioned technical problems, the present invention provides the following technical solution: a pipe end positioning fixture for a pipe drop hammer impact test, comprising a base, two clamping units, two sets of elastic elements, and two locking elements. The two clamping units are symmetrically and slidably disposed on the base, and can switch between a clamping state where they are close to each other and a releasing state where they are far apart. In the clamping state, the two clamping units clamp and position the two ends of the pipe respectively; in the releasing state, the two clamping units move away from each other along the pipe axis, completely disengaging from the pipe ends. The two sets of elastic elements are respectively associated with the two clamping units. In the clamping state, the two sets of elastic elements are stretched and store energy; when switching to the releasing state, the two sets of elastic elements drive the two clamping units to move away from each other. In the clamping state, the two locking elements respectively limit and lock the two clamping units, holding them in the energy-storing position; when the hammer falls to a preset trigger position, the two locking elements release their limit lock on the clamping units, the elastic elements release, and drive the clamping units to spring open.

[0008] In operation, the two clamping units are first pushed to a position close to each other. During this process, the elastic element is stretched and stores energy, while the locking element automatically limits and locks the clamping units, keeping them in the energy-storing position. The two ends of the pipe are placed into the two clamping units respectively, which precisely clamp and position the pipe ends axially and circumferentially, ensuring that the pipe axis is aligned with the center line of the drop hammer and the impact point is precisely controllable. During the test, the drop hammer is released from a set height, and the hammer head falls freely along the guide rail. When the hammer head falls to the preset trigger position, the locking element is triggered and releases the limiting lock on the clamping units. The stretched elastic element is released instantaneously, driving the two clamping units to spring away from each other along the pipe axis, completely disengaging from the pipe ends. At this point, the hammer head has not yet contacted the pipe, and both ends of the pipe are completely free and without any additional constraints. The hammer head then impacts the middle of the pipe, and the impact response of the pipe purely reflects its own structural performance.

[0009] By employing a working logic of clamping and positioning before impact and releasing instantaneously before impact, the contradiction between reliable positioning and interference-free impact is resolved. In the clamped state, the clamping unit applies reliable mechanical constraints to the pipe end, using a baffle for precise axial positioning and fixed and movable clamping components for precise circumferential centering and clamping. This results in good consistency of impact point positions and significantly reduces the dispersion of data from the same batch of tests. When the hammer falls to the preset trigger position, the locking component releases its limit, and the elastic component drives the clamping unit to instantly spring open and completely disengage from the pipe end. This ensures that there are no additional constraints on the pipe end at the moment the hammer contacts the pipe, allowing the impact response to purely reflect the pipe's inherent performance, and providing a clear physical meaning to the test results. After the clamping unit springs open, sufficient space is provided for pipe end deformation, preventing secondary impacts between the pipe end and the clamp, thus avoiding additional damage that could interfere with the failure mode.

[0010] The technical effects and advantages provided by the present invention in the above technical solution are as follows: By setting up a symmetrical sliding clamping unit, axial precision positioning is achieved using a baffle in the clamping state, and circumferential centering clamping is achieved using fixed and movable clamping parts. The impact point position is consistent, significantly reducing the dispersion of test data in the same batch. Through the cooperation of elastic and locking parts, when the hammer falls to the preset trigger position, the clamping unit instantly springs open and completely disengages from the pipe end, ensuring that there is no additional constraint on the pipe end at the moment of impact. The pipe impact response purely reflects its own structural performance, and the physical meaning of the test results is clear. Attached Figure Description

[0011] To more clearly illustrate the technical solutions in the embodiments of this application or the prior art, the drawings used in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments recorded in this invention. For those skilled in the art, other drawings can be obtained based on these drawings.

[0012] Figure 1 This is a schematic diagram of the overall structure of the present invention. Figure 1 ; Figure 2 This is a schematic diagram of the overall structure of the present invention. Figure 2 ; Figure 3 This is a schematic diagram of the overall front view of the present invention; Figure 4 This is a schematic diagram of the three-dimensional structure of the clamping unit of the present invention; Figure 5 This is a three-dimensional structural diagram of the base, side plate, and elastic element of the present invention; Figure 6 This is a three-dimensional structural diagram of the locking element and triggering unit of the present invention; Figure 7This is a schematic diagram of the locking element and lever connection structure of the present invention; Figure 8 This is a bottom view of the base plate structure of the present invention; Figure 9 This is an exploded view of the regulating unit of the present invention; Figure 10 This is a schematic diagram of the overall structure of the present invention mounted on a gantry frame; Figure 11 This is a three-dimensional structural diagram of the mounting plate of the present invention; Figure 12 This is a three-dimensional structural diagram of the V-groove fixture for the existing impact test according to the present invention.

[0013] Explanation of reference numerals in the attached figures: 100. Base; 110. Side panel; 200 Clamping unit; 210 Base plate; 211 Guide block; 212 Guide rail; 220 Baffle; 230 Fixed clamping component; 231 First liner; 240 Movable clamping component; 241 Second liner; 242 Guide bar; 243 Bolt; 250 Ball groove; 260 Ball; 300. Elastic element; 310. Telescopic rod; 320. First spring; 400, Locking element; 410, Limiting groove; 420, Waist-shaped groove; 430, Protrusion; 440, Groove; 500, Triggering unit; 510, Lever; 520, Frame; 530, Second spring; 540, Pull rope; 541, Connecting rod; 542, First magnet; 543, Second magnet; 544, Slot; 545, Through hole; 550, Redirecting roller; 600. Adjustment unit; 610. Threaded sleeve; 620. Threaded rod; 700. Gantry frame; 710. Mounting plate. Detailed Implementation

[0014] To enable those skilled in the art to better understand the technical solution of the present invention, the present invention will be further described in detail below with reference to the accompanying drawings.

[0015] In existing technologies, pipe drop hammer impact tests generally employ integral support V-grooves, such as... Figure 12As shown, the test pipe is directly placed into the V-shaped notch, relying on gravity and contact with the groove wall for support and positioning. While this method is structurally simple, it suffers from poor positioning accuracy, uncontrollable bouncing and slippage of the pipe end during impact, and secondary impact with the V-groove during the pipe's fall. This results in large data dispersion, making it difficult to accurately reflect the pipe's impact resistance. Mechanical clamps have been used to rigidly clamp the pipe to address the positioning problem, but during impact, the clamp itself becomes an additional constraint, absorbing energy and restricting the pipe's free deformation, similarly distorting the results. Therefore, existing pipe end clamps generally face a contradiction: improving positioning accuracy requires mechanical constraints, but the constraint at the moment of impact inevitably interferes with the pipe's free response, making it impossible to simultaneously achieve reliable positioning and non-interference during impact.

[0016] To address the aforementioned problems, this invention provides a pipe end positioning fixture for pipe drop hammer impact testing, such as... Figure 1 , Figure 3 and Figure 6 As shown, the device includes a base 100, two clamping units 200, two sets of elastic elements 300, and two locking elements 400. The two clamping units 200 are symmetrically and slidably mounted on the base 100, and can switch between a clamping state where they are close to each other and a releasing state where they are far apart. In the clamping state, the two clamping units 200 clamp and position the two ends of the pipe respectively; in the releasing state, the two clamping units 200 move away from each other along the pipe axis, completely disengaging from the pipe ends. The two sets of elastic elements 300 are associated with the two clamping units 200 respectively, and are stretched and energy-storing in the clamping state. When switching to the releasing state, they drive the two clamping units 200 to move away from each other. In the clamping state, the two locking elements 400 respectively limit and lock the two clamping units 200, keeping them in the energy-storing position; when the hammer falls to a preset trigger position, the two locking elements 400 release their limit locks, the elastic elements 300 release, and drive the clamping units 200 to spring open.

[0017] In use, the two clamping units 200 are first pushed to a clamping position close to each other. During this process, the elastic element 300 is stretched and stores energy, while the locking element 400 limits and locks the clamping units 200, keeping them in the energy-storing position. The two ends of the pipe are placed into the two clamping units 200 respectively, which clamp and position the pipe ends axially and circumferentially, ensuring that the pipe axis is aligned with the center line of the drop hammer and the impact point is precisely controllable. During the test, the drop hammer is released from a set height, and the hammer head falls freely along the guide rail. When the hammer head falls to the preset trigger position, the locking element 400 is triggered and releases the limiting lock on the clamping units 200. The stretched elastic element 300 is released instantaneously, driving the two clamping units 200 to spring away from each other along the pipe axis, completely disengaging from the pipe ends. At this point, the hammer head has not yet contacted the pipe, and both ends of the pipe are completely free and without any additional constraints. The hammer head then strikes the middle of the pipe, and the impact response of the pipe purely reflects its own structural performance. By employing a working logic of clamping and positioning first, and releasing instantaneously before impact, the contradiction between reliable positioning and non-interference impact is resolved.

[0018] In specific embodiments, such as Figure 1 , Figure 3 , Figure 5 and Figure 10 As shown, the base 100 is a rectangular plate structure, fixedly installed on the gantry 700 of the drop hammer impact testing machine. A side plate 110 is fixed on each side of the top surface of the base 100, the two side plates 110 being parallel to each other and perpendicular to the top surface of the base 100. Four guide rails 212 extending along the pipe axis are provided on the top surface of the base 100, the four guide rails 212 being parallel to each other and symmetrically arranged on both sides of the width direction of the base 100.

[0019] like Figure 2 , Figure 4 As shown, each clamping unit 200 includes a base plate 210, a baffle 220, a fixed clamping member 230, and a movable clamping member 240. The base plate 210 is a rectangular plate, and a guide block 211 is fixedly provided on its bottom surface. The guide block 211 is slidably disposed inside the guide rail 212, so that the entire clamping unit 200 can slide smoothly on the base 100 along the pipe axis. The cooperation between the guide rail 212 and the guide block 211 provides precise linear guidance for the sliding of the clamping unit 200, ensuring that the clamping unit 200 moves along the pipe axis when it is released without swaying.

[0020] A baffle 220 is fixedly mounted on the upper surface of the base plate 210 at the end away from the pipe, with the baffle surface perpendicular to the pipe axis. During testing, the pipe end face abuts against the side of the baffle 220 facing the pipe, and the baffle 220 axially limits and blocks the pipe end, thereby determining the length of the pipe extending into the clamp and the position of the impact point along the pipe length. A fixed clamp 230 is fixedly mounted on the upper surface of the base plate 210, located on the side of the baffle 220 closest to the pipe; that is, the fixed clamp 230 and the baffle 220 are arranged back and forth along the pipe axis. The upper surface of the fixed clamp 230 has a V-shaped groove for supporting the pipe end from below. A movable clamp 240 is mounted on top of the fixed clamp 230, and the lower surface of the movable clamp 240 also has a V-shaped groove, which aligns vertically with the V-shaped groove of the fixed clamp 230. The movable clamping member 240 has a vertical guide groove on the side facing the baffle 220 that cooperates with the guide strip 242, allowing the movable clamping member 240 to move up and down vertically on one side of the baffle 220. A bolt 243 is provided at the top of the movable clamping member 240. One end of the bolt 243 is rotatably connected to the movable clamping member 240 via a bearing, and passes through a block on the baffle 220 and is threadedly connected to it. By rotating the bolt 243, the bolt 243 moves up and down, thereby driving the movable clamping member 240 to press down on or release the end of the pipe upwards.

[0021] A first liner 231 is installed on the inner wall of the V-groove of the fixed clamping member 230, and a second liner 241 is installed on the inner wall of the V-groove of the movable clamping member 240. The first liner 231 and the second liner 241 are made of wear-resistant material and are in direct contact with the outer wall of the pipe end. On the one hand, they protect the pipe surface from being damaged by the V-groove, and on the other hand, after long-term use and wear, only the liner needs to be replaced, without replacing the entire clamping member.

[0022] like Figure 4 As shown, to further reduce the frictional resistance between the clamping unit 200 and the pipe end when it springs open and releases, and to ensure a rapid and smooth release action, multiple ball grooves 250 are provided on the surfaces of the first liner 231 and the second liner 241 that contact the outer wall of the pipe end. A ball 260 is rotatably disposed inside the ball groove 250, protruding from the liner surface and forming a rolling contact with the outer wall of the pipe end. When the clamping unit 200 springs open away from the pipe end, the ball 260 rolls on the pipe surface, converting sliding friction into rolling friction, significantly reducing frictional resistance, allowing the clamping unit 200 to disengage from the pipe end more quickly and smoothly, further ensuring the complete freedom of the pipe end at the moment of impact. If the ball 260 is not provided, a lubricant can also be applied to the inner walls of the first liner 231 and the second liner 241.

[0023] like Figure 1 , Figure 2 , Figure 5As shown, the elastic element 300 stores energy in the clamping state and drives the clamping unit 200 to spring open in the released state. The elastic element 300 includes a telescopic rod 310 and a first spring 320. The telescopic rod 310 consists of two rod sections with inner and outer sleeves, capable of axial extension and retraction, providing guidance and anti-bending support for the first spring 320. The first spring 320 is a helical compression spring, sleeved on the outside of the telescopic rod 310. One end of the telescopic rod 310 and the first spring 320 is fixedly connected to the side of the baffle 220 away from the pipe, and the other end is fixedly connected to the side of the side plate 110 on the same side near the pipe. When the two clamping units 200 are pushed to a clamping position close to each other, the baffle 220 moves away from the side plate 110, and the first spring 320 is stretched to store energy; when the locking element 400 is released, the first spring 320 releases the stored elastic potential energy, pushing the entire clamping unit 200 to spring out along the guide rail 212 away from the pipe through the baffle 220.

[0024] like Figure 3 , Figure 6 , Figure 7 , Figure 8 As shown, the locking member 400 is used to limit and lock the clamping unit 200 in the clamping state. A limiting groove 410 is formed in the middle of the bottom end face of the base plate 210. The limiting groove 410 is a circular groove with its opening facing downward. The main body of the locking member 400 is a vertically arranged pin, the top of which can be inserted into or disengaged from the limiting groove 410. When the top of the locking member 400 is inserted into the limiting groove 410, the base plate 210 is locked and fixed, and the clamping unit 200 cannot slide along the guide rail 212 and is held in the energy storage position; when the top of the locking member 400 disengages from the limiting groove 410, the limiting is released, and the elastic member 300 can drive the clamping unit 200 to spring open.

[0025] A trigger unit 500 is disposed on the bottom end face of the base 100 and is used to drive the locking member 400 to perform the actions of inserting into and disengaging from the limiting groove 410. The trigger unit 500 includes a lever 510, a frame 520, a second spring 530, and a pull rope 540. The frame 520 is fixedly mounted on the bottom end face of the base 100 and has a hinge shaft inside. The middle part of the lever 510 is hinged to the bottom end face of the base 100 through the hinge shaft inside the frame 520, forming a lever fulcrum. The lever 510 can swing around this fulcrum within a certain angle range.

[0026] like Figure 7As shown, one end (short arm end) of lever 510 is movably connected to the lower end of locking member 400. This end of lever 510 has a waist-shaped groove 420, and the lower end of locking member 400 has a protrusion 430. The protrusion 430 is slidably embedded in the groove 440 in the waist-shaped groove 420. The two are linked in the vertical direction and have a certain amount of movement in the horizontal direction to compensate for the displacement difference between the end of lever 510 swinging along the arc trajectory and the vertical linear movement of locking member 400.

[0027] The other end (long arm end) of lever 510 is connected to one end of second spring 530, and the other end of second spring 530 is connected to the bottom surface of base 100. In its natural state, second spring 530 contracts, pulling the long arm end of lever 510 upward, while the short arm end of lever 510 moves downward, causing locking member 400 to disengage downward from limiting groove 410. One end of pull rope 540 is connected to the long arm end of lever 510, and the other end extends upward. A redirecting roller 550 is also provided on the bottom surface of base 100 below the long arm end of lever 510. After the pull rope 540 passes around the redirecting roller 550, it changes direction and extends upward.

[0028] The pull rope 540 has a taut state and a slack state. In the taut state, the pull rope 540 pulls the long arm of the lever 510 downward through the redirecting roller 550, causing the second spring 530 to be stretched and stored. At the same time, the lever 510 rotates around the frame 520, and the short arm moves upward, pushing the locking member 400 upward into the limiting groove 410, thereby limiting and locking the clamping unit 200. When the hammer falls to the preset trigger position, the pull rope 540 switches to the slack state. The downward pull of the pull rope 540 on the long arm of the lever 510 disappears, the second spring 530 releases and contracts, causing the long arm of the lever 510 to move upward. The lever 510 rotates in the opposite direction around the frame 520, and the short arm moves downward. Through the cooperation of the groove 440 and the protrusion 430 at the inner end of the waist-shaped groove 420, the locking member 400 is pulled downward out of the limiting groove 410, releasing the limiting and locking of the clamping unit 200.

[0029] To enable the pull rope 540 to automatically switch from a taut to a slack state when the hammer falls to a preset position, this invention employs a magnetic triggering mechanism. For example... Figure 10 , Figure 11As shown, a mounting plate 710 is fixedly installed on the gantry 700 of the drop hammer impact testing machine. The hammer head is mounted on the mounting plate 710, and the mounting plate 710 can move up and down with the hammer head. A connecting rod 541 and a first magnetic block 542 are fixedly connected to the end of the pull rope 540 away from the lever 510. A slot 544 is provided on the gantry 700, and the position of the slot is the preset trigger point. Before the test begins, the connecting rod 541 and the first magnetic block 542 are inserted into the slot 544, at which time the pull rope 540 is taut. A second magnetic block 543 is embedded at the end of the mounting plate 710. The opposing magnetic poles of the second magnetic block 543 and the first magnetic block 542 are the same, generating a repulsive force between them. As the hammer falls, the mounting plate 710 causes the second magnetic block 543 to move downwards. When the second magnetic block 543 aligns with the slot 544, the magnetic repulsion force generated by the second magnetic block 543 on the first magnetic block 542 reaches its maximum. Under the action of this repulsion force, the first magnetic block 542 causes the insertion rod 541 to disengage from the slot 544, and the end of the pull rope 540 loses its fixed constraint and instantly becomes slack. The bottom surface of the base 100 has a through hole 545 below the slot 544 for the pull rope 540 to pass through.

[0030] To further facilitate adjustment of the triggering timing, an adjustment unit 600 is also connected in series on the pull rope 540. For example... Figure 9 As shown, the adjustment unit 600 includes a threaded sleeve 610 and two threaded rods 620. The outer ends of the two threaded rods 620 are respectively connected to two sections of the pull rope 540, and the inner ends of the two threaded rods 620 are screwed into the threaded sleeve 610 from both ends and threadedly connected to the threaded sleeve 610. By rotating the threaded sleeve 610, the depth to which the two threaded rods 620 are screwed into the threaded sleeve 610 can be adjusted, thereby changing the total length of the adjustment unit 600 connected in series in the pull rope 540, and thus precisely adjusting the falling position of the hammer when the pull rope 540 switches from a taut state to a slack state. The threaded connection has a self-locking function, and the length remains stable after adjustment.

[0031] Method for determining the preset trigger position The preset trigger position is a key parameter, and its determination requires precise calculation based on the dynamic response characteristics of the fixture and the kinematic parameters of the drop hammer. The method and calculation basis for determining the preset trigger position are explained in detail below.

[0032] First, the response time of the fixture needs to be measured. After the fixture is manufactured and assembled, a no-load timing test is performed. Under the initial conditions that the locking element 400 is inserted into the limiting groove 410, the elastic element 300 is stretched and stored energy, and the pull rope 540 is in a taut state, the end of the pull rope 540 is released instantaneously by the quick release mechanism. At the same time, a high-speed camera records the movement process of the locking element 400 and the base plate 210 at a shooting speed of no less than 1000 frames / second. Two key time periods are read frame by frame from the high-speed camera footage: the locking element release time t1, which is the time elapsed from the moment the pull rope 540 relaxes to the moment the top of the locking element 400 completely leaves the limiting groove 410; and the base plate safety clearance establishment time t2, which is the time elapsed from the moment the locking element 400 releases to the moment the base plate 210 moves along the guide rail 212 away from the pipe to a preset safety distance S (usually 10mm to 15mm). The total response time of the fixture is then t3 = t1 + t2. The principle for selecting the preset safety distance S is that, at this distance, the gap between the clamping unit 200 and the pipe end is sufficient to ensure that the pipe will not come into contact with the clamping unit 200 when it is subjected to impact, bending deformation, and vibration.

[0033] Secondly, determine the motion parameters of the drop hammer. Let the release height of the drop hammer be H, which is the vertical distance from the lowest point of the hammerhead to the highest generatrix of the pipe. After being released from rest, the drop hammer undergoes free fall motion, and its falling distance s is related to time t by s = (1 / 2)gt², where g is the acceleration due to gravity, taken as 9.8 m / s². The velocity of the drop hammer when it impacts the pipe is v = (2gH), impact time t4 = (2H / g).

[0034] Then, the latest triggering time is determined based on the clamp response time. To ensure that the clamp has fully springed open and a safety margin is left when the hammer hits the pipe, the following timing condition must be met: t5 + t3 + t6 ≤ t4. Where t5 is the moment when the pull rope 540 slackens and the locking element 400 begins to operate, and t6 is the buffer time margin, usually taken as 5 to 10 milliseconds, to ensure that the clamping unit 200 has completely disengaged from the pipe end and leaves sufficient clearance before the hammer hits the pipe.

[0035] Taking a drop hammer release height H = 2 meters as an example, t4 = (2×2 / 9.8) ≈ 0.639 seconds = 639 milliseconds. Taking t6 = 5 milliseconds and t3 = 8 milliseconds, the latest allowed trigger time is t5. max = 639 - 8 - 5 = 626 milliseconds. At t5 max At that moment, the distance the hammer has fallen is s = (1 / 2)×9.8×(0.626)² ≈ 1.92 meters, that is, the remaining height of the hammer from the pipe is h = 2-1.92 = 0.08 meters = 80 millimeters.

[0036] The calculations show that the pull rope 540 must switch to a slack state when the hammer falls to a distance of 80 mm from the pipe to ensure that the clamp completes its spring-off action before the hammer hits the pipe and allows for a 5-millisecond safety buffer time. This 80 mm distance from the pipe is the preset trigger position.

[0037] Finally, the preset trigger position is converted into an adjustable parameter of the fixture. Once the preset trigger position is determined, it is achieved by finely adjusting the total length of the pull rope 540 by rotating the threaded sleeve 610 of the adjusting unit 600, thereby changing the tension of the pull rope 540 and precisely adjusting the hammer position corresponding to the slack moment. In actual operation, the hammer can be precisely lowered to a height of 80 mm from the pipe, and then the length of the pull rope 540 is adjusted so that the first magnetic block 542 is in a critical state about to be pushed out, thus completing the calibration of the preset trigger position.

[0038] In use, the operator first pushes the two clamping units 200 toward the pipeline to the clamping position, at which point the elastic element 300 is stretched and stores energy. The pull rope 540 is in a taut state, and the locking element 400 is pushed upward into the limiting groove 410 through the lever 510, locking the clamping unit 200 in the energy-storing position. The two ends of the pipeline are respectively placed into the two clamping units 200, and the pipeline end face abuts against the baffle 220 to achieve axial positioning. Rotating the bolt 243 causes the movable clamping element 240 to press down, which, together with the fixed clamping element 230, clamps the pipeline end. When the testing machine is started, the hammer head is released, and the hammer head causes the mounting plate 710 to fall. When the hammer head falls to the preset trigger position, the second magnetic block 543 aligns with the first magnetic block 542. Under the action of magnetic repulsion, the first magnetic block 542 causes the plug rod 541 to disengage from the slot 544. The pull rope 540 is instantly relaxed, the second spring 530 contracts and causes the lever 510 to rotate. The locking member 400 disengages from the limiting groove 410, the elastic member 300 is released and drives the clamping unit 200 to spring away from the pipe end. The hammer head then hits the middle of the pipe to complete the impact.

[0039] Through the cooperation of the magnetic triggering mechanism and the adjusting unit 600, combined with the method for determining the preset trigger position, precise calculation and adjustable control of the triggering timing are achieved, making it suitable for testing requirements of fixtures with different pipe diameters, different drop hammer heights, and different response characteristics. The entire action from the slackening of the pull rope to the complete release of the clamping unit is completed in an extremely short time, far less than the remaining fall time of the hammer head, ensuring that the pipe end is in a completely free state at the moment of impact. The entire fixture is implemented with a purely mechanical structure, ensuring reliable operation without the need for electrical control, and is suitable for various drop hammer impact testing machines.

[0040] The foregoing has only described certain exemplary embodiments of the present invention by way of illustration. Undoubtedly, those skilled in the art can modify the described embodiments in various ways without departing from the spirit and scope of the present invention. Therefore, the foregoing drawings and descriptions are illustrative in nature and should not be construed as limiting the scope of protection of the claims of the present invention.

Claims

1. A pipe end positioning clamp for a pipe drop hammer impact test, characterized in that, include: Base (100); Two clamping units (200) are symmetrically and slidably disposed on the base (100), and the two clamping units (200) can switch between a clamping state in which they are close to each other and a releasing state in which they are far apart from each other; In the clamping state, the two clamping units (200) clamp and position the two ends of the pipe respectively; in the releasing state, the two clamping units (200) move away from each other along the pipe axis and completely disengage from the pipe ends. Two sets of elastic elements (300) are respectively associated with two clamping units (200). In the clamping state, the two sets of elastic elements (300) are stretched and stored. When switching to the release state, the two sets of elastic elements (300) drive the two clamping units (200) to move away from each other. Two locking members (400) respectively limit and lock the two clamping units (200) in the clamping state, keeping the clamping units (200) in the energy storage position; when the hammer falls to the preset trigger position, the two locking members (400) release the limit and lock the clamping units (200), and the elastic member (300) releases and drives the clamping units (200) to spring open.

2. The pipe end positioning fixture for the pipe drop hammer impact test according to claim 1, characterized in that: The clamping unit (200) includes a base plate (210), a baffle (220), a fixed clamping member (230), and a movable clamping member (240). The baffle (220) and the fixed clamping member (230) are fixedly mounted on the base plate (210). The baffle (220) limits and blocks the end of the pipe. The movable clamping member (240) is mounted on top of the fixed clamping member (230) and can move up and down on one side of the baffle (220).

3. The pipe end positioning fixture for the pipe drop hammer impact test according to claim 2, characterized in that: The fixed clamping member (230) and the movable clamping member (240) are respectively equipped with a first liner (231) and a second liner (241) on the inner wall of the V-groove.

4. The pipe end positioning fixture for the pipe drop hammer impact test according to claim 3, characterized in that: The first liner (231) and the second liner (241) have multiple ball grooves (250) on the surfaces that contact the outer wall of the pipe end. Balls (260) are rotatably arranged inside the ball grooves (250), and the balls (260) slide in contact with the outer wall of the pipe end.

5. The pipe end positioning fixture for the pipe drop hammer impact test according to claim 2, characterized in that: The base (100) has a guide rail (212) on its top surface and a guide block (211) is fixed on the bottom surface of the base plate (210). The guide block (211) is slidably disposed inside the guide rail (212).

6. The pipe end positioning fixture for the pipe drop hammer impact test according to claim 2, characterized in that: The elastic element (300) includes a telescopic rod (310) and a first spring (320). The first spring (320) is sleeved on the outside of the telescopic rod (310). A side plate (110) is fixedly provided at both ends of the base (100). The two ends of the telescopic rod (310) and the first spring (320) are respectively fixedly connected to the side of the baffle (220) away from the pipe and the side of the side plate (110) close to the pipe.

7. The pipe end positioning fixture for the pipe drop hammer impact test according to claim 2, characterized in that: A limiting groove (410) is provided in the middle of the bottom end face of the base plate (210). When the locking member (400) limits and locks the clamping unit (200), one end of the locking member (400) is inserted into the limiting groove (410). When the limiting lock is released, one end of the locking member (400) is disengaged from the limiting groove (410).

8. The pipe end positioning fixture for the pipe drop hammer impact test according to claim 7, characterized in that: The base (100) has a trigger unit (500) on its bottom end surface. The trigger unit (500) is used to drive the locking member (400) to insert into and disengage from the limiting groove (410). The triggering unit (500) includes a lever (510), a frame (520), a second spring (530), and a pull cord (540). The locking member (400) is movably connected to one end of the lever (510). The lever (510) is hinged to the bottom surface of the base (100) through the frame (520). The second spring (530) connects the other end of the lever (510) to the bottom surface of the base (100). The pull cord (540) has a taut... In the taut state, the pull rope (540) pulls the other end of the lever (510), the second spring (530) is stretched and stored, and the locking member (400) is inserted into the limiting groove (410). When the hammer falls to the preset position, the pull rope (540) switches to the taut state, the second spring (530) drives the other end of the lever (510) to move, and one end of the locking member (400) disengages from the limiting groove (410).

9. The pipe end positioning fixture for the pipe drop hammer impact test according to claim 8, characterized in that: The end of the pull rope (540) is fixedly connected to a plug rod (541) and a first magnetic block (542). The plug rod (541) and the first magnetic block (542) are inserted into the slot (544) on the gantry (700) before the test begins. The end of the mounting plate (710) on the gantry (700) is embedded with a second magnetic block (543). The magnetic poles of the opposing surfaces of the second magnetic block (543) and the first magnetic block (542) are the same. When the second magnetic block (543) moves to the position of the slot (544), the first magnetic block (542) is repelled and detached from the slot (544), and the pull rope (540) is in a slack state.

10. The pipe end positioning fixture for the pipe drop hammer impact test according to claim 8, characterized in that: An adjustment unit (600) is connected in series on the pull rope (540), and the adjustment unit (600) can adjust the total length of the pull rope (540); The adjustment unit (600) includes a threaded sleeve (610) and two threaded rods (620), the ends of which enter from both ends of the threaded sleeve (610) and are threadedly connected to its interior.

Images