A clamping device of the gripper type for the fatigue test of sucker rods

Abstract

The present invention discloses a clamp - type clamping device for sucker rod fatigue test, which comprises an upper body of the clamping device, a lower body of the clamping device, a clamping bolt and a rotating pin; wherein, one side of the upper body of the clamping device is connected to the lower body of the clamping device through the rotating pin, and the other side is connected through the clamping bolt, and the clamping bolt provides the fastening force required for clamping the sucker rod; a clamping head is further arranged at the top of the lower body of the clamping device; clamping grooves are formed on the inner surfaces of the upper body of the clamping device and the lower body of the clamping device, and the clamping grooves are cylindrical after the clamping device is closed. This device changes the conventional "tooth - type fixture" clamping to an asymmetric clamp - type clamping device; it can meet the minimum yield strength of 793 MPa for class - H sucker rods in strength check. The sucker rod fatigue test requires long - term detection. However, the success rate of existing fatigue detection methods is not high. After adopting this technology, the occurrence of fracture at the fixture can be reduced, and the test success rate can be improved, being in the leading stage of fatigue detection.

Description

Technical Field

[0001] The present invention relates to the technical field of sucker rod detection, and relates to a clamping device for a sucker rod fatigue test with a clamping tongs type. Background Art

[0002] The sucker rod is an important device in the rod pumping system, and bears the load transmission movement between the pumping unit and the oil pump. Due to the alternating load it bears, the main failure form is fatigue failure. During the use of the sucker rod, it is under the action of alternating stress. Although the fatigue performance test of the sucker rod is not required in the routine quality inspection and supervision sampling inspection, the fatigue performance is an important index reflecting the comprehensive performance of the sucker rod. The surface quality, the depth of the hardened layer, and the tensile strength are the key indexes affecting the fatigue performance. On the basis of the routine physical and chemical performance inspection, the fatigue performance test is carried out on the long-term supplying manufacturers by means of regular sampling inspection, which is used as the basis for selecting excellent manufacturers and tender procurement.

[0003] In the structural design of the sucker rod, the anti-fatigue performance of parts such as the rod body, the transition zone, the wrench square, the shoulder, and the thread follows the "barrel principle", that is, the part with the weakest anti-fatigue ability is the most critical factor determining the life of the sucker rod. The surface quality, the depth of the hardened layer, and the tensile strength are the key indexes affecting the fatigue performance. The fatigue performance is the most direct reflection of the comprehensive performance of the sucker rod. Carrying out the evaluation of the fatigue performance of the sucker rod is of great significance for prolonging the service life of the sucker rod, increasing the trouble-free period of the oil well, and realizing cost reduction and efficiency increase.

[0004] Fatigue test parameters: sine wave, tension-tension load, load ratio R = 0.1, test stress 540 MPa, number of cycles 1×10 6 When using type I, couplings are used at both ends to be clamped by the testing machine. When using type II specimens, the rod bodies are directly clamped by the testing machine at both ends. The type II specimen can better illustrate the quality of this batch of sucker rods. However, when conducting the fatigue performance test on the type II specimen, a clamping device is required to clamp the end of the sucker rod. However, due to the complex load conditions at the clamping part of the sucker rod, it often fractures first, rather than the specimen fractures due to fatigue failure, resulting in the failure of the fatigue test.

[0005] Currently, the "tooth-shaped fixture" is used in the fatigue test to clamp the rod body, which destroys the uniformity and continuity of the rod body. The crack sources formed due to local stress concentration are all initiated at the clamping part of the "tooth-shaped fixture" and the rod body surface and the "thick in the middle and thin at both ends" test structure. Due to the external factors of the test, the test is invalid. A total of 79 fatigue tests have been carried out, and 20 effective tests have been carried out, and the success rate is only 25.3%. Summary of the Invention

[0006] The present invention provides a clamping device for a sucker rod fatigue test with a clamping tongs type. This clamp changes the clamping method of the fatigue test, can reduce invalid tests, and improve the success rate of the fatigue test.

[0007] To achieve the above object, the technical solution of the present invention is as follows:

[0008] A clamp-type clamping device for sucker rod fatigue test, which comprises an upper body of the clamping device, a lower body of the clamping device, a clamping bolt and a rotating pin; wherein, one side of the upper body of the clamping device is connected to the lower body of the clamping device through the rotating pin, and the other side is connected through the clamping bolt, and the clamping bolt provides the tightening force required to clamp the sucker rod; a clamping head is also provided at the top of the lower body of the clamping device

[0009] Clamping grooves are provided on the inner surfaces of the upper body of the clamping device and the lower body of the clamping device, and the clamping grooves are cylindrical after the clamping device is closed.

[0010] Further, small cylindrical clamping surfaces are provided on the clamping grooves of the upper body of the clamping device and the lower body of the clamping device. There is a groove between the small cylindrical clamping surfaces, and its diameter is several millimeters smaller than the diameter of the clamped sucker rod. The small cylindrical clamping surfaces provided are arranged oppositely;

[0011] Furthermore, the small cylindrical clamping surfaces provided are arranged staggeredly, that is, the small cylindrical clamping surfaces of the upper body of the clamping device and the lower body of the clamping device are staggeredly arranged after closing, as Figure 4 shown.

[0012] Specifically, a fixing groove is provided on the upper body of the clamping device, and a fixing hole is provided on the lower body of the clamping device; when closed, the bolt passes through the lower body of the clamping device, the upper body of the clamping device and is fixedly connected with a nut.

[0013] A spring washer is also provided between the nut and the upper body of the clamping device.

[0014] The diameter of the small cylindrical clamping surface is 2-5 millimeters smaller than the diameter of the sucker rod, and the length is 1 / 4-1 / 6 of the clamping groove. 3-5 small cylindrical clamping surfaces can be provided

[0015] When arranged oppositely, the number of small cylindrical clamping surfaces on the upper body of the clamping device and the lower body of the clamping device is equal; when arranged staggeredly, the number of small diameter clamping cylindrical surfaces is the same or different.

[0016] Specifically, the small cylindrical clamping surfaces are arranged staggeredly as follows:

[0017] Three small diameter clamping cylindrical surfaces are arranged on the upper body of the clamping device: surface I, surface J, surface K, and two small diameter clamping cylindrical surfaces are arranged on the lower body of the clamping device: surface I, surface J;

[0018] Among them, the I cylindrical surface, J cylindrical surface and K cylindrical surface of the upper body of the clamping device are respectively opposite to the clamping grooves of the lower body of the clamping device;

[0019] The I surface and J cylindrical surface of the lower body of the clamping device are opposite to the clamping grooves of the upper body of the clamping device;

[0020] Furthermore, a cylindrical pin for positioning and centering is also provided between the upper body and the lower body of the clamping device.

[0021] Compared with the prior art, the present invention has the following beneficial effects:

[0022] The clamping device can simultaneously meet the requirements that the sucker rod does not slip when subjected to tensile-tensile loads and that no plastic deformation occurs on the surface of the sucker rod and the clamping device. Using the third or fourth strength theory for verification, according to the theoretical model of clamping the sucker rod on the entire cylindrical surface, it can meet the minimum yield strength of 793 MPa for Class H sucker rods in strength verification. That is, the structure of the clamping device changed from "tooth-type fixture" clamping to "bolt clamping + misaligned cylindrical surface clamping" can meet the clamping requirements of fatigue tests.

[0023] When the clamping part is a small cylindrical surface, its equivalent stress is greater than that of clamping on the entire cylindrical surface, and plastic deformation is more likely to occur. Compared with the entire cylindrical surface as the clamping surface, when the sucker rod is staggered on the small cylindrical surface, the use of misaligned small cylindrical surfaces for clamping makes its deformation present a spiral shape, increasing the friction coefficient and making it easier to clamp. That is, under a smaller pre-tightening force, it can meet the requirements of tightly clamping the sucker rod and no plastic deformation occurs on the clamping device and the sucker rod.

[0024] When clamping with misaligned small cylindrical surfaces, under the condition of unchanged pre-tightening force, a greater frictional force can be obtained, enabling the clamping device to always clamp the sucker rod. Therefore, the pre-tightening force can be appropriately reduced. While meeting the requirement that the clamping device clamps the sucker rod, no plastic deformation occurs on the clamping device and the sucker rod, reducing the occurrence of fractures at the fixture and improving the test success rate.

[0025] Using ANSYS software to establish a finite element analysis model, comparing the finite element and theoretical analysis results, the finite element analysis model of the clamping device is consistent with the force analysis results of theoretical calculations. This clamp-type clamping device for sucker rod fatigue tests can meet the requirements of fatigue test conditions for Class H sucker rods with a diameter of 16 mm to 29 mm. Description of the Drawings

[0026] Figure 1 It is a schematic structural diagram of the present invention.

[0027] Figures 2-1 to 2-2 They are respectively the structural diagram and the exploded view of parts of the present invention.

[0028] Figure 3 It is a three-dimensional structural diagram of the clamping device in the test state.

[0029] Figure 4 It is a schematic diagram of the staggered distribution of small cylindrical surfaces.

[0030] Figure 5 It is a schematic diagram of the clamping principle of the present invention.

[0031] Figure 6 It is a schematic diagram of the mechanical model of the sucker rod during clamping.

[0032] Figure 7 It is a radial load diagram of the clamping part when the sucker rod is clamped on the cylindrical surface.

[0033] Figure 8 It is a schematic diagram of the relative uniform pressure distribution of the small cylindrical surface.

[0034] Figure 9 It is a schematic diagram of the staggered uniform pressure distribution of the small cylindrical surface.

[0035] Figure 10 It is a schematic diagram of the deformation of the sucker rod when it is clamped by the staggered small cylindrical surfaces.

[0036] Figure 11 It is a stress diagram of the entire cylindrical surface as the clamping part.

[0037] Figure 12 It is a relative stress diagram of the small cylindrical surface.

[0038] Figure 13 It is a relative strain diagram of the small cylindrical surface.

[0039] Figure 14 It is a staggered stress diagram of the small cylindrical surface.

[0040] Figure 15 It is a staggered strain diagram of the small cylindrical surface.

[0041] Figure 16 It is the finite element cell division of the clamping device.

[0042] Figure 17 It is the total deformation diagram of the clamping device and the sucker rod.

[0043] Among them, 1 is the upper body of the clamping device, 2 is the cylindrical pin, 3 is the lower body of the clamping device, 4 is the nut, 5 is the spring washer, and 6 is the connecting bolt. Specific implementation mode

[0044] The following further describes the present invention in detail with reference to the attached drawings, which is an explanation rather than a limitation of the present invention.

[0045] See Figures 1 to 3 , a clamp-type clamping device for sucker rod fatigue test, comprising an upper body of the clamping device, a lower body of the clamping device, a clamping bolt and a rotating pin;

[0046] Among them, one side of the upper body of the clamping device is connected to the lower body of the clamping device through a rotating pin, and the other side is connected by a bolt, and the fastening force required for clamping the sucker rod is provided by the bolt connection and fixation;

[0047] The inner surfaces of the upper body and the lower body of the clamping device are both provided with clamping grooves. After the clamping device is closed, the clamping grooves are cylindrical;

[0048] The top of the lower body of the clamping device is also provided with a clamping head for clamping with a testing machine.

[0049] Furthermore, small cylindrical clamping surfaces are opened on the clamping grooves of the upper body and the lower body of the clamping device. There is a groove between the small cylindrical clamping surfaces, and its diameter is several millimeters smaller than the diameter of the sucker rod to be clamped. The opened small cylindrical clamping surfaces are arranged oppositely;

[0050] Even further, the opened small cylindrical clamping surfaces are arranged staggeredly, that is, the small cylindrical clamping surfaces of the upper body and the lower body of the clamping device are staggeredly arranged after closing, as Figure 4 shown.

[0051] Specifically, the upper body of the clamping device is provided with a fixing groove, and the lower body of the clamping device is provided with a fixing hole; when closed, a bolt passes through the lower body of the clamping device, the upper body of the clamping device and is fixedly connected with a nut.

[0052] A spring washer is also provided between the nut and the upper body of the clamping device.

[0053] The diameter of the small cylindrical clamping surface is 2 - 5 millimeters smaller than the diameter of the sucker rod, and the length is 1 / 4 - 1 / 6 of the clamping groove. 3 - 5 small cylindrical clamping surfaces can be provided.

[0054] When arranged oppositely, the number of small cylindrical clamping surfaces of the upper body and the lower body of the clamping device is equal; when arranged staggeredly, the number of small diameter clamping cylindrical surfaces can be the same or different.

[0055] Specifically, the staggered arrangement of the small cylindrical clamping surfaces is as follows:

[0056] Three small diameter clamping cylindrical surfaces are arranged on the upper body of the clamping device: surface I, surface J, and surface K. Two small diameter clamping cylindrical surfaces are arranged on the lower body of the clamping device: surface I and surface J;

[0057] Among them, the I cylindrical surface, J cylindrical surface and K cylindrical surface of the upper body of the clamping device are respectively opposite to the clamping grooves of the lower body of the clamping device;

[0058] The I surface and J cylindrical surface of the lower body of the clamping device are opposite to the clamping grooves of the upper body of the clamping device;

[0059] Furthermore, a cylindrical pin for positioning and centering is also provided between the upper body and the lower body of the clamping device.

[0060] The following gives the mechanical analysis of the clamping device

[0061] The working principle of the clamping device for clamping a sucker rod to perform a tension-tension fatigue experiment is as Figure 5As shown in the figure. The clamping device is mainly divided into two parts: the upper body and the lower body. One end is fixed by a hinge, and the other end is connected by bolts. The sucker rod is clamped by the bolt connection.

[0062] Taking the upper part of the clamping device as the research object, analyze its force condition. Project it on the plane parallel to the cross-section of the sucker rod, and the force is as Figure 6 shown.

[0063] From Figure 6 it can be known that the normal pressure between the clamping device and the clamped part of the sucker rod is:

[0064]

[0065] In the formula:

[0066] N——The normal pressure between the clamping device and the clamped part of the sucker rod;

[0067] F0——The bolt pre-tightening force;

[0068] L j1 ——The distance from the clamping center to the fixed end;

[0069] L j2 ——The distance from the bolt center to the fixed end.

[0070] During the experiment, the clamping device should meet the conditions:

[0071] (1) Clamp the tested sucker rod;

[0072] (2) Neither the surface of the tested sucker rod nor the clamping device can undergo plastic deformation.

[0073] According to the above two requirements, establish mechanical models for the sucker rod and the clamping device respectively for force analysis.

[0074] There are three situations after the sucker rod is clamped: one is that the entire cylindrical surface is the clamped part; the second is that multiple small cylindrical surfaces are formed on the cylindrical surface, with grooves between the small cylindrical surfaces, and the small cylindrical surfaces of the two parts of the clamping device face each other; the third is that the small cylindrical surfaces of the two parts of the clamping tool are staggered. Establish mechanical models based on these three shapes.

[0075] (1) The cylindrical surface is the clamped part

[0076] For the pull-pull fatigue test with bolt pre-tightening, the radial pressure of the sucker rod is evenly distributed along the axial direction, as Figure 7 shown. Its magnitude is:

[0077] F f =fN=fπdLp (2)

[0078] In the formula:

[0079] F f- Friction force between the sucker rod and the clamping device on the cylindrical surface;

[0080] f——friction coefficient of sucker rod;

[0081] d——sucker rod diameter;

[0082] L——clamping part length;

[0083] p——uniform pressure.

[0084] When the friction force is greater than the maximum test load F max , that is, F f ≥F max When the pumping rod is clamped, the uniform pressure is:

[0085]

[0086] Where:

[0087] F max - maximum test load;

[0088] A——cross-sectional area of ​​sucker rod;

[0089] σ zFmax ——Maximum load F in tension-tension fatigue test max Caused stress.

[0090] From the formula, the minimum value of uniform pressure is:

[0091]

[0092] The sucker rod is under two load states: radial uniform load and axial tension. The stresses under these two loads are calculated separately and then superimposed to obtain the total stress.

[0093] 1) Radial uniform load

[0094] The rod body is subjected to radially uniformly distributed loads. The calculation is based on the calculation of a thick-walled cylinder subjected to radially uniformly distributed loads. The stress is:

[0095]

[0096] The axial stress is:

[0097]

[0098] In formula (5) and formula (6):

[0099] σ r —— radial stress;

[0100] σ θ - circumferential stress;

[0101] σ z —— Axial stress;

[0102] μ —— Poisson's ratio;

[0103] p1 —— Internal pressure;

[0104] p2 —— External pressure;

[0105] a —— Minimum radius;

[0106] b —— Maximum radius;

[0107] r —— Radius of any circumference.

[0108] In the formula, for the load state of the sucker rod, there is only external pressure, and the minimum radius is a = 0, then:

[0109]

[0110] In the formula:

[0111] σ za —— Axial stress in the plane stress state;

[0112] σ zb —— Axial stress in the plane strain state.

[0113] 2) Axial tension

[0114] For axial tension, which belongs to the unidirectional stress state, it can be obtained that:

[0115]

[0116] In the formula:

[0117] σ zF —— Stress caused by the pull-pull fatigue test load F;

[0118] F —— Pull-pull fatigue test load.

[0119] The maximum test load F max Under this condition, the maximum axial stress can be obtained as

[0120]

[0121] Therefore, from equations (8) and (9), it can be obtained that:

[0122]

[0123] Substituting each parameter into equation (10), when obtaining the minimum friction force required to clamp the sucker rod under the maximum test load F max The stress is:

[0124]

[0125] According to the fatigue test parameters of sucker rods: tension-tension load, load ratio R = 0.1, stress is 540 MPa, friction coefficient f = 0.1, Poisson's ratio μ = 0.3, clamping length L = 120 mm, diameters: 16 mm, 19 mm, 22 mm, 25 mm, 29 mm, substituting the above data into Equation (11), the stresses of sucker rods with different diameters can be obtained, as shown in Table 1.

[0126] Table 1 Stresses of Sucker Rods with Different Diameters Where the Whole Cylinder is the Clamping Part

[0127]

[0128] According to the working requirements of the clamping device, plastic deformation should not occur while clamping the sucker rod. Therefore, the third or fourth strength theory is used for checking.

[0129] One is from the third strength theory of material mechanics:

[0130] σ r3 = σ1 - σ3 (12)

[0131] In the formula:

[0132] σ r3 —— Equivalent stress;

[0133] σ1 —— The first principal stress;

[0134] σ3 —— The third principal stress.

[0135] Two is from the fourth strength theory of material mechanics:

[0136]

[0137] In the formula:

[0138] σ r4 —— Equivalent stress;

[0139] σ2 —— The second principal stress.

[0140] Since the radial stress σ r and the circumferential stress σ θ are equal, the strength checking results of the third and fourth strength theories are the same, and the checking results are shown in Table 2.

[0141] Table 2 Strength Checking Results When the Sucker Rod is Clamped

[0142]

[0143] According to the strength theory:

[0144] σ r3<[σ s (14)

[0145] In the formula:

[0146] σ s —— Yield strength.

[0147] According to the model of clamping the sucker rod by the whole cylindrical surface, the minimum yield strength of the H-class sucker rod for strength check can be satisfied, which is 793 MPa. That is, the structural design of "bolt clamping + cylindrical surface clamping" can meet the requirements of fatigue test clamping.

[0148] (2) The relative small cylindrical surface

[0149] The distribution of the relative time-averaged pressure on the small cylindrical surface is as Figure 8 shown. At this time, the uniform pressure is located on each small cylindrical surface, and its clamping lengths are L1, L2, L3... etc. Suppose the number of clamping surfaces is n, and the outermost end of the clamped part must be a cylindrical surface. Therefore, the number of grooves is n - 1, and the axial lengths of the cylindrical surface and the grooves are equal.

[0150] The clamping length of each clamping surface is:[[]]

[0151]

[0152] In the formula:

[0153] n—— The number of clamping surfaces;

[0154] L i —— The axial length of each clamping surface.

[0155] At this time, the uniform pressure p is distributed on n small cylindrical surfaces, and the total length of the clamping surface is ∑L i , that is

[0156]

[0157] Substituting each parameter into formula (10), we can get

[0158]

[0159] Substituting the data in Table 2 into the above formula, when n = 3, 4, 5, 6, taking the diameters of 16 mm, 19 mm and 25 mm as examples, the corresponding stresses are shown in Table 3.

[0160] Table 3 Calculated values of the stress of the sucker rod when the small cylindrical surfaces are relative

[0161]

[0162] Checking according to the third strength theory, the results are shown in Table 4.

[0163] Table 4 Checking results when the small cylindrical surfaces are relative

[0164]

[0165] Comparing Table 3 and Table 4, it can be seen that when the clamping part is a small cylindrical surface, its equivalent stress is greater than the clamping on the entire cylindrical surface, and it is more likely to cause plastic deformation. Compared with the clamping surface of the entire cylindrical surface, it is easier to clamp using the relatively small cylindrical surface.

[0166] (3) Small cylindrical surfaces staggered

[0167] The small cylindrical surfaces are staggered, and their uniform pressure distribution is as follows Figure 9 As shown, the clamping part will undergo a spiral-like deformation, such as Figure 10 shown.

[0168] The friction coefficient at this time should be the equivalent friction coefficient, and its magnitude is:

[0169]

[0170] Substituting into (18), we can get:

[0171]

[0172] From formula (19), it can be seen that when the preload force remains unchanged, a larger friction force can be obtained to ensure that the clamping device always clamps the sucker rod. Similarly, the preload force can be appropriately reduced to ensure that the clamping device clamps the sucker rod while neither the clamping device nor the sucker rod undergoes plastic deformation.

[0173] To sum up, when the clamping part is a small cylindrical surface, its equivalent stress is greater than the clamping on the entire cylindrical surface, and it is more likely to undergo plastic deformation. Compared with the clamping surface being the entire cylindrical surface, when the sucker rod is staggered on the small cylindrical surfaces, it is clamped by the mutually staggered small cylindrical surfaces, and its deformation is spiral, which increases the friction coefficient and makes it easier to clamp. That is, under a smaller preload force, the sucker rod can be tightened without plastic deformation of the clamping device and the sucker rod.

[0174] Finite element numerical analysis

[0175] Taking the sucker rod with a diameter of 25 mm as an example, finite element analysis was carried out and the results of finite element and theoretical analysis were compared.

[0176] 1) The entire cylindrical surface is the clamping part

[0177] When the entire cylindrical surface is the clamping part, the finite element analysis model is established using ANSYS software. The finite element analysis stress is as follows: Figure 11 The calculation results are similar to the equivalent stress under plane stress state in Table 4.

[0178] 2) Small cylindrical surface relative to

[0179] When the small cylindrical surface is selected for relative clamping and 5 cylindrical surfaces are clamped, the stress is as shown in Fig. 12. Its calculation result is similar to the equivalent strain in the plane strain state in Table 4, and its strain is as Figure 14 shown.

[0180] 3) Offset of small cylindrical surfaces

[0181] The offset clamping of small cylindrical surfaces means that when the clamping device does not include the two opposite cylindrical surfaces at the ends, the upper half of the clamping device has 3 cylindrical surfaces and the lower half has 2 cylindrical surfaces, and the upper and lower cylindrical surfaces are offset. The stress is as Figure 13 shown, and the strain is as Figure 15 shown, which is similar to the assumption in the theoretical analysis ( Figure 11 ), proving that the theoretical assumption is in line with the actual situation.

[0182] 3.2 Finite element numerical analysis

[0183] Perform finite element analysis on half of the clamping device, establish a finite element analysis model, and the mesh division of the finite element analysis model is as Figure 16 shown.

[0184] According to the established finite element analysis model, obtain the stress and strain values corresponding to the mesh of the finite element analysis model of the clamping device, and calculate the total deformation of the clamping device as Figure 17 shown.

[0185] By comparison, it can be seen that the finite element analysis model of the clamping device provided by the present invention is consistent with the stress analysis result of theoretical calculation. The gripper-type clamping device for the fatigue test of sucker rods can meet the fatigue test working condition requirements of sucker rods of 16 mm to 29 mm H grade with "tension-tension load, sine wave, load ratio R = 0.1, test stress 540 MPa".

[0186] Experimental use effect

[0187] The gripper-type fatigue test clamping device has been cumulatively applied to carry out 7 fatigue tests. Among them, 5 tests were successful, and the success rate was 71.4%. The success rate of the test was increased by 46.1% compared with the "threaded fixture" test, and the test achieved good application effects. At the same time, for the 2 invalid tests, the uniformity and continuity of the rod body at the clamping part did not change. It is analyzed that the main reasons for the invalid test are the defects in the rod body at the clamping part or the poor coaxiality of the samples. Due to the short application time, the test effect needs to be further verified and evaluated by tests.

Claims

1. A clamping device for sucker rod fatigue test by means of a gripper, characterized in that It consists of the upper body of the clamping device, the lower body of the clamping device, the clamping bolt and the rotating pin. Among them, one side of the upper body of the clamping device is connected to the lower body of the clamping device through the rotating pin, and the other side is connected through the clamping bolt, and the clamping bolt provides the tightening force required to clamp the sucker rod. A clamping head is also provided at the top of the lower body of the clamping device. Clamping grooves are provided on the inner surfaces of the upper body of the clamping device and the lower body of the clamping device. After the clamping device is closed, the clamping grooves are cylindrical. Small cylindrical clamping surfaces are provided on the clamping grooves of the upper body of the clamping device and the lower body of the clamping device. There is a groove between the small cylindrical clamping surfaces, and its diameter is several millimeters smaller than the diameter of the sucker rod to be clamped. The provided small cylindrical clamping surfaces are arranged oppositely. The provided small cylindrical clamping surfaces are arranged staggeredly. After the upper body of the clamping device and the lower body of the clamping device are closed, the small cylindrical clamping surfaces are arranged staggeredly. A fixing groove is provided on the upper body of the clamping device, and a fixing hole is provided on the lower body of the clamping device. When closed, the clamping bolt passes through the lower body of the clamping device, the upper body of the clamping device and is fixedly connected with the nut.

2. The clamp-type holding device for sucker rod fatigue test according to claim 1, wherein A spring washer is also provided between the nut and the upper body of the clamping device.

3. The clamp-type gripping device for sucker rod fatigue test according to claim 1, wherein, The diameter of the small cylindrical clamping surface is 2-5 millimeters smaller than the diameter of the sucker rod, and the length is 1 / 4-1 / 6 of the clamping groove. 3-5 small cylindrical clamping surfaces are provided. When arranged oppositely, the number of small cylindrical clamping surfaces on the upper body of the clamping device and the lower body of the clamping device is equal; when arranged staggeredly, the number of small-diameter clamping cylindrical surfaces is the same or different.

4. The clamp-type gripping device for sucker rod fatigue test according to claim 3, characterized in that, The staggered arrangement of the small cylindrical clamping surfaces is as follows: Three small-diameter clamping cylindrical surfaces are arranged on the upper body of the clamping device: surface I, surface J, and surface K, and two small-diameter clamping cylindrical surfaces are arranged on the lower body of the clamping device: surface I and surface J. Among them, the I cylindrical surface, J cylindrical surface and K cylindrical surface of the upper body of the clamping device are respectively opposite to the clamping groove of the lower body of the clamping device. The I surface and J cylindrical surface of the lower body of the clamping device are opposite to the clamping groove of the upper body of the clamping device.

5. The clamp-type holding device for sucker rod fatigue test according to claim 1, wherein A cylindrical pin for positioning and centering is also provided between the upper body of the clamping device and the lower body of the clamping device.

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