Fatigue specimen, fixture and test method for laser drilling of a power transmission tower

Abstract

This application provides a fatigue specimen, fixture, and testing method for laser drilling of transmission towers. The specimen includes a gauge length, which comprises a first wall and a second wall opposite to each other. The width of the first wall is the same as the width of the second wall. The distance between the first and second walls is the thickness of the gauge length, which is t. This invention has the following advantages: the specimen dimensions, drilling process, and stress state are consistent with the actual structure of the transmission tower, which can truly reflect the fatigue characteristics of the plate material under the combined effects of heat-affected zone, residual stress, and hole wall morphology. The test results can be directly used for tower structural strength verification, fatigue life prediction, and safety design, greatly improving the accuracy and reliability of engineering evaluation.

Description

Technical Field

[0001] This application relates to the field of power equipment technology, and in particular to a fatigue specimen, fixture and testing method for laser drilling of transmission towers. Background Technology

[0002] Currently, no dedicated fatigue test specimens have been found specifically designed for perforated transmission tower materials. In fatigue performance testing of laser-perforated transmission tower materials, the industry currently employs two alternative technologies: one is to directly use bone-shaped, non-perforated specimens, adding bolt holes consistent with the actual tower material in their gauge length section using laser perforation, and then using them for fatigue testing; the other is to simply enlarge the specimen size and add bolt holes based on the dimensions of a standard specimen.

[0003] However, the existing perforated fatigue test specimen schemes mentioned above simply involve opening holes or enlarging the size on standard specimens without matching the design based on the tower material thickness, bolt hole diameter, and stress characteristics. The proportions of the gauge length, transition arc, and clamping section of the specimen are unreasonable, and the hole center, cross-sectional width, and thickness do not match the actual engineering situation. This results in the stress distribution, crack initiation location, and failure mode all deviating from the actual failure behavior of the tower, and the test data are not representative of the engineering. Summary of the Invention

[0004] The summary section introduces a series of simplified concepts, which will be further explained in detail in the detailed description section. This part of the invention is not intended to limit the key features and essential technical features of the claimed technical solution, nor is it intended to determine the scope of protection of the claimed technical solution.

[0005] The present invention aims to solve at least one of the technical problems existing in the prior art or related art.

[0006] Therefore, a first aspect of the present invention provides a fatigue specimen for laser drilling of transmission towers, the specimen comprising: The gauge length segment includes a first sample wall and a second sample wall arranged opposite to each other. The width of the first sample wall is the same as the width of the second sample wall. The distance between the first sample wall and the second sample wall is the thickness of the gauge length segment, which is t. A laser-drilled hole is formed at a preset position along the thickness direction of the gauge length segment. The diameter of the laser-drilled hole is d. The length of the gauge length segment is Lp = 3t, and the width of the gauge length segment is B = 3d. The transition section has a first end connected to the gauge length section. The transition section includes a first transition surface and a second transition surface. The first end of the first transition surface is connected to the first wall surface of the sample, and the first end of the second transition surface is connected to the second wall surface of the sample. The radius of the arc of the first transition surface and the second transition surface is R, and R≥2t. The clamping section is connected to the second end of the transition section. The clamping section includes a clamping first wall surface and a clamping second wall surface. The first end of the clamping first wall surface is connected to the second end of the first transition surface, and the first end of the clamping second wall surface is connected to the second end of the second transition surface. The width of the clamping first wall surface and the clamping second wall surface is the same as the width of the first wall surface of the sample. The thickness between the first end of the clamping first wall surface and the first end of the clamping second wall surface is W1, and W1 ≥ 1.5t. The thickness between the second end of the clamping first wall surface and the second end of the clamping second wall surface is W2, and W2 > W1.

[0007] Optionally, W2 = W1 + 20mm.

[0008] Optionally, the length of the clamping section is 35mm-45mm.

[0009] Optionally, the gauge section, transition section, and clamping section are all made of structural steel commonly used in power transmission towers.

[0010] A second aspect of the present invention provides a fixture for a fatigue specimen used in laser drilling of transmission towers as described in the first aspect, the fixture being disposed on both sides of the specimen, the fixture comprising: First clamp body; The second clamp body, the first clamp body and the second clamp body are symmetrically arranged on the clamping section, and are used to clamp and fix the clamping section; A positioning plug is disposed on the first clamp body and the second clamp body, and is used to coaxially position and laterally limit the first clamp body and the second clamp body.

[0011] Optionally, the first clamp body includes: A first positioning segment, wherein a first positioning hole is provided on the first positioning segment; A first connecting segment, wherein a first end of the first connecting segment is connected to the first positioning segment, and the first connecting segment and the first positioning segment are set at an angle; The first fixing segment is connected to the second end of the first connecting segment, and the inner surface of the first fixing segment matches the clamping first wall surface.

[0012] Optionally, the second clamp body includes: The second positioning section has a second positioning hole. The second connecting segment has its first end connected to the second positioning segment, and the second connecting segment and the second positioning segment are set at an angle; The second fixing section is connected to the second end of the second connecting section, and the inner surface of the second fixing section matches the clamping second wall surface.

[0013] Optionally, the positioning plug is disposed within the first positioning hole and the second positioning hole, and matches the first positioning hole and the second positioning hole.

[0014] The third aspect of this application provides a method for testing the fatigue performance of laser-drilled perforated plates for power transmission towers, employing the fatigue specimens for laser-drilled power transmission towers described in the first aspect and the fixtures for the fatigue specimens for laser-drilled power transmission towers described in the second aspect, and includes the following steps: S1. Sample preparation: First, use an electrical discharge wire cutting machine to cut out the overall outline of the sample according to the design drawings. Then, use a laser to make a laser hole at a preset position in the gauge length section. After the laser hole is made, remove the burrs from the hole edge and the sample surface and clean it. S2. Assembly and positioning: The sample is assembled inside the first fixture body and the second fixture body, and the positioning plug is inserted into the first positioning hole and the second positioning hole to achieve coaxial positioning and lateral limitation. S3. Loading test: The clamped sample is clamped in a fatigue testing machine. The fatigue testing machine applies an axial alternating load to the sample to perform fatigue performance testing by clamping and fixing it with the fixture. The failure is determined by the expansion of fatigue cracks at the edge of the laser-drilled hole to fracture or the load dropping to a set threshold. The corresponding number of fatigue cycles is recorded.

[0015] Optionally, the axial alternating load is a sinusoidal alternating load with a stress ratio R=0.1.

[0016] Compared with the prior art, the present invention has at least the following beneficial effects: the size, hole-making process and stress state of the sample of this application are consistent with the actual structure of the power transmission tower, which can truly reflect the fatigue characteristics of the plate under the combined action of factors such as heat-affected zone, residual stress and hole wall morphology. The test results can be directly used for the strength verification of the tower structure, fatigue life prediction and safety design, which greatly improves the accuracy and credibility of the engineering evaluation.

[0017] The above description is merely an overview of the technical solution of the present invention. In order to better understand the technical means of the present invention and to implement it in accordance with the contents of the specification, and in order to make the above and other objects, features and advantages of the present invention more apparent and understandable, specific embodiments of the present invention are described below. Attached Figure Description

[0018] Various other advantages and benefits will become apparent to those skilled in the art upon reading the following detailed description of preferred embodiments. The accompanying drawings are for illustrative purposes only and are not intended to limit the scope of this application. Furthermore, the same reference numerals denote the same parts throughout the drawings. In the drawings: Figure 1 The three-dimensional structural diagram provided in this application; Figure 2 The first fixture body structure diagram provided in this application; Figure 3 The second fixture body structure diagram provided in this application; Figure 4 This is a diagram showing the connection structure between the fixture and the sample provided in this application; Figure 5 The side view of the specimen provided in this application; Figure 6 The top view of the sample provided in this application; Figure 7 Side view of the second clamp body provided in this application; Figure 8 The flowchart provided for this application.

[0019] The correspondence between the reference numerals and the component names is as follows: 1. Specimen; 11. Gauge length section; 111. First wall surface of specimen; 112. Second wall surface of specimen; 113. Laser-drilled hole; 12. Transition section; 121. First transition surface; 122. Second transition surface; 13. Clamping section; 131. Clamping first wall surface; 132. Clamping second wall surface; 2. Fixture; 21. First fixture body; 211. First positioning section; 212. First connecting section; 213. First fixing section; 22. Second fixture body; 221. Second positioning section; 222. Second connecting section; 223. Second fixing section; 23. Positioning plug. Detailed Implementation

[0020] The following description provides numerous specific details to offer a more thorough understanding of the technical solutions provided by this invention. However, it will be apparent to those skilled in the art that the technical solutions provided by this invention can be implemented without one or more of these details.

[0021] It should be noted that the terminology used herein is for the purpose of describing particular embodiments only and is not intended to limit the scope of exemplary embodiments according to the invention. As used herein, the singular form is intended to include the plural form as well, unless the context clearly indicates otherwise. Furthermore, it should be understood that when the terms “comprising” and / or “including” are used in this specification, they indicate the presence of the stated features, integrals, steps, operations, elements, and / or components, but do not exclude the presence or addition of one or more other features, integrals, steps, operations, elements, components, and / or combinations thereof.

[0022] Exemplary embodiments according to the present invention will now be described in more detail with reference to the accompanying drawings. However, these exemplary embodiments may be implemented in many different forms and should not be construed as being limited to the embodiments set forth herein. It should be understood that these embodiments are provided so that the disclosure of the invention is thorough and complete, and that the concept of these exemplary embodiments is fully conveyed to those skilled in the art.

[0023] As the core load-bearing structure of power transmission lines, the safe operation of existing transmission towers directly affects the stability of the power grid. Currently, angle steel towers account for approximately 84% of the total number of towers, mainly relying on bolt connections for formation. Therefore, the processing quality of bolt holes is crucial. Traditional hole-making methods mainly involve punching and mechanical drilling: punching is efficient but only suitable for thin plates, and is prone to defects such as radial cracks and warping; while drilling can meet the precision requirements of thick plates, it has low processing efficiency, high cost, and insufficient flexibility, making it difficult to meet the diverse, large-scale, and high-efficiency demands of tower manufacturing.

[0024] Laser drilling and laser cutting offer advantages such as non-contact operation, high efficiency, high flexibility, and wide material adaptability, and have been initially applied in tower fabrication. However, due to the limitations of the current standard GB / T2694-2018, mechanical drilling is still mandatory for thick plates and critical wiring holes. The main reason for this is that laser processing is a thermal process, which forms a hardened layer (including a recast layer and a heat-affected zone) at the hole edge and introduces residual stress. If the process is not properly controlled, problems such as inclined cut surfaces, slag buildup, and high surface roughness can easily occur, thereby reducing the tensile strength and fatigue performance of the perforated components and posing a threat to the safety of the tower's service life. Therefore, it is necessary to accurately assess the fatigue life of laser-drilled perforated tower materials through professional fatigue testing to provide a safety basis for their engineering applications.

[0025] Currently, axial force controlled fatigue testing of metallic materials follows the national standard GB / T3075-2021 "Methods for Axial Force Control in Fatigue Testing of Metallic Materials". This standard specifies that plate fatigue specimens should have a bone-like, non-porous structure and explicitly states that "fatigue specimen designs that may rely on threads are not recommended". If standard bone-like specimens are directly modified to add bolt holes, stress concentration at the hole locations will cause the specimen fracture location to deviate from the failure zone of the tower material in actual engineering, and the test data cannot accurately reflect the impact of laser-drilled bolt holes on the fatigue performance of the tower material.

[0026] Currently, no dedicated fatigue test specimens have been found specifically designed for perforated transmission tower materials. In fatigue performance testing of laser-drilled transmission tower materials, the industry currently employs two alternative technical solutions: one is to directly use the bone-shaped, non-perforated specimens specified in GB / T3075-2021, adding bolt holes consistent with the actual tower material in its gauge length section using laser drilling technology, and then using the processed specimens for fatigue testing; the other is to simply enlarge the specimen size and add bolt holes, referring to the size proportions of the standard specimen.

[0027] However, the existing perforated fatigue test specimen designs simply involve drilling holes or enlarging the dimensions on standard specimens without considering the tower material thickness, bolt hole diameter, and stress characteristics. The proportions of the gauge length, transition arc, and clamping section are unreasonable, and the hole center, cross-sectional width, and thickness do not match actual engineering conditions. This results in stress distribution, crack initiation locations, and failure modes deviating from the actual failure behavior of the tower, making the test data unrepresentative in engineering applications. Due to the lack of dedicated perforated specimens, fatigue performance testing of laser-perforated tower materials lacks a reliable test platform, making fatigue life assessment difficult and severely restricting the large-scale application of laser processing technology in transmission line tower construction.

[0028] Combined with appendix Figure 1 , 5 As shown in Figure 6, a fatigue specimen for laser drilling of transmission towers is provided according to a first aspect embodiment of this application, wherein the specimen 1 comprises: The gauge length segment 11 includes a first sample wall 111 and a second sample wall 112 arranged opposite to each other. The width of the first sample wall 111 is the same as the width of the second sample wall 112. The distance between the first sample wall 111 and the second sample wall 112 is the thickness of the gauge length segment 11, and the thickness of the gauge length segment 11 is t. A laser-drilled hole 113 is formed at a preset position along its thickness direction in the gauge length segment 11. The diameter of the laser-drilled hole 113 is d. The length of the gauge length segment 11 is Lp=3t, and the width of the gauge length segment 11 is B=3d. Transition segment 12, the first end of which is connected to the gauge length segment 11, the transition segment 12 includes a first transition surface 121 and a second transition surface 122, the first end of the first transition surface 121 is connected to the first wall surface 111 of the sample, the first end of the second transition surface 122 is connected to the second wall surface 112 of the sample, and the radius of the arc of the first transition surface 121 and the second transition surface 122 is R, and R≥2t; The clamping section 13 is connected to the second end of the transition section 12. The clamping section 13 includes a clamping first wall surface 131 and a clamping second wall surface 132. The first end of the clamping first wall surface 131 is connected to the second end of the first transition surface 121, and the first end of the clamping second wall surface 132 is connected to the second end of the second transition surface 122. The width of the clamping first wall surface 131 and the clamping second wall surface 132 is the same as the width of the first wall surface 111 of the sample. The thickness between the first end of the clamping first wall surface 131 and the first end of the clamping second wall surface 132 is W1, and W1 ≥ 1.5t. The thickness between the second end of the clamping first wall surface 131 and the second end of the clamping second wall surface 132 is W2, and W2 > W1.

[0029] The specimen 1 provided in this embodiment includes a gauge length section 11, a transition section 12, and a clamping section 13. The gauge length section 11 is the main structure for testing, comprising a first wall surface 111 and a second wall surface 112 of the specimen arranged relatively parallel to each other. Both have the same width to ensure uniform cross-sectional dimensions of the gauge length section 11 and avoid local stress concentration. The distance between the first wall surface 111 and the second wall surface 112 of the specimen is the thickness t of the gauge length section 11. A laser-drilled hole 113 is opened along the thickness direction at a preset position of the gauge length section 11, which is the geometric center position. The diameter of the laser-drilled hole 113 is d. The length Lp of the gauge length section 11 is 3t, and the width B of the gauge length section 11 is 3d. The gauge length section 11 obtained through the above-mentioned size ratio corresponds to the actual dimensions of the tower material of the power transmission tower. Therefore, the test results obtained are more realistic.

[0030] The transition section 12 is used to connect the gauge length section 11 and the clamping section 13 to avoid stress abrupt changes at the junction of the two sections. The transition section 12 includes a first transition surface 121 and a second transition surface 122. The first end of the first transition surface 121 is connected to the first wall surface 111 of the specimen, and the first end of the second transition surface 122 is connected to the second wall surface 112 of the specimen. At the same time, both the first transition surface 121 and the second transition surface 122 are circular arc transitions with a radius R ≥ 2t, which effectively eliminates stress concentration in the transition section 12 and prevents the specimen 1 from fractured prematurely in the transition section 12 during the fatigue test.

[0031] The clamping section 13 is connected to the second end of the transition section 12 and is used to cooperate with the fixture 2 to clamp the sample 1. The clamping section 13 includes a clamping first wall surface 131 and a clamping second wall surface 132 arranged opposite to each other. The first end of the clamping first wall surface 131 is connected to the second end of the first transition surface 121, and the first end of the clamping second wall surface 132 is connected to the second end of the second transition surface 122. The width of the clamping first wall surface 131 and the clamping second wall surface 132 is the same as the width of the first wall surface 111 of the sample, which is B. Therefore, the width of the clamping section 13 is consistent with that of the transition section 12 and the gauge length section 11, reducing stress concentration at the connection. The first end of the clamping first wall surface 131 is connected to the second end of the first transition surface 12. The thickness between the first end of the clamping second wall 132 is W1, and W1≥1.5t. The thickness between the second end of the clamping first wall 131 and the second end of the clamping second wall 132 is W2, and W2>W1. Therefore, the width of the end of the clamping section 13 away from the transition section 12 is greater than the width of the end of the clamping section 13 connected to the transition section 12, which facilitates the clamping fixture to clamp and fix the clamping section 13, further realizing the fixation of the sample 1, adapting to the clamping requirements of the fixture 2, ensuring that the clamping is firm and without loosening, and improving the accuracy of the test results.

[0032] It is understandable that by using the thickness t of the gauge segment 11 of sample 1 as the baseline variable and designing the width 3d of sample 1 in a uniform proportion, it can cover iron tower plates of different thicknesses and apertures, thereby achieving standardization and universality of testing.

[0033] The dimensions, hole-making process, and stress state of the sample 1 in this application are consistent with the actual structure of the power transmission tower. It can truly reflect the fatigue characteristics of the plate under the combined effects of factors such as heat-affected zone, residual stress, and hole wall morphology of the laser-drilled hole 113. The test results can be directly used for the strength verification of the tower structure, fatigue life prediction, and safety design, which greatly improves the accuracy and credibility of the engineering evaluation.

[0034] In some embodiments of this application, W2 = W1 + 20mm.

[0035] In this technical solution, the width of the end of the clamping segment 13 away from the transition segment 12 is greater than the width of the end where the clamping segment 13 connects to the transition segment 12. Specifically, the width of the end of the clamping segment 13 away from the transition segment 12 is greater than the width of the end where the clamping segment 13 connects to the transition segment 12 by more than 20 mm. This makes the width of the end where the clamping segment 13 connects to the transition segment 12 gradually increase towards the end where the clamping segment 13 is away from the transition segment 12, which facilitates the clamping fixture 2 to clamp and fix it.

[0036] In some embodiments of this application, the length of the clamping segment 13 is 35mm-45mm.

[0037] In this technical solution, the length of the clamping section 1313 is 35mm-45mm, specifically, the length of the clamping section 13 is 40mm, which more accurately restores the size of the sample 1.

[0038] In some embodiments of this application, the gauge section 11, the transition section 12 and the clamping section 13 are all made of structural steel commonly used in power transmission towers.

[0039] In this technical solution, the gauge length section 11, transition section 12 and clamping section 13 are all made of structural steel commonly used in power transmission towers. They are standard structural steels widely used in the manufacturing process of power transmission towers in the industry. Their material composition and mechanical properties are completely matched with the tower materials actually used to build power transmission towers. This can effectively avoid the distortion of fatigue performance test data caused by the inconsistency between the material of sample 1 and the actual tower material in the project, and ensure the accuracy of the test results.

[0040] Combined with appendix Figure 2 , 3 As shown in Figures 4 and 7, a second aspect of this application provides a fixture for a fatigue specimen used in laser drilling of transmission towers as provided in the first aspect embodiment. The fixture 2 is disposed on both sides of the specimen 1, and the fixture 2 includes: First clamp body 21; The second clamp body 22, the first clamp body 21 and the second clamp body 22 are symmetrically arranged on the clamping section 13, and are used to clamp and fix the clamping section 13; Positioning plug 23 is disposed on the first clamp body 21 and the second clamp body 22, and is used to coaxially position and laterally limit the first clamp body 21 and the second clamp body 22.

[0041] In this technical solution, there are two clamps 2, which clamp the clamping section 13 from both sides of the sample 1. Each clamp 2 includes a first clamp body 21 and a second clamp body 22. The first clamp body 21 and the second clamp body 22 cooperate to clamp and fix the clamping section 13 at one end of the sample 1. After the clamping section 13 is clamped and fixed by the first clamp body 21 and the second clamp body 22, the positioning plug 23 passes through the first clamp body 21 and the second clamp body 22 simultaneously, so that the first clamp body 21 and the second clamp body 22 are coaxially positioned, ensuring that they are symmetrically clamped on both sides of the sample 1, and the force is uniform. This can eliminate eccentric loads, additional bending moments and lateral sway, so that the stress distribution is uniform, the loading is stable and controllable, effectively reduce the dispersion of test data, and greatly improve the repeatability, consistency and stability of fatigue test results, meeting the requirements of high-precision testing.

[0042] Understandably, by fixing the first fixture body 21 and the second fixture body 22 with the positioning plug 23, there is no need for repeated centering and adjustment. The clamping steps are simplified and the operation is convenient, which shortens the clamping time of the sample 1. It can realize continuous batch testing, improve the overall test efficiency, and is especially suitable for process comparison, batch sampling inspection and engineering testing.

[0043] It is understandable that the first clamp body 21, the second clamp body 22 and the positioning plug 23 are all made of TC4 titanium alloy material, which has high rigidity, high wear resistance and fatigue deformation resistance. It maintains dimensional accuracy and positioning stability under long-term alternating load, can be reused and does not reduce the reliability of the test.

[0044] In some embodiments of this application, the first clamp body 21 includes: The first positioning segment 211 has a first positioning hole; The first connecting segment 212 has a first end connected to the first positioning segment 211, and the first connecting segment 212 and the first positioning segment 211 are set at an angle. The first fixing segment 213 is connected to the second end of the first connecting segment 212, and the inner surface of the first fixing segment 213 matches the clamping first wall surface 131.

[0045] The second clamp body 22 includes: The second positioning segment 221 has a second positioning hole. The second connecting segment 222 has a first end connected to the second positioning segment 221, and the second connecting segment 222 and the second positioning segment 221 are set at an angle. The second fixing segment 223 is connected to the second end of the second connecting segment 222, and the inner surface of the second fixing segment 223 matches the clamping second wall surface 132.

[0046] In this technical solution, the first clamp body 21 includes a first positioning section 211, a first connecting section 212, and a first fixing section 213; the second clamp body 22 includes a second positioning section 221, a second connecting section 222, and a second fixing section 223, and is symmetrically arranged with the first clamp body 2121.

[0047] The first positioning section 211 has a first positioning hole, and the second positioning section 221 has a second positioning hole. After the first clamp body 21 and the second clamp body 22 are installed on the sample 1, the first positioning hole matches the second positioning hole. At this time, the positioning plug 23 can be inserted into the first positioning hole and the second positioning hole, which can realize the positioning and lateral limitation of the clamped first clamp body 21 and the second clamp body 22, ensuring that the clamped first clamp body 21, the second clamp body 22 and the sample 1 are coaxial, so that there is no eccentricity and no lateral shaking during the force loading process. The first connecting segment 212 is angled to the first positioning segment 211, specifically, the first connecting segment 212 and the first positioning segment 211 are perpendicularly connected. The second segment of the first connecting segment 212 is connected to the first fixing segment 213. The second connecting segment 222 is angled to the second positioning segment 221, specifically, the second connecting segment 222 and the second positioning segment 221 are perpendicularly connected. The second end of the second connecting segment 222 is connected to the second fixing segment 223. After the first clamp body 21 and the second clamp body 22 are installed, the first connecting segment 212, the first fixing segment 213, the second connecting segment 222, and the first positioning segment 211 are angled to each other. The two fixed sections 223 form clamping cavities that match the two sides of the clamping section 13. The internal structures of the first connecting section 212 and the second connecting section 222 match the end face of the clamping section 13 away from the gauge section 11. The inner surface of the first fixed section 213 is completely matched with the shape and size of the clamping first wall 131. The inner surface of the second fixed section 223 is completely matched with the shape and size of the clamping second wall 132. After fitting together, a stable clamping is achieved, preventing the sample 1 from loosening under alternating loads, ensuring that the sample 1 is subjected to uniform force and accurate positioning during fatigue testing, and improving the clamping stability during the testing process.

[0048] In some embodiments of this application, the positioning plug 23 is disposed in the first positioning hole and the second positioning hole, and matches the first positioning hole and the second positioning hole.

[0049] In this technical solution, after the first clamp body 21 and the second clamp body 22 are installed, the positioning plug 23 can be inserted into the first positioning hole and the second positioning hole. The size of the positioning plug 23 matches the size of the first positioning hole and the second positioning hole, which can realize the positioning and lateral limitation of the clamped first clamp body 21 and the second clamp body 22, ensuring that the clamped first clamp body 21, the second clamp body 22 and the sample 1 are coaxial, so that there is no eccentricity and no lateral shaking during the force loading process.

[0050] It is understandable that the diameter of the first positioning hole and the second positioning hole are both 8mm and the height is both 9mm. Therefore, the diameter of the positioning plug 23 is 8mm and the height is 18mm.

[0051] Combined with appendix Figure 1-8As shown, the third aspect of this application provides a method for testing the fatigue performance of laser-drilled perforated plates for power transmission towers. It employs the fatigue specimen provided in the first aspect embodiment and the fixture for the fatigue specimen used in laser-drilled plates for power transmission towers provided in the second aspect embodiment, and includes the following steps: S1. Sample 1 preparation: First, use an electrical discharge wire cutting machine to cut out the overall outline of the sample 1 according to the design drawings. Then, use a laser to make a laser hole 113 at the preset position of the gauge section 11. After the laser hole 113 is completed, remove the hole edge and the burrs on the surface of the sample 1 and clean it.

[0052] S2. Assembly and positioning: The sample 1 is assembled inside the first clamp body 21 and the second clamp body 22. The positioning plug 23 is inserted into the first positioning hole and the second positioning hole to achieve coaxial positioning and lateral limiting.

[0053] S3. Loading test: The clamped specimen 1 is clamped in the fatigue testing machine. The specimen 1 is clamped and fixed by the fixture 2. The fatigue testing machine applies an axial alternating load to the specimen 1 to perform fatigue performance testing. The failure judgment is based on the expansion of fatigue cracks at the edge of the laser-drilled hole 113 to fracture or the load dropping to a set threshold. The corresponding number of fatigue cycles is recorded.

[0054] In some embodiments of this application, the axial alternating load is a sinusoidal alternating load with a stress ratio R=0.1.

[0055] The process is as follows: Fatigue specimen 1 is made of structural steel plate commonly used in power transmission towers. Preparation includes: cutting the overall outline of specimen 1 using an electrical discharge wire cutting machine; using a laser to create laser holes 113 at corresponding positions in the gauge length section 11 of specimen 1; removing burrs and surface impurities from the hole edges after drilling to ensure specimen 1 is free of initial defects; and ensuring that the dimensions of each part of specimen 1 conform to the following design and are suitable for the actual use requirements of the power transmission tower, wherein the thickness t of the gauge length section 11 is selected from commonly used tower material specifications of 12mm, 14mm, 16mm, and 18mm, the length lp of the gauge length section 11 is 3t, and the diameter d of the laser-drilled hole 113 adopts a commonly used thread for power transmission towers. The hole diameters are 17.5mm, 21.5mm, and 25.5mm. The width of the gauge length section 11 is set to B=3d. The transition section 12 adopts an arc transition design with an arc radius r not less than 2t to effectively eliminate stress concentration in the transition section 12 and avoid premature fracture of the sample 1 during fatigue testing. The length of the clamping section 13 is uniformly set to 40mm. The thickness between the first end of the clamping first wall surface 131 and the first end of the clamping second wall surface 132 is W1, and W1≥1.5t. The thickness between the second end of the clamping first wall surface 131 and the second end of the clamping second wall surface 132 is W2, and W2=W1+20mm. The fixture 2 is made of TC4 titanium alloy, which has high rigidity, high wear resistance, and fatigue deformation resistance. It can be reused for a long time without reducing positioning accuracy. Its overall size is closely fitted with the clamping section 13 of the sample 1 to ensure stable clamping without gaps, avoiding tilting or loosening during clamping. The length L of the fixture 2 is adaptively adjusted according to the thickness between the second end of the first clamping wall 131 and the second end of the second clamping wall 132, and satisfies the relationship L=W2 / 2+11. The fixture 2 has a first positioning hole and a second positioning hole with a diameter of 8mm, which are used to cooperate with the positioning plug 23 to realize the positioning constraint of the fixture 2 and the sample 1 and ensure positioning accuracy. The positioning plug 23 is made of TC4 titanium alloy, which is the same material as the fixture 2 to ensure structural stability and durability. The positioning plug 23 is a cylindrical structure with a diameter of 8mm and a height of 18mm, which can realize the rapid positioning and limiting of the fixture 2. During testing, the prepared fatigue specimen 1 is first assembled inside the fixture 2. The positioning plug 23 is inserted into the fixture 2 to achieve rapid coaxial positioning and lateral limitation of the specimen 1 and the fixture 2, ensuring that there is no relative displacement or eccentricity between the two. Then, the assembled fixture 2 and specimen 1 are clamped together in the fatigue testing machine and the clamping position is adjusted to ensure that the loading axis is consistent with the axis of specimen 1. Subsequently, an axial alternating load is applied to specimen 1 to carry out fatigue performance testing. During the test, it is ensured that the failure location of specimen 1 is concentrated in the hole area of ​​gauge length 11. The final test results can truly reflect the fatigue performance and failure characteristics of the laser-drilled hole plate 113 under actual engineering conditions.

[0056] Example 1 In this embodiment, the gauge length 11 of sample 1 has a thickness t of 16 mm, a length lp = 3t = 48 mm, a laser-drilled hole 113 has a diameter d = 21.5 mm, a width 3d = 64.5 mm, and the radius r of the arc of the first transition surface 121 and the second transition surface 122 in the transition section 12 is ≥ 2t = 32 mm. The clamping section 13 has a length of 40 mm and a width of 64.5 mm. The thickness between the first end of the clamping first wall surface 131 and the first end of the clamping second wall surface 132 in the clamping section 13 is W1 = 24 mm, and the thickness between the second end of the clamping first wall surface 131 and the second end of the clamping second wall surface 132 is W2 = W1 + 20 mm = 44 mm. Sample 1 is cut into shape using an electrical discharge wire cutting machine, and laser drilling is performed at the center of the gauge length 11. The laser-drilled hole 113 is then removed, and burrs on the hole edge and sample 1 surface are cleaned. The fixture 2 is made of TC4 titanium alloy. The length of the fixture 2 is calculated as L=W2 / 2+11=33mm based on the thickness W2 between the second end of the first clamping wall 131 and the second end of the second clamping wall 132. The positioning plug 23 is a TC4 titanium alloy cylinder with a diameter of 8mm and a height of 18mm. During testing, the sample 1 is first loaded into the fixture 2, and the positioning plug 23 is inserted to achieve rapid positioning and coaxial constraint. Then, the assembled fixture 2 is clamped onto the axial fatigue testing machine. The test is conducted using a sinusoidal alternating load with a stress ratio of R=0.1. The failure is determined by the expansion of fatigue cracks at the edge of the laser-drilled hole 113 on the sample 1 to fracture or the load dropping to a set threshold. The corresponding number of fatigue cycles is recorded.

[0057] Example 2 In this embodiment, the gauge length 11 of sample 1 has a thickness t of 18 mm, a length lp = 3t = 54 mm, a laser-drilled hole 113 has a diameter d = 17.5 mm, a width of 3d = 52.5 mm, and an arc radius r ≥ 2t = 36 mm for the first transition surface 121 and the second transition surface 122 in the transition section 12. The clamping section 13 has a length of 40 mm and a width of 52.5 mm. The thickness between the first end of the clamping first wall surface 131 and the first end of the clamping second wall surface 132 in the clamping section 13 is W1 = 27 mm, and the thickness between the second end of the clamping first wall surface 131 and the second end of the clamping second wall surface 132 is W2 = W1 + 20 mm = 47 mm. Sample 1 is cut into shape using an electrical discharge wire cutting machine, and a laser-drilled hole 11 is made at the center of the gauge length 11. 3. After the hole is made, remove the burrs from the hole edge and the surface of the sample 1 and clean it. The fixture 2 is made of TC4 titanium alloy. The length of the fixture 2 is calculated as L=W2 / 2+11=47 / 2+11=34.5mm based on the thickness W2 between the second end of the first clamping wall 131 and the second end of the second clamping wall 132. The positioning plug 23 is a TC4 titanium alloy cylinder with a diameter of 8mm and a height of 18mm. During the test, the sample 1 is first loaded into the fixture 2, and the positioning plug 23 is inserted to achieve rapid positioning and coaxial constraint. Then, the assembled fixture 2 is clamped as a whole into the axial fatigue testing machine. The test is carried out using sinusoidal alternating load. The stress ratio is set to R=0.1. The failure judgment is based on the expansion of fatigue cracks at the edge of the laser-made hole 113 on the sample 1 to fracture or the load dropping to the set threshold. The corresponding number of fatigue cycles is recorded.

[0058] In this invention, the terms "first," "second," and "third" are used for descriptive purposes only and should not be construed as indicating or implying relative importance; the term "multiple" refers to two or more unless otherwise explicitly defined. The terms "install," "connect," "link," and "fix" should be interpreted broadly. For example, "connect" can be a fixed connection, a detachable connection, or an integral connection; "link" can be a direct connection or an indirect connection through an intermediate medium. Those skilled in the art can understand the specific meaning of the above terms in this invention according to the specific circumstances.

[0059] In the description of this invention, it should be understood that the terms "upper," "lower," "left," "right," "front," "rear," etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are only for the convenience of describing this invention and simplifying the description, and do not indicate or imply that the device or unit referred to must have a specific orientation or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on this invention.

[0060] In the description of this specification, the terms "one embodiment," "some embodiments," "specific embodiment," etc., refer to a specific feature, structure, material, or characteristic described in connection with that embodiment or example, which is included in at least one embodiment or example of the present invention. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples.

[0061] The above are merely preferred embodiments of the present invention and are not intended to limit the present invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A fatigue test specimen for laser drilling of a power transmission tower, characterized by, The sample (1) comprises: The gauge length segment (11) includes a first sample wall (111) and a second sample wall (112) arranged opposite to each other. The width of the first sample wall (111) is the same as the width of the second sample wall (112). The distance between the first sample wall (111) and the second sample wall (112) is the thickness of the gauge length segment (11). The thickness of the gauge length segment (11) is t. A laser-drilled hole (113) is opened at a preset position along its thickness direction in the gauge length segment (11). The diameter of the laser-drilled hole (113) is d. The length of the gauge length segment (11) is Lp=3t, and the width of the gauge length segment (11) is B=3d. The transition section (12) is connected at its first end to the gauge length section (11). The transition section (12) includes a first transition surface (121) and a second transition surface (122). The first end of the first transition surface (121) is connected to the first wall surface (111) of the sample, and the first end of the second transition surface (122) is connected to the second wall surface (112) of the sample. The radius of the arc of the first transition surface (121) and the second transition surface (122) is R, and R≥2t. The clamping section (13) is connected to the second end of the transition section (12). The clamping section (13) includes a clamping first wall surface (131) and a clamping second wall surface (132). The first end of the clamping first wall surface (131) is connected to the second end of the first transition surface (121). The first end of the clamping second wall surface (132) is connected to the second end of the second transition surface (122). The width of the clamping first wall surface (131) and the clamping second wall surface (132) is the same as the width of the first wall surface (111) of the sample. The thickness between the first end of the clamping first wall surface (131) and the first end of the clamping second wall surface (132) is W1, and W1≥1.5t. The thickness between the second end of the clamping first wall surface (131) and the second end of the clamping second wall surface (132) is W2, and W2>W1.

2. The fatigue specimen for laser drilling of transmission towers according to claim 1, characterized in that, The W2 = W1 + 20mm.

3. The fatigue specimen for laser drilling of transmission towers according to claim 2, characterized in that, The length of the clamping section (13) is 35mm-45mm.

4. The fatigue specimen for laser drilling of transmission towers according to claim 3, characterized in that, The gauge section (11), transition section (12) and clamping section (13) are all made of structural steel commonly used in power transmission towers.

5. A fixture for fatigue specimens used in laser drilling of transmission towers according to any one of claims 1-4, characterized in that, The clamps (2) are disposed on both sides of the sample (1), and the clamps (2) include: First clamp body (21); The second clamp body (22) is symmetrically arranged on the clamping section (13) with the first clamp body (21) and the second clamp body (22) for clamping and fixing the clamping section (13); Positioning plug (23) is disposed on the first clamp body (21) and the second clamp body (22) for coaxial positioning and lateral limiting of the first clamp body (21) and the second clamp body (22).

6. The fixture for fatigue specimens used in laser drilling of transmission towers according to claim 5, characterized in that, The first clamp body (21) includes: The first positioning segment (211) has a first positioning hole. A first connecting segment (212) is provided, wherein the first end of the first connecting segment (212) is connected to the first positioning segment (211), and the first connecting segment (212) and the first positioning segment (211) are set at an angle. The first fixed segment (213) is connected to the second end of the first connecting segment (212), and the inner surface of the first fixed segment (213) matches the clamping first wall surface (131).

7. The fixture for fatigue specimens used in laser drilling of transmission towers according to claim 5, characterized in that, The second clamp body (22) includes: The second positioning section (221) has a second positioning hole. The second connecting segment (222) has its first end connected to the second positioning segment (221), and the second connecting segment (222) and the second positioning segment (221) are set at an angle. The second fixing segment (223) is connected to the second end of the second connecting segment (222), and the inner surface of the second fixing segment (223) matches the clamping second wall surface (132).

8. The fixture for fatigue specimens used in laser drilling of transmission towers according to claim 5, characterized in that, The positioning plug (23) is disposed in the first positioning hole and the second positioning hole, and matches the first positioning hole and the second positioning hole.

9. A method for testing the fatigue performance of laser-drilled perforated plates for power transmission towers, characterized in that, The fixture for the fatigue specimen as described in any one of claims 1-4 and the fatigue specimen for laser drilling of transmission towers as described in any one of claims 5-8 includes the following steps: S1. Sample (1) preparation: First, use an electric wire cutting machine to cut out the overall outline of the sample (1) according to the design drawings. Then, use a laser to make a laser hole (113) at the preset position of the gauge length section (11). After the laser hole (113) is completed, remove the hole edge and the burrs on the surface of the sample (1) and clean it. S2, Assembly and Positioning: The sample (1) is assembled inside the first fixture body (21) and the second fixture body (22), and the positioning plug (23) is inserted into the first positioning hole and the second positioning hole to achieve coaxial positioning and lateral limiting; S3. Loading test: The clamped specimen (1) is clamped in the fatigue testing machine. The fatigue testing machine applies an axial alternating load to the specimen (1) to perform fatigue performance testing. The failure determination is based on the expansion of fatigue cracks at the edge of the laser-drilled hole (113) to fracture or the load dropping to a set threshold. The corresponding number of fatigue cycles is recorded.

10. The fatigue performance testing method for laser-drilled perforated plates in power transmission towers according to claim 9, characterized in that, The axial alternating load is a sinusoidal alternating load with a stress ratio R=0.1.

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