Method and apparatus for determining the structural fatigue s-n curve of a magnetic pole lead

Abstract

The application discloses a kind of determination method and device of structural fatigue S-N curve of magnetic pole lead, it is related to generator technical field, method includes the following steps: S1. preparation and the same chamfer R of the magnetic pole lead to be detected has and can be used to simulate test magnetic pole lead "L" shape test piece;S2. the hotspot stress σ hs Of chamfer position of "L" shape test piece is obtained;S3. the structural hotspot stress amplitude Δσ of "L" shape test piece is calculated;S4. the fatigue life of "L" shape test piece is obtained;S5. the hotspot stress amplitude-fatigue life relationship curve of "L" shape test piece, i.e. the fatigue S-N curve of the structure of the magnetic pole lead to be measured, can be directly used for fatigue calculation, without correction, the fatigue behavior of "L" shape test piece corresponding magnetic pole lead can be accurately and reliably evaluated prediction, in addition, determination device can be used to detect the necessary parameters mentioned in the foregoing method.

Description

Technical Field

[0001] This invention relates to the field of generator technology, and specifically to a method and apparatus for determining the structural fatigue SN curve of magnetic pole leads. Background Technology

[0002] The magnetic pole leads are a critical component of the generator. They connect to the magnetic pole connecting wires, linking the rotor magnetic pole coils to form the rotor windings. Pumped storage power station generators frequently switch between generator and pumping modes. The high head and high generator speed of the power station result in high stress and numerous cycle counts at the chamfer radius (R) of the magnetic pole leads, making these areas highly susceptible to fatigue failure. As the first batch of domestically produced pumped storage units have accumulated operating time, fatigue failure of the magnetic pole leads has gradually emerged, severely impacting the normal operation of pumped storage power station generators and causing significant economic losses. Therefore, accurate and reliable life prediction of the fatigue behavior of the magnetic pole lead structure is necessary, along with corresponding structural optimization design to improve its fatigue life.

[0003] Existing structural fatigue analysis methods generally rely on the stress-strain response of critical locations obtained from finite element analysis, combined with standard material fatigue SN curves, and introduce correction coefficients that consider stress concentration, surface condition, size effect, and safety factors to obtain the structural SN curve for calculating fatigue life. However, the determination of these correction coefficients is largely empirical, and different structures require different correction coefficients, resulting in low accuracy and reliability of the structural fatigue SN curve obtained by correcting the material fatigue SN curve. Furthermore, the magnetic pole lead material is copper plate, which undergoes a bending process to obtain an "L"-shaped magnetic pole lead configuration. During the bending process, significant plastic deformation occurs at the chamfer of the "L"-shaped magnetic pole lead, leading to the formation of micro-initial cracks and high processing stress in local materials. The material properties at the chamfer of the magnetic pole lead differ significantly from those of standard copper material without bending deformation. Therefore, the fatigue life calculation results of the lead structure obtained by correcting the structural SN curve using the standard copper material fatigue SN curve differ significantly from the actual operating life of the current power plant magnetic pole leads, making the test results unreliable for accurately and reliably providing reference value for the fatigue life assessment of generator magnetic pole leads. Summary of the Invention

[0004] The purpose of this invention is to provide a device and method for measuring the structural fatigue SN curve of magnetic pole leads, thereby solving the problems of inaccurate structural SN curves obtained by correcting material fatigue SN curves in existing fatigue analysis, which cannot reflect the local material property inhomogeneity.

[0005] This invention is achieved through the following technical solution: A method for determining the structural fatigue SN curve of a magnetic pole lead includes the following steps: S1. Prepare an "L"-shaped test piece with the same chamfer R as the magnetic pole lead to be tested. During the fatigue life test, the chamfer R of the "L"-shaped test piece will be the first to crack. S2. Select monitoring points along the horizontal distance from the point of maximum stress at the center of the chamfer on the "L"-shaped test specimen. Obtain the strain changes at each monitoring point using a dynamic strain gauge. Calculate the hot spot stress σ at the chamfer position of the "L"-shaped test specimen based on the strain at the monitoring points. hs ; S3. Based on step S2, calculate the structural hot spot stress amplitude Δσ of the "L"-shaped test specimen; S4. The fatigue life of the "L"-shaped test piece is obtained by conducting a fatigue test on the "L"-shaped test piece using a fatigue testing machine; S5. Fit the hot spot stress amplitude and fatigue life data of all “L”-shaped test pieces to obtain the hot spot stress amplitude-fatigue life relationship curve of the “L”-shaped test piece, which is the fatigue SN curve of the magnetic pole lead structure to be tested.

[0006] Furthermore, in step S1, the method for obtaining the "L"-shaped test piece is as follows: an "L"-shaped test piece is prepared using the same material and the same manufacturing process as the magnetic pole lead to be tested. The "L"-shaped test piece is an "L"-shaped structural model with the same chamfer R as the magnetic pole lead to be tested. The "L"-shaped test piece sequentially includes a vertical section with a reduction segment, a chamfer R segment, a horizontally reduced straight segment, and a horizontal segment. The transition between the reduced and unreduced parts of the vertical section, and between the horizontally reduced straight segment and the horizontal segment, are all circular arc transitions. The width of the chamfer R segment is d, the radius of the chamfer R segment is r, the length of the horizontally reduced straight segment is L, and the width of the horizontal segment is D. The structure of the "L"-shaped test piece satisfies the following relationships (I) and (II): d / D≤0.6 (I); L / r≥2 (II).

[0007] Furthermore, the vertical section of the "L"-shaped test piece is provided with fixing holes for fixing the test piece.

[0008] Furthermore, in step S2, strain gauges are arranged horizontally at three monitoring points on the "L"-shaped test piece at horizontal distances of 0.4t, 0.9t, and 1.4t from the point of maximum stress at the center of the chamfer, respectively. Here, t is the plate thickness. The strain changes at these locations during loading are measured using a dynamic strain gauge, and the hot spot stress at the chamfer location is calculated based on the strain at the three monitoring points. σ hs =2.52σ 0.4t -2.24σ 0.9t +0.72σ 1.4t (III) σ 0.4t =E•ε 0.4t ;σ 0.9t =E•ε 0.9t ;σ 1.4t =E•ε 1.4t ; (IV) Where, σ hs It is the hot spot stress of the structure, σ 0.4t σ 0.9t σ 1.4t Let ε represent the stress at three monitoring points located at horizontal distances of 0.4t, 0.9t, and 1.4t from the point of maximum stress at the center of the chamfer on the test specimen. 0.4t , ε 0.9t , ε 1.4t These represent the strains at the three monitoring points measured, and E is the elastic modulus of the material.

[0009] Furthermore, in step S4, the method for obtaining the fatigue life of the "L"-shaped test piece is as follows: The "L"-shaped test piece includes a vertical section and a horizontal section. The vertical section of the "L"-shaped test piece is fixed on the clamping fixture of the fatigue testing machine, and the horizontal section is placed at the gap between the upper and lower rollers of the double roller clamp connected to the actuator of the fatigue testing machine. The fatigue testing machine applies displacement loads to the double roller clamp by moving up and down, and records the vertical displacement and load data of the roller clamp during the test simultaneously. The loading is stopped when the maximum vertical compressive load in the cycle decreases by 20% compared with the initial maximum vertical compressive load in the first cycle. At this time, obvious cracks are generated at the chamfer of the specimen, and the number of cycles at the time of stopping is recorded as the fatigue life.

[0010] Furthermore, in step S4, when testing the fatigue life of the "L"-shaped test piece, multiple identical "L"-shaped test pieces are taken and repeated under the same displacement amplitude; at the same time, the set displacement amplitude is changed to obtain the corresponding fatigue data under multiple displacement amplitudes.

[0011] Furthermore, in step S5, the structural fatigue SN curve of the magnetic pole lead can be expressed by the following formula: Δσ m N = C (V); Where Δσ is the hot spot stress amplitude, N is the fatigue life, and m and C are material parameters that can be obtained by nonlinear fitting based on fatigue test data.

[0012] A measuring device for obtaining the strain signal-to-strain (SN) curve of the aforementioned structure includes a testing machine frame, a load sensor for measuring the load on the testing machine, a displacement actuator for applying vertical displacement, a double-roller clamp, a strain gauge for measuring the strain at the monitoring point of the "L"-shaped test piece as described in claim 1, a fixed bracket for fixing the "L"-shaped test piece to the testing machine frame, a fixing bolt connecting the "L"-shaped test piece and the fixed bracket, and a strain measuring device for acquiring strain signals. The fixed bracket is fixed to the testing machine frame and has horizontally threaded holes for fixing the "L"-shaped test piece. Bolts are passed through the fixing holes of the "L"-shaped test piece and screwed into the corresponding threaded holes of the fixed bracket. Tightening the bolts fixes the "L"-shaped test piece to the bracket.

[0013] Furthermore, the double-roller clamp is a clamp with upper and lower rollers that can rotate freely, applying a vertical load to the "L"-shaped test piece. The double-roller clamp is used to apply a vertical displacement load to the test piece. This clamp has two freely rotating rollers, avoiding horizontal constraints. The distance between the upper and lower rollers is slightly larger than the thickness of the test piece, and they are connected as a whole by fixing plates on both sides. The upper end of the fixing plate is connected to a round rod, which is connected to the actuator of the testing machine via threads.

[0014] Strain gauges were placed at three monitoring points. The strain gauges were placed horizontally at distances of 0.4t, 0.9t, and 1.4t (t is the plate thickness) from the point of maximum stress at the center of the chamfer. The strain gauges were used to measure the stress at the monitoring points and to calculate the hot spot stress at the chamfer of the structure.

[0015] The strain measurement device includes a multi-channel dynamic strain gauge, a computer, and corresponding strain data acquisition software. It can continuously collect strain data at three monitoring points during the test at certain time intervals, and then use the collected strain data to calculate data such as hot spot stress and hot spot stress amplitude.

[0016] The aforementioned measuring device includes a displacement actuator connected to the fatigue testing machine. During the test, the fatigue testing machine applies a set cyclic displacement to the test piece through a double roller clamp and simultaneously collects load, displacement, and strain data. The obtained data is then used to obtain the hot spot stress amplitude-fatigue life relationship curve of the "L"-shaped test piece according to the aforementioned steps, which is the fatigue SN curve of the magnetic pole lead structure to be tested.

[0017] Compared with the prior art, the present invention has the following advantages and beneficial effects: 1) In this invention, an "L"-shaped test piece model with the same configuration as the magnetic pole lead to be tested is first established. The fatigue SN curve of the magnetic pole lead to be tested is obtained by acquiring the fatigue SN curve of the "L"-shaped test piece model. This solves the problem that the actual magnetic pole lead structure is too large to be directly tested for fatigue life. The "L"-shaped test piece model uses the same materials and manufacturing process as the magnetic pole lead to be tested, and its structure is optimized to have the same chamfer R as the magnetic pole lead to be tested. During fatigue life testing, the test piece is guaranteed to crack first at the chamfer R, thus reflecting the influence of actual manufacturing processes, small initial cracks after bending, residual stress, and other factors on the structural life to the greatest extent. The resulting structural fatigue SN curve of the "L"-shaped test piece can be directly used for fatigue calculation without correction, enabling accurate and reliable evaluation and prediction of the fatigue behavior of the magnetic pole lead corresponding to the "L"-shaped test piece.

[0018] 2) In this invention, the device for measuring the fatigue SN curve of the structure can apply cyclic displacement load to the "L"-shaped test piece that is consistent with the actual magnetic pole lead configuration, and measure the stress at three monitoring points to calculate the hot spot stress of the dangerous part of the structure.

[0019] 3) In this invention, the device for measuring the structural fatigue SN curve adopts a double roller clamp, that is, a double roller clamp in which the upper and lower rollers can rotate freely. By changing the vertical displacement of the upper and lower rollers, different loads can be applied, which can avoid the generation of horizontal constraint forces and affect the accuracy of the test. Attached Figure Description

[0020] Figure 1 This is a schematic diagram of the structure of the device for measuring the structural fatigue SN curve of an "L"-shaped test piece.

[0021] Figure 2 This is a three-dimensional structural diagram of the "L"-shaped test piece in this invention.

[0022] Figure 3 yes Figure 2 A schematic diagram of the structure of other observation surfaces of the "L"-shaped test piece.

[0023] Figure 4 This refers to the patching position of the strain gauge in this embodiment of the invention.

[0024] Figure 5 This is the structural fatigue SN curve of the magnetic pole leads obtained in Example 1. Data points marked with "→" indicate that the test piece reached 60,000 cycles without failure, at which point the test was stopped.

[0025] Figure 6This is a flowchart of the method for determining the structural fatigue SN curve of the magnetic pole leads in this invention.

[0026] The components include: 1. Testing machine frame; 2. Load sensor; 3. Displacement actuator; 4. Double roller clamp; 5. "L" shaped test piece; 6. Strain gauge; 7. Fixing bolt; 8. Fixing bracket; 9. Strain measuring device; 5.1 Vertical section; 5.2 Chamfered R section; 5.3 Horizontal reduced straight section; 5.4 Horizontal section; 5.5 Fixing hole. Detailed Implementation

[0027] The present invention will be further described in detail below with reference to embodiments, but the implementation of the present invention is not limited thereto.

[0028] Example 1: This embodiment takes the testing of the magnetic pole leads of a certain model of generator of our company as an example, and measures the fatigue SN curve of the magnetic pole lead structure to further illustrate this solution.

[0029] like Figure 1 The diagram shows the structural fatigue SN curve determination device used in this invention. Specifically, it includes a testing machine frame 1, a load sensor 2 for measuring the testing machine load, a displacement actuator 3 for applying vertical displacement, a double-roller clamp 4, a strain gauge 6 for measuring the strain at the monitoring point of the "L"-shaped test piece 5, a fixing bracket 8 for fixing the "L"-shaped test piece 5 to the testing machine frame 1, fixing bolts 7 connecting the "L"-shaped test piece 5 and the fixing bracket 8, and a strain measurement device 9 for acquiring strain signals. The testing machine frame 1, load sensor 2, and displacement actuator 3 are built into the testing machine, and their function is to apply a vertical displacement load to the test piece and simultaneously measure the vertical load. The double-roller clamp 4 includes two freely rotatable rollers, the distance between which is slightly larger than the thickness of the test piece. These rollers are connected as a whole by fixing plates on both sides. The upper end of the fixing plate is connected to a round rod, which is threaded to the testing machine actuator.

[0030] In this scheme, an "L"-shaped test specimen 5 model with the same configuration as the magnetic pole lead to be tested is first established. The fatigue SN curve of the magnetic pole lead to be tested is obtained by acquiring the fatigue SN curve of the "L"-shaped test specimen 5 model. This solves the problem that the actual magnetic pole lead structure to be tested is too large, making it impossible to directly perform fatigue life testing on the magnetic pole lead. In this invention, the established "L"-shaped test specimen 5 model uses the same materials and manufacturing process as the magnetic pole lead to be tested, and its structure is optimized so that the "L"-shaped test specimen 5 model has the same chamfer R as the magnetic pole lead to be tested. During fatigue life testing, it is ensured that the test specimen first cracks at the chamfer R, thus reflecting to the greatest extent the influence of actual manufacturing process, small initial cracks after bending, residual stress, and other factors on the structural life. The obtained structural fatigue SN curve of the "L"-shaped test specimen 5 can be directly used for fatigue calculation without correction.

[0031] The specific structure and dimensions of the "L"-shaped test piece 5 are referenced below. Figure 2 , 3 The chamfer radius of the "L"-shaped test piece 5 is 6mm. The "L"-shaped test piece 5 includes a vertical section 5.1 with a reduction segment, a chamfered R segment 5.2, a horizontally reduced straight section 5.3, and a horizontal section 5.4. The transition between the reduced and unreduced portions of the vertical section 5.1, and between the horizontally reduced straight section 5.3 and the horizontal section 5.4, is an arc transition. The width of the chamfered R segment 5.2 is d, and the radius of the chamfered R segment 5.2 is r. The length of the horizontally reduced straight section 5.3 is L, and the width of the horizontal section 5.4 is D. The structure of the "L"-shaped test piece 5 satisfies the following relationships (I) and (II): d / D≤0.6 (I); L / r≥2 (II).

[0032] Furthermore, a fixing hole 5.5 for fixing the test piece is provided on the vertical section 5.1 of the “L”-shaped test piece 5. The fixing hole 5.5 has a diameter of 13mm. The horizontal section 5.4 of the “L”-shaped test piece 5 is placed in the gap between the upper and lower rollers of the double roller clamp 4. The “L”-shaped test piece 5 is fixed to the fixing bracket 8 by passing an M12 bolt through the fixing hole 5.5. The fixing bracket 8 is fixed to the column of the test machine frame 1 by bolts. Near the chamfer, three strain gauges 6 are attached to measure the stress at the monitoring point. The attachment positions of these three strain gauges 6 are shown in Figure 4. These three strain gauges 6 are connected to the strain measuring device 9 through wires. The strain measuring device 9 consists of a dynamic strain gauge, data acquisition software and a computer. It can measure the strain at the monitoring point of the three strain gauges 6, and then calculate the structural hot spot stress of the test piece under a given displacement load according to the hot spot stress calculation formula in the IIW (International Institute of Welding) standard.

[0033] In this embodiment, the method for determining the structural fatigue SN curve of the magnetic pole lead is referenced. Figure 6 This includes the following steps: 1) Prepare an "L"-shaped test piece 5 with the same chamfer R as the magnetic pole lead to be tested. During fatigue life testing, cracks first appear at the chamfer R of the "L"-shaped test piece 5. The structure of the "L"-shaped test piece 5 is referenced. Figure 2 , 3 ; 2) Three strain gauges 6 are attached and fixed horizontally at distances of 0.4t, 0.9t and 1.4t (t is the plate thickness) from the point of maximum stress in the middle of the chamfer of the specimen, and the strain gauges 6 are connected to the three strain measurement channels of the dynamic strain gauge through wires. 3) Place the horizontal section 5.4 of the test piece after the strain gauge 6 is attached into the gap between the upper and lower rollers of the double roller clamp 4. Adjust the position of the double roller clamp 4 so that the fixing hole 5.5 of the vertical section 5.1 of the test piece is aligned with the threaded hole on the fixed bracket 8. Then, use an M12 bolt to pass through the fixing hole 5.5 of the test piece and fix the test piece on the fixed bracket 8 of the test machine column. 4) In the control software of the testing machine, set the maximum and minimum values ​​of the cyclic displacement load, the waveform as a sine wave, the test temperature as room temperature, and the test frequency as 0.1Hz; start the test, apply the set displacement cyclic load, and simultaneously collect the displacement, load, and strain values ​​at three measuring points of the specimen during the process; stop loading when the maximum value of the compressive load in the cycle drops to 80% of the maximum value of the compressive load in the first cycle, and record the number of cycles at this time as the fatigue life of the test piece, marked as "failure"; if the cycle reaches 60,000 times and the load does not drop to 80% of the maximum value of the compressive load in the first cycle, also stop the test, and record the fatigue life of the test piece as 60,000 times (corresponding to the number of cycles for 30 years of service of the actual structure), marked as "not failed", indicating that the test piece meets the requirement of 30 years of service under this condition; 5) Repeat steps 2)-4) at the same displacement amplitude to conduct fatigue tests on three test pieces and obtain the corresponding fatigue data; change the set displacement amplitude and repeat steps 2)-6) to conduct fatigue tests on three test pieces at another displacement amplitude and obtain the corresponding fatigue data. In this embodiment, fatigue tests were conducted at four displacement amplitudes within the fatigue life range of 4000-60000 cycles, and the specific loading conditions are shown in Table 1.

[0034] Table 1 Loading conditions for fatigue tests.

[0035] 6) Based on the hot spot stress calculation formula in the IIW (International Institute of Welding) standard, the hot spot stress at the chamfer position of the test specimen is calculated from the strain at three monitoring points on the specimen: σ hs =2.52σ 0.4t -2.24σ 0.9t +0.72σ 1.4t (III) σ 0.4t =E•ε 0.4t ;σ 0.9t =E•ε 0.9t ;σ 1.4t =E•ε 1.4t (IV) Where, σ hs It is the hot spot stress of the structure; σ 0.4t σ 0.9t σ 1.4t Let ε represent the stress at three monitoring points located at horizontal distances of 0.4t, 0.9t, and 1.4t (t being the plate thickness) from the center of the chamfer of the test piece. 0.4t , ε 0.9t , ε 1.4t The values ​​represent the strains at the three monitoring points measured, and E represents the elastic modulus of the material. The structural hot spot stress amplitude at each displacement amplitude is taken as the average of the hot spot stress amplitudes of the three test specimens.

[0036] 7) Based on the hot spot stress amplitude and fatigue life data of all test pieces, obtain the hot spot stress amplitude-fatigue fatigue life relationship curve of the test piece, that is, the structural fatigue SN curve of the magnetic pole lead. For this embodiment, the obtained structural fatigue SN curve of the magnetic pole lead is as follows: Figure 4 As shown. That is, the structural fatigue SN curve of this magnetic pole lead can be expressed by the following formula: Δσ m N=C (V), Where Δσ is the hot spot stress amplitude, N is the fatigue life, and m and C are material parameters, which can be obtained by nonlinear fitting based on fatigue test data. For this embodiment, m=3.671 and C=10 are obtained. 13.050 .

[0037] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention in any way. Any simple modifications or equivalent changes made to the above embodiments based on the technical essence of the present invention shall fall within the protection scope of the present invention.

Claims

1. A method for determining the structural fatigue SN curve of a magnetic pole lead, characterized in that, Includes the following steps: S1. Prepare an "L"-shaped test piece (5) with the same chamfer R as the magnetic pole lead to be tested. During the fatigue life test, the "L"-shaped test piece (5) will first develop cracks at the chamfer R of the "L"-shaped test piece (5). The method for obtaining the "L"-shaped test piece (5) is as follows: The "L"-shaped test piece (5) is made of the same material and the same manufacturing process as the magnetic pole lead to be tested. The "L"-shaped test piece (5) is an "L"-shaped structural model with the same chamfer R as the magnetic pole lead to be tested. The "L"-shaped test piece (5) includes a vertical section (5.1) with a reduction section, a chamfer R section (5.2), a horizontally reduced straight section (5.3), and a horizontal section (5.4) in sequence. The reduction and non-reduction parts of the vertical section (5.1) and the horizontally reduced straight section (5.3) and the horizontal section (5.4) are all circular arc transitions. The width of the chamfer R section (5.2) is d, the radius of the chamfer R section (5.2) is r, the length of the horizontally reduced straight section (5.3) is L, and the width of the horizontal section (5.4) is D. The structure of the "L"-shaped test piece (5) satisfies the following relationships (I) and (II): d / D≤0.6(I); L / r≥2(II); S2. Select monitoring points on the "L"-shaped test piece (5) at the horizontal distance from the point of maximum stress at the center of the chamfer. Obtain the strain changes at each monitoring point using a dynamic strain gauge. Calculate the hot spot stress σ at the chamfer position of the "L"-shaped test piece (5) based on the strain at the monitoring points. hs ; In this step, strain gauges (6) are arranged horizontally at three monitoring points on the "L"-shaped test piece (5) at horizontal distances of 0.4t, 0.9t, and 1.4t from the point of maximum stress at the center of its chamfer, respectively. t is the plate thickness. The strain changes at these locations during loading are measured using a dynamic strain gauge, and the hot spot stress at the chamfer location of the test piece is calculated based on the strain at the three monitoring points. s hs =2.52σ 0.4t -2.24s 0.9t +0.72σ 1.4t (III), s 0.4t =E•e 0.4t ;s 0.9t =E•e 0.9t ;s 1.4t =E•e 1.4t ;(IV), Where, σ hs It is the hot spot stress of the structure, σ 0.4t σ 0.9t σ 1.4t Let ε represent the stress at three monitoring points located at horizontal distances of 0.4t, 0.9t, and 1.4t from the point of maximum stress at the center of the chamfer on the test specimen. 0.4t , ε 0.9t , ε 1.4t These represent the strains at the three monitoring points measured, and E is the elastic modulus of the material. S3. Based on step S2, calculate the structural hot spot stress amplitude Δσ of the "L"-shaped test piece (5); S4. The fatigue life of the "L"-shaped test piece (5) is obtained by conducting a fatigue test on the "L"-shaped test piece (5) using a fatigue testing machine; S5. Fit the hot spot stress amplitude and fatigue life data of all "L" shaped test pieces (5) to obtain the hot spot stress amplitude-fatigue life relationship curve of the "L" shaped test piece (5), which is the fatigue SN curve of the magnetic pole lead structure to be tested.

2. The method for determining the structural fatigue SN curve of a magnetic pole lead according to claim 1, characterized in that: The vertical section (5.1) of the "L"-shaped test piece (5) is provided with a fixing hole (5.5) for fixing the test piece.

3. The method for determining the structural fatigue SN curve of a magnetic pole lead according to claim 1, characterized in that, In step S4, the method for obtaining the fatigue life of the "L"-shaped test piece (5) is as follows: the "L"-shaped test piece (5) includes a vertical section (5.1) and a horizontal section (5.4). The vertical section (5.1) of the "L"-shaped test piece is fixed on the clamping fixture of the fatigue testing machine, and the horizontal section (5.4) is placed at the gap between the upper and lower rollers of the double roller clamp (4) connected to the actuator of the fatigue testing machine. The fatigue testing machine applies displacement loads of up and down movement to the double roller clamp (4), and records the vertical displacement and load data of the roller clamp during the test simultaneously. The loading was stopped when the maximum vertical compressive load in the cycle decreased by 20% compared to the initial maximum vertical compressive load in the first cycle. At this point, obvious cracks appeared at the chamfer of the specimen, and the number of cycles at which the loading stopped was recorded as the fatigue life.

4. The method for determining the structural fatigue SN curve of a magnetic pole lead according to claim 3, characterized in that, In step S4, when testing the fatigue life of the "L"-shaped test piece (5), multiple identical "L"-shaped test pieces (5) are taken and repeated under the same displacement amplitude; at the same time, the set displacement amplitude is changed to obtain the corresponding fatigue data under multiple displacement amplitudes.

5. The method for determining the structural fatigue SN curve of a magnetic pole lead structure according to claim 4, characterized in that, In step S5, the structural fatigue SN curve of the magnetic pole lead is obtained, and this fatigue curve can be expressed by the following formula: Board m N=C(V); Where Δσ is the hot spot stress amplitude, N is the fatigue life, and m and C are material parameters that can be obtained by nonlinear fitting based on fatigue test data.

6. A measuring device for obtaining the fatigue SN curve of the structure as described in claim 1, characterized in that: It includes a testing machine frame (1), a load sensor (2) for measuring the load of the testing machine, a displacement actuator (3) for applying vertical displacement, a double roller clamp (4), a strain gauge (6) for measuring the strain at the monitoring point of the "L"-shaped test piece (5) as claimed in claim 1, a fixed bracket (8) for fixing the "L"-shaped test piece (5) to the testing machine frame (1), a fixing bolt (7) for connecting the "L"-shaped test piece (5) and the fixed bracket (8), and a strain measuring device (9) for collecting strain signals.

7. The measuring device according to claim 6, characterized in that: The double roller clamp (4) is a double roller clamp (4) in which the upper and lower rollers can rotate freely, and the vertical load is applied to the "L" shaped test piece (5) through the double roller clamp (4).

Images