A method for regulating residual stress of a wind turbine rotor shaft

Abstract

The application discloses a wind power generator rotating shaft residual stress regulation method, comprising the following steps: S1, identifying the dangerous section of the rotating shaft, and marking the dangerous section according to stress concentration coefficients; S2, adopting an ultrasonic surface rolling device to perform rolling treatment on the dangerous section; S3, after the ultrasonic rolling is completed, performing laser shock peening treatment on the high stress area, and extending the treatment to the adjacent middle stress area; S4, performing multi-point residual stress detection on the dangerous section after the treatment. The stress partition of the dangerous section of the rotating shaft and the partition strengthening treatment are adopted, the ultrasonic surface rolling and the laser shock peening are respectively implemented in different partitions, the strengthening parameters are matched with the stress concentration degrees of the regions, and a spatial continuous residual compressive stress field is constructed, so that the gradient distribution of the residual stress in the surface layer and the depth direction and the smooth transition of the residual stress in the axial and circumferential directions are realized.

Description

Technical Field

[0001] This invention relates to the field of wind turbine shafts, and more particularly to a method for controlling residual stress in wind turbine shafts. Background Technology

[0002] As wind power equipment develops towards higher power and longer lifespan, the wind turbine shaft, as a key load-bearing component that withstands complex alternating loads, directly affects the safe operation of the entire machine. Especially in direct-drive wind turbines, the shaft typically has a large diameter, long dimensions, and multiple structural transitions. During operation, it must withstand the coupled effects of bending, torsional loads, and random wind impacts for extended periods, making it highly susceptible to fatigue damage in stress concentration areas.

[0003] In existing technologies, the critical sections of shafts are mainly concentrated at geometrically discontinuous locations such as the shoulder transition fillet and the bottom of the keyway. These areas often become preferential sites for fatigue crack initiation due to significant stress concentration effects. To improve the fatigue resistance of shafts, surface strengthening processes are typically used to treat these areas, such as shot peening, rolling, or laser shock peening. These processes introduce residual compressive stress into the material surface to delay crack initiation and propagation.

[0004] However, most existing strengthening methods apply uniform process parameters to the entire area, without differentiating between areas with varying stress concentrations. Since the stress concentration coefficients at different locations within the critical section of the shaft differ significantly, using uniform strengthening parameters makes it difficult to meet the strengthening needs of each area. This can easily lead to insufficient strengthening in high-stress areas and excessive plastic deformation in low-stress areas, thereby affecting the material's microstructure stability and dimensional accuracy. Summary of the Invention

[0005] The present invention provides a method for controlling residual stress on the shaft of a wind turbine, which is used to solve related technical problems in the background art.

[0006] The technical solution provided by this invention is as follows: A method for controlling residual stress on a wind turbine shaft, comprising the following steps: S1. Identify the critical sections of the rotating shaft and divide them into high-stress, medium-stress, and low-stress zones based on the stress concentration factor. S2. Use an ultrasonic surface rolling device to roll the dangerous section; Different rolling pressures and rolling cycles are set according to different zones. A deeper plastic deformation layer is formed in the high stress zone, while a gradually decreasing plastic deformation layer is formed in the medium stress zone and the low stress zone. During the rolling process, the axial reciprocating path and the circumferential wrapping path are alternated; S3. After ultrasonic rolling, the high-stress area is subjected to laser shock strengthening treatment, and the strengthening extends to the adjacent medium-stress area. Laser impact is applied sequentially along a dot matrix path, with overlap between adjacent impact points; S4. Perform multi-point residual stress testing on the reinforced critical section, and compare the test results with the preset target residual stress distribution curve. The preset curve specifies that the residual compressive stress in the surface layer within a depth range of 0~0.5mm should not be lower than -400MPa. When the residual compressive stress at the detection point is lower than the lower limit value corresponding to the curve, the area is subjected to supplementary laser shock strengthening. When the residual stress at the detection point is higher than the upper limit of the curve, the area is subjected to local heating treatment. S5. Perform low-temperature tempering on the treated shaft and conduct surface inspection.

[0007] In one embodiment, in step S1, the high-stress region is the region where the stress concentration factor Kt ≥ 3.0, the medium-stress region is the region where 2.0 ≤ Kt < 3.0, and the low-stress region is the region where Kt < 2.0.

[0008] In one embodiment, in step S2, a static pressure of 600-800N is applied to the high-stress area and rolled 4-5 times; a static pressure of 400-600N is applied to the medium-stress area and rolled 3-4 times; and a static pressure of 300-400N is applied to the low-stress area and rolled 2-3 times.

[0009] In one embodiment, in step S2, the axial reciprocating path and the circumferential surrounding path alternately form a cross rolling trajectory, so that the rolling coverage between each processing area overlaps.

[0010] In one embodiment, in step S2, the thickness of the plastic deformation layer formed in the high-stress region is greater than that in the medium-stress region and the low-stress region, and the thickness of the plastic deformation layer gradually decreases along the spatial direction.

[0011] In one embodiment, in step S3, the dot matrix path is a grid-like impact path arranged along the axial and circumferential directions, and the overlap rate of adjacent impact points is 50%~70%.

[0012] In one implementation, in step S3, the laser shock is gradually applied from the high-stress region to the medium-stress region, with fewer shocks applied to the medium-stress region than to the high-stress region; specifically: High-stress areas are subjected to 10-15J laser energy and impacted 2-3 times; The medium-stress zone is subjected to 7-10J laser energy and impacted 1-2 times; Low-stress areas are not subjected to laser shock peening, or are subjected to only one laser shock peening with a laser energy not exceeding 7J.

[0013] In one embodiment, in step S4, the residual stress difference between adjacent detection points does not exceed 150 MPa.

[0014] In one embodiment, in step S4, the local heating treatment uses electromagnetic induction heating at a temperature of 150~200℃ and is held for 5~10 minutes.

[0015] In one embodiment, in step S4, the laser energy for supplementing laser shock enhancement is 5~10J, and the number of shocks is 1~2.

[0016] Compared with the prior art, the beneficial effects of the present invention are: (1) The residual stress control method of the rotating shaft of the present invention divides the critical section of the rotating shaft into stress zones and implements ultrasonic surface rolling and laser shock strengthening in different regions respectively, thereby achieving matching control of strengthening parameters and stress concentration in each region, and thus constructing a spatially continuous residual compressive stress field in the critical section of the rotating shaft; on this basis, the residual stress forms a gradient distribution from the surface to a certain depth, and achieves a smooth transition in the axial and circumferential directions, thereby effectively improving the problem of unreasonable residual stress distribution under uniform process parameters, avoiding local stress abrupt change, and achieving coordination between surface strengthening effect and strengthening layer depth.

[0017] (2) The residual stress control method of the rotating shaft of the present invention uses different regional differentiated parameters in the ultrasonic rolling stage and combines axial and circumferential cross paths to form a continuous transition structure between different stress zones of the plastic deformation layer, thereby avoiding the problem of residual stress abrupt change at the boundary of the region in the traditional partition strengthening process and improving the overall stress coordination and stability of the dangerous section.

[0018] (3) The residual stress control method of the rotating shaft of the present invention strengthens the high stress area as the core and extends to the medium stress area during the laser shock strengthening stage, so that a gradual distribution is formed between the high-strength strengthening area and the transition area. This ensures the strengthening effect of the high stress area while reducing the risk of new stress concentration at the strengthening boundary, and achieves both strengthening depth and stress distribution smoothness. Attached Figure Description

[0019] Figure 1 This is a schematic flowchart of the residual stress control method for the rotating shaft of the present invention. Detailed Implementation

[0020] The present invention will now be described in detail with reference to specific embodiments. These embodiments will help those skilled in the art to further understand the present invention, but do not limit the invention in any way. It should be noted that those skilled in the art can make several changes and improvements without departing from the concept of the present invention. These all fall within the protection scope of the present invention.

[0021] like Figure 1 As shown, the present invention is a method for controlling residual stress on the shaft of a wind turbine.

[0022] This embodiment uses a 3MW direct-drive wind turbine shaft as an example to explain in detail the residual stress control method of the present invention.

[0023] 1. Experimental Materials and Equipment The shaft is made of 42CrMo4 high-strength alloy steel, with a hardness of 280~320HB after quenching and tempering. The maximum diameter of the shaft is 420mm, and the total length is 2800mm. The critical sections are located at the shoulder transition fillet (radius R20) and the bottom area of ​​the keyway.

[0024] The main equipment includes: Ultrasonic surface rolling device (frequency 20kHz, maximum static pressure 1000N). Nanosecond pulsed laser shock peening equipment (wavelength 1064nm, maximum pulse energy 20J). Portable X-ray residual stress analyzer (Cr target, tube voltage 30kV, tube current 6.7mA). Electromagnetic induction local heating equipment; Vacuum tempering furnace.

[0025] 2. The specific steps are as follows: Step S1: Identify the critical section of the shaft and divide the critical section into high-stress, medium-stress, and low-stress zones according to the stress concentration factor.

[0026] First, the shaft is cleaned, degreased, and sandblasted to remove surface oxide scale and create a uniformly rough surface.

[0027] Based on the shaft structure design drawings and finite element analysis results, the shoulder transition fillet and the bottom of the keyway were identified as stress concentration areas. Finite element calculations showed that the stress concentration factor Kt at the shoulder transition fillet was 3.2, and at the bottom of the keyway was 3.5, both greater than 3.0, thus classifying them as high-stress areas. The Kt values ​​within a 10mm extension on both sides of the fillet were between 2.0 and 2.8, classifying them as medium-stress areas. The remaining mating surface areas had Kt < 2.0, classifying them as low-stress areas.

[0028] The above-mentioned areas are physically marked, a three-dimensional spatial coordinate positioning benchmark is established, and the axial and circumferential boundaries of each partition are recorded.

[0029] Step S2: The dangerous section is rolled using an ultrasonic surface rolling device; Different rolling pressures and rolling cycles are set according to different zones. A deeper plastic deformation layer is formed in the high stress zone, while a gradually decreasing plastic deformation layer is formed in the medium stress zone and the low stress zone. The rolling process alternates between axial reciprocating path and circumferential wrapping path.

[0030] An ultrasonic surface rolling device was used to perform full-coverage rolling treatment on the critical section. Different process parameters were set according to different zones. During the rolling process, an alternating axial reciprocating path and a circumferential wrapping path are used to form a cross-rolling trajectory. Specifically, the axial rolling is completed once by feeding at a constant speed from one end to the other along the axial direction; then, the circumferential rolling is completed once around the shaft; this process is repeated alternately until the set number of rolling cycles is reached. There is a 10% to 15% overlap in the rolling coverage between each processing area to ensure continuous stress transition.

[0031] After treatment, a plastic deformation layer with a depth of approximately 0.6 mm was formed on the surface of the high-stress area, approximately 0.4 mm in the medium-stress area, and approximately 0.25 mm in the low-stress area. The thickness of the plastic deformation layer gradually decreased from the high-stress area to the low-stress area along the spatial direction. X-ray diffraction analysis showed that the residual compressive stress on the surface of the high-stress area was -380 to -420 MPa, in the medium-stress area it was -320 to -360 MPa, and in the low-stress area it was -250 to -300 MPa.

[0032] Step S3: After ultrasonic rolling, the high-stress area is subjected to laser shock blasting, and the area is extended to the adjacent medium-stress area for further strengthening. Laser impact is applied sequentially along a dot matrix path, with overlap between adjacent impact points.

[0033] After ultrasonic rolling, the high-stress area is subjected to laser shock blasting, extending approximately 3-5 mm into the adjacent medium-stress area. The laser shock blasting parameters are as follows: Laser shock is applied sequentially along a grid-like path, which is arranged axially and circumferentially, with a 60% overlap between adjacent impact points. The impact sequence proceeds gradually from high-stress areas to medium-stress areas to ensure sufficient strengthening of the high-stress areas.

[0034] After treatment, the residual compressive stress on the surface of the high-stress zone increased to -620~-680MPa, and the depth of the reinforcement layer expanded to about 1.3mm; the residual compressive stress on the surface of the medium-stress zone increased to -480~-520MPa, and the depth of the reinforcement layer was about 0.8mm.

[0035] Step S4: Perform multi-point residual stress testing on the reinforced critical section, and compare the test results with the preset target residual stress distribution curve. The preset curve specifies that the residual compressive stress in the surface layer within a depth range of 0~0.5mm should not be lower than -400MPa. When the residual compressive stress at the detection point is lower than the lower limit value corresponding to the curve, the area is subjected to supplementary laser shock strengthening. When the residual stress at the test point exceeds the upper limit of the curve, the area is subjected to local heating treatment.

[0036] After the strengthening treatment was completed, a portable X-ray residual stress analyzer was used to perform multi-point residual stress detection on the critical section. The detection points included: the center point and edge points of the high-stress zone, as well as several measuring points spaced 5 mm apart along the axial direction, for a total of 15 detection points.

[0037] The test results were compared with the pre-constructed target residual stress distribution curve. The target residual stress distribution curve was pre-constructed based on the fatigue load spectrum of the rotating shaft and finite element simulation, and it was specified that the residual compressive stress in the surface layer within a depth range of 0~0.5mm was not less than -400MPa, and the residual stress difference between adjacent test points did not exceed 150MPa.

[0038] The test results show that the residual compressive stress at the center point of the high-stress zone is -650MPa, which meets the requirements; however, the measured value at a certain measuring point on the edge of the high-stress zone is -580MPa, which is lower than the target lower limit (-600MPa, the actual control value after considering the safety margin). At the same time, the stress difference between this point and the adjacent point is 170MPa, which exceeds the allowable range of 150MPa.

[0039] For this location, supplementary laser shock peening was performed: 8J laser energy was used for two shocks. After treatment, the residual compressive stress at this point increased to -625MPa, and the stress difference between adjacent points decreased to 125MPa, meeting the requirements.

[0040] At another medium-stress zone, the residual compressive stress at a measuring point was -550 MPa, higher than the target upper limit (-500 MPa). This area was then subjected to localized heating treatment. Electromagnetic induction heating was used, with a heating temperature of 180℃ and a holding time of 8 minutes. After treatment, the residual compressive stress at this point decreased to -510 MPa, falling within the target range.

[0041] After repeated testing and correction, the residual stress values ​​at all test points fell within the target window, and the stress difference between adjacent points did not exceed 150 MPa.

[0042] Step S5: Perform low-temperature tempering on the treated shaft and conduct surface inspection.

[0043] The treated shaft was placed in a vacuum tempering furnace for low-temperature tempering at 160°C for 3 hours to stabilize the material microstructure and residual stress state.

[0044] After tempering, surface integrity testing is performed on the treated area: Magnetic particle testing was performed, and the results showed that there were no cracks or defects. The surface roughness was measured using a roughness tester and was Ra=0.4μm, which is better than the usage requirement (Ra≤0.8μm). The surface hardness was tested using a Vickers hardness tester and found to be approximately 3.2% lower than that of the substrate, which is in line with the design specifications (allowable decrease ≤5%).

[0045] To verify the technical effect of the present invention, untreated samples (control group) and samples treated by the method of this embodiment (treated group) were subjected to a rotational bending fatigue test (stress ratio R=-1, loading frequency 50Hz).

[0046] The experimental results show that: Control group: The fatigue limit after 10^7 cycles was 320 MPa; Treatment group: The fatigue limit after 10^7 cycles is 510 MPa.

[0047] The fatigue limit was increased by 59.4% after treatment, which significantly improved the fatigue resistance of the shaft.

[0048] In this application, the terms "upper," "lower," "left," "right," "front," "rear," "top," "bottom," "inner," "outer," "middle," "vertical," "horizontal," "lateral," and "longitudinal" indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. These terms are primarily for the purpose of better describing the invention and its embodiments, and are not intended to limit the indicated device, element, or component to having a specific orientation, or to be constructed and operated in a specific orientation.

[0049] The above description is merely a preferred embodiment of this application and is not intended to limit this application. Various modifications and variations can be made to this application by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of this application should be included within the protection scope of this application.

Claims

1. A method for controlling residual stress on a wind turbine shaft, characterized in that, Includes the following steps: S1. Identify the critical sections of the rotating shaft and divide them into high-stress, medium-stress, and low-stress zones based on the stress concentration factor. S2. The dangerous section is rolled using an ultrasonic surface rolling device; Different rolling pressures and rolling cycles are set according to different zones. A deeper plastic deformation layer is formed in the high stress zone, while a gradually decreasing plastic deformation layer is formed in the medium stress zone and the low stress zone. During the rolling process, the axial reciprocating path and the circumferential wrapping path are alternated; S3. After ultrasonic rolling, the high-stress area is subjected to laser shock strengthening treatment, and the strengthening extends to the adjacent medium-stress area. Laser impact is applied sequentially along a dot matrix path, with overlap between adjacent impact points; S4. Perform multi-point residual stress testing on the reinforced critical section, and compare the test results with the preset target residual stress distribution curve. The preset curve specifies that the residual compressive stress in the surface layer within a depth range of 0~0.5mm should not be lower than -400MPa. When the residual compressive stress at the detection point is lower than the lower limit value corresponding to the curve, the area is subjected to supplementary laser shock strengthening. When the residual stress at the detection point is higher than the upper limit of the curve, the area is subjected to local heating treatment. S5. Perform low-temperature tempering on the treated shaft and conduct surface inspection.

2. The method for controlling residual stress on a wind turbine shaft as described in claim 1, characterized in that, In step S1, the high stress zone is the region where the stress concentration factor Kt ≥ 3.0, the medium stress zone is the region where 2.0 ≤ Kt < 3.0, and the low stress zone is the region where Kt < 2.

0.

3. The method for controlling residual stress on a wind turbine shaft as described in claim 1, characterized in that, In step S2, a static pressure of 600-800N is applied to the high-stress area and rolled 4-5 times; a static pressure of 400-600N is applied to the medium-stress area and rolled 3-4 times; and a static pressure of 300-400N is applied to the low-stress area and rolled 2-3 times.

4. The method for controlling residual stress on a wind turbine shaft as described in claim 1, characterized in that, In step S2, the axial reciprocating path and the circumferential surrounding path alternately form a cross rolling trajectory, so that the rolling coverage between each processing area overlaps.

5. The method for controlling residual stress on a wind turbine shaft as described in claim 1, characterized in that, In step S2, the thickness of the plastic deformation layer formed in the high stress zone is greater than that in the medium stress zone and the low stress zone, and the thickness of the plastic deformation layer gradually decreases along the spatial direction.

6. The method for controlling residual stress on a wind turbine shaft as described in claim 1, characterized in that, In step S3, the dot matrix path is a grid-like impact path arranged along the axial and circumferential directions, with an overlap rate of 50% to 70% between adjacent impact points.

7. The method for controlling residual stress on a wind turbine shaft as described in claim 1, characterized in that, In step S3, the laser shock is applied progressively from the high-stress region to the medium-stress region, with fewer shocks applied to the medium-stress region than to the high-stress region; specifically: High-stress areas are subjected to 10-15J laser energy and impacted 2-3 times; The medium-stress zone is subjected to 7-10J laser energy and impacted 1-2 times; Low-stress areas are not subjected to laser shock peening, or are subjected to only one laser shock peening with a laser energy not exceeding 7J.

8. The method for controlling residual stress on a wind turbine shaft as described in claim 1, characterized in that, In step S4, the residual stress difference between adjacent detection points shall not exceed 150 MPa.

9. The method for controlling residual stress on a wind turbine shaft as described in claim 1, characterized in that, In step S4, the local heating treatment uses electromagnetic induction heating at a temperature of 150~200℃ and is held for 5~10 minutes.

10. The method for controlling residual stress on a wind turbine shaft as described in claim 1, characterized in that, In step S4, the laser energy for the supplementary laser shock enhancement is 5~10J, and the number of shocks is 1~2.

Images