Film Thickness Decay and Wear Behavior of Grease-Lubricated Point Contact under Cyclic Variable Loads
For wind turbine applications, there is a cyclic load-varying process between rolling elements and raceways in pitch bearings. This kind of motion can also lead to radial fretting. However, this is seldom addressed under grease-lubricated conditions in the literature. In this study, grease-lubricate...
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| Format: | Article |
| Language: | English |
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MDPI AG
2024-02-01
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| Series: | Lubricants |
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| Online Access: | https://www.mdpi.com/2075-4442/12/2/42 |
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| author | Yiming Han Jing Wang Hengrui Du Weimin Li Jingxin Zhao Zongyi Bai Meng Hu Haichao Liu |
| author_facet | Yiming Han Jing Wang Hengrui Du Weimin Li Jingxin Zhao Zongyi Bai Meng Hu Haichao Liu |
| author_sort | Yiming Han |
| collection | DOAJ |
| description | For wind turbine applications, there is a cyclic load-varying process between rolling elements and raceways in pitch bearings. This kind of motion can also lead to radial fretting. However, this is seldom addressed under grease-lubricated conditions in the literature. In this study, grease-lubricated point contact problems have been investigated experimentally under cyclic load-varying conditions. The findings revealed that as the load-varying range diminishes, the variation in grease film distribution becomes more subtle and the rate of discharge of thickener fiber clusters in the stick zone decelerates. This is due to the fact that the rate of change in the Hertz contact radius is reduced and the migration of grease is weakened during the unloading process. Due to the large apparent viscosity of grease with a high soap content, entrapped grease is not easily discharged during loading, and the thickness of the film in the stick zone progressively increases as the soap content of the grease is augmented. This also causes the variable load zone to wear out more easily. As the grease is subjected to repeated loading and unloading, there is a gradual reduction in film thickness, and larger thickener fiber clusters tear, resulting in a flattened form and shear thinning. Grease containing sulphur–phosphorus additives demonstrates a superior effect on reducing fretting wear within the large variable load range but generally proves effective for smaller load-varying ranges. This study may offer insights into the degradation of grease under variable load motion and methods to prevent radial fretting wear. |
| first_indexed | 2024-03-07T22:23:42Z |
| format | Article |
| id | doaj.art-4f8b47c8baa148fdbbecd363e66882bf |
| institution | Directory Open Access Journal |
| issn | 2075-4442 |
| language | English |
| last_indexed | 2024-03-07T22:23:42Z |
| publishDate | 2024-02-01 |
| publisher | MDPI AG |
| record_format | Article |
| series | Lubricants |
| spelling | doaj.art-4f8b47c8baa148fdbbecd363e66882bf2024-02-23T15:24:54ZengMDPI AGLubricants2075-44422024-02-011224210.3390/lubricants12020042Film Thickness Decay and Wear Behavior of Grease-Lubricated Point Contact under Cyclic Variable LoadsYiming Han0Jing Wang1Hengrui Du2Weimin Li3Jingxin Zhao4Zongyi Bai5Meng Hu6Haichao Liu7State Key Laboratory of Solid Lubrication, Lanzhou Institute of Chemical Physics, Chinese Academy of Sciences, Lanzhou 730000, ChinaCollege of Mechanical Engineering, Donghua University, Shanghai 201620, ChinaCollege of Mechanical Engineering, Donghua University, Shanghai 201620, ChinaState Key Laboratory of Solid Lubrication, Lanzhou Institute of Chemical Physics, Chinese Academy of Sciences, Lanzhou 730000, ChinaState Key Laboratory of Solid Lubrication, Lanzhou Institute of Chemical Physics, Chinese Academy of Sciences, Lanzhou 730000, ChinaState Key Laboratory of Solid Lubrication, Lanzhou Institute of Chemical Physics, Chinese Academy of Sciences, Lanzhou 730000, ChinaState Key Laboratory of Solid Lubrication, Lanzhou Institute of Chemical Physics, Chinese Academy of Sciences, Lanzhou 730000, ChinaState Key Laboratory of Solid Lubrication, Lanzhou Institute of Chemical Physics, Chinese Academy of Sciences, Lanzhou 730000, ChinaFor wind turbine applications, there is a cyclic load-varying process between rolling elements and raceways in pitch bearings. This kind of motion can also lead to radial fretting. However, this is seldom addressed under grease-lubricated conditions in the literature. In this study, grease-lubricated point contact problems have been investigated experimentally under cyclic load-varying conditions. The findings revealed that as the load-varying range diminishes, the variation in grease film distribution becomes more subtle and the rate of discharge of thickener fiber clusters in the stick zone decelerates. This is due to the fact that the rate of change in the Hertz contact radius is reduced and the migration of grease is weakened during the unloading process. Due to the large apparent viscosity of grease with a high soap content, entrapped grease is not easily discharged during loading, and the thickness of the film in the stick zone progressively increases as the soap content of the grease is augmented. This also causes the variable load zone to wear out more easily. As the grease is subjected to repeated loading and unloading, there is a gradual reduction in film thickness, and larger thickener fiber clusters tear, resulting in a flattened form and shear thinning. Grease containing sulphur–phosphorus additives demonstrates a superior effect on reducing fretting wear within the large variable load range but generally proves effective for smaller load-varying ranges. This study may offer insights into the degradation of grease under variable load motion and methods to prevent radial fretting wear.https://www.mdpi.com/2075-4442/12/2/42grease lubricationdynamic loadfilm thicknessradial frettingnon-steady stateanti-wear additive |
| spellingShingle | Yiming Han Jing Wang Hengrui Du Weimin Li Jingxin Zhao Zongyi Bai Meng Hu Haichao Liu Film Thickness Decay and Wear Behavior of Grease-Lubricated Point Contact under Cyclic Variable Loads Lubricants grease lubrication dynamic load film thickness radial fretting non-steady state anti-wear additive |
| title | Film Thickness Decay and Wear Behavior of Grease-Lubricated Point Contact under Cyclic Variable Loads |
| title_full | Film Thickness Decay and Wear Behavior of Grease-Lubricated Point Contact under Cyclic Variable Loads |
| title_fullStr | Film Thickness Decay and Wear Behavior of Grease-Lubricated Point Contact under Cyclic Variable Loads |
| title_full_unstemmed | Film Thickness Decay and Wear Behavior of Grease-Lubricated Point Contact under Cyclic Variable Loads |
| title_short | Film Thickness Decay and Wear Behavior of Grease-Lubricated Point Contact under Cyclic Variable Loads |
| title_sort | film thickness decay and wear behavior of grease lubricated point contact under cyclic variable loads |
| topic | grease lubrication dynamic load film thickness radial fretting non-steady state anti-wear additive |
| url | https://www.mdpi.com/2075-4442/12/2/42 |
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