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Youhua Li,Lubing Shi,Zhongming Liu,Xiaopeng Wang,Xuetao Qiao,Zhihong Zhang,Shidang Yan 대한기계학회 2022 JOURNAL OF MECHANICAL SCIENCE AND TECHNOLOGY Vol.36 No.12
For high-speed, heavy-load gear units, the meshing tooth surfaces are generally under the mixed lubrication state, which is crucial for gear pitting or micro pitting damage. To clarify the effects of lubrication state on tooth pitting damage, carrying out both numerical and experimental studies on the contact severity of gears under different lubrication states is necessary. In this paper, a 3D line-contact elasto hydrodynamic lubrication model considering fractal surface roughness was developed and used to investigate the lubrication characteristics of involute gears. Both the distributions of pressure and film thickness fluctuated under the rolling contact of rough surfaces. The fluctuations became more substantial with the increase of load and roughness. Furthermore, from the calculated film thickness ratio λ, the contact of gear tooth surfaces with a fractal roughness of Ra = 0.8 μm was always under full lubrication state (λ > 1). When the roughness was increased to Ra = 3.2 μm, the contact was first transmitted into the mixed lubrication state (0.2 < λ < 1) under the load of 1000 N*m and finally deteriorated to boundary lubrication state (λ < 0.2) under the load of 2000 N*m. The boundary lubrication state that occurred under the contact of highly rough surfaces could induce the formation of gear pitting damage. The contact fatigue test showed the gear tooth surface roughness increased from 0.7 μm to around 2.7 μm after 8 million running cycles and then suffered pitting failure after another 2 million cycles, which was consistent with the simulation analysis prediction.
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Effect of 3C-SiC Intermediate Layer in GaN-Based Light Emitting Diodes Grown on Si(111) Substrate
Youhua Zhu,Meiyu Wang,Yi Li,Shuxin Tan,Honghai Deng,Xinglong Guo,Haihong Yin,Takashi Egawa 대한금속·재료학회 2017 ELECTRONIC MATERIALS LETTERS Vol.13 No.2
GaN-based light emitting diodes (LEDs) have been grown by metalorganicchemical vapor deposition on Si(111) substrate with and without3C-SiC intermediate layer (IL). Structural property has been characterizedby means of atomic force microscope, X-ray diffraction, andtransmission electron microscope measurements. It has been revealedthat a significant improvement in crystalline quality of GaN and superlatticeepitaxial layers can be achieved by using 3C-SiC as IL. Regardingof electrical and optical characteristics, it is clearly observed that theLEDs with its IL have a smaller leakage current and higher light outputpower comparing with the LEDs without IL. The better performance ofLEDs using 3C-SiC IL can be contributed to both of the improvementsin epitaxial layers quality and light extraction efficiency. As aconsequence, in terms of optical property, a double enhancement of thelight output power and external quantum efficiency has been realized.
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Adsorption, Mobility and Degradation of Diphenamid in Chinese Soils
Xiaomao Wu,Ming Li,Youhua Long,Renxiang Liu,Yunlong Yu,Hua Fang 대한토목학회 2012 KSCE Journal of Civil Engineering Vol.16 No.4
The present study was conducted to determine adsorption, mobility, and degradation characteristics of diphenamid in five Chinese soils and their relationships. The adsorption of diphenamid in soils tested could accurately be described by a Freundlich equation. Based on the mobility factor (Rf), diphenamid was seen to be slightly or moderately mobile in soils studied. Regression of Kf and Rf against selected soil properties indicated that Organic Matter (OM) was the most influential factor governing adsorption and mobility of diphenamid (r2 > 0.92 ) followed by clay (r2 > 0.61). There was a significant correlation (p < 0.01) between Kf and Rf of diphenamid. Diphenamid degradation data were fitted the first-order reaction equations, yielding half-lives (T1/2) ranging from 187.3to 247.5 days in unsterilized soils but prolonging to 577.5-630.0 days in sterilized soils. The prolonged T1/2 by sterilization showed that microbial degradation was the dominant pathway for diphenamid degradation in soils. Degradation of diphenamid in soils appeared to be influenced by soil OM (r2 > 0.97) and clay content (r2 > 0.85). The T1/2 of diphenamid was significantly related to both Kf and Rf (p < 0.05), indicating that either Kf or Rf might be used as a model for predicting degradation of diphenamid in soils involved.
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Design and analysis of mechanical flux‑weakening device of axial flux permanent magnet machines
Shaopeng Wang,Jiawei Lu,Bin Li,Chengcheng Liu,Youhua Wang,Gang Lei,Youguang Guo,Jianguo Zhu 전력전자학회 2022 JOURNAL OF POWER ELECTRONICS Vol.22 No.4
Due to the low inductance of an axial flux permanent magnet machine (AFPMM), the constant power speed regulation range is small. A new mechanical flux-weakening method for single-rotor single-stator AFPMMs is proposed in this paper. By installing a mechanical flux-weakening device on one side of the stator and rotating it certain angle, the speed regulation of the flux-weakening can be realized. The device is simple in structure, easy to operate, and can be operated in the process of machine operation. The validity of the device is verified by applying it to a machine. Finite-element software is used to calculate and analyze the performances of two machines with the device.
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