tailieunhanh - Bearing Design in Machinery Episode 3 Part 12

Tham khảo tài liệu 'bearing design in machinery episode 3 part 12', kỹ thuật - công nghệ, cơ khí - chế tạo máy phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả | Unlike the metal-on-metal curve the dynamic f-U curve with UHMWPE has considerable hysteresis for dry friction. This effect suggests that the friction of polymers involves viscous friction. Several cycles are measured and the curve shows a good repeatability of the cycles except for the first cycle dotted line which has a higher stiction force. Unlike what we see with metal-on-metal testing the friction coefficient increases with the velocity reaching a maximum off . In this case the breakaway friction at each cycle approaches zero. However at the first cycle of the experiment dotted line there is a higher stiction force and the breakaway friction coefficient is near . Figure 20-4 is for identical conditions but lubrication is provided with a very light low viscosity oil m N-s m2. This curve simulates the friction in an actual joint implant. The curve indicates that even for a low viscosity and speed the bearing operates in the boundary and mixed lubrication regime and the friction decreases versus sliding velocity. This curve also shows a considerable hysteresis. For lubricated surfaces the first cycle dotted line in Fig. 20-4 also demonstrates a higher stiction force off while the following cycles have a reduced maximum breakaway coefficient off . Copyright 2003 by Marcel Dekker Inc. All Rights Reserved. Bibliography Air Force Aero Propulsion Laboratory 1977 Gas Lubricated Foil Bearing Development for Advanced Turbomachines Report AF APL-TR-76-114 Vol. I and II. ASTM B23 1990 ASTM Standards ASTM Philadelphia Vol. pp. 9-11. Allaire P. E. and Flack R. D. 1980 Journal Bearing Design for High Speed Turbo-machinary. Bearing Design - Historical Aspects Present Technology and Future Problems. W. J. Anderson editor . ASME publication New York pp. 111-160. Amin J. Friedland B. and Harnoy A. 1997 Implementation of a Friction Estimation and Compensation Technique IEEE Control Systems Vol. 17 No. 4 pp. 71-76. Anderson W. J. Fleming D. P. and Parker