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In this study, the MYB-500 high-frequency and high-load oscillatory tribotester was used to carry out life cycle tests to investigate the self-lubricating properties and damage behavior of Kevlar/PTFE fiber-reinforced composite. Wear debris and wear behavior of the frictional surface were analyzed to explore key factors affecting the self-lubricating stability and service life of materials. Results show that the life cycle of Kevlar/PTFE fiber-reinforced composite can be divided into three stages by the change of friction coefficient and wear depth, including running-in, stable and failure stage. The life stage and performance of materials can be evaluated by monitoring the friction temperature and friction coefficient in real time. When the friction coefficient reaches 0.16 or the friction temperature monitored exceeds 150 °C, it can be determined that the material life is terminated. From wear surface analysis and change of wear loss, it is indicated that the wear exhibits notable nonuniform characteristic. Based on the wear surface of material after failure, it is concluded that the initial nonuniformity of the material thickness has significant influence on wear damage as well as life cycle. Therefore, the self-lubricating behavior of material can be improved by modifying relevant process parameters to obtain the uniform material thickness, and meanwhile, the wear life was increased from 242 to 293 h. [ABSTRACT FROM AUTHOR]

The self-lubricating braided composite used in oscillating bearing was tested and evaluated under the extreme operating conditions. The Kevlar/PTFE braided composite was investigated on an oscillatory high load (> 30 MPa) and high frequency (> 2 Hz) tester with oscillating frequency ranging from 2.5 to 10 Hz and load from 30 to 50 MPa. Effects of the oscillating frequency and load on the friction coefficient and wear loss were obtained. Results show that the friction coefficient is mainly affected by oscillating frequency under higher loads. It firstly decreases with frequency and later is toward dynamic stability and fluctuates regionally with varying load. Friction surface and wear debris were analyzed under varied load and oscillating frequency using scanning electron microscope. Effects of the oscillating frequency and load on the friction coefficient and wear loss of the Kevlar/PTFE braided composite under high load condition were discussed. It is obtained that the friction surface is mainly damaged due to high frequency rather than high load. This study could provide a basis for performance matching and selection of composite under varied operating conditions. [ABSTRACT FROM AUTHOR]

In this paper, polydopamine/silver (PDA/Ag) nanoparticles were easily synthesized. Then, the PDA/Ag nanoparticles were sprayed on copper substrate and heat-treated under argon to get carbonized PDA/Ag (CPDA/Ag) composite films. Transmission electron microscopy, field-emission scanning electron microscopy, x-ray diffraction, Raman spectroscopy and x-ray photoelectron spectroscopy were employed to investigate the conversion of PDA and AgNO3 into CPDA and Ag, respectively. Results showed that the PDA/Ag composite films heat-treated at 500 °C had much better friction reduction and anti-wear properties than other samples. The tribofilms containing C, N, O, Ag and Cu played an important role on reducing friction and increasing wear resistance. [ABSTRACT FROM AUTHOR]

Effect of slope inclination on step friction coefficient of human being was studied by gait friction tester developed by Henan University of Science and Technology. It is beneficial to improving the safety of human beings while walking on a ramp. Based on the trajectory of mass center of body (MCOB) and the mechanical analysis of human body while walking, conclusion could be drawn that the required step frictional coefficient (RSFC) exhibited an “M” shaped curve during the foot contacting with the ground and got its maximum and minimum values when MCOB of the subject was at the highest and lowest position respectively. Moreover, the first peak of RSFC decreases firstly and then increases, while the second peak of RSFC increases with the increase of slope inclination at the experimental condition. The position of pivotal point is decided by the relative size of slope inclination and the angle between the plumb line through MCOB and the line from foot to MCOB. [ABSTRACT FROM AUTHOR]