The results demonstrated that it was possible to determine the pv-factors at failure by means of the load enhancing experiment. In the study of Yeo, the friction and wear properties of polymer coatings were studied by stepwise load increasing experimental technique until the failure of the sample took place. Studies of the load changes on the tribological behavior of polymer-based materials are quite sparse. Up till now, it is still not clear how do these load changes affect the subsequent tribological responses due to the distinct temperatures induced by the frictional heating and the initial formation of the transfer films on the counter body and so on. At the end of the test, the friction and wear properties of the tribomaterials were evaluated. Conventional tribological investigations were conducted at constant pv-factors in pre-defined testing period, which means that there are no load changes during the characterization. Alternation of the load conditions, e.g., pressure (p), velocity (v), temperature, etc., does not occur regularly rather accidentally. In the practical applications, such polymer-based triboparts are usually utilized under altering operating conditions owing to the rapid development of the modern technology and global energy-reduction, for example application of the start-stop technology in the commercial vehicles. In addition, a well-formed transfer film leads to a reduction of the direct contact between the two sliding parts, and therefore alleviates the friction and wear in the polymer/steel tribosystems. Investigations on the tribological mechanisms reveal that stress reduction on the CFs, rolling of the particles and isolation of the contact between CFs and counterpart asperities by the rigid particles are the dominant factors improving the friction and wear performance of such PEEK tribocompounds. In recent years, many studies have reported that incorporation of tiny inorganic particles into such PEEK composites leads to further improvement in their tribological properties. Carbon fibers (CFs) and solid lubricants, for instance graphite and polytetrafluorethylene (PTFE), reinforced PEEK composites are frequently utilized in the field, where self-lubrication and anti-wear properties are required. However, PEEK needs to be modified by addition of suitable fillers, in order to meet the high requirements on the tribological applications in service. It exhibits excellent mechanical performance and high thermal resistance. PEEK is one of the high-performance thermoplastic polymers, which has been widely used as a friction-reducing and anti-wear material in mechanical engineering. In addition, the tribological properties clearly correlate with the temperature of the tribosystem. When the pressure is increased to 8 MPa, the impact of the velocity sequences on the wear performance becomes insignificant. For the PEEK composite, its specific wear rate exhibits an obvious dependence on the previous velocity levels at a low nominal pressure of 1 MPa. With respect to the wear performance, the specific wear rate of pure PEEK exhibits a strong dependence on the sequences of the velocity only at the initial pv-levels. In contrast, the testing sequence of the velocity exerts obvious impact on the friction coefficient of the PEEK composite at slow sliding velocities. The friction coefficient of PEEK is independent on previous velocity histories. It is demonstrated that the tribological properties of pure PEEK and its composite show a complex nature of the dependence on the velocity sequences in the studied range. In the present study, effects of the sliding velocity sequences on the friction and wear properties of pure polyetheretherketone (PEEK) and a PEEK hybrid composite were studied.
0 Comments
Leave a Reply. |