Polymer and composite: Contemporary research trends

The current trends of these experimental and analytical results can be used in future to design different tribological and mechanical components

Polymer and its composites are finding ever increasing usage for numerous industrial applications in sliding/rolling components such as bearings, rollers, seals, gears, cams, wheels, piston rings, transmission belts, grinding mills and clutches where their self lubricating properties are exploited to avoid the need for oil or grease lubrication with its attendant problems of contamination. However, when the contact between sliding pairs is present, there is the problem of friction and wear. Yamaguchi add Stolarski  reported that the friction coefficient can, generally, be reduced and the wear resistance increased by selecting the right material combinations. Several researchers observed that the friction force and wear rate depend on roughness of the rubbing surfaces, relative motion, type of material, temperature, normal force, stick slip, relative humidity, lubrication and vibration. The parameters that dictate the tribological performance of polymer and its composites also include polymer molecular structure, processing and treatment, properties, viscoelastic behavior, surface texture etc.. There have been also a number of investigations exploring the influence of test conditions, contact geometry and environment on the friction and wear behavior of polymers and composites. Watanabe , Tanaka  and Bahadur and Tabor  reported that the tribological behavior of polyamide, high density polyethylene (HDPE) and their composites is greatly affected by normal load, sliding speed and temperature. Pihtili and Tosun showed that applied load and sliding speed play significant role on the wear behavior of polymer and composites. They also showed that applied load has more effect on the wear than the speed for composites. Several authors observed that the friction coefficient of polymers and its composites rubbing against metals decreases with the increase in load though some other researchers have different views. Stuart and other researchers showed that value of friction coefficient increases with the increase in load. Friction coefficient and specific wear rate values for different combinations of polymer and its composite were obtained and compared. For all material combinations, it was observed 300 Composites and Their Properties that the coefficient of friction decreases linearly with the increase in applied pressure values. Unal et al. reported that the applied load exerts greater influence on the sliding wear of polymer and its composite than the sliding velocity. Friction and wear behavior of glass fiber reinforced polyster composite were studied and results showed that in general, friction and wear are strongly influenced by all the test parameters such as applied load, sliding speed, sliding distance and fiber orientations . Moreover, it was found that applied normal load, sliding speed and fiber orientations have more pronounced effect on wear rate than sliding distance. Wang and Li  observed that the sliding velocity has more significant effect on the sliding wear as compared to the applied load and variations of wear rate with operating time can be distinguished by three distinct periods. These periods are running-in period, steady-state period and severe wear period, respectively. Tsukizoe and Ohmae  showed that reinforcement of fiber or filler significantly improve the tribological behavior of polymeric material but this is not necessarily true for all cases. Suresha et al. showed that there is a strong interdependence on the friction coefficient and wear loss with respect to the applied loads for steel-composites contact. Friction process with vibration is an important practical phenomenon because the influence of vibration can cause significant change in this process. It is known that vibration and friction are dependent on each other. Friction generates vibration in various forms, while vibration affects friction in turns. Some explanations are given in order to justify the decrease in the friction coefficient under vibration condition though some of the researchers have different views. 

Skare and Stahl  claimed that mean friction force increases as well as decreases depending on the vibration parameters.
Friction and wear of polymer and composites are significantly influenced by normal load, sliding velocity, amplitude of vibration, frequency of vibration, direction of vibration and natural frequency. Friction coefficient also depends on duration of rubbing and it is different for different materials. Friction coefficient can be increased or decreased depending on sliding pairs and operating parameters. There are also some correlations between friction/wear and other influencing parameters. 
The current trends of these experimental and analytical results can be used in future to design different tribological and mechanical components. The researchers can use these results to innovate some design strategies for improving different concerned mechanical processes. It is expected that the research findings of tribological behavior of polymer and composites discussed in this chapter will also be used for future research and development.

The writer is Head of the Department of Mechanical Engineering at Dhaka University of Engineering and Technology (DUET), Gazipur

Polymer and composite: Contemporary research trends

The current trends of these experimental and analytical results can be used in future to design different tribological and mechanical components

Polymer and its composites are finding ever increasing usage for numerous industrial applications in sliding/rolling components such as bearings, rollers, seals, gears, cams, wheels, piston rings, transmission belts, grinding mills and clutches where their self lubricating properties are exploited to avoid the need for oil or grease lubrication with its attendant problems of contamination. However, when the contact between sliding pairs is present, there is the problem of friction and wear. Yamaguchi add Stolarski reported that the friction coefficient can, generally, be reduced and the wear resistance increased by selecting the right material combinations. Several researchers observed that the friction force and wear rate depend on roughness of the rubbing surfaces, relative motion, type of material, temperature, normal force, stick slip, relative humidity, lubrication and vibration. The parameters that dictate the tribological performance of polymer and its composites also include polymer molecular structure, processing and treatment, properties, viscoelastic behavior, surface texture etc.. There have been also a number of investigations exploring the influence of test conditions, contact geometry and environment on the friction and wear behavior of polymers and composites. Watanabe , Tanaka and Bahadur and Tabor reported that the tribological behavior of polyamide, high density polyethylene (HDPE) and their composites is greatly affected by normal load, sliding speed and temperature. Pihtili and Tosun showed that applied load and sliding speed play significant role on the wear behavior of polymer and composites. They also showed that applied load has more effect on the wear than the speed for composites. Several authors observed that the friction coefficient of polymers and its composites rubbing against metals decreases with the increase in load though some other researchers have different views. Stuart and other researchers showed that value of friction coefficient increases with the increase in load. Friction coefficient and specific wear rate values for different combinations of polymer and its composite were obtained and compared. For all material combinations, it was observed 300 Composites and Their Properties that the coefficient of friction decreases linearly with the increase in applied pressure values. Unal et al. reported that the applied load exerts greater influence on the sliding wear of polymer and its composite than the sliding velocity. Friction and wear behavior of glass fiber reinforced polyster composite were studied and results showed that in general, friction and wear are strongly influenced by all the test parameters such as applied load, sliding speed, sliding distance and fiber orientations . Moreover, it was found that applied normal load, sliding speed and fiber orientations have more pronounced effect on wear rate than sliding distance. Wang and Li observed that the sliding velocity has more significant effect on the sliding wear as compared to the applied load and variations of wear rate with operating time can be distinguished by three distinct periods. These periods are running-in period, steady-state period and severe wear period, respectively. Tsukizoe and Ohmae showed that reinforcement of fiber or filler significantly improve the tribological behavior of polymeric material but this is not necessarily true for all cases. Suresha et al. showed that there is a strong interdependence on the friction coefficient and wear loss with respect to the applied loads for steel-composites contact. Friction process with vibration is an important practical phenomenon because the influence of vibration can cause significant change in this process. It is known that vibration and friction are dependent on each other. Friction generates vibration in various forms, while vibration affects friction in turns. Some explanations are given in order to justify the decrease in the friction coefficient under vibration condition though some of the researchers have different views. Skare and Stahl claimed that mean friction force increases as well as decreases depending on the vibration parameters. Friction and wear of polymer and composites are significantly influenced by normal load, sliding velocity, amplitude of vibration, frequency of vibration, direction of vibration and natural frequency. Friction coefficient also depends on duration of rubbing and it is different for different materials. Friction coefficient can be increased or decreased depending on sliding pairs and operating parameters. There are also some correlations between friction/wear and other influencing parameters. The current trends of these experimental and analytical results can be used in future to design different tribological and mechanical components. The researchers can use these results to innovate some design strategies for improving different concerned mechanical processes. It is expected that the research findings of tribological behavior of polymer and composites discussed in this chapter will also be used for future research and development. The writer is Head of the Department of Mechanical Engineering atDhaka University of Engineering and Technology (DUET), Gazipur