Friction Test System Research Articles

Reduction of Friction Using Microabrasive Air Jet Machining

In this paper, we introduce a microabrasive air jet (micro-AAJ) machining system and describe machining results obtained while using it. Our research activities have focused on the development of micro-AAJ machining methods for friction reduction without requiring a mask. Through this study, we want to show that such processing is possible without a mask when using the AAJ method. In this paper, a micro-AAJ machining system is introduced, and the processing results are described. By comparing the friction coefficient of texturing under various conditions, the relative relationship between the surface shape and the friction coefficient can be identified. We investigated the effect of the relationship between rotating velocity, traverse speed, density of the patterned area and injection pressure on friction. The friction is decreased with a low traverse speed and high-density patterned area under high-speed driving conditions, as verified by experiments using a friction test system.

Current-carrying friction in carbon coated ball bearing

In this work, we proposed a method for coating the whole surfaces of bearing balls uniformly by carbon film with a rotatable ball clamp. We studied the carbon/carbon friction with a self-designed current-carrying ball bearing friction test system. A notable and instant friction force drop of 28% and significant carbon film wear alleviation were found when currents were applied. By using TEM-, SEM-, and EDS-analysis, special carbon stacks with a mixture of large wear particles and oxide were found in the wear areas under current applied condition. We elucidated the current-carrying friction mechanisms as follows: (1) wear particles formation; (2) wear particles charged by tribomicroplasma; (3) formation of surface passivated carbon stacks under electric force; (4) sliding between passivated carbon surfaces. This work may facilitate the development of novel solid-lubricated ball bearings and lay some foundations for current-carrying rolling friction.

A novel pneumatic actuator based on high-frequency longitudinal vibration friction reduction

Seals are an indispensable component of ordinary piston type pneumatic cylinders, but their presence inevitably introduces friction. Given that the friction is time-varying, uncertain and difficult to capture precisely, the output force of the pneumatic cylinder is difficult to obtain accurately. In addition, due to the serious negative damping effect in the low speed phase of the pneumatic cylinder friction characteristics, the motion servo control accuracy of pneumatic cylinders at low speeds is relatively poor. In this study, a novel longitudinal-vibration-mode pneumatic actuator with integrated piezoelectric stacks is developed with a resonant frequency of 5908 Hz for first-order longitudinal vibration. A new friction test system is set up and the test results show a maximum reduction of about 38.6 % in the static friction and 46.6 % in the dynamic friction of the pneumatic actuator for the high-frequency longitudinal resonance case. In the study of the effect of two-chamber pressure on friction reduction, it is found that the friction reduction rate decreases with the increase of two-chamber pressure. The preliminary motion trajectory tracking control results show that the high-frequency longitudinal resonance of the pneumatic actuator does help to reduce the maximum tracking error during the reverse process and improve the tracking accuracy of the motion trajectory.

The tribological performance of W-DLC in solid–liquid lubrication system addivated with Cu nanoparticles

Judicious selection of additives having chemical and physical compatibility with the DLC films may help improving the triboligical properties and durability life of DLC-oil composite lubrication systems. In this study, Cu nanoparticles were added to PAO6 base oil to compose a solid-liquid composite lubrication system with W-DLC film. The effects of nanoparticle concentration, test temperature and applied load on tribological performance were systematically studied by a ball-on-disk friction test system. The tribological results illustrated that Cu nanoparticles could lower the coefficient of friction (COF) and dramatically reduce the wear rates of W-DLC films. The optimal tribological behavior was achieved for the 0.1 wt% concentration under 30 °C and the applied load of 100 N. The test temperature and applied load were vital influencing factors of the solid–liquid lubrication system. The bearing effect and soft colloidal abrasive film of spherical Cu nanoparticle contributed to the excellent tribological performance of the composite lubrication system under mild test conditions, meanwhile, the local delamination of W-DLC film and oxidation were the main causes of the friction failure under harsh test conditions. With test temperature and applied loads increase the degree of graphitization of the W-DLC film increased. In conclusion, there are several pivotal factors affecting the tribological performance of solid–liquid lubrication systems, including the number of nanoparticles between rubbing contact area, graphitization of the worn W-DLC films, tribofilms on the worn ball specimens and oxidation formed in friction test, and the dominant factor is determined by the testing condition.

Continuous Lubricant Film Thickness Measurement Between Piston Ring and Cylinder Bore

Measurement of film thickness between piston ring and cylinder bore has been a challenge for decades; laser-induced fluorescence (LIF) method was used by several groups, and promising results are obtained for the investigation of lubricant film transport. In this study, blue light generated by a laser source is transmitted to a beam splitter by means of a fiber optic cable and combined with another fiber optic line, then transmitted to the piston ring and cylinder bore conjunction. The light causes the fluorescence dye present in the lubricant to emit light in a longer wavelength, i.e., green. Reflected light is recollected; blue wavelength components are filtered out using a narrow band pass optical filter, and only components in the florescence wavelength is transmitted to a photomultiplier tube. The photomultiplier produces a voltage proportional to instantaneous lubricant film thickness. Then, the photomultiplier signal is calibrated for lubricant film thickness using a laser textured cylinder bore with known geometries. Additional marks were etched on the liner for calibration. The LIF system is adapted to a piston ring and cylinder bore friction test system simulating engine conditions. Static piston ring and reciprocating liner configuration of the bench test system allow the collection of continuous lubricant film thickness data as a function of crank angle position. The developed system has potential to evaluate new designs, materials, and surface properties in a controlled and repeatable environment.

Effect on friction reduction of micro/nano hierarchical patterns on sapphire wafers

As well as the micro patterns, many functional surfaces exhibit micro/nano hierarchical patterns. Micro- and nano-patterned surfaces can be fabricated using various techniques including photolithography, electron-beams, and so on. However, these processes were developed for semiconductor fabrication and are not convenient for large-area applications. In this paper, we describe a manufacturing process for micro/nano hierarchical patterns using a laser and an abrasive air jet, whereby the laser is used to manufacture microscale patterns, and an abrasive air jet is applied to the micro-patterned surface to generate the nanoscale patterns. This method is a simple process that can be used to rapidly manufacture hierarchical patterns, making it suitable for large-area applications. We also developed a friction test system, which minimizes external vibrations and sample wear during the measurements. Our results showed that the coefficient of friction of the hierarchical patterns was 12% smaller than that of microscale patterns.

Effects of Residual Gas on Tribochemical Reactions of SUJ2 Steel in Vacuum and in Argon Gas Atmosphere

To analyze the mechanisms of tribochemical reactions occurring between atmospheric gases and materials induced by friction, the authors have developed a friction test system with integrated XPS. The system can analyze worn surfaces in various environments using XPS without air exposure. The results of friction tests in vacuum showed that the native oxide film that formed on the bare surface was worn by friction in vacuum. The results of the friction tests in an Ar gas atmosphere also showed the same results as the friction tests in vacuum. However, it has been suggested that some tribochemical reactions with trace amounts of residual gas occur during friction tests in an Ar gas atmosphere. The results of the friction tests and XPS analyses indicated that our friction test system with integrated XPS was useful for analyzing tribochemical reactions between atmospheric gases and materials.

Effect of deposition pressure on the adhesion and tribological properties of a-CN x H films prepared by DC-RF-PECVD

Hydrogenated carbon nitride (a-CNxH films) was deposited on n-type single-crystal Si (100) by direct current radio frequency plasma-enhanced chemical vapor deposition (DC-RF-PECVD), under the working pressure of 5.0–17.0 Pa, using the CH4 and N2 as feedstock. The composition and surface morphology of the a-CNxH films were characterized by means of Raman spectroscopy and atomic force microscopy, while the Young’s modulus, elastic recovery, adhesion strength, and tribological properties were evaluated using nano-indentation, scratch test and friction test system. It was found that the surface roughness and Raman spectra peak intensity ratio ID/IG of the films increased with the increase of working pressure, while the Young’s modulus, elastic recovery and adhesion strength of the films significantly decreased. Moreover, the tribological properties of the films also varied with the working pressure. The wear life sharply increased with the increase of working pressure from 5.0 Pa to 7.5 Pa, further, an increase in the deposition pressure led to a gradual decrease in the wear life, consequently, the a-CNxH film deposited at 7.5 Pa exhibited the longest wear life. The deposition pressure seemed to have slight effect on the average friction coefficients, whereas the surface roughness and adhesion strength have deteriorated with increasing deposition pressure.

Surface roughness of a hot-dipped galvanized sheet steel as a function of deformation mode

A hot-dipped galvanized zinc-coated sheet steel was deformed with three different laboratory test systems: a Marciniak punch system, a flat-die friction test system, and a cupping system. These systems were able to impose various combinations of deformation modes to the sheet. The deformation modes include: (1) strain without die contact, (2) sliding, (3) pressing, and (4) bending. Strain measurements from the electrolitically gridded specimens were made at the same locations as surface profilometry measurements, allowing a direct correspondence of surface roughness with strain. Quantification of the roughening as a function of strain, sliding and bending was determined. The roughening rate depends upon the strain level as well as the strain path. Increased strain without die contact causes an increase in the surface roughness with strain paths close to plane strain exhibiting the highest roughening rate. The deformation modes of sliding, pressing, and bending cause a decrease in the surface roughness (i.e. smoothing) to occur. A first-order model is proposed to account for the surface roughness as a function of these deformation modes.

Angle of contact between sheet and die during stretch–bend deformation as determined on the bending-under-tension friction test system

Laboratory tests, designed to assess the frictional behavior and formability of sheet metal, rely on direct measurement of pulling and contact forces for friction evaluation. The bending-under-tension friction test subjects a strip to bending as it slides over a cylindrical die surface and can evaluate sheet forming behavior during stretch–bend deformation. To gain a better understanding of sheet–die interaction, the bending and unbending response of the sheet as it contacts the cylindrical die was investigated. The existence of bending and unbending pressure peaks as well as the resulting extent of the angle of contact between the sheet and the die was observed experimentally using a Kynar® piezoelectric sensor. Direct evidence of pressure peaks during stretch–bend deformation of sheet steels is presented. The extent of the contact angle is less than the geometrical angle-of-wrap and increases with strip tension. The experimental findings for contact angles compare favorably to the predicted results from a simplified vector analysis of strip tension and strip-bending resistance.

Piston Ring-Cylinder Bore Friction Modeling in Mixed Lubrication Regime: Part II—Correlation With Bench Test Data

A bench friction test system for piston ring and liner contact, which has high stroke length and large contact width has been used to verify the analytical mixed lubrication model presented in a companion paper (Part 1). This test system controls the speed, temperature and lubricant amount and records the friction force, loading force, crank angle signal and contact temperature data simultaneously. The effects of running speed, applied normal load, contact temperature and surface roughness on friction coefficient have been investigated for conventional cast-iron cylinder bores. Friction coefficient predictions are presented as a function of crank angle position and results are compared with bench test data. Analytical results correlated well with bench test results.