Search

This study aimed to evaluate the repeatability of locked-wheel skid trailer (LWST) and sideway-force coefficient routine investigation machine (SCRIM) measurements and investigate the influences of test speed and test temperature on the friction measurements. This study selected 14 test sections from the NCAT Test Track with different surface texture and friction characteristics. The LWST and SCRIM tests were conducted at different test speeds and test times (or temperatures) on the two consecutive days. The repeatability analysis indicates that both LWST skid number (SN) and SCRIM reading (SR) measurements were most repeatable at a test speed of 50 mph and tangent section. The SN measured in the late afternoon and SR measured at noon were more repeatable than those measured at other times. This study recommended an acceptable precision of friction measurement be within 2.5 SN or 3 SR units. In addition, this study concluded that the SN and SR had a good linear correlation. The statistical regression analysis demonstrates that test speed, air temperature, pavement mean profile depth, and pavement type were significant variables affecting asphalt pavement friction. The developed regression models for SN and SR were helpful to correct the friction measurements to a reference speed or temperature. [ABSTRACT FROM AUTHOR]

Concrete pavements comprise a considerable portion of pavements that are currently in use. This paper presents the results from a laboratory investigation on the effect of temperature and surface texture on the skid resistance of concrete pavements. Briquettes representative of concrete pavements were created and textured in the laboratory. Readings of skid resistance on laboratory specimens were obtained using a portable British pendulum tester. Water and liquid hand soaps were used as lubricants in an attempt to separate the adhesion and hysteresis components of friction. In order to simulate the wear and ageing of concrete pavements, several cycles of polishing were applied to the briquettes. Tests were conducted at five different temperatures. The results showed that there is a correlation between the magnitude of friction components and temperature. A normalisation procedure for friction measurements based on temperature was developed, which can be used to normalise measurements to a standard temperature of 293·15 K. [ABSTRACT FROM AUTHOR]

This study examines surface roughness measurements via piezo acoustic disks and appropriate signal processing. Surface roughness is one characteristic of surface texture that can have various irregularities inherent to manufacturing methods. The surface roughness parameters and corresponding surface profiles are acquired by a stylus profilometer. Simultaneously, elastic waves propagated along metal surfaces caused by the friction of a diamond tip are obtained in the form of raw sound via piezo acoustic disks. Frequency spectrum analysis showed apparent correlations between the traditionally obtained measurement parameters and the piezo acoustic measurement data. Thus, it is concluded that acoustic friction measurement shows promising results as a novel measurement method for the surface roughness states of certain materials. [ABSTRACT FROM AUTHOR]

Ungrooved stone mastic asphalt (SMA) provides an alternate to grooved dense graded asphalt (DGA) as a runway surface. To be verified as suitable in this application, SMA must provide similar or better asphalt surface performance, compared to DGA, and must achieve regulated aircraft skid resistance requirements. A pilot runway resurfacing project provided the basis for this laboratory and field comparison of ungrooved SMA to grooved DGA as a runway surface. Laboratory performance testing demonstrated adequate and comparable deformation, fatigue and moisture resistance of SMA, while the quality assurance records indicated acceptable asphalt production. The construction records indicated that SMA had a lower air void content in the compacted layer, which can only provide a more durable surface. Most importantly, the aircraft skid resistance of SMA exceeded that of grooved DGA, based on surface macro-texture and wet friction measurements. It was concluded that SMA performed equal to or better than DGA, particularly with regard to surface texture and wet friction and it is recommended that airports consider ungrooved SMA as a runway surface in the future. The demonstration project should also be monitored in the future, to verify the long-term performance of SMA, compared to the DGA. [ABSTRACT FROM AUTHOR]

This work investigates the mechanisms for friction reduction in textured journal bearings. The measured friction of laser-etched connecting-rod big-end shells was compared with a non-textured reference under engine-like conditions. Experiments covered several working conditions, and the friction and lubricant film temperatures were measured for three texture configurations. The origin of the verified friction reduction was explored using a numerical model that simulates the hydrodynamic lubrication and global thermal effects. The simulation results accurately matched the friction measurements, revealing that the microscopic mechanisms of reduction in lubricant shear stress and effective viscosity due to texture-induced cavitation act simultaneously to reduce the friction coefficient for the textured shells. The findings have practical applications for the optimal design of textured hydrodynamic bearings. • Friction in textured journal bearings was experimental and numerically investigated. • A journal bearing model with thermal effects was validated using experimental data. • Textures reduced the lubricant shear stress and viscosity and lowered friction. • The shear area reduction mechanism for textured hydrodynamic bearings was confirmed. [ABSTRACT FROM AUTHOR]

Maintaining desired pavement friction is an effective way to reduce the crash rate. Pavement texture plays an important role in tire-pavement friction performance. However, the contribution of texture at different depths or wavelengths to friction measurement has not been fully understood. This study conducts a multiresolution analysis using three-dimensional (3D) asphalt pavement texture data to correlate pavement texture to friction measurements. Between 2014 and 2018, multiple rounds of pavement texture and friction data were acquired on two field sites. The top-surface topography of 3D texture data is sliced with eight depths to explore the critical contact depth between pavement texture and tire rubber for friction testing. At each depth, 3D texture data is decomposed into sub-images via discrete wavelet transform to extract texture features at 11 wavelengths ranging from 0.1 mm to 102.4 mm. Subsequently, the wavelet energy of each wavelength is calculated as the texture indicator. Finally, the texture energy matrix at different wavelengths and depths along with the ambient temperature during friction testing are correlated with the measured friction data using cross-validation and step-wise multivariate linear regression. The pavement texture of wavelengths up to 3.2 mm at the top 2.5 mm of top-surface topography is identified as the critical contact zone for pavement-tire interaction. [ABSTRACT FROM AUTHOR]

Skid resistance properties of airfield pavements substantially affect the safety of the conducted aircraft operations. The evaluation of these properties is not limited to the measurements of friction coefficient defining the friction state of pavement, but also includes the measurements of texture depth of pavement (micro- and macro-texture). The authors focused on the currently applied research methods used to assess the skid resistance properties of airfield pavements. In addition, the requirements in this field and the assessment criteria of the obtained results were also addressed. Example results of field tests and their short analysis were also presented. Besides, it was stressed the direction of further works conducted by the authors, which concerns the development of the research method used to assess the skid resistance properties of airfield pavements, precisely in the field of the measurement of texture depth of pavements. [ABSTRACT FROM AUTHOR]

Abstract The ultra-high molecular weight polyethylene (UHMWPE) has become one of the most popular and reliable material for water-lubricated bearings in recent years. In this study, three kinds of new Koch snowflake textures were designed on the surface of the UHMWPE to try to decrease friction and prolong the service life of the bearings. The wear process of the UHMWPE/QSn7-0.2 rubbing pair was analyzed using a specially designed tester under water-lubricated conditions. The analysis results demonstrated the testing velocity and load significantly affected the friction coefficient of the UHMWPE specimens. The UHMWPE specimen without texture-treatment had higher friction coefficient than that of the textured UHMWPE specimens at high velocity, where the maximum rate of increase was 35.2% at the velocity of 350r/min compared with non-texture. The dominant wear mechanism was abrasive wear and slight adhesive wear for the non-texture UHMWPE sample, and the wear mechanism of textured samples was slight abrasive wear. The wear performance of the UHMWPE with composite texture was superior to that of other textures, which was mainly attributed to the micro hydrodynamic bearing effect and stepped bearing effect. As a result, the findings of this work can provide experimental foundation for texture design and optimization on UHMWPE surfaces for better service of the marine water-lubricated bearings. Highlights • The UHMWPE specimen without texture-treatment had higher friction coefficient than that of the textured UHMWPE specimens at high velocity, where the maximum rate of increase was 35.2% at the velocity of 350r/min compared with non-texture. • The dominant wear mechanism was abrasive wear and slight adhesive wear for the non-texture UHMWPE sample, and the wear mechanism of textured samples was slight abrasive wear. The dominant wear mechanism was abrasive wear and slight adhesive wear for the non-texture UHMWPE sample, and the wear mechanism of textured samples was slight abrasive wear. • The wear performance of the UHMWPE with composite texture was superior to that of other textures, which was mainly attributed to the micro hydrodynamic bearing effect and stepped bearing effect. [ABSTRACT FROM AUTHOR]

This paper optimizes the coverage of circular micro-textures on bearing sliders aiming at improving their tribological performance. Grid-like array of textures are arranged to present or absent, which are respectively marked as 1 and 0. Genetic Algorithm is used to evolve the coverages of textures. The algorithm allows the derivation of preferable area for texture coverage in shape of pyramid at the inlet of slider. Evaluation of influences of convergence ratio and width demonstrates that sliders with small convergence ratio and width tend to result in significant tribological improvement effect. Subsequent experimental tests confirmed the achievement of low friction coefficient of the so optimized texture coverage. [ABSTRACT FROM AUTHOR]

This study utilizes close range photogrammetry (CRP) to measure the texture of asphalt pavement surfaces with a view to explaining the variation of friction measurements obtained using a GripTester. A handheld camera was employed to capture images at different locations on both lanes of pavement sections using a scale rule for identification of control points. Proprietary software were employed for creation and analysis of 3D models from the images to determine pavement surface texture parameters. Different scenarios were considered including pavement surface analysis before and after filtering for micro- and macro-texture separation. Thresholding with respect to height to analyze the top 1–2 mm of the surface was also considered. Texture parameters were then related to friction measured at the image capture locations. The lane with higher friction values generally showed higher individual texture parameters across different scenarios. However, meaningful texture-friction correlations along the lanes were only obtained with the top 2 mm of the surface. Stepwise regression indicated that the density of peaks (Spd) and the peak material volume (Vmp) best correlate (R 2  = 0.75–0.76) with friction, but the Spd is more influential. These parameters can be used as indicators of pavement surface friction during its service life. [ABSTRACT FROM AUTHOR]

Ultra high molecular weight polyethylene (UHMWPE) has been the most commonly used bearing material in artificial hip and knee replacements. But wear and wear debris of UHMWPE has been the most important problem which cause aseptic loosening and revision surgery of these replacements. For enhangement of wear resistance, new generation UHMWPE materials have been developed and different surface modification techniques have been tried. The objective of this study is to determine the effect of surface dimples on wear behavior of conventional UHMWPE and vitamin E blended UHMWPE (VE-UHMWPE) in ultra-pure water lubrication conditions. Pin-on-disc tribotester was used for measurement of friction coefficient and wear. 0.5 mm in diameter dimples were machined on the surfaces of UHMWPE and VE-UHMWPE discs. CoCrMo pins were used as counter surface. Results were evaluated in terms of materials and presence of dimples. [ABSTRACT FROM AUTHOR]