トレッド内部の変形を利用したタイヤと接地面間の摩擦係数測定

Measurement of road friction coefficient using strain on tire sidewall

Measurement of the coefficient of friction (COF) between the shoe/sole and the floor is essential in understanding the risk of slipping accidents. COF measurements between the footwear material and floor using a slipmeter were commonly performed using flat footwear pads. Such measurements might underestimate the actual slip resistance of people's daily experiences because tread groove design on footwear is very common. This research investigates the effects of the tread groove width on the measured COF. The results indicated that tread groove width significantly (p＜0.0001) affect COF under various footwear material, floor, and contamination conditions. Wider tread grooves resulted in higher COF values with a few exceptions especially on oil contaminated floor. Stepwise regression was performed to establish a linear regression model between COF and the tread groove width under footwear material/floor/liquid-contamination conditions. A seven-independent-variable model with an adjusted R^2 of 0.74 was obtained. The lack of fit test result for the model was significant at p＜0.0001, indicating that the model adequately fit the friction measurement data.

This study investigates the influences of slopes on objective friction measurements of different floor materials. It is known that a person is more likely to slip when walking on a slope than when walking on a level surface. In term of the prevention of falls for elders and MMH (manual material handling) workers, slope is more commonly in the design of barrier-free environments. However, it could be a potential environmental risk of slip accidents. The environmental problems were generally caused by poor floor slipperiness. The coefficient of friction (COF) is one of important objective indexes to assess floor slipperiness. It is worthy to investigate that the influences of slope on COF. Thus, COF measurements under different slopes, floor materials and surface conditions were conducted in this study. The data were analyzed to investigate the influence of slope on objective friction measurements of floors. The results showed that the rougher surface and dry conditions had the higher COF values. The different slopes result in significant COF values; however, there is no significant trend. Therefore, there should be more warning signs and slip resistance facilities or accessories to reduce the chance to slip and fall on the slopes.

In order to characterize friction and wear behavior between cylindrical specimens and flexible counterface materials such as magnetic tape, a tribometer is suggested. The tribometer is used to investigate the behavior between video cassette recorder (VCR) head drums and VCR tapes. Friction coefficients of uncoated and diamond-like carbon (DLC) film coated head drums of Al alloy are compared before and after a wear test. Before the wear test, an uncoated head drum shows friction coefficients ranging from 0.22 to 0.3 as the applied tension increases from 200 to 600 gf at the sliding speed of 0.16 m/s. The friction coefficients of DLC coated head drum are 14 to 30 % lower than those of uncoated head drums. At the sliding speed of 4.9 m/s, the friction coefficients of both uncoated and DLC coated drums are reduced to less than 0.1. After the wear test, however, the friction coefficients of uncoated head drums increase to the range from 0.3 and 0.47 depending on the applied tensions. Furthermore, the friction coefficients are not reduced even at the high sliding speed of 4.9 m/s. DLC coated head drums, on the other hand, exhibit similar friction coefficients to those before the wear test. Degradation of frictional property in the uncoated head drum is discussed in terms of the surface damages mainly due to magnetic metal oxide particles transferred from VCR tapes. This result shows that the DLC coating of VCR head drum can improve the friction and wear properties. It is also observed that the DLC coating can reduce the damage of VCR tapes.

The shaking table experiments on sliding and overturning of CAP1400 spent fuel storage rack with the effect of FSI

Gels have some unique characteristics such as low frictional properties [1][2], high water content and materials permeability. Double Network (DN) gels having a mechanical strength of 30MPa for the maximum breaking stress in compression was developed [3] in the last decade. Their frictional coefficient and mechanical strength are comparable to human cartilages. Gels are prospective materials that could be used for the parts of the human body. In this study, we focus on the dynamic frictional interface of the friction of polymer gels and aim to develop a new apparatus with a polarized microscope for in-situ observation and frictional measurement. We first rubbed hydrogel and glass plate sandwiching hydroxypropylcellulose (HPC) solution on the stage of a polarization microscope. The birefringence flow of HPC polymer solution enabled the observation of the dynamical interface. After the experiment, we designed an observation instrument that included an inverted microscope and a friction-measuring machine. This new instrument can observe the frictional interface and measure the frictional coefficient at the same time. We hope the comparison between direct observation with this instrument and the measurement of friction coefficient will become a foothold to elucidate distinctive frictional phenomena that can be seen in soft and wet materials.

This paper reviews the literature concerning the measurement of friction coefficients (μ) for elastomers and summarizes our data measured under static or breakaway conditions against epoxy painted steel using ∼ 176 psi contact pressure. Although largely related to missile launch system applications, the μ values presented are specific for interface pairs, normal loading force, and speed. Therefore, this article should serve as a starting point for those requiring specific friction data for selected elastomers.

Friction at the interface of die and workpiece plays an important role in metal forming. This paper introduces measurement methods of friction coefficient at curved surface in recent years, and divides the friction coefficient measurement methods into direct measurement methods and indirect measurement methods. Furthermore, the working principles and technical characteristics of these methods are explained.

Friction and wear measurements of laser-sintered and coated parts

The main aim of this work is to compare the results of different friction models to the experimental data obtained with a Mini Traction Machine (MTM). This test system allows the measurement of friction coefficient in point contacts (ball-disc) under a wide range of parameters, such as temperature, slide-roll ratio, lubricant, material, load or velocity.

Gels are soft and wet materials that differ from hard and dry materials like metals, plastics and ceramics. These have some unique characteristic such as low frictional properties, high water content and materials permeability. A decade earlier, DN gels having a mechanical strength of 30MPa of the maximum breaking stress in compression was developed and it is a prospective material as the biomaterial of the human body. Indeed it frictional coefficient and mechanical strength are comparable to our cartilages. In this study, we focus on the dynamic frictional interface of hydrogels and aim to develop a new apparatus with a polarization microscope for observation. The dynamical interface is observed by the friction of gel and glass with hudroxypropylcellulose (HPC) polymer solution sandwiching. At the beginning, we rubbed hydrogel and glass with HPC solution sandwiching on stage of polarization microscope. Second step, we designed a new system which combined microscope with friction measuring machine. The comparison between direct observation with this instrument and measurement of friction coefficient will become a foothold to elucidate distinctive frictional phenomena that can be seen in soft and wet materials.

In the curling sport, the coefficient of friction between the curling stone and pebbled ice is crucial to predict the motion trajectory. However, the theoretical and experimental investigations on stone–ice friction are limited, mainly due to the limitations of the field measurement techniques and the inadequacy of the experimental data from professional curling rinks. In this paper, on-site measurement of the stone–ice friction coefficient in a prefabricated ice rink for the Beijing Winter Olympics curling event was carried out based on computer vision technology. Firstly, a procedure to determine the location of the curling stone was proposed using YOLO-V3 (You Only Look Once, Version 3) deep neural networks and the CSRT Object tracking algorithm. Video data was recorded during the curling stone throwing experiments, and the friction coefficient was extracted. Furthermore, the influence of the sliding velocity on the friction coefficient was discussed. Comparison with published experimental data and models and verification of the obtained results, using a sensor-based method, were conducted. Results show that the coefficient of friction (ranging from 0.006 to 0.016) decreased with increasing sliding velocity, due to the presence of a liquid-like layer. Our obtained results were consistent with the literature data and the friction model of Lozowski. In addition, the experimental results of the computer vision technique method and the accelerometer sensor method showed remarkable agreement, supporting the accuracy and reliability of our proposed measurement procedure based on deep learning.

Paper X (iii) A preliminary investigation of the ‘cushion bearing’ concept for joint replacement implants

A new device for simultaneous measurement of friction force, normal force and friction coefficient

The standard method of evaluating the lubricity of intermittent urinary catheters with coefficient of friction (CoF) testing is not physiologically relevant, while there is also a dearth of published research on catheter-associated urethral micro-trauma. We developed a novel human urethral epithelial cell-seeded model of the urethra to replace the rubber counter-surface used in standard CoF testing. This cell-seeded model, in conjunction with a novel testing device, allows an investigation of catheter-associated epithelial micro-trauma in vitro for the first time. The CoF of four brands of commercially-available hydrophilic-coated intermittent catheters was measured using both the rubber and urethral model counter-surfaces. Post-catheterisation of the urethral model, the damage to the epithelial layer was analysed using standard cell imaging. The rubber counter-surface was shown to over-estimate the CoF of gel-coated catheters compared to our urethral model due to stick-slip behaviour caused by polymer-on-polymer interaction of the catheter base material on the rubber counter-surface. We identified no deleterious effect due to the presence or design of catheter eyelets to either the CoF measurements or the degree of epithelium damage in our model. Furthermore, the epithelial damage did not correlate with the measured CoF of the low friction catheters, suggesting a more nuanced pathogenesis of urethral irritation and casting doubt on the translatability of a solely mechanical assessment of lubricity of urinary catheters to a clinical effect.