水潤滑下におけるゴムの摩擦機構の解明と耐滑スポーツシューズへの応用

Tohoku University山口健課

An evaluation of shoe tread parameters using FEM

Within this paper, a three-dimensional finite element (FE) model of a uniformly loaded, single rubber block, is described and run using loading conditions replicative of a standard slip resistant footwear test. The FE model considers rubber hyperelastic and viscoelastic material properties, obtained using dynamic mechanical analysis. The performance of the FE model was evaluated through analytical compression analysis and experimental contact area testing. The effect of tread grooves was investigated with relation to slip-resistance during walking. Analysis and discussion are provided of the tread model's sliding contact areas, contact pressure, stress, and front edge mechanics

Pneumatic Tire

For many years, tire engineers relied on the monograph, \u27Mechanics of Pneumatic Tires\u27, for detailed information about the principles of tire design and use. Published originally by the National Bureau of Standards, U.S. Department of Commerce, in 1971, and a later (1981) edition by the National Highway Traffic Safety Administration (NHTSA), U.S. Department of Transportation, it has long been out of print. No textbook or monograph of comparable range and depth has appeared since. While many chapters of the two editions contain authoritative reviews that are still relevant today, they were prepared in an era when bias ply and belted-bias tires were in widespread use in the United States and thus did not deal in a comprehensive way with more recent tire technology, notably the radial constructions now adopted nearly universally. In 2002, it was preposed that NHTSA should sponsor and publish electronically a new book on passenger tires, under editorship of the University of Akron, to meet the needs of a new generation of tire scientists, engineers, designers, and users. This text is the outcome. The chapter authors are recognized authorities in tire science and technology. They have prepared scholarly and up-to-date reviews of the various aspects of passenger car tire design, construction and use, and included test questions in many instances, so that the book can be used for self-study or as a teaching text by engineers and others entering the tire industry

Prediction of Slipping Accidents Using Biomechanical and Traction Analysis of Footwear Outsole Design

Slip-initiated falls due to insufficient traction are a major contributor to occupational injuries. Footwear interventions have a significant potential to mitigate slipping accidents. Unfortunately, performance of the footwear used in these interventions is variable and there is a paucity of empirical evidence supporting the validity of current methods for assessing footwear traction. Furthermore, footwear traction testing methods are expensive and require expertise, which may limit their use. These limitations may guide footwear designers toward suboptimal footwear and create barriers for safety managers to assess and identify appropriate footwear. The goal of this dissertation was to (1) guide the development of valid traction testing methods and (2) create tread assessment methods that are inexpensive and require minimal expertise. The ability of footwear traction tests under different biomechanical parameters (normal force, shoe-floor angle, and sliding speed) to predict slip outcomes were assessed based on human exposures to slippery surfaces. The combination of 250 N normal force and 17° shoe-floor angle best predicted slip risk during gait experiments. Biomechanical analysis of various shoes during human slipping events were performed to guide shoe traction measurements for additional improvements. The findings revealed that the normal force (26.7 %BW, 179 N), shoe-floor angle (22.1°) and contact time (0.02 s) at slip initiation were significantly different from current footwear traction testing standard methods (400 and 500 N, 7º, 0.10-0.30 s). Thus, current methods may need to utilize lower normal forces, larger shoe-floor angles and shorter contact duration to further improve slip risk prediction by mimicking the shoe dynamics at slip initiation. A tread assessment model was developed to predict footwear traction based on outsole design features. The statistical model predicted 88% of variation in traction using contact area, heel shape, shape factor and material hardness while controlling for the floor surface in the presence of canola oil. Safety practitioners can use this information to select shoes with high slip-resistant performance in cases where footwear traction testing apparatuses are not readily available. The findings from this dissertation may reduce slipping accidents by improving the quality and accessibility of shoe traction assessment methods

Biomechanics Of Slips In Alternative Footwear

Injuries in the workplace pose a significant burden to the health of human beings as well as financial or economic losses to occupational organizations. Slips, trips and an induced loss of balance have been identified as the major causative factor for workplace injuries involving falls (Courtney et al, 2001; Redfern et al, 2001). The bureau of labor statistics reported 15% of a total of 4,693 workplace fatalities and a total of 299,090 cases of non-fatal workplace injuries that were due to slips, trips and falls (BLS, 2011). The purpose of the study was to analyze the biomechanics of human locomotion under normal dry flooring conditions and under slippery flooring conditions with three commonly used alternative casual footwear [thong style flip-flops (ff), crocs with clogs (cc) and slip resistant low-top shoe (lt)]. The study will follow a within-subjects repeated measures design with each participant exposed to all three footwear using a counter balanced design. Eighteen healthy male participants with no orthopedic, cardiovascular or neurological abnormalities completed the study. Participants were required to come in for three testing sessions separated by at least 24 hours of rest interval and an initial familiarization day. On each testing day, participants were provided with an alternative footwear based on a counterbalanced selection and were tested for maximal voluntary contraction for lower extremity muscles and were exposed to a series of walking trails that included a normal dry surface non slip gait trial (ns); unexpected slip (us), alert slip (as) and expected slip (es). A 3 x 4 [3 (ff, cc, lt) x 4 (ns, us, as, es)] within-subjects repeated measures anova was used to analyze the dependent slip parameters (heel slip distance and mean heel slip velocity), kinematic and kinetic gait variables (mean and peak vertical ground reaction forces and lower extremity joint angles) and muscle activity (mean, peak and % maximal voluntary contraction in lower extremity muscles). Significant interactions between the footwear and gait trials were found for the slip parameters, gait parameters and muscle activity variables (p\u3c0.05). Significant interactions were folloup with post-hoc multiple comparisons using a Sidak Bonferroni correction. Based on the results from the study the alternative footwear (cc & ff) had greater slip parameters, reduced ground reaction forces and a plantar flexed foot position at heel strike compared to the lt. The us and as had greater incidence of slips than ng and es and moreover with the a priori knowledge of the slippery flooring conditions (es), the individuals were able to modify the gait kinematic and kinetic parameters rather than lower extremity muscle activity to reduce the potential for a slip. Overall, the most hazardous slips were seen with alternative footwear and during the unexpected slips folloby the alert slips. The lt had lower incidence of slips and maintained a normal gait pattern during all gait trial conditions and demonstrates to be the choice of footwear for maneuvering slippery flooring conditions that exist in both occupational and public places

Interfacial Dissipative Phenomena in Tribomechanical Systems

The book is a collection of articles on the themes of contact mechanics and non-linear dynamics. In particular, the contribution focus on the mechanisms that lead to interfacial energy dissipation, which is a crucial quantity to determine in order to correctly predict the non-linear dynamic response of mechanical systems. The book is a collection of nine journal papers, among those one editorial, one review paper, and seven articles. The papers consider different dissipative mechanisms, such as Coulomb friction, interfacial adhesion, and viscoelasticity, and study how the system response and stability is influenced by the interfacial interactions. The review paper describes old and recent test rigs for friction and wear measurements, focusing on their performance and range of operability

Caracterização dos factores de produção num processo de manucfactura de um pneu

Dissertação de mestrado integrado em Engenharia MecânicaThis dissertation has the purpose of describing the tire production methods, production variations, quality issue, specification details and the how the tire will behave. It is noted that due to the nature of the internship in the Continental Group several details cannot be described in full detail to avoid publication of trade secret details. Tires are one of the most important components in the composition of an automobile, because tires are the only connection between the car and the road. With a bad set of tires it doesn’t matter how developed car braking and power systems are unless they can transmit the necessary forces to the ground. During this internship the proponent of this dissertation helped and learnt from the industrialization department verifying several tires for specification purposes. Also a database was developed in order to automatically maintain the industrialization process papers. Once the proponent noticed the cause of the highest cause of scrap, a solution was developed and presented to the department

Assessing floor slipperiness in campus dining halls using objective and subjective measures

Floor slipperiness is a critical issue in slip and fall incidents which are a major source of occupational injuries. The objectives of this study were to investigate if the protocols used in a field study conducted in Taiwan could be used in similar environments and whether consistent results could be obtained. Protocols used in the field study to investigate floor slipperiness in western-style fast-food restaurants in Taiwan, included both objective and subjective measurements. Using the same methods as in Taiwan, friction was measured on tiles in five major working areas of 4 university campus dining hall kitchens as an objective measurement of slipperiness; the subjective measurement was employees' ratings of floor slipperiness of the same areas. The Pearson's correlation coefficient in the dining halls between the averaged friction coefficients and subjective ratings for all 20 evaluated areas across four dining halls was 0.64, which was higher than the correlation of 0.49 obtained in Taiwan. Cultural differences, the amount of water on the floors in the sink areas, and the use of college campus dining halls over fast-food restaurants might be contributors to the higher correlation coefficients in this study. However, the current study confirmed the results obtained in Taiwan, that average friction coefficient and perception values are in fair agreement, suggesting that both might be reasonably good indicators of slipperiness

A tribological investigation of windscreen wiper performance

This project focused on understanding windscreen-wiper/glass interactions with an aim to reduce friction and wear, improve wiping quality and prevent friction induced vibration, (also known as squeak). To achieve this, the contact between windscreen and wiper was simulated under laboratory conditions using a UMT2 Tribometer, which loaded a stationary rubber profile against a rotating glass disc. Then, a range of measurement and analytical techniques were used to characterize the effect of conditions on different aspects of wiper performance. Different surface conditions were reproduced by applying a range of common treatments to the glass, including hydrophobic and hydrophilic coatings. In addition to this, a new method of partially forming self-assembled monolayers was devised in order to produce test specimens with a controlled range of surface energies. It was shown that friction reduces with increasing surface energy, which is attributed to a smaller volume of water being entrained into the contact. Following this, a range of non-steady state friction behaviours were studied. These included combined friction and wear tests, where under severe conditions it was shown how friction performance is dominated by the formation and removal of burs, which prevents water from being entrained into the contact. In addition, drying tests were conducted to understand “tacky” behaviour (i.e., the peak in friction peak under partially lubricated conditions). This was shown to be controlled by decreasing the surface tension of the water, through the addition of detergent, and provided evidence to support the theory that water menisci are responsible for increasing surface area. Static friction behaviour was also investigated, and the effects of start-up velocity and stationary duration on friction were quantified and explained. The practical implications of these results are discussed in terms wiper design and material selection. To study friction induced vibration, (FIV), friction, sound and high speed video measurements were combined with finite element modelling of a rubber wiper/glass contact. In agreement with previous research, FIV only occurs when the friction versus speed curve has a negative gradient; a factor, which, in combination with the low stiffness of the materials, can lead to vibrational instabilities in the mixed regime. Results also showed that friction induced vibration is strongly affected by surface condition, and only occurs for a certain range of surface energies. This is explained by the fact that both high and low surface energies alter the gradient of the Stribeck curve thereby preventing FIV (i.e., low surface energies prevent sufficient liquid entering the contact and high surface energies attract water molecules to the surface of the glass producing a film that reduces friction). In order to study the source of squeak, simultaneous measurements were realised by a high speed camera, microphone, and laser Doppler vibrometer (LDV). This showed that although both the wiper and glass vibrate with the same frequency, it is the latter that transmits sound to the air. Results from the high-speed camera and microphone have shown that the frequency of the rubber vibration equals to the frequency of the emitted sound and the water vibration. This frequency is the same as the eigen frequencies determined from a finite element model of the wiper, which was developed. These observations led to the conclusion that friction induced noise occurs only when bending modes of the wiper are excited and this has important implications for the control of FIV since it shows that emitted sound can be eliminated by modifying the blade geometry during the design stage. Another important observation is that the frequency of squeak decreases with increasing volume of water present on the glass. This is attributed to the water effectively adding mass onto the vibrating system and hence reducing its natural frequency. Additionally, capillary waves have been for the first observed in the water surrounding the wiper contact. Based on the understanding gained, a number of recommendations are made regarding means of reducing windscreen wiper noise. Finally, in order to monitor the wiping performance of the rubber wiper, a fluorescence microscopy technique was developed to view the sliding contact. This has enabled the fluid film thickness within the blade/glass contact to be assessed and also manufacturing defects, such as notches and inclusions, to be identified as the cause of wipe quality issues, such as hazing and hairlines.Open Acces

Laser Cladding for use in Extreme Tribological Interfaces

Coatings are common in engineering applications for protecting the surface of components, either from exposure to environmental conditions or from contact with other components. Laser cladding is a coating technique which allows for thicker coatings of various alloys that enable high load bearing interfaces to operate at a wider range of loads or for longer, for example by increasing durability. This is of great benefit to the railways industry as well as other heavy industries, such as the steel industry. Laser clad coatings have been used extensively in other industries such as oil and gas for increasing the durability of drilling components; in mining and earth moving equipment, for increasing the durability of the components that come in contact with hard soil and rocks. Both are extreme interfaces. In this study, new interfaces and extreme conditions for new industries are investigated, by highlighting the laser clad coating advantages, when used under extreme conditions. The extreme test conditions have not been investigated in published literature, especially with the use of laser clad coatings. This project evaluated the performance of laser cladding coatings on railway components such as the wheel and rail. Other interfaces found in machinery in the steel industry were considered, specifically in the rolling of steel. A variety of interfaces were evaluated by modelling and testing, such as rolling-sliding, high pressure water jet erosion and impact. Three clad materials were identified as suitable for the chosen interfaces, martensitic stainless steel (MSS), Stellite 6 (Co-Cr) and a two-layer clad of Inconel 625 with Technolase. The clad parameters were fixed, resulting in constant material grades, allowing the coatings used in different interfaces to be comparable. The materials choice was based on published research on similar interfaces. Tests were performed on existing test rigs for rolling-sliding and bending tests. The impact test was performed on a rig modified specifically for this study, while a bespoke rig was built for the erosion test. Metallographic techniques were used for all materials, to prepare the samples for characterisation using optical and electron microscopy, as well as nanoindentation and microhardness. Pre- and post-test material analysis was performed. The use of computer modelling was considered mainly for the generation of test parameters, while the results from testing were compared to existing data. Key findings highlight that the use of the selected clad materials under the chosen extreme interfaces can have a positive effect on the durability of the coating, mainly by increasing the wear resistance properties of the coating. Furthermore, the two-layer clad coating showed promising results in stopping crack propagation to the substrate. The test results can be used in predictive tools by researchers in academia, as well as in industry, as a way of introducing laser cladding applications to interfaces of engineering products. Furthermore, the performance of the chosen materials indicates that this study may be used as the basis for selecting similar clad coatings for pilot trials or large scale testing