Analysis of a clutch damper using a discrete model

It is important to have a precise model for the clutch damper in order to simulate the entire powertrain of a vehicle and predict the responses of the system. In this research, we developed a new model in which the spring used in the clutch damper is divided into a finite number of elements. The model takes many unique properties of arc-shaped springs into consideration and is anticipated to be more precise than conventional simple models. With the model, two meaningful results were presented which can be utilized afterwards. One is a simulation concerning the peak torque transmitted via the clutch damper. The other is a simulation that shows the hysteretic characteristics of the clutch damper.     

Design parametric study based fabrication and evaluation of in-pipe moving mechanism using shape memory alloy actuators

An in-pipe moving mechanism based on design parametric study of dynamic characteristics of clamping or moving module comprising shape memory alloy (SMA) spring actuators has been fabricated and evaluated under in-pipe condition. Conventional in-pipe moving mechanisms for pipe inspection, driven by electromagnetic motors, have large volume and mass. The SMA actuator can be an alternative for a small-sized in-pipe moving mechanism due to its great power-to-weight ratio and simple structure. Therefore, spring type SMA actuators are selected to fabricate an inchworm-like moving mechanism that consists of clamping and moving modules. For selection of proper operating type (a bias type or a differential type) for clamping module and moving module, displacements and dynamic characteristics of each operating type have been investigated. Based on experimental results, we decide some design parameters such as wire diameters, spring diameters and the numbers of turns of SMA spring actuators and fabricate the in-pipe moving mechanism according to the designed results. A moving speed of 34 mm/min and traction force of 0.4 N have been obtained from the driving experiment in a pipe with the diameter of 39 mm.     

Towards a model for the number of airborne particles generated from a sliding contact

Recently, much attention has been given to the influence of airborne particles in the atmosphere on human health. Sliding contacts are a significant source of airborne particles in urban environments. Airborne particles may be generated by disc brakes and wheel-rail contacts. This paper presents a new model for determining the number of airborne particles generated by a sliding contact. Previously presented data from a pin-on-disc tribometer equipped with airborne particle counting instrumentation was used to verify the model. The derived particle rate is proportional to the load for the ball bearing steel material evaluated. Furthermore, the model incorporates three particle regimes with distinct number peaks; one with ultra fine particles with a peak around 0.08 μm, one with fine particles with a peak around 0.35 μm and one with coarse particles with a peak around 2 μm, that can be used to rank the number of generated particles from different material combinations and contact conditions.     

Characteristics of Extrusive Wear and Transition of Wear Mechanisms in Elevated-Temperature Wear of a Carbon Steel

The dry sliding wear of a medium carbon steel with different microstructures was measured under the normal load range of 50–150 N at 400°C by a pin-on-disc high-temperature wear setup. The wear behavior and wear mechanism were systematically studied; in particular, the characteristics of extrusive wear and the transition of wear mechanisms were investigated. Under low normal loads, the wear is oxidative type wear. Once the normal load reached a critical value, a mild-to-severe wear transition occurred, and subsequently an extrusive wear prevailed. The mild-to-severe wear transition depended on the microstructure of matrix; the critical normal load of the transition was 112.5 N for tempered sorbite, 125 N for lamellar pearlite, and 137.5 N for tempered martensite and tempered troostite. As oxidative wear prevailed, a thick oxide layer about 20–30 μ m and a plate-like wear debris with regular outline were recognized. However, as the extrusive wear occurred, the wear rate abruptly increased but the friction coefficient was reduced. The extrusive wear predominated due to thermal softening of the matrix and presented a superthin oxide layer (less than 0.5 μ m) and low oxide content on worn surfaces, accompanied by the appearance of ribbon-like wear debris.     

A Study of Wear Chemistry and Contact Temperature Using a Microsample Four-Ball Wear Test

This study demonstrates that insight into the tribological reactions taking place in mixed and boundary lubrication can be provided by combining microsample four-ball wear tests with chemical analysis using gel permeation chromatography (GPC) as the principal analytical tool. At the end of the microsample four-ball wear test the lubricant turns into a grease-like mixture preventing the liquid lubricant from recirculating into the wear track and thus causing failure. Analyses of the various lubricant samples after their failure in the microsample test all show a relatively small amount of insoluble deposits and a large quantity of unreacted fresh lubricant. Virtually no intermediate reaction products were found. Combining this information with lubricant stability and the fact that a large quantity of lubricant flowed through the sliding junction while only a small portion was oxidized suggests that two very different thermal environments exist in the concentrated contact. The insoluble deposits are typical of thermal oxidative reactions that require temperatures of400°C or above. The unreacted lubricant found at failure indicates that this portion of the lubricant sample was maintained at temperatures of 150°C or below. The formation of grease-like mixture with as little as four percent reacted material indicates the remaining liquid lubricant and its insoluble reaction deposits were well mixed throughout the test. These findings suggest that the hot zones causing severe lubricant degradation are in the immediate vicinity of the asperity-asperity contacts while the low temperature zone - the valleys between asperities which are in the majority - are much cooler.     

Effect of Particle Size on the Wear Resistance of Alumina-Filled PTFE Micro- and Nanocomposites

It was long supposed that the ability of hard particle fillers to reduce the wear rate of unfilled PTFE (typically ～ 10^{? 3} mm ³ /Nm) by an order of magnitude or more was limited to fillers of microscale or greater, as nano-fillers would likely be encapsulated within the large microscale PTFE wear debris rather than disrupting the wear mechanism. Recent studies have demonstrated that nano-fillers can be more effective than microscale fillers in reducing wear rate while maintaining a low coefficient of friction. This study attempts to further elucidate the mechanisms leading to improved wear resistance via a thorough study of the effects of particle size. When filled to a 5% mass fraction, 40- and 80-nm alumina particles reduced the PTFE wear rate to a ～ 10^?7 mm ³ /Nm level, two orders of magnitude better than the ～ 10^?5 mm ³ /Nm level with alumina micro-fillers at sizes ranging from 0.5 to 20 μm. Composites with alumina filler in the form of nanoparticles were less abrasive to the mating steel (stainless 304) countersurfaces than those with microparticles, despite the filler being of the same material. In PTFE containing a mixture of both nano- and micro-fillers, the higher wear rate microcomposite behavior predominated, likely the result of the continued presence of micro-fillers and their abrasion of the countersurface as well as any overlying beneficial transfer films. Despite demonstrating such a large effect on the wear rate, the variation of alumina filler size did not demonstrate any significant effect on the friction coefficient, with values for all composites tested additionally falling near the μ = 0.18 measured for unfilled PTFE at this study's 0.01 m/s sliding speed.     

Wear transitions and mechanisms in lubricated sliding of a molybdenum coating

Wear tests were performed for a Mo coating sliding against bearing steel specimen under boundary lubrication conditions. Results were compared with (i) hardened carbon steel sliding against bearing steel and (ii) Mo coating sliding against boron cast iron. Tests indicated that the wear resistance of the Mo coating was superior to that of the uncoated hardened steel. The initial surface topographies of the coatings were suitable to facilitate the transfer of the applied load directly onto the phases and prevented the softer phase directly involved in the wear process. The morphology of the transfer layer formed on the Mo coating was identified by X-ray diffractometry. And the layers were expected to supply an in situ lubrication effect. The wear rates of the coating against a steel slider were lower compared with those worn against a cast iron slider. With increasing applied load, the probability of the harder phases crack and fracture increased until the fraction of the unfragmented phases on the contact surfaces was no longer adequate to support the load. The dominant wear mechanisms in each wear regime were discussed.     

Wear and Friction Characteristics of a Selected Stainless Steel

Dry sliding wear tests were performed for 3Cr13 steel with various tempered states at 25–400°C; wear and friction characteristics as well as the wear mechanism were explored. With an increase in test temperature, the wear rate decreased accompanied by an increase in tribo-oxides. The fluctuation of friction coefficient was slight at 25–200°C but became violent at 400°C. At 25–200°C, adhesive wear prevailed due to trace or less tribo-oxides; at 400°C, oxidative wear prevailed with the predominant tribo-oxides of Fe₃O₄ and Fe₂O₃. It can be suggested that the antioxidation of the stainless steel postponed the occurrence of oxidative wear to a higher test temperature. For adhesive wear, the wear resistance, roughly following Archard's rule, was directly proportional to hardness besides the specimen tempered at 500°C with grain boundary brittleness. But for elevated-temperature wear, a better wear resistance required thermal stability and an appropriate combination of hardness and toughness.     

A Study on the Sliding Wear of Hybrid PTFE/Kevlar Fabric/Phenolic Composites Filled with Nanoparticles of TiO2 and SiO2

TiO₂ and SiO₂ nanoparticles were introduced into hybrid polytetrafluoroethylene (PTFE)/Kevlar fabric/phenolic composites. The results showed the incorporation of TiO₂ nanoparticles can reduce the wear rate of the fabric/phenolic composite at elevated temperatures, although the wear of hybrid PTFE/Kevlar fabric/phenolic composite did not change much when TiO₂ or SiO₂ nanoparticles were used as filler. The wear behavior was explained in terms of morphology of transfer films and worn surfaces. There was a good correlation between the morphology of transfer film and wear results.     

A study of airborne wear particles generated from organic railway brake pads and brake discs

Brake pads on wheel-mounted disc brakes are often used in rail transport due to their good thermal properties and robustness. During braking, both the disc and the pads are worn. This wear process generates particles that may become airborne and thus affect human health. The long term purpose of ‘Airborne particles in Rail transport’ project is to gain knowledge on the wear mechanisms in order to find means of controlling the number and size distribution of airborne particles. In this regard, a series of full-scale field tests and laboratory tests with a pin-on-disc machine have been conducted. The morphology and the matter of particles, along with their size distribution and concentration, have been studied. The validity of results from the pin-on-disc simulation has been verified by the field test results. Results show an ultra-fine peak for particles with a diameter size around 100 nm in diameter, a dominant fine peak for particles with a size of around 350 nm in diameter, and a coarse peak with a size of 3–7 μm in diameter. Materials such as iron, copper, aluminum, chromium, cobalt, antimony, and zinc have been detected in the nano-sized particles.