Este estudo apresenta uma investigação sobre a possibilidade de adotar o processo de solda por agitação e fricção, ou \"friction stir welding\" em substituição ao processo usual de fixação por rebitagem, na construção de um painel de fuselagem aeronáutica de dimensões compatíveis com uma aeronave regional com capacidade aproximada de cinqüenta assentos. A investigação avalia aspectos técnicos de engenharia, tais como capacidade de unir materiais heterogêneos, resistência mecânica, vida em fadiga da estrutura, aspectos de produtividade e custos associados. O processo de solda por agitação e fricção ocorre em estado sólido, não requer a introdução de um terceiro material ou qualquer tipo de arco elétrico ou atmosfera de gás inerte. Os materiais a serem unidos não atingem o ponto de fusão, mas são submetidos à severa deformação plástica, sendo misturados sem que haja fusão. As características mecânicas resultantes dos componentes soldados são equivalentes ou superiores às características dos componentes rebitados. Sob o ponto de vista econômico, existem ganhos em redução de custos de mão de obra e aumento na velocidade de produção, quando comparado ao processo de rebitagem. / This study presents an investigation about the possibility of use friction stir welding process to replace the usual riveting process to build an aeronautic fuselage panel which has its dimensions compatible to a fifty seats regional aircraft. The investigation evaluates engineering technical aspects as the capability to join dissimilar materials, the mechanical strength, structure\'s fatigue life, productivity aspects and associated costs. Friction stir welding is a solid state process where a third material deposition is not required, as well is not required any electric arc or inert gas atmosphere. The materials to be joined do not reach the fusion point, but are subjected to severe plastic deformation, being mixed without melting. The mechanical behavior of welded components is equivalent or better than the behavior of riveted components. From financial standpoint, there are benefits on labor costs reduction and increased production rate, when compared to the riveting process.

The annual cost of corrosion in the United States Navy and Coast Guard is in excess of $2.7 billion dollars. The salt water environment provides a ripe surrounding for rapid corrosion and deterioration of ship decking, which requires frequent and expensive maintenance. Decks of ships are susceptible to corrosion and wear, but must also maintain a non-slip surface in a constantly wet environment. Few options for non-skid deck materials are currently approved for use by the Navy and require frequent and expensive maintenance or replacement. A new material known as Laser Deposited Non-Skid, currently used in industrial flooring applications, shows potential for serving as a more durable non-skid material with extended service life and greater resistance to corrosion. The purpose of this research is to investigate the feasibility of Laser Deposited Non-Skid in decks of ships and to compare the corrosion, wear and cost data with existing deck materials. Sample plates of A36 and A572 steel and 5086 and 5456 marine grade aluminum alloy were coated with selected non-skid materials and subjected to laboratory salt fog testing and corrosion in environmental conditions in the Caribbean Sea. Wear behavior among non-skid materials was evaluated through wear cycles, measurement of coefficient of friction, and surface characterization. Salt fog testing was more corrosive than the actual operational environment in all cases and the Laser Deposited Non-Skid samples had the best resistance to wear and corrosion. The Peel and Stick Non-Skid demonstrated corrosion by undercutting while the Traditional Non-Skid corroded through the material. The relative area did not correlate well with friction or wear mass loss. Aluminum Laser Deposited Non-Skid appears suitable for use as a deck material on small boats. More research is needed to evaluate maintenance issues and possible stress cracking associated with the Laser Deposited Non-Skid on steel decks.

The frictional behaviour of rubber is a topic of great interest and importance due to the invaluable uses of rubber in industry. The very particular behaviour of rubber also makes rubber friction a fascinating subject matter. Despite this it is still a topic not well understood. Previous studies have attempted to link the fracture mechanics of rubber crack propagation to the adhesive friction of rubber. The feasibility of such an approach to the adhesive friction of a rough rubber against a smooth surface, a configuration which can occur in various situations such as rubber seals or windscreen wipers, has been investigated. Rolling friction, described well by a fracture-like peeling process, is used to evaluate the viscoelastic dependence of sliding friction for various combinations of surfaces. A novel use of rubber is proposed as a material for particles to be used for jamming based soft robotics applications. This area of soft robotics is comparatively new and the materials that are being used at present are neither well established nor have been examined in great detail. Rubber would offer a material easily manufactured to desired shapes and dimensions with a wide range of moduli allowing modification to suit specific applications. The effect of jammed rubber particles on the response of a jammed packing to an externally applied load is examined. The evolution of inter-particle forces is studied using a rheometer configuration. Finite element techniques and modelling are employed to study the rubber in more detail.

Thesis (M.S.)--Massachusetts Institute of Technology, Dept. of Mechanical Engineering, 1982. / MICROFICHE COPY AVAILABLE IN ARCHIVES AND ENGINEERING / Bibliography: leaf 68. / by Clarence Teh-Ching Chang. / M.S.

Glycerol monooleate (GMO) is a common engine oil lubricant additive used to reduce friction and wear in engines. The aim of this thesis is to investigate the properties of GMO in bulk and under confined conditions with shear using molecular dynamics simulations. The self-assembly of GMO into reverse micelles (RMs) in toluene and n-heptane solvents is studied at a range of concentrations and subsequently with several common engine impurities over simulation timescales of 5-30 ns. The dimensional properties of the RMs are found to correspond well with experimentally studied SANS/SAXS measurements. Secondly, the properties of GMO confined between mica surfaces are studied under quiescent and shear conditions. Under shear, the performance of GMO as a friction modifier is studied and the structural and frictional properties are examined. In particular, the mass density and velocity profiles of the fluid are used to gain insights into the structure and dynamics of the confined GMO fluid films, under a variety of shear rates and surface separation. The data is found to fit excellently to the universal friction curve. Following this the effect of hydrolysing the GMO to oleic acid is studied in bulk and under shear, it is found that increasing oleic acid concentration typically reduces the propensity to self-assemble and under confinement increases the friction coefficient. And finally, a study on a range of other similar surfactants is conducted to investigate the effect of unsaturation, head group and chain length on the calculated friction coefficient and the structure of the surfactant films.

In the railway industry, and premium luxury and super sports sectors of the automotive industry, traditional cast iron brake discs are gradually being replaced with advanced composites such as carbon fibre reinforced carbon silicon carbide (Cf/C-SiC). These materials offer the ability to operate at higher temperatures, whilst displaying improved friction performance, and vastly reduced wear rates. Their primary benefit comes from being approximately one third of the density of the incumbent material used in the industry, grey cast iron (GCI), a cast iron with a high proportion of graphite flakes formed during solidification. This reduced density means that brake discs manufactured from Cf/C-SiC materials are a highly suitable proposition for a future automotive market, where weight saving in an attempt to meet ever restrictive CO2 emissions is a must. The understanding surrounding the friction mechanisms involved with these new materials has been lacking, until recently, with the majority of the international research focused on the manufacturing methods. Research has shown that friction performance, particularly bedding friction, is highly dependent on the successful formation of a friction transfer film (FTF) at the surface of any disc, comprised from wear debris from both the disc and pad. Prior research carried out at Loughborough University has identified that Cf/C-SiC materials do not readily form such a layer, as might be seen on a GCI equivalent, due to the intrinsically heterogeneous nature of the composite material.

No description available.

<p>Applications relying on a high static friction include various types of fixtures, couplings, bolted joints, torsion joints, etc. The common characteristic of these applications is that they rely on the friction force to maintain the relative position of two mating surfaces. Also applications relying on high dynamic friction are common, the main example being brakes, where a low friction could be devastating.</p><p>The plateau model for the friction of brakes has been refined. By using advanced electron microscopy, it has been shown that during braking a partly amorphous friction film, comprising nanosized iron oxide agglomerates, dissipates the friction energy. The film is only about 100 nm thick. It is separated from the underlying less mobile material by a thin boundary. The actual braking power is thus localised to this very thin film, leading to remarkably high power densities. In a typical case it was estimated to 40 GW/dm3.</p><p>Squeal and vibrations are critical problems for brakes. The present work has shown that a textured disc pattern may counteract squeal efficiently. The most successful pattern has spiral shaped arms in which wear resistant ceramic particles are embedded. The different wear characteristics of treated and untreated disc surface lead to an elevation of the patterned area above the rest of the disc. In a related experiment, laser technique was used to inject the particles deeper into the disc surface, and thus prolonging the time of silence. </p><p>Textured diamond surfaces have been used to study the influence of load, repeated scratching and surface roughness on the static coefficient of friction. It was shown that these surfaces were remarkably stable at high friction levels. A maximum load limit was found above which the coefficient of friction falls. This and a number of other factors were found important for the successful design of high-friction joints.</p>

This research has three parts. Part 1: The Policy on Geometric Design of Highways and Street provides 5 methods of superelevation (e) distribution. Many states use methods 2 and 5 for low speed, urban and rural high-speed facilities. Method 5 aims to address speed variations; but is complicated, computationally intractable and may violate design consistency. Design recommendation by NCHRP439 accounts for speed variation, tractable; but is cumbersome along with irregular/step-wise design curves. New reliability based e distribution method is developed that addresses the speed variation; which is simple in determining and evaluating acceptable required e rates. At 95% level of reliability, the e rate obtained is lower than that from current practice resulting in cost savings. Part 2: Current practice/research does not address safety issue of the left-turn-bay at high degree of saturation (x). Left-Turn-Bay distance has three components: clearance, breaking to a stop and queue. The variation in the queue length reduces clearance and breaking distance resulting in unsafe breaking. Failure = clearance plus breaking distance < demand. The reliability of the left-turn-bay defined as the availability of the three components for left-turning vehicles to complete clearance and breaking maneuver safely; measured as increase in the deceleration rate over limit of 11.2ft/s2, safety index and probability of failure. Results show that at 95% reliability, current design practice fails when x exceeds 50%. Part 3: Current practice uses mean traffic volumes (Vd) as input for traffic signal control at roadway intersections. Variations in traffic flows affect the performance of intersection measured by the delay per vehicle traversing the intersection in seconds. Peak hour factor (PHF), the hourly volume divided by the peak 15-min flow rate within the peak hour is adopted by Highway Capacity Manual (HCM) to control surge. HCM suggests PHF design value of 0.92 for urban and 0.88 for rural areas. Fixed PHF may lead to increase in delay. Effects of variation of peak hour volumes on intersection signal delays are examined with large data. A new model is developed for PHF and Vd and used in signal timing to minimize intersection delay. The results show that the assumption of Poisson distribution for Vd is not reliable; delay reduction of 6.2 seconds per vehicle is achieved. Annual savings in travel time, fuel consumption and emissions cost is estimated in billions of dollars.

Thesis (M.S.)--Virginia Polytechnic Institute and State University, 1983. / Vita. Abstract. Includes bibliographical references (leaves 106-111). Also available via the Internet.