Resumo em Inglês:

The present work compares the high resolution schemes of (1) Yee, Warming and Harten, (2) Harten, (3) Yee and Kutler and (4) Hughson and Beran applied to the solution of aeronautical and aerospace problems. All schemes are TVD flux difference splitting type and are second order accurate in space. The Euler equations in conservative form, employing a finite volume formulation and a structured spatial discretization, are solved in two-dimensions. The time integration is performed by a dimensional splitting method and is first order accurate. The steady state physical problems of the supersonic flows along a ramp and around a blunt body configuration are studied. In the ramp problem, the Hughson and Beran scheme was the most critical because presented the most intense pressure field and the most intense Mach number field. Moreover, this scheme predicts the best value to the shock angle of the oblique shock wave. The shock and the expansion fan pressure distributions are better captured by the Yee, Warming and Harten and the Yee and Kutler schemes. In the blunt body problem, the Harten scheme presented the most intense pressure field. The Harten scheme estimates the best value to the stagnation pressure on the configuration nose.

Resumo em Inglês:

The present work studies some aspects of the turning process applied on hardened steel using multilayer coated carbide tools at high cutting speeds. The influence of cutting parameters (vc, f, and depth of cut - d.o.c.) on tool temperature, tool wear, cutting forces, and surface roughness were analyzed. The current literature reports many studies using PcBN on hardened steel, but it is also important to know the results when using coated carbide tools, mainly for economical reasons. Temperature was measured by a thermocouple positioned at the lowest insert face, underneath it. Temperature near the rake face was calculated using the measured gradient within the insert thickness. To measure the gradient a special technique was used with one embedded thermocouple near the rake face and one underneath. Tool wear measurements demonstrated the capability of such tools in turning hardened steel with reasonable tool life. Forces measured resulted in relatively low values, being the radial component the largest of all. For the different cutting conditions studied, the doc has the greatest influence on force and temperature. Additionally, the best surface roughness values were smaller than 0,4 µm Ra.

Resumo em Inglês:

Vortex-induced vibration of bridges happens at a relatively low wind speed and while vehicles often run on a bridge at that wind speed. Thus, it is necessary to study how the vehicles influence vortex-induced vibration of vehicle-bridge systems. Based on the project of Shanghai Bridge over Yangtse River, the wind tunnel test for vortex-induced vibrations of vehicle-bridge system of a 1:60 model is presented. The wind tunnel test is introduced in detail including the equipments, test procedures and discussion of results. The results show that the vehicles have much influence on vortex-induced vibration of vehicle-bridge system for the Shanghai Bridge over Yangtse River. With speed increasing, the displacement of the bridge with vehicles fluctuates larger than that of the bridge without vehicles. The frequencies of vibration could be divided into three stages, vertical vibration frequency for the first stage, torsional vibration frequency for the second stage, and suspension system vibration frequency for the third stage. For the bridge with vehicles, vertical vortex-induced vibration was accompanied with torsional vibration and the frequencies of the two vibrations are equal. The displacement of vortex-induced vibration for the bridge with vehicles was larger than that of vortex-induced vibration for the bridge without vehicles. Due to the disturbance of vehicles, the lock-in wind speed region of the vortex-induced vibration appears ahead.

Resumo em Inglês:

A variational formulation and solution of general three-dimensional potential flows gave rise to the construction of a special family of ‘trial functions’. This family is composed by circular-sector vortex rings, here named α-rings, i.e., rings that are positioned on the border of a circular sector with aperture angle α. An explicit formula for the velocity potential describing the α-rings family is here derived. A particular case is the well-known circular vortex-ring. The formula is given in terms of a uniformly valid series involving trigonometric and Hypergeometric functions. Results concerning the complete circular ring are compared to the well-known solution given, in closed form, in terms of Bessel functions, validating the present formula. Convergence is discussed. Graphical examples are shown for various rings of different sector angles. As an elementary application, the steady potential flow around three-dimensional bodies in unbounded fluid is formulated and solved under the variational approach. The variational method is fully validated through the sphere problem and for a family of spheroids. Examples concerning either translatory or rotatory motion around a transversal axis are presented for the spheroid family.

Resumo em Inglês:

The use of cutting fluid in milling operations causes increase of temperature variation on the tool and may cause decrease of tool life. However, sometimes its use is necessary due to possible deleterious influence the temperature increase may have on the workpiece. Therefore, it is important to make fluid less harmful for the tool. In this work, two alternatives were tried: the application of emulsion internally to the tool, forcing it to get closer to the cutting edge and the use of an emulsion with higher concentration, trying to increase the lubrication and decrease the fluid cooling capacity. These alternatives were experimented in the face milling operation of stainless steel used in the aeronautic industry (where workpiece damage must be avoided) and were compared to the usual way of fluid application (externally to the tool and with lower concentration) and also to dry cutting, in two different cutting speeds. Tool wear damage was analyzed. The main conclusions were: a) dry cutting generated longer tool lives than cutting with emulsion no matter the way of application and the fluid concentration; b) tool wear mechanism which caused the end of tool life was attrition for dry cutting and cracks and chippings of thermal origin for cutting with emulsion, again, no matter the way of fluid application and the fluid concentration.

Resumo em Inglês:

The present work is an attempt to study the role of emulsifier on the effectiveness of cutting fluids. Cutting tests have been carried out and influence on different parameters is estimated. A mathematical model is proposed to estimate the influences of emulsifier content on tool wear.

Resumo em Inglês:

The influence of a previous deposition treatment on the final amount of alloying elements (Cr and Ni) deposited and diffused into the surface of iron parts sintered in hollow cathode discharge (HCD) was studied. Cylindrical pure iron pressed samples, being a central cathode, were placed concentrically in the interior of an AISI 310 steel machine-made outer cathode, resulting in a 6 mm inter-cathode radial spacing. The study was divided in two steps: a) deposition treatment with the outer cathode acting as target and the iron sample acting as substrate (1123K -850 ºC- and 60 minutes deposition temperature and time, respectively); and b) deposition treatment plus HCD sintering (1423K -1150 ºC- and 60 minutes sintering temperature and time, respectively). The electrical discharge was generated using a pulsed voltage power source. The results indicate the presence of 6.5 at.% Cr and 6.9 at.% Ni on the samples surface. The concentration profiles were mathematically treated to quantify the actual amounts of Cr and Ni deposited on and diffused into the samples, and the integration of the fitted equations yielded the calculated areas of 133 (µm × at.% Cr) and 105 (µm × at.% Ni), respectively.

Resumo em Inglês:

This paper presents an evaluation of the safety of I-section steel columns designed according to the new revision of the Brazilian code for design of steel buildings (NBR8800) and to the code for loads and safety of structures (NBR8681). The safety evaluation is based on structural reliability analysis of columns designed to comply with these codes, and on advanced (FE-based) analysis of actual column resistance. The effects of geometrical imperfections and residual stresses in column resistance are taken into account. The uncertainty in yield stress, elasticity modulus, geometrical imperfections and dead and live loads are considered in the reliability evaluation. Reliability indexes are obtained for several column configurations. These indexes reflect the safety of the columns designed according to the two building codes. Reliability indexes are compared with target reliability indexes used in calibration of the ANSI code and with indexes proposed in the new EUROCODE.

Resumo em Inglês:

The displacement of a fluid by liquid injection occurs in some practical applications like oil recovery in porous media and cementation of drilling wells. The dimensionless numbers that govern this problem are the capillary number, Reynolds number and viscosity ratio. An overview of selected oil recovery processes shows that hydrolyzed polyacrilamide and bio-polymers, as xanthan gun, are commonly pumped into oil reservoir in order to aid oil recovery. These materials are non-Newtonian, presenting high viscoelastic effects. The fractional mass deposited on the tube wall and the shape of the interface on liquid-liquid displacement of two Newtonian materials was studied previously by Soares et al. (2005). The goal of the present work is to conduct an experimental investigation analyzing viscoelastic effects on the fractional coverage and on the shape of the interface for both: a polymer displacing a Newtonian liquid and a Newtonian liquid displacing a polymer.

Resumo em Inglês:

Friction materials are applicable for braking and transmission in various machines and equipment. Their composition keeps changing to keep pace with technological development and environmental/legal requirements. For more than 80 years asbestos has been used as a friction material because of its good physical and chemical properties. However, due to the health hazard associated with its handling, it has lost favour and several alternative materials are being increasingly used. Thus, in this work, a non - asbestos friction material was developed using an agro-waste material base - palm kernel shell (PKS)- along with other constituents. Among the agro-waste shells investigated the PKS exhibited more favourable properties. Taguchi optimization technique was used to achieve optimal friction material formulation and manufacturing parameters. The derived friction material was used to produce automobile disk brake pads. The laboratory brake pads were tested for wear and effectiveness on a car. When compared with a premium asbestos-based commercial brake pad they were found to have performed satisfactorily. However, more pad wear was observed on the PKS pad at high vehicular speeds beyond 80km/hour. The results suggest that palm kernel shell could be a possible replacement for asbestos in friction lining materials.

Resumo em Inglês:

The present paper deals with the determination of thermal stresses in a thick circular plate under steady temperature field. A thick circular plate is considered having constant initial temperature and arbitrary heat flux is applied on the upper face with lower face at initial temperature and the fixed circular edge is thermally insulated. Heat is exchanged through heat transfer at lower boundary surface. The results are obtained in series form in terms of Bessel's functions and they are illustrated numerically.