Resumo em Inglês:

Changes are often necessary during the tryout of stamping tools. These changes may range from adjustments on die and punch designs to the selection of a new material with better formability characteristics. All these actions, however, require time and money creating the need for better initial sheet metal evaluation. Hence, increasing attention has focused on the development of laboratory tests that enable stamping companies to know more about the sheet metal stampability or that can, at least in part, ensure that their stamped products are produced without major problems. Identification of high stress region on stamping may allow for better tool stamping adjustment during tests, rendering a more uniform material’s deformation and leading to the production of higher quality parts. Increasing attention has focused on the material evaluation based on the tool geometries in order to calculate the strain distribution. This study deals with an evaluation of four punch models with varied geometries in addition to the traditional Nakazima test tool. An evaluation was also made of the major true strain distribution profile at points distributed linearly from the region close to the die shoulder to the punch center.

Resumo em Inglês:

Currently, miniaturization is a major trend in the manufacturing and commercialization of new industrial products. When small-sized objects should be manufactured with dimensions of only a few millimeters or less, many difficulties can appear using traditional processes. An alternative to study these new requirements is through the use of rapid prototyping technologies. Stereolithography (SL) has established itself as one of the most popular and reliable process allowing the rapid manufacturing of complex parts. This paper investigates the SL process, which directly produces small parts by rapid manufacturing, and also indirectly by rapid tooling. The processability of small parts was investigated using two different shapes. The POM and ABS materials were used in the indirect manufacturing. The dimensional accuracy, precision and tolerance of micro parts were evaluated using metrological techniques. Results showed accuracy and precision greater than 97% when small-parts are manufactured directly by Stereolithography.

Resumo em Inglês:

Consider a collection of elastic wires folded according to a given pattern induced by a sequence of fractal plane curves. The folded wires can act as elastic springs. Therefore it is easy to build up a corresponding sequence of simple oscillators composed by the elastic springs clamped at one end and carrying a mass at the opposite end. The oscillation periods of the ordered sequence of these oscillators are related following a power law and therefore display a fractal structure. The periods of each oscillator clearly depend on the mechanical properties of the wire, on the mass at the end and on the boundary conditions. Therefore there are infinitely many possibilities to design a dynamical fractal sequence in opposition to the well defined fractal dimension of the underneath geometric sequence. Nevertheless the geometric fractal dimension of the primordial geometric curve is always related somehow to the dynamical fractal dimension characterizing the oscillation period sequence. It is important to emphasize that the dynamical fractal dimension of a given sequence built up after the geometry of a primordial one is not unique. This peculiarity introduces the possibility to have a broader information spectrum about the geometry which is otherwise impossible to achieve. This effect is clearly demonstrated for random fractals. The present paper deals with a particular family of curves, namely curves belonging to the Koch family. The method is tested for the simple Koch triadic and for random Koch curves. The method has also proved to be useful to identify the fractal dimension of a sequence given just one of its terms. Remarkable is the quality of information obtained with this technique based on very simple and basic concepts. Some of these aspects will be presented in this paper but much more, the authors believe, is still hidden behind the dynamic properties of fractal structures.

Resumo em Inglês:

Nowadays rotating machines produce or absorb large amounts of power in relatively small physical packages. The fact that those machines work with large density of energy and flows is associated to the high speeds of rotation of the axis, implying high inertia loads, shaft deformations, vibrations and dynamic instabilities. Viscoelastic materials are broadly employed in vibration and noise control of dynamic rotors to increase the area of stability, due to their high capacity of vibratory energy dissipation. A widespread model, used to describe the real dynamic behavior of this class of materials, is the fractional derivative model. Resorting to the finite element method it is possible to carry out the modeling of dynamic rotors with flexible bearings due to the use of viscoelastic materials. In general, the stiffness matrix is comprised of the stiffnesses of the shaft and bearings. As considered herein, this matrix is complex and frequency dependent because of the characteristics of the viscoelastic material contained in the bearings. Despite of that, a clear and simple numerical methodology is offered to calculate the modal parameters of a simple rotor mounted on viscoelastic bearings. A procedure for generating the Campbell diagram (natural frequency versus rotation frequency) is presented. It requires the embedded use of an auxiliary (internal) Campbell diagram (natural frequency versus variable frequency), in which the stiffness matrix as a frequency function is dealt with. A simplified version of that procedure, applicable to unbalance excitations, is also presented. A numerical example, for two different bearing models, is produced and discussed.

Resumo em Inglês:

The recent development of computer-based tools with more efficient algorithms has allowed a substantial improvement in hydraulic turbine design. The definition of an initial geometry capable to assist certain characteristics of turbine performance is a first step for useful numerical turbine analysis. This paper presents an application of the minimum pressure coefficient criterion for axial-flow hydraulic turbines cascade geometry design. In recent works, the criterion was tested for axial fan and it was showed that it is suitable to define the initial geometry for machine design. The global parameters that supply the principal dimensions of the turbine are obtained from the literature as based upon statistical data of installed power plants. The grid of the simulation domain was generated with CFX-TURBO grid software package and the results were obtained using the commercial package Navier-Stokes 3-D CFX-TASCflow to analyze the fluid flow through blade runner. Using this procedure, a study was carried out on a small axial-flow turbine, specifically designed to operate in a small river in the Amazon region. An interpretation of the flow through the turbine’s hydraulic channels is presented for nominal flow rate operation points. Finally, the results are evaluated to hydraulic efficiency prediction of blade runner turbines

Resumo em Inglês:

The tabular structural fire design method for centrally loaded composite columns consisting of concrete filled steel circular hollow sections proposed in EN 1994-1-2:2005 (Eurocode 4: Design of Composite Steel and Concrete Structures - Structural Fire Design) is described here. A design procedure is then discussed, based on the determination of the temperature distribution in the cross sectional area and along the column length. A finite element based computer program is developed to implement the three-dimensional thermal analysis of different materials and geometries for given time versus temperature fire data. An example problem is shown, comparing the tabular method proposed in EN 1994-1-2:2005 and the method presented in this work.

Resumo em Inglês:

Over the years, grinding has been considered one of the most important manufacturing processes. Grinding is a high precision process, and the loss of a single workpiece in this stage of the production is unacceptable, for the value added to the material is very high due to many processes it has already undergone prior to grinding. This study aims to contribute toward the development of an experimental methodology whereby the pressure and speed of the air layer produced by the high rotation of the grinding wheel is evaluated with and without baffles, i.e., in an optimized grinding operation and in a traditional one. Tests were also carried out with steel samples to check the difference in grinding wheel wear with and without the use of baffles.

Resumo em Inglês:

The steady laminar flow of an incompressible non-Newtonian micropolar fluid impinging on a permeable flat plate with heat transfer is investigated. A uniform suction or blowing is applied normal to the plate, which is maintained at a constant temperature. Numerical solution for the governing nonlinear momentum and energy equations is obtained. The effect of the uniform suction or blowing and the characteristics of the non-Newtonian fluid on both the flow and heat transfer is presented and discussed.

Resumo em Inglês:

Competitive world market trends have long been forcing structural engineers to develop minimum weight and labour cost solutions. A direct consequence of this design philosophy is a considerable increase in problems related to unwanted floor vibrations. This phenomenon is very frequent in a wide range of structures subjected to dynamical loads. The main objective of this paper is to evaluate an orthotropic solution for composite floors subjected to dynamical actions such as rhythmical activities arising from gymnastics, musical and sports events and ballroom dances. The proposed analysis methodology considers the investigation of the dynamic behaviour of a building floor made with a composite slab system with steel beams and an incorporated steel deck. The results indicated that the investigated composite floor violates the vibration serviceability limit state, but satisfied the human comfort criteria.

Resumo em Inglês:

The primary function of a vehicle suspension system is to isolate the road excitations experienced by the tyres from being transmitted to the passengers. In this paper, a suitable optimizing technique is applied at design stage to obtain the suspension parameters of a passive suspension and active suspension for a passenger car which satisfies the performance as per ISO 2631 standards. A number of objectives such as maximum bouncing acceleration of seat and sprung mass, root mean square (RMS) weighted acceleration of seat and sprung mass as per ISO2631 standards, jerk, suspension travel, road holding and tyre deflection are minimized subjected to a number of constraints. The constraints arise from the practical kinetic and comfortability considerations, such as limits of the maximum vertical acceleration of the passenger seat, tyre displacement and the suspension working space. The genetic algorithm (GA) is used to solve the problem and results were compared to those obtained by simulated annealing (SA) technique and found to yields similar performance measures. Both the passive and active suspension systems are compared in time domain analyses subjected to sinusoidal road input. Results show passenger bounce, passenger acceleration, and tyre displacement are reduced by 74.2%, 88.72% and 28.5% respectively, indicating active suspension system has better potential to improve both comfort and road holding.

Resumo em Inglês:

The general purpose of this research is to study the influence of commercial machining parameters on fatigue limits of steels. Specifically in this work, the influence of cutting speeds, depth of cut, feed rate and residual stresses of turned surfaces of AISI 4140 steel specimens on fatigue strength were analyzed. In some specimens, the residual stress was eliminated by heat treatment. The fatigue experiments were carried out at room temperature, applying a cyclical frequency of 58Hz, with mean stress equal to zero (R=-1), on a rotating-bending fatigue testing machine of the constant bending moment type. It was used the staircase (or up-and-down) method to determine the fatigue limit of the specimens.

Resumo em Inglês:

Geometrically nonlinear static and dynamic behaviour of laminate composite shells are analyzed in this work using the Finite Element Method (FEM). Triangular elements with three nodes and six degrees of freedom per node (three displacement and three rotation components) are used. For static analysis the nonlinear equilibrium equations are solved using the Generalized Displacement Control Method (GDCM) while the dynamic solution is performed using the classical Newmark Method with an Updated Lagrangean Formulation (ULF). The system of equations is solved using the Gradient Cojugate Method (GCM) and in nonlinear cases with finite rotations and displacements an iterative-incremental scheme is employed. Numerical examples are presented and compared with results obtained by other authors with different kind of elements and different schemes.