Resumo em Inglês:

This paper presents a "fast and simple" (FAS) detection algorithm based on the digital image correlation for measurement of the surface deformation of planar objects. The proposed algorithm uses only fine search at the pixel level resolution and surface fitting for sub-pixel level. Two different specimens are investigated to explore the feasibility of this proposed algorithm. The displacements calculated by the FAS algorithm are compared with the ones obtained from Newton-Raphson method (N-R) and Enhanced Sequential Similarity Detection Algorithm (ESSDA). The results show that the experimental data are in good agreement with the theoretical solution. The proposed algorithm is found to be much faster than Newton-Raphson method with inferior, yet reasonable, accuracy for displacement and strain evaluation in the cases of uniaxial tension and disk under diametrical compression tests.

Resumo em Inglês:

This work presents the experimental results of the facing turning of an Al-Mg alloy. This aluminium alloy was mechanically and metallurgically modified, by means of cold rolling reduction and refining grain size previous to machining. The samples were cut and compared with samples in the as-received form, machined under the same cutting conditions. Surface finishing and work hardening were measured. Results show that theoretical surface roughness values are always smaller than the measured ones for all samples. Also, the surface roughness of the as-received samples is larger than that of mechanically modified samples. This difference of surface roughness was attributed to the swelling effect of the material. Microhardness values of the machined samples showed a decreasing trend with increasing loads. The surface of the cold rolled sample did not present a detectable microhardness alteration. Optical microscopy was used to observe qualitative aspects of the machined surface.

Resumo em Inglês:

Among the aluminum welding processes, the GMAW (Gas Metal Arc Welding) process can be easily made automatic, has high productivity and great versatility regarding the type and thickness of material used in welding. The possibility of changing the transfer mode to adapt to different thickness, joint types, among other aspects, is another important and attractive feature. However, little is known about the transfer modes in aluminum GMAW process. For this reason, in this study an analysis of the metal transfer modes in the aluminum welding was made, and the objective was to generate maps that could identify the metal transfer modes and their regions in relation to the shielding gas and the wire diameter. The experimental procedure was the execution of weld on aluminum plate in a flat position with a constant voltage power source. The methodology used was laser Shadowgraphy combined with a high-speed movie camera. Therefore, it was possible to design the maps in which four metal transfer modes and their respective transition zones were determined. The maps also permit determination of the transition current zone between the globular and the spray mode, and modeling of the melting rate.

Resumo em Inglês:

This paper analyzes the effects of the mathematical models of flexible couplings in rotating mechanical systems in terms of their vibrational behavior. The residual unbalance of the coupled shafts is considered to be the main source of vibration in the rotating system. The moments and the frequencies of the forces, which result from these effects, are close to the natural frequencies of the mechanical system. Since the coupling is considered to be a flexible component in the power transmission system, it introduces a certain amount of mass, damping and stiffness to the system, influencing its natural frequencies. The present work shows the modeling of a mechanical rotor-bearing-coupling system, through the finite element method, used in this case to analyze the transverse vibrations of the system. Different modeling techniques were taken into account for this purpose. Such models are recommended for flexible couplings to analyze their influence on the natural frequencies of the system and on the unbalance response of the system. Afterwards, a model updating was carried out to fit the coupling stiffness and damping coefficients, using the minimum quadratic technique. Some sensitivity of the proposed models was observed in relation to the coupling parameters.

Resumo em Inglês:

There have been considerable efforts in research to understand the basics of chip formation. Models developed for turning and adapted to milling, yield reasonable results, except in some particular applications. This work develops an experimental method capable of providing cutting data in a fast and reliable way to evaluate the specific cutting presure(Ks), the friction coefficient (m) and the ploughing/elastic forces (F E). Different models for the cutting force can be tested, and the coefficient of determination (R²) assesses the adequacy of models. The particular adopted model, used to test the experimetal method hereby proposed, resulted in a good agreement with experimental data, expressed by R² values very close to the unity

Resumo em Inglês:

The design of injection mould inserts obtained by stereolithography (SL) has various recommendations that are based on experimental work done by researchers over the last decade. There are no final conclusions about the best cooling technique for SL inserts. Moreover, no criteria are presented concerning structural and thermal designs based on stress-strain analysis, although a number of researchers consider ejection forces as the main failure effect of the SL tool. This work presents an alternative technique to cool down SL inserts, based on heat flux canals that are strategically positioned on hot areas along the cavity walls. Using this approach it is possible to keep direct contact between the back metal filling of the stereolithography insert and the injected thermoplastic material. This paper shows the results of aspects such as thermal evaluation in a FEM analysis, where the heat flux canals, solid SL moulds and the traditional Direct AIM™ process performances have been compared. The results indicate that this evolution of the Direct AIM™ process may improve the average life of SL inserts while keeping the traditional one-week development for the tool.

Resumo em Inglês:

The coupling loss factors are of critical importance when building and solving Statistical Energy Analysis (SEA) models. This paper proposes a methodology to numerically estimate these factors for frame-type structures. The estimated factors are compared with those obtained through analytical expressions for frame structures, where members are joined at right angles. The example used to verify the proposed technique consists of two infinite beams connected at a right angle modeled via the Spectral Element Method (SEM) using throw-off elements. It is shown that the obtained coupling loss factors compare very well with the analytical expressions that may be derived for this simple right-angle connection case. By using the SEM approach, the coupling loss factors can be obtained for arbitrary frame structure connections, thus facilitating the analysis via SEA.

Resumo em Inglês:

A porous exponential slider bearing was studied with a ferrofluid lubricant whose flow is governed by Jenkins flow behaviour considering slip velocity at the porous interface. Expressions for dimensionless pressure, load capacity, friction on the slider, coefficient of friction and the position of the centre of pressure were obtained. Computed values were displayed in graphical from. The load capacity as well as friction decreased and the coefficient of friction increased when the slip parameter increased. But, increase in the material parameter caused decrease in load capacity and increase in friction as well as coefficient of friction. Increase in the slip parameter did not significantly affect the position of the centre of pressure. But, it shifted towards the bearing inlet for large values of the material parameter.

Resumo em Inglês:

We consider a mathematical framework for spatially describing accessory aquatic systems that belong to a major hydric complex like a large reservoir created by damming a river. The central purpose is to provide a precise and complete mathematical covering of short-scale or localized water bodies, with typical lengths between 1 to 10 km, that are laterally attached to the main river. Such bodies may deserve a more detailed mathematical representation due, for instance, to their tendency to develop stagnant like hydric behaviors. The proposed framework may work as an infrastructure for developing and/or installing dynamic water quality models. It can generate tetrahedrizations of the aquatic system in question by working according to a procedure which builds, successively, reliable candidates for the following entities: (a) Free Surface Triangular Mesh; (b) Submerged Terrain Triangular Mesh; (c) Three Dimensional Partition of the Domain; (d) Basic Tetrahedrization of 3D Partitions; and (e) Refinement of the Basic Tetrahedrization through a Multi-Layer Tetrahedrization Algorithm. The required input for this procedure is only composed by terrain contour data and 3D located points. We present example applications including a real scenario belonging to a recent flooded system in Brazil.

Resumo em Inglês:

This work evaluates proposed methods to correct engine power output as a function of atmospheric conditions. The analysis was made through experiments carried out in a vehicle on the road, under different temperature, pressure and air humidity conditions. The vehicle had a four-cylinder gasoline-fuelled engine, with multi-point fuel injection system, variable intake pipe length and variable intake valve camshaft position. The vehicle was tested at sea level and at 827 m above sea level, corresponding to atmospheric pressures between 1027 and 926 mbar. Air temperature varied from 22,8 to 33,8 °C at the test locations. The measured performance parameter in the tests was the vehicle acceleration time. The acceleration times from 0 to 400 m, 0 to 1000 m, 40 to 100 km/h and 80 to 120 km/h were all recorded, leaving from an initial vehicle speed of 40 km/h. The engine power curve obtained in laboratory under a standard ambient condition was corrected to the conditions of the road tests by the correction factors proposed by the methods under evaluation, and the corresponding acceleration times were calculated and compared with the measurements from the road tests. The evaluated methods for power correction were the following: DIN 70020, SAE J 1349, JIS D 1001 and ISO 1585. The SAE J 1349 method provided the best approach between the experimental and calculated acceleration times.

Resumo em Inglês:

This work proposes to perform a dynamic analysis of the friction force and the vibrations produced in pin-on-disk sliding tests. The sliding tests were run under dry condition with austenitic stainless steel and high-speed steel pairs. The obtained results were the pin mass loss, the average friction force and power spectrum density (PSD) graphs of the friction force and vibrations in normal and tangential directions to the contact. It was possible to notice that some natural frequencies of the machine system are excited during the tests. Analyses of the magnitudes of a specific frequency could show the existence of a relation between the machine system dynamics and the average friction and wear results, and it depended on the tested materials.

Resumo em Inglês:

A general mesh independent filter as a mean to control the complexity of topology optimization designed structures is discussed. A new mesh-independent filter, applied over the move-limits of the sequential linear programming is proposed, and it is shown that its use alleviates common problems in the continuum topology optimization, like checkerboarding, mesh dependency, as well as effects associated to non-structured meshes, like numerical anisotropy. The structural optimization formulation adopted in this work is the minimization of a penalized function of the volume, with constraints on the compliance of each load case. Aspects of this penalized objective function are discussed, and several numerical examples are shown.

Resumo em Inglês:

In the welding process, the most interesting regions for heat transfer analysis are the fusion zone (FZ) and the heat affected zone (HAZ), where high temperatures are reached. These high temperature levels cause phase transformations and alterations in the mechanical properties of the welded metal. The calculations to estimate the temperature distribution in multiple pass welding is more complex than in the single pass processes, due to superimposed thermal effects of one pass over the previous passes. In the present work, a comparison is made between thermal cycles obtained from analytical models regarding point (concentrated) and Gaussian (distributed) heat sources. The use of distributed heat source prevents infinite temperatures values near the fusion zone. The comparison shows that the thermal cycles obtained from the distributed heat source model are more reliable than those obtained from the concentrated heat source model.

Resumo em Inglês:

The composite materials are well known by their excellent combination of high structural stiffness and low weight. Their inherent anisotropy allows the designer to tailor the material in order to achieve the desired performance requirements. Thus, it is of fundamental importance to develop tools that allow the designer to obtain optimized designs considering the structural requirements, functional characteristics and restrictions imposed by the production process. Within these requirements, this work considers the dynamic behavior of components manufactured from fiber reinforced composite materials. To this end, some beams were made using the hand-lay-up process followed by a molding under pressure and heating. Experimental dynamic tests were carried out using specimens with different fiber orientations and stacking sequences. From the results, the influence of the fibers orientations as well as the stacking sequences on the natural frequencies and modal damping were investigated. Also, these experiments were used to validate the theoretical model and the results obtained from the finite element analysis.

Resumo em Inglês:

In this note we use elementary facts from 3-dimensional linear algebra to demonstrate the formula for area changes under arbitrary linear maps A : R³ -> R³. We do it in general, from a hint given by the well known invertible case, which is an important result used in continuum mechanics. An intrinsic formula for the case when rank A = 2 is obtained and we finish by showing that we are really exploring a property of the cofactor matrix of A for an orthonormal basis.