Resumo em Inglês:

This paper reports results obtained in a theoretical and experimental study involving micro channel/louvered fin condensers for automotive applications. A simulation model has been developed based upon three zones related to the thermodynamic states of the refrigerant in the condenser. Experiments with condensers have been performed in a set up developed for thermal performance evaluations of automotive air conditioning systems. Comparisons between simulation model and experimental results for refrigerant HFC-134a have been performed with respect to three important condenser parameters: heat rejection rate, refrigerant pressure drop and overall heat transfer coefficient. It has been shown that model results for the particular tested condenser compare very well with the experimental data, with deviations being within an acceptable range.

Resumo em Inglês:

The most basic mass conservation method is described here in detail. A simplified version of this method is then applied to estimate the wind field over a region of complex topography, the Metropolitan Region of São Paulo City, Brazil. The resulting adjusted wind field and its horizontal divergence patterns compare well with observed wind field, indicating that the topography has a major effect in the investigated area.

Resumo em Inglês:

The "elliptic-bi-parabolic transfer" orbit for an artificial satellite is an extension of the bi-parabolic transfer that uses a Swing-By with a natural satellite of the main body to reduce the amount of fuel required by the maneuver. The objective is to find the minimum cost trajectory, in terms of fuel consumed, to transfer a spacecraft from a parking orbit around a planet to an orbit around a natural satellite of this planet or to a higher orbit around the planet. Graphics are built to show in more details the potential savings given by this technique. After that, the idea of using a natural satellite in the maneuver is applied to the problem of making a spacecraft to escape from the main planet to the interplanetary space with maximum velocity at infinity.

Resumo em Inglês:

The knowledge of realistic dynamic models to robotic actuators would be of great aid in the synthesis of control laws to robot manipulators, mainly in cases of great precision robotic or even for manipulators with flexible links. In this paper we present a training scheme and propose a structure of neural network (NN) to learn the friction torque of a geared motor drive joint robotic actuator. To train the NN was used experimental data obtained by an harmonic-drive actuator, equipped with an encoder to measure the rotor angular position. It was considered the motor torque and the rotor angular velocity as NN input, while the friction torque was the only output, which was used in the proposition of a non-linear friction compensation mechanism. The experimental results attested the efficiency of the NN friction estimation and compensation with the proposed mechanism.

Resumo em Inglês:

In this paper a method for the simulation of convection and diffusion of the vorticity, generated on a body surface is presented. A purely Lagrangian scheme is used for the vorticity convection, and thereby avoiding mesh associated problems. The body surface is simulated by straight-line panels, with constant-strength vortex distribution. The strength of the discrete vortices is obtained directly without going through any additional calculation. Using a primary diffusion process this vorticity is replaced by Lamb vortices located nearby the body surface. The diffusion process of the vorticity is simulated using the random walk scheme. Turbulence sub-grid scale modelling employs a Second Order Velocity Structure Function model adapted to the Lagrangian scheme. With a cloud of discrete vortices this velocity structure function model is employed to simulate the micro structures of the flow. The flow over a circular cylinder and a NACA 0012 aerofoil are considered to evaluate the integrated aerodynamic loads. Comparisons are made with previous theoretical and experimental studies.

Resumo em Inglês:

A probe test device has been developed to assess CMM touch trigger probe errors. A precise single axis translational table triggers the probe through the use of gauge blocks fixed to the table carriage. The position of the carriage is monitored by a laser interferometer. The gauge block surface is brought into contact with the probe ball tip until the probe is triggered at which point the coordinate position is displayed by the laser. The probe is rotated 360° using the motorized probe head in 7.5° intervals and the coordinate of each position is computed. Repeatability errors (i.e. the ability of the probe to trigger at the same point each time with a 95% confidence level) and pre-travel variation (i.e. the distance traveled by a probe between the actual touching of a surface and the trigger event) are then calculated. This paper reports the measurement strategy and the design of the prototype rig. Results are also provided to demonstrate the test apparatus performance.

Resumo em Inglês:

The main objective of this research project is the investigation of multirecess hydrostatic journal bearings with active hybrid (hydrostatic and hydrodynamic) lubrication. This paper gives a theoretical contribution to the modeling of this kind of bearing, combining computational fluid dynamics and control techniques. The feasibility of influencing the dynamic fluid film coefficients (stiffness and damping) by means of a controllable fluid injection into opposed bearing recesses is investigated. By controlling the pressure and flow injection using servo control systems, it is possible to obtain significant modifications of active hybrid forces, which can be useful while reducing vibration and stabilizing rotating machines.

Resumo em Inglês:

High-temperature pressurized pipelines design requires special attention, as restrained thermal stresses are high. Due consideration should be given to thermal expansion, as stresses in bends of expansion loops are significant. Also, the modelling of the soil-pipe interaction using soil characteristics, especially friction and lateral resistance, is important when analyzing high-temperature pipelines. This paper describes a numerical procedure for the analysis of global and local buckling behavior of high temperature pressurized buried pipelines. Results of finite element calculations are presented and discussed.

Resumo em Inglês:

This paper presents a study concerning the toughness anisotropic behavior of two high-strength low-alloy steel sheets having ferrite-martensite (dual-phase) and ferrite-perlite grain-refined structures. The anisotropic behavior quantification was possible through tension and Charpy impact tests. It has been concluded that mechanical resistance has higher values in the longitudinal direction for both steels, and the inverse occurs for ductility. This could be explained with the microstructure preferential orientation with rolling direction. The higher tensile strength found in dual-phase steel is related to the presence of martensite islands, and the higher yield strength found in ferrite-perlite grain-refined steel is related to the fine structure observed. The higher toughness is a ferrite-perlite grain-refined steel characteristic, and this could be explained with the presence of only globular-oxide type inclusions, which reduces fracture nucleation sites, and does not promote fracture easy-propagation. Sulfide type inclusions found in dual-phase steel, associated with globular-oxide ones, give to this material a more brittle behavior. Toughness anisotropy is clearly noted, and in both cases the highest values are found in the longitudinal direction, related to the preferential inclusion alignment achieved in rolling. The low ductile-to-brittle transition temperature found in both steels, however, could be related to the very fine structures found.

Resumo em Inglês:

Polymeric composites are frequently modeled as linear elastic materials. However, matrix-dominated properties, such as transverse and shear modulus, can display significant nonlinear time-dependence, especially under conditions of high stress and aggressive environment. This behavior is primarily due to the viscoelastic nature of the polymeric matrix. In addition, polymeric composites also present time-dependent damage growth. In this work, nonlinear viscoelastic constitutive equations were used to represent the time-dependent behavior of a rubber-toughened carbon/epoxy composite during damage growth. These equations were originally devised to characterize material response in a stable damage state. In this approach, however, nonlinearities due to damage and viscoelasticity were incorporated by the model stress-dependent functions, allowing its use in the presence of damage accumulation. A procedure was proposed and applied to separate viscoelastic and damage effects. An experimental program consisting of multiple cycle creep and recovery tests was performed to determine the time-dependence of the shear compliance and to verify the theory as well. The results obtained indicated an excellent agreement between theory and experiment. Constant stress rate tests were also used to validate the application of the theory.

Resumo em Inglês:

The deformation of the partially solidified strand during near net shape continuous casting of thin slabs is only one example of a technologically important process where a mushy zone is mechanically altered in order to achieve improved grain structures and homogeneity. However, the phenomena occurring during plastic deformation of a solidifying mush are poorly understood, have not been observed directly, and have not been modeled in detail. A mathematical model that predicts the temperature and solid fraction profiles, liquid concentration evolution, and solid phase displacement during the deformation of a solidifying mush is presented. This model is derived considering a two-dimensional case, the volume averaging method, the enthalpy technique, and a coordinate transformation to avoid a changing mesh in a numerical solution. The numerical results are found to match the experimental behavior of metallic alloys during solidification with or without deformation.

Resumo em Inglês:

Designing of the chemical composition of the steel heats having the demanded properties, e.g. the defined shape of the hardenability curve, is the crucial task from the manufacturing point of view. Rapid development of computer science and technology as well as of modern computer tools, artificial intelligence among them, prompts their increasingly common use in different domains of science and technology. There is a great interest in these methods, which seems justified, since they can be applied both to solving novel problems and to dealing with the ones considered classical. For a couple of years, such trends have been present also in the domain of materials engineering. Contemporary software tools, especially methods of artificial intelligence, make it possible to develop the method, presented in the paper, of designing of the chemical composition of constructional alloy steels, which still are one of the basic groups of metallic engineering materials. It lets the designer abandon the classical approach to the material selection according to which one of the catalogued materials has to be selected. The paper presents the method of designing of the chemical composition basing on the known and the required shape of the hardenability curve with the use of the dedicated neural networks models.

Resumo em Inglês:

This contribution discusses the transient chaos on a pin-ended elasto-plastic beam with both kinematic and isotropic hardening. An iterative numerical procedure, based on the operator split technique, is developed. Numerical simulations show that transient chaos causes sensitivity on initial conditions, which imply that the system response may become unpredictable.

Resumo em Inglês:

The paper presents the results of investigations of the 5% cobalt and 2% molybdenum additions in the W-Mo-V and W-V high-speed steels of the 9-2-2, 11-2-2 and 11-0-2 types with economically designed chemical composition on the wear mechanism during cutting and erosion tests. The 5% cobalt addition results in increasing the secondary hardness effect by 1.6 to 1.9 HRC, depending on a steel grade. Secondary hardness effect is caused by the dispersive carbides of the M4C3 type and martensite transformation of the retained austenite. The maximum secondary hardness effect about 66.3-67.6 HRC, depending on a grade of steel, occurs in each steel after tempering at 540oC and austenitizing at 1240oC. The 5% cobalt addition results in enhancing the working properties of tools, longer tool life and makes it possible to increase cutting speed by about 50%, compared with the steels of identical concentration of other alloying elements but without cobalt addition. Cobalt does not have any significant influence on erosion resistance, which is independent of the steel hardness but depends on molybdenum addition in steel.

Resumo em Inglês:

The synthesis of materials by high energy ball milling of powders was first developed for the production of complex oxide dispersion-strengthened nickel alloys for structural, high temperature applications but has been attracting attention in the field of fabrication processes like the production of intermetallic compounds, supersaturated solid solutions, amorphous materials and metal matrix composites. However, due to the high level of deformation imposed, the aluminum mechanically alloyed undergo extensive grain growth during the extrusion process, resulting in serious damage in the extruded materials. This work investigates the effects of mechanical alloying on the extrusion of AA6061 aluminum alloy and the same alloy reinforced with silicon nitride. In both cases, the energy of deformed particles produced extruded bars with coarse grains in the core, while in the periphery the higher rate of deformation in the extrusion process has prevented this coarsening, resulting in a material with heterogeneous microstructure and with poor mechanical properties. This grain growth can be prevented by a higher percentage of reinforcement in the composite materials or by annealing before extrusion.

Resumo em Inglês:

The production of alloys with rheocast structure, where the primary phase consists of globularized particles, by partial melting, involves grain recrystallization and secondary phases melting. In the process known as SIMA (Strain Induced Melt Activation), the raw material is cold deformed by a two-step rolling, making it little efficient. This work investigates the production of thixotropic material, by alternative thermomechanical treatments, of an Al-3.35wt%Cu alloy. Two treatments, which avoid the hot deformation step of SIMA, are performed: Recrystallization and Partial Melting (RAP) and Overaging (OAT) processes. In the first, the as-cast, dendritic, alloy is cold deformed at ambient temperature and then heated to a constant temperature in the mushy zone, to obtain the rheocast structure. In the second, the alloy undergoes a solution and precipitation heat treatment, before cold-deformation, with the aim of obtaining second phase precipitated particles with size and interparticle spacing favourable to the increasing of the nucleation rate of recrystallized grains, during heating of the alloy. It was found that the two routes produce globularized structures, with grain reduction of 85 % and 90 % for RAP and OAT, respectively, with respect to initial grain sizes. In general, OAT process resulted in more rounded and smaller globules than RAP.