RCAAP Repository

Conselho Nacional de Desenvolvimento Científico e Tecnológico

This work aims to study the niobium influence in the crystallographic texture and the corrosion resistance of ferritic stainless steels on aerated and de-aerated environments. For this objective the ferritic stainless steels P409, P410, P430A, P430E (Nb stabilized) were used; and austenitic stainless steel, P304, and carbon steel, A36, were used as comparative materials. These materials had a mechanical characterization (hardness and tension test), and the steels P430A and P430E had a crystallographic characterization too. That crystallographic characterization (by EBSD) was analyzed through to inverse pole figure (IPF) and crystal orientation distribution function (CODF). The samples were submitted to anodic potentiodynamic polarization test in solutions: 3.56% NaCl, and 1N H2SO4 on aerated environment, and 3.56% NaCl at de-aerated environment. The samples were examined by SEM after the polarization tests. The analysis of the results clearly showed that the crystallographic texture influence the corrosion resistance. The niobium in the stainless steel reduces the presence of preferential orientation, therefore, the influence of the texture in the corrosion resistance, but helps to increase the corrosion resistance by the formation of niobium carbbonites. Finally it was observed that for polarization tests in aerated environments and de-aerated have a very small variation in behavior that depends on the steel, but this variation is not statistically significant.

The development of data acquisition techniques able to monitor the performance of an automated welding system could be, for example, applied to a system able to repair pipes full of operating fluid. In this case, the system must precisely control and monitor the heat input during the weld. For this purpose, it would be necessary to develop data acquisition techniques able to monitor the performance of such a system. Digital oscilloscopes, which are usually the kind of equipment used for this purpose, present high-cost as well as other solutions offered by the market. Moreover, those systems do not offer a specific solution to the welding area. Thus, the aim of this work was to develop a synchronized data acquisition system with integrated webcam that was suitable for the study of the several types of welding processes. It could be used for automation of pipeline repair systems, as well as, for other types of welding operations, including experimental evaluations into laboratories. A software package was developed using LabVIEW as programming language. It is able to do synchronized acquisition of signals and image and post analysis of the acquired data. The use of low-cost cameras like webcams was introduced aiming to determine arc characteristics as arc length, for instance. The acquisition of the emitted sound by the arc during the welding was also considered, what could increase the feeling of the professional working away and could be used for studies related to welding quality. Using the existent resources in the laboratory, a hardware prototype with enough flexibility and suitable for several types of welding processes was designed. Afterwards, a system with a physical configuration more appropriate to the work environment and lower cost was built. This system was assessed with two different welding operations, Gas Metal Arc Welding and Resistance Spot Welding, when its limitations and advantages were explored and identified.

Conselho Nacional de Desenvolvimento Científico e Tecnológico

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior

Fundação de Amparo a Pesquisa do Estado de Minas Gerais

Fundação de Amparo a Pesquisa do Estado de Minas Gerais

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior

Due to the surge and success of bone integrated implants, dental implants have been consolidated as an important rehabilitation technique within the general context of dentistry. Functional force, bio-mechanical compatibility and tension transfer to the neighboring tissues are among the factors envolved in the line of dental implants. In this aspect, one of the main elements of a dental implant is the pillar screw that makes the connection between the pillar and the dental implant itself. Several cases of loosening and even fractures have been reported in literature. As to Brazilian implants there is still not a standard that can differentiate the systems in such a way the indicates a level of quality and efficacy. In this work, to facilitate a preview of the mechanical behavior and function of all these factors, considering the pressure involved, a tri-dimensional model of finite elements of a Brazilian dental implant was developed. The main objective was to numerically evaluate the pillar screw, the level of torque supported by the screw, the tension distribution and the possibility of tightening and un-tightening while considering external pressure on the implant. An analytical model to determine the distribution of tension and estimate the torque of tightening was proposed and validated as a numerical model. The numeric results were compared with the analytical formulations using a standard Brazilian implant manufactured by Conexão Sistemas de Prótese Ltda.

Conselho Nacional de Desenvolvimento Científico e Tecnológico

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior

Conselho Nacional de Desenvolvimento Científico e Tecnológico

Numerical simulations in rotating flows similar to that in cyclones and combustion chambers were performed in this work, in order to verify and characterize the formation of vortex breakdown phenomenon. Cylindrical and conical-cylindrical geometries, both closed, were used in simulations. The rotating flow is induced by the bottom wall, which rotates at constant angular velocity, and the other walls are nonmoving with no-slip boundary conditions. First, the numerical results were compared to experimental results available in references, aiming to verify the capacity of the computational code to predict the vortex breakdown phenomenon. Afterwards several simulations varying the parameters which govern the characteristics of the flows analyzed in this work, i.e. the Reynolds number and the aspect ratio, were performed. In these simulations, the transitional limit and the limit of vortex breakdown formation were verified. Steady and transient cases, with and without turbulence modeling, specifically dynamic model, were simulated. In general, some aspects of the process of vortex breakdown in conical-cylindrical geometries was observed to be different from that in cylinders.

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior

This study aimed to identify the effect of interference produced by mechanical vibration on the average values of roughness parameters and associated measurement uncertainty by means of an electromechanical model TR200 roughness - Homis. Tests were performed by applying vibration in the direction perpendicular to the probe travel path, for different values of frequency and amplitude. The generating system consisted of an electrodynamics vibration exciter and the acceleration measurement was performed by means of a piezoelectric accelerometer. The work was carried out according to the following steps: i) measurement of roughness parameters (Ra, Rq, Rz and Rt) of three samples in conditions without vibration. For comparison and analysis, the roughness was also measured, non-contact, using an interferometer; ii) pre - testing, which consisted of roughness measurement and vibration simultaneously on an aluminum sample considering a frequency band of 50 Hz to 150 Hz and four levels of acceleration; iii) 3² factorial design, which was defined from the results obtained in the pre-tests, which were measured Ra, Rq, Rz and Rt in three samples, independent variables were the frequency and acceleration, both on three levels, namely 60Hz, 80 Hz and 100 Hz for the frequency, with acceleration from 0,6 m/s², 1.0 m/s² and 1.6m/s². Analysis of variance, was used to verify if the differences between the mean values of roughness parameters evaluated are significant or not. Finally the measurement uncertainty was evaluated using the Monte Carlo method. The procedure has shown that the mechanical vibration produces changes in the mean values of roughness parameters evaluated and the highest values of expanded uncertainty were found for frequencies of 80 Hz and 100 Hz and acceleration of 1.0 m/s².