Accessibility Tools
Grosso, Marcella ; Margarit-Mattos, Isabel C. P. ; R. PEREIRA, GABRIELA. (2020).
Resumo: The use of anticorrosive coatings has been a powerful method to be applied on the surface of metallic materials to mitigate the corrosive process. In this study, the focus is composite coatings that are commonly used on the internal surface of storage tanks in petrochemical industries. The development of non-destructive methods for inspection of faults in this field is desired due to unhealthy access and mainly because undercoating corrosion is difficult to detect by visual inspection. Pulsed thermography (PT) was employed to detect undercoating corrosion and adhesion loss of anticorrosive composite coatings defects. Additionally, a computational simulation model was developed to complement the PT tests. According to the experimental results, PT was able to detect all types of defects evaluated. The results obtained by computational simulation were compared with experimental ones. Good correlation (similarity) was verified, regarding both the defect detection and thermal behavior, validating the developed model. Additionally, by reconstructing the thermal behavior according to the defect parameters evaluated in the study, it was estimated the limit of the remaining thickness of the defect for which it would be possible to obtain its detection using the pulsed modality.
LEAL, P. H. M. ; BARCIA, O. E. ; MATTOS, O. R. (2020).
Resumo: This paper presents a numerical analysis of the effect of different parameters (rotation speed, equilibrium constant and Schmidt numbers) on the diffusion (ZD) and electro-hydrodynamic (ZEHD) impedances of chemical-electrochemical (CE) systems in a rotating disk electrode (RDE) configuration. For this purpose, we used a finite difference algorithm to discretize and solve the governing equations. Our results show that the separation between convection-diffusion and reaction impedance loops depends on the ratio between diffusion layer thickness ( ) and reaction layer thickness ( ). Also, we have demonstrated that the characteristic frequency of the reaction impedance loop is a function of As for ZEHD data, we found that, for slow kinetics, the plots do not overlap for different rotation speeds. Further, the upper limit of the negative phase is different for both, slow and fast kinetics, from the usual 180° value found for single charge transfer systems. The increment of the equilibrium constant, obtained via increasing the reaction rate constant of the electroactive species, caused the magnitude ZD to decrease and that of ZEHD to increase. Lastly, we found that changing ScA mainly affects the concentration gradient at the surface while the effect of ScB will depend on the kinetic regime.
FERREIRA, C.G. ; Lopes, R.T. ; DOS SANTOS, T.M.P. ; OLIVEIRA, D.F. ; MARTINS, F.D.F. ; Pereira, G.R. (2020).
Resumo: The objective of the present study is to apply digital radiography (DR) and computed microtomography (microCT) techniques to the inspection of laminated pipe Joints in polymeric composite material reinforced by fiberglass. The study comprises a structural assessment, defect characterization and void distribution of each sample. Non-destructive X-ray testing is increasingly present in composite material analyses and has advantages over other laboratory techniques since it is non-invasive and allows for the 2D/3D visualization of the inner structures without previous preparation. The results showed that the techniques detected the defects inserted. The digital radiography made an extension defect measurement possible. The microCT volumetrically quantified these defects as well as the reinforcement and matrix layers.
VIANA, PEDRO R.P. ; de Sousa, Flávio V.V. ; Barcia, Oswaldo E. ; TRIBOLLET, BERNARD ; Mattos, Oscar R. (2020).
Resumo: The hydrogen evolution reaction (HER) in H2S and H2S/CO2 solutions at different pressures was studied using platinum and stainless steel as working electrodes, with polarization curves and electrohydrodynamic impedance. When Pt was the working electrode, the polarization curves in H2S solutions without CO2 presentedonly one current plateau, while two plateaus were seen when a mixture of H2S/CO2 was used. However, when steel was the working electrode, two plateaus always existed even in the presence of H2S without CO2. HER was interpreted by another source of H2 coming from the H2S reaction coupled to the classical direct reduction of H+.
CASTRO, LUIZ C. V.; MATOS, TOSELI D. F. ; OLIVEIRA, SYLVIO J. R. D. ; BRUM, NÍSIO. D. C. L. (2020).
Resumo: The elastohydrodynamic (EHD) lubrication straight line contact conjunction is studied to evaluate the mixed lubrication heat generation experimentally over bordering operating conditions in a disc-on-disc machine. An experimental investigation is carried out using an accessory device that collects and measures the outlet lubricant temperature. The experimental results show the typical transition from mixed to elastohydrodynamic lubrication, tracking the difference of outlet lubricant temperature and the total average full-film EHD temperature. A new variable coupling flash temperature was introduced as an in situ approach to demonstrate the lubricant capacity of removing heat from asperity interaction in mixed lubrication contacts. It was possible to estimate the metal–metal contact area in mixed lubrication by coupling flash temperature as a direct correlation to the true flash temperature in relation to correspondence to final surface roughness characterizations.
