Time filter

Source Type

Franquetto P.R.,Navy Technology Center in Sao Paulo | Neto M.M.,Energetic and Nuclear Research Institute
Journal of Offshore Mechanics and Arctic Engineering | Year: 2016

During the pressure hull manufacturing, processes like cold bending and welding are often applied. These processes lead to permanent plastic deformations which are associated with residual stresses. The presence of residual stresses is equivalent to the introduction of an initial preload in the structure, which accelerates the plastification process, decreasing pressure hull resistance. To quantify this reduction, a case study that considers residual stresses due to cold bending on hull plates and frame flanges had been performed using finite element models. The study encompasses hull diameters of 6, 8, and 10m with hull plates and frame flange thickness from 20 to 30 mm, with HY100 steel. Finite element numerical analyses were done considering material and geometric nonlinearities. First, the cold bending residual stresses were determined using finite element models. Then, these cold bending residual stresses were introduced as initial stresses in the submarine pressure hulls' finite element models. In the end, it was possible to verify that the presence of cold bending residual stress reduces the submarine hull collapse pressure up to 4.3%. © 2016 by ASME.

Botta S.B.,University of Sao Paulo | Ana P.A.,Energetic and Nuclear Research Institute | De Sa Teixeira F.,University of Sao Paulo | Da Silveira Salvadori M.C.B.,University of Sao Paulo | Matos A.B.,University of Sao Paulo
Photomedicine and Laser Surgery | Year: 2011

Objective: The aim of this study was to assess by atomic force microscopy (AFM) the effect of Er,Cr:YSGG laser application on the surface microtopography of radicular dentin. Background: Lasers have been used for various purposes in dentistry, where they are clinically effective when used in an appropriate manner. The Er,Cr:YSGG laser can be used for caries prevention when settings are below the ablation threshold. Materials and Methods: Four specimens of bovine dentin were irradiated using an Er,Cr:YSGG laser (λ=2.78μm), at a repetition rate of 20Hz, with a 750-μm-diameter sapphire tip and energy density of 2.8J/cm 2 (12.5mJ/pulse). After irradiation, surface topography was analyzed by AFM using a Si probe in tapping mode. Quantitative and qualitative information concerning the arithmetic average roughness (Ra) and power spectral density analyses were obtained from central, intermediate, and peripheral areas of laser pulses and compared with data from nonirradiated samples. Results: Dentin Ra for different areas were as follows: central, 261.26 (±21.65) nm; intermediate, 83.48 (±6.34) nm; peripheral, 45.8 (±13.47) nm; and nonirradiated, 35.18 (±2.9) nm. The central region of laser pulses presented higher ablation of intertubular dentin, with about 340-760nm height, while intermediate, peripheral, and nonirradiated regions presented no difference in height of peritubular and interperitubular dentin. Conclusion: According to these results, we can assume that even when used at a low-energy density parameter, Er,Cr:YSGG laser can significantly alter the microtopography of radicular dentin, which is an important characteristic to be considered when laser is used for clinical applications. © Copyright 2011, Mary Ann Liebert, Inc. 2011.

Botta S.B.,University of Sao Paulo | Ana P.A.,Federal University of ABC | Santos M.O.,Energetic and Nuclear Research Institute | Zezell D.M.,Energetic and Nuclear Research Institute | Matos A.B.,University of Sao Paulo
Journal of Biomedical Materials Research - Part B Applied Biomaterials | Year: 2012

This study aimed to evaluate the chemical interaction of collagen with some substances usually applied in dental treatments to increase the durability of adhesive restorations to dentin. Initially, the similarity between human dentin collagen and type I collagen obtained from commercial bovine membranes of Achilles deep tendon was compared by the Attenuated Total Reflectance technique of Fourier Transform Infrared (ATR-FTIR) spectroscopy. Finally, the effects of application of 35% phosphoric acid, 0.1M ethylenediaminetetraacetic acid (EDTA), 2% chlorhexidine, and 6.5% proanthocyanidin solution on microstructure of collagen and in the integrity of its triple helix were also evaluated by ATR-FTIR. It was observed that the commercial type I collagen can be used as an efficient substitute for demineralized human dentin in studies that use spectroscopy analysis. The 35% phosphoric acid significantly altered the organic content of amides, proline and hydroxyproline of type I collagen. The surface treatment with 0.1M EDTA, 2% chlorhexidine, or 6.5% proanthocyanidin did not promote deleterious structural changes to the collagen triple helix. The application of 6.5% proanthocyanidin on collagen promoted hydrogen bond formation. © 2012 WILEY PERIODICALS, INC.

Loading Energetic and Nuclear Research Institute collaborators
Loading Energetic and Nuclear Research Institute collaborators