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- 저자 : Juan Carlos Campos Rubio (검색결과 2 건)
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Cementitious Porous Material Applied to Precision Aerostatics Bearings
Leandro Jos da Silva,Tulio Hallak Panzera,Luciano Machado Gomes Viera,Christopher Rhys Bowen,Jaime Gilberto Duduch,Juan Carlos Campos Rubio 한국정밀공학회 2018 International Journal of Precision Engineering and Vol.19 No.2
The use of porous materials as restrictor in aerostatic bearings provides many advantages over conventional restrictors, such as small variation of temperature, high damping, high operational speeds, limited wear and capacity to support radial, axial, and combined loads, being considered important features for precision machines and instruments. This work evaluates the load carrying capacity for different air gaps and pressures of thrust porous bearing made with cementitious composites. The cementitious composites consisted of Portland cement and monomodal silica particles (44 μm) were fabricated via uniaxial cold-pressing (10 MPa). The load capacity was determined for different air pressures, such as 3, 4, 5 and 6 bar. The air gap was measured using pneumatic transducers. A pneumatic instability was observed when the air pressure level increased from 3 to 6 bar. A similar loading capacity, for bearing gaps between 7 and 30 μm, was achieved in comparison to hot-pressed porous alumina found in the literature. In addition, the cementitious porous bearing provided a superior loading capacity for gaps higher than 10 μm when compared to graphite porous bearing found in the literature. The results revealed the cementitious composites are promising materials for porous restrictor in aerostatic thrust bearings.
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Bruno Dorneles de Castro,Kláudia Maria Machado Neves Silva,Rômulo Maziero,Paulo Eustáquio de Faria,Priscila Pereira Silva-Caldeira,Juan Carlos Campos Rubio 한국섬유공학회 2020 Fibers and polymers Vol.21 No.8
The use of treatments in natural fibers is largely used, because it can improve the interfacial adhesion of polymercomposites. However, the choice of the most appropriate treatment should take into account environmental factors, due to theneed of new materials to meet requirements related to the concept of sustainability. This article investigated the influence ofthe mercerization, acetylation and gamma radiation treatments on the mechanical properties of sisal fibers, to use incomposite materials. Experimental conditions were defined with different concentrations of reagents and radiation doses inorder to understand the impact of these reactions on the tensile properties of sisal fibers. Thermal gravimetric analysis (TGA)and Fourier Transform Infrared (FTIR) spectroscopy were used to investigate the fiber degradation process and the chemicalmodifications after the treatments. The use of mercerization (0.1 M and 1.0 M NaOH concentrations) combined withacetylation increased the hydrophobic character of the sisal fiber, which may improve its interaction with polymeric matrices. In addition, mercerized sisal fiber at 0.5 M NaOH concentration, exposed to 25 kGy gamma radiation dose, showed physicaland chemical structural changes that positively influence the fiber-matrix adhesion in polymer composite materials. Alltreatments made can reduce the natural tensile properties of the sisal fibers, because they can remove fundamentalcomponents to the structure and the stiffening of these fibers. Considering changes in the mechanical behavior, the use ofgamma radiation presented similar results of the traditional chemical treatments, being less aggressive to the fibers and notcausing the same negative impact on the environment.
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