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Pelin C.-E.,National Institute for Aerospace Research and Development Elie Carafoli | Pelin C.-E.,Polytechnic University of Bucharest | Ficai D.,Polytechnic University of Bucharest | Andronescu E.,Polytechnic University of Bucharest | And 4 more authors.
Current Nanoscience | Year: 2016

Background: One of the major issues of carbon fiber reinforced polymeric composites is the weak interface between the phases, that supports crack propagation and leads to premature mechanical failure. The paper presents a study involving carbon fiber compatibilization with the polymeric matrix via oxidative treatment and the effect that the modified carbon fiber fabric has on the mechanical performance of its polyamide 6 composites. Methods: Thermoplastic polyamide 6 matrix/fabric based composites are obtained using carbon fiber fabric that is oxidized using K2Cr2O7/H2SO4 mixture in different reaction conditions. The oxidized carbon fiber surface is analysed using FTIR spectroscopy and the composite materials are mechanically tested in terms of tensile and flexural properties, the fracture cross section is analyzed by SEM and optical microscopy to evaluate the interface and the fracture mode. Results: FTIR spectroscopy showed that higher temperature oxidation generates more functional groups on the carbon fiber surface that are able to interact with the polymer, enhancing the interface strength. Tensile and flexural tests showed significant improvement of strength and stiffness when using surface oxidized carbon fabric, results owned to the excellent bonding between the matrix and the fibers that compose the fabric, illustrated by SEM and optical microscopy analysis. Conclusion: The obtained results prove that carbon fiber oxidation in certain condition is efficient for achieving stronger fiber/themoplastic matrix interface, by creating hydrogen bonding sites that prevent delamination and are able to improve the mechanical performance of the composites. © 2016 Bentham Science Publishers.

Pelin G.,National Institute for Aerospace Research and Development Elie Carafoli | Pelin G.,Polytechnic University of Bucharest | Pelin C.-E.,National Institute for Aerospace Research and Development Elie Carafoli | Pelin C.-E.,Polytechnic University of Bucharest | And 5 more authors.
Bulletin of Materials Science | Year: 2016

This paper presents a preliminary study on obtaining and characterization of phenolic resin-based composites modified with nanometric silicon carbide. The nanocomposites were prepared by incorporating nanometric silicon carbide (nSiC) into phenolic resin at 0.5, 1 and 2 wt% contents using ultrasonication to ensure uniform dispersion of the nanopowder, followed by heat curing of the phenolic-based materials at controlled temperature profile up to 120.C. The obtained nanocomposites were characterized by FTIR spectroscopy and scanning electron microscopy analysis and evaluated in terms of mechanical, tribological and thermal stability under load. The results highlight the positive effect of the nanometric silicon carbide addition in phenolic resin on mechanical, thermo-mechanical and tribological performance, improving their strength, stiffness and abrasive properties. The best results were obtained for 1 wt% nSiC, proving that this value is the optimum nanometric silicon carbide content. The results indicate that these materials could be effectively used to obtain ablative or carbon.carbon composites in future studies. © Indian Academy of Sciences.

Palade S.,University of Bucharest | Pantazi A.,University of Bucharest | Berbecaru C.,University of Bucharest | Berbecaru C.,Growth Science | And 8 more authors.
Journal of Optoelectronics and Advanced Materials | Year: 2015

Resin and functionalized multiwall carbon nanotubes (fMWCNT) were used to obtain composites, cured at room temperature (RT). Dielectric measurements show changes of permittivity and losses in cooling-heating cycle with nonreproducible values above 50 oC. Interplay of segments with increased mobility due to increasing resin temperature, the differences between thermal expansion coefficients between resin and fMWCNT, spatial rearrangements in samples and post curing effects could explain the evolution of dielectric parameters versus temperature. Permittivity and losses show strong frequency dependence associated with reducing contributions of different polarization mechanisms at increasing frequencies. Permittivity, losses and electrical conductivity of the samples reveal a tremendous increase with nanotubes concentration at the percolation threshold. Percolation and tunneling mechanisms at RT and thermally activated mechanisms, which dominates the electrical conduction at high temperatures, can explain the temperature dependence of samples' conductivity. Electrical measurements also showed non-reproducible values at heating and cooling beyond 55 °C.

Pelin C.E.,National Institute for Aerospace Research and Development Elie Carafoli | Pelin C.E.,Polytechnic University of Bucharest | Stefan A.,National Institute for Aerospace Research and Development Elie Carafoli | Dinc I.,National Institute for Aerospace Research and Development Elie Carafoli | And 6 more authors.
Journal of Optoelectronics and Advanced Materials | Year: 2015

The work presents a novel simple route to obtain new laminated composites based on carbon fiber fabric layers and polyamide 6 plates, processed via hot melting pressing technique. The paper describes the obtaining process of the composite and the evaluation of its characteristics. Polyamide 6 was used as thermoplastic matrix in form of extruded plates, and it was reinforced with two layers of carbon fiber plain weave fabric. The assembly was pressed at high temperature in order to obtain a laminated structure material. Electronic microscopy and infrared spectroscopy analyses as well as mechanical tests were performed on the final composites as well as on the raw matrix material. The laminated composite was characterized using a relatively new technique consisting of FTIR microscopy. The results of these analyses confirmed the results obtained for the mechanical testing of the tension and flexural strength and modulus. The carbon fabric laminate presented remarkable increase of mechanical characteristics regarding both tensile and flexural strength and excellent improvement of elasticity modulus, with minor increase of density. The characteristics of the new composites based on carbon fiber make them potential candidates for different applications where high mechanical performance and lightweight are crucial elements.

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