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    The effect of halloysite nanotube modification on wear behavior of carbon-aramid fiber reinforced hybrid nanocomposites
    (Wiley, 2022) Cetin, Mehmet Emin; Bastosun, Yusuf; Tatar, Ahmet Caner; Cetin, M. Huseyin; Demir, Okan; Onal, Gurol; Avci, Ahmet
    In this study, the carbon-aramid fiber reinforced hybrid composites are fabricated using a vacuum-assisted hand lay-up method using halloysite nanotubes (HNTs) modified epoxy matrix. Ball-on-disk wear tests are performed to analyze the tribological effect of neat and HNTs-added specimens at 10, 15, and 20 N loads and 1 m/s sliding speed. Additionally, the wear rate and friction coefficient results are obtained to investigate the effect of the HNTs on the tribological behavior of hybrid composites. The wear mechanism of neat and nanocomposite specimens is specified by scanning electron microscopy (SEM) images, and the elemental analysis of worn surfaces is performed using EDX. Finally, the surface morphology is evaluated with 3D topography images. Additionally, thermal camera images are used to identify the thermal conductivity effect of HNTs on wear. The wear test results show that HNTs-addition to composite decreased the friction coefficient by 9%, 10%, and 11% for 10 N, 15 N, and 20 N loadings, respectively. The wear rate is also decreased average by 75% for wear loadings. Surface form images acquired from 3D topography support the enhancement in the friction coefficient and wear rate values. Furthermore, thermal camera images show that thermal conductivity improvement on the contact region is attributed to well thermal properties of HNTs. Furthermore, the solid-lubricant characteristic of HNTs as forming tribofilm is determined as the main reason for the enhanced tribological performance of nanocomposites. Finally, a detailed wear mechanism is proposed to explain the wear behavior of HNTs-added carbon-aramid hybrid composites based on SEM images.
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    Effects of cryogenic and warm temperatures on quasi-static penetration resistance of carbon-aramid hybrid nanocomposites reinforced using halloysite nanotubes
    (Elsevier, 2021) Cetin, Mehmet Emin; Tatar, Ahmet Caner; Demir, Okan; Onal, Gurol; Avci, Ahmet
    The quasi-static penetration test of a composite structure aims to measure impact behavior under the out-of plane loadings without dynamic and rate effects. In this study, carbon-aramid reinforced nanocomposites were manufactured by vacuum-assisted resin transfer molding and hand lay-up techniques and characterized by quasi-static penetration tests. Halloysite nanotubes (HNTs) were added to epoxy resin as nanofillers. Quasi-static punch shear test (QS-PST) was performed using a 12.7-mm cylindrical punch with a 50.8-mm support span. QSPSTs tests were carried out at-50 degrees C,-25 degrees C, 0 degrees C, 25 degrees C, and 50 degrees C to determine the effect of temperature on quasi-static penetration behavior of neat and HNT-reinforced carbon-aramid nanocomposites. Absorbed energy values and penetration force-displacement curves were acquired from QS-PSTs for each sample. Photographs of the front and rear sides of the samples were taken and analyzed. Moreover, the samples were cut from the middle, and the damage throughout the thickness of the composite samples were examined. It was observed that for all test samples, damages increased when the temperatures decreased. For the same temperature, nano particle addition to the samples resulted in higher penetration force and less damage. We confirmed the possibility of increasing penetration resistance and energy absorption capacity by adding HNT to carbon-aramid fibers at cryogenic and warm temperatures.
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    Investigation of Electrical Conductivity of Polyacrylonitrile (PAN) Nanofibers/Nano Particul (Ag, Cu, CNT and GNR)
    (Trans Tech Publications Ltd, 2017) Onal, Gurol; Erdal, Mehmet Okan; Dincer, Kevser
    In this study 1% Ag (silver), Cu (copper), CNT (carbon nanotube) and graphene nanoribbon (GNR) nanoparticle reinforced PAN fibers were prepared and the effects of nanoparticle reinforcements upon electrical conductivity were investigated. In experimental study, graphene nanoribbon powders were produced from multiwalled carbon nanotube (MWCNT) through using the chemical approach of Hummers method. Fiber layer was dissolved at room temperature in magnetic mixer with Polyacrylonitrile(PAN) and Dimethil Formamide (DMF) which was at the rate of 10 % by mass. Thus, a viscou gel solution was obtained then nanoparticles were added to the PAN/DMF solution and the solution was vigorously stirred for one hour at room temperature. After stirring that solution was continued for 15 m in ultrasonic bath. The polymeric solution was first transferred to a 5 mL syringe, which was connected to a capillary needle with an inside diameter of 0,8 mm. A copper electrode was attached to the needle, a DC power supply produces 25 kV against a grounded collector screen distant 15cm. With the syringe pump set at 2 mL/h, the electric force overcomes the surface tension of the solution at the capillary tip, and a jet emerges. Produced fibers were collected on the rotary collector which spins at 250 rpm. Nanofiber was dried at 60 degrees C for 12 h in vacuum oven. Eventually, nanofiber of polyacrylonitrile (PAN) reinforced by metallic nanoparticles and graphene nanoribbon (GNR) were prepared by electro spinning process. Electrical conductivity of the obtained nanofiber were studied by measuring the electrical resistance thanks to home-made plate electrodes.