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    Boron nitride-MWCNT/epoxy hybrid nanocomposites: Preparation and mechanical properties
    (Elsevier, 2014) Ulus, Hasan; Ustun, Tugay; Eskizeybek, Volkan; Sahin, Omer Sinan; Avci, Ahmet; Ekrem, Mursel
    In this study, production and mechanical properties of hybrid nanocomposites have been investigated. Hybrid nanocomposites are consisting of boron nitride nanoplatelets (BN) and multiwall carbon nanotubes (MWCNT) embedded in epoxy resin. The BN and MWCNT were mixed to epoxy resin in different weight fractions and mixtures were utilized for tensile test specimen production. The synthesized BN and produced hybrid nanocomposites were characterized by SEM, TEM, XRD, FT-IR and TGA analyses. The elasticity modulus and tensile strength values were obtained via tensile tests. The fracture morphologies were investigated after tensile test by means of scanning electron microscopy. (C) 2013 Elsevier B.V. All rights reserved.
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    Effect of composite to aluminum single lap joints reinforced with graphene doped nylon 6.6 nanofibers
    (Sage Publications Ltd, 2021) Senyurt, Muhammet Ali; Ekrem, Mursel; Duzcukoglu, Hayrettin; Avci, Ahmet
    In this study was investigated the effect of nylon 6.6 (N6.6) nanofiber and nylon 6.6 by weight of 1%, 3% and 5% Graphene Nanoplates (GNPs) doped N6.6 nanofiber reinforced epoxy adhesives on single lap joint of AISI AA2024-T3 Aluminum Alloy (AA 2024)- Carbon Fiber Reinforced Composite (CFRC) plates. First of all, N6.6 nanofibers with/without GNPs in different proportions were produced by the electrospinning method with the help of a rotating and moving drum. Epoxy resin as the adhesive, nanofibers as the second interface to increase the strength of the epoxy and AA 2024 - CFRC were used as the bonded material and the plates cut in 101.6 x 25.4 mm according to ASTM D 1002-10 and ASTM D 5868-01, respectively. In this research was focused on the application of single lap joints by reinforcing with N6.6 nanofibres to decrease the brittleness and increase the toughness of the epoxy resin. When compared with epoxy resin, the shear strength of epoxy adhesive reinforced with N6.6 nanofibers with 3% GNPs by weight increased by 31.20%. Thermal analysis of epoxy resin and hybrid adhesives was examined by Differential Scanning Calorimeter (DSC). In addition, the physical properties of N6.6 nanofibers doped/undoped GNPs in different proportions by weight were observed with scanning electron microscopy (SEM) by damage analysis of fracture surfaces.
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    The effects of carbon nanotubes added polyvinyl alcohol nanofibers on mechanical properties of carbon reinforced composite laminates
    (Springer India, 2019) Ekrem, Mursel
    This study investigates tensile and flexural behaviors of carbon fiber reinforced epoxy (CFRE) composite laminates strengthened in different weights multi walled carbon nanotubes (MWCNT) with/without polyvinyl alcohol (PVA) nanofiber mats. First, PVA nanofiber mats modified with 1, 3, 5wt% MWCNT were produced by electro spinning. Characterization of 1, 3 and 5 MWCNT reinforced/unreinforced PVA nanofiber mats was achieved via transmission electron microscopy (TEM) and scanning electron microscopy (SEM). Then, the produced nanofiber mats were placed in the middle of eight-layer twill carbon fabrics by hand layup after carbon composites were produced by vacuum infusion. Three flexural tests were performed in accordance with ASTM D 7264/D standard so that flexural strength properties of the composites and flexural modulus of elasticity can be found. After that, tensile test was carried out in accordance with ASTM D 3039 for the composites to have single axis tensile strength and modulus of elasticity nanofibers. The tensile strengths of PVA nanofiber mats and 1wt% MWCNT/PVA nanofiber mats reinforced CFRE composites increased by 4% and 34%, respectively when compared to the CFRE composite.
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    The effects of harsh aging environments on the properties of neat and MWCNT reinforced epoxy resins
    (Elsevier Sci Ltd, 2021) Aslan, Abdullah; Salur, Emin; Duzcukoglu, Hayrettin; Sahin, Omer Sinan; Ekrem, Mursel
    In this study, the effects of different harsh aging environments on the chemical and mechanical properties of neat and multiwall carbon nanotubes (MWCNT) reinforced epoxy resins were investigated. The neat and 1 wt% MWCNT reinforced epoxy resins were exposed to four different corrosive environments, namely deionized water, NaCl solution (10 wt% NaCl), H2SO4 solution (10 wt% H2SO4), and HCl solution (10 wt% HCl. The mass variation results revealed that the highest absorption rates were found in specimens aged in both acidic environments. The highest amount of absorption was observed in the H2SO4 environment, measured approximately 3% for neat epoxy, and 6.5% for MWCNT reinforced epoxy resin. FT-IR spectrums showed that the most affected peaks belong to specimens aged in both acidic environments. Tensile test results revealed that the aging process in H2SO4 solution and deionized water deteriorated the strength of specimens. According to the literature, it was reported that the strength of specimens aged in NaCl solution environment is decreased. However, the same trend has not been in this study. In our study, the strength of specimens aged in NaCl solution environment increased impressively by 29%, which makes this study more striking. Another important point analyzed from the tensile test results was that the MWCNT nanoparticle reinforcement adversely affects the strength of the epoxy resin. So, it can be clearly stated that the use of expensive MWCNTs as filler of epoxy resin is not useful to improve its aging resistance. The scanning electron microscope (SEM) and optical microscope images showed that acidic environments result in different fracture mechanisms from typical polymer damaged surfaces reported in available researches. (C) 2020 Elsevier Ltd. All rights reserved.
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    Effects of polyvinyl alcohol nanofiber mats on the adhesion strength and fracture toughness of epoxy adhesive joints
    (Elsevier Sci Ltd, 2018) Ekrem, Mursel; Avci, Ahmet
    The brittle nature of the polymer based adhesive joints is the major drawback limiting the service life. In this study, electrospun polyvinyl alcohol (PVA) nanofiber mat were introduced within the epoxy adhesive joint region to improve mechanical performance of the joints. The epoxy resin wetted electrospun PVA nanofiber mat were placed in between aluminum adherends and cured uncer vacuum conditions to remove air bubbles and volatiles. The mechanical performance of the reinforced aluminum joints was investigated by utilizing single lap joint (SIJ) and double cantilever beam (DCB). To reveal nano- and micro-scale toughening mechanics of the nanofiber reinforcements, the fracture surfaces were analysed using scanning electronmicroscope (SEM). Mod I fracture toughness and lap shear strength of the adhesively bonded joints were found to increase with addition of PVA nanofiber mats into epoxy adhesive.
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    Enhancement of Wear and Friction Characteristics of Epoxy Resin by Multiwalled Carbon Nanotube and Boron Nitride Nanoparticles
    (Taylor & Francis Inc, 2015) Duzcukoglu, Hayrettin; Ekinci, Serafettin; Sahin, Omer Sinan; Avci, Ahmet; Ekrem, Mursel; Unaldi, Mahmut
    Epoxy resins are widely used in engineering applications. However, their low thermal stability limits their usage at high sliding velocities and loads. The mechanical properties and thermal stability of a machine element subjected to friction and wear are very important. In this study, friction and tribology behaviors of multiwalled carbon nanotubes (MWCNTs) and boron nitride (BN)-modified epoxy resin have been investigated. Epoxy resin modified by three different nanoparticle configurations, 0.3% MWCNT, 0.5% BN, and 0.5% MWCNT/0.3% BN, was investigated. The tribological characteristics of nanoparticle-modified epoxy resin were compared with properties of neat resin. The friction and tribological behavior of modified epoxy resin were tested using a ball-on-disc test stand at 1.2 and 1.5 ms(-1) sliding velocities under 10 N applied load. The tests were done under dry condition and 1,800 m distance. The friction coefficient, wear loss, and temperature increase during testing were recorded and compared with that obtained for neat epoxy. It is observed that nanoparticle modification resulted in enhanced wear resistance and a reduction in friction coefficient and working temperatures.
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    An experimental evaluation on the dynamic response of water aged composite/aluminium adhesive joints: Influence of electrospun nanofibers interleaving
    (Elsevier Sci Ltd, 2022) Ulus, Hasan; Kaybal, Halil Burak; Berber, Nihat Erdem; Tatar, Ahmet Caner; Ekrem, Mursel; Ataberk, Necati; Avci, Ahmet
    The impact response of adhesives is a critical design parameter considering their lifetime. Additionally, environmental effects such as water or moisture may cause to degrade of the polymer-based adhesive and shorten its service life. This study aimed to investigate the impact response of water-aged aluminium-composite adhesively bonded single lap joints (SLJs). Nylon 6.6 nanofibers modified with graphene nanoplatelets (GNPs) were introduced in the adhesion areas to increase adhesive performance. The water aging resulted in decreased impact resistance in all cases. However, nanofiber-modified SLJs exhibited comparatively higher impact performance under both non-aged and water-aged conditions. Further, the GNP reinforced nylon 6.6 nanofibers increased the maximum impact load by 15 and 19% compared to neat nanofibers before and after aging, respectively. The fracture surfaces were examined via scanning electron microscopy (SEM) to understand damage and toughness mechanisms. A schematic model has been developed to explain the mechanisms leading to improved bonding performance by applying N6.6 nanofiber reinforcement to the adhesion zone.
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    Fatigue behavior of composite to aluminum single lap joints reinforced with graphene doped nylon 66 nanofibers
    (Elsevier Sci Ltd, 2018) Polat, Safa; Avci, Ahmet; Ekrem, Mursel
    It is an important approach to prevent the damage mechanisms that cause sudden fractures during fatigue loading in bonding joints by modifying the matrix with nanostructured materials. The aim of this study is to examine the effect of graphene nanoplates (GNPs) doped nylon 66 (N66) nanofiber mats reinforcement on the fatigue life of composite to aluminum single lap joint. For this purpose, 1 wt%, 3 wt% and 5 wt% GNPs doped N66 nanofibers were produced by electrospinning method. The morphological characteristics, chemical bond structures and % crystallinity of these nanofiber mats was investigated by SEM, TEM, FTIR, DSC analysis. The fatigue tests of the bonding joints with single axis periodic cycle loading were performed at five different load levels as 20%, 30%, 40%, 50% and 60% of the maximum shear strength of each samples. Fatigue life of bonding joints was assessed by S-N curves plotted according to the fatigue results. Damage mechanisms of fractured surface in the bonding joints were investigated with the macro and micro images. The results show that, these composite nanofiber mats have increased the fatigue life of bonding joints in all case.
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    Friction and Wear Performance of Epoxy Resin Reinforced With Boron Nitride Nanoplatelets
    (Asme, 2018) Ekrem, Mursel; Duzcukoglu, Hayrettin; Senyurt, Muhammet Ali; Sahin, Omer Sinan; Avci, Ahmet
    In this study, the effects of addition of boron nitride nanoplatelets (BNNPs) upon friction and wear behavior of epoxy resin have been investigated by using pin-on-disk test. It has been reported in the literature that certain amounts of BNNP addition can be useful for enhancement of mechanical properties. Therefore, it is very important to obtain the effect of such addition upon friction and wear performance of epoxy resin. BNNPs have been incorporated at 0.3-0.5-0.7-1 wt %. It is shown that BNNP addition results in decrease in friction coefficient and wear. It is also shown that the best results are obtained with 0.5% nanoplatelet addition. It is also observed that heat conduction of epoxy resin is enhanced by the nanoplatelet addition.
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    Improving electrical and mechanical properties of a conductive nano adhesive
    (Taylor & Francis Ltd, 2017) Ekrem, Mursel; Ataberk, Necati; Avci, Ahmet; Akdemir, Ahmet
    In this experimental study, lap shear strength and electrical conductivity of nanohybrid adhesives containing multi-walled carbon nanotubes (MWCNT) and silver (Ag) nanoparticles were investigated. Ag nanoparticles were produced via arc-discharge method in liquid nitrogen. For characterizing the Ag nanoparticles, X-ray diffraction analysis, transmission electron microscopy, and scanning electron microscopy (SEM) were performed. Tensile lap shear properties were determined in accordance with ASTM D 1002-10 standard. Mechanical and the electrical properties of nanohybrid adhesives were compared with neat epoxy adhesive. The best electrical conductivity of nanohybrid adhesive was obtained for the 1% wt MWCNT-2% wt Ag-contained sample. However, the samples which contain 0.5% wt. MWCNT-0.5% wt. Ag nanoparticles reached the highest lap shear strength. The results showed that Ag nanoparticles enhance the conductivity in the presence of MWCNT. It is concluded that the MWCNT act as conductivity bridges among epoxy adhesive and facilitate the electron transfer. As seen in the tensile test results, the ductility of the adhesive was improved by adding the nanoparticles in to the epoxy resin.
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    Measurement of the elastic properties of epoxy resin/polyvinyl alcohol nanocomposites by ultrasonic wave velocities
    (Budapest Univ Technol & Econ, 2022) Oral, Imran; Ekrem, Mursel
    The polyvinyl alcohol (PVA) nanofiber mats are produced using the electrospinning method. The epoxy resin (ER)/polyvinyl alcohol (PVA) nanocomposites are obtained by adding PVA nanofiber mats into neat epoxy resin (ER) as 5, 10, and 15 layers. The elastic properties (elastic constants, Young's modulus, Poisson's ratio, and Shear modulus) of the neat ER, and the ER/PVA nanocomposites, are determined by ultrasonic longitudinal wave velocity (V-L) and shear wave velocity (V-S) measurements. The morphology of the neat ER and the ER/PVA nanocomposites is investigated using scanning electron microscopy (SEM). The results obtained from SEM images showed the ER/PVA nanocomposites have a transversely isotropic structure. The V-L value of isotropic neat ER was obtained higher than the value of V-L33 and V-L45 degrees but lower in x(1) direction for V-L11 in the ER/PVA nanocomposites. The velocity values of ultrasonic shear waves propagated in x(1) direction and polarized in y(2) direction in the ER/PVA nanocomposites are determined as higher than the velocity values of ultrasonic shear waves propagated in z(3) and polarized in x(1) direction. Also, the value of E-3 determined in the z(3) direction is found to be significantly higher than the value of E-1 determined in the x(1) direction when the number of PVA layers increased in the ER matrix. The value of shear modulus (G(31)) is found as 1.53, 1.76, and 1.61 GPa for the ER/PVA-5, the ER/PVA-10, and the ER/PVA-15, respectively. The Poisson's ratio values of the ER/PVA nanocomposites are determined as between 0.473-0.502 and 0.247-0.276 for mu(11) and mu(31), respectively. On the other hand, the degree of anisotropy in the ER/PVA nanocomposites is determined using ratios of E-1/E-3 and mu(11)/mu(31). A small degree of anisotropy in dynamic Young's modulus (0.93-0.99) is observed, while a higher ratio is observed for Poisson's ratio (1.71-2.03) with increasing PVA layers in neat ER.
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    Mechanical Properties and Damage Behaviours of Polyurethane Composites Reinforced With BNNP and MWCNT Hybrid Nanoparticles
    (Sage Publications Ltd, 2023) Bahtiyar, Guelay; Ekrem, Mursel; Unal, Bayram; Ak, Safa
    In recent years, with increasing engineering applications, structural adhesives have played an increasingly important role in joining both metallic and non-metallic components. Polyurethane is frequently used in the adhesive industry due to its morphological structure, versatile material, and excellent matrix material. In addition, by doping polyurethane with single/multi-walled carbon nanotubes and boron nitride nanoplates materials, the mechanical properties of the polyurethane adhesive can be further increased. This study aimed to increase the mechanical properties of PU (thermoset polyurethane), which is frequently used in adhesively bonded joints by addition of MWCNT (multi-walled carbon nanotubes), BNNP (boron nitride nanoplates). For this purpose, nanoparticles synergistic interaction was investigated by adding a mass of 0.25%, 0.35%, and 0.45% MWCNT into PU, which was reinforced by 0.5% BNNP before. Samples mechanical properties were determined by tensile test according to ASTM D638-10 standard, flexure test according to ASTM D790-02 standard, and Shore D test according to ASTM D2240 standard. All sample test results were graphed, and each graph was compared. Also, broken surfaces were analyzed by scanning electron microscopy (SEM) to examine the damage mechanism of nanoparticles.