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Öğe Acetylsalicylic acid assisted hydrothermal growth of NiO, CuO and Co3O4 nanostructures and their application in the electro-catalytic determination of nalbuphine hydrochloride(ELSEVIER SCIENCE SA, 2017) Kalwar, Nazar Hussain; Tunesi, Mawada Mohamed; Soomro, Razium Ali; Amir, Md.; Avci, Ahmet; Hallam, Keith Richard; Kilislioglu, AybenThis study describes the hydrothermal synthesis of NiO, CuO and Co3O4 nanostructures using acetylsalicylic acid (ASA) as a growth-controlling/directing agent. The as-synthesised nanostructures were shown to possess unique structural features and distinct morphologies, portraying the efficiency of ASA as a suitable growth modifier. The formed metal oxide nanostructures, when used for electrode modification purposes, exhibited excellent electrocatalytic capabilities against the oxidation of nelbuphine hydrochloride (NAL) in aqueous buffer solution. The modified electrodes exhibited distinct electrochemical characteristics, with CuO-based electrodes exhibiting a superior signal sensitivity and lower over-potential value compared to the NiO and Co3O4 nanostructures. The study further explores the variation in the observed electro-catalytic oxidation signal referenced to the distinct morphologies of the metal oxides nanostructures. The CuO-based electrode was selected for the sensitive quantification of NAL in aqueous solution over the linear range 0.001-2.25 mu M. The electrode demonstrated excellent working linearity, with signal sensitivity achieved down to 1 x 10(-4) mu M. Moreover, the successful quantification of NAL in complex matrices, such as human urine and clinical waste water, further reflected the analytical capability of the proposed sensor.Öğe Arterial Stiffness and Carotid Intima-Media Thickness in Diabetic Peripheral Neuropathy(INT SCIENTIFIC LITERATURE, INC, 2014) Avci, Ahmet; Demir, Kenan; Kaya, Zeynettin; Marakoglu, Kamile; Ceylan, Esra; Ekmekci, Ahmet Hakan; Yilmaz, AhmetBackground: We investigated the relationship between peripheral neuropathy and parameters of arterial stiffness and carotid intima media thickness (CIMT) in patients with type 2 diabetes mellitus (T2DM). Material/Methods: The study included 161 patients (80 females and 81 males), 69 of whom had peripheral neuropathy. All patients underwent 24-h blood pressure monitoring, and arterial stiffness parameters were measured. The CIMT was measured using B- mode ultrasonography and patients also underwent transthoracic echocardiographic examination. Results: Patients with peripheral neuropathy, compared with those without it, were older (54.68 +/- 8.35 years vs. 51.04 +/- 7.89 years; p= 0.005) and had T2DM for longer periods (60 vs. 36 months; p= 0.004). Glycated hemoglobin (HbA1c) values (8.55 +/- 1.85 mg/dL vs. 7.30 +/- 1.51 mg/dL; p<0.001), pulse wave velocity (PWV) (7.74 +/- 1.14 m/s vs. 7.15 +/- 1.10 m/s; p= 0.001), CIMT (anterior 0.74 +/- 0.15 mm vs. 0.67 +/- 0.13 mm; p= 0.01), and left ventricular mass (LVM) index (98.68 +/- 26.28 g/m(2) vs. 89.71 +/- 19.70 g/m(2); p= 0.02) were all significantly increased in the group with peripheral neuropathy compared to the group without peripheral neuropathy. We determined that duration of diabetes, HbA1c, and LVM index were predictors of peripheral neuropathy. Conclusions: A significant relationship was found between diabetic neuropathy and increased PWV, a parameter of arterial stiffness, as well as CIMT, a marker of systemic atherosclerosis. Diabetic peripheral neuropathy may be a determinant of subclinical atherosclerosis in T2DM.Öğe Assessment of atrial electromechanical delay and P-wave dispersion in patients with type 2 diabetes mellitus(ELSEVIER, 2016) Demir, Kenan; Avci, Ahmet; Kaya, Zeynettin; Marakoglu, Kamile; Ceylan, Esra; Yilmaz, Ahmet; Ersecgin, AhmetObjectives: Diabetes mellitus is an independent and strong risk factor for development of atrial fibrillation (AF). Electrophysiologic and electromechanical abnormalities are associated with a higher risk of AF. In this study we aimed to determine the correlation of atrial conduction abnormalities between the surface electrocardiographic and tissue Doppler echocardiographic measurements in type 2 diabetes mellitus (T2DM) patients. Methods: A total of 88 consecutive T2DM patients and 49 age-, gender-, and body mass index-matched healthy volunteers were included in the present study. Baseline characteristics were recorded and 24 hour ambulatory blood pressure monitoring, transthoracic echocardiography, and 12-lead surface electrocardiography were performed for all study participants. Atrial electromechanical delay (EMD) intervals were measured. Results: Maximum P-wave duration and P-wave dispersion (Pd) were significantly higher in patients with T2DM (105.7 +/- 10.2 ms vs. 102.2 +/- 7.5 ms, p = 0.02; 40.6 +/- 7.6 ms vs. 33.6 +/- 5.9 ms, p < 0.001, respectively). Interatrial, intraatrial, and intraleft atrial EMD were significantly higher in the T2DM patients when compared with the controls (16.5 +/- 7.8 ms vs.11.2 +/- 4.4 ms, p < 0.001; 9.0 +/- 7.3 ms vs. 6.0 +/- 3.8 ms, p = 0.002, and 7.4 +/- 5.2 ms vs. 5.1 +/- 3.2 ms, p = 0.002 respectively). Correlation analysis showed a positive correlation between interatrial EMD and Pd (r = 0.429, p < 0.001) and left atrial volume (r = 0.428,p < 0.001). Conclusions: In this study, there was significant EMD and Pd in patients with T2DM as compared with healthy volunteers. Additionally, interatrial EMD was correlated with Pd and left atrial volume index. (C) 2015 Japanese College of Cardiology. Published by Elsevier Ltd. All rights reserved.Öğe Assessment of Inhomogeneities of Repolarization in Patients with Systemic Lupus Erythematosus(WILEY, 2014) Avci, Ahmet; Demir, Kenan; Altunkeser, Bulent Behlul; Yilmaz, Sema; Yilmaz, Ahmet; Ersecgin, Ahmet; Demir, TarikObjectives: Systemic lupus erythematosus (SLE) is a chronic disease that affects many organ systems and manifests a broad spectrum of laboratory and clinical features. SLE patients have an increased risk of developing cardiovascular disease. The aim of this study was to evaluate inhomogeneities of repolarization by using T-peak-T-end (Tp-e) interval and Tp-e/QT ratio were measured from the 12-lead surface electrocardiogram (ECG) in patients with SLE. Material and method: This study included 69 SLE patients (69 females; mean age 35.8 +/- 10.2) and 57 control subjects (57 females; mean age 34.5 +/- 8.9). Transthoracic echocardiographic examination was done in all participants. QT parameters, Tp-e intervals and Tp-e/QT ratio were measured from the 12-lead ECG. These parameters were compared between groups. Results: No statistically significant difference was found between two groups in terms of basic characteristics. Diastolic function parameters were similar between the two groups (P > 0.05). In electrocardiographic parameters analysis, QT dispersion (QTd) and corrected QT dispersion (cQTd) were significantly increased in SLE patients compared the control group (49.5 +/- 16.4 ms vs. 32.8 +/- 11.7 ms and 56.7 +/- 19.5 ms vs. 36.4 +/- 13.1 ms, all P value < 0.001). Tp-e interval and Tp-e/QT ratio were also significantly higher in SLE patients (82.8 +/- 18.9 vs. 72.4 +/- 17.6 and 0.22 +/- 0.05 vs. 0.19 +/- 0.05, P = 0.002 and P = 0.001, respectively). Tp-e interval and Tp-e/QT were positively correlated with disease duration (r = 0.29, P = 0.01 and r = 0.24, P = 0.04, respectively). Conclusion: Our study revealed that QTd, cQTd, Tp-e interval and Tp-e/QT ratio increased in patients with SLE. Also, Tp-e interval and Tp-e/QT were positively correlated with disease duration.Öğe Biosynthesis of Linden Protected Silver Nanoparticles and their Safe Application as a Catalyst for Reduction of Methylene Blue Hydrate(IEEE, 2017) Unver, Yasemin; Altun, Turkan; Pehlivan, Erol; Hussain, Masood; Avci, AhmetGreen synthetic protocol was developed for fabrication of silver nanoparticles (AgNPs) using linden extract as stabilizing and reducing agent. Green synthetic protocols preferred over other reduction procedures due to its nontoxic, easy, nonexpensive and environmental friendly behavior. The effect of various reaction parameters and additives on morphology such as, concentration of silver nitrate, effect of pH, temperature, volume of extract and stirring rate were optimized in order to achieve small size stable silver nanoparticles by using Ultra Violet-Visible (UV-Vis) spectroscopy. Trasmission electron microscopy (TEM) was performed to study the morphology and dimensions of biologically synthesized silver nanoparticles. TEM study confirmed that the synthesized nanoparticles were spherical in nature having an average size of 24.4 +/- 2nm. The synthesized plant protected AgNPs were applied homogeneously as well as heterogeneously for reduction of methylene blue hydrate (MB) by immobilizing the nanoparticles on small pieces of glass cover slip. These NPs act as an efficient heterogeneous catalyst and completely reduced MB within 8 min.Öğe Boron nitride-MWCNT/epoxy hybrid nanocomposites: Preparation and mechanical properties(ELSEVIER SCIENCE BV, 2014) Ulus, Hasam; Ustun, Tugay; Eskizeybek, Volkan; Sahin, Omer Sinan; Avci, Ahmet; Ekrem, MurselIn 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.Öğe Carbon Monoxide Poisoning Presenting with Atrial Fibrillation(MODESTUM LTD, 2015) Avci, Ahmet; Yilmaz, Ahmet; Demir, Kenan; Celik, Mustafa; Karatas, RecepCarbon monoxide intoxication is one of the most common types of poisoning and it is the leading cause of death by poisoning in the world. We report a carbon monoxide intoxication case presenting with atrial fibrillation on 17 years old healthy boy. 17 years old boy admitted to emergency service after exposuring carbon monoxide gas approximately 3 hours. His first electrocardiography (ECG) showed atrial fibrillation with rapidly ventricular response. After oxygen supply sinus rhythm was achieved spontaneously. Emergency physicians should be aware of the clinical presentation of carbon monooxide intoxication. Every patient that arrived emergency service with acute or chronically carbon monoxide poisoning should undergo cardiovascular investigation, including ECG and measurement of cardiac enzymes.Öğe Chemical synthesis of single-layer graphene by using ball milling compared with NaBH4 and hydroquinone reductants(INST ENGINEERING TECHNOLOGY-IET, 2018) Niftaliyeva, Aysel; Pehlivan, Erol; Polat, Safa; Avci, AhmetGraphene materials especially single-layer graphene have been identified as a new generation of nanomaterials having various potential applications in material industries. However, the synthesis procedure of single-layer graphene to improve its quality, size and amount has been still under research for commercial applications. The graphene oxide (GO) is synthesised from graphite by Hummer's spontaneous approach which is the most suitable reaction for a large-scale production. For the single-layer graphene, in this work, GO was exfoliated by using a ball milling in an inert atmosphere. Owing to using ball milling as intermediate treatment degreased oxygen functional groups and number of layers, it facilitates to synthesise graphene. Sodium borohydride (NaBH4) and hydroquinone were used as a reductant for the chemical conversion of the exfoliated GO to graphene. The results showed that due to the strong reduction feature, both reducing agents can be applied in the graphene production. As a preferred reductant, hydroquinone can be successfully applied for the synthesis of the single-layer graphene compared to NaBH4. The obtained graphene particles by two different chemicals were characterised by various analytical techniques. The big difference in the structure of GO and graphene was observed in transmission electron microscope analysis.Öğe Closed-form solution of the frictional sliding contact problem for an orthotropic elastic half-plane indented by a wedge-shaped punch(TRANS TECH PUBLICATIONS LTD, 2014) Kucuksucu, Aysegul; Guler, Mehmet A.; Avci, AhmetIn this paper, the frictional contact problem of a homogeneous orthotropic material in contact with a wedge-shaped punch is considered. Materials can behave anisotropically depending on the nature of the processing techniques; hence it is necessary to develop an efficient method to solve the contact problems for orthotropic materials. The aim of this work is to develop a solution method for the contact mechanics problems arising from a rigid wedge-shaped punch sliding over a homogeneous orthotropic half-plane. In the formulation of the plane contact problem, it is assumed that the principal axes of orthotropy are parallel and perpendicular to the contact. Four independent engineering constants E-11, E-22, G(12), V-12 are replaced by a stiffness parameter, E, a stiffness ratio, delta, a shear parameter, K, and an effective Poisson's ratio, V. The corresponding mixed boundary problem is reduced to a singular integral equation using Fourier transform and solved analytically. In the parametric analysis, the effects of the material orthotropy parameters and the coefficient of friction on the contact stress distributions are investigated.Öğe CNT-PAN hybrid nanofibrous mat interleaved carbon/epoxy laminates with improved Mode I interlaminar fracture toughness(ELSEVIER SCI LTD, 2018) Eskizeybek, Volkan; Yar, Adem; Avci, AhmetInterleaving laminated composites with electrospun nanofibrous mats comes out as a promising micro scale strategy to strengthen interlaminar regions of laminated composites. The aim of this study is to evaluate the synergetic contribution of nano- and micro-scale mechanisms on interlaminar delamination. For this, carbon nanotubes (CNTs) reinforced polyacrylonitrile (PAN) electrospun hybrid mats were successfully fabricated and utilized as interleaves within the interlaminar region of carbon/epoxy laminated composites. The Mode I interlaminar fracture toughness values were enhanced up to 77% by introducing CNTPAN nanofibrous interleaves. Specifically, the nano-scale toughening mechanisms such as CNTs bridging, CNTs pull-out, and sword-sheath increased the Mode I fracture toughness by 45% with respect to neat PAN nanofibrous interleaves. The related micro- and nano-scale toughening mechanisms were evaluated based on the fracture surface analysis. Atomic force microscopy was also utilized to quantify the magnitude of surface roughness changes on the interlaminar region with respect to multi scale interleaving reinforcement and correlate surface roughness changes due to crack deflection to increased fracture toughness. (C) 2018 Elsevier Ltd. All rights reserved.Öğe Comparison Between Prospectively Electrocardiogram-Gated High-Pitch Mode and Retrospectively Electrocardiogram- Gated Mode for Dual-Source CT Coronary Angiography(INT SCIENTIFIC INFORMATION INC, 2015) Koplay, Mustafa; Celik, Mahmut; Avci, Ahmet; Erdogana, Hasan; Demir, Kenan; Sivri, Mesut; Nayman, AlaaddinBackground: We aimed to report the image quality, relationship between heart rate and image quality, amount of contrast agent given to the patients and radiation doses in coronary CT angiography (CTA) obtained by using high-pitch prospectively ECG-gated "Flash Spiral" technique (method A) or retrospectively ECG-gated technique (method B) using 128x2-slice dual-source CT. Material/Methods: A total of 110 patients who were evaluated with method A and method B technique with a 128x2-detector dual-source CT device were included in the study. Patients were divided into three groups based on their heart rates during the procedure, and a relationship between heart rate and image quality were evaluated. The relationship between heart rate, gender and radiation dose received by the patients was compared. Results: A total of 1760 segments were evaluated in terms of image quality. Comparison of the relationship between heart rate and image quality revealed a significant difference between heart rate <60 beats/min group and >75 beats/min group whereas <60 beats/min and 60-75 beats/min groups did not differ significantly. The average effective dose for coronary CTA was calculated as 1.11 mSv (0.47-2.01 mSv) for method A and 8.22 mSv (2.19-12.88 mSv) for method B. Conclusions: Method A provided high quality images with doses as low as <1 mSv in selected patients who have low heart rates with a high negative predictive value to rule out coronary artery disease. Although method B increases the amount of effective dose, it provides high diagnostic quality images for patients who have a high heart rate and arrhythmia which makes it is difficult to obtain images.Öğe Diagnostic accuracy and effective radiation dose of high pitch dual source multidetector computed tomography in evaluation of coronary artery bypass graft patency(SPRINGER WIEN, 2016) Koplay, Mustafa; Guneyli, Serkan; Akbayrak, Hakan; Demir, Kenan; Sivri, Mesut; Avci, Ahmet; Erdogan, HasanThe aim of the study was to evaluate the diagnostic accuracy and effective radiation dose (ERD) of high pitch dual source multidetector computed tomography (MDCT) for coronary artery bypass graft (CABG) patency. Fourty-five patients who underwent 128 x 2aEuroslice MDCT angiography with a prospective electrocardiogram-triggering, low-dose, high pitch, dual source, flash spiral acquisition mode after CABG surgery were included in the study. The interobserver agreement of the image quality was evaluated with Cohen kappa value. The image quality was compared to the heart rates (HRs) using Mann-Whitney U test and to the graft segments using chi(2) test. The findings for the CABG patency on MDCT were compared to those determined on catheter coronary angiography. Dose-length product (DLP) and ERD were compared to the gender, HRs, and body mass index (BMI) of the patients using Kruskall Wallis and Mann-Whitney U tests. A total of 110 grafts and 330 vessel segments were evaluated with a good interobserver agreement (kappa = 0.80). The image quality was better in proximal and middle graft segments (p < 0.05), as well as in the patients with low HRs (p < 0.05). High pitch MDCT had the following sensitivity, specificity, positive predictive value, negative predictive value, and diagnostic accuracy for evaluation of graft patency: 92.8, 99.3, 92.8, 99.3 and 98.8 %, respectively. ERD was correlated to the HRs and BMI. High pitch 128 x 2aEuroslice dual source CT angiography is a noninvasive imaging modality, and it can be safely and effectively used in evaluation of CABG patency with lower radiation dose.Öğe Drilling performance of functionally graded composite: Comparison with glass and carbon/epoxy composites(KOREAN SOC MECHANICAL ENGINEERS, 2017) Koklu, Ugur; Demir, Okan; Avci, Ahmet; Etyemez, AyhanFunctionally graded composite (FGC) materials are categorized as advanced materials that display different thermal and mechanical responses compared with well-known composites, such as carbon fiber or glass fiber-reinforced composites. This paper presents the experimental results for the drilling of three materials, namely glass/epoxy, carbon/epoxy, and FGC material. FGC was compared with carbon and glass/epoxy composites in terms of thrust force, delamination factor, diameter of hole, and roundness during drilling. This study illustrated that the drilling performance of FGC is considerably more complicated than that of more common composite materials, such as glass/epoxy and carbon/epoxy. Delamination factor at the exit of hole during drilling of FGC was mainly affected by the material placed at the exit of the hole. The proposed cutting parameters and drill geometries to minimize the occurrence of delamination during drilling of carbon/epoxy and glass/epoxy apparently does not meet the expectation in drilling FGC.Öğe Effect of non-penetrating impact damages of pre-stressed GRP tubes at low velocities on the burst strength(ELSEVIER SCI LTD, 2014) Kara, Memduh; Uyaner, Mesut; Avci, Ahmet; Akdemir, AhmetIn this study, failure behavior of pre-stressed Glass Fiber Reinforced Plastic (GRP) tubes subjected to low velocity impact was investigated. Filament wound E-glass/epoxy composite tubes with a winding angle of +/- 55 degrees were used in the experiments. The tubes pre-stressed to 32 bars internal pressure, one of the specified operating pressures according to ANSI/AWWA C950 standards. Both prestressed and non-prestressed GRP tubes were subjected to low velocity impact tests at 5, 10 and 15 J low energy levels. Plots of contact force and internal pressure with respect to time and those of force-displacement were obtained and damages occurred on the specimens were examined by means of reflected and transmitted light photography and light microscope. No marked fiber breakages are observed; however, debonding and some sort of delamination on the layers were observed. The GRP tubes with impact damages were subjected to monotonic burst pressures up to failure based on the ASTM D 1599-99 standards. Burst damages on the tubes were studied and variations of their corresponding burst strengths were spotted. Besides that, diameter changes with internal pressures were determined during the tests. Diameter changes with internal pressures for the impacted and the non-impacted tubes were found to be the same. (C) 2014 Elsevier Ltd. All rights reserved.Öğe Effects of alumina nanoparticles on dynamic impact responses of carbon fiber reinforced epoxy matrix nanocomposites(ELSEVIER - DIVISION REED ELSEVIER INDIA PVT LTD, 2018) Kaybal, Halil B.; Ulus, Hasan; Demir, Okan; Sahin, Omer S.; Avci, AhmetThe influence of alumina (Al2O3) nanoparticles addition upon low-velocity impact behaviors of carbon fiber (CF) reinforced laminated epoxy nanocomposites have been investigated. For this purpose, different amounts of Al2O3 nanoparticles ranging from 1 to 5 wt% were added to the epoxy resin in order to observe the effect of nanoparticle loadings. CF reinforced epoxy based laminated nanocomposites were produced using Vacuum Assisted Resin Infusion Method (VARIM). The low velocity impact (LVI) tests performed according to the ASTM-D-7136 standard under 2, 2.5 and 3 m/s impact velocities. After LVI testing, the damage formations within composites were examined by using scanning electron microscopy (SEM). The results of this study showed that addition of Al2O3 nanoparticles provided a significant improvement in impact damage resistance. The highest damage resistance and minimum energy absorption were observed for 2 wt% Al2O3 nanoparticles loadings. As a result, we can confidently claim that the addition of the Al2O3 nanoparticles in CF/epoxy composites has considerably affected the dynamic response of the nanocomposites. (C) 2018 Karabuk University. Publishing services by Elsevier B.V.Öğe Effects of polyvinyl alcohol nanofiber mats on the adhesion strength and fracture toughness of epoxy adhesive joints(ELSEVIER SCI LTD, 2018) Ekrem, Mursel; Avci, AhmetThe 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.Öğe Electrospun TiO2/ZnO/PAN hybrid nanofiber membranes with efficient photocatalytic activity(ROYAL SOC CHEMISTRY, 2017) Yar, Adem; Haspulat, Bircan; Ustun, Tugay; Eskizeybek, Volkan; Avci, Ahmet; Kamis, Handan; Achour, SlimaneElectrospun polyacrylonitrile (PAN) nanofibers were decorated with TiO2, ZnO and TiO2/ZnO nanoparticles for the first time to prepare flexible multifunctional nanofibrous membranes. First, the arc-discharge process was utilized to prepare TiO2, ZnO and TiO2/ZnO nanoparticles and then the hybrid electrospun nanofibers were spun from PAN/nanoparticle colloids. X-ray diffraction, scanning electron microscopy (SEM) and transmission electron microscopy (TEM) were utilized to characterize the resulting nanoparticles and nanofiber loaded nanoparticles. The microscopic investigations revealed that the specifically TiO2 nanoparticles tend to agglomerate within the PAN nanofiber resulting increased surface roughness; however, ZnO nanorods with 1D morphology are aligned as parallel to the fiber axis. Photocatalytic activity of the hybrid nanofibers was performed by pursuing the degradation of malachite green (MG) dye under UV light irradiation. The fabricated TiO2/ZnO/PAN hybrid nanofibers showed excellent photocatalytic efficiency with at least two times higher reaction rates compared to the bare PAN nanofibers. The results suggest that the photocatalytically active TiO2/ZnO/PAN hybrid nanofibers can be considered as filtering materials for a variety of applications in the fields of wastewater systems without the need of post processing stages for separating catalysts from the liquid medium.Öğe Enhanced fatigue performances of hybrid nanoreinforced filament wound carbon/epoxy composite pipes(ELSEVIER SCI LTD, 2016) Ustun, Tugay; Eskizeybek, Volkan; Avci, AhmetIn filament wound composite pipes matrix cracking, as an initial damage mechanism during fatigue loading, can initiate a damage sequence that can result in catastrophic failure of the pipes. Matrix modification using nanostructured fillers is an emerging approach to develop new fatigue-resistant composite materials. The aim of this study to investigate the fatigue performance experimentally, and observe macroscopic and microscopic damage mechanisms of carbon fiber/epoxy filament wound composite pipes toughened by carbon nanotubes ( CNTs) and boron nitride nanoplates (BNNPs). The effectiveness of nanofillers with different morphologies on fatigue damage development and their micro/nano reinforcing mechanisms were discussed. The fatigue tests with positive cycling pressure loading were performed at three different load levels as 50%, 60%, and 70% of the static burst strength of each samples. S-N curves were obtained according to fatigue test and lifetime of the fabricated hybrid composite pipes were evaluated. The addition of nanoscale reinforcements increase fatigue performance of the composite pipes for all cases. To analyze damage initiation and final damage, microscopic analyses of the fracture surfaces were utilized. The fractographic investigations revealed that the morphologies of nanofillers play a key role on improving mechanical performance by generating different nano- and micro-scale toughening mechanisms. (C) 2016 Elsevier Ltd. All rights reserved.Öğe Enhancement of Flexural and Shear Properties of Carbon Fiber/Epoxy Hybrid Nanocomposites by Boron Nitride Nano Particles and Carbon Nano Tube Modification(KOREAN FIBER SOC, 2015) Ulus, Hasan; Sahin, Omer Sinan; Avci, AhmetIn this study, the effect of boron nitride nano particle (BNNP) and/or carbon nanotube (CNT) adding for epoxy modification upon tensile, flexural and shear properties of epoxy resin and carbon fiber (CF) laminated nanocomposites were investigated. Epoxy based polymer nanocomposites were prepared by conventional casting in stainless steel mold and the CF/epoxy laminated nanocomposites were produced via vacuum assisted resin transfer molding (VARTM). Experimental results showed that the tensile, shear and flexural properties of epoxy nanocomposites and CF/epoxy laminated nanocomposites considerably increased by adding nanoparticle. Scanning electron microscopy (SEM) was utilized in order to determine damage formation of experimented nanocomposite samples. The results of laboratory tests showed that the highest values of mechanical properties were obtained for BNNP-CNT hybrid nanocomposite specimens. Bending stiffness increasement values of BNNP-CNT/Epoxy and BNNP-CNT-Epoxy/CF achieved by 27.5 %, and 38.5 %, respectively. Shear strength increasement for BNNP-CNT/Epoxy and BNNP-CNT-Epoxy/CF were determined by 23 %, and 90 %, respectively.Öğe 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, MahmutEpoxy 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.