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Öğe Boron nitride-MWCNT/epoxy hybrid nanocomposites: Preparation and mechanical properties(Elsevier, 2014) Ulus, Hasan; 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 Effect of long-term stress aging on aluminum-BFRP hybrid adhesive joint's mechanical performance: Static and dynamic loading scenarios(Wiley, 2022) Ulus, Hasan; Kaybal, Halil Burak; Cacik, Fatih; Eskizeybek, Volkan; Avci, AhmetComposite-aluminum hybrid adhesive joints represent an ideal solution for designing lightweight structures for the marine industry. However, seawater aging is a serious concern, limiting the safe service life of the joint. Notably, efforts to understand the impact of aging have largely focused on the short-term periods without considering actual operating conditions. Here, we report the mechanical performance of hybrid joints subjected to the long-term stress aging. Besides, we modified the epoxy adhesive with halloysite nanotubes (HNTs) to limit the aging driven adhesive degradation and improve the adhesive's rigidity. We evaluated mechanical performances of hybrid joints by performing tensile, flexural, and drop-weight impact tests. While we increased the load-carrying capacity by over 25% with the HNTs modification before the stress aging process, modified adhesive withstood almost 55% higher tensile load than the neat epoxy adhesive after six-month stress aging. The modified adhesive also absorbed 41% less impact energy, indicating the efficiency of HNTs on limiting the degradation due to the stress aging. Furthermore, the damage mode transformed from adhesion to cohesion, thanks to the improved adhesive-composite interface performance. We envisage that these exciting results will pave the way for designing robust hybrid joints for the marine industry.Öğe Enhanced Salty Water Durability of Halloysite Nanotube Reinforced Epoxy/Basalt Fiber Hybrid Composites(Korean Fiber Soc, 2019) Ulus, Hasan; Kaybal, Halil Burak; Eskizeybek, Volkan; Avci, AhmetIn this study, we report the effect of halloysite nanotube (HNT) modification on salty water aging durability of epoxy (Ep)/basalt fiber (BF) hybrid composites. For this, various amounts of HNTs were introduced into the Ep matrix, and the HNTs/Ep mixture was used to impregnate basalt fabrics to fabricate hybrid laminated composites. The hybrid composites were exposed substantial increases in the tensile strength and the fracture toughness. Besides, after salty water aging for 6 months, the hybrid composites exhibited remarkably improved aging performance with almost 10 % less reduction in both tensile and flexural strengths and fracture toughness compared to the neat basalt-epoxy composites. SEM analysis showed relatively less number of cracks, micro-voids and better interfacial bonding for the 2 wt% HNTs reinforced hybrid composite specimens in comparison to the neat counterpart, similarly conditioned in all cases. The consequences of salty water aging on micro-scale morphology were discussed based on the fracture morphologies to reveal degradation mechanisms in the existence of HNTs reinforcement.Öğe An experimental study on low velocity impact performance of bolted composite joints part 1: Influence of halloysite nanotubes on dynamic loading response(Elsevier Sci Ltd, 2021) Kaybal, Halil Burak; Ulus, Hasan; Eskizeybek, Volkan; Avcl, AhmetMechanical joints are a widely utilized to assembly fiber reinforced polymer composites in marine applications. Impact is one of the most encountered unpredictable loading types which significantly diminishes the mechanical properties of structures. The goal of this study is to investigate the dynamic loading response of bolted basalt-epoxy composite laminates under different impact energies. Unlike the existing low velocity impact tests of bolted composite joints, to reveal the effect of localized impact damage, the low-velocity impact tests were conducted on two different regions as the top of bolt (ToB) and the side of washer (SoW). In addition, the effects of HNTs reinforcement on the impact response and the damage propagation were also evaluated. It was obtained that ToB damage was comparatively severe for the composite joints due to the propagation of the damage through the hole center. Moreover, HNTs improved the impact resistance about %15, especially at lower impact energies. However, the nanoreinforcement efficiency diminished with increasing impact energy levels. The obtained results were further supported with macro-size images and scanning electron microscopy (SEM). Together with Part II, this study reports an extensive work of impact tests of bolted composite joints utilized in the marine industry.Öğe An experimental study on low velocity impact performance of bolted composite joints-part 2: Influence of long-term seawater aging(Elsevier Sci Ltd, 2021) Kaybal, Halil Burak; Ulus, Hasan; Eskizeybek, Volkan; Avci, AhmetIn the first part of this two-part paper (Part 1), the low-velocity impact (LVI) response of bolted fiber-reinforced polymer joints was investigated considering with two scenarios based on the localized impact damage as the impactor hit on the top of the bolt (ToB) and the side of the washer (SoW). Moreover, the influence of halloysite nanotubes (HNTs) reinforcement of the epoxy matrix on the impact performance was also evaluated. As the second part of the research, this paper represents the effects of seawater aging on the LVI response of FRPs. For this, the composite joints were submerged in an artificial seawater environment for six months to accelerate aging. Afterward, as following the systematic experimental path exhibited in Part 1, LVI tests were conducted by dropping the impactor on ToB and SoW regions. The test results showed that the seawater aging impaired almost 30% of the composite joints' impact resistance, where HNTs reinforced multi-scale composite joints exhibited a 13% higher impact loading performance. The ToB impact scenario was considered as visually and quantitatively more detrimental than the SoW tests. The detrimental impact of seawater aging was validated by tracking the elemental evolution in the seawater environment. Based on the mechanical, morphological, and structural analyses, a novel damage mechanism was introduced to address seawater aging's progress, including the role of nanoreinforcements.Öğe Fracture and dynamic mechanical analysis of seawater aged aluminum-BFRP hybrid adhesive joints(Pergamon-Elsevier Science Ltd, 2022) Ulus, Hasan; Kaybal, Halil Burak; Cacik, Fatih; Eskizeybek, Volkan; Avci, AhmetAdhesively bonded hybrid FRP-aluminium structures have recently become an efficient solution for marine engineering applications. However, polymer adhesives' bond performance is sensitive to the marine environment due to polymer and interfacial degradation. This study aims to develop mode I, mode II delamination toughness, and Tg data as a comprehensive design guideline for hybrid BFRP-aluminum modified-adhesively bonded joints subjected to seawater aging. The hybrid joints were exposed to long-term seawater aging (for 6 months) to reveal their fracture and thermomechanical performances. Besides, the adhesive was reinforced with HNTs to increase fracture resistance with additional nano-scale toughening mechanisms and to delay the water absorption. After the long-term aging, reinforced adhesively bonded joints exhibited -36% higher fracture toughness than neat adhesively bonded joints. Moreover, DMA was conducted on miniaturized SLJ samples, which revealed that HNT modified adhesive joints showed -11.5 degrees C higher Tg. The calculated aging rates also proved the effectiveness of HNTs modification on the epoxy adhesive's aging performance since the HNT reinforced adhesive represented 43% lower aging rates in terms of storage modulus. It is considered that experimental results will help comprehend long-term aging influences on the composite-aluminum hybrid designs' fracture and thermomechanical performances. These exciting findings will pave the way for the safe use of high stiffness and cost-effective aluminum-BFRP hybrid structures for the marine industry.Öğe GaN/ZnO hybrid nanostructures for improved photocatalytic performance: One-step synthesis(Tubitak Scientific & Technological Research Council Turkey, 2023) Ustun, Tugay; Haspulat Taymaz, Bircan; Eskizeybek, Volkan; Kamis, Handan; Avci, AhmetNanostructured semiconductor materials are considered potential candidates for the degradation of textile wastewater via the photocatalytic process. This study aims to produce hexagonal gallium nitride (GaN) nanoplates and zinc oxide (ZnO) nanoparticles in a deionized water environment utilizing a one-step arc discharge process. Detailed characterization of samples has been completed via scanning electron microscope (SEM), transmission electron microscope (TEM), X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), and UV visible spectroscopy methods. The hybrid nanostructure morphologies consist of nanoplates and nanorods of different sizes. The photoperformance of GaN/ZnO hybrid nanostructures was assessed via the malachite green (MG) dye degradation under UV exposure. Under UV exposure, the degradation yield reached 98% in 60 min. Compared to individual ZnO and GaN nanoparticles, the photocatalytic reaction rate of the GaN/ZnO photocatalyst is 2.2 and 3.6 times faster, respectively. Besides, the GaN/ZnO hybrid nanostructures show excellent photocatalytic stability. The energy consumption of the photocatalytic degradation in the presence of GaN/ZnO hybrid nanostructures was 1.688 kWhL-1. These results demonstrate that the GaN/ZnO hybrid nanostructures with improved photocatalytic activity are a reasonable option for the decomposition of textile wastewater under UV light exposure.Öğe Halloysite nanotube reinforcement endows ameliorated fracture resistance of seawater aged basalt/epoxy composites(Sage Publications Ltd, 2020) Ulus, Hasan; Kaybal, Halil Burak; Eskizeybek, Volkan; Avci, AhmetSeawater aging-dominated delamination failure is a critical design parameter for marine composites. Modification of matrix with nanosized reinforcements of fiber-reinforced polymer composites comes forward as an effective way to improve the delamination resistance of marine composites. In this study, we aimed to investigate experimentally the effect of halloysite nanotube nanoreinforcements on the fracture performance of artificial seawater aged basalt-epoxy composites. For this, we introduced various amounts of halloysite nanotubes into the epoxy and the halloysite nanotube-epoxy mixtures were used to impregnate to basalt fabrics via vacuum-assisted resin transfer molding, subsequently. Fracture performances of the halloysite nanotubes modified epoxy and basalt/epoxy composite laminated were evaluated separately. Single edge notched tensile tests were conducted on halloysite nanotube modified epoxy nanocomposites and the average stress intensity factor (K-IC) was increased from 1.65 to 2.36 MPa.m(1/2) (by 43%) with the incorporation of 2 wt % halloysite nanotubes. The interlaminar shear strength and Mode-I interlaminar fracture toughness (G(IC)) of basalt-epoxy hybrid composites were enhanced from 36.1 to 42.9 MPa and from 1.22 to 1.44 kJ/m(2), respectively. Moreover, the hybrid composites exhibited improved seawater aging performance by almost 52% and 34% in interlaminar shear strength and G(IC) values compared to the neat basalt-epoxy composites after conditioning in seawater for six months, respectively. We proposed a model to represent fracture behavior of the seawater aged hybrid composite based on scanning electron microscopy and infrared spectroscopy analyses.Öğe Hybrid nanoparticles embedded polyvinyl butyral nanocomposites for improved mechanical, thermal and microwave absorption performance(Sage Publications Ltd, 2021) Akman, Erdi; Sonmezoglu, Savas; Yigit, Enes; Eskizeybek, Volkan; Avci, AhmetPolymer-based nanocomposites have been broadly investigated to improve its specific properties such as thermal and mechanical properties to use in different application areas. In this study, we aimed to ameliorate the desired physical properties of polyvinyl butyral (PVB) by introducing various amounts of silver (Ag) and cobalt (Co) nanoparticles (NPs) in the polymer matrix. The arc-discharge method submerged in liquid nitrogen was performed to synthesize the metal NPs. To produce hybrid nanocomposites, we demonstrated embedding Ag:Co nanoparticles in the PVB matrix via easy/low-cost solution casting process without any additional materials. In the results of analysis for nanocomposites, it was observed that there were improvements in thermal, mechanical and microwave absorption characteristics of the PVB polymer with interaction of NPs with the polymer. As a result of these interactions, the hybridization of PVB with the metal NPs resulted in the improved thermal stability since the glass transition temperature was increased from 45.6 to 55.1 degrees C. Besides, while the tensile strength (sigma) of the bare PVB film was calculated as 20.52 MPa, the strength of the corresponding tensile strength (sigma) of 1.0 wt.% Ag:Co nanocomposite film was improved to 43.41 MPa. Moreover, in order to determine the effect of these changes on the radar absorption feature of nanocomposites, one-dimensional A-Scan measurements were performed on 2-18 GHz frequency band. In the results, it was observed that 1.0%.wt Ag:Co nanocomposite film absorbed approximately 90% of the incoming energy. The characterization results revealed that a positive synergetic effect raised in the case of the modification of the PVB matrix with both Ag and Co NPs. In the light of these data, it was understood that the characteristics of PVB were improved with the NPs combining, and the usage area of that will also increase thanks to this improvement. These regenerated properties made the hybrid nanocomposite a promising substrate material with considerable potential applications for various transparent, flexible, and portable surface coatings.Öğe Impact response of nanoparticle reinforced 3D woven spacer/epoxy composites at cryogenic temperatures(Sage Publications Ltd, 2021) Yildirim, Ferhat; Tatar, Ahmet Caner; Eskizeybek, Volkan; Avci, Ahmet; Aydin, MustafaFiber-reinforced polymer composites serving in harsh conditions must maintain their performance during their entire service. The cryogenic impact is one of the most unpredictable loading types, leading to catastrophic failures of composite structures. This study aims to examine the low-velocity impact (LVI) performance of 3D woven spacer glass-epoxy composite experimentally under cryogenic temperatures. LVI tests were conducted under various temperatures ranging from room temperature (RT) to -196 degrees C. Experimental results reveal that the 3D composites gradually absorbed higher impact energies with decreasing temperature. Besides, the effect of multi-walled carbon nanotube and SiO2 nanofiller reinforcements of the matrix on the impact performance and the damage characteristics were further assessed. Nanofiller modification enhanced the impact resistance up to 30%, especially at RT. However, the nanofiller efficiency declined with decreasing temperature. The apparent damages were visually examined by scanning electron microscopy to address the damage formation. Significant outcomes have been achieved with the nanofiller modification regarding the new usage areas of 3D woven composites.Öğe Selectively Reinforced Functionally Graded Composite-like Glass/Carbon Polymer Nanocomposites: Designed for Efficient Bending and Impact Performance(Korean Fiber Soc, 2022) Demir, Okan; Tatar, Ahmet Caner; Eskizeybek, Volkan; Avci, AhmetOffshore wind turbine blades (OWTBs) are exposed to various types of loadings during their service life. Moreover, due to their tremendous size, huge investment costs are established, including advanced engineering materials and production process solutions. To decrease their investment cost without sacrificing their mechanical performances, advanced engineering solutions in the view of material selection and design should be implemented. With this motivation, we aimed to develop a novel laminated composite design considering reducing investment costs without compromising the bending and impact resistance of an OWTB. For this, an efficient and cost-effective design of a functionally graded composite (FGM)-like glass/carbon fibers reinforced hybrid polymer composite with a specific stacking sequence was presented. To evaluate mechanical performance of the composite structure, tensile, flexural, and to simulate environmental conditions, low-velocity impact tests were conducted. Furthermore, multi-walled carbon nanotubes (MWCNTs) were also introduced into the polymer matrix to evaluate their effectiveness in the hybridized composite. Drastic improvements in the bending strength (55.8 %) and strain (39.7 %) were obtained compared to the neat carbon fiber reinforced epoxy composites (CFs), especially with the aid of MWCNTs. According to impact tests, it was pointed out that it is possible to obtain higher impact peak forces (around 15 %) compared to neat CFs. However, MWCNTs contributed with slight increments in impact resistance but effectively restricted the impact damage propagation. This study reveals it is possible to tune the bending performance, the absorbed energy, and the damage extension by utilizing glass and carbon fiber laminates in an FGM-like structure.Öğe Significantly improved shear, dynamic-mechanical, and mode II fracture performance of seawater aged basalt/epoxy composites: The impact of halloysite nanotube reinforcement(Elsevier - Division Reed Elsevier India Pvt Ltd, 2021) Ulus, Hasan; Kaybal, Halil Burak; Eskizeybek, Volkan; Avci, AhmetThe primary concern of fiber-reinforced polymers (FRPs) subjected to seawater environment is losing their initial mechanical performance since water can diffuse into the composite and deteriorates the fiber-matrix interface. Recent studies related to aging performance in the seawater environment have shown that introducing halloysite nanotubes (HNTs) into the polymer matrix offers a combination of an efficient barrier effect and an improved fiber-matrix interface. Hereupon, the principal objective of this study was to experimentally investigate the impact of HNTs on shear and mode II fracture performances of the seawater aged basalt fiber (BF) reinforced epoxy (EP) composites. After six months of aging in sea -water, the findings indicated that HNTs reinforced multi-scale composites exhibited 34 and 46% higher shear strength and mode II delamination toughness compared to the neat specimens. Moreover, accord-ing to the dynamic-mechanical analysis, higher glass transition temperatures (8%) were obtained for the multi-scale composites. The reduction in mechanical performances induced by fiber-matrix interfacial degradation was also confirmed by scanning electron microscopy analysis. Chemical deterioration of the polymer matrix was explored by Raman spectroscopy to reveal the efficiency of HNTs induced barrier effect. As a result of these investigations, HNT modified BF/EP multi-scale composites were offered for future advanced engineering applications. (C) 2021 Karabuk University. Publishing services by Elsevier B.V.
