DSpace Arşivi :: by Yazar "Ulus, Hasan" değerine göre listeleniyor

Yazar "Ulus, Hasan" seçeneğine göre listele

Listeleniyor 1 - 13 / 13

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.
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, Ahmet
Composite-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.
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, Ahmet
In 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.
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.
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, Ahmet
Mechanical 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.
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, Ahmet
In 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.
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, Ahmet
Adhesively 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.
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, Ahmet
Seawater 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.
Quasi-Static tensile loading performance of Bonded, Bolted, and hybrid Bonded-Bolted Carbon-to-Carbon composite Joints: Effect of recycled polystyrene nanofiber interleaving
(Elsevier Sci Ltd, 2023) Tinastepe, Mehmet Talha; Kaybal, Halil Burak; Ulus, Hasan; Erdal, Mehmet Okan; Cetin, Mehmet Emin; Avci, Ahmet
Although hybrid bolted/bonded (HBB) joints possess each joint technique's benefits, the adhesive layer performance significantly affects the load-carrying capacity of hybrid joints. Nanofiber interleaving has become an efficient solution to improve the adhesion performance of bonded and HBB joints. This paper reveals the effectiveness of polystyrene (PS) nanofibers interleaving on the mechanical properties of adhesively bonded and HBB single lap joints (SLJs). For this purpose, PS nanofibers are produced via electrospinning from wasted polymers as a nature-friendly implementation. The PS nanofiber mats were interleaved between adherends as a reinforcement layer, and specimens were tested under quasi-static tensile loading. A significant improvement was seen in the peak load value of 10% for the HBB joint, and the fracture energy of the bonded joint increased by 15% with PS nanofiber modification. The failure modes of PS-reinforced specimens developed as more gradually progressive compared to neat specimens thanks to the compatibility of the recycled PS nanofiber with the epoxy and improved adhesive layer performance with PS modification. Furthermore, the morphological analyses of post-fracture specimens were monitored to realize the damage and nano-toughness mechanisms.
Seawater Aged Basalt/Epoxy Composites: Improved Bearing Performance with Halloysite Nanotube Reinforcement
(Korean Fiber Soc, 2021) Kaybal, Halil Burak; Ulus, Hasan; Avci, Ahmet
Although they enable for facile disassembly and inspection of critical assemblies, bolted joints are common damage initiation sites in laminated composite structures. Sudden failure can occur at these locations especially with the combination of corrosive environments. In order to well understand and characterize for marine applications, we aimed to research the impact of seawater aging and halloysite nanotube (HNT) nano reinforcements on the bearing performance of basalt-epoxy composites. For this, basalt fabrics were impregnated with HNT modified epoxy matrix via vacuum infusion and the resultant multi-scale laminates submerged in seawater up to 6 months after assembling via bolted joints. Single shear tensile tests of seawater aged joints were performed according to ASTM D5961 and the results compared with the HNTs reinforced hybrid laminates. HNTs nano reinforcements remarkably improved the bearing strength basalt/epoxy composite laminates with a 18% increase. In addition, seawater aging drastically impairs the bearing response of composite laminates with an almost 45% reduction in bearing strength after 6 months of exposure. Bearing fracture modes were also affected with the addition of HNTs and seawater aging, the resultant fracture surfaces were examined to reveal degradation mechanisms related to seawater aging and HNTs reinforcement after single shear tensile tests. The results can contribute to a better understanding of mechanical design parameters for bolted fiber reinforced polymer composites exposed to corrosive environments.
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, Ahmet
The 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.
Tribological behavior of epoxy nanocomposites under corrosive environment: effect of high-performance boron nitride nanoplatelet
(Yildiz Technical Univ, 2023) Sukur, Emine Feyza; Kaybal, Halil Burak; Ulus, Hasan; Avci, Ahmet
This paper sheds light on the impact of corrosive service conditions on the mechanical and tribological performances of epoxy nanocomposites containing 0.5 wt.% hexagonal boron nitride (BN) nanoplatelets as fillers. The composite samples were aged in 10 wt% H2SO4 solutions by immersion for 504 hours. Variation in mechanical and tribological behaviors during immersion was investigated using tensile and ball-on disk tests. The ball-on disk tests were performed at room temperature under a 10 N constant load and 0.8 m/s speed for 3000 seconds. The high-performance BN nanoplatelets improved neat Epoxy's tensile strength, toughness, and wear performance by 17%, 27%, and 56%, respectively. The aging results revealed that H2SO4 exposure deteriorates the mechanical performance of all epoxy composite samples, even though BN/Epoxy nanocomposites exhibited better resistance to the corrosive environment. In contrast, the tribological performance increased with the acidic solution exposure that acts as a lubricant and forms a corrosive protective layer after the immersion of 504 hours.
Tribological behavior of epoxy nanocomposites under corrosive environment: effect of high-performance boron nitride nanoplatelet
(Yildiz Technical Univ, 2023) Sukur, Emine Feyza; Kaybal, Halil Burak; Ulus, Hasan; Avci, Ahmet
This paper sheds light on the impact of corrosive service conditions on the mechanical and tribological performances of epoxy nanocomposites containing 0.5 wt.% hexagonal boron nitride (BN) nanoplatelets as fillers. The composite samples were aged in 10 wt% H2SO4 solutions by immersion for 504 hours. Variation in mechanical and tribological behaviors during immersion was investigated using tensile and ball-on disk tests. The ball-on disk tests were performed at room temperature under a 10 N constant load and 0.8 m/s speed for 3000 seconds. The high-performance BN nanoplatelets improved neat Epoxy's tensile strength, toughness, and wear performance by 17%, 27%, and 56%, respectively. The aging results revealed that H2SO4 exposure deteriorates the mechanical performance of all epoxy composite samples, even though BN/Epoxy nanocomposites exhibited better resistance to the corrosive environment. In contrast, the tribological performance increased with the acidic solution exposure that acts as a lubricant and forms a corrosive protective layer after the immersion of 504 hours.

Yazar "Ulus, Hasan" seçeneğine göre listele

Sayfa Başına Sonuç

Sıralama seçenekleri