Browsing by Author "Ulus, Hasan"

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Citation - WoS: 48
Citation - Scopus: 48
Enhanced Salty Water Durability of Halloysite Nanotube Reinforced Epoxy/Basalt Fiber Hybrid Composites
(KOREAN FIBER SOC, 2019) Ulus, Hasan; Kaybal, Halil Burak; Eskizeybek, Volkan; Avcı, 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.
Citation - Scopus: 9
Evaluation of Low-Velocity Impact Behavior of Epoxy Nanocomposite Laminates Modified With Sio2 Nanoparticles at Cryogenic Temperatures
(2019) Tatar, Ahmet Caner; Kaybal, Halil B.; Ulus, Hasan; Demir, Okan; Avcı, Ahmet
Epoxy based fiber reinforced composites are widely utilized in aerospace applications due to mechanical properties, thermal stability and, chemical resistance. However, it is known that materials become brittle and due to the poor crack resist restricts their applications in cryogenic engineering applications. The purpose of this paper is to experimentally investigate the cryogenic temperatures’ effect on the low-velocity impact (LVI) test of composite laminates. In addition, the effect of matrix modification in the studied composites was investigated. The LVI tests were conducted at RT (room temperature), 0 °C, -50 °C, -150 °C and -196 °C (liquid nitrogen temperature) on the composite laminates to measure influence on their energy absorption capacity. LVI tests performed according to ASTM-D-7136 standard under 10, 20 and 30 J impact energy levels. The results show that the contact forces and energy absorption capacities are improved by adding SiO2 nanoparticles into the epoxy matrix. The absorbed energy at cryogenic temperatures is increased by 24.87% from 18.1 J of pure epoxy resin to 22.7 J of modified epoxy. For the purpose of comparison, the LVI properties of composites at room temperature (RT) are also investigated. It is noted that the energy absorption capacity is not higher at cryogenic temperatures than that at RT for the modified and neat epoxy composites. Moreover, the peak contact forces are reduced in low-temperature conditions.
Citation - WoS: 29
Citation - Scopus: 26
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, Mürsel; Ataberk, Necati; Avcı, 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.
Citation - WoS: 45
Citation - Scopus: 48
Halloysite Nanotube Reinforcement Endows Ameliorated Fracture Resistance of Seawater Aged Basalt/Epoxy Composites
(SAGE PUBLICATIONS LTD, 2020) Ulus, Hasan; Kaybal, Halil Burak; Eskizeybek, Volkan; Avcı, 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.
Citation - Scopus: 4
Influence of Seawater on Mechanical Properties of Sio2-Epoxy Polymer Nanocomposites
(2019) Kaybal, Halil Burak; Ulus, Hasan; Tatar, Ahmet Caner; Demir, Okan; Avcı, Ahmet
In this study, dispersion of nano SiO2 in epoxy composite aged in seawater and its effect on mechanical properties were studied. The SiO2-epoxy polymer nanocomposite materials were kept in seawater for a total of six months to be tested every two months. Tensile and bending tests were applied to composite materials as a mechanical test. According to the mechanical test results, there was less decrease in strength in SiO2-epoxy polymer nanocomposite material compared to unmodified material. In usage of seawater, the mechanical properties were observed to be the best in 3 % added SiO2-epoxy nanocomposite material.
Tuzlu Su Yaşlandırmasının Halloysit Nanotüp-epoksi/bazalt Fiber Nanokompozitlerin Mekanik ve Kırılma Performansına Etkisi
(Konya Teknik Üniversitesi, 2019) Ulus, Hasan; Avcı, Ahmet
Fiber takviyeli epoksi kompozitler, sanayinin çeşitli alanlarında yaygın olarak kullanılmakta olmasına rağmen, su ve gerilme gibi çevresel faktörler, kompozitlerin matris çatlaması, plastikleşme ve delaminasyon gibi etkilerle erken bozulmalarına neden olabilmektedir. Polimer kompozitlerin nanopartiküller ile matris modifikasyonu, matris ile ilişkili özelliklerini geliştirmek için etkili bir yöntemdir. Bu çalışmada, bazalt fiberler (BF) ile güçlendirilmiş halloysit nanotüp (HNT) / epoksi nanokompozitlerin tuzlu suda yaşlandırılmasının mekanik ve kırılma performansına etkisi incelenmiştir. Bunun için öncelikle epoksi (Ep) matrisine çeşitli miktarlarda HNT katılmış ve em uygun HNT miktarı mekanik testlerle belirlenmiştir. Daha sonra, BF takviyeli HNT-Ep matrisli tabakalı nanokompozitler vakum destekli reçine infüzyon metodu (VARIM) ile üretilmiştir. Hazırlanan nanokompozitler çekme, eğilme, tek kenar çentikli eğilme, kısa kiriş kayma testi ve mod-I tabakalar arası kırılma tokluğu testlerine tabi tutulmuştur. Sonuçlar epoksi içerisine ağırlıkça %2 HNT eklenmesiyle yapılan matris modifikasyonunun epoksinin ve tabakalı kompozitlerin mekanik özelliklerini geliştirdiğini göstermiştir. Ayrıca HNT takviyesi yapılmış numunelerin tuzlu suda 6 ay yaşlandırılmış saf epoksi kompozitlere kıyasla belirgin bir şekilde daha iyi yaşlanma performansı sergilediği görülmüştür. Kompozitlerin kırılma morfolojileri mikroskopik incelemelerle araştırılarak tuzlu su yaşlandırmasına bağlı olarak gelişen hasar ve bozunma mekanizmaları ortaya çıkarılmış, tuzlu su ile kompozit yapı arasındaki kimyasal etkileşimler Fourier dönüşümü kızılötesi spektroskopisi ile incelenmiştir.