Mechanical Engineering / Makina Mühendisliği
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Article Poliamid 6/6 (pa 66) Mikrofiberler ile Toklaştırılmış Tabakalı Kompozitlerin Mod-ı Delaminasyon Direncinin İstatiksel Analizi(Niğde Ömer Halisdemir Üniversitesi, 2019) Beylergil, Bertan; Tanoğlu, Metin; Aktaş, EnginFiber takviyeli kompozitler, ağırlıklarına oranla yüksek mukavemet ve rijitlikleri nedeniyle uzay ve otomotiv yapısal parçalarında yaygın olarak kullanılmaktadır. Delaminasyon, bu kompozitlerde görülen en yaygın ve kritik hasar modudur. Bu kompozitlerin delaminasyon direncini arttırmak amacıyla, nanokatkılar ile epoksi toklaştırması, dikişleme, z-pimler ve arayüzeyde mikro/nanofiber kullanılması gibi pek çok sayıda teknik geliştirilmiştir. Bu çalışmada, poliamid 6/6 (PA 66) mikrofiberler ile toklaştırılmış karbon fiber/epoksi kompozitlerin Mode-I delaminasyon direnci Weibull dağılımı kullanılarak istatiksel olarak analiz edilmiştir. Test verilerinin istatiksel olarak değerlendirilmesi sonucunda PA 66 mikrofiberlerin kullanılmasının %90 güven seviyesinde kırılma tokluğunu yaklaşık %445 mertebesinde arttırdığı gözlemlenmiştir.Article Citation - WoS: 97Citation - Scopus: 110Effect of Polyamide-6,6 (pa 66) Nonwoven Veils on the Mechanical Performance of Carbon Fiber/Epoxy Composites(Elsevier Ltd., 2018) Beylergil, Bertan; Tanoğlu, Metin; Aktaş, EnginIn this study, carbon fiber/epoxy (CF/EP) composites were interleaved with polyamide-6,6 (PA 66) nonwoven veils at two different areal weight densities (17 and 50 gsm) to improve their delamination resistance against Mode-I loading. Mode-I fracture toughness (DCB), tensile, open hole tensile (OHT), flexural, compression, short beam shear (ILSS) and Charpy-impact tests were performed on the reference and PA 66 interleaved composite specimens. The DCB test results showed that the initiation and propagation Mode-I fracture toughness values of the composites were significantly improved by 84 and 171% using PA 66-17 gsm veils respectively, as compared to reference laminates. The use of denser PA 66-50 gsm veils in the interlaminar region led to higher improvement in fracture toughness values (349% for initiation and 718% for propagation) due to the higher amount of veil fibers involved in fiber bridging toughening mechanism. The incorporation of PA 66-50 gsm nonwoven veils also increased the ILSS and Charpy impact strength of the composites by 25 and 15%, respectively. On the other hand, the PA 66 veils reduced in-plane mechanical properties of CF/EP composites due to lower carbon fiber volume fraction and increased thickness.Article Citation - WoS: 31Citation - Scopus: 33Modification of Carbon Fibre/Epoxy Composites by Polyvinyl Alcohol (pva) Based Electrospun Nanofibres(Adcotec Ltd., 2016) Beylergil, Bertan; Tanoğlu, Metin; Aktaş, EnginIn this study, the effects of modifying interlaminar region of unidirectional carbon fibre/epoxy composites by the incorporation of electrospun polyvinyl alcohol (PVA) nanofibres were investigated. PVA nanofibres were directly deposited onto the carbon fabrics by electrospinning method to improve mechanical performance of those composites. The features of the electrospun nanofibres were characterized by microscopy techniques. The unidirectional carbon fibre/epoxy composite laminates with/without PVA nanofibre interlayers were manufactured by vacuum-infusion technique in a [0]4 configuration. Tensile, three-point bending, compression, Charpy-impact and Mode-I fracture toughness tests (Double Cantilever Beam (DCB)) were carried out in accordance with ASTM standards to evaluate mechanical performance of the composites. Scanning electron microscopy (SEM) observations were made on the specimens to evaluate microstructural features. It was observed that the carbon fabrics were successfully coated with a thin layer of PVA nanofibres by electrospinning technique. The results showed that P VA nanofibres improve the mechanical properties of unidirectional carbon/epoxy composite laminates when subjected to in-plane loading. On the other hand, PVA nanofibres slightly reduced the mode-I fracture toughness values although they led to more stable crack propagation.Article Citation - WoS: 108Citation - Scopus: 117Enhancement of Interlaminar Fracture Toughness of Carbon Fiber–epoxy Composites Using Polyamide-6,6 Electrospun Nanofibers(John Wiley and Sons Inc., 2017) Beylergil, Bertan; Tanoğlu, Metin; Aktaş, EnginIn this study, carbon fiber–epoxy composites are interleaved with electrospun polyamide-6,6 (PA 66) nanofibers to improve their Mode-I fracture toughness. These nanofibers are directly deposited onto carbon fabrics before composite manufacturing via vacuum infusion. Three-point bending, tensile, compression, interlaminar shear strength, Charpy impact, and double cantilever beam tests are performed on the reference and PA 66 interleaved specimens to evaluate the effects of PA 66 nanofibers on the mechanical properties of composites. To investigate the effect of nanofiber areal weight density (AWD), nanointerlayers with various AWD are prepared by changing the electrospinning duration. It is found that the electrospun PA 66 nanofibers are very effective in improving Mode-I toughness and impact resistance, compressive strength, flexural modulus, and strength of the composites. However, these nanofibers cause a decrease in the tensile strength of the composites. The glass-transition temperature of the composites is not affected by the addition of PA 66 nanofibers. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017, 134, 45244.Article Citation - WoS: 25Citation - Scopus: 39An Experimental Study on Friction Drilling of St12 Steel(Canadian Society for Mechanical Engineering, 2014) Kaya, Mehmet Tuncay; Aktaş, Alaattin; Beylergil, Bertan; Akyıldız, Hamza K.The aim of this study is to investigate the effects of drilling parameters such as friction angle, friction contact area ratio (FCAR), feed rate and spindle speed on workpiece surface temperature, thrust force and torque in friction drilling of ST12 material. The tool material is tungsten carbide coated with TiN treatment. Experimental results reveal that the thrust force and torque increases gradually with increasing friction angle, feed rate and FCAR. On the other hand, the thrust force and torque decreases with increasing drilling speed. It is found that drilling speed has an important effect on the workpiece surface temperature. As the drilling speed increases, the workpiece surface temperature increases. Increasing or decreasing the friction angle and FCAR has no significant effect on the workpiece surface temperature.Article Citation - WoS: 23Citation - Scopus: 23Free Vibration Analysis of Laminated Composite Beam Under Room and High Temperatures(Techno Press, 2014) Cünedioğlu, Yusuf; Beylergil, BertanThe aim of this study is to investigate the effects of the beam aspect ratio(L/h), hole diameter, hole location and stacking layer sequence ([0/45/-45/90]s, [45/0/-45/90]s and [90/45/-45/0]s) on natural frequencies of glass/epoxy perforated beams under room and high (40, 60, 80, and 100°C) temperatures for the common clamped-free boundary conditions (cantilever beam). The first three out of plane bending free vibration of symmetric laminated beams is studied by Timoshenko's first order shear deformation theory. For the numerical analyses, ANSYS 13.0 software package is utilized. The results show that the hole diameter, stacking layer sequence and hole location have important effect especially on the second and third mode natural frequency values for the short beams and the high temperatures affects the natural frequency values significantly. The results are presented in tabular and graphical form. © 2014 Techno-Press, Ltd.Article Shear Strength of Pultruded Composite Pins With External Confinement(Taylor and Francis Ltd., 2014) Beylergil, Bertan; Aktaş, Alaattin; Pekbey, YelizWeight reduction using composites has gained increasing attention in recent times. In this study, pultruded composite pins (unconfined and confined) were manufactured and tested by using a custom double shear testing fixture. Different configurations were applied for confinement of the composite pins, including weft-knitted fabrics (plain, 1 × 1 rib, and Milano), woven fabrics and E-glass 130 tex fibers/adhesive cloth. They were externally wrapped and bonded to the unconfined composite pins. In each case, five identical specimens were tested, and shear strength data were analyzed by using two-parameter Weibull statistics. The results showed that the maximum shear strength took its highest value in the unconfined case for both average values of the test results and for 99% reliability under Weibull distribution. The confinement had a negative effect on the average shear strength of the unconfined pins. It was also seen that the 99% reliability values of shear strength were approximately equivalent to the 0.7 average value of the shear strength.Article Citation - WoS: 4Citation - Scopus: 4Enhancement of Flexural Performance of Wood Beams Using Textile Fabrics(Walter De Gruyter Gmbh, 2013) Beylergil, Bertan; Aktaş, Alaattin; Pekbey, YelizThe aim of this study was to investigate the flexural performance of wood beams (beech - Fagus orientalis Lipsky) reinforced with woven and selected weft knitted glass fabrics, namely, Milano and plain knit. Some physical and mechanical properties of the beech wood and the textile fabrics were determined in accordance with relevant ASTM standards. Twenty-four wood beams which have two different cross sections (I-shaped and square hollow) were manufactured and tested under a threepoint load. They were divided into two groups: Group A specimens were not reinforced to serve as a reference, whereas Group B specimens were reinforced with textile fabrics combined with adhesion. The flexural behavior of the specimens was studied through their load-deflection characteristics. The modes of failure were identified and categorized. The experimental results showed that the load-bearing capacity of reinforced beams increased significantly compared to the beam without reinforcement. This method can be used to repair and strengthen damaged wood beams.