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    Experimental and statistical analysis of carbon fiber/epoxy composites interleaved with nylon 6,6 nonwoven fabric interlayers
    (Sage Publications Ltd, 2020) Beylergil, Bertan; Tanoğlu, Metin; Aktaş, Engin
    Thermoplastic interleaving is a promising technique to improve delamination resistance of laminated composites. In this study, plain-weave carbon fiber/epoxy composites were interleaved with nylon 6,6 nonwoven fabrics with an areal weight density of 17 gsm. The carbon fiber/epoxy composite laminates with/without nylon 6,6 nonwoven fabric interlayers were manufactured by VARTM technique. Double cantilever beam fracture toughness tests were carried out on the prepared composite test specimens in accordance with ASTM 5528 standard. The experimental test data were statistically analyzed by two-parameter Weibull distribution. The results showed that the initiation and propagation fracture toughness Mode-I fracture toughness of carbon fiber/epoxy composites could be improved by about 34 and 156% (corresponding to a reliability level of 0.50) with the incorporation of nylon 6,6 interlayers in the interlaminar region, respectively. The results also revealed that the percent increase in the propagation fracture toughness value was 67 and 41% at reliability levels of 0.90 and 0.95, respectively.
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    Experimental failure analysis and mechanical performance evaluation of fiber-metal sandwich laminates interleaved with polyamide-6,6 interlayers through the combined usage of acoustic emission, thermography and microscopy techniques
    (Sage Publications Ltd, 2020) Beylergil, Bertan; Tabrizi, İsa E.; Zanjani, Jamal S. M.; Saeidiharzand, Shaghayegh; Poudeh, Leila H.; Yıldız, Mehmet
    Fiber-metal laminates are hybrid sandwich composite structures made of thin metallic sheets and layers of fiber-reinforced plastics. In this study, for the first time, the effects of polyamide 66 nonwoven interlayers on the tensile, three-point bending, interlaminar shear strength, and low velocity impact responses of fiber-metal laminates are investigated by coupling acoustic emission, thermography, and microscopy techniques. The fiber-metal laminates are interleaved with polyamide 66 nonwoven fabrics at two different areal weight density, namely, 17 gsm (grams per square meter) and 50 gsm. The tensile, bending, interlaminar shear strength, and low velocity impact tests are carried out in accordance with the ASTM standards. During the tensile and flexural tests, acoustic emission data are collected to understand damage types occurring under various loading conditions and, in turn, clearly shed light on the performance of polyamide 66 for interfacial strengthening in fiber-metal laminates. The results of acoustic emission investigation are correlated with the optical and scanning electron microscope-based microscopic analysis. It is shown that the interlaminar shear strength of fiber-metal laminates can be increased significantly (about 42%) by using polyamide 66 nonwoven interlayers. The impacted fiber-metal laminate specimens are examined to determine damage area and length using the lock-in thermography method. It is found that the polyamide 66 interlayers decrease the debonded length and damaged area up to 39 and 32%, respectively. The tensile and flexural strength and modulus of the fiber-metal laminate are not significantly affected by the presence of polyamide 66 interlayers, except a negligible drop in the value of tensile and flexural strength by 6 and 4%, respectively. The polyamide 66 interlayers are proved to be very successful in enhancing plastic deformation ability of the matrix and bonding efficiency between aluminum and composite sections.
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    Free vibration and torsional buckling analysis of E- Glass/epoxy composite shafts with Polyamide-6,6 (PA 66) Nanofiber interlayers
    (2018) Beylergil, Bertan
    In this study, the effects of polyamide-6,6 (PA 66) nanofibers on the free vibration and torsional buckling of fourlayered E-glass/epoxy composite drive shaft were investigated numerically. The numerical analyses were carried out by using ANSYS 16.2 software package. Three different nanofiber areal weight densities (AWDs), 8, 10 and 12 g/m2, were considered to reveal the relationship between the amount of nanofibers in the interlaminar region and natural frequencies/critical torsional buckling loads. The numerical results showed that the PA-66 nanofibers had a positive effect on natural frequencies and torsional buckling load of E-glass/epoxy composite shaft. The natural frequencies and buckling load of the composite shaft can be increased by about 10 % and 22% using PA 66 nanofibers as the secondary reinforcing material in the interlaminar region. The failure torque values were not significantly affected with the inclusion of PA 66 nanofibers in the interlaminar region.
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    Load-carrying capacity of filament-wound E glass/epoxy composite rings
    (Csme Trans, 2019) Beylergil, Bertan
    In this study, three different types of E glass/epoxy composite rings were produced by the filament-winding technique: (i) O ring (Type A), (ii) ring with a radial notch (Type B), and (iii) C-shaped ring (Type C). To evaluate the effect of winding angle on the load-carrying capacity of composite rings, five different winding angles were considered: +/- 45 degrees, +/- 55 degrees, +/- 65 degrees, +/- 75 degrees, and +/- 88 degrees. The load capacity of the manufactured composite rings in the tensile hoop direction were determined experimentally using a special test fixture. The experimental results showed that the optimum winding angle was +/- 88 degrees in terms of load-carrying capacity. The rings wound at 55 degrees had the lowest load-carrying capacity. Type A rings had the highest capacity while Type C rings had the lowest.
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    Mode-I fracture toughness of carbon fiber/epoxy composites interleaved by aramid nonwoven veils
    (Techno-Press, 2019) Beylergil, Bertan; Tanoğlu, Metin; Aktaş, Engin
    In this study, carbon fiber/epoxy (CF/EP) composites were interleaved with aramid nonwoven veils with an areal weight density of 8.5 g/m(2) to improve their Mode-I fracture toughness. The control and aramid interleaved CF/EP composite laminates were manufactured by VARTM in a [0]4 configuration. Tensile, three-point bending, compression, interlaminar shear, Charpy impact and Mode-I (DCB) fracture toughness values were determined to evaluate the effects of aramid nonwoven fabrics on the mechanical performance of the CF/EP composites. Thermomechanical behavior of the specimens was investigated by Dynamic Mechanical Analysis (DMA). The results showed that the propagation Mode-I fracture toughness values of CF/EP composites can be significantly improved (by about 72%) using aramid nonwoven fabrics. It was found that the main extrinsic toughening mechanism is aramid microfiber bridging acting behind the crack-tip. The incorporation of these nonwovens also increased interlaminar shear and Charpy impact strength by 10 and 16.5%, respectively. Moreover, it was revealed that the damping ability of the composites increased with the incorporation of aramid nonwoven fabrics in the interlaminar region of composites. On the other hand, they caused a reduction in in-plane mechanical properties due to the reduced carbon fiber volume fraction, increased thickness and void formation in the composites.
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    Multi-objective optimal design of hybrid composite laminates under eccentric loading
    (Elsevier, 2020) Beylergil, Bertan
    Laminated composites are being used in many engineering applications since they provide significant weight reduction, better fatigue and corrosion resistance. In this study, design optimization of a hybrid composite laminate subjected to eccentric loading was carried out using multi-objective genetic algorithm (MOGA). The ply material (carbon fiber or E glass) and fiber orientations (-90 <= theta <= 90) were considered as design variables. The objective function was to minimize cost and weight with the maximization of the stiffness. The design constraints were the maximum Tsai-Wu failure index, first mode natural frequency. The numerical analyses were carried out by using ANSYS software package. Genetic aggregation model was used to generate the response surfaces which were used to obtain the optimum design variables. The optimum lay-up sequence and ply materials were determined for weight saving and cost reduction of hybrid composite plates. It was shown that the hybridization of carbon fiber and E glass fiber provided the optimal designs offers lower cost and higher mechanical performance. MOGA method was very effective to optimize the structural performance of the hybrid composite plates under eccentric loading. (C) 2020 The Author. Published by Elsevier B.V. on behalf of Faculty of Engineering, Alexandria University.
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    Numerical investigation on composite mono-leaf springs reinforced with Polyurethane/Carbon nanotubes (PU/CNTs) nanoweb interlayers
    (2019) Beylergil, Bertan
    Composite materials have been widely used in automobile industry to reduce vehicle weight and cut CO2 emissions. With the rapid advancement of nanotechnology, it is now possible to improve the mechanical performance of these materials more than ever before. In this study, mechanical behavior of carbon fiber/epoxy (CF/EP) composite mono-leaf springs reinforced with polyurethane/carbon nanotubes (PU/CNTs) nanoweb interlayers was investigated numerically. The effect of hybridization in composite leaf springs was revealed. The numerical analyses were carried by using ANSYS Workbench with ACP module. The numerical verification of the finite element model was carried out by comparing numerical results against analytical calculations. Then, the verified FE model was extended to this study. The numerical results showed that the stiffness of the composite wave springs could be increased by 18% with the addition of PU/CNTs nanofibers (CNT content: 5 wt.%) in the interlaminar region without weight and thickness increase. It was also observed that the natural frequency values increased by 8% (CNT content: 5 wt.%) after the addition of these nanofibers.
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    Poliamid 6/6 (Pa 66) mikrofiberler ile toklaştırılmış tabakalı kompozitlerin mod-ı delaminasyon direncinin istatiksel analizi
    (2019) Beylergil, Bertan; Tanoğlu, Metin; Aktaş, Engin
    Fiber 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.
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    Tek-katlı kompozit dalgalı yayların tasarımı, modellenmesi ve yapısal analizi
    (2020) Beylergil, Bertan
    Bu çalışmada, tek-katlı kompozit dalgalı yayların bası yükü altındaki mekanik davranışları nümerik olarak incelenmiştir. Nümerik analizler, Ansys Workbench ve ACP Modülü sonlu elemanlar programı kullanılarak yapılmıştır. Numerik doğrulama çelik dalgalı yay probleminin nümerik sonuçları ile analitik sonuçlar karşılaştırılarak yapılmıştır. Doğrulamadan sonra, sonlu elemanlar modeli bu çalışma için genişletilmiştir. Kompozit malzeme olarak karbon fiber/epoksi ve cam fiber/epoksi seçilmiştir. Tasarım parametreleri olarak dalga sayısı (4, 6 ve 8) ve kompozit kalınlığı (tabaka sayısı; 4, 6, 8, 10 ve 12) ele alınmıştır. Bu tasarım parametreleri ve malzeme türleri için yay rijitlikleri hesaplanmış ve çelik yay ile kıyaslamalar yapılmıştır. Yayların hasar yükleri, Tsai-Wu hasar kriteri kullanılarak belirlenmiştir. Buna ek olarak, hibritleştirme etkisinin yayın mekanik davranışa etkisi incelenmiştir. Nümerik sonuçlar, kompozit tasarım parametreleri doğru olarak seçildiğinde çeliğe yakın rijitlik değerlerinin ve yayda önemli ağırlık azaltımının sağlanabileceğini göstermiştir.