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    Analysis of employability for the civil aviation maintenance graduates of Turkey
    (Emerald Group Publishing Ltd, 2017) Denizhan, Berrin; Dogru, Alperen
    Purpose - With every passing day, the center of gravity for air traffic for the Middle East and Turkey is shifting toward becoming a center for airway transport, maintenance, repair, overhaul (MRO) and transfer. The MRO sector is gaining importance because of this increase in Turkey. The purpose of this study is to examine the future employability of the graduates receiving civil aviation maintenance training in Turkey. Design/methodology/approach - The paper uses past seven years' data about maintenance personnel of Turkey. It includes all-level students, recently working personnel and retired personnel of each year. Regression analysis and Markov analysis were used to show the prediction of aviation maintenance personnel. Findings - The paper provides quantitative results about employability of maintenance personnel under the real numbers of alumni and working and retired personnel in Turkey. The results show that the number of graduates will be greater than the number of staff members in certifying categories in 2018. Presently, Turkey meets the employment expected, but in the future, aviation maintenance personnel number is rising, and there will be an excess number of graduates left over in Turkey. Research limitations/implications - Because of the chosen region, Turkey, the research results may lack generalizability. Therefore, researchers are encouraged to conduct analysis for other countries which have an important role in aviation. Practical implications - The paper includes implications for the government maintenance personnel policy and educational policy for managing all types of maintenance personnel in Turkey. Originality/value - This kind of personnel needs analysis has not been done before, and this is the originality of this paper. It will in turn lead to an analysis of planning for allocation of maintenance staff and alumni. The authors collected all official numbers about maintenance personnel from Turkish Student Selection and Placement Center of Turkey, Turkish Technic and Turkish Civil Aviation Reports.
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    The effect of interface enhancement on the mechanical properties of fibre-reinforced PA6 matrix composites in material extrusion-based additive manufacturing
    (Springernature, 2024) Dogru, Alperen; Seydibeyoglu, Mehmet ozgur; Ayranci, Cagri
    Using different fibres and ratios can considerably enhance the mechanical properties of thermoplastic composites, and the fibre-matrix interface plays a crucial role in realizing the effects of reinforcements. This research aims to enhance the fibre-matrix interface using sustainable resources to increase the mechanical properties of composites produced using additive manufacturing. To do this, cellulose nanofibrils (CNF) were used for surface modification of carbon, glass, and hybrid (carbon + glass) fibres used in reinforcements in the PA6 matrix. Samples were produced by 3D printing done through material extrusion (MEX). and the effects of fibre types and ratios, print layer thickness, and interface enhancement between fibre-matrix on mechanical properties were investigated experimentally. Results reveal a 5 to 11% increase in the tensile strength of the carbon fibre-reinforced samples, whereas a 72 to 88% increase was observed for the glass fibre-reinforced samples. Furthermore, the tensile modulus value has been increased 4 times in carbon fibre reinforcement samples that used modified fibre compared to PA6 pure. Finally, different types and ratios of fibres had an impact on the glass transition temperature, but there was little to no change in the melting and crystallization temperatures. Our work highlights the potential of the proposed CNF modification made to the fibres for MEX production to produce parts with higher mechanical properties.
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    The effect of printing parameters on the mechanical properties of fiber-reinforced PA6 matrix composites in material extrusion-based additive manufacturing
    (Emerald Group Publishing Ltd, 2024) Dogru, Alperen; Seydibeyoglu, M. Ozgur
    PurposeThis study aims to understand the effect of the use of different proportions and types of fibers in the polyamide 6 (PA6) matrix during material extrusion-based additive manufacturing (MEX) and the effect of the manufacturing parameters on the mechanical properties. The mechanical, thermal and morphological properties of PA composites that are reinforced with carbon fiber (CF), glass fiber (GF) and as well as hybrid fiber (HF) were investigated.Design/methodology/approachIn this study, the effect of nozzle temperature and layer thickness on the mechanical properties of composite samples was investigated in terms of their behavior under tensile, impact and compression loads, manufacturing parameters as well as fiber ratio and type. The results were also consolidated by scanning electron microscopy.FindingsAt 20 Wt.% CF reinforcement PA6 samples, a tensile strength value of 125 MPa was obtained with a 60% increase in tensile strength value compared to neatPA6. The HF-reinforced ones also measured a tensile strength value of 106.69 MPa. This corresponds to an increase of 38% compared to neatPA6. The results also show that HF reinforcement can be an important component for many composites and a suitable material for use under compression loading.Originality/valuePA6, an engineering polymer, can be produced by MEX, which offers several advantages for complex geometries and customized designs. There are studies on different carbon and GF ratios in the PA6 matrix. Using these fibers together in a HF, the examination of their mechanical properties in the MEX method and the examination of the effect of GF reinforcement in the hybrid structure, which has a cost-reducing effect, has been an innovative approach. In this study, the results of the optimization of the parameters affecting the mechanical properties in the production of samples reinforced with different ratios and types of fibers in the PA6 matrix by the MEX method are presented.
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    Improving the Flexibility of Ship Propellers Additively Manufactured from High-Density Polyethylene/Long Carbon Fiber Composites by Prepreg Coating
    (Mdpi, 2024) Neser, Goekdeniz; Sozen, Ayberk; Dogru, Alperen; Liu, Pengfei; Altunsaray, Erkin; Halilbese, Akile Nese; Turkmen, Serkan
    In efforts to achieve the goal of reducing ship emissions in the fight against climate change, reducing fuel consumption by making ships lighter is stated as one of the solutions. In this study, the possibilities of making composite equivalents of propellers, which are the most complex ship elements and traditionally produced from metal materials, are investigated with the advantages of additive manufacturing, which offers a rapid production opportunity for such forms. In this way, a lighter composite propeller and, therefore, a lighter ship will be achieved, and negative environmental impacts, especially harmful emissions, will be reduced. In the study, a 1/14-scale ship propeller was produced through the material extrusion method of additive manufacturing using an HDPE composite containing long carbon fiber with a 15% weight fraction. An attempt to reduce flexibility with an epoxy-carbon fabric prepreg coating was made, as the flexibility has negative effects on the performance of the produced propeller. The propeller tunnel test showed that the applied carbon fabric epoxy prepreg helped to improve the propeller's performance by decreasing the flexibility of the propeller and reducing the deformation at the tips. At the same time, the propeller weight was decreased by 60% compared to its metal counterparts.
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    The microstructural evolution of material extrusion based additive manufacturing of polyetheretherketone under different printing conditions and application in a spinal implant
    (Wiley, 2024) Irez, Alaeddin Burak; Dogru, Alperen
    With the advances in additive manufacturing, polyetheretherketone (PEEK), a biocompatible polymer, can be used in biomedical applications such as spinal implants. This paper aims to investigate the evolution of the microstructure of PEEK parts manufactured by material extrusion (MEX)-based additive manufacturing with different printing parameters. The effect of layer thickness (LT) and nozzle diameter on mechanical properties was investigated using tensile, Charpy impact, and short beam strength (SBS) tests. Two different LTs, 0.1 and 0.2 mm, and two different nozzle diameters, 0.6 and 0.8 mm, were used as printing parameters. By increasing the LT, tensile strength dropped by around 24%, and impact strength by almost 55%. Moreover, altering the LT resulted in a 15% decrease in interlaminar shear strength (ILSS) from the SBS test. In addition, increasing the nozzle diameter also led to a significant reduction in all of the results as tensile strength, Charpy impact strength, and ILSS. The results were also consolidated by scanning electron microscopy. The main findings were that increasing LT leads to an increase in microstructural defects that act as stress concentrators. Following the tests, response surface methodology (RSM) was used to determine optimal printing parameters. In the end, using the optimum printing parameters from the RSM study, a structural analysis of a MEX-printed spinal implant was conducted through finite element method, considering the loading cases mimicking daily human body motions.Highlights As layer thickness increased, tensile and impact strength dropped. Tensile and impact strength dropped truly with increasing nozzle diameter. SEM revealed that increasing layer thickness causes more microstructural flaws. FEM analysis showed that PEEK-based implant provides structural integrity. A visual representation of the study's flow.image
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    On the Hydrodynamic and Structural Performance of Thermoplastic Composite Ship Propellers Produced by Additive Manufacturing Method
    (MDPI, 2024) Altunsaray, Erkin; Turkmen, Serkan; Sozen, Ayberk; Dogru, Alperen; Liu, Pengfei; Halilbese, Akile Nese; Neser, Gokdeniz
    In the marine industry, the search for sustainable methods, materials, and processes, from the product's design to its end-of-life stages, is a necessity for combating the negative consequences of climate change. In this context, the lightening of products is essential in reducing their environmental impact throughout their life. In addition to lightening through design, lightweight materials, especially plastic-based composites, will need to be used in new and creative ways. The material extrusion technique, one of the additive manufacturing methods, is becoming more widespread day by day, especially in the production of objects with complex forms. This prevalence has not yet been reflected in the marine industry. In this study, the performances of plastic composite propellers produced by the material extrusion technique is investigated and discussed comparatively with the help of both hydrodynamic and structural tests carried out in a cavitation tunnel and mechanical laboratory. The cavitation tunnel test and numerical simulations were conducted at a range of advance coefficients (J) from 0.3 to 0.9. The shaft rate was kept at 16 rps. The thrust and torque data were obtained using the tunnel dynamometer. Digital pictures were taken to obtain structural deformation and cavitation dynamics. The structural performance of the propellers shows that an aluminum propeller is the most rigid, while a short carbon fiber composite propeller is the most flexible. Continuous carbon fiber composite has high strength and stiffness, while continuous glass fiber composite is more cost-effective. In terms of the hydrodynamic performance of the propellers, flexibility reduces the loading on the blade, which can result in thrust and torque reduction. Overall, the efficiency of the composite propellers was similar and less than that of the rigid aluminum propeller. In terms of weight, the composite carbon propeller containing continuous fiber, which is half the weight of the metal propeller, is considered as an alternative to metal in production. These propellers were produced from a unique composite consisting of polyamide, one of the thermoplastics that is a sustainable composite material, and glass and carbon fiber as reinforcements. The findings showed that the manufacturing method and the new composites can be highly successful for producing ship components.
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    Review on Hybrid Reinforced Polymer Matrix Composites with Nanocellulose, Nanomaterials, and Other Fibers
    (MDPI, 2023) Seydibeyoglu, Mehmet Ozgur; Dogru, Alperen; Wang, Jinwu; Rencheck, Mitch; Han, Yousoo; Wang, Lu; Seydibeyoglu, Elif Alyamac
    The use of composite materials has seen many new innovations for a large variety of applications. The area of reinforcement in composites is also rapidly evolving with many new discoveries, including the use of hybrid fibers, sustainable materials, and nanocellulose. In this review, studies on hybrid fiber reinforcement, the use of nanocellulose, the use of nanocellulose in hybrid forms, the use of nanocellulose with other nanomaterials, the applications of these materials, and finally, the challenges and opportunities (including safety issues) of their use are thoroughly discussed. This review will point out new prospects for the composite materials world, enabling the use of nano- and micron-sized materials together and creating value-added products at the industrial scale. Furthermore, the use of hybrid structures consisting of two different nano-materials creates many novel solutions for applications in electronics and sensors.