Person: EKİCİ, BÜLENT
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EKİCİ
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BÜLENT
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Publication Metadata only An experimental investigation on ballistic efficiency of silica-based crosslinked aerogels in aramid fabric(ELSEVIER SCI LTD, 2020) EKİCİ, BÜLENT; Ayten, Ali Imran; Tasdelen, Mehmet Atilla; Ekici, BulentThe ballistic performance of crosslinked aerogels which were synthesized using a micelle swelling and structure directing agent against Level IIIA threat was experimentally investigated in this study. Firstly, silica-based aerogels were synthesized in a small scale, and then, isocyanate crosslinking was applied to them. According to the characterization results, the best sample with a desired pore structure for energy absorption was determined. Then, scale-up manufacturing was realized for this sample to use in ballistic tests. Subsequently, neat aramid fabrics with different numbers of layers were tested, and back-face deflection values were determined. The neat aramid fabrics with 24, 30 and 36 layers were deflected as 57.32, 43.58 and 40.38 mm, respectively. To understand the efficiency of the crosslinked aerogel sample, it was placed into the 30 layers of the aramid fabric as the back-face deflection value of its neat form was closest to the critical back face deflection value which is defined in the related standard. Three types of aerogel monoliths, as rectangular, large diameter of circular and small diameter of circular were tested with aramid fabrics. Fewer fabrics were perforated at the rate of 72% in all ballistic test samples including aerogel monoliths in comparison to the neat aramid fabric tests. 7 or 8 layers of fabric were perforated in the test of the neat aramid fabric samples, while 2 layers of fabric were perforated in the samples containing aerogel.Publication Open Access Effect of air pressure on nanofiber production in solution blowing method(GAZI UNIV, FAC ENGINEERING ARCHITECTURE, 2020-07-21) EKİCİ, BÜLENT; Polat, Yusuf; Yangaz, Murat Umut; Calisir, Mehmet Durmus; Gul, Mehmet Zafer; Demir, Ali; Ekici, Bulent; Kilic, AliIn this study, effect of air pressure on nanofiber diameter and morphology was studied for solution blowing technique. A computational fluid dynamics (CFD) analysis was realized via ANSYS (R) Fluent software, and the results were compared with experimental solutions. The results showed that an increase in air inlet pressure from 100 kPa to 300 kPa has significant effect on nanofiber diameter and morphology. In contrast, as the air inlet pressure increases above 300 kPa to 600 kPa, both nanofiber diameter increases, and the fiber agglomerations are observed due to high turbulence intensity. The droplets were observed at 100 kPa air inlet pressure due to low driving force applied to the polymer solution. The effects of air pressure on nanofiber diameter and morphology have been investigated by using finite volume method, and the results are compared with the experimental results.Publication Metadata only A numerical and experimental investigation on quasi-static punch shear test behavior of aramid/epoxy composites(SAGE PUBLICATIONS LTD, 2020) EKİCİ, BÜLENT; Ayten, Ali Imran; Ekici, Bulent; Tasdelen, Mehmet AtillaIn this study, quasi-static punch shear behavior of aramid epoxy composites was investigated both numerically and experimentally. Firstly, material model parameters used in numerical simulations were obtained by various mechanical tests such as tensile, compression, and in-plane shear tests. Different damage mechanisms that were observed during each test were the focus of interest. Then quasi-static punch shear test was performed and verified with numerical simulations. After the verification of material model, punch tests, which have different boundary conditions, were run numerically, and the effect of thickness and span-to-punch ratio (SPR) were determined for aramid/epoxy composites. It is concluded that failure mechanisms of composite samples were related to SPR. When SPR increases, the failure mode was shifted from shear-dominated failure to bending-dominated failure behavior. Additionally, punch shear strength value at minimum SPR (1.1) was eight times bigger than the value at maximum one (8).Publication Metadata only Effect of fiber set-up and density on mechanical behavior of robotic 3D-printed composites(2022-03-01) EKİCİ, BÜLENT; Ipekci A., EKİCİ B.The further development of composite manufacturing methods is characterized by the progress of their mechanical properties which are widely used in many applications as automotive, aerospace, and marine industries. The automated composite production techniques are as follows: automatic tape layering, automatic fiber placement, and filament winding methods used in many industries. Photopolymerized composites and their additive manufacturing methods are promising with new advances in technology. This method for printing continuous fiber-reinforced plastic composite parts by a six-axis industrial robotic arm is based on fused deposition modeling technology. The objective of this work is to obtain a better understanding of the mechanical properties of robotic three-dimensional printed photopolymer resin continuous fiberglass-reinforced composites (CFGRCs) as a function of different printing speeds (10, 20 and 30mm/s), fiber densities (45, 55 and 65%), and fiber orientations (0, 0/90 and +/- 45 degrees). This work infers that mechanical properties are significantly affected by the fiber density and fiber orientation of CFGRC. With this method, approximately 300MPa tensile strength can be obtained and structurally preferred instead of ferrous materials in many areas.Publication Open Access Mechanical performance of carbon - aramid fiber-reinforced laminated composites under impact and shear loading(2021-11-01) EKİCİ, BÜLENT; ATMACA B. N., ORUÇ R., AŞÇI G., YİĞİT K., YÜZER S., POLAT Y., EKİCİ B.In this study, the drop weight impact response and the interlaminar shear strength of hybrid carbon/aramid fiber-reinforced laminated composites with different stacking sequences were investigated. Seven different laminates including two types of sandwich-like interply hybrid, three types of interply hybrid, and two types of non-hybrid named carbon and aramid were produced using the vacuum-assisted resin transfer molding method. Drop weight impact and short-beam shear tests were applied to the laminates to calculate the low-velocity impact response and the interlaminar shear strength, respectively. It is observed that while the outer layer of the hybrid structure is carbon, the structure can carry less load but absorb more energy. Pure carbon and pure aramid composites cannot carry loads but can absorb energy as much as their hybrid versions can. Sandwich-like interply hybrid with central carbon showed the best results when load and energy values were compared. Also, sandwich-like interply hybrid with central carbon has higher ILSS among hybrid structures because its center region consists of carbon layers.Publication Metadata only Effect of solution blown nanofibers on Mode-I fracture toughness and dynamic mechanical properties of carbon fiber-reinforced composites(WILEY, 2021) EKİCİ, BÜLENT; Polat, Yusuf; Ekici, Bulent; Kilic, AliIn this study, solution-blown nanofibers were coated on carbon fiber (CF) fabrics to improve Mode-I fracture toughness and dynamic mechanical properties of the composite laminates. Nanofiber coatings of various basis weights were directly spun over CF fabrics, which were then formed into composite laminates via vacuum-assisted resin transfer molding. A double cantilever beam test was conducted to analyze the Mode-I fracture toughness of CF-reinforced epoxy composites. The results showed that solution-blown nanofiber coatings stabilized the crack propagation and increased the delamination strength hence increased the Mode-I fracture toughness by nearly 48% for the addition of 1 g/m(2) nanofibrous web. Dynamic mechanical analysis was performed to investigate the effect of nanofibers on the stiffness of materials and the homogeneity of samples. Storage modulus, loss modulus, and damping factor were calculated, and corresponding Cole-Cole plots were drawn. DMA results showed that the stiffness of the composite sample increased up to 17% even after a minor amount (1 g/m(2)) of nanofiber coating.Publication Metadata only Experimental and statistical analysis of robotic 3D printing process parameters for continuous fiber reinforced composites(SAGE PUBLICATIONS LTD, 2021) EKİCİ, BÜLENT; Ipekci, Ahmet; Ekici, Bulent3D printing technology has gradually taken its place in many sectors. However, expected performance cannot be obtained from the structural parts with this method due to the raw material properties and constraints of Cartesian motion systems. This technology cannot replace structural parts produced by traditional manufacturing methods. In order to avoid these constraints, it is preferred to use continuous fiber reinforced polymer composites in many areas such as automotive and aerospace industries due to their low weight and high specific strength properties. These automated composite manufacturing methods currently have limited production of geometric shapes due to the need for additional molds and production as flat surfaces. To overcome all these constraints, fiberglass reinforced ultraviolet ray-curing polymer matrix composite material are selected for robotic 3 D printing process and various parameters are examined. Fiber-polymer combination and layer structure formation was examined. Scanning Electron Microscopy (SEM) images of sections of 3 D printed test samples were taken and fiber resin curing was examined. The nozzle diameter, printing speed, fiber density and Ultra Violet (UV) light intensity parameters, which will provide effective 3 D printing process, are optimized with the Taguchi method. Tensile strength, flexural strength and izod impact values are considered as result parameters for optimization. It was found that it would be appropriate for 3D printing with a 1.0 mm nozzle diameter, 600 tex fiber density, 4 UV light, 600 mm/min printing speed. With these 3D printing process parameters, approximately 125 MPa tensile strength and 450 MPa flexural strength can be obtained. With this study, support and contribution was provided to researchers, composite producers, tool manufacturer and literature who want to use and develop this 3D printing process.