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 Metadata only Effect of surface geometry on low-velocity impact behavior of laminated aramid-reinforced polyester composite(SAGE PUBLICATIONS LTD, 2016) GÜLLÜOĞLU, ARİF NİHAT; Ayten, Ali Imran; Ekici, Bulent; Gulluoglu, Arif NihatThe aim of this study is to investigate the effect of surface geometry for low-velocity impact applications. To achieve this purpose, aramid fiber-reinforced laminated polyester composite with various geometries such as cylindrical, elliptical, and spherical were prepared, and low-velocity impact properties were investigated numerically and experimentally. All properties such as orientation, fiber volume fraction, matrix material, and average thickness are the same in all samples. Experimental low-velocity impact behaviors of structure were determined by drop weight tester at low velocity 2.012 m/s. Simulations were carried out by LS-Prepost 4.2 and LS-Dyna v971 software. By this way, results of impact tests were verified and modeled with finite element method. Results of the impact tests showed that the elliptical samples have the highest energy absorption capability due to effective stress transfer capacity. According to experimental results, maximum energy absorption rate difference is 17% between elliptical 10mm and cylindrical 5mm geometries.Publication Metadata only Ballistic resistance of high hardness armor steels against 7.62 mm armor piercing ammunition(ELSEVIER SCI LTD, 2013) EKİCİ, BÜLENT; Kilic, Namik; Ekici, BulentAlthough advanced lightweight composite based armors are available, high hardness steels in military vehicles are often used to provide ballistic protection at a relatively low cost and is an interesting material due to its widespread usage in vehicle structure. In this study, ballistic limit of 500 HB armor steel was determined against 7.62 mm 54R B32 API hardened steel core ammunition. Lagrange and smoothed particle hydrodynamics (SPH) simulations were carried out using 3D model of bullet and high hardness armor target. Perforation tests on 9 and 20 mm thickness armor were performed to validate simulation methodology. Also material tests were performed for armor steel and ammunition hardened steel core to develop Johnson-Cook constitutive relations for both strength and failure models. Finally, results from 3D numerical simulations with detailed models of bullet and target were compared with experiments. The study indicates that the ballistic limit can be quantitatively well predicted independent of chosen simulation methodology, but qualitatively some differences are seen during perforation and fragmentation. As shown in results, good agreement between Ls-Dyna simulations and experimental data was achieved by Lagrange formulation with the full bullet model. (c) 2012 Elsevier Ltd. All rights reserved.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 Metadata only Improving Sound Absorption Property of Polyurethane Foams by Adding Tea-Leaf Fibers(POLSKA AKAD NAUK, POLISH ACAD SCIENCES, INST FUNDAMENTAL TECH RES PAS, 2012) KENTLİ, AYKUT; Ekici, Bulent; Kentli, Aykut; Kucuk, HalukThe sound absorption property of polyurethane (PU) foams loaded with natural tea-leaf fibers and luffa cylindrica (LC) has been studied. The results show a significant improvement in the sound absorption property parallel to an increase in the amount of tea-leaf fibers (TLF). Using luffa-cylindrica as a filler material improves sound absorption properties of soft foam at all frequency ranges. Moreover, an increase in the thickness of the sample resulted in an improvement of the sound absorption property. It is pleasing to see that adding tea-leaf fibers and luffa-cylindrica to the polyurethane foam demonstrate a significant contribution to sound absorption properties of the material and it encourages using environmental friendly products as sound absorption material in further studies.Publication Metadata only A NUMERICAL AND AN EXPERIMENTAL INVESTIGATION OF A HIGH-PRESSURE DIE-CASTING ALUMINUM ALLOY(SPRINGER INTERNATIONAL PUBLISHING AG, 2016) EKİCİ, BÜLENT; Boydak, Ozlem; Savas, Mahmut; Ekici, BulentIn this paper, a computer simulation of a high-pressure die casting of aluminum alloy was performed using a commercially available software and also compared with the real castings of the same alloy. The commercial aluminum alloy was Etial 150 (AlSi12Cu) that is used for flange which is a washing machine part. Mold filling, solidification, temperature distribution, porosity, and velocity of the liquid metal during high-pressure die casting were investigated using the model through numerical simulation. The simulation results proved that the model values used in simulations were accurate in order to apply for experimental casting. After this numerical model, the flange part was cast experimentally according to the obtained optimum parameters from simulation results. Then, specimens from the experimental casting were tested for tensile, hardness, and microstructure analyses. Accordingly, the test results are rather sound which demonstrates that simulation provides profitable die casting. Consequently, it was observed from this study that simulation is not only useful for enhancing casting quality but also very economical and practical, which helps to reduce time spent on experiments. Moreover, simulation can reveal porosity and helps to minimize this defect. Thus, computer simulation should be used for casting applications more often, and simulation programs should be developed further.Publication Metadata only Optimization of design parameters for Turkish Tirkes (war) bow(ELSEVIER SCI LTD, 2014) EKİCİ, BÜLENT; Demir, Sermet; Ekici, BulentThe bow and arrow is a projectile weapon system that predates recorded history and is common to most cultures. The Turkish bow is the most efficient one in its category. Despite of its superiority, Turkish bow is the one which is least documented in the literature. Technical drawings for the Turkish bow are missing. Turkish bow is a system consisting of different elements. Each element has its own distinctive feature and serves for a specific purpose. Recent interest in Turkish bow simply involves the replication of museum samples without any consideration about the performance characteristics of the replica. The present work aims at describing the Turkish bow, war bow known as Tirkes in specific. Characteristic shape parameters will be identified and the effect of each parameter on bow performance will be discussed. Parametric optimization to maximize bow efficiency will then be introduced. The bow shape will first be described. Characteristic shape parameters defining the bow geometry will be identified and the range in which they vary will be determined. The bow is drawn in the ANSYS (R) environment. Based on the design drawing a model bow is manufactured. Due to its superior flexing characteristics, E-glass fiber epoxy system is used in the composite structure. The model bow is tested to determine the characteristic draw weight - draw distance behavior of a typical bow. A mathematical model which is a simplified analysis of recurved bow types is used to compare behavior of model and manufactured bow draw weight - draw distance graph. Using ANSYS, bow is optimized over the related domain. Only geometrical parameters are considered. Bow length, width and thickness are varied over their domain of definition and their effect on the bow performance is investigated. Limb part is taken as the working element and is optimized for high deflection and low weight. The optimization process results in response charts showing the effect of the design variables on output. Sensitivity analyses of the input parameters resulted in the influence weight of each parameter and how each parameter affects the output. Using a goal-driven optimization approach, different design points were rate and the best design is identified. As compared to the effect of the other variable thickness is found to be the most influential variable affecting the draw weight. (C) 2014 Elsevier Ltd. All rights reserved.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 The Size of the Esophageal Hiatus in Gastroesophageal Reflux Pathophysiology: Outcome of Intraoperative Measurements(SPRINGER, 2010) GİRAL, ADNAN; Batirel, Hasan Fevzi; Uygur-Bayramicli, Oya; Giral, Adnan; Ekici, Buelent; Bekiroglu, Nural; Yildizeli, Bedrettin; Yueksel, MustafaThe aim of the study was to investigate the impact of the size of the esophageal hiatus on lower esophageal sphincter pressure (LESP) and acid reflux. Patients with gastroesophageal reflux disease who underwent Nissen fundoplication in 2006-2008 were included. All underwent esophageal manometry and 22 had 24-h pH monitoring. The area of the esophageal hiatus was calculated from a photograph shot during surgery. A hiatal index was calculated via division of hiatal area with body mass index (BMI). Correlation and logistic regression analysis were performed. Twenty-eight patients (average age 44, 14 males) were enrolled. The mean BMI, LESP, DeMeester score, hiatal area, and hiatal index were 27 +/- 3.9 kg/m(2), 11.7 +/- 6.6 mmHg, 43 +/- 34, 3.83 +/- 1.24 cm(2), and 0.143 +/- 0.048, respectively. There was a significant negative correlation between hiatal area, hiatal index and LESP (-0.513, p = 0.005, r = -0.439, p = 0.019 respectively). Additionally there was a negative correlation between hiatal area and total LES length (r = -0.508, p = 0.013) and a significant positive correlation between hiatal area, hiatal index, and DeMeester scores (0.452, p = 0.035, 0.537, p = 0.01, respectively). Height and hiatal area were significant factors in multiple linear regression. The size of the esophageal hiatus significantly affects LESP and acid reflux, and hiatal index is a new value, which appears to reflect the amount of acid reflux. Total LES length is also shortened in patients with a large hiatus.