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 The similar and dissimilar spot welding of 304 and 316l austenitic stainless steels(2017-11-01) ÇINAR, ÖZGÜR; ÇETİNER, BURCU NİLGÜN; GÜLLÜOĞLU, ARİF NİHAT; EKİCİ, BÜLENT; ÇINAR Ö., ÇETİNER B. N., TOPCU İ., GÜLLÜOĞLU A. N., EKİCİ B.Publication Open Access Ballistic behavior of high hardness perforated armor plates against 7.62 mm armor piercing projectile(ELSEVIER SCI LTD, 2014-11) EKİCİ, BÜLENT; Kilic, Namik; Bedir, Said; Erdik, Atil; Ekici, Bulent; Tasdemirci, Alper; Guden, MustafaIn this paper, some of the important defeating mechanisms of the high hardness perforated plates against 7.62 x 54 armor piercing ammunition were investigated. The experimental and numerical results identified three defeating mechanisms effective on perforated armor plates which are the asymmetric forces deviates the bullet from its incident trajectory, the bullet core fracture and the bullet core nose erosion. The initial tests were performed on the monolithic armor plates of 9 and 20 mm thickness to verify the fidelity of the simulation and material model parameters. The stochastic nature of the ballistic tests on perforated armor plates was analyzed based on the bullet impact zone with respect to holes. Various scenarios including without and with bullet failure models were further investigated to determine the mechanisms of the bullet failure. The agreement between numerical and experimental results had significantly increased with including the bullet failure criterion and the bullet nose erosion threshold into the simulation. As shown in results, good agreement between Ls-Dyna simulations and experimental data was achieved and the defeating mechanism of perforated plates was clearly demonstrated. (C) 2014 Elsevier Ltd. All rights reserved.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 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 Open Access Sustainable machining of the magnesium alloy materials in the CNC lathe machine and optimization of the cutting conditions(KAUNAS UNIV TECHNOL, 2014-06-25) BAKIR, BARKIN; Eker, Beni; Ekici, Bulent; Kurt, Mustafa; Bakur, BarkinIn this study, MQL turning performance was compared to dry conditions. The magnesium based material will be formed by applying the orthogonal cutting. The CNC Lathe shall be used for both cutting processes. The experiment used MINITAB 16 software to establish the experiment plan. In this study, workpiece was turned at cutting speeds of 230, 330 and 430 m/min, feed rates of 0.20, 0.35 and 0.50 mm/rev and cutting depth of 1, 2 and 3 mm. Taguchi experimental design method was used for determining the settings of turning parameters. Orthogonal arrays of Taguchi, the signal-to-noise (S/N) ratio, the analysis of variance (ANOVA) were carried out to determine the optimum levels and to analyze the influence of cutting speed, feed rate, cutting depth on surface roughness, temperature and cutting forces during dry and MQL turning.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.
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