Person: EKİCİ, BÜLENT
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EKİCİ
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BÜLENT
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Publication Metadata only Influence of occlusal forces on stress distribution in preloaded dental implant screws(MOSBY-ELSEVIER, 2004) EKİCİ, BÜLENT; Alkan, I; Sertgoz, A; Ekici, EStatement of problem. Abutment and prosthetic loosening of single and multiple screw-retained, implant-supported fixed partial dentures is a concern. Purpose. The purpose of this study was to investigate stress distribution of preloaded dental implant screws in 3 implant-to-abutment joint systems under simulated occlusal forces. Material and methods. Three abutment-to-implant joint systems were simulated by using the 3-dimensional finite element analysis method: (1) Branemark external hexagonal screw-retained abutment, (2) ITI 8-degree Morse tapered cemented abutment, and (3) ITI 8-degree Morse tapered plus internal octagonal screw-retained abutment. A thermal load and contact analysis method were used to simulate the preload resulting from the manufacturers' recommended torques in implant screw joint assemblies. The simulated preloaded implants were then loaded with 3 simulated static occlusal loads (10 N; horizontal, 35 N; vertical, 70 N; oblique) on the crown position onto the implant complex. Results. Numeric and graphical results demonstrated that the stresses increased in both the abutment and prosthetic screws in the finite clement models after simulated horizontal loading. However, when vertical and oblique static loads were applied, stresses decreased in the external hexagonal and internal octagonal plus 8-degree Morse tapered abutment and prosthetic screws with the exception of the prosthetic screw of ITI abutment after 70-N oblique loading. Stresses increased in the ITI 8-degree Morse tapered cemented abutment after both vertical and oblique loads. Conclusion. Although an increase or decrease was demonstrated for the maximum calculated stress values in preloaded screws after occlusal loads, these maximum stress values were well below the yield stress of both abutment and prosthetic screws of 2 implant systems tested. The results imply that the 3 implant-to-abutment joint systems tested may not fail under the simulated occlusal forces.Publication Metadata only The effects of static, dynamic and fatigue behavior on three-dimensional shape optimization of hip prosthesis by finite element method(ELSEVIER SCI LTD, 2007) EKİCİ, BÜLENT; Kayabasi, Oguz; Ekici, BulentThe finite element method, one of the most advanced simulation techniques in solid mechanics, is used for orthopedic biomechanics. It is used as a tool for the design and analysis of total joint replacement and other orthopedic devices. The design of hip joint prostheses is a complex process that requires close co-operation between engineers and surgeons. To design highly durable prostheses one has to take into account the natural processes occurring in the bone. One of the most important factors in the implant design is to reduce stress on the femur and the bone-cement. The purpose of this study is to investigate the behavior of newly designed implants under body weight load during stumbling by parametric modeling. Two different implant materials have been selected to study appropriate material and fatigue life resistant. In the parametric design, the prosthesis functional requirement is that the locking of stem to the femur head using cement should be strong enough to preclude unlocking during the life time of a patient and to prevent sliding of the implant into the bone-cement. In the finite element analysis, physical interactions among joints are simulated by contact algorithms. The femur-bone-cement interface and the bone-cement-implant interface surface to surface contact algorithms of ANSYS were used for implicit static analysis. Three stem-cement interface conditions are considered: completely bonded, debonded with coefficient of friction 0, and debonded with coefficient of friction 0.2. In the analysis, a viscoelastic material model is utilized for bone-cement. Numerical shape optimization is applied to the prosthesis. The results of finite element simulations are compared with Charnley's implant results and appropriate material for the implant is proposed. The best stem shapes fulfilling the desired functional requirements are chosen for the design. These findings can form a base for further research such as the optimum design of bone-implant hip prosthesis. (C) 2006 Published by Elsevier Ltd.Publication Metadata only Static, dynamic and fatigue analysis of a semi-automaticgun locking block(PERGAMON-ELSEVIER SCIENCE LTD, 2009) EKİCİ, BÜLENT; Ozmen, Dogan; Kurt, Mustafa; Ekici, Bulent; Kaynak, YusufReduction of the recoil forces on shotgun parts and even effects on the human body are a considerable importance during design of the semi-automatic shotgun parts. These forces are strongly affected by the dynamics of motion of rifle parts upon firing. Therefore, managing of these recoil forces would be crucial issue to produce functional, ergonomic, safe, reliable, and robust designs. in the literature, many researchers have investigated static, dynamic, and fatigue behaviors of most mechanical parts which especially take a role under the dynamic loads. However, shotgun parts have not been investigated formally yet. Therefore, in this study we particularly focused on investigating static, dynamic, and fatigue behaviors of a semi-automatic shotgun's locking block, which is an integral part of the shotgun mechanism during firing. In this study, techniques such as hardness measurements, analysis of the recoil forces of a semi-automatic shotgun, and finite element analysis were performed. Pro/Engineer Wildfire 3.0 series software was used to model the locking block and the other parts of the gun. Moreover, the finite element code ANSYS/LS-DYNA, and ANSYS Workbench were used to determine the stress distribution, and fatigue behaviors of the locking block, based on the Morrow Theorem. (C) 2009 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 Metadata only Probabilistic design of a newly designed cemented hip prosthesis using finite element method(ELSEVIER SCI LTD, 2008) EKİCİ, BÜLENT; Kayabasi, Oguz; Ekici, BulentThe finite element method is an important tool used in the design of orthopedic prosthesis. One of the important orthopedic applications is hip prosthesis replacement. This operation is so complex that it requires close co-operation between engineers and surgeons. They have to work together in order to produce durable and reliable hip joint prosthesis. The reason for this is that the nature of bone strongly affects the design. In reality, uncertainties exist in the system and environment that may make the application of a deterministic design decision unreliable. That is, the values of the variables that are acting on the system cannot be predicted with certainty. For instance, probabilistic approach was applied to the model after deterministic design results. Thus, using probabilistic approach reliability of newly design cemented hip prosthesis was quantified. The new design is modeled parametrically to investigate the effects of different geometrical parameters on the relative displacement. These parameters are then optimized. Using the results of this investigation, the probability of failure was investigated for both the initial and shape-optimized prosthesis designs using several simple performance functions describing fatigue theory (Goodman, Gerber, Soderberg), static and dynamic failure of the cement-pros thesis interface. The optimum geometry and material properties are then compared with Charnley's implant results. 0 2007 Elsevier Ltd. All rights reserved.Publication Metadata only Automated design methodology for automobile side panel die using an effective optimization approach(ELSEVIER SCI LTD, 2007) EKİCİ, BÜLENT; Kayabasi, Oguz; Ekici, BulentIn this study, two approaches are proposed to improve formability of an automobile side panel. In the first approach, the effect of using double binder on springback, wrinkling and thickness reduction is studied. In the second approach, the use of optimization method in further improving formability of the automobile panel is investigated. With the optimization method, the most appropriate values of forming process parameters are calculated for optimum formability characteristics. Positions of the upper die and draw-bead, draw-bead radius, forces applied on the upper die surface and double binder surfaces are considered as process parameters. In finding optimum values, finite element analysis, response surface methodology and genetic algorithm are integrated. To achieve efficient and effective integration, a computer program is written. From this study it is observed that double binder with an appropriate stamping force improves formability significantly. Application of optimization method also improves further formability characteristics of the automobile panel. (c) 2006 Elsevier Ltd. All rights reserved.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.