Person: EKİCİ, BÜLENT
Loading...
Email Address
Birth Date
Research Projects
Organizational Units
Job Title
Last Name
EKİCİ
First Name
BÜLENT
Name
21 results
Search Results
Now showing 1 - 10 of 21
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 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 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 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.
- «
- 1 (current)
- 2
- 3
- »