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 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 Effects of residual stress patterns on TBC systems(MANEY PUBLISHING, 2004) EKİCİ, BÜLENT; Ekici, BIn recent studies, interfacial toughness in thermal barrier coating (TBC) systems was measured by indentation tests. The layers existing in the TBC systems were simplified to a system consisting of a coating and a substrate. The second simplification is that the residual stress values were taken as average values in the calculation. The types of residual stresses which may occur in TBC systems have not been studied. In the present paper, different residual stress patterns are applied to the model, and they are not taken as average values because some residual patterns are not scalar values but linear or parabolic functions. Results are presented for application in the measurement of the interfacial toughness of TBC systems using a simple indentation test simulation technique.Publication Metadata only DETERMINATION OF THE SHEAR-STRENGTH REQUIREMENT FOR THE ADHESIVE USED BETWEEN CAVITY FILLING MATERIALS AND DENTIN(ELSEVIER SCI LTD, 1993) EKİCİ, BÜLENT; EKICI, B; ALTINTAS, SA finite element technique is used to examine the stress distribution in a human first premolar with and without cavity preparation by using 2- and 3-dimensional models. The effects of different adhesive materials as cavity fillers on stress distribution are investigated. Since one of the most important factors affecting the success of a restoration process in clinical applications is the strength of the adhesive, the shear stresses obtained from numerical research are investigated in detail. Although in clinical applications the interfacial space between filling material and dentine is very important, it is assumed to be negligible here since it will not help in calculating the shear strength requirements of the adhesive. Therefore, one of the assumptions used throughout the analysis is that there are no interfacial spaces. In order to determine the effects of adhesive, all possible situations are included in the analyses. Different adhesives and different cavity filling materials are used in the model. In addition to these conditions, the effects of spring support conditions and temperature are also considered in the study.Publication Metadata only Probabilistic design of sheet-metal die by finite element method(ELSEVIER SCI LTD, 2008) EKİCİ, BÜLENT; Demir, Ilker; Kayabasi, Oguz; Ekici, BulentIn sheet-metal forming dies, highest stresses occur in bars which connect die to the frame. Considering fatigue behavior of bars with finite element method and probabilistic analyze provide many advantages predicting the life of dies in the design process. An effective and efficient design strategy is proposed to design sheet-metal die in order to reduce stress and increase fatigue life of sheet-metal die. In this strategy, finite element analysis, Approximate model, a numerical optimization algorithm and probabilistic design method Monte Carlo simulation are integrated to create an automated design tool. The reliability of the results are checked and refined by using probabilistic design techniques. Finally with the help of probabilistic design results, fatigue behaviors of the bars are predicted. At the end of the analysis process 43% volumes is gained. Stress value is 46.3% lower than the initial design. Safety factor of fatigue is reduced 36%. (C) 2007 Elsevier Ltd. All rights reserved.