Phd Degree / Doktora

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End date: 2009Department: search.filters.department.Thesis (Doctoral)--İzmir Institute of Technology, Mechanical Engineering

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Now showing 1 - 4 of 4
  • Doctoral Thesis
    Development of Multi and Double Walled Carbon Nanotubes (cnts) / Vinylester Nanocomposites
    (Izmir Institute of Technology, 2008) Seyhan, Abdullah Tuğrul; Tanoğlu, Metin
    This study focuses on development and characterization of thermosetting resin based nanocomposites containing multi and double walled carbon nanotubes with and without amine functional groups (MWCNT, DWCNTs, MWCNT-NH2 and DWCNTNH2).A novel 3-roll milling technique was conducted to prepare the resin suspensions with carbon nanotubes (CNTs). Rheological measurements performed on the resin suspensions showed that addition of very low contents (0.05, 0.1 and 0.3 wt. %) of MWCNTs and MWCNT-NH2 affected the flow characteristic of the resin, significantly.Further, the curing behavior of a vinylester-polyester hybrid resin suspensions containing 0.3 wt % of MWCNTs and MWCNT-NH2 was intensively studied. It was found that regardless of amine groups, presence of CNTs affected the polymerization of the hybrid matrix resin. Final individual fractional conversion rates of styrene and vinylester monomers were found to be vastly dependent on the type of CNTs. Glass transition temperature (Tg) values of the nanocomposites with MWCNTs and MWCNTNH2 were found to increase with filler content. Moreover, nanocomposites containing MWCNTs and MWCNT-NH2 were found to possess higher tensile strength, elastic modulus as well as fracture toughness and fracture energy as compared to the neat hybrid resin. On the other hand, electrical properties of the nanocomposites were also investigated and it was found that nanocomposites with MWCNTs exhibited the lowest percolation threshold value. In addition, nanocomposites with amino functionalized CNTs were found to exhibit lower electrical conductivity as compared to those with untreated CNTs. Nanocomposites with AC electric field induced aligned CNTs were also prepared. Finally, based on the findings obtained for CNT/ resin suspensions, as a case study, electrically conductive glass fiber reinforced composite laminates were successfully produced, using the CNT modified resin suspensions as matrix material, via Vacuum Assisted Resin Transfer Molding (VARTM) and Resin Transfer Molding (RTM) methods.
  • Doctoral Thesis
    Numerical Optimization of a Finned Tube Gas To Liquid Heat Exchanger
    (Izmir Institute of Technology, 2009) Bilir, Levent; İlken, Zafer
    The optimization of the fin and protrusion dimensions and shapes of finned tube gas to liquid heat exchangers are performed numerically in this thesis. The dimensions of a commercially available heat exchanger of a combi boiler apparatus are taken as basic dimensions and various parameters about plate fin and three different protrusions, namely balcony, winglet and imprint, are examined step by step. The study is realized within the geometrical dimension range used in actual applications. The numerical analyses of several heat exchangers are performed using Fluent CFD software. The boundary conditions used in the numerical investigation are taken from the actual operating conditions of the combi boiler heater apparatus. Firstly, the best plate fin geometry is determined. Secondly, the best protrusion dimensions are obtained. Finally, the effects of three protrusion placement on plate fin surface are examined. The fin I5B2W3 is determined as the best among the investigated fins. The use of actual operating conditions as boundary conditions and the investigation of the individual and cumulative effects of three different protrusions are the novelties of the study. In order to validate the numerical models, a comparison with a computational and experimental study performed by Wu and Tao is also made. The results of the models created for comparison purpose show good agreement with the results given by Wu and Tao. It is also observed that results obtained from the two alternatives for the modeling, one with symmetrical and the other with periodic boundary condition, are very close. According to these results, it is concluded that the numerical outcomes obtained in the present study are reliable.
  • Doctoral Thesis
    Analysis and Synthesis of Parallel Manipulators
    (Izmir Institute of Technology, 2008) Can, Fatih Cemal; Alizade, Rasim
    In this study, novel parallel manipulators are introduced for industrial and medical applications. New methods are developed for the structural synthesis of Euclidean platform robot-manipulators with variable general constraints (EPRM). New mechanical structures such as serial, parallel and serial-parallel EPRM are designed along with proposed method.A new dimensional synthesis method of two DoF planar and spherical seven link mechanisms is presented. Interpolation and least square approximations are used to design the mechanism. In the solution of dimensional synthesis problems, nonlinear equations are converted to system of linear equations. The motion generation problem of a 3 DoF platform robot manipulator is solved for three, four and five precision poses. It is shown that the synthesis problem can be solved analytically for three prescribed poses. However, the solution is achieved by using a numerical method for four and five poses. The result, which is obtained from three prescribed poses, is used as an initial guess for four and five poses. Kinematic analysis of the manipulators is investigated. After the derivation of vector-loop equations, inverse and direct position analyses of the manipulators are presented. Constant orientation workspace of a three DoF spatial parallel manipulator is presented. The mechanical elements which are necessary for the construction of manipulators are introduced. The information about the motors which is needed for actuation of manipulators is given. Three DoF parallel manipulator is constructed for a industrial packaging system. Assembly of manufactured parts and mechanical elements are shown.
  • Doctoral Thesis
    Optimization of the Axial Crushing Behavior of Closed-Cell Aluminum Foam Filled Welded 1050 Al Square-Cross Section Crashboxes
    (Izmir Institute of Technology, 2009) Toksoy, Ahmet Kaan; Güden, Mustafa
    The crushing behavior of partially Al closed-cell foam (Alulight AlSi10) filled 1050H14 Al crash boxes was investigated at quasi-static and dynamic deformation velocities. The quasi-static crushing of empty and filled boxes was further simulated using LS-DYNA. Finally, the crushing of partially foam filled 1050H14 crash boxes was optimized using the response surface methodology. The used optimization methodology was also applied to the boxes made of a stronger Al alloy, 6061T4 Al, and filled with a higher strength Al foam, Hydro Al closed cell foam, in order to clarify the effect of box material and foam filler strength on the crushing behavior of the filled boxes. Within the investigated tube thickness and foam relative density range, the energy absorption of 1050H14 boxes was optimized at 3 mm wall thickness and 0.1114 (Alulight) and 0.0508 (Hydro foam) foam filler relative density. The increase in specific energy absorption of 1050H14 crash box was 5.6% with Alulight and 21.9% for Hydro foam filling. The SEA values of empty, partially and fully foam filled boxes were predicted as function of box wall thickness between 1 and 3 mm and foam filler relative density between 0 and 0.2, using the analytical equations developed for the mean crushing loads. The analysis indicated that both fully and partially foam filled boxes were energetically more efficient than empty boxes above a critical foam filler relative density. Partial foam filling however decreased the critical foam filler density at increasing box wall thicknesses.