Phd Degree / Doktora
Permanent URI for this collectionhttps://hdl.handle.net/11147/2869
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Doctoral Thesis Dynamic Wear Simulations of Hip Implants for Daily Life Activities(01. Izmir Institute of Technology, 2024) Alpkaya, Alican Tuncay; Mihçin, ŞenayTotal hip replacement is widely used around the world for patients whose hip joints lost their functionality. Despite its wide applications and technological developments taking place in the recent years, it still does not produce near-perfect results. It has been observed that many patients with implants have their range of motion often restricted. Although there has been literature covering the daily life motion profiles in Western societies, , it has been observed that a through database of activities including sitting, worship, and lifestyles suitable for Middle Eastern societies is non-existent.Therefore, it is difficult to determine the lifespan of implants used especially in these societies and to determine their wear rates with accuracy. In this thesis, I have utilized the first comprehensive database of daily activities of Turkish population, which was formed using the state-of-the-art motion capture (MOCAP) technologies at Biomechanics and Motion Capture Laboratory of IZTECH. The range of motion and reaction force data were calculated using the inverse kinematics and kinetics methods previously. This previously calculated boundary conditions are fed into the finite element models of hip implants to simulate ten distinct daily life activities Asian style sitting, normal walking cycle, obstacle crossing, Stoop lifting, Squat lifting, Ruku' and I'tıdal, Ruku to Sujud, Sujud, Ascending stairs, and Descending Stairs. The dynamic simulations of hip implants under these boundary conditions are performed in this thesis. In this thesis, a computational wear methodology is utilized to assess the wear performance of hip bearing surfaces under these boundary conditions. Each comprehensive computational wear simulations of each of these daily life activities over five million cycles is performed to provide omputational evidence on the wear rates to assess the wear performance of the bearing couple. The wear prediction model could be utilized to provide guidance on the design parameters with the aim of prolonging the life span of hip implants.Doctoral Thesis Experimental and Numerical Investigation of the Impact Resistance and Impact Damage Tolerance of a Carbon Fiber Reinforced Thermoplastic Polyphenylene Sulfide (pps) Matrix Composite(01. Izmir Institute of Technology, 2024) Seven, Semih Berk; Güden, Mustafa; Taşdemirci, AlperThe impact resistance and impact damage tolerance of an aerospace grade high performance 5 Harness Satin woven fabric carbon fiber reinforced/polyphenylene sulfide matrix (CF/PPS) thermoplastic composite were investigated experimentally and numerically. The numerical modeling was performed using the experimentally determined parameters of material model MAT-58 and Hashin failure criteria in LS-DYNA using the single shell and stacked shell models. The numerical models of the low velocity impact (LVI) tests showed good correlations with the experimental tests while the stacked shell model showed nearer results with the experimental tests. The stacked shell model also estimated the LVI test delamination areas, which were comparable with the experimental damage areas. The LVI tested coupons were further subjected to the compression after impact (CAI) tests in order to determine the damage tolerance of CF/PPS composite. The CAI tests were modeled using the single shell model. The numerical models of the CAI tests showed very similar trends with the experimental CAI tests. The trends were shown to be more converging in the specimens tested at 3 m/s and above in the LVI tests. Lastly, three high velocity impact (HVI) tests were performed at around 100 m/s. The failure mode of the HVI tests was shown to be very different from that of the LVI tests. The long longitudinal and transverse cracks were formed in the HVI tests. The delamination damage in the HVI tests determined using the stacked shell model was found to be more comparable with the experimental delamination damage determined by the C-Scan.Doctoral Thesis Designing Composite-Based Cylindrical Structures and Manufacturing Composite Prototypes by Filament Winding Method(01. Izmir Institute of Technology, 2024) Martin, Seçkin; Tanoğlu, MetinThis study reports the design, finite element modeling, optimization, fabrication and testing of relatively thick (radius/thickness ~ 7) and long carbon fiber reinforced polymers produced by filament winding against buckling damage under axial loading. The optimum winding angle and stacking sequence against Linear (Eigenvalue) buckling were determined in accordance with the predetermined design requirements utilizing genetic algorithm (GA) optimization via MATLAB. During the optimization process, the critical buckling load factor (λcr) was assigned as objective function, design constraints were natural frequency (fn) and angle of twist (Φ), and ply angles were considered to be variable and restricted with 20 to 87-degree continuous fiber angles in the laminate sequences. As a consequence of the test results, λcr of the proposed optimum model was found to be 3.2 times better than the reference model and both the analytical and finite element model satisfactorily predicted the critical buckling load for all CFRP rods consistent with the test results. The critical buckling loads calculated by applying a KDF of 0.95 for the finite element model and a KDF of 0.9 for the analytical solution were found to be reasonably appropriate for use in the preliminary design input. Additionally, results showed that a higher axial to the circumferential ratio of axial and bending stiffness (A11/A22, D11/D22) promises better buckling performance than other possible candidates. Finally, the microstructures of the produced rods were examined and the fiber volume ratios were calculated by means of chemical characterization.Doctoral Thesis Advanced Material Characterization and Modeling the Foreign Body Impact Damage Initiation and Progression of a Laminated Carbon Composite(01. Izmir Institute of Technology, 2023) Bayhan, Mesut; Taşdemirci, Alper; Güden, MustafaThe coupon level composite sample tests and the accompanying numerical models were carried out to predict the response of woven carbon fiber composite structures against impact. The numerical models of the coupon-level tests were implemented in LSDYNA software using the MAT_162 and MAT_58 composite material models. The results obtained by both quasi-static and dynamic tests were used to determine their constants. In addition to the tests that were used for the determination and calibration of the material model parameters, separate tests and their models were performed for the validation, including punch shear tests and low-velocity impact tests. It could be said that the material models examined were considered comprehensive and precise as the experimental results were well predicted by the numerical models. Also, the rate sensitivity of the woven carbon composite in the in-plane and thickness directions was investigated experimentally and numerically. In the tests, the DIC method was employed in the determination of the displacement and strain of the specimen. Based on the results obtained, it was concluded that the in-plane tensile properties are rate insensitive. Besides, the simulations of the component level tests, such as bird strike and drone impact, were established to investigate the damage initiation and propagation within the composite. It was found that the drone impact results in more severe damage compared to the bird impact. It is worth noting that the development of such precise composite material models to simulate dynamic loadings will definitely shorten the time between the beginning of designing and the component testing.Doctoral Thesis Geometric Properties of Coupler-Curve Equation of Planar Slider-Crank and Four-Bar Linkages(01. Izmir Institute of Technology, 2022) Eraz, Talha; Kiper, GökhanThis thesis study focuses on coupler-curve of planar slider-crank and four-bar mechanisms. The geometric properties of the coupler-curve equations are investigated. The coupler-curve equations of both slider-crank and four bar mechanisms are shown to consist of quadratic and linear components. The quadratic components that appear in the coupler-curve equations are circles which determine the area the coupler-curve may be located. The path generation problem of the slider-crank mechanism is another aspect of this thesis. A limited solution to the path generation problem is introduced and tested numerically. A method that is a combination of the discovered geometric properties of the coupler-curve and numerical approximation methods is introduced. The solution approach works for the task of fitting a coupler-curve on a cluster of points and five precision points problem.Doctoral Thesis Compliant Control of Robotic Co-Workers in Surgical Applications(01. Izmir Institute of Technology, 2023) Ayit, Orhan; Dede, Mehmet İsmet CanIn recent years, robots have taken place in surgical operations due to their advantages over humans, such as power, endurance, dexterity, and accuracy. Because of the lack of abilities, such as decision-making, adaptability, and creativity, human surgeons supervise the robots. The robots share the operation places with humans, called co-worker robots. Robots have the power to harm their environment; therefore, robots can generate dangerous situations for surgeons and patients. To deal with the issues, this dissertation aims to design active compliant control algorithms such as impedance control, admittance control, and hybrid position/force control to achieve safe interaction forces in surgical operations by considering the performance. The surgical co-worker robot’s type, actuation system, robot dynamics, and environment dynamics are important factors for designing the active compliant controller. Besides these, stability and robustness for safety, and agility and human effort for performance are considered for designing the controller. This dissertation takes into account three interaction scenarios encountered in surgical operations. In these scenarios, it is expected from the co-worker robot that it adapts to the sudden change in its environment dynamics. For instance, safe interaction is desired when the robot interacts with the stiff and soft tissues. To handle the issue, a switching control methodology is presented where the predefined control parameters are switched according to their environments. The methodology is implemented in a novel co-worker robot named NeuRoboScope, designed to assist the endoscopic pituitary gland surgery with the support of The Scientific and Technological Research Council of Turkey (TUBITAK). Moreover, active compliant control algorithms require a motion control algorithm as a low-level controller. In this dissertation, the computed torque method and independent joint controllers with gravity compensation are used as motion control algorithms. The computed torque method requires the dynamic model of the robot. Due to that, the dissertation proposes a simplified dynamic model with a correction coefficient for computational efficiency. ARM Cortex M4 processor runs the computed torque method with the proposed dynamic modeling method at 500 Hz. Also, this dissertation presents an independent joint controller which uses the simplified gravity matrix as a feedforward term for compensating the NeuRoboScope’s gravitational effect. The experimental results of both controllers are discussed in this dissertation.Doctoral Thesis Experimental Investigation of a Hybrid Thermal Management System for an Electric Vehicle Battery Module(Izmir Institute of Technology, 2022) Coşkun, Turgay; Çetkin, ErdalEnvironmental concerns and limited energy sources of the world are driving force in electric vehicle technology improvements. One of the main components of the electric vehicles is battery cell. Using batteries in electric vehicles brings up new concerns such as safety problems, limit of range and so on. The temperature of the battery cell increases during charging/discharging and operation. There is an optimal temperature range (15ºC ─ 35ºC) for battery cells to maximize efficiency and prevent safety issues. The high temperature values in the battery cells can be result with fire and explosion. In addition, the performance of the battery cells is highly affected by operating temperatures. Therefore, thermal management of the battery cells is a necessity to overcome safety issues and maximize the battery performance. The feasibility of microchannel heat sink for battery cooling is investigated numerically and it is decided to continue with conventional length scales because of the higher pressure drop values in micro scales. Thus, a hybrid cooling system, using air and liquid solely or simultaneously, is developed and is introduced to a battery module. The battery module created by connecting three lithium-ion pouch cells in serial. According to the results, air cooling gives the more homogeneous temperature distribution. The lowest temperature values are observed in hybrid cooling system and temperature difference between the cells are reduced by 30% when compared to the water-cooling system. The temperature profile in air cooling shows that any increase in the ambient temperature (23ºC) or discharge rate will undergo a temperature rise in battery cells and optimal temperature ranges will be exceeded in that case. A step function, in a sequence of various discharge rate, is introduced to the battery module to determine cooling capacity of the air system during operation. The result show that the temperature of the cells is kept below 30ºC. The hybrid cooling is enabled to select cooling systems for the battery module with respect to operating condition; hence, the efficiency of the system is increased.Doctoral Thesis Numerical Investigation of Gas Transport Through Micro/Nano-scale Porous Media at Slip Flow Regime(Izmir Institute of Technology, 2021) Sabet, Safa; Barışık, MuratGas flow in micro/nano-scale porous systems is observed in many applications and technologies. Gas dynamics at such small scales differ from conventional fluid dynamics estimations due to rarefaction effects. In the literature, the Knudsen number (Kn) for the characterization of rarefaction effects on permeability is calculated based on a characteristic flow height estimated from the pore size, while the geometric parameters such as pore shape and pore-throat ratios are mostly ignored. Therefore, an accurate characterization of rarefaction effects could not be ascertained. For the first time in literature, a general characterization of gas transport through systems at different porosity and pore throat size values and at different rarefaction levels was obtained using a modified Kn definition. The characteristic height required for an accurate Kn of a porous system is defined using the "equivalent diameter" calculated from the corresponding permeabilities. Pore-level calculations were performed in a wide range of systems while the observed permeability variation by porous parameters was successfully described by an extended volume-averaged model developed as a combination of the Darcy, Kozeny-Carman, and Klinkenberg models. The characterization systematic and volume-averaged model was applied for various cases of (i) two-dimensional porous, (ii) two-dimensional multi- porous, and (iii) three-dimensional complex porous system. For all these systems, the permeability values could be estimated in terms of the geometric parameters of the porous structures and rarefaction levels. In addition, the rarefaction effects on heat convection in metal foams were studied through Darcy to Forchheimer flow regimes using the Kelvin Cell structure. A 60% increase in permeability and a substantial decrease in inertial effects developed due to rarefaction, while Nusselt numbers were found mostly related to Reynolds number. Further, the influence of variation in gas thermophysical properties coupled with rarefaction as a function of increasing gas temperature for high heat flux applications was described. A 40% decrease in hydraulic conductivity for a temperature increase from 300K to 400K is observed, independent from the Kn number.Doctoral Thesis Molecular Dynamics Studies on Interface Heat Transfer Control Using Electric Field(Izmir Institute of Technology, 2021) Yenigün, Onur; Barışık, MuratThermal management is considered as a bottleneck for the development of next generation micro/nano-electronics with high heat dissipation rates. When component sizes decrease to nanoscales, increase in surface to volume ratio leads the interfacial thermal resistance (ITR) to dominate the heat transfer behavior. The current study focuses on characterizing ITR at molecular level and exploring smart thermal management concepts for nano-scale systems. In sequence, the effect of solid thickness on ITR was investigated such that the altered phonon spectrum inside the solid domain creating the size dependency on thermal conductivity was also found to create a size dependency in ITR. Next, an active and local manipulation of heat transfer between water and various solids by an applied uniform and/or non-uniform electric field was examined. When the water molecules underwent electric field induced orientation polarization and liquid dielectrophoresis (LDEP), a substantial increase in heat transfer was developed due to the decrease in ITR and increment in thermal conductivity. Finally, an interface-localized heat transfer control technique was proposed, where interdigitated electrodes (IDEs) were embedded into the heat dissipating surface. IDEs created an electric field gradient exclusively near the electrode surface which resulted in LDEP forces on the water dipoles at near surface region enhancing solid/liquid interface energy and almost eliminating the ITR. We developed semi-empirical and theoretical relations to describe ITR variation by the electric field, which will be important for thermal management of current and future technologies.Doctoral Thesis Development and Characterization of Innovative Fiber Reinforced Prepregs and Their Composites Containing Functional Fillers(Izmir Institute of Technology, 2021) Uz, Yusuf Can; Tanoğlu, MetinThis Ph.D. thesis aims to prepare laboratory-scale carbon fiber reinforced prepregs and improve the performance of their composites by incorporating functionalized single-wall carbon nanotubes (SWCNTs). The effect of nano-scale functional fillers on the characterization of prepregs and their composites was investigated to develop innovative materials for primary structures. To affect dispersion characteristics, SWCNTs were functionalized by oxidizing their surface with the carboxyl (-COOH) group using acid treatment. The modified resin system containing 0.05, 0.1, and 0.2 wt. % F-SWCNTs were developed with novel multi-step dispersion techniques. FTIR spectroscopy was performed to identify new bonding groups formed after the covalent functionalization. Unidirectional carbon fiber reinforced prepregs with/without F-SWCNTs were prepared using a drum-type winding technique by utilizing the solvent-dip (solution impregnation) process. The effect of F‐SWCNTs on the curing process and kinetic parameters of the carbon fiber/epoxy-based prepregs were investigated using non‐isothermal DSC. The activation energy of the curing reaction was calculated by the isoconversional methods. Also, the new numerical approach called GMN was developed to determine the activation energy of the thermosetting materials. For the fabrication of prepreg-based composite laminates, the vacuum bag-only (VBO) method was performed. The fiber volume fractions of the CFRP samples changed between 55.3% and 50.16%. The mechanical and thermomechanical properties of prepreg-based CFRP composites with/without F-SWCNTs were investigated. The optimum mechanical properties of F-SWCNTs filled CFRP composite was achieved at 0.05 wt.% of F-SWCNTs. However, mechanical properties were decreased due to the addition of higher content of F-SWCNTs, in comparison with neat CFRP.