Mechanical Engineering / Makina Mühendisliği
Permanent URI for this collectionhttps://hdl.handle.net/11147/4129
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Article Citation - WoS: 2Citation - Scopus: 4A Study on a Computationally Efficient Controller Design for a Surgical Robotic System(Springer, 2023) Ayit, Orhan; Dede, Mehmet İsmet CanThe control algorithms of the surgical robotic system using the robot’s dynamics produce a relatively high computational load on the processor. This paper develops a computationally efficient computed torque controller by using a simplified dynamic modeling method and implemented in a novel surgical robot experimentally. In addition, an independent joint controller is designed and implemented to compare the results of the computed torque controller. © 2023, The Author(s), under exclusive licence to Springer-Verlag GmbH Germany, part of Springer Nature.Article Citation - WoS: 3Citation - Scopus: 1Corrosion Resistance and Mechanical Properties of Quenched and Tempered 28mncrb5 Steel in Two Acidic Environments(Carl Hanser Verlag, 2017) Yazıcı, Aysel; Zeybek, M. Sadrettin; Güler, Hüseyin; Pınar, Ahmet Murat; Tücer, RenasMicrostructure, hardness distribution, tensile properties and fracture behavior of the quenched and tempered steel 28MnCrB5 were investigated before and after corrosion tests. The corrosion behavior of the quenched and tempered steel 28MnCrB5 was examined in two different acidic environments, namely a hydrochloric acid solution and fertilizer-containing soil. The specimens were immersed in corrosive environments for 24, 48, 72, 96, 120, 144 and 168 hours, and additionally into fertilizer-containing soil for 240 days. The corrosion losses were determined by measuring the weight changes and the respective corrosion rates were calculated. Ductile fracture was observed in the sample of the quenched and tempered material before and after 168 hours of exposure to the hydrochloric acid solution and fertilizer-containing soil environment. But, in the sample subjected to corrosion in the fertilizer-containing soil environment for 240 days, brittle fracture took place and the fracture topography on the surface exhibited inter-granular cleavage. After 240 days of corrosion test in the fertilizer-containing soil environment, the ductility of the material decreased to a very great extent. The surface of the quenched and tempered 28MnCrB5 samples was covered by corrosion pits, cracks and peelings at the end of 168 h tests in the hydrochloric acid solution environment. At the end of 240 day tests in the fertilizer-containing soil environment, the surface of the samples showed deep peelings and cracks.Article Citation - WoS: 4Citation - Scopus: 5Effects of Tib2 Nanoparticle Content on the Microstructure and Mechanical Properties of Aluminum Matrix Nanocomposites(Walter de Gruyter GmbH, 2017) Kandemir, SinanThe present work reports the fabrication of A357 alloy matrix nanocomposites reinforced with 0.5, 1.0 and 2.0 wt.-% TiB2 nanoparticles (20-30 nm) by a novel method which is the combination of semi-solid mechanical mixing and ultrasonic dispersion of nanoparticles in liquid state. The microstructural and mechanical properties of the fabricated nanocomposites were investigated. The microstructural studies conducted with optical and advanced electron microscopes indicated that reasonably effective deagglomeration and uniform distribution of TiB2 nanoparticles into the matrix were achieved. Transmission electron microscopy studies also confirmed that the nanoparticles were embedded into the matrix and a good bonding was obtained between the matrix and the reinforcement. Increasing nanoparticle content led to grain refinement and significant enhancement in the mechanical properties of nanocomposites. The addition of 0.5, 1.0, and 2.0 wt.-% TiB2 nanoparticles increased the 0.2 % proof stress of matrix alloy by approximately 31, 48 and 61 %, respectively. The contribution of different mechanisms to the strength enhancement is discussed. It is proposed that the strengthening is mainly due to Orowan mechanism and dislocation generation effect by the coefficient of thermal expansion mismatch between the TiB2 nanoparticles and the matrix.Article Citation - WoS: 23Citation - Scopus: 24An Extended Kozeny-Carman Model for Gas Permeability in Micro/Nano-porous Media(American Institute of Physics, 2019) Sabet, Safe; Barışık, Murat; Mobedi, Moghtada; Beşkök, AliGas transport in micropores/nanopores deviates from classical continuum calculations due to nonequilibrium in gas dynamics. In such a case, transport can be classified by the Knudsen number (Kn) as the ratio of gas mean free path and characteristic flow diameter. The well-known Klinkenberg correction and its successors estimate deviation from existing permeability values as a function of Kn through a vast number of modeling attempts. However, the nonequilibrium in a porous system cannot be simply modeled using the classical definition of the Kn number calculated from Darcy's definition of the pore size or hydraulic diameter. Instead, a proper flow dimension should consider pore connectivity in order to characterize the rarefaction level. This study performs a wide range of pore-level analysis of gas dynamics with different porosities, pore sizes, and pore throat sizes at different Kn values in the slip flow regime. First, intrinsic permeability values were calculated without any rarefaction effect and an extended Kozeny-Carman model was developed by formulating the Kozeny-Carman constant by porosity and pore to throat size ratio. Permeability increased by increasing the porosity and decreasing the pore to throat size ratio. Next, velocity slip was applied on pore surfaces to calculate apparent permeability values. Permeability increased by increasing Kn at different rates depending on the pore parameters. While the characterization by the Kn value calculated with pore height or hydraulic diameter did not display unified behavior, relating permeability values with the Kn number calculated from the equivalent height definition created a general characterization based on the porosity independent from the pore to throat size ratio. Next, we extended the Klinkenberg equation by calculating unknown Klinkenberg coefficients which were found as a simple first order function of porosity regardless of the corresponding pore connectivity. The extended model as a combination of Kozeny-Carman for intrinsic permeability and Klinkenberg for apparent permeability correction yielded successful results. Published under license by AIP Publishing.Article Citation - WoS: 9Citation - Scopus: 12Void Fraction and Speed of Sound Measurement in Cavitating Flows by the Three Pressure Transducers (3pt) Technique(Elsevier, 2020) Esposito, Claudia; Yenigün, Onur; Gouriet, Jean-Baptiste; Steelant, Johan; Vetrano, Maria RosariaSpeed of sound and void fraction are two key parameters in the characterisation of two-phase flows. However, accurate measurements require either intrusive or complex techniques. This paper reports on the Three Pressure Transducers (3PT) technique, which derives the speed of sound by measuring pressure fluctuations and which, thanks to its robustness and simplicity, could be applicable in harsh conditions. Therefore, the aim of this paper is to study in detail the feasibility of this technique against its limits and constraints in a cavitating flow. First, a numerical assessment of the technique is proposed to determine both the optimal transducers configuration and the sampling frequency. Then, the implemented algorithm was applied to a two-phase air-water mixture with well-known properties. Finally, the 3PT algorithm was used to study the behaviour of a cavitating flow induced by an orifice. This last application highlighted the possibility to use this technique to characterize the bubble flow generated by an orifice without the use of any optical access and by using a very compact experimental arrangement. The results obtained are also qualitatively compared to the images of the flow simultaneously acquired by a high-speed camera.Article Citation - WoS: 16Citation - Scopus: 19A Novel Finite Element Model for Vibration Analysis of Rotating Tapered Timoshenko Beam of Equal Strength(Elsevier Ltd., 2010) Yardımoğlu, BülentA new finite element model based on the coupled displacement field and the tapering functions of the beam is formulated for transverse vibrations of rotating Timoshenko beams of equal strength. In the coupled displacement field, the polynomial coefficients of transverse displacement and cross-sectional rotation are coupled through consideration of the differential equations of equilibrium. The tapering functions of breadth and depth of the beam are obtained from the principle of equal strength in the longitudinal direction of the beam. After finding the displacement functions using the tapering functions, the stiffness and mass matrices are expressed by using the strain and kinetic energy equations. A semi-symbolic computer program in Mathematica is developed and subsequently used to evaluate the new model. The results of the illustrative example regarding the problem indicated in the title of this paper are obtained and compared with the results found from the models created in ABAQUS. Very good agreement is found between the results of new model and the other results. © 2010 Elsevier B.V.