Omer Keles
Gazi University
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Publication
Featured researches published by Omer Keles.
Journal of Materials Engineering and Performance | 2007
Faleh A. Al-Sulaiman; B.S. Yilbas; C. Karatas; Omer Keles; Ibrahim Uslan; Yusuf Usta; M. Ahsan; A. Bazoune
In the present study laser cutting of composite structure, consisting of Kevlar laminate at the top and mild steel sheet at the bottom, is considered. The end product quality is assessed using the thermal cutting standards. To compare the end product quality of composite structure cuts, Kevlar laminate and mild steel sheet are cut using the same cutting parameters. The kerf widths for Kevlar laminate and mild steel sheet cuts are predicted from the analytical formulation based on the lump parameter analysis. It is found that the end product quality of composite structure cuts is lower than that corresponding to Kevlar laminate and mild steel sheet cuts.
Machining Science and Technology | 2013
B.S. Yilbas; S. S. Akhtar; Omer Keles
Laser cutting of large diameter hole in aluminum foam is carried out and morphological changes in the cutting section are examined using scanning electron microscopes, energy dispersive spectroscopy and X-ray diffraction. The thermal stress fields in the cutting section are computed in line with the experimental conditions. Finite element code is incorporated in the numerical simulations. It is found that the cut section is free from defects such as large size burrs and dross attachments. The thermal stress predicted is less than the yielding limit of the workpiece. The presence of air trapped within the pores prior to laser irradiation in the workpiece results in the formation of oxide compounds at the cut sections.
Powder Metallurgy | 2011
M Übeyli; A Acır; Omer Keles; C E Akçay
Abstract This paper presents the effect of main cutting parameters on cutting force and surface roughness in machining of alumina reinforced Al–6Zn–2Mg–2Cu composites. The composites were produced using powder metallurgy route. After an application of annealing heat treatment to these composites, their microstructural and mechanical characterisations were carried out. Then, machining was performed using the face milling operation with three different cutting tools and at various cutting speeds and feed rates for comparison. Results show that both cutting force and surface roughness increased with increasing the feedrate significantly. Furthermore, the cutting speed practically did not affect the cutting force in milling operation.
Materials and Surface Engineering#R##N#Research and Development | 2012
B.S. Yilbas; S. S. Akhtar; Omer Keles
: Laser straight cutting of titanium alloy is carried out. Thermal stress fields in the cutting section are examined using the finite element numerical code. The morphological changes in the laser cutting region are investigated using optical microscopy, scanning electron microscopy and x-ray diffraction technique. It is found that von Mises stress attains high values in the vicinity of the top and bottom surfaces as well as at the mid-thickness of the workpiece. Some small sideways burns in the cut section are observed, which are associated with the high temperature oxidation variations during the cutting process. Due to the brittle structure in the re-cast layer, a few locally scattered microcracks are observed at the re-cast layer surface.
Advances in Materials and Processing Technologies | 2015
Omer Keles; B.S. Yilbas
Abstract Laser gas-assisted cutting of aluminium alloy is carried out and nitrogen at high pressure is used in the cutting section to prevent oxidation reactions during the cutting process. Morphological changes in the cutting section are examined using optical and scanning electron microscopes and kerf width size is examined at the front and back surfaces of the cutting section using the moving microscope. The lamp parameter analysis is introduced to determine the kerf width size for different laser cutting speeds, and the predictions are compared with the experimental data. It is found that predictions of the kerf width size agree well with the experimental data. The laser cutting section is free from large size asperities, such as large size cracks. Some small dross attachments are observed at the back surface of the cutting section. The dross attachments are local and do not extend along the kerf edges.
Archive | 2013
B.S. Yilbas; S. S. Akhtar; Omer Keles
In laser cutting process, thermal stress is formed around the cut edges, which becomes important for the geometries having the corners. In the present study, laser cutting of triangular shape in aluminum foam is carried out. Temperature and stress fields are predicted using a finite element method in line with experimental conditions. Metallurgical and morphological changes in the cut sections are examined incorporating scanning electron microscope (SEM) and energy-dispersive spectroscopy. It is found that the cut sections are free from defects such as sideways burning and large-scale burrs. von Mises stress is high in the corners of the triangular-shaped laser cut workpieces.
Advanced Materials Research | 2012
Ibrahim Uslan; S. Erdogan; Omer Keles; Yusuf Usta; B.S. Yilbas; B. Tuc
Parameters on a CO2 laser machine effects the variations on hole diameters. In this study, a CO2 laser machine is used for drilling processes. Processing parameters are selected between 1.2-4 mm workpiece thickness, 2500-4000 W laser output power, -4 to 2 laser focus setting, 8-14 bar assisted gas pressure and 500-1200 Hz laser frequency. After the drilling process, with the diameter measurements, pictures were taken with an optic microscope then the effect of the processing parameters on hole diameter variations were investigated.
Advanced Materials Research | 2009
M. Sunar; Omer Keles
Quasi-static equations are presented for a magnetostrictive medium where mechanical and magnetic fields interact with each other. Finite element method is used in conjunction with the Hamiltons principle to deduce equations for the dynamic behavior of the magnetostrictive material. These equations form the basis for the magnetostrictive material to be utilized as a sensor or as an actuator. When used as an actuator, the material can provide enough power to actuate mechanical systems for vibration control. In this work, a cantilever beam with a magnetostrictive actuator is taken to demonstrate the modeling and use of the magnetostrictive actuator in attenuating structural vibrations. The position of the actuator is changed to observe its effect on the response of the system. This is important because it is a well-known fact that the actuator location has impact, sometimes big, on its performance.
Journal of Materials Processing Technology | 2006
C. Karatas; Omer Keles; Ibrahim Uslan; Yusuf Usta
Applied Surface Science | 2006
B.S. Yilbas; C. Karatas; Uslan; Omer Keles; I.Y. Usta; M. Ahsan