The Experts below are selected from a list of 303 Experts worldwide ranked by ideXlab platform
Bekir Sami Yilbas - One of the best experts on this subject based on the ideXlab platform.
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Analytical methods in laser cutting
The Laser Cutting Process, 2018Co-Authors: Bekir Sami YilbasAbstract:In some laser cutting processes, laser repetitive pulses are more favorable than laser continuous wave heating. The presence of assisting gas generates cooling effects at the surface while modifying the thermal field in the Irradiated Region. Thermal stress analysis incorporating the convection cooling of the surface becomes necessary. Two-dimensional heating of metallic substrates, with a constant velocity of a moving laser beam, results in nonsymmetric isothermal lines in the Irradiated Region of the substrate material. When the beam is focused onto a plane surface, a fraction of the beam is reflected and the rest is absorbed by the substance. The influence of assisting gas, including the cooling and exothermic reaction contribution on the cutting process, needs to be modeled prior to dross formulation. The liquid film formed at the solid surface due to a laser irradiation pulse is modeled and dross formation is analyzed using a Lump parameter analysis.
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Laser pulse heating of steel mixing with WC particles in a Irradiated Region
Optics & Laser Technology, 2016Co-Authors: Shahzada Zaman Shuja, Bekir Sami Yilbas, Haider Ali, Cihan KaratasAbstract:Abstract Laser pulse heating of steel mixing with tungsten carbide (WC) particles is carried out. Temperature field in the Irradiated Region is simulated in line with the experimental conditions. In the analysis, a laser pulse parameter is introduced, which defines the laser pulse intensity distribution at the Irradiated surface. The influence of the laser parameter on the melt pool size and the maximum temperature increase in the Irradiated Region is examined. Surface temperature predictions are compared with the experimental data. In addition, the distribution of WC particles and their re-locations in the treated layer, due to combination of the natural convection and Marangoni currents, are predicted. The findings are compared to the experimental data. It is found that surface temperature predictions agree well with the experimental data. The dislocated WC particles form a streamlining in the near Region of the melt pool wall, which agree with the experimental findings. The Gaussian distribution of the laser pulse intensity results in the maximum peak temperature and the maximum flow velocity inside the melt pool. In this case, the melt pool depth becomes the largest as compared to those corresponding to other laser pulse intensity distributions at the Irradiated surface.
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Laser heating of a moving slab: Influence pulse intensity parameter on temperature and stress fields
Optics & Laser Technology, 2015Co-Authors: Shahzada Zaman Shuja, Bekir Sami YilbasAbstract:Abstract Laser repetitive pulse heating of a moving slab is considered. Temperature and stress fields in the Irradiated Region are predicted for various laser pulse intensity distributions at the workpiece surface. The laser pulse intensity parameter is introduced to alter the intensity distribution at the workpiece while keeping the pulse energy constant for each distribution. An experiment is carried out to validate the predictions of surface temperature. It is found that surface temperature predictions agree well with the experimental data. Laser intensity distribution has significant effect on temperature and stress fields. In this case, Gaussian intensity distribution results in high values of von Mises stress in the Irradiated Region, which oscillates with the laser repetition rate. Altering the laser intensity through increasing the pulse intensity parameter ( β ) while keeping the pulse energy constant minimizes the effects of high cyclic thermal and stress loadings of the surface.
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Characterization of microplastic deformation produced in 6061-T6 by using laser shock processing
The International Journal of Advanced Manufacturing Technology, 2014Co-Authors: Simge Gencalp Irizalp, Nursen Saklakoglu, Bekir Sami YilbasAbstract:High dislocation densities are formed in the Irradiated Region of the workpiece during the laser shock processing; in which case, surface hardening is resulted. The process involves with recoil pressure loading at the workpiece surface with the minimum heating effects in the Irradiated Region. This favors the process to be a good candidate for the surface treatment of metallic materials. Therefore, in the present study, laser shock processing of 6061-T6 aluminum alloy is carried out and the influence of a number of laser pulses and Irradiated spot diameter on the treated layer characteristics, including morphology and hardness, are investigated. It is found that the number of laser pulses has significant influence on the resulting surface characteristics such as surface roughness, crystallite size, micro-strain, and microhardness of the alloy. In this case, surface roughness is deteriorated by increasing number of laser pulses and pulse intensity. In addition, fine crystallite structure takes place in the laser-treated Region.
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Equilibrium Laser Pulse Heating and Thermal Stress Analysis
Materials Forming Machining and Tribology, 2013Co-Authors: Bekir Sami Yilbas, Ahmad Y. Al-dweik, Nasser Al-aqeeli, Hussain Al-qahtaniAbstract:When the heating duration becomes greater than the thermalization time of the substrate material, equilibrium heating takes place in the laser Irradiated Region. In this case, the classical Fourier heating law governs the energy transport. Although the heating process is complicated, some useful assumptions enable to obtain the closed form solution for temperature and stress fields. Since the analytical solution provides the functional relation between the dependent variable and the independent parameters, it provides better physical insight into the heating problem than that of the numerical analysis. In this chapter, equilibrium heating of solid surfaces heated by a laser beam is considered. The closed form solution for the resulting temperature and stress fields are presented for various heating situations. The study also covers the phase change taking place at the Irradiated Region during the laser treatment process.
Cihan Karatas - One of the best experts on this subject based on the ideXlab platform.
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Laser pulse heating of steel mixing with WC particles in a Irradiated Region
Optics & Laser Technology, 2016Co-Authors: Shahzada Zaman Shuja, Bekir Sami Yilbas, Haider Ali, Cihan KaratasAbstract:Abstract Laser pulse heating of steel mixing with tungsten carbide (WC) particles is carried out. Temperature field in the Irradiated Region is simulated in line with the experimental conditions. In the analysis, a laser pulse parameter is introduced, which defines the laser pulse intensity distribution at the Irradiated surface. The influence of the laser parameter on the melt pool size and the maximum temperature increase in the Irradiated Region is examined. Surface temperature predictions are compared with the experimental data. In addition, the distribution of WC particles and their re-locations in the treated layer, due to combination of the natural convection and Marangoni currents, are predicted. The findings are compared to the experimental data. It is found that surface temperature predictions agree well with the experimental data. The dislocated WC particles form a streamlining in the near Region of the melt pool wall, which agree with the experimental findings. The Gaussian distribution of the laser pulse intensity results in the maximum peak temperature and the maximum flow velocity inside the melt pool. In this case, the melt pool depth becomes the largest as compared to those corresponding to other laser pulse intensity distributions at the Irradiated surface.
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Laser bending of steel sheets: corrosion testing of bended sections
Industrial Lubrication and Tribology, 2011Co-Authors: Bekir Sami Yilbas, Sohail Akhtar, Mazen Khaled, Cihan KaratasAbstract:Purpose – Laser bending is a good candidate to replace the flame bending process. The electrochemical response of laser bending Region changes due to the microstructural modifications and high level of residual stress developed in the laser‐Irradiated Region after the bending process. Consequently, investigation into laser bending and microstructural changes in the Irradiated Region as well as the electrochemical response of bending section becomes essential. This paper aims to focus on the laser bending process.Design/methodology/approach – The laser bending of steel sheets was carried out. The microstructural changes in the bending Region are examined using the scanning electron microscopy and X‐ray diffraction. The electrochemical response of the bended sections is investigated through potentiodynamic tests.Findings – It is found that laser‐Irradiated surface is free from cracks and cavitations. However, deep pit sites due to secondary pitting are observed in the bending sections.Research limitations/i...
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laser carbonitriding of alumina surface
Optics and Lasers in Engineering, 2011Co-Authors: S Yilbas, S S Akhta, Cihan KaratasAbstract:Laser carbonitriding of alumina surfaces is examined. Temperature and stress fields developed during the laser heating of the substrate surface are predicted using the finite element method in line with the experimental conditions. The formation of Al(C, N) and AlN compounds in the surface Region of Irradiated workpiece is examined using X-ray Photoelectron Spectroscopy (XPS) and X-ray Diffraction (XRD). The microstructural and morphological changes in the laser Irradiated Region are examined using Scanning Electron Microscope (SEM). The microhardness of the resulting surface is measured and compared with the base material hardness. It is found that high temperature gradient is developed in the Irradiated Region, which in turn, results in high residual stress levels in this Region. XPS and XRD data reveal the presence of Al (C, N) and AlN compounds in the surface Region. The microhardness in the surface Region of the laser treated workpiece increases significantly.
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Laser remelting of alumina tile surfaces: corrosion testing in aqueous solution
Corrosion Engineering Science and Technology, 2011Co-Authors: Bekir Sami Yilbas, Mazen Khaled, Cihan KaratasAbstract:Laser treatment of alumina surfaces in a nitrogen gas environment was carried out and the corrosion response of the resulting surfaces is examined. The corrosion tests were carried out using 5% NaCl solution for seven days, with continuous steering by a magnetic stirrer. Metallurgical and morphological changes in the laser Irradiated Region are examined using the scanning electron microscope, optical microscope, X-ray diffraction. It was found that formation of nitride (AlN) compounds was evident with a compact and dense structure formed in the laser Irradiated Region. Moreover, a few shallow pit sites are evident around the crack tips after the static corrosion tests, especially at a high laser output power.
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Laser control melting of alumina surfaces and thermal stress analysis
Optics & Laser Technology, 2011Co-Authors: Bekir Sami Yilbas, Cihan Karatas, Abul Fazal M. Arif, B.j. Abdul AleemAbstract:Abstract Laser gas assisted melting of alumina surface is carried out and temperature as well as stress fields developed in the Irradiated Region are predicted using the finite element method (FEM). An experiment is conducted resembling the simulation conditions. Optical and scanning electron microscope (SEM) are used to examine the morphological and the metallurgical changes in the laser treated Region. The X-ray diffraction (XRD) technique is used to determine the residual stress developed in the Irradiated Region. It is found that the residual stress predicted agreed with the measurement result. High heating and cooling rates result in high von Mises stress levels in the surface Region.
Jeremy D. Pickett-heaps - One of the best experts on this subject based on the ideXlab platform.
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Structure of kinetochore fibres in crane-fly spermatocytes after irradiation with an ultraviolet microbeam: neither microtubules nor actin filaments remain in the Irradiated Region.
Cell motility and the cytoskeleton, 2003Co-Authors: Arthur Forer, Tim Spurck, Jeremy D. Pickett-heaps, Paula WilsonAbstract:We studied chromosome movement after kinetochore microtubules were severed. Severing a kinetochore fibre in living crane-fly spermatocytes with an ultraviolet microbeam creates a kinetochore stub, a birefringent remnant of the spindle fibre connected to the kinetochore and extending only to the edge of the Irradiated Region. After the irradiation, anaphase chromosomes either move poleward led by their stubs or temporarily stop moving. We examined actin and/or microtubules in Irradiated cells by means of confocal fluorescence microscopy or serial-section reconstructions from electron microscopy. For each cell thus examined, chromosome movement had been recorded continuously until the moment of fixation. Kinetochore microtubules were completely severed by the ultraviolet microbeam in cells in which chromosomes continued to move poleward after the irradiation: none were seen in the Irradiated Regions. Similarly, actin filaments normally present in kinetochore fibres were severed by the ultraviolet microbeam irradiations: the Irradiated Regions contained no actin filaments and only local spots of non-filamentous actin. There was no difference in Irradiated Regions when the associated chromosomes continued to move versus when they stopped moving. Thus, one cannot explain motion with severed kinetochore microtubules in terms of either microtubules or actin-filaments bridging the Irradiated Region. The data seem to negate current models for anaphase chromosome movement and support a model in which poleward chromosome movement results from forces generated within the spindle matrix that propel kinetochore fibres or kinetochore stubs poleward. Cell Motil. Cytoskeleton 56:173–192, 2003. © 2003 Wiley-Liss, Inc.
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UV-microbeam irradiations of the mitotic spindle: spindle forces and structural analysis of lesions.
European journal of cell biology, 1991Co-Authors: J. A. Snyder, L. Armstrong, O. G. Stonington, Timothy P. Spurck, Jeremy D. Pickett-heapsAbstract:Mitotic PtK1 spindles were UV Irradiated (285 nm) during metaphase and anaphase between the chromosomes and the pole. The irradiation, a rectangle measuring 1.4 x 5 microns parallel to the metaphase plate, severed between 90 and 100% of spindle microtubules (MTs) in the Irradiated Region. Changes in organization of MTs in the Irradiated Region were analyzed by EM serial section analysis coupled with 3-D computer reconstruction. Metaphase cells Irradiated 2 to 4 microns below the spindle pole (imaged by polarization optics) lost birefringence in the Irradiated Region. Peripheral spindle fibers, previously curved to focus on the pole, immediately splayed outwards when severed. We demonstrate via serial section analysis that following irradiation the lesion was devoid of MTs. Within 30 s to 1 min, recovery in live cells commenced as the severed spindle pole moved toward the metaphase plate closing the lesion. This movement was concomitant with the recovery of spindle birefringence and some of the severed fibers becoming refocused at the pole. Ultrastructurally we confirmed that this movement coincided with bridging of the lesion by MTs presumably growing from the pole. The non-Irradiated half spindle also lost some birefringence and shortened until it resembled the recovered half spindle. Anaphase cells similarly Irradiated did not show recovery of birefringence, and the pole remained disconnected from the remaining mitotic apparatus. Reconstructions of spindle structure confirmed that there were no MTs in the lesion which bridged the severed spindle pole with the remaining mitotic apparatus. These results suggest the existence of chromosome-to-pole spindle forces are dependent upon the existence of a MT continuum, and to a lesser extent to the loss of MT initiation capacity of the centrosome at the metaphase/anaphase transition.
Abul Fazal M. Arif - One of the best experts on this subject based on the ideXlab platform.
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Laser treatment of silicon at nitrogen ambient: thermal stress analysis
Surface Engineering, 2011Co-Authors: Bekir Sami Yilbas, Abul Fazal M. Arif, Cihan KaratasAbstract:Laser control melting of silicon surface is carried out at nitrogen gas environment and temperature rise as well as thermal stress developed in the Irradiated Region is simulated using the finite element method. The residual stress developed in the surface Region after the laser treatment is measured using the XRD technique and the measurement results are compared with the predictions. The fracture toughness of the laser treated surface is also measured using the indentation tests. The structural and morphological changes in the laser Irradiated Region are examined using the scanning electron microscope. It is found that β phase silicon nitride was formed in the surface Region of the laser treated workpiece. The temperature gradient close to the laser beam spot attains significantly high values due to the high heating and cooling rates. This, in turn, results in high stress levels in this Region during the laser treatment process. The laser treated surface was free from the defects including microcracks, ...
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Laser control melting of alumina surfaces and thermal stress analysis
Optics & Laser Technology, 2011Co-Authors: Bekir Sami Yilbas, Cihan Karatas, Abul Fazal M. Arif, B.j. Abdul AleemAbstract:Abstract Laser gas assisted melting of alumina surface is carried out and temperature as well as stress fields developed in the Irradiated Region are predicted using the finite element method (FEM). An experiment is conducted resembling the simulation conditions. Optical and scanning electron microscope (SEM) are used to examine the morphological and the metallurgical changes in the laser treated Region. The X-ray diffraction (XRD) technique is used to determine the residual stress developed in the Irradiated Region. It is found that the residual stress predicted agreed with the measurement result. High heating and cooling rates result in high von Mises stress levels in the surface Region.
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Laser treatment of aluminum surface: Analysis of thermal stress field in the Irradiated Region
Journal of Materials Processing Technology, 2009Co-Authors: Abul Fazal M. Arif, Cihan Karatas, Kabeer RazaAbstract:Laser surface treatment of aluminum is considered and the temperature as well as the stress fields developed in the laser Irradiated Region are predicted using the finite element method (FEM). The predictions are obtained for two laser pulses with different pulse lengths. In the simulations, the variable thermal properties of the substrate material are used. The experiment is conducted to treat the aluminum specimen surface with the laser beam. The laser output pulse intensity consists of repetitive pulses, which are used in the model study to examine the metallurgical changes in the Irradiated Region. SEM and XRD are carried out in this regard. It is found that the von-Mises stress reaches the maximum in the surface vicinity, particularly at the onset of cooling cycle starts. The von-Mises stress attains values less than the critical values for the crack formation, which is particularly true after the end of the cooling cycle. The residual stress formed in the surface Region is in the order of a few MPa.
Kabeer Raza - One of the best experts on this subject based on the ideXlab platform.
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Laser treatment of aluminum surface: Analysis of thermal stress field in the Irradiated Region
Journal of Materials Processing Technology, 2009Co-Authors: Abul Fazal M. Arif, Cihan Karatas, Kabeer RazaAbstract:Laser surface treatment of aluminum is considered and the temperature as well as the stress fields developed in the laser Irradiated Region are predicted using the finite element method (FEM). The predictions are obtained for two laser pulses with different pulse lengths. In the simulations, the variable thermal properties of the substrate material are used. The experiment is conducted to treat the aluminum specimen surface with the laser beam. The laser output pulse intensity consists of repetitive pulses, which are used in the model study to examine the metallurgical changes in the Irradiated Region. SEM and XRD are carried out in this regard. It is found that the von-Mises stress reaches the maximum in the surface vicinity, particularly at the onset of cooling cycle starts. The von-Mises stress attains values less than the critical values for the crack formation, which is particularly true after the end of the cooling cycle. The residual stress formed in the surface Region is in the order of a few MPa.
