The Experts below are selected from a list of 2685 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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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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co2 laser heating of surfaces melt pool formation at surface
Optics and Laser Technology, 2012Co-Authors: O Momin, Shahzada Zaman Shuja, Bekir Sami YilbasAbstract:Abstract The melt pool formation during the heating of titanium and steel surfaces by a moving CO 2 laser beam is examined. The repetitive pulses are introduced in the simulations and the Marangoni effect in the melt pool is incorporated in the model study. The influence of laser scanning speed and the laser intensity parameter on the melt pool size is also considered. The enthalpy–porosity method is adopted to account for the phase change in the Irradiated Spot. It is found that the influence of laser scanning speed on the melt pool size is considerable, which is more pronounced for laser beam parameter β =1. The melt pool size is smaller for stainless steel as compared to that corresponding to titanium.
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laser repetitive pulse heating of tool surface
Optics and Laser Technology, 2011Co-Authors: Bekir Sami Yilbas, Shahzada Zaman Shuja, Shafique M A KhanAbstract:Abstract Laser heating of a cemented carbide tool is considered and the temperature field as well as phase changes in the heated region is modeled. Temperature rise, liquid layer thickness, and mushy size are predicted numerically. A control volume approach is introduced to solve the governing equations of heat transfer and phase change. Consecutive pulses with the duty cycle of 60% are accommodated in the simulations in line with the experimental conditions. An experiment is carried out to treat the cemented carbide tool surfaces using the CO2 laser delivering consecutive pulses. The treated surfaces and their cross-sections are examined using the scanning electron microscope (SEM). It is found that the temperature gradient is high along the laser beam axis resulting in cracks at the Irradiated surface. The rapid solidification of the surface causes compact structures with very fine grains in the surface region of the laser Irradiated Spot.
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Temperature and Stress Fields in Silver due to Laser Picosecond Heating Pulse
Numerical Heat Transfer Part A: Applications, 2002Co-Authors: Bekir Sami Yilbas, Abul Fazal M. ArifAbstract:Laser short-pulse heating of metallic surfaces is involved with nonequilibrium energy transport in the region Irradiated by a laser beam. In this case, the Fourier heating model fails to predict correct temperature rise in this region. Moreover, for completeness of analysis, the thermomechanical coupling needs to be incorporated in the governing equations. In the present study, electron kinetic theory approach is introduced to model the heating process and thermomechanical coupling is formulated and accommodated in the energy transport equation. Temperature and stress fields are computed numerically for silver. It is found that electron temperature well in excess of lattice site temperature occurs in the surface vicinity of the substrate material. Although lattice site temperature rise is low (~170°C), stress levels as high 3 2 10 8 Pa are computed in the region heated by a laser beam. The thermal expansion of the surface at the Irradiated Spot center reaches 0.5 nm after 4 ns of the heating period.
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The influence of gas jet velocity in laser heating—a moving workpiece case:
Proceedings of the Institution of Mechanical Engineers Part C: Journal of Mechanical Engineering Science, 2000Co-Authors: Shahzada Zaman Shuja, Bekir Sami YilbasAbstract:AbstractIn the present study, gas jet-assisted laser heating of a moving steel substrate with finite thickness is considered. Three-dimensional flow and energy equations with variable properties of the gas are introduced in modelling the heating process. The low Reynolds number k-e model is employed to account for the turbulence. A numerical scheme using a control volume approach is introduced to discretize the governing equations. The simulation is repeated for three assisting gas jet velocities (100, 10, 1 m/s) and a constant workpiece speed (0.3 m/s). It is found that the effect of assisting gas jet velocity on the surface temperature is more pronounced in the cooling cycle than in the heating cycle of the laser heating process. The workpiece movement affects the location of the maximum temperature at the surface, which moves away from the initially Irradiated Spot centre in the direction of motion of the workpiece.
Abul Fazal M. Arif - One of the best experts on this subject based on the ideXlab platform.
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Temperature and Stress Fields in Silver due to Laser Picosecond Heating Pulse
Numerical Heat Transfer Part A: Applications, 2002Co-Authors: Bekir Sami Yilbas, Abul Fazal M. ArifAbstract:Laser short-pulse heating of metallic surfaces is involved with nonequilibrium energy transport in the region Irradiated by a laser beam. In this case, the Fourier heating model fails to predict correct temperature rise in this region. Moreover, for completeness of analysis, the thermomechanical coupling needs to be incorporated in the governing equations. In the present study, electron kinetic theory approach is introduced to model the heating process and thermomechanical coupling is formulated and accommodated in the energy transport equation. Temperature and stress fields are computed numerically for silver. It is found that electron temperature well in excess of lattice site temperature occurs in the surface vicinity of the substrate material. Although lattice site temperature rise is low (~170°C), stress levels as high 3 2 10 8 Pa are computed in the region heated by a laser beam. The thermal expansion of the surface at the Irradiated Spot center reaches 0.5 nm after 4 ns of the heating period.
Shahzada Zaman Shuja - One of the best experts on this subject based on the ideXlab platform.
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co2 laser heating of surfaces melt pool formation at surface
Optics and Laser Technology, 2012Co-Authors: O Momin, Shahzada Zaman Shuja, Bekir Sami YilbasAbstract:Abstract The melt pool formation during the heating of titanium and steel surfaces by a moving CO 2 laser beam is examined. The repetitive pulses are introduced in the simulations and the Marangoni effect in the melt pool is incorporated in the model study. The influence of laser scanning speed and the laser intensity parameter on the melt pool size is also considered. The enthalpy–porosity method is adopted to account for the phase change in the Irradiated Spot. It is found that the influence of laser scanning speed on the melt pool size is considerable, which is more pronounced for laser beam parameter β =1. The melt pool size is smaller for stainless steel as compared to that corresponding to titanium.
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laser repetitive pulse heating of tool surface
Optics and Laser Technology, 2011Co-Authors: Bekir Sami Yilbas, Shahzada Zaman Shuja, Shafique M A KhanAbstract:Abstract Laser heating of a cemented carbide tool is considered and the temperature field as well as phase changes in the heated region is modeled. Temperature rise, liquid layer thickness, and mushy size are predicted numerically. A control volume approach is introduced to solve the governing equations of heat transfer and phase change. Consecutive pulses with the duty cycle of 60% are accommodated in the simulations in line with the experimental conditions. An experiment is carried out to treat the cemented carbide tool surfaces using the CO2 laser delivering consecutive pulses. The treated surfaces and their cross-sections are examined using the scanning electron microscope (SEM). It is found that the temperature gradient is high along the laser beam axis resulting in cracks at the Irradiated surface. The rapid solidification of the surface causes compact structures with very fine grains in the surface region of the laser Irradiated Spot.
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The influence of gas jet velocity in laser heating—a moving workpiece case:
Proceedings of the Institution of Mechanical Engineers Part C: Journal of Mechanical Engineering Science, 2000Co-Authors: Shahzada Zaman Shuja, Bekir Sami YilbasAbstract:AbstractIn the present study, gas jet-assisted laser heating of a moving steel substrate with finite thickness is considered. Three-dimensional flow and energy equations with variable properties of the gas are introduced in modelling the heating process. The low Reynolds number k-e model is employed to account for the turbulence. A numerical scheme using a control volume approach is introduced to discretize the governing equations. The simulation is repeated for three assisting gas jet velocities (100, 10, 1 m/s) and a constant workpiece speed (0.3 m/s). It is found that the effect of assisting gas jet velocity on the surface temperature is more pronounced in the cooling cycle than in the heating cycle of the laser heating process. The workpiece movement affects the location of the maximum temperature at the surface, which moves away from the initially Irradiated Spot centre in the direction of motion of the workpiece.
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Laser-induced thermal stresses on steel surface
Optics and Lasers in Engineering, 1998Co-Authors: Bekir Sami Yilbas, M. Sami, Shahzada Zaman ShujaAbstract:Abstract In laser heat treatment of steels, a thin surface layer of austenite forms during heating and subsequent phase change process in the cooling period. However, thermal stress develops due to high-temperature gradient attainment in the surface vicinity which in turn results in microcrack development at the surface. The present study is carried out to compute the temperature profiles due to step input pulse laser radiation and determine the resulting thermal stresses. The study is extended to include three-step input pulses having the same energy content. This provides the comparison for the influence of the pulse length on the resulting thermal stresses. To validate the theoretical predictions, an experiment is conducted to irradiate the AISI 4142 steel surface by an Nd–YAG laser. Microphotography and EDS analysis of the heated regions are carried out. It is found that considerable thermal stress is eveloped at the workpiece surface due to attainment of high-temperature gradient in this region. In addition, microcracks are observed at the surface of the Irradiated Spot.
Tsuguo Sawada - One of the best experts on this subject based on the ideXlab platform.
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Formation of ring patterns surrounded by ripples by single-shot laser irradiation with ultrashort pulse width at the solid/liquid interface
Applied Physics Letters, 2003Co-Authors: Kenji Katayama, Hideaki Yonekubo, Tsuguo SawadaAbstract:A single pulse (pulse width: 200 fs) was Irradiated onto a water/silicon interface. The processed surface had many ring patterns surrounded by sinusoidal patterns within the Irradiated Spot. The diameter of their rings ranged from 500 nm to 10 μm. It was proposed that the oscillation of a bubble at the interface emitted an acoustic wave around itself and that the melted silicon surface, deformed due to acoustic pressure, solidified instantaneously in the course of the propagation of the acoustic wave on the silicon surface.
Shamaila Arooj - One of the best experts on this subject based on the ideXlab platform.
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Effect of UV laser irradiation on the hardness and structural parameters of AgxPd1−x (0.4 ≤ x ≤ 0.6) alloys
Applied Surface Science, 2012Co-Authors: Muhammad Zakria Butt, Farooq Bashir, Shamaila AroojAbstract:Abstract Strips of high-purity AgxPd1−x alloys, with x = 0.4, 0.5 and 0.6, were solution treated at 800 °C for 2 h. Specimens of each composition were then Irradiated with 100, 200, 300, and 400 shots of KrF Excimer laser (maximum energy 20 mJ, wavelength 248 nm, pulse width 20 ns, repetition rate 20 Hz). For each alloy, Vickers hardness of un-Irradiated and Irradiated specimens was measured as a function of the number of laser shots, and was found to increase with increasing number of shots. The increase in surface hardness at the midpoint of laser irradiation Spot on Ag40Pd60, Ag50Pd50, and Ag60Pd40 specimens was up to 27.6, 30.2, and 17.3%, respectively. The surface hardness profile for each Irradiated specimen shows a decreasing trend till a distance of 3 mm from the midpoint of the Irradiated Spot. XRD study of the alloy specimens of each composition shows that the dislocation line density increases with increasing number of shots, and the surface hardness is a function of it.