The Experts below are selected from a list of 19062 Experts worldwide ranked by ideXlab platform
M. Reininghaus - One of the best experts on this subject based on the ideXlab platform.
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time resolved investigations of the non thermal Ablation Process of graphite induced by femtosecond laser pulses
Journal of Applied Physics, 2016Co-Authors: Christian Kalupka, Johannes Finger, M. ReininghausAbstract:We report on the in-situ analysis of the Ablation dynamics of the, so-called, laser induced non-thermal Ablation Process of graphite. A highly oriented pyrolytic graphite is excited by femtosecond laser pulses with fluences below the classic thermal Ablation threshold. The Ablation dynamics are investigated by axial pump-probe reflection measurements, transversal pump-probe shadowgraphy, and time-resolved transversal emission photography. The combination of the applied analysis methods allows for a continuous and detailed time-resolved observation of the non-thermal Ablation dynamics from several picoseconds up to 180 ns. Formation of large, μm-sized particles takes place within the first 3.5 ns after irradiation. The following propagation of Ablation products and the shock wave front are tracked by transversal shadowgraphy up to 16 ns. The comparison of Ablation dynamics of different fluences by emission photography reveals thermal Ablation products even for non-thermal fluences.
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High power ultra-short pulse laser Ablation of IN718 using high repetition rates
Journal of Materials Processing Technology, 2015Co-Authors: Johannes Finger, Christian Kalupka, M. ReininghausAbstract:Abstract Laser Ablation using ultra-short pulsed laser radiation with pulse durations below 10 ps is known to be capable of high-precision machining with very small thermal load for the Processed workpiece. Although the Processing quality is excellent, the productivity is too small for many applications. Therefore, an upscaling of the achievable Ablation rate is one major research topic in the field of ultra-short pulse laser Ablation. In this study, we identify and investigate a novel high-speed Ablation Process for the Ablation of Inconel 718 using ultra-short pulsed laser radiation. The formation of a thin layer of molten material avoids the formation of rough microstructures on the workpiece surface that usually appear for the Processing with high average powers and high spatial pulse overlaps. Thus, Processing with high average power of more than 50 W using conventional, high efficient and high flexible beam deflection technology becomes applicable. The presented Process is approximately 20 times faster than conventional ultra-short pulse laser Ablation with average powers of less than 5 W. The influence of the repetition rate, average power, pulse duration and hatch distance on the high-speed Ablation Process is investigated. The potential of an optional finishing Process to remove the molten layer by melt-free Ablation with the same laser system but different Processing parameters is demonstrated.
R Dwayne J Miller - One of the best experts on this subject based on the ideXlab platform.
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digital interference microscopy and density reconstruction of picosecond infrared laser desorption at the water air interface
Journal of Applied Physics, 2018Co-Authors: Frederik Busse, Sebastian Kruber, Wesley D Robertson, R Dwayne J MillerAbstract:Material Ablation and evaporation using pulsed infrared lasers pose promising approaches for matrix-free laser desorption ionization and in laser surgery. For the best results, key parameters such as laser wavelength, pulse duration, and pulse energy need to be carefully adjusted to the application. We characterize the dynamics at the water-air interface induced by a 10 ps infrared laser tuned to the water absorption band at 3 μ m, a parameter set facilitating stress confined desorption for typical absorption depths in biological samples and tissue. By driving the Ablation faster than nucleation growth, cavitation induced sample damage during the Ablation Process can be mitigated. The resultant explosive Ablation Process leads to a shock front expansion and material ejection which we capture using off-axis digital interference microscopy, an interference technique particularly useful for detecting the phase shift caused by transparent objects. It is demonstrated that the method can yield local density...
Seock Sam Kim - One of the best experts on this subject based on the ideXlab platform.
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improvement of tribological characteristics of multi scale laser textured surface in terms of lubrication regime
Journal of the Korean Society of Tribologists and Lubrication Engineers, 2014Co-Authors: Jonghyoung Kim, Si Geun Choi, Dawit Zenebe Segu, Yongsub Jung, Seock Sam KimAbstract:Laser Surface Texturing(LST) is a surface engineering Process used to improve tribological characteristicsof materials by creating patterned microstructures on the mechanical contact surface. In LST technology, a pulsatedlaser beam is used to create arranged dimples on a surface by a material Ablation Process, which can improve such asload capacity, wear resistances, lubrication lifetime, and reduce friction coefficients. In the present study, the effect ofmulti-scale LST on lubricant regime was investigated. A pulsed Nd:YAG laser was applied on the bearing steel(AISI52100) to create arranged dimples. To optimize the surface texturing effect on friction, multi-scale texture dimples withsome specific formula arrays were fabricated by combining circles, ellipses and the laser Ablation Process. The tri-bological testing of multi-scale textured surface was performed by a flat-on-flat unidirectional tribometer under lubri-cation and the results compared with that of the non-textured surface. Through an increase in sliding speed, thebeneficial effect of multi-scale LST performance was achieved. The multi-scale textured surface had lower frictioncoefficient performances than the non-textured surface due to the hydrodynamic lubrication effect.Keywords: laser surface texture (레이저 표면 텍스처), lubrication regime (윤활영역), friction (마찰), surfacemodification (표면개질)
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Influence on friction behavior of micro-texturing under lubricated non-conformal contact
Meccanica, 2014Co-Authors: Dawit Zenebe Segu, Seock Sam KimAbstract:Laser surface texturing (LST) is a well-known surface engineering Process used to create arranged dimples on surface using a material Ablation Process. In this Process, a well arranged micro-dimple can produce significant improvements of engineering components in aspects such as load carrying capacity, wear resistance, wetting characteristics and reduction of friction coefficient. In the present work, we investigated the effect of multi-dimple LST steel surfaces on tribological properties under non-conforming contact. The multi-dimple textured surfaces with some specific formula arrays were fabricated by laser Ablation Process on steel disc by combining patterns of circles and triangles, and circles and squares, having different dimple densities to optimize the surface texturing effect on tribological performance. The tribological test of multi-dimple textured surface was performed by a ball-on-flat unidirectional tribometer in lubricated condition, and the results compared with that of a single-dimple and untextured (polished and ground) surfaces. The results indicate that the surface with multi-dimple textured patterns had better friction performance than the untextured and single-dimple textured surfaces. The beneficial effect of multi-dimple textured patterns was associated with transition of lubrication from boundary to mixed lubrication regime.
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The effect of multi-scale laser textured surface on lubrication regime
Applied Surface Science, 2013Co-Authors: Dawit Zenebe Segu, Si Geun Choi, Jae Hyouk Choi, Seock Sam KimAbstract:Abstract Laser surface texturing (LST) is a surface engineering Process used to improve tribological characteristics of materials by creating patterned microstructures on the mechanical contact surface. In LST technology, a pulsated laser beam is used to create arranged dimples on surface by a material Ablation Process, which can improve load capacity, wear resistances, lubrication lifetime, and reduce friction coefficients. In the present study, the effect of multi-scale LST on lubricant regime was investigated. A pulsed Nd:YAG laser was applied on steel (AISI 52100) to create arranged dimples. To optimize the surface texturing effect on friction, multi-scale texture dimples with some specific formula arrays were fabricated by laser Ablation Process by combining circles and ellipses. The tribological testing of multi-scale textured surface was performed by a flat-on-flat unidirectional tribometer under lubrication, and the results compared with that of untextured surface. Through an increase in sliding speed and dimple depth the beneficial effect of multi-scale LST performance was achieved. The multi-scale textured surface had lower friction coefficient performance than the untextured surface due to hydrodynamic lubrication effect.
Frederik Busse - One of the best experts on this subject based on the ideXlab platform.
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digital interference microscopy and density reconstruction of picosecond infrared laser desorption at the water air interface
Journal of Applied Physics, 2018Co-Authors: Frederik Busse, Sebastian Kruber, Wesley D Robertson, R Dwayne J MillerAbstract:Material Ablation and evaporation using pulsed infrared lasers pose promising approaches for matrix-free laser desorption ionization and in laser surgery. For the best results, key parameters such as laser wavelength, pulse duration, and pulse energy need to be carefully adjusted to the application. We characterize the dynamics at the water-air interface induced by a 10 ps infrared laser tuned to the water absorption band at 3 μ m, a parameter set facilitating stress confined desorption for typical absorption depths in biological samples and tissue. By driving the Ablation faster than nucleation growth, cavitation induced sample damage during the Ablation Process can be mitigated. The resultant explosive Ablation Process leads to a shock front expansion and material ejection which we capture using off-axis digital interference microscopy, an interference technique particularly useful for detecting the phase shift caused by transparent objects. It is demonstrated that the method can yield local density...
Dawit Zenebe Segu - One of the best experts on this subject based on the ideXlab platform.
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improvement of tribological characteristics of multi scale laser textured surface in terms of lubrication regime
Journal of the Korean Society of Tribologists and Lubrication Engineers, 2014Co-Authors: Jonghyoung Kim, Si Geun Choi, Dawit Zenebe Segu, Yongsub Jung, Seock Sam KimAbstract:Laser Surface Texturing(LST) is a surface engineering Process used to improve tribological characteristicsof materials by creating patterned microstructures on the mechanical contact surface. In LST technology, a pulsatedlaser beam is used to create arranged dimples on a surface by a material Ablation Process, which can improve such asload capacity, wear resistances, lubrication lifetime, and reduce friction coefficients. In the present study, the effect ofmulti-scale LST on lubricant regime was investigated. A pulsed Nd:YAG laser was applied on the bearing steel(AISI52100) to create arranged dimples. To optimize the surface texturing effect on friction, multi-scale texture dimples withsome specific formula arrays were fabricated by combining circles, ellipses and the laser Ablation Process. The tri-bological testing of multi-scale textured surface was performed by a flat-on-flat unidirectional tribometer under lubri-cation and the results compared with that of the non-textured surface. Through an increase in sliding speed, thebeneficial effect of multi-scale LST performance was achieved. The multi-scale textured surface had lower frictioncoefficient performances than the non-textured surface due to the hydrodynamic lubrication effect.Keywords: laser surface texture (레이저 표면 텍스처), lubrication regime (윤활영역), friction (마찰), surfacemodification (표면개질)
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Influence on friction behavior of micro-texturing under lubricated non-conformal contact
Meccanica, 2014Co-Authors: Dawit Zenebe Segu, Seock Sam KimAbstract:Laser surface texturing (LST) is a well-known surface engineering Process used to create arranged dimples on surface using a material Ablation Process. In this Process, a well arranged micro-dimple can produce significant improvements of engineering components in aspects such as load carrying capacity, wear resistance, wetting characteristics and reduction of friction coefficient. In the present work, we investigated the effect of multi-dimple LST steel surfaces on tribological properties under non-conforming contact. The multi-dimple textured surfaces with some specific formula arrays were fabricated by laser Ablation Process on steel disc by combining patterns of circles and triangles, and circles and squares, having different dimple densities to optimize the surface texturing effect on tribological performance. The tribological test of multi-dimple textured surface was performed by a ball-on-flat unidirectional tribometer in lubricated condition, and the results compared with that of a single-dimple and untextured (polished and ground) surfaces. The results indicate that the surface with multi-dimple textured patterns had better friction performance than the untextured and single-dimple textured surfaces. The beneficial effect of multi-dimple textured patterns was associated with transition of lubrication from boundary to mixed lubrication regime.
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The effect of multi-scale laser textured surface on lubrication regime
Applied Surface Science, 2013Co-Authors: Dawit Zenebe Segu, Si Geun Choi, Jae Hyouk Choi, Seock Sam KimAbstract:Abstract Laser surface texturing (LST) is a surface engineering Process used to improve tribological characteristics of materials by creating patterned microstructures on the mechanical contact surface. In LST technology, a pulsated laser beam is used to create arranged dimples on surface by a material Ablation Process, which can improve load capacity, wear resistances, lubrication lifetime, and reduce friction coefficients. In the present study, the effect of multi-scale LST on lubricant regime was investigated. A pulsed Nd:YAG laser was applied on steel (AISI 52100) to create arranged dimples. To optimize the surface texturing effect on friction, multi-scale texture dimples with some specific formula arrays were fabricated by laser Ablation Process by combining circles and ellipses. The tribological testing of multi-scale textured surface was performed by a flat-on-flat unidirectional tribometer under lubrication, and the results compared with that of untextured surface. Through an increase in sliding speed and dimple depth the beneficial effect of multi-scale LST performance was achieved. The multi-scale textured surface had lower friction coefficient performance than the untextured surface due to hydrodynamic lubrication effect.
