• Journal of the Korean Institute of Illuminating and Electrical Installation Engineers
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• v.24 no.5
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• pp.160-168
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• 2010

This paper tried to find out NO generation and removal mechanisms in the space of the atmospheric pulsed barrier discharge using laser induced fluorescence method, which is a very effective approach to the measurement of spatio-temporal density of specific molecules. The propagation velocity of the primary streamer reaches about $2.7{\times}10^6$[m/s] and the secondary streamer is produced in the vicinity of positive electrode after the primary streamer finished. In this work, pulse Nd:Yag and Dye lasers are used for generating the specific wavelength of 226[nm], which is possible to excite NO molecules into $A^2{\Sigma}^+{\rightarrow}X^2{\prod}$(0,0) and fluorescence signals as the transition of $A^2{\Sigma}^+{\leftarrow}X^2$(0,2) is measured. For the effective removal of NO molecules in the plasma discharge process, the lower oxygen contents are needed and the influence of secondary streamer for the reduction mechanism of NO molecules is important

• Korean Journal of Materials Research
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• v.16 no.12
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• pp.777-781
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• 2006

Recently, there are a lot of study to alternate polycarbonate which is being used as storage material in CD, DVD. In this study, we alternated polycarbonate with glass. We observed the change of shape in a surface of the glass which was focused by Nd:YAG Laser. The change of shape and property was studied by thermal mechanical analysis (TMA), UV-Vis spectrometer, AFM and SEM. According to Laser power and quantity of additives, the Bump's size and shape are showed differently. In high energy, the Bump will be transformed into Pit. And also according to CTE, $T_d$ and absorption ratio of glass, difference between Bump and Pit is confirmed. From these investigation, we could control that the minimum size of bump which is more useful shape than pit's is about 1.3 $\mu$m, H 70 nm, and it is near same the spot size.

• The Journal of Advanced Prosthodontics
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• v.11 no.4
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• pp.223-231
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• 2019

PURPOSE. The purpose of this study was to evaluate the shear bond strength (SBS) of an indirect resin composite (IRC) to the various resin matrix ceramic (RMC) blocks using different surface treatments. MATERIALS AND METHODS. Ninety-nine cubic RMC specimens consisting of a resin nanoceramic (RNC), a polymer-infiltrated hybrid ceramic (PIHC), and a flexible hybrid ceramic (FHC) were divided randomly into three surface treatment subgroups (n = 11). In the experimental groups, untreated (Cnt), tribochemical silica coating (Tbc), and Neodymium-Doped Yttrium Aluminum Garnet (Nd:YAG) laser irradiation (Lsr) with 3 W (150 mJ/pulse, 20 Hz for 20 sec.) were used as surface treatments. An indirect composite resin (IRC) was layered with a disc-shape mold ($2{\times}3mm$) onto the treated-ceramic surfaces and the specimens submitted to thermal cycling (6000 cycles, $5-55^{\circ}C$). The SBS test of specimens was performed using a universal testing machine and the specimens were examined with a scanning electron microscope to determine the failure mode. Data were statistically analyzed with two-way analysis of variance (ANOVA) and Tukey HSD test (${\alpha}=.05$). RESULTS. According to the two-way ANOVA, only the surface treatment parameter was statistically significant (P<.05) on the SBS of IRC to RMC. The SBS values of Lsr-applied RMC groups were significantly higher than Cnt groups for each RMC material, (P<.05). Significant differences were also determined between Tbc surface treatment applied and untreated (Cnt) PIHC materials (P=.039). CONCLUSION. For promoting a reliable bond strength during characterization of RMC with IRC, Nd:YAG laser or Tbc surface treatment technique should be used, putting in consideration the microstructure and composition of RMC materials and appropriate parameters for each material.

• Journal of the Korean Crystal Growth and Crystal Technology
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• v.23 no.4
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• pp.167-172
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• 2013

Titanium dioxides nanoparticles coated aluminum oxide powders were fabricated by pulsed laser deposition (PLD) with Nd : YAG laser at 266 nm. The Pulse laser energy is 100 mJ/pulse. During the irradiation of the focused laser on the $TiO_2$ target, Ar gas is supplied into the chamber. The gas pressure is varied in a range of $1{\times}10^{-2}$ to 100 Pa. Titanium dioxides nanoparticles deposited aluminum oxide powders were characterized by using energy dispersive X-ray spectroscopy (EDX), high resolution transmission electron microscopy (HR-TEM), in order to understand the effect of Ar background gas on surface morphology and properties of the powders. The coated $TiO_2$ nanoparticles had nanosized spherical shape and the crystallite sizes of 10~30 nm. The morphology of coated $TiO_2$ nanoparticles is not affected by gas pressure. However, the particle size and crystallinity slightly increased with the increase of gas pressure. According to this technique, the size and crystallinity of nanoparticles can be easily controlled by controlling pressure during the laser irradiation.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.19 no.10
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• pp.346-351
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• 2018

Metal three-dimensional (3D) printing technologies are mainly classified as powder bed fusion (PBF) and direct energy deposition (DED) methods according to the method of application of a laser beam to metallic powder. The DED method can be used to fabricate fine and hard 3D metallic structures by applying a strong laser beam to a thin layer of metallic powder. The PBF method involves slicing 3D graphics to be a certain height, laminating metal powders, and making a 3D structure using a laser. While the DED method has advantages such as laser cladding and metallic welding, it causes problems with low density when 3D shapes are created. The PBF method was introduced to address the structural density issues in the DED method and makes it easier to produce relatively dense 3D structures. In this paper, thin lines were produced by using PBF 3D printers with stainless-steel powder of roughly $30{\mu}m$ in diameter with a galvano scanner and fiber-transferred Nd:YAG laser beam. Experiments were carried out to find the optimal conditions for the width of a line depending on the processing times, laser power, spot size, and scan speed. The optimal conditions were two scanning processes in one line structure with a laser power of 30 W, spot size of $28.7{\mu}m$, and scan speed of 200 mm/s. With these conditions, a minimum width of about $85.3{\mu}m$ was obtained.

• Journal of Welding and Joining
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• v.26 no.5
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• pp.74-78
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• 2008

The laser welding of the car body and components has been spread in the automotive industry. The Nd:YAG laser welding system could be used in 3D welding with robot. However, this system cannot efficiently reduce the welding cycle time according to various welding sequences because the robot's moving time is same that of the resistant spot welding system. But the remote welding system with high power $CO_2$ laser and scanner makes it possible welding cycle time much faster than the robot laser welding system. In the $CO_2$ laser remote welding system, laser beam can be rapidly transferred to a workpiece by moving mirrors of scanner system. So, it makes reducing the cycle time of welding process and shaping various welding patterns easily. Therefore, in this paper, the characteristic of weld strength according to patterns of weld bead on $CO_2$ laser welding was investigated. Also, the relationship between shape of weld bead and value of tensile load was studied. Finally, the optimum remote welding condition for car bumper was investigated.

• Korean Journal of Heritage: History & Science
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• v.44 no.4
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• pp.142-153
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• 2011

'Silla Monument Stone in Jungseong-ri, Pohang' was discovered in Pohang City, Gyeongsangbuk Province of Korea in 2009. The monument stone with irregular shape has dimensions of maximum height of 105cm, width of 47.6~49.6cm, thickness of 13.8~14.7cm and weight of 115kg. The results of monument stone was found to be granitite. Conservation treatment procedure was carried out in the order of production of Weathering map, cleaning of surface pollutants, consolidation using ethyl silicate. Black pollutant(crust) that covered more than 60% of the surface was analyzed first in order to remove the pollutants on the surface of the monumental stone by cleaning of surface pollutants using laser. The purpose on analysis was not only to verify the pollutants on the stone but also to carry out preliminary cleaning by securing rocks with same pollutant as the monumental stone. As the results of analysis using p-XRF(PMI. INNOV-X, USA) on the site, high level of Mn and Fe were detected, and the analysis of small section that had been fallen off with SEM/EDX for the purpose of quantitative analysis also detected high level of Mn. The Similar contaminants on Stone secured in the manner described above were made into 10 samples ($5cm{\times}5cm$) and was subjected to preliminary cleaning by Nd-YAG Laser(Laser&Physics, Korea). The results of surface observation through portable microscope during cleaning revealed that the power of 460mJ, wavelength of 1064nm and irradiation frequency of 1,800~2,300 per $25cm^2$ were most effective. Evaluation on the preservative treatment was made through confirmation of the extent of removal through color-difference meter measurement and component analysis prior to and following removal of the pollutants. As the result of color-difference meter measurement increase in the brightness was evidenced by the increase in the brightness ($L^*$)value from 33 to 49, and it was possible to ascertain the reduction in the pollutants as the content of Mn was reduced by about 80% from $50,000{\pm}5,000ppm$ to $10,000{\pm}2,000pmm$ from the result of component analysis.

• Proceedings of the KSME Conference
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• 2007.05a
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• pp.1312-1316
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• 2007

Strip casted and rolled magnesium sheet is become exiting material for car manufacturer, due to its better formability and specific strength compare with conventional extruded sheet. TWB technology was attractive for car body designer, because it saves the weight of the car without strength loss. In this study, the laser welding performance of magnesium sheet was investigated for Mg TWB panel manufacturing. The material was strip casted and rolled magnesium alloy sheet contains 3 wt% Al and 1 wt% Zn (AZ31). Lamp pumped Nd:YAG laser of 2kW was used and its laser light was delivered by optical fiber of 0.6mm core diameter to material surface with focusing optics of 200mm focal length for TWB welding. The microstructure of weld bead was investigated to check internal defects such as inclusion, porosity and cracks. Also mechanical properties and formability were evaluated for press forming of car body. For the results, there was no crack but inclusion or porosity on weld at some conditions.The tensile strength of weld was over 95% of base metal. Inner and outer panel of engine hood were press formed and assembled at elevated temperature.

• Structural Engineering and Mechanics
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• v.62 no.6
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• pp.739-748
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• 2017

Notches such as slots are typical geometric features on mechanical components that promote fatigue crack initiation. Unlike for components with open hole type notches, there are no conventional treatments to enhance fatigue behavior of components with slots. In this work we evaluate the viability of applying laser shock peening (LSP) to extend the fatigue life of 6061-T6 aluminum components with slots. The feasibility of using LSP is evaluated not only on damage free notched specimens, but also on samples with previous fatigue damage. For the LSP treatment a convergent lens was used to deliver 0.85 J and 6 ns laser pulses 1.5 mm in diameter by a Q-switch Nd: YAG laser, operating at 10 Hz with 1064 nm of wavelength. Residual stress distribution was assessed by the hole drilling method. A fatigue analysis of the notched specimens was conducted using the commercial code FE-Safe and different multiaxial fatigue criteria to predict fatigue lives of samples with and without LSP. The residual stress field produced by the LSP process was estimated by a finite element simulation of the process. A good comparison of the predicted and experimental fatigue lives was observed. The beneficial effect of LSP in extending fatigue life of notched components with and without previous damage is demonstrated.

• Electrical & Electronic Materials
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• v.8 no.3
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• pp.285-290
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• 1995

High quality $Y_{1}$Ba$_{2}$Cu$_{3}$$O_{7-x}$ thin films have been fabricated by pulsed Nd:YAG laser deposition using an unusual 'off-axis' target-substrate geometry. Various properties of superconducting $Y_{1}$Ba$_{2}$Cu$_{3}$$O_{7-x}$ thin films have been studied systematically as a function of oxygen pressure during the deposition, in both 'on-axis' and the unusual 'off-axis' target substrate geometries. In the 'off-axis' geometry, one can completely eliminate the so-called 'laser droplets' from the film surface and thus obtain smooth high quality films. It is found that films with optimum structural and electrical properties are obtained at a lower oxygen pressure range during the 'off-axis' deposition when compared with that required in the 'on-axis' deposition geometry.