• 대한기계학회:학술대회논문집
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• 대한기계학회 2003년도 추계학술대회
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• pp.187-192
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• 2003

The heat (mass) transfer characteristics in the tip-leakage flow region of a high-turning first-stage turbine rotor blade has been investigated by employing the naphthalene sublimation technique. The heat transfer data in the tip-leakage flow area for the tip clearance-to-span ratio, h/s, of 2.0% are compared with those in endwall three-dimensional flow region without tip clearance (h/s = 0.0 %). The result shows that the thermal load in the tip-leakage flow region for h/s = 2.0% is more severe than that in the endwall flow region for h/s = 0.0%. The thermal loads even at the leading and trailing edges for h/s = 2.0% are found larger than those for h/s = 0.0%. The tip-leakage flow results in heat transfer augmentations near the tip on both pressure and suction sides in comparison with the mid-span results.

• 한국재료학회지
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• 제23권2호
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• pp.81-88
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• 2013

In this study, using a tin chloride solution as the raw material, a nano-sized tin oxide powder with an average particle size below 50 nm is generated by a spray pyrolysis process. The properties of the tin oxide powder according to the nozzle tip size are examined. Along with an increase in the nozzle tip size from 1 mm to 5 mm, the generated particles that appear in the shape of droplets maintain an average particle size of 30 nm. When the nozzle tip size increases from 1 mm to 2 mm, the average size of the generated particles is around 80-100 nm, and the ratio of the independent particles with a compact surface structure increases significantly. When the nozzle tip size is at 3 mm, the majority of the generated particles maintain the droplet shape, the average size of the droplet-shaped particles increases remarkably compared to the cases of other nozzle tip sizes, and the particle size distribution also becomes extremely irregular. When the nozzle tip size is at 5 mm, the ratio of droplet-shaped particles decreases significantly and most of the generated particles are independent ones with incompact surface structures. Along with an increase in the nozzle tip size from 1 mm to 3 mm, the XRD peak intensity increases, whereas the specific surface area decreases greatly. When the nozzle tip size increases up to 5 mm, the XRD peak intensity decreases significantly, while the specific surface area increases remarkably.

• 한국재료학회지
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• 제14권4호
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• pp.300-306
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• 2004

A laser welding has been made between sintered tip of Fe-Co-W and low carbon steel shank for the diamond saw blade. The welding characteristics and formation of defect has been investigated carefully for the weld fusion zone in different welding condition. Full penetration has been observed for the whole range of heat input investigated in the present work. Bead width and under-fill have been increased with the increase of heat input. With increasing of heat input small cavities were decreased while large cavities were increased. The ratio of total cavity area to the entire weld bead area was not changed significantly with change of heat input. Most of cavities were found near the tip, and supposed to be formed from the pore in the tip.

• 한국정밀공학회지
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• 제21권12호
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• pp.167-173
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• 2004

Recently, it has been reported that frictional behavior at nanometer scale can be different from that at macro scale. In this article, friction and wear tests were conducted using an AFM to investigate the effect of real contact area on the coefficient of friction and wear property. SiO$_2$, Hica, and SiGe were used in friction test and the AFM tip was Si$_3$N$_4$. The real contact area between an AFM tip and flat surface was calculated by the Johnson-Kendall-Roberts (JKR) theory. Wear specimen was Mica, and the diamond tip was used. We found that the coefficient of friction is constant below a critical area, but it is degraded over the area. Moreover, it is found that wear depth increased rapidly from a certain load and was degraded as a function of the number of the scanning cycles. Also, the range of scanning velocity used in this study had little effect on the wear depth.

• 대한기계학회논문집A
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• 제30권11호
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• pp.1455-1460
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• 2006

The relationship between fatigue crack growth behavior and cyclic crack tip opening displacement is studied. An elastic-plastic finite element analysis (FEA) is performed to examine the growth behavior of fatigue crack, where the contact elements are used in the mesh of the crack tip area. We investigate the relationship between the reversed plastic zone size and the changes of the cyclic crack tip opening displacement along the crack growth. We investigate the effect of the element size when predict fatigue crack opening behavior using the cyclic crack tip opening displacement obtained from FEA. The cyclic crack tip opening displacement is related to fatigue crack opening behavior.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2004년도 춘계학술대회
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• pp.1126-1129
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• 2004

Because of the various length condition of carbon nanotube, it is very confined the application area of the single CNT tip. In this paper, it was proposed the cutting technique of single CNT tip and the relationship between the etched volume and the amount of the applied charge. It is possible to control the length of single CNT tip arbitrary using this technique. The etched volume and length in the single CNT tip can be predicted with the amount of the applied charge. It is very easy to make a single CNT tip with proper length using this technique and to make nanotweezer that was composed two single CNT tips.

• Journal of Periodontal and Implant Science
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• 제39권2호
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• pp.139-148
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• 2009

Purpose: Ultrasonic scalers have been widely used for removing biofilm which is considered as major etiologic factor of periodontal disease. The purpose of this study was to evaluate the effect of working parameters of piezoeletric ultrasonic scaler with scaler tip (No. 1 tip) on casting gold alloy removal. Methods: Type III dental casting gold alloy (Firmilay$^{circledR}$, Jelenko Inc, CA, USA) was used as substitute for tooth substance. Piezoeletric ultrasonic scaler and No.1 scaler tip (P-Max$^{circledR}$, Satelec, France) were selected. The selected working parameters were mode (P mode, S mode), power setting (2, 4, 8) and lateral force (0.5 N, 1.0 N, 2.0 N). The effect of working parameters was evaluated in terms of ablation depth, ablation width and ablation area. Results: Mode influenced ablation depth and ablation area. Power also influenced ablation depth and ablation area. Especially, Power 2 and power 8 showed statistically significant difference. Lateral force had influence on ablation width, and 0.5 N resulted significant increase compared with 1.0 N and 2.0 N. Ablation depth was influenced by mode, power and lateral force and defect width was influenced by lateral force. Ablation area was influenced by mode and power. Conclusions: It can be concluded that the use of piezoelectric ultrasonic scaler with No. 1 scaler tip in S mode and high power may result in significant loss of tooth substance.

• 대한기계학회논문집B
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• 제28권5호
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• pp.535-544
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• 2004

The heat (mass) transfer characteristics in the tip-leakage flow region of a high-turning first-stage turbine rotor blade has been investigated by employing the naphthalene sublimation technique. The heat transfer data in the tip-leakage flow area for the tip clearance-to-span ratio, h/s, of 2.0% are compared with those in endwall three-dimensional flow region without tip clearance (h/s : 0.0 %). The result shows that the thermal load in the tip-leakage flow region for h/s = 2.0% is more severe than that in the endwall flow region for h/s : 0.0%. The thermal loads even at the leading and trailing edges for h/s = 2.0% are found larger than those for h/s = 0.0%. The tip-leakage flow results in heat transfer augmentations near the tip on both pressure and suction sides in comparison with the mid-span results.

• 한국유체기계학회 논문집
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• 제12권2호
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• pp.39-45
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• 2009

Leakage flow through turbine blade tip gap causes strong leakage vortex near the blade suction side and induces large aerodynamic losses. In this study, the conventional plane tip and various squealer tip blades were tested in a linear cascade in order to measure the effect of the tip shape on the total pressure loss. Three tip gap clearances of 0.6%, 1.3%, and 2.0% of blade span were tested. Flow measurement was conducted at one chord downstream from the trailing edge with a five-hole probe. Results showed that the leakage vortex was stronger than passage vortex and the mass averaged overall total pressure loss through the cascade was the lowest for suction side blade tip case. For all tested cases, the area averaged overall total pressure loss was increased as the tip clearance increased.

• 한국재료학회지
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• 제25권12호
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• pp.690-693
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• 2015

Fatigue crack growth experiments were carried out on a 304 L stainless steel compact-tension(CT) specimen under load control mode. Neutron diffraction was employed to quantitatively measure the residual strains/stresses and the evolution of stress fields in the vicinity of a propagating fatigue-crack tip. Three principal stress components (i.e. crack growth, crack opening, and through-thickness direction stresses) were examined in-situ under loading as a function of distance from the crack tip along the crack-propagation path. The stress/strain fields, measured both at the mid-thickness and near the surface of the CT specimen, were compared. The results show that much higher compressive residual stress fields developed in front of the crack tip near the surface than developed at the mid-thickness area. The change of the stresses ahead of the crack tip under loading is more significant at the mid-thickness area than it is near the surface.