• 비파괴검사학회지
• /
• 제19권4호
• /
• pp.288-293
• /
• 1999

고온에서 사용중인 터빈 로터의 안전성을 평가하기 위해서는 열화된 재료의 물성이 필요하다. 실제로 발전소에서 사용되고 있는 열화도가 다른 로터강을 종류별로 입수하기가 어렵기 때문에, 터빈 로터재로 널리 사용되고 있는 1Cr-1Mo-0.25V 강으로 인공열화 시료를 제작하였다. 실제로 사용된 재료의 미세조직과 유사한 미세조직을 갖는 시료를 얻기 위하여 실제 사용온도보다 높은 $630^{\circ}C$의 등온에서 열처리시간을 다르게 하여 열화도가 다른 7종류의 시료를 얻었다. 열화도를 비파괴적으로 평가하기 위하여 상온에서 측정한 보자력을 이용하였다. 열화도의 증가에 따라 경도와 보자력은 감소하였는데, 이 원인을 미세조직 및 EPMA 분석에 의해 구명하였고, 경도와 보자력과의 상관관계를 만들어 비파괴적으로 열화도를 평가할 수 있는 기초를 마련하였다.

• 대한치과보철학회지
• /
• 제37권6호
• /
• pp.767-775
• /
• 1999

The purpose of this study was to evaluate the effect of wattage and curing time on surface hard-ness, three-point bending strength and internal porosity of microwave curing denture base resin. Two sizes of resin specimens were made of Acron $MC^{(R)}\;;\;3.5{\times}10{\times}60mm$ for surface hardness and three-point bending strength measurement and $5{\times}12{\times}60mm$ for internal porosity measurement. They were cured by microwave energy at varing wattages(500W, 700W) and curing times(2min., 3min., 4min.) to determine if a certain wattage/curing time combination would improve physical properties. Surface hardness was measured with Vikers hardness tester, three-point bend-ing strength with universal testing machine and internal porosity was calculated by measuring the weight in air and in water. The results obtained were as follows: 1. There was no significant difference in percent porosity among experimental groups(p>0.05). 2. 500W/3min. group showed the higher surface hardness than 700W/2, 3, 4min. groups(p<0.05), and 700W/4 min. group showed the lower surface hardness than 500W/2, 3, 4min. groups(p<0.05), but there was no significant difference among others(p>0.05). 3. 500W/3min. group yielded the higher value of bending strength than 500W/2min., 700W/3, 4min. groups(p<0.05), but there was no significant difference among others(p>0.05).

• 한국윤활학회:학술대회논문집
• /
• 한국윤활학회 1997년도 제25회 춘계학술대회
• /
• pp.80-88
• /
• 1997

Repeated sliding contact wear test was performed with copper specimens to obtain the relationship between wear and surface hardening. Wear surface and wear track section were observed by optical microscopy. Wear volume and micro-vikers hardness of sublayer below wear surface were obtained. These results suggested that wear mechanism depended on contact load than sliding velocity. Therefore wear mechanism was abrasive wear within critical contact load and adhesive wear over critical contact load. Wear rate increased with contact load, sliding distance but decreased with sliding velocity. Surface hardening increased with sliding velocity and sliding distance but decreased with contact load.

• 한국표면공학회:학술대회논문집
• /
• 한국표면공학회 2012년도 추계총회 및 학술대회 논문집
• /
• pp.101-102
• /
• 2012

Thermal Diffusion Process(TD Process)을 통하여 베어링강 소재인 SUJ2 표면에 Vanadium Carbide를 석출시켜 표면 물성에 관한 연구를 진항하였다. $900{\sim}950^{\circ}C$ 온도와 2~6H 공정시간에 따라 TD Process에 의한 코팅층의 변화를 Micro Vikers Hardness Tester와 광학현미경, SEM, EDS를 통하여 관찰하였다. 그 결과 공정시간 및 온도는 코팅층 성장과 비례한다는 것을 확인 할 수 있었고 SUJ2 표면에 성장된 코팅층은 높은 경도값을 갖는 VC, CrC 코팅층임을 확인하였다.

• 한국정보디스플레이학회:학술대회논문집
• /
• 한국정보디스플레이학회 2003년도 International Meeting on Information Display
• /
• pp.771-774
• /
• 2003

The mechanical properties of barrier ribs in PDP require quantification in order to control the defects and to increase the yield in the process. Several different types of rib materials were tested for hardness (H) and Young's modulus (E) with a microtip indenter (Berkovich type). For the assessment of fracture toughness of the rib, a macro Vikers indenter was used. The materials with 30wt% of filler were fired at between $490^{\circ}C$ and $570^{\circ}C$. As a result, the composite became fully densified at $520^{\circ}C$, which is near the T s (Littleton softening point) of glass frit. As the filler content increased, the fracture toughness also $(K_{IC})$ increased in the range of 0.60 to 2.63 $MPa{\cdot}m^{0.5}$ after sintering at $550^{\circ}C$. The results suggest that the application of a nano-indenter would be useful for testing the mechanical properties of barrier ribs.

• Journal of Welding and Joining
• /
• 제27권3호
• /
• pp.73-79
• /
• 2009

This present paper investigated the mechanical properties and the microstructures of each penetration shapes classifying the conduction shape area and the keyhole shape area about electron beam welded 120(T)mm thick plated aluminum 5052 112H. As a result the penetration depth is increased linearly according to the output power, but the aspect ratio is decreased after the regular output power. In the conduction shape area, the Heat affected zone is observed relatively wider than the keyhole shape area. In the material front surface of the welded specimen, the width is decreased but the width in the material rear surface is increased. After the measuring the Micro Vikers Hardness, it showed almost similar hardness range in all parts, and after testing the tensile strength, the ultimate tensile strength is similar to the ultimate tensile strength of the base material in all the specimens, also the fracture point was generated in the base materials of all the samples. In the result of the impact test, impact absorbed energy of the Keyhole shape area is turned up very high, and also shown up the effect about four times of fracture toughness comparing the base material. In the last result of observing the fractographs, typical ductile fraction is shown in each weld metal, and in the basic material, the dimple fraction is shown. The weld metals are shown that there are no other developments of any new chemical compound during the fastness melting and solidification.

• Journal of Periodontal and Implant Science
• /
• 제25권3호
• /
• pp.614-622
• /
• 1995

Root caries is very frequently developed on exposed root surface after periodontal surgical treatment. In order to determine the anti-caries effect of Nd : YAG laser irradiation on periodontally exposed root surface, 40 mandibular molar teeth that had been extracted due to excessive periodontal destruction were used as the experimental teeth. All teeth were treated by the same procedure as conventional periodontal root treatment, ie thorough scaling, root planing and root conditioning with tetracycline HCl(100mg/ml, 5min.). Within middle one third of root, mesial half surface(20) or distal half surface(20) was randomly irradiated at various power of 1.0W, 2.0W, 3.0W and 4.0W for 60 seconds by non-contact(5mm) delivery of a pulsed Nd : YAG laser(EN.EL.EN060, Italy). The microhardness was measured by Vikers microhardness tester(Wilson, USA) at 2mm/second of jog speed under 100gm load. The difference of microhardness between irradiated side and non-irradiated side was statistically analyzed ANOVA and Duncan's method. Following results were obtained ; 1. The microhardness(Knoop hardness number) was significantly higher in laser irradiated surface than non-irradiated surface(p<0.05). 2. There was no significant difference in microhardness between experimental groups classified by different laser power(p>0.1). The results suggest that Nd : YAG laser irradiation on exposed root suface after periodontal therapy may inhibit the root caries development by enhancing surface microhardness.

• 한국해양공학회:학술대회논문집
• /
• 한국해양공학회 2006년 창립20주년기념 정기학술대회 및 국제워크샵
• /
• pp.162-165
• /
• 2006

In this study, Liquid Phase Sintered SiC (LPS-SiC) was fabricated by hot pressing method with $\beta$-SiC powder whose a particle size is 30nm and less on the average in argon condition at 1780 and $1800^{\circ}C$ under 20MPa. Alumina ($Al_2O_3$), yttria ($Y_2O_3$) and silica ($SiO_2$) were used for sintering additives. To investigate effects of particle-size and temperature on $SiO_2$, LPS-SiC was fixed $Al_2O_3$, $Y_2O_3$ and then particle-size of $SiO_2$ were changed as two kinds. The system of particle-size and temperature on sintering additives which affects a property of sintering os well os the influence depending on particle-size and temperature of sintering additives were investigated by measurement of sintering properties. Such as measurement of sintering density, vikers hardness and observing of microstructure were investigated to make sure of the optimum condition which is about matrix of $SiC_f/SiC$ composites. Base on the composition of sintering additives, microstructure and sintering property correlation, the effect of particle-size of sintering additives are discussed. An experimental method to investigate the dynamic characteristics of bums in extreme environmental condition is established.