• 대한기계학회:학술대회논문집
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• 대한기계학회 2001년도 춘계학술대회논문집A
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• pp.211-216
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• 2001

The components with the circular cross section have the symmetric combination parts for rotating balance and the crack emanates from the symmetric combination parts. The symmetric cracks from symmetric combination parts make a decrease in the component fatigue life more than single crack. In this study, to estimate the behavior of symmetric cracks, the fatigue test was performed using rotary bending tester on the specimen with a symmetric defects in circular cross section. The material used in this study is Ni-Cr-Mo steel alloy. Under the same stress, the result from the rotary bending fatigue test turned out that the symmetric cracks made a decrease in the fatigue life by 35% more than single crack and the relation between log a and cycle ratio $N/N_f$ obtained linearly.

• 한국가구학회지
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• 제21권6호
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• pp.499-504
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• 2010

한국의 전통가옥인 한옥은 대각재와 원형목으로 만든다. 이들은 열기건조하면 심각한 결함이 발생하기 때문에 보통 수개월에서 1년까지 천연건조하는데 그래도 사용중 결함이 생긴다. 열처리기술을 이용하여 이들을 $170^{\circ}C$이상에서 건조하면서 건조결함을 조사하였다. 온도곡선은 모두 하나 또는 두개의 변곡점을 나타냈다. 표면에서 37.5mm 깊이지점이 $100^{\circ}C$에 도달하는데 걸리는 시간은 열처리온도 $170^{\circ}C$ 과 $190^{\circ}C$가 두 배의 차이를 나타냈다. 열처리 후에 $148mm{\Phi}$ 원형목에 내부할렬이 많이 발생한 것이 발견되었으나, 이에 빈해 표면할렬은 거의 닫혀 있었다. 이러한 표면할렬의 변화를 $300{\times}300mm$ 대각재의 사진을 통해 관찰하였다. 중공재와 무중공재의 건조시간을 비교하였더니 두 배의 차이를 나타냈다.

• 대한치과보철학회지
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• 제45권4호
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• pp.522-533
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• 2007

Statement of problem: Despite of the recent development of the titanium casting system methods, the casting defects such as imperfect casting and internal porosity were frequently observed. Purpose: The purposes of this study were to compare and measure the castability, microhardness, and surface reaction between Grade 2 pure titanium and Ti-6Al-4V by casting these alloys from the different sprue design conditions. Material and methods: Depending on the sprue designs and titanium alloys, 42 ready-made wax patterns were used. By analyzing the remodeling of the cast, internal porosity, microhardness, and titanium surface layer of SEM, there were several results we observed. Results: 1. The measured castability of titanium were categorized in the ascending order: individual sprue group, runner bar group, and single group. This data are based on the statistically signigicant differences. 2. The castability of titanium has not showed the statistically significant differences among the alloys. However, CP-Ti groups were superior to Ti-6Al-4V groups by showing the noticeable castability. 3. The surface layers of the castings of all groups have showed $5{\mu}m$ titanium oxide layers irrespective of sprue designs and titanium alloys. Conclusion: From the above study results, by fabricating the restorations from the centrifugal casting machine direct sprue designs revealed better castability. As we increased the number of sprues in the wax pattern, it revealed better castability. The castability of pure titanium rather than that of Ti-6Al-4V was remarkable. To fabricate the complex forms of the restorations, further researches on the efficient sprue designs and titanium alloys must be made.

• 센서학회지
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• 제5권3호
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• pp.25-31
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• 1996

제철소에서 생산되고, 활용되는 빌렛은 두 종류로 나누어, 밀도가 높은 강편 빌렛과 밀도가 낯은 연주 빌렛이 있다. 강편 빌렛은 밀도가 높고 표면이 매끄러워, 비교적 탐상이 용이하였으나, 연주 빌렛은 밀도간 낮고, 표면이 거칠어 탐상이 어려웠다. 연주 빌렛의 탐상도 가능케하기 위하여 초음파 탐촉자의 재질 및 치수등을 개선하고자 하였다. 주요 실험 결과로는, 초음파의 발신용 부분과, 수신용 부분이 서로 나뉘어 있는 분할형 탐촉자를 채택하였으며, 탐촉자의 치수는 탐상체의 치수와 밀접히 관계됨을 알았다. 예로써, 폭/두께가 각각 160mm인 연주 빌렛의 경우, 압전소자의 길이가 21mm, 폭이 8.5mm, 두께가 0.95mm, 인 것 두장이 나란히 내장된 탐촉자가 가장 적당하였다. 소자의 두께에 의존하는 이 때의 중심 주파수는 2.25MHz 였으며, 두 장의 압전소자간 각도에 의존하는 촛점 거리는 70mm 이었다.

• 한국구조물진단유지관리공학회 논문집
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• 제11권1호
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• pp.95-102
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• 2007

박리, 박락 및 들뜸현상과 같은 결함으로 노후화된 숏크리트 자체가 통행차량이나 시설물에 위험요소로 존재함으로써 이에 대한 피해예방이 요구되는 실정이다. 그러나 급격한 경사와 고소작업 등으로 인해 접근이 곤란하며, 외관상으로는 숏크리트 내부 상황 파악이 힘들다는 한계가 지적되고 있다. 본 연구에서는 이러한 기술적 한계를 극복하고자 적외선 열화상을 이용하여 숏크리트면의 미소한 열이동을 측정해 표면에서 관찰할 수 없는 내부의 결함을 조사하고자 하였다. 현장조사, 측정자료 분석과 내시경 카메라를 이용한 현장조사 작업을 통해 검증을 실시한 결과 숏크리트의 과도한 피복으로 인해 습윤부의 정확한 판정은 불가하였으나 내부의 공동부위를 비파괴 비접촉 방식에 의해 효과적으로 추출할 수 있었다.

• 대한전기학회논문지:시스템및제어부문D
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• 제55권2호
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• pp.68-71
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• 2006

Active thermography has been used for several years in the field of remote non-destructive testing. It provides thermal images for remote detection and imaging of damages. Also, it is based on propagation and reflection of thermal waves which are launched from the surface into the inspected component by absorption of modulated radiation. For energy deposition, it use external heat sources (e.g., halogen lamp or convective heating) or internal heat generation (e.g., microwaves, eddy current, or elastic wave). Among the external heat sources, the ultrasound is generally used for energy deposition because of defect selective heating up. The heat source generating a thermal wave is provided by the defect itself due to the attenuation of amplitude modulated ultrasound. A defect causes locally enhanced losses and consequently selective heating up. Therefore amplitude modulation of the injected ultrasonic wave turns a defect into a thermal wave transmitter whose signal is detected at the surface by thermal infrared camera. This way ultrasound thermography(UT) allows for selective defect detection which enhances the probability of defect detection in the presence of complicated intact structures. In this paper the applicability of UT for fast defect detection is described. Examples are presented showing the detection of defects in PCB material. Measurements are performed on various kinds of typical defects in PCB materials (both Cu metal and non-metal epoxy). The obtained thermal image reveals area of defect in row of thick epoxy material and PCB.

• 한국안전학회지
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• 제34권6호
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• pp.7-12
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• 2019

Flux Cored Arc Welding (FCAW), which has been widely used in many industries, was developed in the 1950s to supplement shortcomings of the Shielded Metal Arc Welding (SMAW). FCAW has an advantage in that it can weld regardless of postures and give good quality results in the filed with many different working conditions. In this study, SM490A (rolled steel for welding structural purpose) with different thicknesses (L:25T+R:30T) were welded using FCAW. Then the mechanical properties (tension test, bending test, hardness test, impact test and macro test) were analyzed and the following conclusions were drawn. In the tensile test, it exceeds the KS standard tensile strength range (400~510) in all welding positions, which means there is a problem in the tensile force transmission performance. In the bending test, it was found that most of the specimens did not exhibit surface rupture or other defects during bending test and they exhibit sufficient toughness even after plastic deformation. In the hardness test, all the results were lower than the standard value of 350 Hv of KS B 0893, which means they have good hardness. In the impact test, all results were larger than the KS reference value of 27J. In the macro test, they showed uniform structure state by the shape of the weld, and there was risk of lamination because no internal defects, bubbles, or impurities were found on the surface of the weld.

• Maxillofacial Plastic and Reconstructive Surgery
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• 제12권3호
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• pp.8-22
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• 1990

This study was performed to evaluate the histopathologic changes of the rabbit tibial compact bone using internal irrigation with both cold and room - temperature saline on drilling. The medial surface of the rabbit tibia was drilled with specially designed pilot drill (2.0mm in diameter) at 300 rpm. When drilling, two different temperature salines were injected (experimental group I : $4^{\circ}C$ saline, experimental goup Ⅱ : room - temperature saline). And the control group was drilled without cooling agent. The three rabbits in each two experimental and control groups were sacrificed 1, 2, 4, and 8 weeks after. The bone tissues including the bony defects were fixed with 10% neurtal buffered formalin, decalcified with formic acid, embedded in paraplast, and sterile sectioned at 5-6${\mu}m$. And then tissue specimens were stained with H - E and observed under light microscope. The results were as follow : The experimental groups showed early bone repair than the control group at all intervals. They underwent the same course of bone repair until 4 weeks. But the experimental group I showed slightly better bone maturation than the experimental group Ⅱ at 8 weeks.

• Journal of Welding and Joining
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• 제30권6호
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• pp.36-41
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• 2012

General condensers consist of many tubes supported by tube sheets and support plates to prevent the deflection of the condenser tubes. When a fluid at high pressure and temperature runs over the tubes for the purpose of transferring heat from one medium to another, the tubes vibrate and their surface comes into contact with the support plates. This vibration causes damage to the tubes, such as cracks and wear. We propose an ultrasonic guided wave technique to detect the above problems in the support plate region. In the proposed method, the ultrasonic guided wave mode, L(0,1), is excited using an internal transducer probe from a single position at the end of the tube. In this paper, we present a preliminary experimental verification using a super stainless tube and show that the defects can be discriminated from the support signals in the support region.

• 한국전기전자재료학회:학술대회논문집
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• 한국전기전자재료학회 2005년도 하계학술대회 논문집 Vol.6
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• pp.221-222
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• 2005

In this paper, application of NN (Neural Network) as a method of pattern discrimination of PD(partial discharge) which occurs at the stator coil of traction motor was studied. For PD data acquisition, three defective models are manufactured such as internal discharge model, slot discharge model and surface discharge model. PD data for recognition were acquired from PD detector and DAQ board which is able to analysis the PD signal and perform the pattern discrimination. Statistical distributions and parameters are calculated to discriminate PD sources. And also these statistical distribution parameters are applied to classify PD sources by BP and has good recognition rate on the discharge sources.