• 한국콘크리트학회:학술대회논문집
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• 한국콘크리트학회 2006년도 추계 학술발표회 논문집
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• pp.777-780
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• 2006

Recently, owing to the development of industry and the improvement of building techniques, the concrete structure is becoming larger and higher. In hardening these large concrete, the heat of hydration gives rise to considerable thermal stress depending on the size and environmental condition of concrete, which might cause thermal cracking. Especially, the crack may cause severe damage to the safety and the durability of concrete structure. This study is investigated the thermal properties of concrete according to several binder conditions, such as OPC, Belite Rich Cement(BRC), Low-Heat-Mixed Cement(LHC), Fly ash added cement. As a result of this study, the Flowability of concrete was beetter with BRC and LHC than FA(25) and OPC. On the other hand, LHC gets superior effect in the control of heat hydration, it's caused by the volume of OPC.

• 한국전기전자재료학회:학술대회논문집
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• 한국전기전자재료학회 2000년도 추계학술대회 논문집
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• pp.57-60
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• 2000

In this paper, study on the properties of the thermal degradated epoxy resin which is used in indoor insulation apparatus is performed to investigate the problems of the decreasing insulation characteristics and crack in the indoor insulation apparatus. As a parameter of variation, SEM, contact angle, surface resistivity, relative dielectric constant and weight loss are measured. As the results of the above measurements, the contact angle and surface resistivity of the epoxy resin has increased to 200$^{\circ}C$ in but at the above 200$^{\circ}C$ the values have decreased. The relative dielectric constants the thermal treated samples have increased on with the temperature increase. We find the volatile components of the epoxy resin compound has disappeared during thermal degradation by SEM. The insulation properties of the epoxy resin have increased by the 200$^{\circ}C$ but decreased in the above 200$^{\circ}C$.

• 한국세라믹학회지
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• 제39권5호
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• pp.484-489
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• 2002

테이프 캐스팅된 알루미나/지르코니아 또는 뮬라이트/지르코니아를 표면층으로 알루미나/지르콘(소결시 반응결합 뮬라이트/지르코니아 유도)을 내부층으로 적층하고 고온가압소결함으로써 층상 복합체를 제조하였다. 소결체에서 다양한 형태의 균열을 관찰 할 수 있었으며, 이는 주로 표면층으로의 횡단균열(channel crack, 계면에 수직방향으로 전파되는 균열), 중간층 내에서의 종단균열(transverse crack, 계면에 거의 평행한 방향으로 전파되는 균열)과 증간사이를 분리시키는 계면균열(interface crack, 계면을 따라 전파되는 균열)들로 구성되어 있었다. 이러한 균열들은 층을 이루는 복합산화물간의 열팽창계수의 차이에 의해 형성된 것으로 여겨졌다. 특히, 표면층을 뮬라이트/지르코니아로 적층하였을 경우 층간 계면에 평행한 균열과 중간층 내로의 종단균열이 생성되었으나, 알루미나/지르코니아로 하였을 경우는 이러한 균열이 확인되지 않았다. 한편, 압흔하중에 의한 적층체의 잔류응력 역시 표면층의 종류에 따라서 상이한 양상을 나타내었다.

• E2M - 전기 전자와 첨단 소재
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• 제10권6호
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• pp.519-527
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• 1997

The micro crack was occurred where the stress concentrated by the thermal stress which was induced during the cooling period after molding process or by the various reliability tests. In order to estimate the possibility of development from inside micro crack to outside fracture, the fracture toughness of EMC should be measured under the various applicable condition. But study was conducted very rarely for the above area. In order to provide a was to decide the fracture resistance of EMC (Epoxy Molding Compound) of plastic package which is produced by using transfer molding method, measuring fracture is studied. The specimens were made with various EMC material. The diverse combination of test conditions, such as different temperature, temperature /humidity conditions, different filler shapes, and post cure treatment, were tried to examine the effects of environmental condition on the fracture toughness. This study proposed a way which could improve the reliability of LOC(Lead On Chip) type package by comparing the measured $J_{IC}$ of EMC and the calculated J-integral value from FEM(Finite Element Method). The measured $K_{IC}$ value of EMC above glass transition temperature dropped sharply as the temperature increased. The $K_{IC}$ was observed to be higher before the post cure treatment than after the post cure treatment. The change of $J_{IC}$ was significant by time change. J-integral was calculated to have maximum value the angle of the direction of fracture at the lead tip was 0 degree in SOJ package and -30 degree in TSOP package. The results FEM simulation were well agreed with the results of measurement within 5% tolerance. The package crack was proved to be affected more by the structure than by the composing material of package. The structure and the composing material are the variables to reduce the package crack.ack.

• 한국항행학회논문지
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• 제23권5호
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• pp.460-465
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• 2019

본 연구에서는 항법정보 산출용 컴퓨터에 탑재되는 단일보드컴퓨터를 대상으로 야전 운용간 발생한 전기적 고장현상에 대하여 구조해석 관점에서 해소방안을 도출하고자 하였다. 특성요인도 분석을 통해 단일보드컴퓨터의 구조적인 문제로 중앙처리장치 기판에 크랙이 발생한 것을 확인할 수 있었고, 크랙발생 부위에 가해진 물리적인 영향으로 인해 통신기능 수행이 불가해지면서 동시에 부팅이 불가한 현상이 나타난 것으로 확인되었다. 이에 대하여 크랙현상을 유발시키는 과도응력의 위치를 찾고자 구조해석을 수행하였다. 구조해석을 통해 응력집중현상이 발생하는 부위를 확인할 수 있었고, 이를 해소시키기 위해 과도응력의 원인이 되는 부품과 구조물을 변경하는 개선방안을 수립하였다. 개선방안에 대한 검증은 구조해석을 통해 개선 전과 후의 구조물에 작용하는 응력분포를 비교하여 응력의 감소정도를 보였다. 추가적으로, 열 해석을 통해 부품 및 구조물 변경으로 인한 방열기능 유지여부를 확인하였고, 개선방안을 적용한 실 장비의 방열판 온도를 측정함으로써 실제 장비의 방열 영향성을 확인하였다.

• 한국재료학회지
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• 제13권3호
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• pp.137-143
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• 2003

The air gap between the metal and mold, formed by shrinkage during solidification, causes surface and subsurface cracks in the continuous casting process. Molten crack on the surface might also occur due to improper heat transfer between them. In order to compensate the air gap in mold design, the thermal contraction is an essential factor. In this study, the thermal contraction and expansion behaviors were examined from the ($\alpha$ and pearlite)/${\gamma}$ to ${\gamma}$/$\delta$ transformations in continuous casting steels by the commercial dilatometer and the self- assembled dilatometer with laser distance measurement. It was found that the thermal contraction and expansion behaviors were very dependant on the phase transformation of the ${\gamma}$/$\delta$ as well as ($\alpha$ and pearlite)/${\gamma}$. The sudden volume change from $\delta$ to ${\gamma}$ which might cause cracks in the continuous casting process, was observed on cooling just below the melting temperature by the self-assembled dilatometer.

• 열처리공학회지
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• 제9권2호
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• pp.147-158
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• 1996

Generally, analytical consideration on the behaviour of metallic structures during quenching process, and analysis on the thermal stress and deformation after heat treatment are very important in presumption of crack and distorsion of quenched material. In this study a set of constitute equations relevant to the analysis of thermo elasto-viscoplastic materials with strain hysteresis during quenching process way presented on the basis of contimuum thermo-dynamics mechanics. The thermal stresses were numerically calculated by finite element technique of weighted residual method and the principle of virtual work. In the calculation process, the temperature depandency of physical and mechaniclal properties of the material in consideration. On the distribution of elasto-viscoplastic thermal stresses according to radial direction, axial and tangential stress are tensile stress(50MPa, 1.5GPa and 300MPa) in surface and compressive stress(-1.2GPa, -1.14GPa and -750MPa) in the inner part on the other hand, radial stress is tensile stress(900MPa) in area of analysis. According to axial direction, tangential stress gradients are average 60MPa/mm on the whole. The reversion of stress takes place at 11.5 to 16.8mm from the center in area of analysing.

• 한국재료학회지
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• 제24권9호
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• pp.481-487
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• 2014

The effect of alpha phase on the fatigue properties of Fe-29%Ni-17%Co low thermal expansion alloy was investigated. Two kinds of alloys (Base alloy and Alpha alloy) were prepared by controlling the minimal alloy composition. Microstructure observation, tensile, high-cycle fatigue, and low-cycle fatigue results were measured in this study. The Base alloy microstructure showed typical austenite ${\gamma}$ phase. Alpha alloy represented the dispersed phase in the austenite ${\gamma}$ matrix. As a result of tensile testing, Alpha alloy was found to have higher strengths (Y.S. & T.S.) and lower elongation compared to those of the Base alloy. High cycle fatigue results showed that Alpha alloy had a higher fatigue limit (360MPa) than that (330MPa) of the Base alloy. The Alpha alloy exhibited the superior high cycle fatigue property in all of the fatigue stress conditions. SEM fractography results showed that the alpha phase could act to effectively retard both fatigue crack initiation and crack propagation. In the case of low-cycle fatigue, the Base alloy had longer fatigue life in the high plastic strain amplitude region and the Alpha alloy showed better fatigue property only in the low plastic strain amplitude region. The fatigue deformation behavior of the Fe-29%Ni-17%Co alloy was also discussed as related with its microstructure.

• 분석과학
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• 제10권4호
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• pp.300-306
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• 1997

직류전압강하법을 이용한 균열길이 측정방법은 입출력 도선의 위치 및 보정방법에 큰 영향을 받는다. 본 실험에서는 CT 시편을 실제 시편보다 9배 크기로 제작하여, 입출력 도선의 위치, 열 유도 EMF 및 기준전압의 위치가 기존의 보정곡선에 미치는 영향을 연구하였다. 연구 결과 입력전류 도선의 위치가 하중선에 위치할 때, Hicks-Pickard 관계식이 매우 정확하게 a/W와 V/Vo간의 관계를 나타내었으며, 이 때 Vo값을 a/W=0.241에서 측정 또는 계산된 값을 사용하고, 열유도 EMF를 보정함으로써 더욱 정확성을 향상시킬 수 있음을 알았다. 또한 입력도선이 하중선에 위치할 때 기준전압을 CT 시편에서 일반적으로 사용되는 위치인 시편 끝 하단에서 측정할 경우, 기준전압으로 보정한 전압값은 매우 큰 오차를 나타내었다.

• 대한기계학회논문집A
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• 제26권11호
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• pp.2390-2398
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• 2002

For integrity analysis of nuclear reactor pressure vessel, including the Pressurized thermal shock analysis, the fast and accurate calculation of the stress intensity factor at the crack tip is needed. For this, a simple approximation scheme is developed and the resulting stress intensity factors for axial semi-elliptical cracks in cylindrical vessel under various loading conditions are compared with those of the finite element method and other approximation methods, such as Raju-Newman's equation and ASME Sec. Xl approach. For these, three-dimensional finite-element analyses are performed to obtain the stress intensity factors for various surface cracks with t/R = 0.1. The approximation methods, incorporated in VINTIN (Vessel INTegrity analysis-INner flaws), utilizes the influence coefficients to calculate the stress intensity factor at the crack tip. This method has been compared with other solution methods including 3-D finite clement analysis for internal pressure, cooldown, and pressurized thermal shock loading conditions. The approximation solutions are within $\pm$2.5% of the those of FEA using symmetric model of one-forth of a vessel under pressure loading, and 1-3% higher under pressurized thermal shock condition. The analysis results confirm that the VINTIN method provides sufficiently accurate stress intensity factor values for axial semi-elliptical flaws on the surface of the reactor pressure vessel.