• 열처리공학회지
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• 제36권4호
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• pp.237-241
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• 2023

Recently, research on flexible sensors for personal health management has been gaining attention. In this study, we fabricated a crack-based flexible sensor in thin film form to measure the pulse on the wrist. We evaluated the characteristics of the sensor based on the curing conditions of the PDMS (Polydimethylsiloxane) film to optimize the sensor's gauge factor. The modulus of PDMS varies depending on the curing conditions. In this case, the modulus of PDMS has a significant influence on crack formation, leading to changes in the sensitivity of the sensor. This study examined the changes in the gauge factor associated with these variations.

• 대한조선학회논문집
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• 제45권6호
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• pp.679-687
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• 2008

The fatigue life of ship structure under cyclic loading condition is made up of crack initiation and propagation stages. For a welding member in ship structure, the fatigue crack propagation life is more important than the fatigue crack initiation life. To calculate precisely the fatigue crack propagation life at the critical welding location, the knowledge of the residual stress sensitivity on the fatigue strength is necessary. In this study, thermo elastic-plastic analysis was conducted in order to examine the effect of residual stress on the fatigue crack propagation life. Also the fatigue crack propagation lives considering residual stress were calculated using fatigue crack growth code, AFGROW, on the basis of fracture mechanics. AFGROW is widely used for fatigue crack growth predictions under constant and variable amplitude loading. The reliability of AFGROW on the fatigue of ship structure was confirmed by the comparison of the estimated results with the fatigue propagation test results.

• 한국재료학회지
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• 제12권6호
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• pp.508-512
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• 2002

$2000{\AA}-SiO_2/Si(100)$ and $560{\AA}-Si_3N_4/Si(100)$ wafers, which are 10 cm in diameter, were directly bonded using a rapid thermal annealing method. We fixed the anneal time of 30 second and varied the anneal temperatures from 600 to $1200^{\circ}C$. The bond strength of bonded wafer pairs at given anneal temperature were evaluated by a razor blade crack opening method and a four-point bonding method, respectively. The results clearly slow that the four-point bending method is more suitable for evaluating the small bond strength of 80~430 mJ/$\m^2$ compared to the razor blade crack opening method, which shows no anneal temperature dependence in small bond strength.

• 한국태양에너지학회:학술대회논문집
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• 한국태양에너지학회 2012년도 춘계학술발표대회 논문집
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• pp.91-95
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• 2012

본 연구에서는 열충격 시험을 통하여 Cell레벨에서의 효율저하 특성을 분석하였다. 열충격 시험은 PV모듈의 시험 규격인 KS C IEC-61215를 이용하여 보다 가혹한 조건인 $-40^{\circ}C$에서 $120^{\circ}C$의 조건으로 500사이클 수행하였다. I-V 측정을 통하여 효율을 분석한 결과, 열충격 시험 전 13.9%에서 열충격 시험 후 11.0%로 효율이 저하 됐으며, 감소율은 20.9% 나타났다.EL촬영을 통해 표면을 분석한 결과 Ribbon접합부 및 Gridfinger의 손상으로 확인 됐으며, 보다 정확한 효율 저하의 원인을 분석하기 위해 단면분석을 실시한 결과 표면손상으로 확인 되었던 위치의 Cell내부에서도 Crack을 확인 할 수 있었다. 또한 FF값을 분석한 결과 열충격 시험 전 72.3%에서 시험 후 62.0%로 11.8%의 감소율을 보였다. 따라서, 경년 시 나타나는 효율저하는 Cell자체의 소모전력 증가와 외부환경에 의한 표면 손상 및 Cell내부의 Crack에 기인하여 가속된다고 판단된다.

• 마이크로전자및패키징학회지
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• 제8권4호
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• pp.47-52
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• 2001

Sn-Cu-Ni계 솔더를 이용한 AC Adapter의 Pb-Free Wave 솔더링 공정을 Six Sigma기법으로 개발하였다. 솔더 접합부의 외관, 미세조직, Lift-off현상 및 Crack발생 유.무를 관찰하여 접합기구를 규명하고자 하였으며 열 충격시험을 통하여 신뢰성평가를 수행하였다. 솔더 접합부의 Sn-Cu-Ni계 솔더와 Cu Land 사이에는 약 5 $\mu\textrm{m}$ 두께의 $(Cu,Ni)_6/Sn_5$ 형태의 금속간화합물이 발견되었고 열 충격후 750사이클까지는 Crack이 발견되지 않았다. 본 연구로 개발된 제품은 기존의 Sn-Pb솔더를 사용한 제품에 비해서 양산성 및 신뢰성 측면에서 우수한 특성을 나타내었다.

• 한국정밀공학회지
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• 제27권12호
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• pp.99-106
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• 2010

Gas turbines operation for power generation increased rapidly since 1990 due to the high efficiency in combined cycle, relatively low construction cost and low emission. But the operation and maintenance cost for gas turbine is high because the expensive superalloy hot gas path parts should be repaired and replaced periodically This study analyzed the initiation and propagation of the crack at the gas turbine blades which are coated with MCrAIY as a bond coat and TBC as a top coat. The sample blades had been serviced at the actual gas turbines for power generation. Total 7 sets of blades were analyzed and they have different EOH(equivalent operation hour). Blades were sectioned and the cracking distribution were measured and analyzed utilizing SEM(scanning electron microscope) and optical microscope. The blades which had 52,000 EOH of operation had cracks at the substrate and the maximum depth was 0.2 mm. Most of the cracks initiated at the boundary layer between TBC and bond coat and propagated down to the bond coat. Once bond coat is cracked, the base metal is exposed to the oxidation condition and undergoes notch effect. Under this environment, the crack branched at the inter-diffusion layer and propagated to the substrate. Critical cracks affecting the blade life were analyzed as those on suction side and platform.

• 한국재료학회지
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• 제4권3호
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• pp.329-333
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• 1994

1시간 주기로 -$35^{\circ}C$에서 +$125^{\circ}C$까지의 온도 변화에 지배되는 Leadless Ceranic Chip Carriers(LLCC'S)의 Solder접합부에서 균열이 계면을 따라 일어났다. 이런 균열이 계면을 취약하게 하는 어떤 불순물에 의한 것이 아닌지를 Scanning Auger Microprobe(SAM)을 이용해 조사했다. 그 결과 계면을 따라 일어나는 균열이 계면의 산화에 의해 일어날 수 있다는 것이 발견되었고, 그에 따라 산화에 취약해진 계면을 따라 일어나는 이런 종류의 피로 파괴현상에 대한 모델을 제시했다.

• Journal of Welding and Joining
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• 제17권3호
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• pp.90-95
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• 1999

The increase in high speed, multi-function and high I/O pin semiconductor devices highly demands high pin count, very thin, and high density packages. BGA is one of the solutions, but the package has demerits in package reliability, surface mounting problems due to the PCB warpage and solder joint crack related with TCE mismatch between the materials. On this study to verify the thermal fatigue lifetime of the solder joint FEM and experiments were performed after surface mounting BGA with different solder composition and reliability conditions. FEM showed optimum composition of Ag3.2-Sn96.5 and under the composition minimum creep deformation of the solder joint was calculated, and the thermal fatigue lifetime was improved. In view of temperature cycle condition, the conditions of $-65^{\circ}C$to $150^{\circ}C$ showed minimum lifetime and t was 1/3 of $0^{\circ}C$ to $125^{\circ}C$ condition. Test board was prepared and solder joint crack was verified. Until 1000cycle on soder joint crack was observed.

• 대한기계학회논문집
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• 제19권9호
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• pp.2133-2141
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• 1995

The thermo-mechanical fatigue tests were performed on the specimens extracted from 1.5Cr-0. 67Mo-0.33V alloy. The characteristics of thermo-mechanical fatigue crack propagation were examined and reviewed in view of fracture mechanics. The results obtained from the present study are summarized as follows : (1) The propagation characteristics of isothermal low-cycle fatigue crack are dominated by .DELTA.J$_{f}$ in case of PP waveform, and .DELTA.J$_{c}$ in case of CP waveform. (II)The propagation characteristics of thermo-mechanical fatigue crack are dominated by .DELTA.J$_{c}$ for in-phase case, and by .DELTA.J$_{c}$ for out-of-phase. The present results were in good agreement with the equation of propagation law for isothermal low-cycle fatigue crack in case of thermo-mechanical fatigue.tigue.e.

• 대한용접접합학회:학술대회논문집
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• 대한용접접합학회 2002년도 Proceedings of the International Welding/Joining Conference-Korea
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• pp.145-150
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• 2002

It has been well known that ductile fracture of steels is accelerated by triaxial stresses. The characteristics of ductile crack initiation in steels are evaluated quantitatively using two-parameters criterion based on equivalent plastic strain and stress triaxiality. It has been demonstrated by authors using round-bar specimens with circumferential notch in single tension that the critical strain to initiate ductile crack from specimen center depends considerably on stress triaxiality, but surface cracking of notch root is in accordance with constant strain condition. In order to evaluate the stress/strain state in the specimens, especially under dynamic loading, a thermal, elastic-plastic, dynamic finite element (FE) analysis considering the temperature rise due to plastic deformation has been carried out. This study provides the fundamental clarification of the effect of strength mismatching, which can elevate plastic constraint due to heterogeneous plastic straining, loading mode and loading rate on critical condition to initiate ductile crack from notch root using equivalent plastic strain and stress triaxiality based on the two-parameter criterion obtained on homogeneous specimens under static tension. The critical condition to initiate ductile crack from notch root for strength mismatched bend specimens under both static and dynamic loading would be almost the same as that for homogeneous tensile specimens with circumferential sharp notch under static loading.