• 열처리공학회지
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• 제31권1호
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• pp.18-23
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• 2018

In this study, low cyclic fatigue test was carried out at room temperature condition for rolled STS304 steel. The results of this study show that rolled STS304 steel has excellent static tensile strength and fatigue characteristics. The relationship between plastic strain range and fatigue life was examined using the triangular wave in order to predict the low cycle fatigue life of rolled STS304 steel by Coffin-Manson equation. Cyclic behavior of rolled STS304 steel was characterized by cyclic hardening with increasing number of cycle through the Hysteresis loop analysis and cyclic response of maximum stress versus number of cycles. It is found that the plastic deformation energy consumed per cycle is reduced by calculating the area of the hysteresis loop.

• 대한기계학회논문집A
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• 제41권8호
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• pp.765-770
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• 2017

Ni기 초내열합금인 GTD111 DS는 가스터빈 블레이드에 사용된다. 본 논문에서는 실제 운전조건과 유사한 조건을 설정하여 GTD111 DS의 저주기 피로시험을 실시하였다 상온, $760^{\circ}C$, $870^{\circ}C$의 온도범위와 다양한 변형률에서 저주기 피로시험을 수행하였다. 실험결과 총 변형률이 증가함에 따라 피로수명은 감소하였다. 상온 및 $760^{\circ}C$에서는 주기적 경화반응이 나타났으며 $870^{\circ}C$에서는 주기적 연화반응이 나타났다. $870^{\circ}C$에서 응력완화 현상은 유지시간에 따른 크리프의 영향으로 나타났다. 피로수명과 총 변형률의 관계는 Coffin-Manson 식을 통해 얻었다. 파단면은 SEM을 통해 초기균열 및 피로진전지역을 관찰하였다.

• 한국항해항만학회지
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• 제29권10호
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• pp.871-876
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• 2005

기존의 기계적인 센서들보다 높은 민감도와 선형성을 가지는 반도체 압력 센서들은 크기가 작고 일괄공정에 의해 제작될 수 있는 반도체 공정 기술로 제작되므로 다양한 산업에서 적용되고 있다. 하지만 열과 반복적인 외부 하중은 센서의 수명에 치명적인 영향을 미치고 있고, 특히 외부에서 가해지는 열은 센서를 구성하는 구조물보다 신호를 전달하는 금속 배선의 피로 수명에 지대한 영향을 미치고 있으므로 이에 대한 영향성을 분석할 수 있는 프로세스를 확립하고, 이후 다양한 재료의 반복적인 열하중에 대한 피로 수명을 Manson & Coffin식에 따라서 평가하였다. 금속 배선의 밑단에서 피로수명이 가장 낮고, 굽힘하중은 피로 수명보다는 응력분포에 큰 영향을 미치고 있다.

• 한국추진공학회:학술대회논문집
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• 한국추진공학회 2009년도 춘계학술대회 논문집
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• pp.18-21
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• 2009

높은 열하중하에 있는 부품의 수명은 일반적으로 다른 부품에 비해 짧은 수명을 가지고 있다. 액체 로켓의 터보펌프 터빈은 작동시간 동안 높은 회전속도로 인한 높은 원심력과 높은 온도와 같은 환경하에서 작동된다. 이와 같은 환경은 터보펌프 터빈의 저주기 피로를 야기한다. 우선 열응력을 해석하기 위해 ABAQUS/CAE가 사용되었으며 탄성변형률과 소성변형률을 고려하기 위해 Coffin-Manson 방정식을 사용하였다. 평균응력의 변화를 고려하기 위해 S.W.T법을 사용하였으며, 열응력해석 결과로 얻어진 변형률 이력을 이용하여 터보펌프 터빈의 취약지점에 저주기피로해석을 수행하였다. 본 연구에서는 저주기 수명을 해석하기 위해 변형룰 수명 방법이 적용되었다.

• 대한기계학회논문집A
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• 제36권8호
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• pp.835-841
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• 2012

철도차량의 제동 디스크에 사용될 수 있는 주물재료 4 종에 대해 인장강도, 압축강도, 경도, 비열, 비중, 열전도도 등 여러 특성값을 측정하였다. Ni, Cr, Mo 의 조성비에 따라 인장강도, 압축강도, 경도 등을 조절할 수 있었다. 이들 재료에 대해 열피로 시험을 수행할 수 있는 장치를 사용하여 원통형 시편에 대해 열크랙의 발생과 길이를 측정하여 재료의 내열성을 평가하였다. 그리고 열피로 시험과정을 유한요소법으로 해석하고 Manson-Coffin 식과 주변형률을 이용하여 열피로수명을 평가하여 시험결과와 비교, 검토하였다. 해석에 의한 예측수명은 관찰영역의 균열의 총 길이가 $40{\mu}m{\sim}1mm$ 사이에 있을 때의 수명에 해당함을 알 수 있다.

• Journal of Welding and Joining
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• 제17권1호
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• pp.124-132
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• 1999

Thermal fatigue strength of the solder joints is the most critical issue for TSOP(Thin Small Outline Package) because the leads of this package are extremely short and thermal deformation cannot be absorbed by the deflection of the lead. And the TSOP body can be subject to early fatigue failures in thermal cycle environments. This paper was discussed distribution of thermal stresses at near the joint between silicon chip and die pad and investigated their reliability of solder joints of TSOP with 42 alloy clad lead frame on printed circuit board through FEM and 3 different thermal cycling tests. It has been found that the stress concentration around the encapsulated edge structure for internal crack between the silicon chip and Cu alloy die pad. And using 42 alloy clad, The reliability of TSOP body was improved. In case of using 42 alloy clad die pad(t=0.03mm). $$\sigma$_{VMmax}$ is 69Mpa. It is showed that 15% improvement of the strength in the TSOP body in comparison with using Cu alloy die pad $($\sigma$_{VMmax}$=81MPa). In solder joint of TSOP, the maximum equivalent plastic strain and Von Mises stress concentrate on the heel of solder fillet and crack was initiated in it's region and propagated through the interface between lead and solder. Finally, the modified Manson-Coffin equation and relationship of the ratio of $N_{f}$ to nest(η) and cumulative fracture probability(f) with respect to the deviations of the 50% fracture probability life $(N_{f 50%})$ were achieved.

• 한국신재생에너지학회:학술대회논문집
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• 한국신재생에너지학회 2011년도 추계학술대회 초록집
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• pp.62.2-62.2
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• 2011

To guarantee 20-25 years to the lifetime of the PV modules without failure, reliability test of the module is very important. Field-aged test of the outdoor environment is required. However, due to time constraints, accelerated testing is required to predict the lifetime of PV modules and find causes of failure. Failure is caused by many complex phenomena. In this study, we experimented two accelerated tests about corrosion and fatigue, respectively. First, temperature cycling test for fatigue were tested and Coffin-Manson equation was analyzed. Second, damp heat test for corrosion were tested and Eyring equation were analyzed. Finally, using two-mode failure model, we suggest a new lifetime model that analyze the phenomenon by combining two kinds of data.

• International Journal of Korean Welding Society
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• 제4권1호
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• pp.61-66
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• 2004

In this paper, the effect of underfill packages was investigated by numerical approach and experimental test. Reliability improvement was the main issue in the package technology. BGA, CSP and small-sized packages, have problems due to concentration of the stress in solder joints. One of the latest technologies to overcome is underfill encapsulant. Mainly, it is noticed the effect of the underfill in the packages. The predicted thermal fatigue lifes are performed by Coffin-Manson's equation with ANSYS (v.5.62). Also, thermal cycle test during from 218K to 423K was included. Finally we could find that underfill greatly reduce the concentration stress in solder joint, thus the fatigue life was improved than without underfill.

• Journal of Welding and Joining
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• 제21권4호
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• pp.25-30
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• 2003

There have been many researches for small scale packages such as CSP, BGA, and Flipchip. Underfill encapsulant technology is one of the latest assembly technologies. The underfill encapsulant could enhance the reliability of the packages by flowing into the gap between die and substrate. In this paper, the effects of underfill packages by both aspects of thermal and mechanical reliabilities are studied. Especially, it is focused to value board-level reliability whether by the underfill is applied or not. First of all, The predicted thermal fatigue lifes of underfilled and no underfilled $\mu$ BGA solder joints are performed by Coffin-Manson's equation and FEA program, ANSYS(version 5.62). Also, the thermal fatigue lifes of $\mu$ BGA solder joints are experimented by thermal cycle test during the temperature, 218K to 423k. Consequently, both experimental and numerical study show that $\mu$ BGA with underfill has over ten times better fatigue lift than $\mu$ BGA without underfill.

• 한국안전학회지
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• 제33권3호
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• pp.8-14
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• 2018

Ni-base superalloy has excellent resistance to extreme environments such as high temperatures and high stresses and are used as materials for large gas turbines. In this paper, the specimens were taken from the blade that were used for a long time, and their life span was studied by microstructure analysis and avoidance of cursing. The microstructural analysis of the specimens was carried out using a OM and SEM to observe the coarsening, carbides on gamma prime. Low-cycle fatigue tests were performed on new material and airfoil of long time-used blade. The test was conducted under various deformation conditions and temperature conditions of $760^{\circ}C$ and $870^{\circ}C$. The low cycle fatigue test was carried out using the Coffin-Manson equation and the fatigue life was predicted. After the test, crack path and fracture surface were analyzed using SEM.