• JSTS:Journal of Semiconductor Technology and Science
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• 제3권3호
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• pp.122-131
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• 2003

In this study, some characteristics of conductive and non-conductive adhesive inter-connections are derived, based on data from literature and own projects. Assembly of flip chip on flex is taken as a carrier. Potential failure mechanisms of adhesive interconnections reported in literature are reviewed. Some methods that can be used to evaluate the quality of adhesive interconnections and to evaluate their aging behavior are given. Possible finite element simulation approaches are introduced and the required critical materials properties are summarized. Response to temperature and moisture, resistance to reflow soldering and resistance to rapid change in temperature and humidity are elaborated. The effect of post cure during accelerated testing is discussed. This study shows that only a combined approach using finite element simulations, and use of appropriate experimental evaluation methods can result in revealing, understanding and quantifying the complex degradation mechanisms of adhesive interconnections during aging.

• 한국안전학회지
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• 제15권4호
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• pp.8-14
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• 2000

The remaining life estimation for the aged components in power plants as well as chemical plants are very important because mechanical properties of the components are degraded with time of service exposure in the high temperature. Since it is difficult to take specimens from the operating components to evaluate mechanical properties of components, accelerated aging technique are needed to estimate and analyse the material degradation. In the this study, test materials with 4 different degradation levels were prepared by isothermal aging heat treatment at $630^{\circ}C$. And tensile test, $k_{IC}$ test, hardness test and Scanning Electron Microscope analysis were performed in order to evaluate the degradation of 1Cr-1Mo-0.25V steels.

• 한국주조공학회지
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• 제21권1호
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• pp.7-14
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• 2001

The research on new DRA(discontinuous reinforced alloy) and CRA(continous reinforced alloy) composites has been carried out to improve the properties of ceramic fiber and particle reinforced metal matrix composites(MMCs). Effects of alloying elements and aging conditions on the microstructures and aging behavior of Al-Si-Cu-Mg-(Ni)-SiCp composite have been examined. The specimens used in this study were manufactured by duplex process. The first squeeze casting is the process to make precomposite and the second squeeze casting is the process to make final composite. The hardening behavior was accelerated with decreasing the size of SiCp particle in the composites. It is considered that the dislocation density increased with increasing SiCp size, due to the different thermal deformation between Al matrix and SiCp during quenching after the solution treatment. Peak aging time to obtain the maximum hardness in 3 ${\mu}m$ SiCp reinforced Al composite was reduced than that in large size(5, 10 ${\mu}m$) of SiCp because of difference in dislocation density. Aging hardening responce(${\Delta}H$ = $H_{Max}.-H_{S.T}$) of composites was greater than that of unreinforced Al alloy because of higher density of second phases in matrix.

• 한국재료학회지
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• 제18권1호
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• pp.38-44
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• 2008

The micro-structural changes, strength characteristics, and micro-fractural behaviors at the joint interface between a Sn-4.0wt%Ag-0.5wt%Cu solder ball and UBM treated by isothermal aging are reported. From the reflow process for the joint interface, a small amount of intermetallic compound was formed. With an increase in the isothermal aging time, the type and amount of the intermetallic compound changed. The interface without an isothermal treatment showed a ductile fracture. However, with an increase in the aging time, a brittle fracture occurred on the interface due mainly to the increase in the size of the intermetallic compounds and voids. As a result, a drastic degradation in the shear strength was observed. From a microshear test by a scanning electron microscope, the generation of micro-cracks was initiated from the voids at the joint interface. They propagated along the same interface, resulting in coalescence with neighboring cracks into larger cracks. With an increase in the aging time, the generation of the micro-structural cracks was enhanced and the degree of propagation also accelerated.

• 대한기계학회논문집A
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• 제27권8호
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• pp.1398-1408
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• 2003

Tensile and LCF(low cycle fatigue) tests were carried out in air at wide temperature range 20$^{\circ}C$-750$^{\circ}C$ and strain rates of 1${\times}$10$\^$-4//s-1${\times}$10$\^$-2/ to ascertain the influence of strain rate on tensile and LCF properties of prior cold worked 316L stainless steel, especially focused on the DSA(dynamic strain aging) regime. Dynamic strain aging induced the change of tensile properties such as strength and ductility in the temperature region 250$^{\circ}C$-600$^{\circ}C$ and this temperature region well coincided with the negative strain rate sensitivity regime. Cyclic stress response at all test conditions was characterized by the initial hardening during a few cycles, followed by gradual softening until final failure. Temperature and strain rate dependence on cyclic softening behavior appears to result from the change of the cyclic plastic deformation mechanism and DSA effect. The DSA regimes between tensile and LCF loading conditions in terms of the negative strain rate sensitivity were well consistent with each other. The drastic reduction in fatigue resistance at elevated temperature was observed, and it was attributed to the effects of oxidation, creep and dynamic strain aging or interactions among them. Especially, in the DSA regime, dynamic strain aging accelerated the reduction of fatigue resistance by enhancing crack initiation and propagation.

• 대한기계학회논문집A
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• 제24권9호
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• pp.2183-2190
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• 2000

A thermal aging is observed in a primary reactor cooling system(RCS) made of a casting stainless steel when the RCS is exposed for long period at the reactor operating temperature, 290~3300C An investigation of effects of thermal aging on a low cycle fatigue characteristics included a stress variations caused by a reactor operation and trip, is required. The purpose of the present investigation is to find an effect of a thermal aging of the CF8M on a low cycle fatigue life. The specimen of CF8M are prepared by an artificially accelerated aging technique holding 300 and 1800hr at 4300C respectively. The low cycle fatigue tests for the virgin and two aged specimens are performed at the room temperature for various strain amplitudes($\varepsilon$ta), 0.3, 0.5, 0.8, 1.0, 1.2 and 1.5% strain. Through the experiment, it is found that the fatigue life is rapidly reduced with an creasing of the aging time. The experimental fatigue life estimation formulas between the virgin and two aged specimen are obtained and are proposed to a analysis purpose.

• 대한기계학회논문집A
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• 제24권8호
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• pp.1910-1916
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• 2000

The five classes of the thermally aged CF8M specimen are prepared using an artificially accelerated aging method. Namely, after the specimens are held for 100, 300, 900, 1800, and 3600hrs at 430$^{\circ}C$ respectively, the specimens are water-cooled to room temperature. The impact energy variations are measures for both the aged and virgin specimens through the Charpy impact tests in addition to the microstructure observation, tensile, hardness and fatigue crack growth tests. From the present investigation the following results are obtained : 1) The difference among the thermally degraded specimens can be distinguished through their microstructures, 2) Hardness and tensile strength are increased to 300hrs, degradation specimen, while elongation and reduction area are decreased to 3600hrs degradation specimen, and impact energy is decreased to 1800hrs degradation specimen, 3) The FCG rates for thermally degraded specimens are larger than that of the virgin specimen.

• 한국추진공학회지
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• 제22권5호
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• pp.59-65
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• 2018

hydroxyl-terminated polybutadiene(HTPB) 추진제는 자연 저장 기간 동안 내부 시효성 물질들에 의한 물리 화학적 반응으로 인해 서서히 노화가 진행된다. 각기 다른 시간-온도 조건에서 이들 시효성 물질의 가속 노화 시험을 통해 자연 상태에서의 노화 특성을 모사할 수 있다. 본 논문에서는 장기 저장 기간 동안 느리게 진행되는 HTPB 추진제의 물리 화학적 반응에 의한 노화 특성을 HFC(Heat Flow Calorimeter)로 분석 평가하여 수행한 HTPB 추진제의 신개념 수명 예측 기술에 대하여 고찰하였다.

• KIEE International Transaction on Electrical Machinery and Energy Conversion Systems
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• 제5B권2호
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• pp.142-145
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• 2005

The life expectancy of a transformer largely depends on the temperature-rise it experiences. If the temperature-rise exceeds limits specified in the design standards, the aging of insulating materials is accelerated and the capability of the cooling medium is deteriorated. Consequently, applicable limits for the temperature-rise are essential in designing the transformer and the coolers, demanding the estimation of the transformer's thermal behavior. In order to analyze the temperature characteristics of the transformer, numerical analysis by way of the commercial CFD code has been carried out, and temperature-rise testing to verify computed results was performed. The results obtained in this study show that there is a good agreement between computed outcomes and experimental outcomes.

• 한국전기전자재료학회:학술대회논문집
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• 한국전기전자재료학회 2009년도 추계학술대회 논문집
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• pp.286-286
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• 2009

According to previous report, aged sleeves for old transmission lines have various defect such as biased installation or corrosion of steel sleeve. These defects can cause serious accidents such as rapid increasing of sag or falling out of overhead conductor from sleeves. Moreover, the defects have been limited power capacity of transmission line. This paper study on mechanical and thermal behavior of ACSR $410mm^2$ conductor and sleeve with various defect model. The conductor has been aged artificially for 50 years. The detailed results were presented in the text.