고압 커패시터의 고장 분석을 통한 신뢰도 예측

양석준,김진우,신승우,이희진,신승훈,유동수,장석원 한국비파괴검사학회 2001 한국비파괴검사학회지 Vol.21 No.6

본 논문은 고압 커패시터의 고장분석과 신뢰성 예측 결과를 다루고 있다. 부품의 수명과 고장률을 예측하기 위해서 두 가지 방법으로 고장 모드와 고장 메커니즘을 연구하였다. 에폭시 수지로 성형된 고압 커패시터가 절연내압 시험 하에서 저항이 제로로 되는 고장에 대하여, 근본원인 고장분석 체계를 효과적으로 수립함으로써 고장 메커니즘의 원인을 분석하였다. 특히 세라믹-에폭시 계면에서의 절연파괴 고장 현상이 강조되었으며, 본 연구에서 얻어진 결과의 타당성은 마그네트론에 장착된 고압 커패시터의 열사이클 시험 수행에 의한 가속시험 결과로부터 입증되었다. 시험 결과들은 결함이 있는 로트를 신속히 규명하고 B10수명을 결정하는데 유용하게 사용할 수 있다. 또한, 유전체의 절연파괴에 대해서 부하-강도 간섭모델을 이용하여 고장률을 예측하였다. This paper presents a result of failure analysis and reliability evaluation for high voltage ceramic capacitors. The failure modes and failure mechanisms were studied in two ways in order to estimate component life and failure rate. The causes of failure mechanisms for zero resistance phenomena under withstanding voltage test in high voltage ceramic capacitors molded by epoxy resin were studied y establishing an effective root cause failure analysis. Particular emphasis was placed on breakdown phenomena at the ceramic-epoxy interface. The validity of the results in this study was confirmed by the results of accelerated testing. Thermal cycling test for high voltage ceramic capacitor mounted on a magnetron were implemented. Delamination between ceramic and epoxy, which might cause electrical short in underlying circuitry, can occur during curing or thermal cycle. The results can be conveniently used to quickly identify defective lots, determine B10 life estimation each lot at the level of inspection, and detect major changes in the vendors processes. Also, thd condition for dielectric breakdown was investigated for the estimation of failure rate with load-strength interference model.

Type 316L(N) 스테인리스 강의 최적질소함량 평가

金大煥,金雨坤,柳禹錫 대한금속재료학회 2002 대한금속·재료학회지 Vol.40 No.6

Tensile, fatigue, creep-fatigue, creep tests were conducted at R.T.∼600℃ to evaluate the effect of nitrogen on mechanical properties and the optimum nitrogen content for type 316L(N) stainless steel containing the different nitrogen content from 0.04% to 0.15%. Tensile strength decreased with temperature and increased with the addition of nitrogen but elongation was not decreased with the addition of nitrogen. Fatigue life was almost same up to 300℃ and decreased drastically at 600℃. Fatigue life increased with the addition of nitrogen but decreased at above 0.10% nitrogen content. Fatigue crack propagation increased with temperature, decreased with the addition of nitrogen, and increased at above 0.10% nitrogen content. The time to rupture for creep increased with the addition of nitrogen and saturated at above 0.10% nitrogen content. Minimum creep rate of creep decreased with the addition of nitrogen. Creep-fatigue life increased with the addition of nitrogen but decreased at above 0.10% nitrogen content. Mechanical properties were improved up to 0.10% nitrogen content but saturated or decreased at above 0.10% nitrogen content. The optimum nitrogen content for the high temperature mechanical properties of type 316L(N) stainless steel was evaluated as 0.10% in the 0.02% carbon content.

316LN 스테인리스 강에서 질소에 의한 결정립 미세화가 고온 기계적 특성에 미치는 영향

김대환,이요섭,류우석 대한금속재료학회 2004 대한금속·재료학회지 Vol.42 No.7

Mechanical tests, such as tensile, fatigue and creep, of type 316L(N) stainless steel containing 0.04 and 0.10 wt% nitrogen content were conducted at 600℃ to investigate the grain size effect on the behaviors of mechanical properties since grain size was refined with the addition of nitrogen. Yield strength and fatigue life increased with the addition of nitrogen and the decrease of grain size. The creep rupture time was increased with the addition of nitrogen but decreased with increasing grain size. The change in minimum creep rate with grain size was consistent with the result predicted from Garofalo's equation. (Received November 17, 2004)

인장시험 시 불안정과 네킹 거동의 유한요소해석

김형섭,김성호,류우석 대한금속재료학회 2004 대한금속·재료학회지 Vol.42 No.8

A tensile test is the most widely used mechanical property testing method to measure inherent material behaviour including full flow curves as well as Young's modulus, yield strength, tensile strength and elongation. In the present study, tensile deformation and necking behaviour was investigated using the finite element method code MSC.MARC and the plasticity instability theory. It is shown that the finite element analysis for the tensile test of cylindrical samples can reproduce necking instability by applying a radial constraint at the loading points without assuming initial imperfections. The predicted finite element results compared to the Hart's instability criterion shows that the Hart's analytical solution overestimates necking strains a little in strain hardening materials. The finite element analysis of tensile tests with the geometric constraint is useful for interpreting deformation and developing new materials in that it can successfully reproduce not only uniform elongation and necking initiation but also post necking behaviour.

316(LN)스테인리스강의 열피로 특성에 미치는 질소의 영향

김대환,한창희,류우석 대한금속재료학회 2005 대한금속·재료학회지 Vol.43 No.5

Three different fatigue tests for 316 and 316LN stainless steels were conducted at RT, 600℃ and Ast= 1% for low cycle fatigue, at 200~400℃, 300~600℃ and Δε_(t) = 0% for thermal fatigue, and at 300~600℃ and Δε_(t) = 2% for thermomechanical fatigue. Low cycle, thermal and thermomechanical fatigue lives increased with the addition of nitrogen. Low cycle, thermal fatigue strength was increased but thermomechanical fatigue strength was almost same with the addition of nitrogen. Thermal fatigue life was decreased but thermal fatigue strength was increased at the higher temperature range. Thermomechanical fatigue life of in-phase was longer than that of out-of-phase. Fracture mode was transgranular for all tests. (Received September 3, 2004)

Bar와 Beam 구조물의 기본적인 유한요소 모델의 수치해석

Ryu, Yong-Hee,Ju, Bu-Seog,Jung, Woo-Young,Suchart Limkatanyu 한국복합신소재구조학회 2013 복합신소재구조학회논문집 Vol.4 No.1

The finite element analysis (FEA) is a numerical technique to find solutions of field problems. A field problem is approximated by differential equations or integral expressions. In a finite element, the field quantity is allowed to have a simple spatial variation in terms of linear or polynomial functions. This paper represents a review and an accuracy-study of the finite element method comparing the FEA results with the exact solution. The exact solutions were calculated by solid mechanics and FEA using matrix stiffness method. For this study, simple bar and cantilever models were considered to evaluate four types of basic elements - constant strain triangle (CST), linear strain triangle (LST), bi-linear-rectangle(Q4),and quadratic-rectangle(Q8). The bar model was subjected to uniaxial loading whereas in case of the cantilever model moment loading was used. In the uniaxial loading case, all basic element results of the displacement and stress in x-direction agreed well with the exact solutions. In the moment loading case, the displacement in y-direction using LST and Q8 elements were acceptable compared to the exact solution, but CST and Q4 elements had to be improved by the mesh refinement.

EFFECTS OF IRRADIATION ON THERMAL CONDUCTIVITY OF ALLOY 690 AT LOW NEUTRON FLUENCE

Ryu, Woo Seog,Park, Dae Gyu,Song, Ung Sup,Park, Jin Seok,Ahn, Sang Bok Korean Nuclear Society 2013 Nuclear Engineering and Technology Vol.45 No.2

Alloy 690 has been selected as a steam generator tubing material for SMART owing to a near immunity to primary water stress corrosion cracking. The steam generators of SMART are faced with a neutron flux due to the integrated arrangement inside a reactor vessel, and thus it is important to know the irradiation effects of the thermal conductivity of Alloy 690. Alloy 690 was irradiated at HANARO to fluences of (0.7-28) ${\times}10^{19}n/cm^2$ (E>0.1MeV) at $250^{\circ}C$, and its thermal conductivity was measured using the laser-flash equipment in the IMEF. The thermal conductivity of Alloy 690 was dependent on temperature, and it was a good fit to the Smith-Palmer equation, which modified the Wiedemann-Franz law. The irradiation at $250^{\circ}C$ did not degrade the thermal conductivity of Alloy 690, and even showed a small increase (1%) at fluences of (0.7~28) ${\times}10^{19}n/cm^2$ (E>0.1MeV).

Effect of Grain Size on Creep Properties of Type 316LN Stainless Steel

Ryu, Woo Seog,Lee, Dok Yol,Lee, Yo Seob,Kim, Dae Whan 대한금속재료학회(대한금속학회) 2001 METALS AND MATERIALS International Vol.7 No.2

The effect of grain size on creep properties of type 316LN stainless steel has been investigated at 600℃ under different stresses. The initial strain at the beginning of creep tests decreased with the decrease of grain size. This was confirmed by the Hall-Petch relationship. The steady state creep rate decreased to a minimum value at the intermediate grain size (dm=80-130 ㎛) and then increased with the fiuther increase of grain size. This result agreed with Garofalo's model stating that grain boundaries act simultaneously as both dislocation sources and barriers to dislocation movement. The rupture elongation at the intermediate grain size was minimal due to the cavity formed easily by carbide precipitates in the grain boundaries.

Thermal treatment improving creep properties of nitrogen-added Mod.9Cr-1Mo steels

Ryu, Woo Seog,Kim, Sung Ho Springer-Verlag 2010 Transactions of the Indian Institute of Metals Vol.63 No.2

Differentially Expressed Genes in Marine Medaka Fish (Oryzias javanicus) Exposed to Cadmium

Woo, Seon-Ock,Son, Sung-Hee,Park, Hong-Seog,Vulpe, Chris D.,Ryu, Jae-Chun,Yum, Seung-Shic The Korean Society of Toxicogenomics and Toxicopro 2008 Molecular & cellular toxicology Vol.4 No.4

To screen the differentially expressed genes in cadmuim-exposed marine medaka fish (Oryzias javanicus), a candidate marine test fish for ecological toxicity, the differential display polymerase chain reaction (DD-PCR) was carried out, since the genome-wide gene expression data are not available in this fish species yet. A total of 35 clones were isolated from cadmium-exposed fish and their nucleotide sequences were analyzed. The differentially expressed gene candidates were categorized to response to stimulus (3); ion binding (3); DNA binding (1); protein binding (6); carbohydrate binding (1); metabolic process (4); biological regulation (3); cellular process (2); protein synthesis (2); catalytic activity (2); sense of sight (1); immune (1); neurohormone (1); signaling activity (1); electron carrier activity (1) and others (3). For real-time quantitative RT-PCR, we selected catalase, glucose-6-phosphate dehydrogenase, heat shock protein 70, and metallothionein and confirmed that cadmium exposure enhanced induction of these four genes.