• 제목/요약/키워드: Stress condition

검색결과 4,066건 처리시간 0.032초

반무한 탄성체의 헤르츠 접촉하의 경사진 표면균열의 전파거동 (Propagation Behavior of Inclined Surface Crack of Semi-Infinite Elastic Body under Hertzian Contact)

  • 김재호;김석삼;박중한
    • 대한기계학회논문집
    • /
    • 제14권3호
    • /
    • pp.624-635
    • /
    • 1990
  • 본 연구에서는 마멸과정을 선형파괴역학적 관점에서 해석하여, 탄성체의 표면 에 산재되어 있는 표면균열의 전파거동을 마멸과정규명의 입장에서 살펴보고자 한다. 우선 마멸거동에 관한 파괴역학적 접근방식에 의한 마멸이론의 확립을 위해서, 표면균 열이 내부균열보다 그 전파 가능성이 높다고 한 Keer등의 주장에 착안하여 Hertz 접촉 압력하의 경사진 표면균열의 전파거동을 선형파괴역학적으로 해석하고자 한다. 이론 해석에 있어서는 표면균열을 인상전립의 연속분포로 치환하고, 전립밀도분포함수에 관 한 특이적분방정식을 유도해서 Erdogangupta의 방법을 이용하여 그 해를 구하였다.

MATERIAL RELIABILITY OF Ni ALLOY ELECTRODEPOSITION FOR STEAM GENERATOR TUBE REPAIR

  • Kim, Dong-Jin;Kim, Myong-Jin;Kim, Joung-Soo;Kim, Hong-Pyo
    • Nuclear Engineering and Technology
    • /
    • 제39권3호
    • /
    • pp.231-236
    • /
    • 2007
  • Due to the occasional occurrences of stress corrosion cracking(SCC) in steam generator tubing(Alloy 600), degraded tubes are removed from service by plugging or are repaired for re-use. Since electrodeposition inside a tube does not entail parent tube deformation, residual stress in the tube can be minimized. In this work, tube restoration via electrodeposition inside a steam generator tubing was performed after developing the following: an anode probe to be installed inside a tube, a degreasing condition to remove dirt and grease, an activation condition for surface oxide elimination, a tightly adhered strike layer forming condition between the electro forming layer and the Alloy 600 tube, and the condition for an electroforming layer. The reliability of the electrodeposited material, with a variation of material properties, was evaluated as a function of the electrodeposit position in the vertical direction of a tube using the developed anode. It has been noted that the variation of the material properties along the electrodeposit length was acceptable in a process margin. To improve the reliability of a material property, the causes of the variation occurrence were presumed, and an attempt to minimize the variation has been made. A Ni alloy electrodeposition process is suggested as a primary water stress corrosion cracking(PWSCC) mitigation method for various components, including steam generator tubes. The Ni alloy electrodeposit formed inside a tube by using the installed assembly shows proper material properties as well as an excellent SCC resistance.

신생아 중환자실에 입원한 환아 어머니의 스트레스 (A Study on the Perceived Stress Level of Mothers in the Neonatal Intensive Care Unit Patients)

  • 김태임
    • Child Health Nursing Research
    • /
    • 제6권2호
    • /
    • pp.224-239
    • /
    • 2000
  • This descriptive study was conducted to understand the contents and degree of parental stress level in the NICU patients, and to give a baseline data in developing nursing intervention program. Subjects were the 62 mother of hospitalized newborn in NICU of 1 University Hospital in Taejon City from May 1st, 1999 to November 30th, 1999, who agreed to take part in this study. The instrument used in this study were Parental Stressor Scales : NICU(PSS:NICU) developed by Miles et al. and validated by 3 NICU practitioners and 3 child health nursing faculties. The questionnaire has 4 dimensions and 45 items; sight and sounds of NICU(5 items), babies' appearance and behavior(19 items), parental role alteration and relationship with their baby(10 items), communication with health team(11 items). The questionnaire asks parents to rate each item on a five-point Likert type scale that ranges from (1) to (5). Total scores representing overall stress from the NICU environment are calculated by summing response to each item. A high score indicates high stress. A subscale score is calculated by summing the responses to each item in the subscale. Cronbach's α coefficients were .93. The data was analyzed as average, Frequency, Standard deviation, t-test, ANOVA, Pearson correlation coefficient by use of SPSS/PC+. The results of this study is summarized as follows ; 1. The total perceived stress level score of mothers was slightly high(3.6±.7). The highest scored dimension was 'appearance and behavior of the baby'(3.9±1.5), and next were 'relationship with their baby and parental role change'(3.5±1.4), 'communication with health team'(3.4±.9), 'sight and sounds of NICU'(3.2±.8). 2. Two variables were statistically significant with PSS:NICU total scale ; mother's perceived severity of the baby's condition (r=.482, P=.002) and mother's religious attendance(t=2.83, P=.01). The more the mother perceive their baby's condition severe, the higher the total stress score. There were high stress score noted in the mother of no religious attendance. 3. Four variables were statistically significant with NICU environment subscale ; mother's educational background(F=3.45, P=.04), religious attendance(t=2.28, P=.04), sex of the baby(t=2.83, P=.01) and NICU patients' hospital day(r=.359, P=.004). That is mother with high educational background and girl baby were high NICU environment subscale score. 4. Four variables were statistically significant with appearance and behavior of the baby subscale ; when first saw baby(F=3.52, P=.04), incubator care(t=2.83, P=.01), mother's perceived severity of the baby's condition(r=.303, P=.017), number of NICU visit(r=.441, P=.002). That is, seeing the baby first in the NICU and recieved incubator care was very stressful. Also, the more the mother perceive their baby's condition severe and more NICU visit, the higher the appearance and behavior of the baby subscale stress score. 5. Four variables were statistically significant with relationship with their baby and parental role change subscale ; when first saw baby(F=3.37, P=.04), sex of the baby(t=2.36, P=.03), incubator care(t=5.60, P=.00), mother's perceived severity of the baby's condition(r=.401, P=.001). That is, seeing the baby first in the NICU and girl baby was very stressful. Also, the more the mother perceive their baby's condition severe, the higher the relationship with their baby and parental role change subscale stress score. 6. Three variables were statistically significant with communication with health team subscale ; mother's educational background (F=3.63, P=.04), incubator care(t=4.24, P=.00), gestational age(r=-.394, P=.047), and birth weight(r=-.460, P=.004). That is, mother with high educational background and receiving incubator care were high communication with health team subscale score. Also, the shorter the gestational age and smaller the baby's birth weight, the higher the communication with health team subscale score. In conclusion, information about physical environment of NICU, the mother's perceived severity of baby's illness state, maternal role change related variables and the knowledge of characteristics of NICU patients must be included in nursing intervention program of mother's of NICU patients in reducing the maternal stress and anxiety level.

  • PDF

광양만 조석 해수면 변동의 미고결 퇴적층에 대한 영향 (Effect of the Tidal Sea Level Change on the Unconsolidated Sediment in Gwangyang Bay)

  • 조태진
    • 한국수산과학회지
    • /
    • 제24권1호
    • /
    • pp.9-20
    • /
    • 1991
  • 광양만에 분포하는 미고결 퇴적충의 물성특성을 Core 시료를 채취하여 분석하였다 퇴적상태의 특성을 지시하는 퇴적층의 공극율이 퇴적깊이에 따라 일정한 변화를 나타내지 않으며, 이는 자체하중에 의한 자연적 압밀이 매우 미세한 것을 나타내고 있다. 조석에 의한 해수면 변동이 퇴적층 거동에 미치는 영향을 수치해석적으로 분석한 결과, 퇴적층에 형성되는 공극수압이 이토층의 낮은 투수계수에 기인하여 해수면 변동에 따른 표층 수압변화보다 느리게 진행되고 있다. 따라서, 최소 해수면시점에 발생되는 공극수압이 해수압에 의한 역학적 응력보다 커서 퇴적층의 유효응력이 인장력으로 반전되며 일정깊이에서의 현장유효응력도 인장력상태(quick sand condition)인 것으로 나타난다. 이러한 현상은 퇴적물조직의 재구성이 내부적으로 발생될 수 있는 가능성을 제시해 주고 있다. 모래질이토층(sandy mud layer)이 이토층내에 존재할 경우에도 이토층과의 경계부분에서 인장력강태의 현장유효응력(quick sand condition)이 발생한다. 이는 퇴적물 재구성작용에 의해 모래질 입자가 표층에서 하부층으로 하강될 수 있는 역학적 이론근거를 제시해 주고 있으며, 본 연구결과에 의하면 모래질 입자들이 약 40cm 깊이에 하강될 때까지 quick sand condition이 형성된다.

  • PDF

생식생장기 수분스트레스 처리가 억새의 출수율 및 생육 변화에 미치는 영향 (Changes in Miscanthus sacchariflorus Growth and Heading Rate Influenced by Water Stress Treatment at Reproductive Growth Stage)

  • 이지은;차영록;문윤호;김광수;권다은;강용구
    • 한국작물학회지
    • /
    • 제63권4호
    • /
    • pp.390-398
    • /
    • 2018
  • 생식생장기 장기간의 건조와 침수 스트레스 하에서 물억새와 거대1호의 생육 및 양분함량 변화를 비교분석한 결과는 다음과 같다. 1. 건조 처리에 의한 두 억새 종의 형태적 특성 변화는 없었으나, 침수 처리에 의해 거대1호의 초장은 256.6 cm로 증가하였으며 마디수 또한 16.8개로 증가하였다. 2. 물억새의 출수율은 건조 조건에서 18.9%로 감소하였으나 침수 조건에서는 대조구와 통계적 유의성을 보이지 않았다. 거대1호는 대조구와 건조구에서 모두 출수하지 않았으며, 침수처리에 의해 48.6%의 출수율을 보였다. 3. 주요 양분인 유리당, 전질소, 인산, 칼륨, 마그네슘은 두 억새 모두 건조처리구에서 가장 높았으며, 칼슘과 마그네슘의 경우 침수처리구에서 두 억새 모두 3배이상 감소하였다. 4. 이러한 양분 변화는 건조처리에 의해 억새의 노화가 촉진되어 양분 이동이 저해된 결과로 사료되며, 침수 처리는 거대1호의 출수를 촉진한다는 결과를 처음으로 확인하였다.

조향장치용 볼 조인트 더스트 커버의 형상최적설계 (Shape optimal design of a dust cover for ball joint of automotive steering system)

  • 이부윤;김지호
    • Journal of Advanced Marine Engineering and Technology
    • /
    • 제37권6호
    • /
    • pp.603-610
    • /
    • 2013
  • 유한요소해석을 수행하여 조향장치용 타이로드 볼 조인트의 주름 형상 더스트 커버의 응력과 변형을 평가하였다. 조립상태 및 작동상태 하에서 기존 설계안의 더스트 커버를 해석한 결과, 밀봉성이 우수하고 최대응력은 인장강도보다 낮게 나타났다. 더스트 커버의 최대응력을 저감시키기 위하여 형상설계변수를 선정하고, 다구찌 기법을 사용하여 최적형상을 구하였다. 도출된 최적설계안의 작동상태에서의 최대응력은 초기설계안 대비 22 % 감소되는 것으로 나타났다. 본 연구에서 제시된 방법을 사용하면 더스트 커버의 평가 및 설계를 효율적으로 할 수 있다.

인장-전단하중을 받는 IB형 일점 Spot 용접이음재의 파괴역학적 피로강도 평가 (Fracture Mechanical Fatigue Strength Evaluation of IB-Type Spot Welded Lap Joint under Tension-Shear Load)

  • 손일선;정원석;이휘광;배동호
    • 한국자동차공학회논문집
    • /
    • 제6권5호
    • /
    • pp.20-27
    • /
    • 1998
  • According as the member of the automobile body structure have been thinned their thickness and have become high strength, each part of the body structure has been put more severe stress condition. And, because fatigue strength of the spot welded lap joint is influenced by its geometrical and mechanical factors, welding condition and etc., there needs a quantitative and systematic evaluation method for them. In this study, by considering nugget edge of the spot weld part of the IB-type spot welded lap joint under tension-shear load to the ligament crack. fatigue strength of various IB-type spot welded lap joints was estimated with the stress intensity factor(S.I.F.) KIII which is fracture mechanical parameter. We could find that fatigue strength evaluation of the IB-type spot welded lap joints by KIII is more effective than the maximum principal stress ($\sigma$1max) at edge of the spot weld obtained from FEM analysis.

  • PDF

스프링강의 파괴인성에 미치는 쇼트피닝 효과에 관한 연구 (A Study on Effect of Shot Peening on Fracture Toughness of Spring Steel)

  • 하경준;박경동
    • 동력기계공학회지
    • /
    • 제7권2호
    • /
    • pp.66-72
    • /
    • 2003
  • Recently, the steel parts used at the aerospace and automobile industries are required to be used light weight parts. Therefore, used material, steel have to be a high stress, which is an indispensable condition in this field. At the consideration of parts design, high hardness of the lightweight parts have an benefit of saving fuel and material. A high stress of metal has a point of difference according to the shape of design, external cyclic load and condition of vibration. A crack generates on the surface of metal or under yield stress by defect of inner metal defect or surface defect and slowly, this crack grow stable growth. Finally, rapidity failure phenomena is happen. Fatigue failure_phenomena, which happen in metal, bring on danger in human life and property therefor, anti-fatigue failure technology take an important part of current industries Currently, the shot peening is used for removing the defect from the surface of steel and improving the fatigue strength on surface. Therefore, this paper investigated the effect on frcature toughness using shot peening which is improve the resistance of crack growth and crack expansion rate by fatigue that make a compressive residual stress on surface.

  • PDF

엔진 배기매니폴드의 열응력 발생에 관한 설계 인자들의 이론적 연구 (Theoretical Study of Design Parameters for the Thermal Stress in Engine Exhaust Manifold)

  • 최복록
    • 한국기계가공학회지
    • /
    • 제6권1호
    • /
    • pp.50-56
    • /
    • 2007
  • Exhaust manifold is generally subjected to thermal cycle loadings ; at hot condition, large compressive plastic deformations are generated, and at cold condition, tensile stresses are remained in highly deformed critical zones. These phenomena originate from the fact that thermal expansions of the runners are restricted by inlet flange clamped to the cylinder head, because the former is less stiff than the latter and, the temperature of the inlet flange is lower than that of the runners. Since the failure of an exhaust manifold is mainly caused by geometric constraints between the cylinder head and the manifold, the thermal stress can be controlled by geometric factors. The generic geometric factors include the inter distance (2R), the distance from the head to the outlet (L), the tube diameter(d) and the tube thickness (t). This criteria based on elastic analysis up to onset of yield apparently indicate that the pre-stress also reduces the factor; however, high temperature relaxation may reduce this effect at later operation stage.

  • PDF

Differently expressed genes of soybean by ambient heat stress

  • Jung, Inuk;Kim, Jin Hyeon;Jung, Woosuk
    • 한국작물학회:학술대회논문집
    • /
    • 한국작물학회 2017년도 9th Asian Crop Science Association conference
    • /
    • pp.156-156
    • /
    • 2017
  • Plants are grown under constitutive changing of environmental conditions and response to external conditions at both protein and transcription level. The effects of heat on plant growth are broad and influence the yield directly. Heat stresses could be classified depend on intensity and duration. Fundamental changes of growth condition by climate change maybe or maybe not classified as a stress on plant growth. The effects of a short and unanticipated impact of elevated heat on plant could be different with those of under longer extension of ambient heat. To examine differently expressed gene sets by ambient heat stress of soybean, we grow the soybean in normal condition for three weeks. After that, soybean plants move to growth chamber. The temperature of growth chamber increase up to $9^{\circ}C$ for four days. We have extracted mRNA and micro RNA every 24 hours and carried RNA sequence analysis. We found major metabolic pathways affected by ambient heat stress. Mainly carbon metabolism, translation machinery and amino acid synthesis are affected. We discussed the expression patterns of genes of heat sensing and hormone responses.

  • PDF