• 대한용접접합학회:학술대회논문집
• /
• 대한용접접합학회 1999년도 특별강연 및 춘계학술발표대회 개요집
• /
• pp.288-291
• /
• 1999

Fatigue crack propagaion rates and characteristics of the SA516-70 steel which is used for the low temperature pressure vessels, were studied in the room temperature of 1$0^{\circ}C$ and low temperature ranges of -1$0^{\circ}C$, -3$0^{\circ}C$, -5$0^{\circ}C$, -7$0^{\circ}C$ with stress ratio of R＝0.05.

• 대한기계학회:학술대회논문집
• /
• 대한기계학회 2004년도 춘계학술대회
• /
• pp.353-358
• /
• 2004

We got the following characteristics from fatigue crack growth test carried out in the environment of room temperature and low temperature at $25^{circ}C$, $-60^{circ}C$, $-80^{circ}C$, and $-100^{circ}C$ in the range of stress ratio of 0.3 by means of opening mode displacement. And there is a difference between shot peened specimen and unpeened specimen. The purpose of this study is to predict the behavior of fatigue crack propagation as one of fracture mechanics on the compressive residual stress. Fatigue crack growth rate of shot peened metal was lower than that of unpeened metal. The compressive residual stress made an impact on tension and compression of the plasticity deformation in fatigue crack plasticity zone. That is. the constrained force about plasticity deformation was strengthened by resultant stress, which resulted from plasticity deformation and compressive residual stress in the process of fatigue crack propagation.

• 동력기계공학회지
• /
• 제4권1호
• /
• pp.81-87
• /
• 2000

In this study, CT specimens were prepared from ASTM SA516 Gr. 70 which was used for pressure vessel plates for room and low temperature service. And we got the following characteristics from fatigue crack growth test carried out in the environment of room and low temperature at $25^{\circ}C,\;-60^{\circ}C,\;-80^{\circ}C\;and\;-100^{\circ}C$ and in the range of stress ratio of 0.05 by means of opening mode displacement. At the constant stress ratio, the threshold stress intensity factor range ${\Delta}K_{th}$ in the early stage of fatigue crack growth (Region I) and stress intensity factor range ${\Delta}K$ in the stable of fatigue crack growth (Region II) was increased in proportion to descend temperature. It assumed that the fatigue resistance characteristics and fracture strength at low temperature is considerable higher than that of room temperature in the early stage and stable of fatigue crack growth region. The straight line slope relation of logarithm $d{\alpha}/dN\;-{\Delta}K$ in Region II, that is, the fatigue crack growth exponent m increased with descending temperature at the constant stress ratio. It assumed that the fatigue crack growth rate $d{\alpha}/dN$ is rapid in proportion to descend temperature in Region II and the cryogenic-brittleness greatly affect a material with decreasing temperature.

• 대한용접접합학회:학술대회논문집
• /
• 대한용접접합학회 2001년도 춘계학술발표대회 개요집
• /
• pp.224-227
• /
• 2001

In this study, CT specimens were prepared hem ASTM SA516 which was used for pressure vessel plates for room and low temperature service. And we got the following characteristics from fatigue crack growth test carried out in the environment of room and low temperature at $25^{\circ}C$, -3$0^{\circ}C$, -6$0^{\circ}C$, -8$0^{\circ}C$, -l$0^{\circ}C$ and -l2$0^{\circ}C$ and in the range of stress ratio of 0.1, 0.3 by means of opening mode displacement. At the constant stress ratio, the threshold stress intensity factor range $\Delta K_{th}$ in the early stage of fatigue crack growth ( Region I ) and stress intensity factor range $\Delta$K in the stable of fatigue crack growth ( Region II) was increased in proportion to descend temperature. It assumed that the fatigue resistance characteristics and fracture strength at low temperature is considerable higher than that of room temperature in the early stage and stable of fatigue crack growth region. The straight line slope relation of logarithm da/dN - $\Delta$K in Region II, that is, the fatigue crack growth exponent m increased with descending temperature at the constant stress ratio. It assumed that the fatigue crack growth rate da/dN is rapid in proportion to descend temperature in Region H and the cryogenic-brittleness greatly affect a material with decreasing temperature.

• Journal of Applied Biological Chemistry
• /
• 제63권4호
• /
• pp.347-355
• /
• 2020

기상이변으로 인한 식물 스트레스를 평가하기 위해 토양과 식물에 적용할 수 있는 여러 센서가 개발되었다. 따라서 본 연구의 목적은 식물의 온도 스트레스를 평가하기 위해 다양한 센서를 사용하여 기후 및 토양 상태와 식물 반응을 모니터링하는 것이다. 식물 반응을 평가하기 위한 식물 센서로 식물 줄기의 전기전도도, sap flow rate를 모니터링하였다. 식물 줄기의 전기전도도는 물과 이온 수송을 포함한 식물의 생리적 활성을 반영한다. 완전히 자란 Brassica oleracea var. italica를 온도 20/15 ℃ (낮/밤), 16시간 광주기로 하여 대조구로 설정하였으며 저온 15/10 ℃ 및 고온 35/30 ℃에 노출시키면서 토양 및 식물 상태를 모니터링하였다. 식물 줄기의 전기전도도, sap flow rate는 낮에는 증가하고 밤에는 감소하였다. 저온 스트레스 하에서 Brassica oleracea var. italica 줄기의 전기전도도는 대조구보다 낮았고, 고온 스트레스 하에서는 대조구보다 높아 물과 이온 수송이 온도에 의해 영향을 받았음을 나타낸다. 그러나 엽록소 a와 b 함량은 저온 스트레스를 받은 잎에서 증가했고 고온 스트레스를 받은 잎에서는 대조구와 차이가 없었다. 잎의 프롤린 함량은 저온 스트레스에서는 대조구와 차이가 없는 반면, 고온 스트레스에서는 증가했다. 프롤린 합성은 환경 스트레스 하에서 식물의 방어 메커니즘으로 작용한다. 따라서 Brassica oleracea var. Italica는 저온보다 고온 스트레스에 더 민감한 것으로 판단된다.

• International Journal of Industrial Entomology and Biomaterials
• /
• 제33권2호
• /
• pp.102-107
• /
• 2016

Stress may be defined as any modification of environmental parameters that leads to a response by biological organisms. Stresses that affect biolpgical structures may be nonthermal, such as ultraviolet radiation, pH, or salinity, or thermal. Temperture is one of the major stresses that all living organism face. The major effects of cold(low emperature) are decrease of membrane fluidity and the stabilization of secondary structures of RNA and DNA in the cells, which may effect the efficiency of translation, transcription, and DNA replication. In this study, we focus on discovering the genes that are expressed by the cold(low temperature) stress in the silkworm. In cold(low temperature) stress test, we found 100% survive from cold stress at $0^{\circ}C$ up to 12h and $-5^{\circ}C$ up to 2h, and then, survive rate was rapidly decrease in silkworm. Thereafter two whole genes have selected by SSH(Suppression subtractive hybridization). (GenBank accession : GQ149511, GQ338156)

• 동력기계공학회지
• /
• 제4권4호
• /
• pp.41-47
• /
• 2000

Fatigue crack propagation rate and threshold characteristics of the SA516/70 steel which is used for the low temperature pressure vessels, were studied in the room temperature of $25^{\circ}C$ and low temperature ranges of $-10^{\circ}C,\;-30^{\circ}C,\;-60^{\circ}C\;and\;-80^{\circ}C$ with stress ratio of R=0.1. In the logarithmic relationship between the fatigue crack propagation rate($d{\alpha}/dN$) and stress intensity factor range ${\Delta}K$, the linear relationship was obtained up to $d{\alpha}/dN=4.425{\times}10^4mm/cycle$ in the same of room temperature, but in low temperature case, the relationship was extended to the range of low crack propagation rate. The fractured specimens were examined by SEM. Tested results showed that specimen failed at low temperature exhibit the quasi-cleavage fracture formation however considerable ductility proceed final fracture.

• 한국해양공학회지
• /
• 제10권2호
• /
• pp.106-119
• /
• 1996

The ceramic has various high mechanical properties such as heat, abrasion, corrosion resistance and high temperature strength compared with metal. It also has low speciffic weight, low thermal expansibillity, low thermal conductivity. However, it could not be used as structural material since it is brittle and difficult for the machining. Therefore, there have been many researches to attempt to join ceramic with metal which is full of ductillity in order to compensate the weakness of ceramic.The problem is that residual stress develops around the joint area while the ceramic/metal joint material is cooled from high joining temperature to room temperature due to remarkable difference of thermal expansion coefficients between ceramic and metal. Especially, the residual stress at both edges of the specimen reduces the strngth of joint to a large amount by forming a singular stress field. In this study, two dimensional finite element method is attempted for the thermal elastic analysis. The joint residual stress of ceramic/metal developed in the cooling process is investigated and the change of joint residual stress resulted from the repetitive heat cycle is also examined. In addition, it is attempted to clarify the joint stress distribution of the case of tensile load and of the case of superposition of residual stress and actual loading stress.

• 한국환경과학회지
• /
• 제14권4호
• /
• pp.389-395
• /
• 2005

The changes of O-J-I-P transients were investigated using leaves of four subtropical plant species (Crinum asiaticum var. japonicum, Osmanthus insularis, Chloranthus glaber and Asplenium antiquum) under the natural conditions in winter, in order to select the stress indicators for diagnosing physiological states of plants under low temperature. In the O-J-I-P transients of these species, the fluorescence intensity was found to be higher in O-step and lower in P-step in winter than in summer. Particularly, the fluorescence intensity of the P-step in Crinum asiaticum var. japonicum was lower than those of other three plant species, indicating that Crinum asiaticum var. japonicum is the most sensitive to low temperature. Of the chlorophyll fluorescence parameters derived from O-J-I-P transients of four subtropical plants, Fm, Fv/Fo, ABS/CS, TRo/CS, $\phi_{po}$ and $\phi_{po}/(1-\phi_{po})$ decreased significantly with the increase of Fo, Sm, N, EToICS, ETo/RC and $\psi_o/(1-\psi_o)$ depending on temperature drop in winter. Therefore, these parameters could be used as indicators for estimating low temperature stress and diagnosing physiological states of plants under the natural conditions in winter.

• 한국해양공학회:학술대회논문집
• /
• 한국해양공학회 2001년도 추계학술대회 논문집
• /
• pp.264-268
• /
• 2001

In this study, CT specimens were prepared from spring steel(SUP9) processed shot peening which was room temperature, low temperature and high temperature experiment. And we got the following characteristics from fatigue crack growth test carried out in the environment of room, and high temperature at $25^{\circ}C,\; 50^{\circ}C, \;100^{\circ}C,\; 150^{\circ}C,\; and\; 180^{\circ}C$ in the range of stress ratio of 0.05 by means of opening mode displacement. The threshold stress intensity factor range $\DeltaK_{th}$ in the early stage of fatigue crack growth (Region I ) and stress intensity factor range $\Delta$K in the stable of fatigue crack growth (Region II) was decreased in proportion to descend temperature. It assumed that the fatigue resistance characteristics and fracture strength at low temperature and high temperature is considerable higher than that of room temperature in the early stage and stable of fatigue crack growth region.