• 한국정밀공학회지
• /
• 제8권2호
• /
• pp.27-35
• /
• 1991

We propose the crack growth rate equation which applied over three regions (threshold region, stable region, unstable region) of fatigue crack propagation. Constant stress amplitude fatigue tests are conducted for four materials under three stress ratios of R=0.05, R=0.2 and R=0.4. Materials which have different mechanical properties i.e. stainless steel, low carbon steel, medium carbon steel and aluminum alloy are used. The fatigue crack growth rate equation is given by $da/dN={\beta} (1-R)^{\delta}\({\DELTA}K-{\DELTA}K_t)^{\alpha} / (K_{cf}-K_{max})$${\alpha}, {\beta}$ , and ${\delta}$ are constants, and ${\Delta}K_t$ is stress intensity factor range at low ${\Delta}K$ region. The constants are obtained from nonlinear least square method. $K_{ef}$is critical fatigue stress intensity factor. The relation between half crack length and number of cycles obtained by integrating the crack growth rate equation is in agreement with the experimental data. It is also experimented with constant maximum stress and decreasing stress ratios, and the fatigue growth rate of each material is in accord with the proposed equation.

• Journal of Welding and Joining
• /
• 제28권5호
• /
• pp.45-50
• /
• 2010

The fatigue crack growth characteristics of base metal and weld joint of 9% Ni steel for LNG storage tank was carried out using CT specimen at room temperature and $-162^{\circ}C$. Fatigue crack growth rate of base and weld metals at RT and $-162^{\circ}C$ was coincided with a single line independent of the change of stress ratio and temperature. In the region of lower stress intensity factor range, fatigue crack growth rate at $-162^{\circ}C$ was slower than that at RT, and the slop of fatigue crack growth rate at $-162^{\circ}C$ increased sharply with propagating of fatigue crack, fatigue crack growth rate at RT and $-162^{\circ}C$ was intersected near the region of $2{\times}10-4\;mm$/cycle, and after the intersection region, fatigue crack growth rate at $-162^{\circ}C$ was faster than that at RT. The micro-fracture mechanism using SEM shows the ductile striation in the stable crack growth region. Also the defects of weld specimen after fatigue testing were detected using the A scan of ultrasonic apparatus.

• 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.

• 한국경제지리학회지
• /
• 제18권1호
• /
• pp.45-59
• /
• 2015

우리나라에서 도농복합시는 도시지역과 농촌지역의 균형발전을 도모하기 위하여 1995년부터 등장하였다. 본 연구에서는 경기도의 11개 도농복합시를 대상으로, 도시내 산업입지에 따른 경제공간의 변화가 어떻게 양상으로 전개되었는지를 고찰하였다. 경기도의 도농복합시에서는 산업활동의 입지가 활발하게 이루어짐에 따라, 분석 대상에 포함된 모든 도시의 사업체수가 증가하였다. 그러나 개별 도시를 도시지역과 농촌지역으로 구분하여 경제공간의 변화를 고찰한 결과, 이천시와 안성시를 제외한 9개 도시에서 도시지역으로의 경제활동 쏠림현상이 심화되었다. 도시지역으로의 경제활동 쏠림현상은 남양주시 포천시 용인시에서 특히 두드러졌다. 주요 산업부문별 도시지역과 농촌지역의 경제활동 입지 변화를 토대로 실시한 도농복합시의 유형화에서는 5개의 유형이 도출되었다. 경제공간의 변화 유형은 도농격차 심화형, 도시지역 성장둔화형, 농촌지역 성장형, 도농균형 성장형, 도시지역 성장주도형 등이다. 경기도의 도농복합시에서는 거대도시 서울이나 도시화 수준이 높은 도시에 접한 도시일수록 도농격차가 심화되었고, 대도시로부터 멀리 떨어진 도시일수록 도시지역의 성장이 상대적으로 둔화되었다.

• 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.

• Journal of Welding and Joining
• /
• 제13권4호
• /
• pp.155-162
• /
• 1995

Redistribution of residual stress and its effects during fatigue crack propagates from tensile residual stress region in weldment are investigated. Tests are performed by using welded CCT specimens of structual rolling steel (SS400) and it makes fatigue crack propagate from tensile residual stress region. For this study tension-tension loading type is selected by external loading condition and magnetizing stress indicator is used correctly to measure redistribution of residual stress according to fatigue crack growth and number of loading cycles. From this result, it is proved that redistribution of residual stress is mainly consist of residual stress released by fatigue crack growth. When fatigue crack propagates from tensile residual stress region residual stress are redistributed and it makes fatigue crack growth rate largely increase. Fatigue crack growth rate is low in case of redistributed residual stress compare with initial distributed residual stress.

• 한국해양공학회지
• /
• 제16권5호
• /
• pp.80-87
• /
• 2002

In this study, CT specimens were prepared from spring steel(SUP9) which was used in suspension of automobile for room temperature and low temperature service. We got the following characteristics from fatigue crack growth test carried out in the environment of room temperature and low temperature at $25^{\circ}C$, ­3$0^{\circ}C$, ­5$0^{\circ}C$, ­7$0^{\circ}C$ and ­10$0^{\circ}C$ in the range of stress ratio of 0.05 by means of opening mode displacement. The threshold stress intensity factor range ΔKth in the early stage of fatigue crack growth (Region I) and stress intensity factor range ΔK in the stable of fatigue crack growth (Region II) was decreased in proportion to descend temperature. It is 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.

• 한국자동차공학회논문집
• /
• 제12권1호
• /
• pp.83-90
• /
• 2004

In this study, CT specimens were prepared from spring steel(SUP9) processed shot peening which was room temperature and low temperature experiment. And we got the following characteristics from fatigue crack growth test carried out in the environment of room temperature and low temperature at $25^{\circ}C$, $-30^{\circ}C$, $-50^{\circ}C$, $-70^{\circ}C$,$-100^{\circ}C$, and $-150^{\circ}C$, in the range of stress ratio of 0.05 by means of opening mode displacement. The threshold stress intensity factor range ΔKth in the early stage of fatigue crack growth (Region I)was increased but stress intensity factor range ΔK in the stable of fatigue crack growth (Region II) was decreased in proportion to decrease temperature. It is assumed that the fatigue resistance characteristics and fracture strength at low temperature and high temperature is considerably higher than that of room temperature in the early stage and stable of fatigue crack growth region.

• 한국안전학회지
• /
• 제18권3호
• /
• pp.1-7
• /
• 2003

In this study, CT specimens were prepared from spring steel(SPS5) processed shot peening. The fatigue crack growth tests were carried out in the environment of the room temperature md low temperature at $25^{\circ}C$, $-30^{\circ}C$, $-50^{\circ}C$, $-70^{\circ}C$ $-100^{\circ}C$ and $-150^{\circ}C$ in the range of stress ratio of 0.05 by means of opening mode displacement. The threshold stress intensity factor range ΔKth 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) were decreased in proportion to descend temperature. It was shown that the fatigue resistance characteristics and fracture strength at low temperature are considerable higher than those of mom temperature in the early stage and stable of fatigue crack growth region.

• Asian-Australasian Journal of Animal Sciences
• /
• 제10권5호
• /
• pp.491-494
• /
• 1997

The growth performance in the first year of life of 892 Black Bengal kids was studied in four different locations in Bangladesh, e. g. (1) Bhabakhali, (2) Trisal, (3) Aishara and (4) Akhrail. Birth weight of kids of region 1, 2 and 3 were almost similar (1.01 kg) with significantly lower birth weight in region 4 (0.88 kg). Effect of birth type and sex were significant with higher weights for single (1.03 kg) v. twin (0.98 kg) v. triplet (0.92 kg) and male kids (1.03 kg) v. female (0.93 kg). Monthly weights of kids followed the same pattern as birth weight. Monthly weights of kids in region 1, 2 and 3 were similar with significantly lower weight for region. 4 Birth type and sex affected monthly weights in different regions where single and male kids had significantly higher weights for all the regions. The analysis of variance reveals that regional significant differences for average daily gains were noticed for the periods from birth to 3 and 9 to 12 months of age. The highest gains were noticed for region 2 ($51.9{\pm}2.4kg$) and the lowest for region 1 ($38.2{\pm}2.3kg$) with similar values for region 4. From the results it is revealed that growth performance of Black Bengal kids varied in different regions, which might be caused by inappropriate management and inadequate feed availability around the year and stressful environmental conditions.