• 한국해양공학회지
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• 제15권3호
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• pp.100-106
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• 2001

In this study, CT specimens were prepared from Pressure Vessel Steel 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$0^{\circ}C$, -10$0^{\circ}C$ and -12$0^{\circ}C$ and in the range of stress ratio of 0.05 and 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 descent 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 was assumed that the fatigue crack growth rate da/dN in proportion to descending temperature in Region II and the cryogenic-brittleness greatly affect a material with decreasing temperature.

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

• 한국정밀공학회지
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• 제8권2호
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• pp.27-35
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• 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.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2001년도 춘계학술대회논문집A
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• pp.205-210
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• 2001

Fatigue crack growth tests were carried out using high manganese cast steel under constant amplitude loading. Average crystal grain sizes of the material are $200{\mu}m$ and $1000{\mu}m$. For this material, ${\Delta}K_{th}$ is about $8MPa{\sqrt{m}}$ which is quiet large as compared to the general structural steels and the crack growth rate is lower than the general structural steels especilly in the low ${\Delta}K$ regsion. The reason of this behavior is crack closure due to fracture surface roughness and fretting oxide. The relationship between da/dN and the ${\Delta}K_{eq}$ was represented by narrow band regardless of the stress ratio.

• 한국기계가공학회지
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• 제3권4호
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• pp.88-94
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• 2004

High manganese steel was maintained stability of Non-Magnetics performance. Fatigue tests were carried out under constant stress amplitude, using a non-magnetic high manganese steel. The fatigue crack growth mechanism of the high manganese steel was clarified from results such as observation of crack growth path and fracture surface. The result of getting this study was shown as following: 1) Remarkably ${\Delta}Kth$ of the high manganese steel is big with about 3 times of the general steel product. 2) In the low ${\Delta}K$ value region, da/dN is dependent on Kmax, and in the high ${\Delta}K$ value region, it is dependent on ${\Delta}Keff$. The reason of this behavior is crack closure due to fracture surface roughness and fretting oxide. 3) It seems to ease the stress concentration of crack tip crack growth behavior in the ${\Delta}Kth$ vicinity by the generation of the secondary crack.

• 한국해양공학회:학술대회논문집
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• 한국해양공학회 2000년도 추계학술대회 논문집
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• pp.147-153
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• 2000

The fatigue crack propagation behavior of the SA516/70 steel which is used for pressure vessels was examined experimentally at room temperature, $150^{\circ}C$, $250^{\circ}C$ and $370^{\circ}C$ with stress ratio of R=0.1 and 0.3. The fatigue crack propagation rate da/dN related with the stress intensity factor range $\Omega\textrm{K}$ was influenced by the stress ratio within the stable growth of fatigue crack(Region II) with an increase in $\Omega\textrm{K}$. The resistance to the fatigue crack growth at high temperature is higher in comparison with that at room temperature, and the resistance attributed to the extent of plasticity-induced by compressive residual stress according to the cyclic loads. Fractographic examinations reveal that the differences of the fatigue crack growth characteristics between room and high temperatures are mainly explained by the crack closure and oxide-induced by high temperature.

• 대한기계학회논문집A
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• 제34권6호
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• pp.717-723
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• 2010

많은 연구자들이 평직 탄소섬유강화플라스틱에 대해서 연구해왔지만 피로 균열 진전에 관한 연구는 아직도 미지한 상태이다. 그리고 하중과 섬유 배열 각도에 따라 균열 진전 양상이 다름을 알 수 있다. 본 연구에서는 서로 다른 두 개의 섬유 배열각도($0^{\circ}$, $45^{\circ}$)에서 평직 탄소섬유강화플라스틱의 피로 균열 진전에 대해 연구하였다. 평직 탄소섬유강화플라스틱의 피로 균열 진전 테스를 하중비 0.1에 10Hz로 수행하였다. 그 시험 결과로써, 피로 균열 진전 속도(da/dN)와 에너지해방률(${\Delta}G$)과의 그래프를 도출하였고, 섬유 배열 각도에 따른 균열 진전 양상을 $0^{\circ}$의 경우에는 Mode I를 적용하였고, $45^{\circ}$의 경우에는 Mixed Mode를 적용하였다.

• 한국해양공학회지
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• 제1권1호
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• pp.104-110
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• 1987

Fatigue tests by axial loading (R = 0.05) were carried out to investigate fatigue crack growth characteristics of small surface cracks in 2 1/4 Cr-1 Mo steel at room temperature by using flat specimens with a small artificial pit. All the data of the fatigue crack growth rate obtained in the present test are determined as a function of the stress intensity factor range about a semi-elliptical crack, so that the application of linear fracture mechanics to the surface fatigue crack growth and to the fatigue crack growth into depth, and all the data obtained from tests were discussed in comparison with the data of Type 304 stainless steel and two type of mild steel under the same test conditions. The obtained results are as follows: 1)When the cycle ratios are same, surface fatigue crack length and its depth are almost same and fall within a narrow scatter band in spite of different stress levels. 2)Relations of the surface fatigue crack growth rate (da/dN) and fatigue crack growth rate into depth (db/dN) to its stress intensity factor range ($\Delta K_{Ia}, \Delta K_{Ib}$) can be plotted as a straight line at log-log diagram without dependence of stress level and coincide with the data of part-through crack in various steels.

• 대한기계학회논문집A
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• 제27권1호
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• pp.200-207
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• 2003

In this paper, the effect of the compressive residual stresses which were obtained under the various shot velocities of shot balls on the fatigue behaviors of a spring steel, were investigated. The examination of CT specimen test were executed with the materials(JISG SUP9) which are being commonly used for the springs of automotive vehicles. As a result, the optimal shot velocity of shot balls were acquired considering the peak values of the compressive residual stresses on the surface of specimen and effect on the speed of the fatigue crack propagation da/dN in stage II and the threshold stress intensity factor range Δ$K_{th}$ in stage I. Also the material constant C and the crack propagation index m in the formula of paris law da/dN= C $({\Delta}K^m)$ were suggested in this work to estimate the dependency on the shot velocity.

• 대한기계학회논문집
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• 제19권2호
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• pp.475-485
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• 1995

In this study, statistical analysis of fatigue data which had obtained from respective 24 fatigue crack, was examined for SiC whisker reinforced aluminium 6061 composite alloy (SiC$_{w}$/A16061) and aluminium 6061 alloy. SiC volume fraction in composite alloy is 25%. The analysis results stress intensity factor range and 0.1 mm fatigue crack initiation life for SiC$_{w}$/A16061 composite & A16061 matrix are the log-normal distribution. And regression analysis by linear model, exponential model and multiplicative model were performed to find out the relationship between fatigue crack growth rate(da/dN) and stress intensity for find out the relationship between fatigue crack growth rate(da/dN) and stress intensity factor range(.DELTA.K) in the SiC$_{w}$/A16061 composite and examine the applicability of Paris' equation to SiC$_{w}$A16061 composite. Also computer simulation was performed for fatigue life prediction of SiC$_{w}$/A16061 composite using the statistical results of this study.udy.