• Journal of the Korean Society for Precision Engineering
• /
• v.7 no.2
• /
• pp.39-46
• /
• 1990

In this study, the mechanical behavious of a center crack which propagates between two holes in a panel are investigated. It is confirmed experimentally and analytically that a center crack stops and a small crack initiates from holes and propagates to fracture because of the compressive stress arising along the path of the fatigue crack propagation. Futhermore, it is noted that regardless of the configuration of the crack and the structure, Paris' law can be applied to the fatigue crack propagation.

• Journal of Industrial Technology
• /
• v.30 no.B
• /
• pp.17-23
• /
• 2010

Since the propagation of a short fatigue crack is directly related to the large crack which causes the fracture of bulk specimen, the detailed study on the propagation of the short crack is essential to prevent the fatigue fracture. However, a number of recent studies have demonstrated that the short crack can grow at a low applied stress level which are predicted from the threshold condition of large crack. In present study, the threshold condition for the propagation of short fatigue crack is examined with respect to the micro-structure and cyclic loading history. Specimens employed in this study were decarburized eutectoid steels which have various decarburized ferrite volume fraction. Rotating bending fatigue test was carried out on these specimens with the special emphasis on the "critical non-propagating crack length" It is found that the reduction of the endurance limit of their particular micro-structures can be due to the increase of the length of critical non-propagating crack, and the quantitative relationship between the threshold stress ${\sigma}_{wo}$ and the critical non-propagating crack length $L_c$ can be written as ${\sigma}_{wo}{^m}{\cdot}L_c=C$ where m,C is constant. Further experiments were carried out on cyclic loading history on the length of critical non-propagating crack. It shown that the length of critical non-propagating crack is closely related to cyclic loading history.

• Journal of the KSME
• /
• v.28 no.2
• /
• pp.177-180
• /
• 1988

파괴안전설계를 하기 위하여 파괴역학원칙을 성공적으로 적용시키기 위해서는 주로 믿을 수 있는 크랙성장을 예측하는데 달려있다. 일정크기의 피로하중을 받는 구조물 구성요소의 경우 안전계수로 빈도수와 환경의 영향을 설명할 수 있다면 경험적인 데이터를 바탕으로 하여 그 피로거동은 상당히 쉽게 예상될 수 있다. 그러나 구조물 구성요소가 변화크기의 피로하중을 받는다면, 크랙성장예측을 위한 데이터를 마련하는데는 무엇보다도 그러한 변화크기의 피로하 중상태의 적용모델이 확실히 필요하며, 일어날 수 있는 여러 가지 상황들을 통합할 수 있는 모 델에 입각하여야 한다.

• Transactions of the Korean Society of Mechanical Engineers
• /
• v.14 no.2
• /
• pp.382-392
• /
• 1990

This study investigates the behavior of fatigue crack propagating between holes of holes filled with another materials. When holes of the holes filled with another materials are located symmetrically near a center crack, it is noted that the crack propagation rate is influenced by both the bonding force of the brazing part and the elastic modulus of another material. It is experimentally and analytically confirmed that the center crack stops when its tip reaches near the center line of the holes and a small crack is initiated from the boundaries of holes of the holes filled with another materials and it propagates to final fracture.

• Transactions of the Korean Society of Mechanical Engineers
• /
• v.12 no.4
• /
• pp.738-746
• /
• 1988

Fatigue crack propagation of duplex stainless steel weldments was studied to develop further phenomenological understanding of the influences of welding heat cycle accompanying microstructural changes. Fatigue tests were carried out under constant amplitude of load in air at room temperature. The results showed that the crack propagation rate was different in base metal, heat affected zone and welding line. The crack propagation behavior in each part of duplex stainless steel was strongly dependent on phase ratio(.gamma../.alpha.) and several factors of microstructure also affected this propagation behavior. The fractographic feature in each part of steel were discussed on crack propagation behaviors.

• Proceedings of the Korean Society of Precision Engineering Conference
• /
• 1997.10a
• /
• pp.786-789
• /
• 1997

Ti-6Al-4V has been used widely in biomedical field. But because of its toxicity, the ${\beta}$ stabilizing element, V, in Ti-6Al-4V has been replaced by Nb, Ta. Ti-10Ta-10Nb has been developed for biomedical applications. The fatigue crack propagation behavior of Ti-alloy(Ti-10Ta-10Nb) was investigated, in comparison with that of pure Ti. In order to better understand the fundamental fatigue behavior of Ti-10Ta-10Nb, rotating bending fatigue tests have been carried out. Ti-10Ta-10Nb has a better fatigue strength than pure Ti. In this paper, fatigue life has been predicted with Nisitani's equation of the fatigue crack propagation that can be established by measuring fatigue crack growth rates.

• Proceedings of the Korean Society of Machine Tool Engineers Conference
• /
• 1998.10a
• /
• pp.140-145
• /
• 1998

In this study, analysis for fatigue crack propagation behavior of interface and aroud interface under rotary bending stress. Though K values are nearly the same in around interface by BEM 2-D, fatigue crack propagated H.A.Z. Around Interface crack propagation speed is m=0.678 in H.A.Z by Paris' law. In this case(friction welded materials: STS304, SM15C), fatigue crack growth is considered SM15C metal microstructure and elastic flow from this result. Result is more metal microstructute dependence than stress dependence by analysis (BEM 3-D, BEM 2-D) and fatigue crack propagation

• Journal of Ocean Engineering and Technology
• /
• v.1 no.2
• /
• pp.83-92
• /
• 1987

Inorder ot estimate the running life of turbine rotors, fatigue crack propagation low, da/dN = C(${\DELTA}K)^m$, proposed by paris et al. has been widely applied. In this study, fatigue crack propagation rates for 16 samples of 1% Cr-Mo-V rotor steel were measured and statistical characteristics of m and C values in above equation were reviewed. The results are summarized as follows. 1. C and m follow a log-normal distribution and normal distribution, respectively. And the relation of C and shows a strong negative correlation. 2. Fatigue crack propagation equation can be expressed as da/dN=$4.11{\times}10^{-4}({\Delta}K/153.8)^m$, introducing the ralationship C=$C_oK_o^{-m}$. In this case, contribution of $C_o$ distribution to the distribution of log C shows very small compared to degrees of contribution by m.

• Journal of the Korean Society for Precision Engineering
• /
• v.11 no.4
• /
• pp.47-57
• /
• 1994

This study investigates the crack propagation behavior to examine the effect of welding residual stress by the superposition method. Especially, as the crack propagation behavior is affected by the applied stress and the stress ratio in compressive residual stress filed, it is studied for three cases as follows; (1) $K_{min}$is smaller than l $K_{r}$l, (2) $K_{min}$ is smaller than l $K_{r}$l in the later stage, (3) $K_{min}$is lager than l $K_{r}$l. The resuslts show that the superposition method is very useful in all the three cases of compressive residual stress field, but is inappropriate in predicting the crack propagation behavior in tensile residual stress field.field.field.

• Journal of Ocean Engineering and Technology
• /
• v.13 no.3 s.33
• /
• pp.108-113
• /
• 1999

In this study, CT specimens were prepared from ASTM A516 Gr. 65 which was used for pressure vessel plates for moderate and lower temperature service. Fatigue crack growth test was carried out in the environment of low temperature of $10^{circ}C, -10^{circ}C, -30${circ}C\;and\;-50^{circ}C$ and in the range of stress ratio of R=0.05 and 0.3 by means of opening mode displacement. Based on these test results, the characteristics from temperature and stress ration were shown as follows. 1) As the stress ratio, R increased da/dN and ${Delta}K$ of 2nd stage gradually decreased. And as R decreased, the effect of temperature became greater and greater. 2) As the temperature descended, da/dN decreased on a certain ${Delta}K$, and ${Delta}K$ did in a same da/dN. And the stress ratio, R exerted greater influence at the lower temperature. 3) The fatigue crack growth constant, m increased at $10^{circ}C$ and $-10^{circ}C$, snd decreased at $-30^{circ}C$ and $-50^{circ}C$ following the increment of stress ratio R. And m increased along with the reduction of temperature greatly decreased at $-30^{circ}C$ to come close to two(2).