• 한국안전학회지
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• 제15권2호
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• pp.8-12
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• 2000

The fatigue crack propagation tests were performed in triangular and holding-time stress waveforms at $650^{\circ}C$. The behavior of fatigue crack propagation was investigated according to waveform. The analysis of high temperature fatigue crack propagation by the stress intensity factor range ${\Delta}K$, elastic fracture mechanics parameter, was not available. The behaviors of high temperature fatigue crack propagation by the J-integral(${\Delta}J_f$, J' and ${\Delta}J_c$), elasto-plastic fracture mechanics parameter, were investigated in a number of stress waveforms. The fast-fast waveform exhibited cycle-dependent(fatigue type), the slow-fast and the hold time with 500sec waveforms appear to be time-dependent(creep type) and the fast-slow and the hold time with 5, 25sec waveforms exhibited conbined behavior of both types(fatigue-creep conbined type).

• 대한기계학회논문집A
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• 제41권9호
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• pp.853-860
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• 2017

본 연구는 균열 발생 및 전파단계에서 하중모드 II의 영향을 평가하기 위해 피로균열 하한계 영역의 혼합모드 I+II 하중을 통해 실험적으로 평가하였다. 균열 발생단계(Stage I)에서는 혼합모드상태에서 하중작용 각도(${\theta}$)가 증가할수록 모드 II 영향으로 인하여 낮은 하중에서 균열이 발생하고, 균열 전파단계 (Stage II)에서는 균열전파 속도는 감소하였다. 다단계 하중작용 각도변화에 따른 하중모드 II영향은 균열전파단계 실험을 통해 평가하였다. 혼합모드 I+II 하중 작용 시 작용각도 ($0^{\circ}{\rightarrow}{\theta}{\rightarrow}60^{\circ}$) 증가에 따라 피로균열전파속도는 감소하였으며 늦게 발생한 균열에서도 마찬가지로 감소하였다. 작용각도가 ${\theta}{\geq}75^{\circ}$ 범위에서는 하중작용각도 증가에 따라 피로균열전파속도가 증가하고 피로수명이 감소하는 것을 확인하였다.

• 한국정밀공학회:학술대회논문집
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• 한국정밀공학회 2000년도 추계학술대회 논문집
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• pp.473-476
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• 2000

Recently, many studies focus on mixed-mode fatigue-fracture characteristics of characteristics of materials. In order to reveal crack initiation and propagation mechanisms in combined -mode fatigue. This paper investigates the initiation and propagation behavior of the fatigue crack of the STS304 specimens under mixed mode loading conditions. moreover crack arrest and branch phenomena were analyzed with respect to the change do the angle of inclined loading. The relationship between the angle of inclined loading and the angle of branched crack was studied. A greate number of cycles are necessary to initiate a new crack from the initial crack. The direction of the new crack propagation is determined by MTS theory.

• 한국정밀공학회지
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• 제20권2호
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• pp.136-145
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• 2003

The integrity of stiffened panels with stringers in airplane structure is generally enhanced by investigating the fatigue crack propagation behavior in detail and providing the technical methodology to deal with the propagating crack. This paper attempts to clarify the effect of load-ratio on the fatigue crack propagation rate and the fatigue life for the thin aluminum 2024-T3. Both the variable and the constant fatigue loading conditions are considered for the fatigue crack propagation behavior in stiffened panels with stringers.

• 한국안전학회지
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• 제12권3호
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• pp.38-44
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• 1997

6063-T5 alloys are tested in laboratory air, water and 3% NaCl solution to investigate the effects of corrosive environment on the retardation behavior through single overload fatigue test. Also, the fatigue crack propagation and the crack closure behavior are studied. The results obtained in this experimental study are summarized as follows. 1) Behaviors of fatigue crack growth retardation are observed in water and 3% NaCl solution as they do in air. The number of delay cycles and the size of affected region by single overload decrease greatly in water and 3% NaCl compared with those in air. 2) In fractographic results, the overload marking by single overload appear remarkably in air, but indistinctly in water and 3% NaCl solution. 3) The effect of crack closure on crack propagation is most remarkable in the beginning of crack propagation. With crack propagation, the crack closure level and its effect decrease greatly.

• 한국주조공학회지
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• 제25권1호
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• pp.16-22
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• 2005

This study aims to investigate the effects of the microstructures and nodule type on the fatigue characteristics of cast iron. Fatigue tests were carried out in tension-tension mode using a servo-hydraulic testing machine with load control mode operating at a frequency of 15 Hz. The tests were conducted at stress ratio R=Kmin/Kmax, of 0.1. Initial crack ${\Dalta}K$ values were highly performed with increase in tensile strength of DCI fatigue specimens. ${\Dalta}K_{th}$ region, fatigue crack propagation was primarily advanced through cell boundary and in periphery of near nodule. Fatigue crack propagation rate of D2 consisted with 2Phase(Ferrite+Pearlite) was slow due to crack closure enhanced by crack deflection and occurred crack branching. The generation of crack branch was occurred due to interaction of crack-nodule. At Threshold and Paris zone, the fractographs of the fatigue fracture surface for DCI show typical striations of a ductile fracture and isolated cleavage planes near graphite. The effect of microstructure on fatigue crack propagation of GC strongly depends on the type of flake. The generation of crack branch occurred due to interaction of crack-nodule. The fractographs of the fatigue fracture surface for GC show cleavage plane along the flake graphite.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2004년도 춘계학술대회
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• pp.13-18
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• 2004

The objective of this study is to investigate fracture toughness and fatigue crack propagation behavior in the Reduced Activation Ferritic Steel (RAFs) JLF-I. The fracture toughness tests were performed with various size(plane size and thickness) and various side groove of specimens. The fatigue crack propagation behavior of the JLF-I steel was investigated by the constant-amplitude loading test for the stress ratios R=O.I, 0.3 and 0.5 respectively. The effects of stress ratios and specimen size on the fatigue crack growth behaviors for JLF-I steel were discussed within the Paris law. The test results showed the standard CT specimen with the side groove of 40 % represented a valid fracture toughness. The fracture resistance curve increased with increasing plane size and decreased with increasing thickness. However, the fracture resistance curve of half size specimen was similar to that of the standard specimen. The fatigue crack propagation rate of a half size specimen was similar to that of a full size specimen at the stress ratios of 0.1, 0.3 and 0.5 respectively. The fatigue crack propagation behavior of this material were evaluated by using a half size specimen.

• 한국해양공학회:학술대회논문집
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• 한국해양공학회 2000년도 추계학술대회 논문집
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• pp.240-245
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• 2000

Fatigue crack propagation rates and characteristics of the SA516-60 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,\; -10^{\circ}C,\; -30^{\circ}C,\; -50^{\circ}C, \;and\; -70^{\circ}C4 with stress ratio of R=0.05. The obtained experimental results are as follows; 1) In the logarithmic relationship between the fatigue crack propagation rate(da/dN) and stress intensity factor K, the linear relationship was obtained up to da/dN 〉$8\times10^{-3}$/mm/cycle in the same of room temperature, but in low temperature case, the relationship was extended to the range of crack propagation rate. 2) The lower limit stress intensity factor of SA516-60 $\DeltaK_{th}$ was 15.8MPa and in the case of low temperature $-50^{\circ}C\; and\; -70^{\circ}C$, the crack propagation rate da/dN which showed a linear relation, reached rapidly to the $\DeltaK_{th}$/. As the results, the crack propagation rates of $-50^{\circ}C\; and\; -70^{\circ}C$ were lower than that of room temperature and according to the testing temperature the rates were decreased rapidly to the $\DeltaK_{th}$/. 3) On the relationship between the stress intensity factor $\DeltaK$ and the crack propagation cycle, the stress intensity factors of low cycle region was rapidly increased at low temperature, but $\DeltaK$ was increased rapidly at room temperature of high cycle. 4) On the relationship between the fatigue crack propagation rate and cycle, the fatigue crack propagation rate showed higher gradient in the room temperature than the low temperature due to the increment in ductility at low temperature.

• 한국정밀공학회지
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• 제21권6호
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• pp.109-116
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• 2004

In this study, when variable-amplitude load with various applying mode acts on the pre-crack tip, we examined how fatigue cracks behave. Hence aspects of the deformation caused by changing the applying mode of single overload and propagation behavior of fatigue crack were experimentally examined: What kinds of the deformation would be formed at pre-crack and its tip\ulcorner What aspects of the residual plastic deformation field would be formed in front of a crack\ulcorner How aspects of the plastic zone could be evaluated\ulcorner As applying mode of single overloading changes, the deformation caused by tensile and shear loading variously showed in each applying mode. The different aspects of deformation make influence on propagation behavior of cracks under constant-amplitude fatigue loading after overloading with various modes. We tried to examine the relationship between aspects of deformation and fatigue behavior by comparing the observed deformation at crack and crack propagation behavior obtained from fatigue tests.

• 한국공작기계학회:학술대회논문집
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• 한국공작기계학회 2002년도 춘계학술대회 논문집
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• pp.64-69
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• 2002

The purpose of this paper was to investigate the welding characteristics and the fatigue crack propagation behavior of titanium commonly using power station, aircraft and ship. The experimented material was TIG welded in order to look over the characteristics according to the notch position and compare with other materials. We compared and reviewed the fatigue crack propagation behavior of nontch base metal and welded specimens having different notch position to evaluate the fatigue crack propagation behavior by welding condition.