• Title/Summary/Keyword: Corrosion fatigue fracture

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An Evaluation of Fatigue Life for Aging Aircraft Structure (장기운용항공기 구조물의 잔여 피로수명예측 기법)

  • Lee, Eungyeong;Jeong, Yooin;Kim, Sangshik
    • Korean Journal of Materials Research
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    • v.25 no.10
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    • pp.516-522
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    • 2015
  • Aging aircraft structures are inevitably exposed to environment for a long time facing many potential problems, including corrosion and wide spread fatigue damage, which in turn cause the degradation of flight safety. In this study, the environmental surface damages on aging aircraft structures induced during service were quantitatively analyzed. Additionally, S-N fatigue tests were performed with center hole specimens extracted from aging aircraft structures. From the results of quantitative analyses of the surface damages and fatigue tests, it is concluded that corrosion pits initiated during service reduce the fatigue life significantly. Finally, using the fracture mechanics and the EIFS (equivalent initial flaw size) concepts, the remaining fatigue life was predicted based on actual fatigue test results.

A Study on the Corrosion Fatigue Fracture of U-notch Radius (U-노치반경에 따른 부식피로 파괴거동)

  • 이장규;윤종희;인승현;우창기;신관수;최양호;박성완
    • Proceedings of the Korean Society of Machine Tool Engineers Conference
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    • 2002.10a
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    • pp.58-63
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    • 2002
  • This study has performed rotary bending fatigue testing that smooth specimen using SM45C materials and notched specimen whose radii were R6, R4 and R2, were processed in 3% NaCl aqueous solutions or in the air. The results are as followed; 1. In the air fatigue limit at 10$^{7}$ cycles remarkably reduced as notch radius goes small. 2. In 3% NaCl aqueous solution fatigue strength at 10$^{6}$ cycles also had large range of reduction as notch radius goes small. 3. Comparing fatigue strength in the air, fatigue strength at 10$^{6}$ cycles in 3% NaCl aqueous solution reduced by 46.2% at smooth specimen, 55.3% at R6 notch radius, 45.8% at R4 and 39.7% at R2 respectively. 4. The reason that fatigue strength reduced in the reduction of notch radius sire was because the surface of notch exposed in corrosion was small and consequently it was less corroded.

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Study on corrosion fatigue of high strength steel (고장력강의 부식피로에 관한 연구)

  • 유헌일;천기정;택목양삼
    • Journal of the korean Society of Automotive Engineers
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    • v.5 no.1
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    • pp.32-44
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    • 1983
  • In case of $K_{Imax}$ < $K_{Iscc}$, the corrosion fatigue of high strength steel in 0.1N $H_{2}$S $O_{4}$ solution and 3.5% salt water is as follows. 1. The fatigue life shortens in order of 3.5% salt water and 0.1N $H_{2}$S $o_{4}$ solution. 2. The fatigue crack growth rate in air is obtained as the following equation. (dc/dN)$_{atr}$=7.23*10$^{-6}$ (.DELTA. K)$^{2.23}$ 3. The corrosion fatigue crack growth rate in environment is divided into three regions, that is, First Region, Second Region and Third Region from the small cyclic stress intensity. 4. The formation rate of the active surface on metal is slower than the mechano-chemical reaction rate in First Region. The crack growth rate depends on time and the cyclic stress intensity and is expressed as the following equation. (dc/dN)$_{I}$=C(/DELTA. K)$^{\delta}$ 5. The formation rate of the active surface is faster than the mechano-chemical reaction rate in Second Region and the synergistic effect by stress and corrosion becomes slow. In case the fatigue load is large, we have the critical crack growth rate which is not related to the cyclic stress intensity. 6. The corrosion crack growth rate by the mechano-chemical reaction is the same in $H_{2}$S $O_{4}$ solution and salt water, so Hydrogen accelerates the crack growth. 7. The environment has no effect on the corrosion fatigue crack growth rate in Third Region. 8. In First Region and Second Region, dimple is observed on the fatigue fracture surface in 0.1N $H_{2}$S $O_{4}$ solution. 9. The striation is observed in any environment as in air in Third Region and its interval approximately coincide with the crack growth rate.ate.e.e.

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A Study on Corrosion Fatigue Crack Growth Behavior in Al 7075-T651(II) (Al 7075-T651의 부식피로균열 성장 거동에 관한 연구(II))

  • 한지원;우흥식
    • Journal of the Korean Society of Safety
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    • v.14 no.2
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    • pp.3-10
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    • 1999
  • Fatigue crack growth rates in commercial plate of high strength Al 7075-T651 were investigated for the T-L direction in air, water and sea water. In this paper the effect of cyclic load wave-form(trapezoid and triangle) on fatigue crack growth rates in air, water and sea water environments were investigated using standard LEFM testing procedures. It was founded that the fatigue crack growth behaviors were not affected by cyclic load wave-forms. In region II (stable crack growth region), the fatigue crack growth behaviors were insensitive to cyclic load wave-forms and were sensitive to environment i.e. fatigue crack growth behaviors were higher in sea water than in air for all cyclic load wave-form. The result of fractographical morphology in air, water and sea water by SEM showed obvious dimple rupture and typical striation in air, but transgranular fracture surface in water and sea water. The values m are not affected by corrosion environments but C are different values.

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Evaluation of Corrosion Fatigue Crack Propagation Characteristics at Equivalent Potential of Zinc Sacrificial Anode (아연(Zn)희생양극 등가전위에서 부식피로균열 진전특성에 관한 연구)

  • Won Beom Kim
    • The Journal of the Convergence on Culture Technology
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    • v.10 no.1
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    • pp.363-368
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    • 2024
  • Steel structures used in marine environments, such as ships, offshore structures or sub-structures in wind power generation facilities are prone to corrosion. In this study, the corrosion fatigue crack propagation characteristics due to the environmental load are examined by experiment at -1050 mV vs. SCE, which is equivalent to the anti-corrosion potential of zinc anodes that are widely used as sacrificial anodes. In this study, for this purpose, an experimental study is conducted on the effect of cathodic protection on the propagation of fatigue cracks in the seawater environment under the condition of -1050 mV vs. SCE, considering the wave period in synthetic seawater. Cathodic protection prevents corrosion; however, excessive protection generates hydrogen through chemical reactions as well as calcareous deposits. The fatigue crack propagation rate appeared to be faster than the rate in a seawater corrosion environment at the early stages of the experiment. As the crack length and stress intensity factor K increased, the crack propagation rate became slower than the fatigue crack propagation rate in seawater. However, the crack growth rate was faster than that in the atmosphere.

Stress Corrosion Crack Rate of STS 304 Stainless Steel in High Temperature Water (고온수중에서 STS 304 스테인리스강의 응력부식균열 성장속도)

  • Kim, Jeong-Gi
    • Transactions of the Korean Society of Mechanical Engineers A
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    • v.24 no.1 s.173
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    • pp.156-162
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    • 2000
  • Sensitized STS 304 stainless steel crack growth rate(CGR) in high temperature water was investigated under trapezoidal wave loading test using fracture mechanics techniques. The CGR, due to stress corrosion cracking(SCC), were systematically measured as a function of the stress intensity factor and stress. holding time under trapezoidal wave loading. In high temperature water, CGR was enhanced by a synergistic effects in combination with an aggressive environment and mechanical damage. The CGR, $(da/dN)_{env}$ was basically described as a summation of the environmentally assisted crack growth rate $(da/dN)_{SCC}$, $(da/dN)_{CF}$ and fatigue crack growth rate in air $(da/dN)air,. The CGR, $(da/dN)_{env}$, increased linearly with increasing stress holding time. The CGR, $(da/dN)_{SCC}$ decreased linearly with increasing stress holding time. Fracture surface mode varied from trans-granular cracking to inter-granular cracking with increasing stress holding time.

Complex Leakage Probability Evaluation of Nuclear Pipes by Fatigue and Stress Corrosion Cracking (피로 및 응력부식균열에 의한 원전 배관의 복합누설확률 평가)

  • Kim, Seung Hyun;Goni, Nasimul;Chang, Yoon-Suk;Jang, Changheui
    • Transactions of the Korean Society of Pressure Vessels and Piping
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    • v.11 no.2
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    • pp.25-30
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    • 2015
  • In the present study, complex leakage probabilities of nuclear pipes due to fatigue and stress corrosion cracking are evaluated by using the PINTIN(Piping INTegrity INner flaws) that is developed based on the existing PRAISE(Piping Reliability Analysis Including Seismic Events) program. With regard to the aging and crack instability, small leak and big leak probabilities are calculated for several pipes in a reactor coolant system of domestic nuclear plant. Moreover, sensitivity analysis is also performed to find out the effect of parameters for the leakage of pipes, which shows the coolant temperature is the most influencing parameter.

Corrosion Fatigue Crack Propagation Behaviour of TMCP Steel Plate at Ballast Tank of Ship Structure under the Condition of Cathodic Overprotection (선체구조 Ballast Tank 고장력 TMCP강판의 과방식중 부식피로균열 전파거동)

  • Kim, Won-Beom
    • Journal of the Korea Academia-Industrial cooperation Society
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    • v.13 no.6
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    • pp.2465-2471
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    • 2012
  • For the steel structures those are used in harsh sea environments, corrosion fatigue is a challenging issue in connection with design life. In this research, in order to investigate the influence of cathodic overprotection on the corrosion fatigue crack propagation behavior, corrosion fatigue crack propagation test under the condition of -950mV vs SCE was conducted by using of high tensile TMCP steel plate and the relationships between da/dN-${\Delta}K$ were obtained. At this test, when ${\Delta}K$ is low, the crack propagation rates were accelerated compared to those of seawater condition, however, when ${\Delta}K$ is high, the crack propagation rates were lower than those of seawater condition. As the cause for the acceleration and deceleration of corrosion fatigue crack propagation rates under the condition of cathodic overprotection, the role of hydrogen and calcareous deposits are discussed.

Integrity Evaluation of Bogie Frame by Ultrasonic Fractography Analysis (초음파 파면해석에 의한 대차 프레임의 건전성 평가)

  • 윤인식;권성태;선종성;명노종;정우현;손태순;김경국;김순철
    • Journal of the Korean Society for Railway
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    • v.3 no.2
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    • pp.77-83
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    • 2000
  • This study proposes the integrity evaluation of the bogie frame using ultrasonic fractography analysis. Analysis objectives in this study are to investigate fracture planes of damaged zone by the A-scan method. The surface condition of fracture planes shows degree of degradation by the stress concentration. The detection of the natural defects in the bogie frame is performed using the characteristics of echodynamic pattern in ultrasonic signal. Results of ultrasonic testing agree fairly well with those of actual fracture plane. In quantitative fractography analysis, microstructures of actual fracture plane turned out to be intergranular and transgranular fracture. Proposed ultrasonic fractography analysis in this study can be used for the integrity evaluation of the bogie frame.

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The effects of 3.5% NaCl solution on the corrosion fatigue crack propagation characteristics of SS41 steel (SS41강의 부식피로 균열 전파특성에 미치는 3.5% NaCl수용액의 영향)

  • 오세욱;김재철;최영수
    • Journal of Ocean Engineering and Technology
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    • v.1 no.1
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    • pp.111-119
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    • 1987
  • The corrosion fatigue crack propagation characteristics of SS41 steel in 3.5% NaCl solution have been evaluated for loading frequencies of 1Hz and 0.2Hz. A sine wave loading profile was used for fatigue testing. Each test was carried out at a constant stress ratio, R(0.1). The main results are summarized as follows; 1. Fatigue crack propagation rate was higher in 3.5% NaCl solution than in air, higher in the base metal than in the weld metal, and higher at f =0.2Hz than at f =1Hz. 2. The crack closure level of the base metal was not influenced by cyclic frequencies, but that of the weld metal was much influenced. 3. When the crack closure effect was eliminated in the evaluation of crack propagation characteristics by using $\Delta K_{eff}$, the envirommental influence was distinctly observed. At the base metal, crack propagation rate was enhanced by the hydrogen embrittlement, and the weld metal was reduced by the crac closure. 4. There was clearly observed hydrogen embrittlement and severely corroded aspect at fracture surface of lower frequency than that of higher frequency, and at that of base metal than that of the weld metal.

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