• 대한조선학회논문집
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• 제44권4호
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• pp.417-424
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• 2007

With regard to corrosion fatigue crack initiation life (Nc), it has been treated ambiguously for the member which doesn't have stress concentration area. In this research, in order to clarify the corrosion fatigue crack initiation life (Nc), corrosion fatigue tests were carried out. Reasonable and universal corrosion fatigue crack initiation life (Nc) was defined and corrosion fatigue crack initiation/propagation model was suggested also. As the fatigue crack which emanates from the pit is usually small, accordingly it is treated as a small crack. In addition, the observation of the corrosion fatigue fracture surfaces using SEM was conducted. And the fracture mechanics analysis using an intrinsic crack model was conducted for the treatment of the small crack. Finally, the followings were obtained. When there is no clear stress concentration point which seems to fall into a corrosion fatigue crack initiation life, the significance of the definition and suggestion of the moment of the reasonable and universal corrosion fatigue crack initiation life (Nc), at which the fatigue crack propagation rate becomes faster than the corrosion pit growth rate so that the fatigue crack initiates from the pit and propagates in earnest, has been clarified.

• 수산해양기술연구
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• 제25권2호
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• pp.87-104
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• 1989

Recently, with the tendency of more lightening, high-strength and high-speed in the marine industries such as marine structures, ships and chemical plants, the use of the aluminium Alloy is rapidly enlarge and there occurs much interest in the study of corrosion fatigue crack characteristics. In this paper, the initiation of surface crack and the propagation characteristics on the base metal and weld zone of 5086-H116 Aluminium Alloy Plate which is one of the Al-Mg serious alloy(A5000serious) used most when building the special vessels, were investigated by the plane bending corrosion fatigue under the environments of marine, air and applying cathodic protection. The effects of various specific resistances on the initiation, propagation behavior of corrosion fatigue crack and corrosion fatigue life in the base metal and heat affected zone were examined and its corrosion sensitivity was quantitatively obtained. The effects of corrosion on the crack depth in relation to the uniform surface crack length were also investigated. Also, the structural, mechanical and electro-chemical characteristics of the metal at the weld zone were inspected to verify the reasons of crack propagation behavior in the corrosion fatigue fracture. In addition, the effect of cathodic protection in the fracture surface of weld zone was examined fractographically by Scanning Electron Microscope(S.E.M.). The main results obtained are as follows; (1) The initial corrosion fatigue crack sensitibity under specific resistance of 25Ω.cm% show 2.22 in the base metal and 19.6 in the HEZ, and the sensitivity decreases as specific resistance increases (2) By removing reinforcement of weldment, the initiation and propagation of corrosion crack in the HAZ are delayed, and corrosion fatigue life increases. (3) As specific resistance decreases, the sensitivity difference of corrosion fatigue life in the base metal and HAZ is more susceptible than that of intial corrosion fatigue crack. (4) Experimental constant, m(Paris' rule) in the marine environment is in the range of about 3.69 to 4.26, and as specific resistance increases, thje magnitude of experimental constant, also increases and the effect by corrosion decreases. (5) Comparing surface crack length with crack depth, the crack depth toward the thickness of specimen in air is more deeply propagated than that in corrosion environment. (6) The propagation particulars of corrosion fatigue crack for HAZ under initial stress intensity factor range of $\Delta$k sub(li) =27.2kgf.mm super(-3/2) and stress ratio of R=0 shows the retardative phenomenon of crack propagation by the plastic deformation at crack tip. (7) Number of stress cycles to corrosion fatigue crack initiation of the base metal and the welding heat affected zone are delayed by the cathodic protection under the natural sea water. The cathodic protection effect for corrosion fatigue crack initiation is eminent when the protection potential is -1100 mV(SCE). (8) When the protection potential E=-1100 mV(SCE), the corrosion fatigue crack propagation of welding heat affected zone is more rapid than that of the case without protection, because of the microfissure caused by welding heat cycle.

• 한국해양공학회지
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• 제1권2호
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• pp.93-100
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• 1987

Corrosion fatigue cracking of the austenitic stainless steel(bese metal & heat affected zone by TIG weld) was studied experimentally under the environments of various specific resistance and air. The characteristics of corrosion fatigue crack growth rate and the environmental constants of paris' rule were investigated for SUS 304 weldments in the various specific resistance. The influences of stress intensity factor range and corrosion on the crack growth rate were compared. The characteristics of corrosion fatigue cracking for the weldments were inspected from mechanical, electrochemical and microstructural point of view. Main results obtained are as follows: 1) As the specific resistance decreases, the environmental constant C of paris'rule increases(hence the corrosion fatigue crack growth rate is rapid), but the environmental constant m decreases, so the effect of corrosion to the crack growth rate is more susceptible than thet of stress intensity factor range. 2) As the stress intensity factor range decreases, the corrosion fatigue crack growth rate of heat affected zone is more susceptible than that of the base metal. 3) The corrosion fatigue crack growth rate of the heat affected zone is more rapid than that of the base metal, because of the phenomenon of softening and the less noble potential coused by wedlding heat cycle. 4) The corrosion fatigue cracking of SUS 304 weldment appears transgranular fracture.

• 수산해양기술연구
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• 제34권1호
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• pp.30-36
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• 1998

Recently, with rapid increase of gas demand, there occurs much interest their security of safety in the gas storage tanks and pressure vessels etc. In order to solve the problems, the occurrence of corrosion fatigue crack and the propagation behavior must be investigated. Especially the occurrence of corrosion fatigue crack and the propagation behavior in the part which has concentrated stress or defects, must be studied more carefully. In this paper, the high-tensile steel of SPV 50 which is much used for building the LPG storage tanks was tested by the use of a plane bending corrosion fatigue tester under the various marine environments and in the air. These experiments were done to investigate the corrosion fatigue crack propagation behavior, the variation of aspect ratio for part through crack and electro-chemical characteristics of the metal. The main results obtained are as follows ; 1. Comparing the same surface crack length with the crack depth, the crack depth toward the thickness of specimen in air propagated faster than that in corrosion environment. 2. The aspect variation of the half elliptical crack can be estimated as following equation; b/a=i-jb/t where a : surface crack length, b : crack depth, t : specimen thickness, i,j : experimental constants but the slope j is decreased as specific resistance decreases. 3. As the specific resistance of corrosion environment decrease or the corrosion fatigue crack propagates, the corrosion potential become less noble.

• 수산해양기술연구
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• 제28권3호
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• pp.286-294
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• 1992

In this paper, the corrosion fatigue crack propagation behavior of structure rolled steel (SWS 41C) was investigated by changing the thickness, and this experiment was done by the three point bending corrosion fatigue tester. The main results obtained are as follows: 1) As the thickness of specimen becomes thicker, the corrosion sensitivity to initial stage crack becomes some sensitive, and that the fatigue life becomes more sensitive. 2) The crack growth rate to initial stage crack (da/dN) was retarded as the thickness of specimen becomes thicker. But after initial stage crack, as the thickness of specimen is more thicker, da/dN is more rapid. 3) As the corrosion fatigue crack length grows, the accelerative factor of thick specimen (t=12mm) is more higher than that of thin specimen (t=6mm). 4) As the corrosion fatigue crack length grows, the corroson potential of both thick specimen and thin specimen becomes more less noble potential, however thick specimen (t=12mm) tends to more less noble potential than that of thin specimen(t=6mm).

• 한국마린엔지니어링학회:학술대회논문집
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• 한국마린엔지니어링학회 2005년도 후기학술대회논문집
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• pp.228-229
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• 2005

The compressive residual stress, which is induced by shot peening process, has the effect of increasing the intrinsic fatigue strength of surface and therefore would be beneficial in reducing the probability of fatigue damage. However, it was not known that the effect of shot peening in corrosion environment. In this study, the effect of shot peening on corrosion fatigue crack growth of sping steel immersed in 6% $FeCl_3$ solution and corrosion characteristics with considering fracture mechanics. The results of the experimental study corrosion fatigue characteristics of spring steel are as follows; the fatigue crack growth rate of the shot peening material was lower than of the un peening material. And fatigue life shows more improvement in the shot peening material than un peening material. This is because the compressive residual stress of surface operate resistance of corrosion fatigue crack propagation. It is assumed that the shot peening process improve corrosive resistance and mechanical property.

• Journal of Advanced Marine Engineering and Technology
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• 제30권6호
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• pp.731-739
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• 2006

Corrosion and lassitude are very important in the metal construction Currently, the shot peening is used much for removing the defect on the surface, improving the fatigue strength on surface. In this study. the influence of shot peening to the corrosion property were investigated in 3.5% NaCl, 10% HNO3 + 3% HF. 6% FeC13. The immersion test was performed on two kind of specimen(Removed corrosion product. RCP and Continuous immersed specimen: CIS). The immersion periods was 3600hours. Corrosion potential. weight loss, and fatigue crack growth characteristics were investigated. The result, shot peening in corrosion potential showed stable potential. Also, shot peening displayed small Weight loss than un peening. And Fatigue crack resistivity of shot peening in corrosion solution's fatigue crack appeared greatly than un peening.

• 한국해양공학회지
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• 제2권2호
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• pp.122-129
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• 1988

Recently with the rapid development in marine and shipbuliding industries such as marine structures, ship and chemical plants, there occurs much interest in the study of corrosion fatigue characteristics which was closed up an important role in mechanical design. In this study, the 5086 Al-alloy was tested by use of rotary bending fatigue tester. The retardation effect of overload on the corrosion fatigue crack propagation in sea environment was quantitatively studied. 1) Retardation effect of corrosion fatigue crack propagation is most eminent when overload ratio is 1.52, overload magnitude corresponds to about 77% and 55% of yield strength and tensile strength respectively. 2) After overload ratio 1.52 was used, retardation of corrosion fatigue crack growth rate is largely retarded and quasi-threshold stress intensity factor range($\Delta\textrm{K}_{th}$) appears. 3) According to m of experimental constant, retardation effect of corrosion fatigue crack propagation corresponds to about 25% of constant stress amplitude when overload ratio is 1.52. 4) When overload ratio 1.52 was used, retardation parameter (RP) decreases to about 0.43 and corrosion sensitivity (S)decreses to about 2.1.

• 대한기계학회논문집
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• 제11권6호
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• pp.867-876
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• 1987

본 연구에서는 보통강재인 SS 41 강을 열처리하여 얻은 M.E.F.복합조직강의 모상입경변화와 3.5% NaCl수용액의 pH변화 조건하에서 반복굽힘피로실험을 하여 부식 피로파괴에 미치는 영향에 대해 고찰하였다.

• Journal of Mechanical Science and Technology
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• 제18권1호
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• pp.114-121
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• 2004

In order to investigate the corrosion fatigue characteristics in the weld of multi-pass welded A 106 Gr B steel pipe, corrosion fatigue tests were performed under the various stress ratios and 3.5 wt% NaCl solution at room temperature. The corrosion fatigue characteristic curves were represented using crack closure concept. The obtained results are as follows : when the load frequency is 1.0 Hz, the crack opening point is transited in the region of $K_{max}$=20∼32 MPaㆍ $m^{1}$2/. In the low stress intensity factor range, the crack opening point is higher than that in air. However, in the high stress intensity factor range, it is lower than that in air. In the cases of 0.1 Hz and 0.01 Hz, the crack opening point gradually decreases to $K_{min}$ with $K_{max}$ increase.rease.