• 한국정밀공학회:학술대회논문집
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• 한국정밀공학회 2003년도 춘계학술대회 논문집
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• pp.409-412
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• 2003

Fatigue strength. especially crack initiation behavior of high strength steel under marine water environment was investigated. Marine structures were usually constructed by lot of weld joints and were designed by basis of the fatigue strength of weld joints. This study was carried out to mini. The fatigue initiation behavior is more important rather than crack propagation behavior under the design of marine structures, because it is very difficult to find out the crack propagation phenomena and repair the damaged part of welded joints in sea water Then, the new configuration specimen for fatigue crack initiation tests was proposed. Using this new specimen, it is easy to carry out the crack initiation tests with relatively low cycling loading and clearly find out a crack initiation fatigue life.

• 한국공작기계학회:학술대회논문집
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• 한국공작기계학회 2002년도 추계학술대회 논문집
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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.

• 한국철도학회논문집
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• 제12권5호
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• pp.725-731
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• 2009

강 교량, 선로 구조물, 차량 구조물 등 철도분야에서 강 재료가 많이 사용되고 있다. 설계, 강도평가, 잔존수명 평가 등을 위하여 부식된 강 재료에 대한 인장강도, 피로강도 등이 필요하지만 우리나라의 경우 이 분야의 연구가 미진하여 축적된 데이터가 많지 않다. 본 연구에서는 철도 분야에서 많이 사용되는 대표적인 강 재료에 속하는 SM490A와 SS400에 대해 대기부식 시험절차를 확립하고 많은 시편을 대기부식에 노출시켜 일정한 시간 간격으로 수거하여 인장 및 피로시험을 수행하여 부식시간의 경과에 따른 인장 및 피로강도의 변화를 측정하였다. 처음 3-4개월 기간에 피로강도가 많이 저하하였고 그 이후에는 완만히 변화하였다. 그리고 후열처리 한 시편이 부식에 대한 저항이 더 크다는 것도 알 수 있었다.

• 한국자동차공학회논문집
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• 제14권3호
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• pp.88-94
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• 2006

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, the effect of shot peening in corrosion environment was not known. In this study, investigated is the effect of shot peening on corrosion fatigue crack growth of SAE 5155 steel immersed in 6% $FeCl_3$ solution and corrosion characteristics with considering fracture mechanics. The results of the experimental study corrosion fatigue characteristics of SAE 5155 are as follows; the fatigue crack growth rate of the shot peening material was lower than that of the non-peening material. And fatigue life shows more improvement in the shot peening material than in non-peening material. This is due to the compressive residual stress of surface increases resistance of corrosion fatigue crack propagation. It is assumed that the shot peening process improve corrosive resistance and mechanical property.

• 한국해양공학회지
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• 제17권3호
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• pp.39-45
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• 2003

Shot peening is an effective method of improving the fatigue strength of components and structures. The compressive residual stress produced by surface plastic deformation with shot peening is usually regarded as the major factor in increasing fatigue strength. In this study, the influence of shot peening on corrosion was investigated. Spring steel immersed in $3.5\%$ NaCl prior was used to evaluate the effect of shot peening on fatigue properties. The immersion test was performed on the five kinds of specimens with shot peened and unpeened. The distributions of residual stresses of shot peened spring steels were measured in an X-ray diffraction apparatus, using the two-point method. Corrosion potential, polarization curve, residual stress, etc. were investigated, based on the experimental results. From test results, the effect of shot peening on the corrosion was evaluated.

• 한국항공우주학회지
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• 제33권2호
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• pp.60-66
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• 2005

부식은 기계류나 금속 부품의 성능과 수명을 저해하는 가장 큰 요인으로 작용하고 있다. 이 논문에서는 쇼트피닝이 부식환경하에서 Al 7075-T6의 피로수명에 미치는 쇼트피닝의 효과를 연구하였다. 쇼트피닝한 시험편의 피로한도는 약 52% 증가하는 것으로 나타났으며, 금속재 부품의 피로수명을 크게 연장시키는 것으로 보인다. 쇼트피닝을 한 시험편과 쇼트피닝 하지 않은 시험편을 1주에서 1년까지 비교 시험한 결과 부식은 피로강도를 현격히 감소시켰다. 쇼트피닝을 하였을 경우에는 부식에 의해 6개월 까지는 피로강도 및 피로수명이 감소하지 않은 것으로 나타났다. 따라서 쇼트피닝 가공이 금속재료의 수명에 대한 부식의 영향을 크게 감소시키는 효과가 있음을 알 수 있다.

• International Journal of Concrete Structures and Materials
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• 제11권2호
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• pp.247-259
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• 2017

This paper presents a fatigue assessment model that was developed for corroded reinforced concrete (RC) beams strengthened using prestressed carbon fiber-reinforced polymer (CFRP) sheets. The proposed model considers the fatigue properties of the constituent materials as well as the section equilibrium. The model provides a rational approach that can be used to explicitly assess the failure mode, fatigue life, fatigue strength, stiffness, and post-fatigue ultimate capacity of corroded beams strengthened with prestressed CFRP. A parametric analysis demonstrated that the controlling factor for the fatigue behavior of the beams is the fatigue behavior of the corroded steel bars. Strengthening with one layer of non-prestressed CFRP sheets restored the fatigue behavior of beams with rebar at a low corrosion degree to the level of the uncorroded beams, while strengthening with 20- and 30%-prestressed CFRP sheets restored the fatigue behavior of the beams with medium and high corrosion degrees, respectively, to the values of the uncorroded beams. Under cyclic fatigue loading, the factors for the strengthening design of corroded RC beams fall in the order of stiffness, fatigue life, fatigue strength, and ultimate capacity.

• 대한기계학회논문집A
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• 제26권2호
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• pp.374-379
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• 2002

Corrosion fatigue tests were carried out to clarify the influence of acid fog as environmental factor on the fatigue strength of SM55C using rotary bending fatigue tester. The fatigue strength of acid fog specimen extremely decreased about 80% compared to that of distilled water specimen. In acid fog environment, a number of cracks commenced at corrosion pit and coalesced with the adjacent cracks during they propagate, and they formed a single non-propagating circumferential crack under the endurance stress of N=5$\times$10$\^$7/ cycles. Also, the depth of the crack is smaller than that of normal fatigue crack, so the crack has a veil small aspect ratio. The reason of this peculiar crack growth characteristics is that the crack opening-closure behaviors are hindered by corrosion products on the surface crack faces, and hence it is thinkable that the strong corrosion action like anodic dissolution for crack growth in depth direction is weaker compared with surface, resulting from faint pumping action of crack during loading-shedding processes.

• 한국기계가공학회지
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• 제2권4호
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• pp.53-60
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• 2003

Large sized marine structures are used under corrosion environment of seawater and applied by severe service loading such as an ocean current, a billow and a tempest. Marine structures are usually constructed by lots of thick wall steel pipes joining welded joints. The thickness of such as steel pipes is usually more than 40mm. The such as steels are called "Thermo-Mechanical Control Process steel (TMCP steel)" strengthened by a heat treatment in process of steel manufactures. The failure, especially crack initiation, of marine structures was starting at weld joints under service condition. Then they should be designed by basis of the fatigue strength under seawater corrosion environment of weld joints. To clarity the fatigue crack initiation behavior is important more than to clarify the crack propagation behavior on the strength design of marine structures, because it is very difficult to find out the crack initiation and propagation phenomena and then even if it will be able to find out, it is considered that the refit of the damaged parts of welded joints have a technical difficulty under the sea. Therefore, it is most important to clarify the corrosion fatigue crack initiation behavior under the seawater condition. But, there is one big difficulty to make a test for thick plate specimen, for example thicker than 40mm. Because, it is need large capacity loading apparatus to test such as thick plate specimen. In this research, the new configuration specimen for fatigue crack initiation tests was proposed. Using this new specimen, it is easy to carry out the fatigue clack initiation tests with relatively low cyclic loading and to observe a fatigue crack initiation behavior.

• Journal of Advanced Marine Engineering and Technology
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• 제9권2호
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• pp.126-142
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• 1985

The plane bending corrosiion fatigue test for the welded metal parats was performed in the air and in the natural sea water with and without applying cathodic protection. The specimens tested were the weld of SM41 steel plates, SM58 steel plates and of SM41 to SM58, which were all prepared by submerged arc welding. The main results obtained from the experiment are summarized as follows: (1) In case with SM41 and SM58 steel plates, lower value of impact strength, higher value of hardness and more noble electrode potential were observed in the welded metal part than in the HAZ and base metal. Also the lowest hardness zone in the HAZ was observed with SM58 which was not found with SM41. In case with weld specimen of SM41 to SM58, the impact strength and the electrode potential of the welded metal part showed again the lowest and most noble value but the hardness value was located between those of SM41 and SM58 base metal. (2) In the fatigue test, the specimens tested in the air and under the cathodic protection were both cracked in a purely mechanical mode, but the specimens tested without cathodic protection were cracked by the combination of mechanical fracture and electro-chemical corrosion. (3) The corrosion fatigue limit of the welded metal parts of the specimen was increased by the cathodic protection. As the protection potential was varied down to -800 mV vs. SCE the fatigue limit was increased to the value tested in the air, and the maximum fatigue limit appeared at the -1, 000 - -1, 200 mV vs. SCE. However, as the protection potential was further decreased below -1, 200 mV vs.SCE, the fatigue limit of weld of SM58 and of SM41-SM58 joining was decreased but the limit was almost constant in the case of weld of SM41. (4) It is suggested that when designing steel ship the corrosion fatigue limit of welded metal parts should be stressed as a designing strength of the structure of steel ship in addition to the conventional basis considering simply tensile strength of steel and safety factor.