• 수산해양기술연구
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• 제24권1호
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• pp.44-49
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• 1988

본 연구에서는 피로파괴에 영향을 주는 여러 인자중에서 우선 피로크랙전파에 대한 시험편 두께의 영향을 검토하기 위하여 최초 두께 25mm인 일반구조용 압연강재를 평면가공하여 두께 5, 10, 15, 20, 25mm인 CT 시험편을 가공한 후 인장-인장편진반 복피로시험을 행하여 실험한 결과 다음과 같은 결론을 얻었다. 1. 피로수명이 가장 짧게 나타나는 임의의 시험편 두께가 존재하며, 본 실험의 경우에는 두께 15m인 시험편의 경우 피로수명이 가장 짧게 나타났다. 2. 피로크랙의 발생은 두께가 두꺼운 시험편의 경우가 늦지만 피로크랙 성장은 두꺼운 시험편의 경우가 빠르게 나타났다. 3. 본 실험에서 paris시의 계수 m의 값은 절위는 1.98~4.59로서 시험편의 두께가 두꺼울수록 m의 값이 크게 된다.

• 대한기계학회논문집
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• 제19권9호
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• pp.2133-2141
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• 1995

The thermo-mechanical fatigue tests were performed on the specimens extracted from 1.5Cr-0. 67Mo-0.33V alloy. The characteristics of thermo-mechanical fatigue crack propagation were examined and reviewed in view of fracture mechanics. The results obtained from the present study are summarized as follows : (1) The propagation characteristics of isothermal low-cycle fatigue crack are dominated by .DELTA.J$_{f}$ in case of PP waveform, and .DELTA.J$_{c}$ in case of CP waveform. (II)The propagation characteristics of thermo-mechanical fatigue crack are dominated by .DELTA.J$_{c}$ for in-phase case, and by .DELTA.J$_{c}$ for out-of-phase. The present results were in good agreement with the equation of propagation law for isothermal low-cycle fatigue crack in case of thermo-mechanical fatigue.tigue.e.

• 대한기계학회논문집A
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• 제24권7호
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• pp.1841-1846
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• 2000

To examine the effect of acid fog on the corrosion fatigue behavior in structural steel, fatigue tests under acid fog atmosphere were carried out in comparison with distilled water. The corrosive c omponents contained in acid fog pile up the corrosion products on crack face and show a crack branching and crack tip blunting. Therefore, due to these workings crack growth rate was reduced by decreasing the effective stress range in crack tip rather than under distilled water. Also the effect of sulfuric acid, which is the main component of acid fog, and testing speed on fatigue crack growth were examined. It was found that corrosion behavior was remarkably dependent upon pH and Hz rather than components of acid fog. According as pH and testing speed decrease below a specific value, crack growth was accelerated in comparison with distilled water. This reveals that due to liquid having strong acidity and slow speed of test the crack face dissolution was promoted, so crack closure was disturbed in the process of stress descent.

• Journal of Welding and Joining
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• 제10권4호
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• pp.230-239
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• 1992

The specimens of two base metals and material friction-welded with hetrogeneous steels of SM40C and STS304 have been prepared and the characteristics of rupture and crack propagation of them have been examined. In the friction-welded material, the width of HAZ is 3.0mm for STS304 and 3.4mm for SM40C. The hardness distribution in HAZ of SM40C is decreased gradually as being getting off interface, but that in HAZ of STS304 is decreased remarkedly and the value of hardness becomes a little lower than that of the base metal in region of 1mm from interface and becomes a little higher than that of the base metal. The tensile strength of the friction-welded material appeared a little lower than that of the base metal and rupture by tensile load is developed in HAZ of STS304 and the position of rupture is at region of low hardness(1mm from interface). The crack propagation rates(da/dN) in both HAZ of the friction-welded material are a little higher than those in both base metals, but the difference are less except for the case of SM45C in low .DELTA. K value. It has been ascertained that the crack in the interface propagates selectively along the HAZ of SM40C and consequently the crack propagation rate is almost similar to that in the HAZ of SM40C.

• 대한기계학회논문집
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• 제9권2호
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• pp.150-157
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• 1985

본 연구에서는 자연적인 미소흠함주위에 발생, 전파하는 피로크랙의 거동을 검토하기 위하여, 기존재료가 갖고 있는 흠함이나 비금속개재물을 대신할 수 있다고 생각되는 크기가 다른 비관통 인공미성구멍을 갖는 여러 종류의 시험편을 준비하고, 이 시험편들이 갖는 인공미성구멍주위에 발생전파하는 피로크랙의 거동을, 금속현미경 관찰을 토대로 상세히 고찰하였다. 그리고 이러한 관찰을 기초로 하여 비관통인공미 성구멍의 대성에 따른 피로한계도거동에 대해서도 고찰하였다.

• 한국자동차공학회논문집
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• 제6권6호
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• pp.185-194
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• 1998

In this study, the rotary bending fatigue test was carried out with two kinds of material, S43C and S50C, using in the Front engine and Front drive wheels(F.F.) of vehicle. The one part of specimens was heated by high frequency induction method(about 1mm depth and $H_RC$ 56~60) and tested environment temperature were $-30^{\circ}C$, $+25^{\circ}C$ and $+80^{\circ}C$ in order to look over the influence of the heat treatment and the temperatures. In the experimented result at $+25^{\circ}C$ and $+80^{\circ}C$, the fatigue life of non-heated specimens were decreased about 35%, but that of heated specimens were decreased about only 5% at $+80^{\circ}C$ more than at $25^{\circ}C$. And in the experiment result at $-30^{\circ}C$ and $+25^{\circ}C$, the non-heated and heated specimens were about 110%, 120% higher fatigue life at $-30^{\circ}C$ than at the $+25^{\circ}C$ each other. On the other hand, the fatigue crack propagation rate of S50C was higher than that of S43C.

• 한국정밀공학회지
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• 제5권3호
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• pp.71-80
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• 1988

This paper dealt with experimentally the effect of $N_2$ and $H_2$ gas mixtures ratio in the fatigue characteristics of SM45C on Ion-nitrided. The specimen were treated water cooling after Ion-nitriding at $500^{\circ}C$ and 5 torr. in 80% $N_2$and 50% $N_2$gas mixtures ratio in the atmosphere for 3 hrs. The hardness distribution and the depth of nitriding layer shows more increase in 80% $N_2$gas mixture ratio than 50% $N_2$. Ion-nitrided specim- en for 80% $N_2$gas mixture ratio show more increase infatigue strenght in the $>1.5{\times}10^5$ cycles region than 50% $N_2$. In the $<1.5{\times}10^5$cycles region, fatigue failure is due to cracking of the brittle nitrided case, and the propergation of the surface cracks into the core. But in the $>1.5{\times}10^5$cycles region, it is found that cracks propagate from the non-metallic inclusions in the subsurface.

• 한국정밀공학회:학술대회논문집
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• 한국정밀공학회 1994년도 추계학술대회 논문집
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• pp.826-830
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• 1994

Making Brinell indentations facing each other near the crack tip is very effective method in increasing fatigue life. In this paper, fatigue test was performed after indentation to investigate the effect of thickness of specimen. The results show that fatigue lives increased my making indentation and retardation cycle is inverse proportional to thickness of specimen.

• 한국해양공학회지
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• 제16권5호
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• pp.80-87
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• 2002

In this study, CT specimens were prepared from spring steel(SUP9) which was used in suspension of automobile for room temperature and low temperature service. We got the following characteristics from fatigue crack growth test carried out in the environment of room temperature and low temperature at $25^{\circ}C$, ­3$0^{\circ}C$, ­5$0^{\circ}C$, ­7$0^{\circ}C$ and ­10$0^{\circ}C$ in the range of stress ratio of 0.05 by means of opening mode displacement. The threshold stress intensity factor range ΔKth in the early stage of fatigue crack growth (Region I) and stress intensity factor range ΔK in the stable of fatigue crack growth (Region II) was decreased in proportion to descend temperature. It is assumed that the fatigue resistance characteristics and fracture strength at low temperature and high temperature is considerable higher than that of room temperature in the early stage and stable of fatigue crack growth region.

• 한국정밀공학회:학술대회논문집
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• 한국정밀공학회 1997년도 추계학술대회 논문집
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• pp.759-764
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• 1997

In this study, Fatigue behavior of laser weldment in heterogeneous materials was investigated. Fatigue strength test and fatigue crack propagation test were performed for specimens with laser weldment in heterogeneous materials, and hardness test was performed. From the fatigue strength test. it was observed that the difference of strength between heterogeneous materials had eflect on crack initiation position and fatigue limit. From the fatigue crack propagation test. it was observed that fatigue behavior of laser weldment in heterogeneous materials is different from that in same materials. The difference of strength between heterogeneous materials and laser weldment had effect on fatigue crack propagation rate.