• Transactions of the Korean Society of Mechanical Engineers
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• v.18 no.12
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• pp.3227-3235
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• 1994

This paper deals with an evaluation of the residual stress due to shot peening induced in a carburized gear tooth and its application to the fatigue crack propagation problem. A practical method is proposed on the basis of the assumption that the residual stress is caused by the difference of volume expansion in the case and the core, and the influence of both the reduction of retained austenite and the strain due to shot peening are considered. The evaluated residual stress is close to the measured stress, though the surface stress is rather overestimated. The stress intensity factor is computed by the influence function method, and it is shown that the factor is decreased by the residual stress in shot peened gear tooth. The shot peening is fairly effective to the reduction of fatigue crack growth rate. The crack propagation is simulated and the resistance due to shot peening is quantitatively demonstrated and discussed.

• Journal of Ocean Engineering and Technology
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• v.1 no.2
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• pp.83-92
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• 1987

Inorder ot estimate the running life of turbine rotors, fatigue crack propagation low, da/dN = C(${\DELTA}K)^m$, proposed by paris et al. has been widely applied. In this study, fatigue crack propagation rates for 16 samples of 1% Cr-Mo-V rotor steel were measured and statistical characteristics of m and C values in above equation were reviewed. The results are summarized as follows. 1. C and m follow a log-normal distribution and normal distribution, respectively. And the relation of C and shows a strong negative correlation. 2. Fatigue crack propagation equation can be expressed as da/dN=$4.11{\times}10^{-4}({\Delta}K/153.8)^m$, introducing the ralationship C=$C_oK_o^{-m}$. In this case, contribution of $C_o$ distribution to the distribution of log C shows very small compared to degrees of contribution by m.

• Journal of Welding and Joining
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• v.7 no.1
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• pp.2-16
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• 1989

종은 타명기로서, 소리(음향)를 내기 위해서는 동양종은 외부에서 타격하고 서양종은 내부에서 타격한다. 그러므로 종을 사용하는 사이에 이 타격으로 인하여 종에는 누적된 피로(Cumulated fatigue)가 생기고, 이것이 원인이 되어 크랙의 발생.rarw.성장.rarw.파괴로 진전되어 사용 불가 능케 된다는 것은 잘 알려진 사실이다. 이와같은 사례는 국내에서 그 실례를 많이 볼 수 있다. 예 1) 상원사종(국보 36호), 2) 보신각종(보물 2호), 3) 완주송광사종, 또한 외국의 경우, 미국의 자유의종 (Liberty Bell)등 대단히 많다. 여기서는 위의 종에 대한 크랙과 상원사종의 용접을 중 심으로 달아보겠다.

• Proceedings of the KWS Conference
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• 1997.05a
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• pp.70-73
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• 1997

• Transactions of the Korean Society of Mechanical Engineers
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• v.10 no.4
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• pp.477-486
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• 1986

본 연구에서는 SM20C를 모재로 하여 입경의 크기가 다른 3종의 복합조직강을 제작 동일한 분위기에서 저 및 고사이클 전영역에 걸쳐 피로특성을 검토하고져 한다. 제일보는 그 중 저사이클특성에 대한 보고이다. 일반적으로 저사이클 피로현상은 재 료가 탄소성 상태하에서 전위, 미소크랙, 보이드(void) 등의 인자가 복합적으로 작용 하여 발생함으로 변형률속도, 제어파형, 온도, 시험방법 및 분위기에 따라 많은 영향 을 받는다. 따라서 본 연구에서는 두가지 실험방법을 사용, 응력-변형율거동을 검토 복합조직강의 피로특성과 입경크기가 피로거동 및 강도에 미치는 영향을 비교 고찰하 였다.

• Journal of Ocean Engineering and Technology
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• v.11 no.2
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• pp.28-38
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• 1997

The corrosion fatigue test was conducted in air to investigate the corrosion fatigue strength of SM 30 C steel by which was corroded in the under sea and surface in the conditions of 3.0% NaCl salt solution. The fatigue tests were carried out on a rotary bending testing machine of cantilever type. The corrosion effect of the sea surface conditionwas served more than that of the under sea condition which was due ti the periodic contact of air thus accelerate the corrosion. The difference of the fatgue strength between sea surface and under sea conditions decreased with increase of stree level and corroded period. Inthe case of the solid shaft and thickness 2mm of hollow shaft, the difference of corrosion fatigue strength decreased as stress level and corrosion periodic increasing. Onthe contrary in the case of thickness 1mm of hollow sgaft, the difference of it increased as stress level, corrosionn periooodic increasing and also the condition of corrosion chaanged. The main factors affecting the degradation of fatigue strength due to corrosion were the reduction of sectional area and the increase of surface roughness. The interference phenomenon increase with stress level got higher.

• Transactions of the Korean Society of Mechanical Engineers
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• v.12 no.3
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• pp.473-480
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• 1988

In this study, a method that can realize the effect of residual stresses on fatigue crack propagation has been proposed. This method requires that the relaxation quantities of residual stresses are measured by experimental method according to fatigue cycles and are employed to the experimental results of base materials by introducing the concept of superposition. SS41 material has been analyzed as an example. The results show that the relaxation factor of residual stresses for fatigue cycles is .alpha.$_{i}$= 1/0.6903+0.0380 $a_{I}$ the effective stress ratio for fatigue crack propagation length is ( $R_{eff}$)$_{i}$ = 1/1.1274+0.0118$_{I}$ and the fatigue crack propagation rate for relaxation quantities of residual stresses is (da/dN)$_{t}$ = 0.5 $K_{cf}$ - .DELTA.K/{1-1/1.1274+0.0118$_{ai}$ } $K_{cf}$ - .DELTA. K(da/dN), for stress ratio /R=0.5.io /R=0.5.5.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.24 no.7 s.178
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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.

• Transactions of the Korean Society of Mechanical Engineers
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• v.13 no.5
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• pp.901-910
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• 1989

Corrosion fatigue crack propagation behavior of duplex stainless steel weldments in substitute ocean water was investigated to evalulate effects of micro-structural change and residual stresses. Fatigue crack propagation rate was found influenced markedly .alpha./.gamma. phase ratio but little by residual stresses. Fatigue crack propagation rate is higher in the corrosive environment than in room atmosphere. The crack propagation rate estimated by the measurement of striation spacing was higher than that, obtained by crack length measurement in low .DELTK.K region. At hight .DELTK.K region, however, both crack propagation rates were found to be identical.

• Journal of the Korean Society for Precision Engineering
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• v.12 no.2
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• pp.154-161
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• 1995

In order to analysis of the stress distribution around flaws and the interaction effects between fatigue cracks, stress around micro hole was analyzed by Finite Element Method(F.E.M.) and micro hole specimens were tested using rotary bending fatigue machine and twisting fatigue machine to identify stress effects for fatigue cracks initiating from micro holes and interaction effects between micro holes. The results are as follows : Interaction effects of .sigma. $_{y}$for the micro hole side is larger than the large micro hole side when the interval between micro holes is near. Stress concentration factor increase as the diameter of micro hole becomes smaller. But, stress field of micro hole is smaller than that of large micro hole at h .leq. r (h:depth of micro hole, r:radius of micro hole) and that of large hole is larger than that of small micro hole at h >r expect the small range from micro hole.e.