• Proceedings of the KSME Conference
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• 2003.04a
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• pp.381-388
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• 2003

The material deficiencies in the form of pre-existing defects can initiated cracks and fractures. The stress distribution and fatigue crack initiation life of engineering materials may be associated with the size, the shape and the relative location of defects contained in the component. The objective of this study is to investigate the effect of arbitrarily located hole defect around the rivet hole of a wing section in monolithic aluminum and Al/GFRP laminates under cyclic bending moment during a service load. The stress distribution and the fatigue crack initiation behavior near a rivet hole of on the relationships between stress concentration factor ($K_t$) and relative position of defects were considered. The test results indicated the features of different stress field. Therefore, the stress concentration factor ($K_t$) and the fatigue crack initiation behavior was illustrated different behavior according to each position of hole defect around the rivet hole in monolithic aluminum and Al/GFRP laminates.

• Journal of Advanced Marine Engineering and Technology
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• v.18 no.3
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• pp.52-62
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• 1994

기계나 구조물 파괴의 대부분은 노치부를 기점으로 하여 발생하기 때문에 첨단복합재료를 노지부 재로서 안전하면서도 경제적으로 사용하기 위해서는 각종 조건하에 있어서 강도특성을 명확히 하는 것은 대단히 중요하다. 본 연구에서는 노치를 갖는 복합재료를 이용하여 각종조건하에서 강도특성평가실험을 행하였으 며, 얻어진 결과를 종합하면 다음과 같다. (1) 첨단복합재료 노치재는 試驗片의 幾可學的 形狀과는 관계없이 노치반경 p만에 의해 결정되는 최대탄성응력 $\sigma_{max}$일정의 條件下에서 破t짧된다. (2) 破斷時 최소단면에서의 공칭응력 $\sigma_{c}$와 응력집중계수 $K_{t}$와의 관계에 있어서,$\sigma_{c}$의 값이 $K_{t}$의 증대와 더불어 떨어지고 있는 부분과, $K_{t}$와 관계없이 거의 일정하게 되고 있는 부분으로 나누어지는 現象은 노치재의 回轉굽힘 또는 인장압축파열에서 보여지는 현상과 外觀上 對應하고 있다. 즉, 정적파괴와 피로파괴는 파괴의 양상이 비슷하다 (3) PEN수지단체의 경우, 피로균열발생은 점발생적 피로균열이 최대탄성응력에 의해 지배되며, 노치에 만감하며,균열전파수명은전수명에 비해 상당히 짧다. (4) 단탄소섬유강화복합재료의 경우, 피로균열은 섬유端에 응력이 집중하기 때문에 일반적으로 섬유端에서 아주 빠른 시기에 발생하지만, 섬유가 피로균열진전에 대해 방해물로 작용하기때문에 아주 천천히 전파한다. (5) 短탄소鐵維는 피로균열발생에 대해서는 負의 강화작용 전수명의 극히 초기단계에 피로균열 발생을, 피로균열전파에 대해서는 正의 강화작용을 한다. (6) 단탄소섬유를 PEN에 강화함으로 인해 정적강도 보다 피로강도에 더 큰 강화효과를 초래했으며, 선형노치역학의 개녀은 첨단 복합재료의 강도평가에 대단히 유효했다.

• Journal of the Korean Society for Railway
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• v.7 no.2
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• pp.125-129
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• 2004

This study investigates the fatigue lift estimation of butt weld specimen for the railway vehicle by examining butt weld bead profiles. The butt weld beads, which are welded by semi-robot method, have non-uniform bead profiles described by $\theta$, p and h. The stress concentration factors, K$\_$t/, are changed by different $\theta$, p and h from 1.395 to 2.863. Hence, the sensitivity of K$\_$k/ is changed by each $\theta$, p and h. As $\theta$ becomes lower and p and h become higher, K$\_$t/ increases. The fatigue life can be estimated very closely for the AAY specimens without residual stress using only butt weld bead profiles. But, for the AAN specimens with residual stress, the fatigue life must be estimated by considering both the weld bead profiles and the residual stress data.

• Transactions of the Korean Society of Mechanical Engineers
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• v.5 no.4
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• pp.354-361
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• 1981

This study aims to compare stress concentratior factors in a loaded elastic body of the infinite plate with pressure coefficients of a fluid in the potential flow. First in view of hydrodynamics, when a single elliptic cylinder in the form of a bluff body stands in the potential flow, the pressure distribution(doefficient, C$\_$p/around the elliptic cylicder which is changed according to the position(angular displacements)is theoretically analyzed and calulated; secondly, in view of theory of elasticity, when an eliptic hole which is made on a flat plate gets tension, the stress distribution(factor) around the elliptic hole which is changed according to the position(angular displacements )is theoretically(K$\_$t/) and experimentally (K$\_$e/) measured; and finally. The results are compard and examined.

• Journal of Ocean Engineering and Technology
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• v.4 no.1
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• pp.110-119
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• 1990

This study is concerned about the stress concentration factor measurement by photoelastic method, for the case of two circular holes arrangement in 3mm semi-infinite plate under tensile load, the ratio of those two circular holes diameter, the ratio of distance apart from circular holes to breadth and the two holes arrangement angle with loading direction were varied. Besides, the measured stress concentration by photoelastic method around one circular hole was compared with that by strain-gage method.

• Journal of Ocean Engineering and Technology
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• v.9 no.1
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• pp.83-91
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• 1995

Surface defects in structural members are apt to be origins of fatigue cracks growth, which may cause serious failure of whole structures. Most structure has a part where stress concentrates such as welded joints, corner parts, etc. And then, analysis on crack growth and penetration from these defects, therefore, is one of the most important subjects for the reliability of LBB design. The present paper has performed an experimental and analysis on the fatigue crack propagation by variety in crack length of surface cracked plate with stress concentration part. The crack growth behavior can be explained quantitatively by using Newman-Raju equation and the stress partitioning method proposed by ASME B&P Code Sec. XI. The stress concentration factor $K_t$ has affected on the crack growth. The crack growth after penetration depends upon the initial front side crack length.

• Journal of Ocean Engineering and Technology
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• v.6 no.2
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• pp.71-75
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• 1992

기구나 구조물의 피로수명은 노치에서의 피로균열 방생수명에 의하여 지배되기때문에 노치로 인한 피로강도감소계수 $K_f$는 피로설계상 대단히 중요한 인자이다. 노치 선단(Notch root)에서의 피로균열발생명수 N$_c$를 기준으로하면 탄성응력집중계수 $K_t$가 10 정도까지 $K_f$와 $K_t$간에는 거의 직선적인 관계가 있음이 이다- 고에 의하여 명석해졌으나 이는 인장,압축의 축력이 작용하였을 때이며 따라서 기구나 구조부재는 축력외에도 굽힘 피로 하중이 작용하였을때도 많으므로 본 연구에서는 굽힘 피로 하중을 받았을때도 있다. -고의 결론이 적용되는지는 검시코져 본 연구를 실시하였다.

• Proceedings of the KSME Conference
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• 2001.06a
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• pp.217-222
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• 2001

For the life evaluating of notched members, it is the best way that performing the real fatigue test of structure containing notch. But this method required generally much times and costs to evaluate fatigue life. So, generally we use the modified S-N curve or several methods to predict fatigue life. In this study, crack initiation life was evaluated by fatigue testing the SAE keyhole specimen and smooth specimen made of Al 7075-T6 alloys using the constant load then obtained S-N curve of smooth specimen and P-N curve of SAE keyhole specimen. And, fatigue lives of keyhole specimen are predicted using some life prediction methods (Nominal range I method, Nominal range II method, FEM analysis) for investigating experimented results, and that were compared with experimental data. Predicted fatigue lives by FEM analysis were corresponded with experimental data between 1/3times and 3times on the whole, and predicted fatigue lives using modified S-N curve (Nominal range I method, Nominal range II method) were nonconservative compared with that of FEM analysis.

• Journal of the Society of Naval Architects of Korea
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• v.38 no.3
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• pp.93-106
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• 2001

T-joint and hopper knuckle joint models are typical welded joints in ship structure, which are very susceptible to fatigue damage under service condition. Fatigue test and fracture mechanical analysis were performed on these joints to find out characteristics of fatigue behavior. Unified S-N curve was developed from the test results of these two types of joint using hot spot stress concept, and also propagation life was also estimated using Paris' crack propagation law. Residual stress effect on propagation life was considered in calculating propagation life, as was done with thermo-elasto-plastic FE analysis and residual stress intensity factor calculation. Fatigue life of similar kinds of welded joint could be predicted with this unified S-N curve and fracture mechanical analysis technique.

• Journal of the Korean Society of Fisheries and Ocean Technology
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• v.21 no.2
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• pp.142-150
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• 1985

In this paper, stress distribution were given in consideration of bending effects in hemi-spherical shell and a modified equation of buckling load was represented with implicating the effects of plastic deformations and shape parameters. Especially, the distributions of shell near it's vertex were analyzed numerically, according to several cases of loading. For the sake of more good estimation of plastic dissipating energy, we used the yield-line method from plate theory. The modified criterion of bucking, P super(*) sub(cr), that was suggested in this study, was applied to SUS 302 stain-less steel hemi-spherical shell which had it's Poisson's ratio and Young's modulus with 0.33 and 19700 kg/mm$^2$. From some experiments and comparisons with other results, 재 suggested the critical buckling-load-equation with P super(*) sub(cr)=2E super(*).(t super(2)/a super(2)).{3(1-ν super(*2)} and computed the buckling initiation load with this equation. Because these result from modified criterion have more coincidence than previous one, we prospect this equation can be magnified it's utilities to the other materials.