• Transactions of the Korean Society of Mechanical Engineers
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• v.16 no.8
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• pp.1536-1544
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• 1992

A relatively simple prediction method is proposed for initially semicircular surface crack growth under axial loading. The method takes into account the difference in surface crack closure behavior at the depth point and at the surface intersection point, and also the relationship of crack closure for surface crack and through-thickness crack. The prediction method provides conservative estimation for fatigue life within factor of two, and the predicted crack geometry variations agree well with the observed results. As a result, the prediction method proposed here is considered to be useful for engineering application.

• Transactions of the Korean Society of Mechanical Engineers
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• v.13 no.5
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• pp.938-946
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• 1989

Using the CT specimen of carbon steel(SM45C), we estimated the fatigue crack propagation behavior in stable crack propagation range. Furthermore the fatigue crack propagation rate, Acoustic Emission(AE) count rate, and fractography characteristics were also compared among others. The following results were confirmed by experimental observation. Near-threshold stress intensity factor range(.DELTA. $K_{th}$) is influenced by stress ratio but not at the upper limit of stable crack propagation range. As stress intensity factor range(.DELTA.K) and(or) stress amplitude increase (s), both crack propagation rate(da/dN) and AE count rate(dn/dN) increase. Effective stress intensity factor range(.DELTA. $K_{off}$) determined from the crack closure point measurement by AE method is useful for the evaluation of fatigue crack propagation rate. Fractography in stable crack propagation range showed striation, and agreed with the crack propagation rate obtained either by experiment of by the results of microscopic measurements.s.

• Composites Research
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• v.22 no.3
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• pp.74-81
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• 2009

Reversed plane bending fatigue tests were conducted on SiC particle reinforced and SiC whisker reinforced aluminum composite. The initiation and growth behaviors of small surface fatigue cracks were continuously monitored by the replica technique and the causes of fracture and fracture mechanism were investigated by SEM. The relationship between da/dn and $K_{max}$ show that da/dn increases in high stress level while decrease and again increases with increasing of $K_{max}$ in low stress level for two materials.

• Journal of the Korea institute for structural maintenance and inspection
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• v.22 no.1
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• pp.129-136
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• 2018

The estimation of the fatigue design life for large welded structures is usually performed using the liner cumulative damage method such as Palmgren-Miner rule or the equivalent damage method. When a fatigue crack is detected in a welded steel structure, the residual service life has to be estimated base on S-N curve method and liner elastic fracture mechanics. In this study, to examine the 3D fatigue crack behavior and estimate the fatigue life of out-of-plane gusset fillet welded joint, the fatigue tests were carried out on the model specimens. Investigations of three-dimensional fatigue crack propagation on gusset welded joint was used the finite element analysis of FEMAP with NX NASTRAN and FRANC3D. Fatigue crack growth analysis was carried out to demonstrate the effects of aspect ratio, initial crack length and stress ratio on out-of-plane gusset welded joints. In addition, the crack behaviors of fatigue tests were compared with those of the 3D crack propagation analysis in terms of changes in crack length and aspect ratio. From this analysis result, SIFs behaviors and crack propagation rate of gusset welded joint were shown to be similar fatigue test results and the fatigue life can also be predicted.

• Proceedings of the KSME Conference
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• 2000.11a
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• pp.141-146
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• 2000

Crack closure and growth behavior of physically short fatigue cracks under random loading are investigated by performing narrow- and wide-band random loading tests for various stress ratios. The importance of the crack closure phenomenon is examined by predicting the growth lives of short cracks using obtained crack opening behavior. Artificially prepared two-dimensional, short through-thickness cracks are used. The crack opening load of short cracks is much lower under random loading than under constant-amplitude loading corresponding to the largest load cycle in a random load history. This result indicates that the largest load cycle in a random load history has an effect to enhance crack opening of short cracks. Most of the life prediction ratios are within the factor of 2 scatter band except several data at very short crack sizes, indicating that crack growth predictions based on the measured crack opening data are excellent. From the results obtained in this study, it can be concluded that crack closure is the primary factor governing fatigue crack growth of short cracks under random loading as well as under constant-amplitude loading.

• Transactions of the Korean Society of Mechanical Engineers
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• v.13 no.1
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• pp.125-134
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• 1989

Pseudo-random load waves for fatigue testing were generated by personal computer simulation and preliminary study was performed on the growth behavior of surface fatigue crack under random ladings. The closure behavior and growth rates of surface fatigue crack were significantly influenced by the characteristics of random waves. It was also found that the growth rates of surface fatigue crack under random loadings could not be always described by the effective stress intensity factor based on the concept of crack closure.

• Journal of the KSME
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• v.28 no.4
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• pp.401-407
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• 1988

해수 중에 있는 구조용강에 음극방식을 실시했을 때의 피로균열진전 특성을 공기 중에서와 비교 하면서 정리하였으며 또한 몇 가지 영향인자들의 역할에 대해서도 기술하였다. 그러나, 이러한 특성들은 아직까지 그 정확한 메커니즘이 규명되지 못하고 있으며, 특히 균열선단에서의 소성 거동이 부식분위기나 수소분위기에서 어떻게 변화하는가 하는 문제에 대해서는 앞으로도 많은 연구가 이루어져야 할 것이다. 응력조건과 부식조건이 동시에 적용될 때, 재료의 거동을 직접 적으로 해석하기 어려운 경우가 많으며, 따라서 관련되는 많은 영향인자들의 역할에 대한 상세한 정보들이 요구되고 있으며, 또한 관련 정보들을 유기적으로 결합시키는 이론적인 근거를 마련 해야 할 필요가 있다.

• Proceedings of the Korean Nuclear Society Conference
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• 1999.10a
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• pp.230.1-230
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• 1999

• Journal of the Korean Society for Precision Engineering
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• v.16 no.4 s.97
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• pp.13-18
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• 1999

섬유강화금속적층재(Fiber Reinforced Metal Laminates. FRMLs)는 고강도금속과 섬유강화복합재료(Fiber Reinforced Composite Materials)를 적층한 새로운 종류의 하이브리드 재료이다. 국산 아라미드 섬유인 헤라크론(Heracron, 코오롱)과 국내 복합재료 제작기술(한국화이바)을 사용하여 섬유강화금속적층재를 제작하고, 이를 HERALL(Heracron Reinforced Aluminum Laminate)이라 명명하였다. HERALL(Heracron Reinforced Aluminum Laminate)의 피로균열성장특성 및 피로균열진전 방해기구를 ARALL(Aramid-fiber Reinforced Aluminum alloy Laminates) 및 Al 2024-T3과 비교해석하였다. HERALL과 ARALL은 균열진전을 저지하는 아라미드 섬유로 인해 뛰어난 피로균열성장특성 및 피로저항성을 보여주었다. 아라미드 섬유의 균열브리드징으로 인한 $K_{max}$의 감소량과 Al 2024-T3의 균열닫힘으로 인한 $K_{max}$의 증가량을 구할 수 있는 응력-COD법을 사용하여 실제로 균열성장에 영향을 준 유효응력확대계수범위를 측정하였다. 균열선단으로부터 균열을 가공하면서 COD 변화량을 측정하여 균열브리징 영역을 구하였다.

• Transactions of the Korean Society of Mechanical Engineers
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• v.16 no.1
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• pp.63-69
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• 1992

Plane-strain fatigue crack growth behavior of 7075-76 aluminium alloy was investigated by using side-grooved through-thickness center cracked tension(CCT) specimens. The effect of side-groove on the stress intensity factor value was examined. The effective thickness expression of $B_{e}$= $B_{o}$-( $B_{o}$-( $B_{ o-B_{n}^{2}}$ $B_{o}$ is the most appropriate to evaluate the stress intensity factor of side-grooved CCT specimen for fatigue testing. Fatigue crack growth rates can be well described by the effective stress intensity factor range based on closure measurements, for both side-grooved and uniform thickness specimens. Provided that the thickness of specimen meets the requirements for valid plane-strain fracture toughness, uniform thickness specimen data may be assumed to approximately represent the plane strain through-thickness crack growth behavior.ehavior.r.