• Composites Research
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• v.21 no.6
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• pp.15-22
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• 2008

Reversed plane bending fatigue tests were conducted on SiC particle aluminum composite. The initiation and growth behaviors of small surface fatigue cracks were continuously monitored by the replica technique and investigated in detail. The fatigue life of MMC is shorter than that of matrix because there exists interface debonding of SiC particles and matrix on the whole face of the notch part in the casting metal matrix composite(MMC). The coalescence of micro-cracks was observed in the tests conducted at high stress levels. Due to the coalescence, a higher crack growth rate of small cracks rather than those of long cracks was recognized in da/dn-$K_{max}$ relationship.

• 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.

• Journal of the KSME
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• v.28 no.4
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• pp.328-336
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• 1988

파괴인성은 내적 및 외적요인 등에 의해 변할 뿐만 아니라 조직의 불균질성 때문에 소성둔화 및 파괴가 균일하게 일어나지 않으므로 이에 대응한 파괴인성을 선택하여 평가함이 가장 중요하다. 또한 기계의 고속화에 따라 충격적인 하중에 의한 동적파괴의 문제가 중요하게 되고 이에 따라 동적파괴인성 평가법의 확립에도 많은 연구가 필요하다. 한편 피로균열진전거동의 실험에는 많은 시간과 인적 노력이 필요로 하며 이러한 문제점을 해결하여 균열진전 측정의 정밀화 및 효율성을 높이기 위해서는 컴퓨터의 이점을 적극적으로 응용할 필요가 있다.

• Journal of the Korean Society of Propulsion Engineers
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• v.20 no.2
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• pp.11-17
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• 2016

Powder metallurgy nickel based superalloy has been used in a high temperature part of turbine engine for airplane. The fatigue crack growth behavior was investigated using CT specimens for the materials at room temperature(R.T.), $600^{\circ}C$ and $700^{\circ}C$. The direct current potential drop(DCPD) method suggested by ASTM E647 was used to measure the crack length during fatigue crack growth at various stress ratios. The fatigue crack growth rate at R=0.5 was faster than that at R=0.1 for all temperature conditions and increased with the increase of stress ratio and temperature. Fractography was conducted for analysis of fracture mechanism.

• Proceedings of the Computational Structural Engineering Institute Conference
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• 2010.04a
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• pp.310-313
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• 2010

본 논문에서는 등가소성힌지길이 개념을 새롭게 개선하여 도입함하여 구조물의 거동특성을 평가하는 프로그램을 개발하였다. 시간의 경과 및 외부환경 변화와 더불어 발생 가능한 지하구조물의 변상은 해당 구조물의 구성재료 및 작용하는 외압의 형태 등에 의해 다르게 나타나게 된다. 즉, 장기적인 지반외력의 변화에 의해 콘크리트 구조체의 천단부에 큰 휨압축응력과 인장을력이 생기는데, 내측에는 압축이 생기고 외측에는 인장균열이 발생한다. 또한 측벽이나 어깨부에서는 인장응력과 전단응력에 의한 균열이 발생하기도 한다. 따라서 개발된 프로그램으로 균열발생단면에 대하여 축력, 휨모멘트, 균열폭을 서로 연관 지을 수 있게 될 뿐만 아니라 균열폭의 확장을 추적해 나갈 수 있다. 해석기법을 토대로 개발된 해석모듈을 이용하여, 본 해석 기법의 타당성에 대한 검증을 실시하였다. 검증을 위해서는 수평보구조와 터널구조에 대해 각각 해석을 수행하였다. 그 결과, 구조물 내에서의 균열의 진전이 점차적으로 확장되어 가는 것이 표현 가능한 것을 확인하였으며, 해석결과의 타당성을 확인하였다.

• Proceedings of the Korean Ceranic Society Conference
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• 2004.04b
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• pp.27.4-27.4
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• 2004

• Proceedings of the KWS Conference
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• 1997.10a
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• pp.9-12
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• 1997

• Proceedings of the Korean Nuclear Society Conference
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• 1997.05b
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• pp.104-109
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• 1997

인코넬600 합금을 열처리상태 및 변형속도등이 서로 다른 응력부식균열(SCC) 발생 조건하에서 정변형속도 시험법으로 인장시켜 그때 발생되는 AE신호와 부식전류를 측정하여 균열거동과 비교하므로서 SCC 발생 및 진전을 AE로서 적절히 탐지할 수 있는가를 연구하였다. 그 결과 SCC. 연성파괴 및 기계적인 변형에서 발생되는 AE는 amplitude 준위에 의해 식별가능하며, 이것은 AE amplitude 준위가 AE발생원을 식별할 수 있는 중요한 변수가 될 수 있음을 의미한다. 또한 AE 발생시점과 전기 화학적 전류변동이 들 일치하는 것으로 나타나 입계응력부식 균열 진전이 AE에 의해 적절히 탐지될 수 있음을 알 수 있다.

• Transactions of the Korean Society of Mechanical Engineers
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• v.12 no.4
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• pp.781-789
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• 1988

The fatigue crack growth and crack closure behavior of long through-thickness cracks and small half-penny shaped surface cracks were investigated in 5083-H113 Aluminum alloy under constant amplitude testing by the unloading elastic compliance method. It was found that, in the Region II, the crack growth behavior of both through-thickness and surface cracks exhibited the tri-linear form with two transitions and no concern with stress ratio R. In the Region I $I_{ab}$ and I $I_{b}$, through-thickness cracks grew faster than surface cracks in length direction, but at .DELTA. K .leq.4 MPa.root.m for R=0.1 the growth rates of surface cracks in depth direction, grew faster than those of through-thickness cracks. When the crack closure was considered, the growth rates of through-thickness cracks lay between the growth rates of depth direction and the growth rates of length direction in surface cracks. It is suspected that this was caused by the difference of crack closure at depth and length direction of surface cracks.s.

• International Journal of Highway Engineering
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• v.9 no.2 s.32
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• pp.39-49
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• 2007

The objective of this study was to investigate features of transverse crack occurrence and propagation in continuously reinforced concrete pavement(CRCP) when subjected to environmental loading. The finite element model of CRCP was developed and the element removal method was implemented to predict the crack propagation process. To investigate the effect of the type of environmental loading on the CRCP behavior and cracking aspects, the following three different cases were considered: (1) the temperature gradient between top and bottom of the slab does not vary and the constant temperature drop throughout the depth occurs; (2) the temperature at the slab bottom does not vary and the temperature gradient increases; and (3) the temperature between the mid-depth and the bottom of the slab is the same and does not vary and the temperature at the top decreases. The analysis results showed that the crack occurrence and propagation through the depth of the slab in CRCP were significantly affected by the type of environmental loading. The changes in stress distribution and displacements during the crack occurrence and propagation process could also be investigated.