• 한국소음진동공학회논문집
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• 제19권12호
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• pp.1244-1251
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• 2009

In this paper the vibrational behavior of a multi-packet blade system having a cracked blade is investigated. Each blade is assumed as a slender cantilever beam. The coupling stiffness effect that originates from either disc flexibility or shroud is considered in the modeling. Hybrid deformation variables are employed to derive the equations of motion. The flexibility due to crack, which is assumed to be open during the vibration, is calculated basing on a fracture mechanics theory. In the paper, the results of the change in modal parameters due to crack appearance are presented. The influence of the crack parameters, especially of the changing location of the crack is examined.

• 한국재료학회지
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• 제10권2호
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• pp.138-143
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• 2000

화력발전설비의 주요 손상 요인 중의 하나인 응력부식 균열 성장에 대한 확률론적 잔존 수명평가에 대하여 연구하였으며, 손상해석 및 수명평가에 확률해석 기법을 도입한 확률론적 수명평가 프로그램을 개발하였다. 확률론적 수명평가는 재료물성치, 형상, 하중조건, 운전조건 등과 같은 불확실성과 변동 가능성을 고려하여 해석을 수행하며, 일정 시간 운전후 구조물의 손상이 일어날 확률을 예측하는 것이다. 응력부식 균열 성장에 대한 확률론적 잔존 수명평가 연구를 통하여 확률론적 수명평가 기술의 기반을 구축하였으며, 다른 손상기구에 대한 확률론적 수명평가를 수행하여 발전설비에 발생하는 모든 손상에 대하여 확률론적 수명평가가 가능하도록 확대할 계획이다.

• 오토저널
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• 제13권6호
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• pp.101-108
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• 1991

During torsional fatigue of externally cracked cylindrical specimen, crack face rubbing may occur. At this time, normal contact forces arise when shear displacements cause the crack faces to be wedged open due to mismatch of the fracture surface asperities. These normal forces, in turn, generate friction force which act in opposition to the applied shear stresses and reduce the effective stress intensity factor. The premise of the proposed work is that friction and wedging can be studied by measuring the shear and normal displacement across the crack mouth. We have measured the crack mouth compliance using the new biaxial extensometer.

• The Korean Journal of Ceramics
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• 제4권4호
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• pp.356-362
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• 1998

Hertzian crack suppression phenomena and relatively high damage tolerance were investigated in hard/soft silicon nitride ($Si_3N_4$) bilayers. Coarse $\alpha}-Si_3N_4$ powder was wsed for the hard coating layer and fine $\alpha}-Si_3N_4$ powder was used for the soft substrate layer. The two layers were designed with a strong interface. Hertzian indentation was used to investigate contact fracture and damage tolerance property. Hertzian crack suppression has occurred with increasing applied load and decreasing coating thickness. The crack suppression contributed strength improvement, especially in the bilayers with thinner coatings. Ultimately, the combination of hard coating with soft but tough underlayer improved the damage tolerance of brittle $Si_3N_4$ ceramics.

• Steel and Composite Structures
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• 제2권6호
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• pp.429-440
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• 2002

A finite strip method is developed for fatigue reliability analysis of steel highway bridges. Flat shell strips are employed to model concrete slab and steel girders, while a connection strip is formed using penalty function method to take into account eccentricity of girder top flange. At each sampling point with given slab thickness and modulus ratio, a finite strip analysis of the bridge under fatigue truck is performed to calculate stress ranges at fatigue-prone detail, and fatigue failure probability is evaluated following the AASHTO approach or the LEFM approach. After the failure probability is integrated over all sampling points, fatigue reliability of the bridge is determined.

• Structural Engineering and Mechanics
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• 제37권3호
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• pp.257-265
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• 2011

Plant-specific analyses of 5 types of domestic reactors in Korea are performed to assure the structural integrity of the reactor pressure vessel (RPV) during transients which are expected to initiate pressurized thermal shock (PTS) events. The failure probability of the RPV due to PTS is obtained by performing probabilistic fracture mechanics analysis. The through-wall cracking frequency is calculated and compared to the acceptance criterion. Considering the fluence at the end of life expected by surveillance test, the sufficient safety margin is expected for the structural integrity of all reactor pressure vessels except for the oldest one during the pressurized thermal shock events. If the flaw with aspect ratio of 1/12 is considered to eliminate the conservatism, the acceptance criteria is not exceeded for all plants until the fluence level of $8{\times}10^{19}\;n/cm^2$, generating sufficient margin beyond the design life.

• 대한조선학회논문집
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• 제29권2호
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• pp.79-91
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• 1992

본 논문에서는 균열 보수에 사용되는 Patch와 균열진 판 사이에 컴프라이언스 개념을 적용하여 Patch된 균열진 판의 응력확대계수를 이론유도하고, 이에 대한 실험과 균열진전 거동규명을 통하여 그 유효성을 충분히 검증하였다. 또한, 이와같은 컴프라이언스를 이용한 이론방법을 바탕으로 균열진 구조물의 잔존수명이 고려된 Patch를 간단히 설계할 수 있는 기법을 제시하였다.

• 대한용접접합학회:학술대회논문집
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• 대한용접접합학회 1999년도 특별강연 및 춘계학술발표대회 개요집
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• pp.241-244
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• 1999

The purpose of this study is to examine the characteristics of stress corrosion cracking(SCC) and acoustic emission(AE) signals for the weld HAZ of HT-60 steel under corrosion control in synthetic seawater. Corrosive environment was controlled by potentiostat, and SCC experiment was conducted using a slow strain rate test method at strain rate of 10$^{-5}$ /sec. In order to verify the miroscopic fracture behaviour of the weldment during SCC phenomena, AE test was done simultaneously. Besides, correlationship between mechanical parameters and AE ones was investigated. In case of the parent, reduction of area(ROA) at -0.5V was samller than any other applied voltage such as -0.8V and -1.1V. In addition, reduction of area for the PWHT specimens at -0.8mV was larger than that of the weldment due to the softening effect according to PWHT. In case of the weldment, a lots of events was produced because of the singularities of the weld HAZ compared with the parent.

• 한국소성가공학회:학술대회논문집
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• 한국소성가공학회 2009년도 춘계학술대회 논문집
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• pp.306-309
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• 2009

The influence of equal-channel angular pressing (ECAP) route on dynamic deformation behavior of ultra-fine grained Al-4.4%Mg alloys was investigated in this study. The 8-pass ECAPed specimens consisted of ultra-fine grains of $0.5{\mu}m$ in size, and contained the considerable amount of second phase particles, which were fragmented and distributed homogeneously in the matrix. The result of dynamic torsional tests indicated that the maximum shear stress and fracture shear strain were lowest in the specimen deformed by ECAP via route A among the 8-pass ECAPed specimens. The formation of adiabatic shear bands was addressed by concepts of critical shear strain, deformation energy required for void initiation, and microstructural homogeneity related to ECAP routes.

• 한국표면공학회지
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• 제37권4호
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• pp.208-214
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• 2004

The influence of the boron content on the various properties of Ni-B alloy films produced by electrodeposition was investigated. The considerable reduction in grain size was observed with increasing boron content. The internal stress was tensile and increased linearly with increasing boron content. Hardness increased up to $750H_{v}$ at 2 at% boron and then kept the value to 11 at% boron for as-plated Ni-B coatings. The hardness of Ni-B films increased up to $1,250H_{v}$ due to the intermetallic$ Ni_3$B precipitation by the heat treatment, and maximum hardness of each coating increases with boron content. Wear resistance decreased with increasing the boron content because of high friction coefficient and brittle fracture of film which has higher content of boron.