• KSCE Journal of Civil and Environmental Engineering Research
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• v.26 no.3D
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• pp.499-509
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• 2006

Precast concrete deck has many advantages comparing with the in-situ concrete deck, and has been successfully applied to replacement of the deteriorated decks and to the newly constructed highway bridges in domestic region. In order to apply the precast decks into the railway bridges, however, differences of the load characteristics between the highway and the railway should be properly taken into account including the train load, longitudinal force of the continuous welded rail, acceleration or braking force, temperature change and shrinkage. Proper level of the longitudinal prestress of the tendons that can ensure integrity of the transverse joints in the deck system is of a primary importance. To this aim, the longitudinal tensile stresses induced by the design loads are derived using three-dimensional finite element analyses for the frequently adopted PSC composite girder railway bridge. The effect of the temperature change is also investigated considering the design codes and theoretical equations in an in-depth manner. The estimated proper prestress level to counteract those tensile stresses is above 2.4 MPa, which is similar to the case of the highway bridges.

• Journal of the Korean Geosynthetics Society
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• v.11 no.3
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• pp.1-9
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• 2012

If the railways consisting of soil subgrade is applied to repetitive loading, elastic deformation and plastic deformation will occur at the same time. So the repeat traffic loading condition should be considered to predict the long-term deformation on railway roadbed. In this study, laboratory data from the repeated load triaxial tests and cylinder model test were used to predict accumulated settlement on railway foundation and results were analyed based on the nonliear models and stress state considered. It has proposed predict model using power function model on plastic settlement of roadbed materials.

• Composites Research
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• v.17 no.1
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• pp.18-28
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• 2004

In order to evaluate the strength of carbody structures of railway rolling stock made of laminated fiber-reinforced composite materials, total laminate approach was introduced. Structural analyses were conducted to check the basic design of hybrid composite carbody structures of the Korean Tilting Train eXpress(TTX) with the service speed of 180km/h. The mechanical tests were also conducted to obtain strengths of composite laminates. The results show that all stress components of composite carbody structures are inside of failure envelopes and total laminate approach is recommended to predict the failure of hybrid composite carbody structures at the stage of the basic design.

• Korean Journal of Materials Research
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• v.6 no.5
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• pp.483-488
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• 1996

InP 기판위에 InP와 격자정합된 undoped-InGaAs에서 zine의 확산 특성을 Electrochemical Capacitance-Voltage 법(polaron)과 Secondary Ion Mass Spectrometry(SIMS)로 조사하였다. Metallorganic Chemical Vapor Deposition (MOCVD)를 이용하여 undoped-InGaAs 층을 성장시켰으며 확산방법으로는 Zn3P2 확산원 박막과 Rapid Thermal Annealing (RTA)를 이용하였다. 450-55$0^{\circ}C$온도범위에서 30-300초 동안 확산을 수행한 결과 zinc의 확산계수는 D=Doexp(-$\Delta$E/kT)의 특성을 만족하였으며, Do와 $\Delta$E는 각각 1.3x105$\textrm{cm}^2$/sec와 2.3eV였다. 얻어진 확산계수는 다른 확산방법을 이용한 값들에 비해 매우 큰 값인데, 이것은 RTA 처리시 빠른 온도 증가에 의한 확산원 박막, 보호막, 그리고 InGaAs 에피층이 가지는 열팽창계수의 차이로인한 응력의 효과에 의한 것으로 생각되며, 이를 sealed-ampoule 법을 사용한 경우의 확산특성과 비교를 통하여 확인할 수 있었다.

• Tunnel and Underground Space
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• v.18 no.1
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• pp.33-43
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• 2008

The techniques for measuring the bulking factor of rock mass in subsidence area have never been well known all over the world. The volumetric expansion ratios obtained from blasting operation were the only way of acquiring the bulking factor of rock mass. The bulking factor of rock mass obtained from blasting operation, however, has been seldom classified in a certain criterion. Also the bulking factor of rock mass can be very dependent upon rock types. In order to overcome this limitation obtained from these reasons, the authors studied the experimental bulking factor of rock mass according to the stacking shapes as well as the overburden stresses. Gneiss, limestone and shale were chosen for testing specimens, and each bulking factor has been measured with laboratory test of applying a constant load on the fragmented rock specimens.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.20 no.7
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• pp.2159-2166
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• 1996

The stochastic properties of variation in fatigue crack growth are important in reliability and stability of structures. In this study,the stochastic model for the variation of fatigue crack growth rate was proposed in consideration of nonhomogeneity of materials. For this model, experiments were ocnducted on 7075-T6 aluminum alloy under the constant stress intensity factor range. The variation of fatigue crack growth rate was expressed by random variables Z and r based on the variation of material coefficients C and m in the paris-Erodogan's equation. The distribution of fatigue life with respect to the stress intensity factor range was evaluated by the stochastic Markov chain model based on the Paris-Erdogan's equation. The merit of proposed model is that only a small number of test are required to determine this this function, and fatigue crack growth life is easily predicted at the given stress intensity factor range.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.24 no.6 s.177
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• pp.1584-1592
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• 2000

Reversed plane bending fatigue tests were conducted on SiC whisker reinforced aluminum composite which were consolidated by squeeze casting process. Initiation and growth of small surface fatigue c racks were investigated by means of a plastic replica technique. The fatigue crack initiated in the vicinity of SiC whisker/matrix interface. It was found that a fatigue crack deflected along SiC whisker and grew in a zig-zag manner microscopically, although the crack propagated along the direction normal to the loading axis macroscopically. The coalescence of micro-cracks was observed in the tests conducted at high stress levels, but were not evident in tests in which lower levels of stress were applied. Due to the coalescence, a higher crack growth rate of small cracks rather than those of long cracks was recognized in da/dn -ΔK realtionship.

• Journal of the Korean Geophysical Society
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• v.7 no.1
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• pp.23-30
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• 2004

To evaluate the compaction in the domestic construction sites, mainly(PBT) plate bearing test is used. PBT may result in over-estimation in the well-compacted area. Estimation method for the degree of compaction was developed from the penetration index of the surface by cone penetration. The developed system is easily attached to the mobile transportation and directly can acquire the degree of compaction.

• Tunnel and Underground Space
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• v.12 no.3
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• pp.179-188
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• 2002

This study is to understand the effect of the vibration and the stress changes due to the excavation of 2 arch parts of a tunnel, which is a Gyungbu Express Railway tunnel, on the tunnel itself and adjacent slopes in advance, and to analyze the stability. For the estimation of ground conditions, borehole tests, borehole camera logging and seismic logging were performed. Ground properties at a specific location were determined as input constants by performing 2 dimensional analyses with possible ranges of uncertain ground properties. Static and pseudo-static (due to blasting vibration) factors of safety were calculated. The behavior of the tunnel and its vicinity due to the tunnel excavation were predicted by 3 dimensional analyses. It was also tested whether the support system was proper.

• Proceedings of the Korean Nuclear Society Conference
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• 1996.05c
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• pp.176-181
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• 1996

중수로 원자로에서 핵심 구조물인 압력관은 합금이 사용되고 있는데, 고온, 고압의 방사선 분위기에서 사용되기 때문에 가동중 변형을 받는다. 따라서 본 연구에서는 압력관의 건전성 평가기술을 확보하기 위하여 Zr-2.5wt.% Nb 압력관의 집합조직과 온도 변화에 따른 강도 특성을 조사하였다. 집합조직의 변화는 시편의 채취방향을 달리하여 네 가지의 집합조직 변화를 주었으며, 이들 시편에 대해 상온에서 부터 45$0^{\circ}C$까지 온도를 변화시가면서 인장시험을 실시하였다. 온도가 증가함에 따라 시편의 집합조직과 관계없이 네 종류의 시편 모두가 30$0^{\circ}C$까지는 강도가 직선적으로 감소하는 현상을 보이며, 30$0^{\circ}C$에서 37$0^{\circ}C$ 사이의 온도에서 강도가 약간 증가하는 현상을 보였다. 또한 37$0^{\circ}C$이상의 온도에서는 강도가 다시 직선적으로 감소하는 경향을 나타냈다. 이 같은 현상은 30$0^{\circ}C$ 까지는 프리즘 슬림(-slip)으로 전위가 움직이다가 30$0^{\circ}C$ 이상의 온도에서부터 37$0^{\circ}C$까지는 피라미드 슬림(-slip)계의 경쟁 상호작용에 의한 추가적인 응력이 필요하여 나타난 현상이라 사료된다. 온도의 변화에 따른 강도와 연신율의 curve에서 30$0^{\circ}C$와 37$0^{\circ}C$의 범위에서 plateaus region과 연신율이 최소값을 갖는 것은 동적변형시효(dynamic strain ageing)현상과 관련이 있는 것으로 생각되나 추가적인 연구가 필요하다. 집합도가 변함에 따라 인장강도는 T(transverse)>L(longitudinal)> 30。> 45 。순으로 나타났으며 이는 slip과 twin의 복합적인 작용에 의한 것으로 해석된다.