• 국제초고층학회논문집
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• 제6권1호
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• pp.11-19
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• 2017

High-rise buildings move during construction due to time-dependent material properties of concrete (creep and shrinkage), construction sequences, and structural shapes. The building movements, including vertical and horizontal displacements, result from the sum of axial and lateral deformation of vertical members at each level. In addition to the vertical shortenings, the lateral movement induced by differential shortening can have adverse effects on the construction tolerance and serviceability of non-structural elements such as elevators and curtain walls. In this study a construction stage analysis method is developed to predict lateral movement induced by shortening, including the effect of creep and shrinkage. The algorithm of construction stage analysis is combined with the FE analysis program. It is then applied to predict lateral movement of a 58-story reinforced concrete building that was constructed in Kuala Lumpur, Malaysia. Gravity induced lateral movement of this building is predicted by the construction stage analysis. A field three-dimensional laser scanning survey is carried out to verify the prediction results, and satisfactory agreement is obtained.

• 대한지리학회지
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• 제45권3호
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• pp.375-389
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• 2010

한라산 표고 1,710m에 발달한 나지 표층에 2개의 페인트 라인을 설치하여 자갈의 이동량을 관측하고, 이동 프로세스와 관련된 요인을 검토하였다. 관측 기간에 발생한 자갈의 이동량은 평균 58.2cm로서 일평균 이동 거리는 0.24cm이다. 계절별로 비교하면 동결기 0.3cm에 대하여 비동결기는 0.05cm에 불과하여 표층 자갈은 주로 동결기에 주빙하 프로세스를 통하여 이동하고 있다. 특히 서릿발 포행을 비롯한 동상 포행이 자갈의 이동을 주도하고 있다. 사면 경사각의 영향은 관측 기간 내내 측선 II의 이동량이 측선 I보다 큰 결과에 반영되어 있지만, 암괴와 식생이 자갈의 이동을 방해하므로 절대적이지는 않다. 자갈의 크기와 비중도 이동량에 관여하는 요인으로서 특히 스코리아의 작은 비중이 매우 큰 이동량을 가져왔다.

• 한국해양공학회지
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• 제15권3호
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• pp.58-62
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• 2001

The objective of research is to clarify the interaction between dislocations and precipitates during high temperature creep deformation behaviors of high n austenitic steels. After measuring the internal stress in minimum creep rate state under applied stress of 236MPa at 873K, a transmission electron microscope (TEM) observation was performed to investigate the interaction between dislocations and precipitates during high temperature creep deformation. The band widths and values of internal stress increased when the nitride precipitates distribute more densely. Fine nitrides disturbed the dislocation movement with pinning the dislocations and perfect dislocations were separated into Shockley partial dislocations by fine nitrides. Coarse nitrides disturbed the dislocation movement with climb mechanism.

• 한국해양공학회:학술대회논문집
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• 한국해양공학회 2001년도 춘계학술대회 논문집
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• pp.332-337
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• 2001

The objective of research is to clarify the interaction between dislocations and precipitates during high temperature creep deformation behaviors of high Mn austenitic steels. After measuring the internal stress in minimum creep rate at 873K, a transmission electron microscope (TEM) observation was performed to investigate the interaction between dislocations and precipitates during high temperature creep deformation. The band width of effective stress and internal stress increased when the nitride precipitates distribute more densely. Fine nitrides disturbed the dislocation movement with pinning the dislocations and perfect dislocations were separated into Shockley partial dislocations by fine nitrides. Coarse nitrides disturbed the dislocation movement with climb mechanism.

• 한국농공학회논문집
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• 제54권1호
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• pp.19-26
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• 2012

Soils exhibit creep behavior in which deformation and movement proceed under a state of constant stress or load. In this study, A series of triaxial tests were performed under constant principal stress in order to interpret the undrained creep characteristics of silty sands. Although samples are non-plastic silty sands, the results of tests show that the creep deformation increasing over time. Based on the results of test, Singh-Mitchell model parameters and Generalized model coefficients were calculated. Generalized model showed slightly larger deformation in the primary creep range but secondary creep deformation was almost identical. Although Singh-Mitchell model showed relatively large errors compared to Generalized model because it uses the average of test results, but Singh-Mitchell model can be easily represented by three creep parameters.

• 연구논문집
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• 통권33호
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• pp.137-145
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• 2003

The effects of antimony addition on the microstructures and creep behavior of AZ31 magnesium alloy have been investigated. Constant load creep tests were carried out at temperatures ranging from $150^{\circ}C$ to $200^{\circ}C$, and an initial stress of 50MPa for AZ31 alloys containing antimony up to 0.84% by weight. Results show that small additions of antimony to AZ31 effectively decreased the creep extension and steady state creep rates. The steady state creep rate of AZ31 was reduced 2.5 times by the addition of 0.84% of antimony. The steady state creep rate of AZ31-0.84Sb alloy was controlled by dislocation climb in which the activation energy for creep was 128 kJ/mole. The microstructure of as-cast AZ31-0.84%Sb alloy showed the presence of $Mg_3Sb_2$ precipitates dispersed throughout the matrix. The main reason for the higher creep resistance in AZ31-Sb alloys is due to the presence $Mg_3Sb_2$, which effectively hindered the movement of dislocations during the elevated temperature creep.

• International Journal of Automotive Technology
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• 제6권1호
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• pp.45-52
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• 2005

Interrupted creep tests for investigating the structural degradation during creep were conducted for a Mod.9Cr-1Mo steel in the range of stress from 71 to 167 MPa and temperature from 873 to 923 K. The change of hardness and tempered martensitic lath width was measured in grip and gauge parts of interrupted creep specimens. The lath structure was thermally stable in static conditions. However, it was not stable during creep, and the structural change was enhanced by creep strain. The relation between the change in lath width and creep strain was described quantitatively. The change in Vickers hardness was expressed by a single valued function of creep LCR(life consumption ratio). Based on the empirical relation between strain and lath width, a model was proposed to describe the relation between change in hardness and creep LCR. The comparison of the model with the empirical relation suggests that about 65% of hardness loss is due to the decrease of dislocation density accompanied by the movement of lath boundaries. The role of precipitates on subboundaries was discussed in connection with the abnormal subgrain growth appearing in low stress regime.

• 한국압력기기공학회 논문집
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• 제16권1호
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• pp.92-99
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• 2020

High-temperature mechanical behaviors of Type 316L stainless steel (SS), which is considered as one of the major structural materials of Generation-IV nuclear reactors, were investigated through the tension and creep tests at elevated temperatures. The tension tests were performed under the strain rate of 6.67×10^-4 (1/s) from room temperature to 650℃, and the creep tests were conducted under different applied stresses at 550℃, 600℃, 650℃, and 700℃. The tensile behavior was investigated, and the modeling equations for tensile strengths and elongation were proposed as a function of temperature. The creep behavior was analyzed in terms of various creep equations: Norton's power law, modified Monkman-Grant relation, damage tolerance factor(λ), and Z-parameter, and the creep constants were proposed. In addition, the tested tensile and creep strengths were compared with those of RCC-MRx. Results showed that creep exponent value decreased from n=13.55 to n=7.58 with increasing temperature, λ = 6.3, and Z-parameter obeyed well a power-law form of Z=5.79E52(σ/E)^9.12. RCC-MRx showed lower creep strength and marginally different in creep strain rate, compared to the tested results. Same creep deformation was operative for dislocation movement regardless of the temperatures.

• Computers and Concrete
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• 제6권2호
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• pp.167-185
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• 2009

Reinforced concrete floors constructed between movement restraints often crack seriously due to shrinkage after completion. One common mitigation measure is to construct the concrete floors in stages to allow part of the shrinkage movement to take place before completion. However, shrinkage movement analysis of concrete floors constructed in stages is quite cumbersome, as the structural configuration changes during construction, thus necessitating reanalysis of the partially completed structure at each stage. Herein, a finite element method for shrinkage movement analysis of concrete floors constructed in stages is developed. It analyses the whole structure, including the completed and uncompleted portions, at all stages. The same mesh is used all the time and therefore re-meshing and location matching are no longer necessary. This is achieved by giving negligibly small stiffness to the uncompleted portions, which in reality do not exist yet. In the analysis, the locked-in strains due to increase in elastic modulus as the concrete hardens and the creep of the hardened concrete are taken into account. Most important of all, this method would enable fully automatic shrinkage movement analysis for the purpose of construction control.

• 대한기계학회논문집A
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• 제29권2호
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• pp.214-219
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• 2005

To investigate the change of internal stress and mobile dislocation density in the creep, stress relaxation test was examined from each strain range. Mobile dislocation density increased until it reached minimum creep rate but after that, it decreased. Internal stress did not change until it reached minimum creep rate but after that, it decreased. The stress relaxation rate is fast and approached zero later 1.5 seconds, which were begun in the stress relaxation. When the applied stress is large, the internal stress is large. It is cleared that dislocations glide viscously which N passes by cutting Cr atom rather than typical viscosity movement by the evaluation of mobility of dislocation in STS310J1TB.