• Geomechanics and Engineering
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• 제11권6호
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• pp.771-785
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• 2016

The thermal conductivity of soils is an important property in energy-related geotechnical structures, such as underground heat pumps and underground electric power cable tunnels. This study explores the effects of geotechnical engineering properties on the thermal conductivity of soils. The thermal conductivities of quartz sands and Korean weathered silty sands were documented via a series of laboratory experiments, and its variations with effective stress, porosity, and water saturation were examined. While thermal conductivity was found to increase with an increase in the effective stress and water saturation and with a decrease in porosity, replacing air by water in pores the most predominantly enhanced the thermal conductivity by almost one order of magnitude. In addition, we have suggested an improved model for thermal conductivity prediction, based on water saturation, dry thermal conductivity, saturated thermal conductivity, and a fitting parameter that represents the curvature of the thermal conductivity-water saturation relation.

• 한국전산구조공학회논문집
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• 제30권5호
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• pp.381-387
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• 2017

섬유강화 복합재료는 열팽창 계수의 방향성을 갖고 있을 뿐만 아니라 제작과정 온도와 실제 사용온도 사이의 차이 때문에 필연적으로 열응력 효과를 받게 된다. 이러한 열응력에 의한 파손현상은 실제 항공우주산업에서의 응용이 증대되고 있는 두꺼운 복합 적층판의 경우에 더욱 현저한 현상으로 적층판의 역학적 기능 및 파단강도에 큰 영향을 미치게 된다. 본 연구에서는 복잡한 재질로 구성되고 높은 세장비를 가진 블레이드 날개 구조의 차원축소 및 열 응력 복원 이론을 소개하고 3차원 유한요소모델과 비교결과를 통해 효율성과 정확성을 입증한다. 또한 차원을 축소한 모델링을 구성하고 복원이론를 이용하여 열적 환경에 적용된 복합재 보 단면의 열응력을 차원 복원하고 시각적으로 형상화하는 효율적인 복원해석 과정을 소개하고자 한다.

• 한국광학회지
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• 제32권5호
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• pp.230-234
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• 2021

열응력 완화 기술은 고출력 레이저 다이오드의 빔의 품질과 안정성을 향상시키기 위한 주요 요소기술로 큰 주목을 받고 있다. 본 연구에서는 레이저 다이오드 바(LD-bar) chip-on-submount (CoS)에 발생하는 열응력 분포 양상을 SolidWorks 소프트웨어를 사용하여 해석하고, 마이크로-홈 구조 도입에 따라 열응력 완화에 미치는 영향을 체계적으로 분석한다. 마이크로-홈 구조는 누적응력을 차단하는 효과가 있는 반면, 열흐름을 방해하는 역기능도 있으므로, 시스템 구조와 방열금속판 두께에 따라 홈 깊이를 최적화할 필요가 있다. 간단히 도입된 예시구조에 대하여, LD-bar CoS의 칩 홀더 금속판에 도입하는 마이크로-홈 구조 최적화를 통해 칩 전면부 표면 응력을 마이크로-홈 구조가 없는 경우의 약 1/5 정도로 낮추었다. 향후 초고출력 시스템에서 방열을 위한 열저항과 광출력 빔크기를 최소한으로 유지하면서, 열응력을 효과적으로 완화시키는 구조로 활용이 기대된다.

• 한국기계가공학회지
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• 제21권6호
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• pp.50-59
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• 2022

The design of the substrate significantly affects the thermal history and the residual stress formation in the vicinity of a repaired region by a directed energy deposition (DED) process. The occurrence of defects in the repaired region depends on the thermal history and residual stress formation. The objective of this study was to investigate the influence of the inclined angle and depth of the substrate on the thermal and residual stress characteristics in the vicinity of a repaired region by a DED process through two-dimensional finite element analyses (FEAs). The temperature and residual stress distributions in the vicinity of the repaired region were predicted according to the combination of the inclined angle and depth of the substrate. The effects of the inclined angle and depth on the depth of the heat affected zone and the maximum value of the residual stress were examined. A proper combination of the inclined angle and depth of the substrate was estimated to decrease the residual stress in the vicinity of the repaired region.

• 대한기계학회논문집
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• 제14권2호
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• pp.276-287
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• 1990

In this paper research result of transient thermal stress analysis of power plant turbine rotors for life prediction under severs operating conditions is presented. Galerkin's recurrence scheme is used for numerical solution of discretized FEM equation of transient heat conduction equation. Boundary conditions for the equation and operating conditions are intensively investigated for accurate life prediction of turbine rotors in operation. A computer program for on-site application is developed and tested. Distribution of thermal stress in turbine rotors during various operating condition is analyzed with the program and it is found that the peak thermal stress appears during cold stage conditions at the first stage of high pressure rotors.

• 한국기계가공학회지
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• 제8권1호
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• pp.18-23
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• 2009

This study analyzes the thermal stress at automotive radiators on steady and transient states. The maximum displacement is shown at the lower corner of upper tank with the value of 0.51mm. The displacement becomes smaller at the center of radiator and it becomes larger at this edge. The maximum thermal stress with the value of 62 MPa is shown at the contact between upper tank and cooling plate. Thermal maximum stress with the transient state at the elapsed time of 10 second is lower than that at steady state as much as 0.7%.

• Tribology and Lubricants
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• 제24권6호
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• pp.308-314
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• 2008

The thermal stress have an effect on the frictional factor such as applied load, sliding speed, sliding distance and number of ventilated disk hole. However, it is difficult to know the mutual relation of these factors on thermal stress of motorcycle break disk. For this, temperature of motorcycle break disk is measured using a disk-on-pad type friction tester with full factorial design containing above 4 elements. and the thermal stress analysis of it was carried out using with ANSYS workbench. From this study, the result was shown that the regression equation which have a trust rate of 95% for thermal stress presumption of motorcycle break disk with frictional factor was composed. It is possible to apply for another automobile parts.

• Nuclear Engineering and Technology
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• 제40권3호
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• pp.239-250
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• 2008

If there is a water flow with a range of temperature inside a pipe, the wanner water tends to float on top of the cooler water because it is lighter, resulting in the upper portion of the pipe being hotter than the lower portion. Under these conditions, such thermal stratification can play an important role in the aging of nuclear power plant piping because of the stress caused by the temperature difference and the cyclic temperature changes. This stress can limit the lifetime of the piping, even leading to penetrating cracks. Investigated in this study is the effect of thermal stratification on the structural integrity of the pressurizer surge line, which is reported to be one of the pipes most severely affected. Finite element models of the surge line are developed using several element types available in a general purpose structural analysis program and stress analyses are performed to determine the response characteristics for the various types of top-to-bottom temperature differentials due to thermal stratification. Fatigue analyses are also performed and an allowable environmental correction factor is suggested.

• Steel and Composite Structures
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• 제45권2호
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• pp.263-279
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• 2022

With the span and arch rib size of concrete-filled steel tube (CFST) arch bridges increase, the hydration heat of pumped mass concrete inside large-size steel tube causes a significant temperature variation, leading to a risk of thermal stress-induced cracking during construction. In order to tackle this phenomenon, a hydration heat conduction model based on hydration degree was established through a nonlinear temperature analysis incorporating an exothermic hydration process to obtain the temperature field of large-size CFST. Subsequently, based on the evolution of elastic modulus based on hydration degree and early-age creep rectification, the finite element model (FEM) model and analytical study were respectively adopted to investigate the variation of the thermal stress of CFST during hydration heat release, and reasonable agreement between the results of two methods is found. Finally, a comparative study of the thermal stress with and without considering early-age creep was conducted.

• 대한기계학회논문집A
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• 제21권10호
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• pp.1541-1550
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• 1997

Since the ceramic/metal joint material is made at a high temperature, the residual stress develops when it is cooled from bonding temperature to room temperature due to remarkable difference of thermal expansion coefficient between ceramic and metal. As residual stress at ceramic/metal joints influences the strength of joints, it is important to estimate residual stress quantitatively. In this study, it is attempted to estimate joint residual stress of Si$_3$N$_4$STS304 joints quantitatively and to compare the strength of joints. The difference of residual stress is measured when repeated thermal cycl is loaded, under the conditions of the practical use of the ceramic/metal joint. The residual stress increases at 1 cycle of thermal load but decreases in 3 cycles to 10 cycles of thermal load. And 4-point bending test is performed to examine the influence of residual stress on fracture strength. As a result, it is known that the stress of joint decreases as the number of thermal cycle increases.