• Proceedings of the Korean Reliability Society Conference
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• 2011.06a
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• pp.125-130
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• 2011

발전 설비는 기대 수명동안의 안정성을 확보하기 위하여 해당 규격에 부합하도록 설계하여 건설된다. 하지만 가동 중 다양한 복합 환경에 노출됨에 따라 구조물을 이루고 있는 재료의 열화 현상이 가속화되어 예기치 못한 파손이 발생할 수 있다. 기계적 물성은 재료의 기계적 거동을 나타내는 주요 척도가 되며 이는 신뢰성 및 안전과 직결된다. 하지만 기존의 역학물성을 측정하는 대부분의 시험법들은 특정 크기의 시편을 요구하고 파괴적인 시험법이기 때문에 가동 중 시설물에 적용하기가 불가능하였다. 이러한 한계점을 극복하고자 비파괴적이고 정량적인 시험이 가능한 연속압입시험법이 최근 각광받는 시험법으로서 많은 연구자들에 의해 연구되고 있다. 이 시험법은 시험 대상물의 형상에 제약을 받지 않으며 시험 절차가 매우 간단하다는 장점을 가진다. 또한 대상의 국소 부위에 시험할 수 있어 취약 부위 판별이 가능하다. 본 연구에서는 대표응력-대표변형률 기법을 통하여 인장물성을 평가하고, 압입 하중 차이를 이용하여 소재에 존재하는 잔류응력을 평가하는 기법을 소개한다. 또한, 연속압입시험을 이용하여 실제 발전소 파이프의 취약부위로 알려진 용접부에 대하여 인장물성 및 잔류응력을 측정함으로써 실제 산업체의 신뢰성 평가가 적용할 수 있음을 확인하였다.

• Tunnel and Underground Space
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• v.11 no.2
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• pp.96-108
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• 2001

A concrete lining of NATM tunnel is the final product of a process that involves planning and evaluation of user needs, geotechnical investigations, analysis of ground-lining interaction, construction, and observations and modifications during construction. The designer must consider the lining in context of the many function, construction, and geotechnical requirements. Also, the loss of supporting capacity of shotcrete lining due to poor rock qualities and shotcrete erosion must be considered. The values, shapes, and estimating methods of rock load and water pressure are very different with every designers. Estimating methods of rock loads used in the design of NATM tunnel concrete lining are investigated. Structural analyses are done in various load combinations, and the member forces(moment, axial force and shear force) are compared. The adequate load combination of rock load and water pressure is proposed.

• Journal of the Korean Society of Propulsion Engineers
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• v.12 no.4
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• pp.7-15
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• 2008

In manufacturing aircraft, safety and lightness of structure are important factors. Utilizing autofrettage technique, these benefits can be obtained. This technique is most frequently applied to a single cylinder. However, the Bauschinger effect reduces the benefits of autofrettage process Therefore, there is increasing interest in the use of compound cylinder that combine shrink fit and autofrettage. In this paper, single and compound cylinders that has same geometry were considered. It was found that compound cylinder which was autofrettaged has lower tangential hoop stress and plastic strain than single cylinder at bore. This means a reduction in the impact of the Bauschinger effect after shrink-fitting which produces the beneficial bore hoop stress.

• Journal of the Korean Ceramic Society
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• v.40 no.8
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• pp.770-776
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• 2003

#140 mesh and #600 mesh wheels were adopted to grind (111) and (100) oriented single crystalline silicon wafer and the grinding induced change of the surface integrity was investigated. For this purpose, microroughness, residual stress and phase transformation were analyzed for the ground surface. Microroughness was analyzed using AFM (Atomic Force Microscope) and crystal structure was analyzed using micro-Raman spectroscopy. The residual stress and phase transformation were also analyzed after thermal annealing in the air. As a result, microroughness of (111) wafer was larger than that of (100) wafer after grinding. It was observed using Raman spectrum that the silicon was transformed from diamond cubic Si-I to Si-III(body centered tetragonal) or Si-XII(rhombohedral). Residual stress relaxation was also shown in cavities which were produced after grinding. The thermal annealing was effective for the recovery of the silicon phase to the original phase and the residual stress relaxation.

• Journal of the Korean GEO-environmental Society
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• v.11 no.11
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• pp.55-62
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• 2010

The settlements by liquefaction seldom occur uniformly because of soil homogeneity, however differential settlements are major cause of the damages to structures. From the past researches, author paid attention to the fact that stress history during undrained cyclic shear process affects greatly on the volumetric strains of the post-liquefaction. Therefore, the effect of the residual shear strain in cyclic shear process was examined in this study. The experiment apparatus based on strain control with volumetric strain control device was used for the study to investigate the effect of the residual strain on the relationship between volumetric strain and effective stress of clean and granite sandy soil. It could be seen an insignificant difference in the volumetric strain after liquefaction under various residual shear strain conditions in the case of clean sand. On the other hand, in granite sandy soil, the volumetric strain after liquefaction was small when the lower level of the residual shear strain was applied. And, the residual shear strain during cyclic shear affected the shape of the relation curve between effective stress and volumetric strain as well.

• Journal of Korea Water Resources Association
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• v.55 no.spc1
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• pp.1283-1293
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• 2022

The purpose of this study is to predict residual chlorine in order to maintain stable residual chlorine concentration in sedimentation basin by using artificial intelligence algorithms in water treatment process employing pre-chlorination. Available water quantity and quality data are collected and analyzed statistically to apply into mathematical multiple regression and artificial intelligence models including multi-layer perceptron neural network, random forest, long short term memory (LSTM) algorithms. Water temperature, turbidity, pH, conductivity, flow rate, alkalinity and pre-chlorination dosage data are used as the input parameters to develop prediction models. As results, it is presented that the random forest algorithm shows the most moderate prediction result among four cases, which are long short term memory, multi-layer perceptron, multiple regression including random forest. Especially, it is result that the multiple regression model can not represent the residual chlorine with the input parameters which varies independently with seasonal change, numerical scale and dimension difference between quantity and quality. For this reason, random forest model is more appropriate for predict water qualities than other algorithms, which is classified into decision tree type algorithm. Also, it is expected that real time prediction by artificial intelligence models can play role of the stable operation of residual chlorine in water treatment plant including pre-chlorination process.

• Journal of Korean Society of Steel Construction
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• v.10 no.3 s.36
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• pp.407-421
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• 1998

The purpose of this paper is to provide and verify an analytical method, based on the spline finite strip method, which can be used to investigate the buckling mode and stress of thin-walled steel sections. Geometric imperfection and initial stress of plates and plate assemblies, which are resulted from various preloadings and may cause prebuckling deformations before buckling, are included in the analysis. Material nonlinearity and residual stress are also considered. It can be applied to sections with simple or non-simple boundary conditions and arbitrary loading. The method has been applied to investigate the buckling behavior of plates and plate assemblies which are subjected to compression with initial imperfections and residual stresses.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.26 no.8
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• pp.1653-1665
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• 2002

One of the most significant problems in the processing of composite materials is residual stresses. The residual stresses may be high enough to cause cracking in the matrix even before external loads are applied and can degrade the integrity of composite structures. In this study, thermo-viscoelastic residual stresses occurred in the polymeric composite cylinder are investigated. This type of structure is used for the launch vehicle fuselage. The time and degree of cure dependent thermo-viscoelastic constitutive equations are developed and coupled with a thermo-chemical process model. These equations are solved with the finite element method to predict the residual stresses in the composite structures during cure. A launch vehicle experiences high thermal loads during flight and re-entry due to aerodynamic heating or propulsion heat, and the thermal loads may cause thermal buckling on the structure. In this study the thermal buckling analysis of composite cylinders are performed. Two boundary conditions such as all clamped and all simply supported are used for the analysis. The effects of laminates stacking sequences, shapes and residual stresses on the critical buckling temperatures of composite cylinders are investigated. The thermal buckling analysis is performed using ABAQUS.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.27 no.5
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• pp.713-723
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• 2003

In this study, a state of art review of existing residual stress analysis techniques and representative solutions is presented in order to develope the residual stress analysis procedure for fitness-for-service (FFS) assessment of welded structure. Critical issues associated with existing residual stress solutions and their treatments in performing FFS are discussed. It should be recognized that detailed residual stress evolution is an extremely complicated phenomenon that typically involves material-specific ther-momechanical/metallurgical response, welding process physics, and structural interactions within a component being welded. As a result, computational procedures can vary significantly from highly complicated numerical techniques intended only to elucidate a small part of the process physics to cost-effective procedures that are deemed adequate for capturing some of the important features in a final residual stress distribution. Residual stress analysis procedure for FFS purposes belongs to the latter category. With this in mind, both residual stress analysis techniques and their adequacy for FFS are assessed based on both literature data and analyses performed in this investigation.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.39 no.12
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• pp.1107-1114
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• 2011

In this paper, the fatigue life of a laser peened structure was predicted. In order to calculate residual stress induced by laser peening finite element simulation was carried out. Modified Goodman equation was used to consider the effect of compressive residual stress induced by laser peening in fatigue analysis. In addition, additive adjustment factor approach was applied to consider S-N curve model uncertainty. Consequently, the reliable bounds of the predicted fatigue life of the laser peened structure was determined.