• Journal of Welding and Joining
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• v.15 no.3
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• pp.20-28
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• 1997

용접부에는 많은 취약조건들이 존재하며 파괴의 주 원인이 되고 있어 이들에 대한 많은 연구가 진행되고 있다. 따라서, 현재 용접재료, 용접 조건 및 용접방법 등 을 개선함으로써 여러 방면에서 좋은 결과를 얻고 있다. 그러나 아직도 용접시의 열소 성변형과 구속조건에 따라 분포하는 잔류응력에 의한 피로균열거동에 대한 연구는 정확한 잔류응력 측정의 어려움으로 미흡한 상태이다. 특히 잔류응력의 측정기술과 반복하중에 의한 피로균열 진전시 잔류응력의 이완 등은 이들을 해석하는데 많은 어 려움을 주고 있다. 용접시 높은 열에 의한 재료의 팽창과 냉각시의 수축변형은 용접 부재에 인장 및 압축 잔류응력을 유발시키고, 인장잔류응력은 균열 진전될 때 잔류 응력은 오히려 균열을 지연시키기도 한다. 또한 잔류응력장에서 피로 균열이 진전될 때 잔류응력은 일반적으로 작용하중의 크기와 반복 수 그리고 균열 진전 등으로 인하 여 이완되고 재분포된다. 본 해설에서는 용접재의 피로거동중에 발생하는 잔류응력의 재분포 현상을 하중의 범위, 하중 반복수, 균열 진전의 영향으로 구분하여 각각의 영향에 대해서 기술하고자 한다.

• Computational Structural Engineering
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• v.1 no.1
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• pp.113-122
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• 1988

A practical model for predicting the risk of fatigue failure of steel highway bridges is developed in this study. The proposed model is derived from fatigue reliability methods by incorporating various factors which may affect the fatigue life of bridges. The fatigue reliability function is assumed to follow the Weibull distribution. The computational form of the Weibull is adopted from Ang-Munse's approach that includes all the statistical uncertainties of the fatigue life of steel members and the stress ranges under variable amplitude loadings. The model accounts for the variation in ADTT, the change in stress history and the effects of inspections, which may occur during the serivce life of bridges. Stress range histograms are collected from the random stress spectra based on the field measurements of an existing bridge, and, thus, the resulting stress range frequency distribution is modelled with a beta distribution. The results of applications of the proposed fatigue analysis methods to an existing bridge show that the proposed models with the computer program developed for numerical computations can be used as a practical tool for the fatigue rating or for the predictions of the remaining fatigue life of deteriorated existing steel bridges.

• Journal of Korean Society of Steel Construction
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• v.15 no.5 s.66
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• pp.475-487
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• 2003

This study developed an analysis model of estimating fatigue damage using the linear elastic fracture mechanics method. Stress history occurring to an element when a truck passed over a bridge was defined as block loading and crack closure theory explaining load interaction effect was applied. Stress range frequency analysis considering dead load stress and crack opening was done. Probability of stress range frequency distribution was applied and the probability distribution parameters were estimated. The Monte Carlo simulation of generating the probability various of distribution was performed. The probability distribution of failure block numbers was obtained. With this the fatigue reliability of an element not occurring in failure could be calculated. The failure block number divided by average daily truck traffic remains the life of a day. Fatigue reliability analysis model was carried out for the welding member of cross beam flange and vertical stiffener of steel box bridge using the proposed model. Consequently, a 3.8% difference was observed between the remaining life in the peak analysis method and in the proposed analysis model. The proposed analysis model considered crack closure phase and crack retard.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.11 no.1
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• pp.153-166
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• 1991

In an attempt to investigate the effect of intermedate principal stresses which are related to the stress-strain behavior of standard sands, a series of three-Principal stress control tests were conducted for individual stress paths. The results have shown that shear strengths of sands vary with the stress paths. The variations in internal friction angle are accorded with the Habibs stress parameter, b which represents Stress paths, showing on abropt increase at the values between 0.0 and 0.268, a moderate level between 0.268 and 0.682, and a slight decrease between 0.682 and 1.0 However, the friction angles under a triaxial extention state, were found relatively larger than under a triaxial compression state. In general, such veriations were found to have the same tendency without any relevant relation with the density of specimens and confining pressures. Therefore, it is concluded, that the shear strength of sands are positively influeced by the intermediate principal stresses present in the media. And the influnce of intermediate principal stresses on shear strengths of sands found from the present study are well compared with the previous studies by Lade-Duncan and Matsuoka-Nakai revealing a similar tendency within the failure criteria proposed by them.

• Journal of the Korean Vacuum Society
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• v.13 no.4
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• pp.157-163
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• 2004

Dependence of residual compressive stress of diamond-like carbon (DLC) films on relative humidity was investigated. Polymeric, graphitic and diamond-like carbon films were prepared by r.f.-PACVD using methane or benzene with the negative self bias voltage of the substrate ranging from -100 to -800 V. In-situ measurements of the residual stress were carried out in an environment chamber where the relative humidity was varied from 10％ to 90％. In dense DLC film of high residual compressive stress and hardness, we could not observe any change in the residual compressive stress with relative humidity. However, in the cases of graphitic and polymeric DLC films, abrupt change in the residual stress occurred by changing the relative humidity. The quantity of the stress change was inversely proportional to the film thickness, which means that the stress change with humidity is not due to the penetration of the water molecule into the film structure, but due to surface interaction between water molecules and film surface.

• Journal of the Korean Geotechnical Society
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• v.18 no.5
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• pp.99-108
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• 2002

The nonlinear-brittle-plastic model derived from experiments as well as elastic and elasto-plastic models was applied to the analysis of the rock damaged zone around a highly stressed circular tunnel. The depths of stress redistribution and disturbed zone as well as the characteristic behaviors predicted from each numerical model were compared, As the magnitudes and stress differences of in situ stresses increased, influences of stress redistribution and stress disturbance on un(tiled region of rock mass also intensified. As a result, larger stress redistribution and disturbed zone as well as greater deviatoric stress and displacement were obtained by the nonlinear-brittle-plastic model rather than other conventional models such as elasto-plastic and elastic models. from such results, it was concluded that as the magnitudes and stress differences of in situ stresses increased, larger rock damaged zone might be predicted by the nonlinear-brittle-plastic model. Therefore, it is thought that the damage analysis may be indispensable far highly stressed tunnels.

• Magazine of the Korea Concrete Institute
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• v.7 no.3
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• pp.139-148
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• 1995

The test results from three one fourth scale models using high strength Reinforced Concrete $f_x=704\;kg/cm^2,\;f_y=5.830\;kg/cm^2$ are presented. Such specimens are considered to represent the critical 3 storics of 60-story tall building of a structural wall system in area of high seismicity respectively. They are tested under inplane vertical and horizontal loading. The main varlable is the level of axial stress. The amounts of vertical and horizontal reinforcement are identical for the three walls testcd. The cross-section of all walls is barbell shape. The aspectratio($h_w/I_w$) of test specimen is 1.8. The aim of the study is to investigate the effects of levels of applied axial stresses on the inelastic behavior of high-strength R /C tall walls. Experimental results of high strength R /C tall walls subjected to axial load and simulated sels rnic loading show that it is possible to insure a ductlle dominant performance by promotmg flex ural yielding of vertical reinforcement and that axial stresses within $O.21f_x$ causes an increase in horizontal load-carrying capacity, initial secant st~ffness characteristics, but an decrease in displacement ductility. energy dissipation index and work damage index of high strength K /C tall walls

• Nuclear Engineering and Technology
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• v.27 no.3
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• pp.418-426
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• 1995

설계의 신뢰성은 응력해석을 통하여 확인될 수 있으며, 해석결과는 대상 부품의 구조적 건전성을 입증하는 근거가 된다. 본 보고서는 ANSYS의 피로해석 모듈을 이용한 CANDU 6핵연료채널의 응력해석 및 ASME Code에 따른 해석 절차 개발을 소개하였다. 응력해석은 ASME Code Section III NB-3200 의 $\ulcorner$Design by Analysis$\lrcorner$에 기초한 해석절차에 따라 수행하였으며, 체계적인 해석을 위해 자료 처리용 ANSYS 매크로 및 FORTRAN 프로그램을 개발하였다. 해석은 각 조건에 따라 기계적응력과 열응력해석으로 분리하여 수행한 후 조합되었으며, ANSYS 피로해석 모듈을 이용하여 선정된 절점들의 기계적응력과 열응력의 합에 대한 최대응력강도범위를 계산하였다. 응력해석 결과, CANDU 6 핵연료채널의 구조적 건전성이 입증되었으며, ANSYS를 이용한 ASME Code해석절차가 확립되어 CANDU 원자로 해석의 신뢰성을 크게 향상 시켰음은 물론 독자적인 수행을 위한 발판을 마련하였다.

• Computational Structural Engineering
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• v.11 no.3
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• pp.173-185
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• 1998

본 연구에서는 자동차엔진 및 트랜스미션 성능시험을 위한 다이나모 베드구조물을 분석하고 설계하였다. 해석상에 고려된 베드구조물은 Ⅰ형강 구조물, 보강된 박스구조물 그리고 블록구조물로 제작되었으며, 시험을 위한 엔진 및 트랜스미션은 베드상판에 장착된다. 엔진구동시 회전에 의한 진동이 발생된다. 공진을 피하기 위해 베드구조는 충분한 구조적 일체성을 가져야 한다. 본 연구에서는 베드 구조물의 응력, 변위 그리고 자유진동해석이 ANSYS Code를 이용한 유한요소해석이 수행되었다. Ⅰ형강 구조형 베드 구조물에서 최대 응력은 23.2MPa에서 90.3MPa까지 나타났으며, 최대 처짐은 0.25㎜에서 0.92㎜까지 나타났다. 박스 구조형 베드 구조물에서 최대 응력은 0.028MPa에서 0.259MPa까지 나타났으며, 최대 처짐은 0.031㎜에서 0.413㎜까지 나타났다. 그리고 박스구조형 베드 구조물에서 최대 처짐은 0.92MPa에서 2.15MPa까지 나타났으며, 최대 처짐은 1.1㎜에서 2.7㎜까지 나타났다. 모든 구조물이 응력과 처짐 값에서 매우 안정적인 범위 내에서 발생됨을 볼 수 있었다. 구조진동해석에서 Ⅰ형강 베드구조물의 고유진동수는 112.03㎐에서 141.66㎐까지의 범위에 발생되었다. 박스 구조형 베드구조물에서의 고유진동수는 396.93㎐에서 755.11㎐까지의 범위에서 발생되었다. 마지막으로 블록구조형 베드구조물에서는 266.51㎐에서 244.67㎐까지의 고유진동수를 찾을 수 있었다. 모든 구조물에서 베드구조물의 무게증가에 따른 기본진동수는 증가된다. 베드시스템의 지지기초시스템은 2자유도계 시스템으로 설계되었으며, 다양한 질량변화 및 스프링상수 변화에 따른 진동해석을 수행하였다. 질량비가 증가될수록 고유진동수는 크게 감소되며, 스프링상수가 증가될수록 고유진동수는 감소된다.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.40 no.12
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• pp.1027-1035
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• 2016

In this study, a strain-controlled fatigue test of widely-used 316L stainless steel with excellent corrosion resistance and mechanical properties was conducted, in order to assess its fatigue life. Low cycle fatigue behaviors were analyzed at room temperature, as a function of the strain amplitude and strain ratio. The material was hardened during the initial few cycles, and then was softened during the long post period, until failure occurred. The fatigue life decreased with increasing strain amplitude. Masing behavior in the hysteresis loop was shown under the low strain amplitude, whereas the high strain amplitude caused non-Masing behavior and reduced the mean stress. Low cycle fatigue life prediction based on the cyclic plastic energy dissipation theory, considering Masing and non-Masing effects, showed a good correlation with the experimental results.