• 대한기계학회:학술대회논문집
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• 대한기계학회 2008년도 추계학술대회A
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• pp.1349-1354
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• 2008

In this study, we try to find the root cause of water condensing failures in a headlamp using chemical and mechanical analysis. Through the surface inspection by OM, SEM and CT, it was found that water infiltrate into the headlamp through hotmelt adhesive debonding part caused by adhesion force degradation and poor quality. IR spectra shows that adhesion force degradation are characterized by increase of some functional group(1742, 1710, 1649, 1016). Through the ESPI measurement, it is turned out that bonding structural change by thermal expansion and degradation of adhesive can be the cause of void generation. So it is recommended that cooling passage and the bonding part should be redesigned to give a guarantee of less thermal stress and high adhesion quality.

• Journal of the Korean Wood Science and Technology
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• 제49권3호
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• pp.274-282
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• 2021

Transparent and colorless melamine-urea-formaldehyde (MUF) resins make it difficult to identify the area of wood failure percentage (WFP) in the fracture surface of bonded wood specimens. Therefore, in this study, we develop a method of measuring WFP after the adhesion strength measurement of MUF resins under shear stress. The fractured wood surface of b lock shear strength (BSS) specimens bonded with cold-setting MUF resins at three melamine contents (20%, 30%, and 40%) was marked black, and then, WFP was accurately measured via image analysis. WFP values measured using this method consistently increased with BSS as the melamine content increased, showing the reliability of this new method. The results suggested that this new method is useful and reliable for measuring the WFP of the fracture surface of wood specimens bonded with colorless adhesives such as urea-formaldehyde, MUF, and melamine-formaldehyde resins.

• 대한토목학회논문집
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• 제33권5호
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• pp.1947-1955
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• 2013

본 논문의 목적은 얕은 기초 하중을 받는 입상체 내의 응력의 분포와 변위를 측정하는 광탄성 기법의 적용 방안을 제시하는 데 있다. 광탄성 측정기법은 입자 집합체의 힘 전달을 시각화하기 위해 사용 되었다. 실내 모형시험은 스틸 프레임으로 경계면을 만들고 폴리카보네이트 탄성중합체로 만들어진 이차원 원형 입자들을 적층하여 구성하였다. 광탄성 시트를 원형 입자에 코팅함으로써 힘 전달의 패턴을 밝은 빛의 줄무늬 형태로 확인할 수 있었고, 광탄성 측정 기법을 통해 접촉되어 있는 입자들에서의 주 응력차의 크기, 방향 또한 측정 할 수 있었다. 변위장은 디지털 이미지 해석 기법을 사용하여 측정 하였다. 하중 재하 초기 상태와 파괴 근처의 상태에서 서로 다른 접촉력의 분포를 정량적으로 분석하였다. 파괴 이전 단계에서 관측된 광탄성 패턴과 변위장은 접촉력 사슬의 좌굴 발생 이후 즉시 사라짐을 확인하였다.

• 터널과지하공간
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• 제10권1호
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• pp.59-69
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• 2000

암석 재료의 변형에 따른 미시적 파괴 현상으로부터 발생하는 미소파괴음(Acoustic Emission, AE)을 측정하여 암석 구조물 내의 미세균열의 생성과 전파를 탐지하는 연구는 지하 암반 구조물의 안정성을 비파괴검사로 평가하는데 대단히 중요하다. 본 연구에서는 암반 구조물의 보강재로 사용되는 콘크리트와 대리석 암석 시험관에 대하여 전과정 응력-변형률 곡선을 얻기 위한 강성압축시험을 실시하였고, 시험 중에 미소파괴음 발생을 측정하여 미소파괴음 파라미터 분석 및 음원추적을 수행하여 대리석과 콘크리트의 변형 및 파괴거동 특성을 살펴보았다. 또한 시험편에 계단식 반복재하시험을 수행하여 그 변형거동을 고찰하였으며, 미소파괴음 측정을 통하여 재료의 손상, 암반의 현지응력 및 콘크리트 구조물의 응력이력 등과 관련된 카이저효과를 검증하였다

• 터널과지하공간
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• 제14권4호
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• pp.295-303
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• 2004

연약층과 견고한 암반층이 습곡형태로 혼재된 지질조건의 지하 심부 채굴 현장을 대상으로, 심부 급경사 연약층의 단계적 굴착 진행에 따른 갱도 및 주변 암반의 거동 양상을 전산해석과 현장계측을 통하여 비교 분석하였다. 전산해석에서는 Hoek ＆ Brown의 경험적 파괴기준 및 변형률연화모델을 적용한 탄소성 해석 기법을 이용하였다. 현장계측에서는 유압캡슐, 지중변위계, 내공변위계를 갱도 및 주변 암반에 설치하여 응력과 변위를 계측하였다. 경험적 파괴조건 및 변형률연화모델을 이용한 탄소성 해석은, 현장 지질조건 및 채굴과정의 복잡함에도 불구하고 현장계측결과와 유사한 양상을 보여주어 타당성을 검증할 수 있었다. 이러한 전산해석 및 현장계측의 비교를 통해 지하 굴착 갱도의 변형 거동 과정을 예측하고 이후의 굴착 및 지보보강 설계의 지침을 제공할 수 있을 것이다.

• 소성∙가공
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• 제16권6호
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• pp.479-487
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• 2007

Die life is generally estimated taking failure life and wear amount into consideration. In this study, the forging die life was investigated considering both of these two factors. The fatigue life prediction for the die was performed using the stress-life method, i.e. Goodman's and Gerber's equations. The Archard's wear model was used in the wear life simulation. These die life prediction techniques were applied to the die used in the forging process of the socket ball joint of a transportation system. A rigid-plastic finite element analysis for the die forging process of the socket ball was carried out and also the elastic stress analysis for the die set was performed in order to get basic data for the die fatigue life prediction. The wear volume of the die was measured using a 3-dimensional measurement apparatus. The simulation results were relatively in good agreement with the experimental measurements.

• Geomechanics and Engineering
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• 제18권5호
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• pp.459-469
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• 2019

It is important to estimate the shear strength of shallow compacted soils as a construction material. A series of constant water content triaxial compression (CWCC) tests under low confining state in this study were performed on compacted geomaterials. For establishing a relationship of the shear strengths between saturated and unsaturated states on compacted geomaterials, the suction stresses were derived by two methods: the conventional suction-measured method and the Suction stress-SWRC Method (SSM). Considering the suction stress as an equivalent confining stress component in the (${\sigma}_{net}$, ${\tau}$) plane, it was found that the peak deviator stress states agree well with the failure line of the saturated state from the triaxial compression test when the SSM is applied to obtain the suction stress. On the other hand, the cavitation phenomenon on the measurement of suction affected the results of the conventional suction-measured method. These results mean that the SSM is distinctly favorable for obtaining the suction value in the CWCC test because the SSM is not restricted by the cavitation phenomenon. It is expected that the application of the SSM would reduce the time required, and the projected cost with the additional equipment such as a pore water measuring device in the CWCC test.

• 한국안전학회지
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• 제8권4호
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• pp.16-20
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• 1993

The combined effect of increased pressure/temperature and the reduced material thicknesses act to increase the stress on the radiator componets. The design life of the radiator is influenced by the cyclic stresses and corrosion, which act to weaken the materials, radiator mechanical failure occurs when a tube or solder Joint ruptures, causing coolant loss or insufficient heat rejection. Therefore, in this study, through strain measurement of the tubes in copper/brass radiator, the strain distribution of the tubes in radiator as function of temperature and pressure is obtained.

• 한국안전학회지
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• 제35권5호
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• pp.1-8
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• 2020

Mobile elevating work platforms (MEWPs) consist of a work platform, extending structure, and chassis, and are used to move persons to working positions. MEWPs are useful but are composed of pieces of equipment, and accidents do occur owing to equipment defects. Among these defects, accidents caused by the fracture of bolts fixed to the extension structure and swing system are increasing. This paper presents a failure analysis of the fixing bolts of MEWP. Standard procedure for failure analysis was employed in this investigation. Visual inspection, chemical analysis, tensile strength measurement, microstructural characterization, fractography analysis by Optical Microscope(OM) and Scanning Electron Microscopy(SEM), and finite element analysis (FEA) were used to analyze the failure of the fixing bolts. Using this failure analysis approach, we found the root cause of failure and proposed a means for solving this type of failure in the future. First, the chemical composition of the fixing bolt is obtained by a spectroscopy chemical analysis method, which determined that the chemical composition matched the required standard. The tensile test showed that the tensile and yield strengths were within the required capacity. The stress analysis was carried out at five different boom angles, and it was determined that the fixing bolt of MEWP can withstand the loads at all the boom angles. The outcomes of the fatigue analysis revealed that the fixing bolt fails before reaching the design requirements. The results of the fatigue analysis showed primarily that the failure of the fixing bolt was due to fatigue. A visual inspection of the fractured section of the fixing bolt also confirmed the fatigue failure. We propose a method to prevent failure of the fixing bolt of the MEWP from four different standpoints: the manufacturer, safety certification authority, safety inspection agency, and owner.

• Steel and Composite Structures
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• 제18권4호
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• pp.1045-1062
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• 2015

Concrete-filled circular t steel tubular joints (CFSTJs) in practice are frequently subjected to fluctuated loadings caused by wind, earthquake and so on. As fatigue crack is sensitive to such cyclic loadings, assessment on performance of CFSTJs with crack-like defect attracts more concerns because both high stress concentration at the brace/chord intersection and welding residual stresses along weld toe cause the materials in the region around the intersection to be more brittle. Once crack initiates and propagates along the weld toe, tri-axial stresses in high gradient around the crack front exist, which may bring brittle fracture failure. Additionally, the stiffness and the load carrying capacity of the CFSTJs with crack may decrease due to the weakened connection at the intersection. To study the behaviour of CFSTJs with initial crack, experimental tests have been carried out on three full-scale CFCST T-joints with same configuration. The three specimens include one uncracked joint and two corresponding cracked joints. Load-displacement and load-deformation curves, failure mode and crack propagation are obtained from the experiment measurement. According to the experimental results, it can be found that he load carrying capacity of the cracked joints is decreased by more than 10% compared with the uncracked joint. The effect of crack depth on the load carrying capacity of CFCST T-joints seems to be slight. The failure mode of the cracked CFCST T-joints represents as plastic yielding rather than brittle fracture through experimental observation.