• 한국건축시공학회:학술대회논문집
• /
• 한국건축시공학회 2021년도 가을 학술논문 발표대회
• /
• pp.4-5
• /
• 2021

In irregular curtain walls, the nominal stress required for each member varies greatly depending on the shape, so it is inefficient to design members based on the maximum required stress. Then, built-up members are absolutely necessary, but built-up members manufactured by Manpower-welding cannot be constructed in an irregular curtain wall building because it' not precise. In order to address the problems, this paper presents why Robotic-laser-welding should be used in irregular curtain walls using Gwanggyo Galleria Department Store involving 3D printing as an example. Results verify the performance of Robot-Laser-Welding as an efficient solution for precise steel curtain wall members.

• 한국강구조학회 논문집
• /
• 제12권3호통권46호
• /
• pp.239-250
• /
• 2000

본 연구에서는 강바닥판의 실물 대형시험체를 제작하여 정적시험 및 피로시험을 실시하였다. 정적 및 영향면 재하시험 결과를 통하여 다이아프램의 유무에 따른 강바닥판 슬릿부의 면내와 면외응력을 검토하였으며, 피로시험결과로부터는 강바닥판의 피로거동, 피로균열의 발생과 진전에 대한 연구를 수행하였다. 다이아프램이 설치된 상세는 설치되지 않은 상세에 비하여 지점조건에 상관없이, 종리브 횡리브 교착부의 종리브측으로는 약 50%의 응력경감효과가 있으나, 횡리브측 하단부에는 오히려 상당히 큰 응력을 야기함을 알 수 있었으며, 피로균열 진전해석결과로부터는 슬릿부의 노치에 의한 초기균열길이가 피로균열성장에 상당한 영향을 끼치고 있음을 알 수 있었다. 측정자료와 FEM 해석을 통하여 공칭응력과 핫스폿응력에 의한 피로강도를 추정한 결과, 다이아프램이 설치되지 않은 상세는 규정된 피로등급에서 안전한 것으로 판단되나 다이아프램이 설치된 상세는 피로등급이하의 거동을 보였다.

• 한국강구조학회 논문집
• /
• 제10권1호통권34호
• /
• pp.85-99
• /
• 1998

본 논문은 케이슨의 인양작업중 Fitting Anchor의 취성파괴로 인한 들고리의 붕괴원인을 조사하기 위한 실험적 연구이다. 또한, 본 연구에서는 응력해석을 통하여 들고리의 붕괴메카니즘을 분석하고 이를 실제 붕괴과정과 비교한다. 본 연구에서는 파괴된 강재에 대한 파면해석 뿐만아니라 화학성분시험, 인장시험 및 샤르피 V-노치 충격시험을 실시한다. 그리고 이의 시험 결과를 정상적인 강재에 대한 시험결과와 비교한다. 본 연구의 거시적, 미시적인 방법으로 결함을 관찰한 결과, Fitting Anchor 내부에 원주방향으로 나타난 표면결함은 케이슨의 진수시 발생하는 들고리의 인장응력이 작용하기 전에 발생한 것임을 확인할 수 있었다. 이는 균열선단의 응력집중이 발생하여 작용응력보다 큰 응력이 결함에 발생한 것임을 알 수 있다. 또한, 잠재한 결함의 크기가 임계값 이상으로 증가하여 본 연구대상 강재의 응력확대계수가 증가하였을 것으로 판단된다. 그래서 균열선단의 응력확대계수가 본 강재의 파괴인성보다 크게 되어 케이슨의 인양작업중에 취성파괴를 일으킨 것으로 사료된다. 본 연구결과에 따르면 케이슨 들고리의 붕괴는 Fitting Anchor의 취성파괴로 발생한 것으로 사료된다.

• Geomechanics and Engineering
• /
• 제7권3호
• /
• pp.233-246
• /
• 2014

Estimation of fracture initiation pressure is one of the most difficult technical challenges in hydraulic fracturing treatment of vertical or horizontal oil wells. In this study, the influence of in-situ stresses and pore pressure values on fracture initiation pressure and its profile in vertical and horizontal oil wells in a normal stress regime have been investigated. Cohesive elements with traction-separation law (XFEM-based cohesive law) are used for simulating the fracturing process in a fluid-solid coupling finite element model. The maximum nominal stress criterion is selected for initiation of damage in the cohesive elements. The stress intensity factors are verified for both XFEM-based cohesive law and analytical solution to show the validation of the cohesive law in fracture modeling where the compared results are in a very good agreement with less than 1% error. The results showed that, generally by increasing the difference between the maximum and minimum horizontal stress, the fracture pressure and its profile has been strongly changed in the vertical wells. Also, it's been clearly observed that in a horizontal well drilled in the direction of minimum horizontal stress, the values of fracture pressure have been significantly affected by the difference between overburden pressure and maximum horizontal stress. Additionally, increasing pore pressure from under-pressure regime to over-pressure state has made a considerable fall on fracture pressure in both vertical and horizontal oil wells.

• 한국수산과학회지
• /
• 제38권5호
• /
• pp.304-308
• /
• 2005

The effects of diethylhexyl phthalate (DEHP) on various oxidative stress responses in liver, kidney and gill tissues of freshwater bagrid catfish Pseudobagrus fulvidraco were investigated under laboratory conditions. Bagrid catfish were intraperitoneally injected with sunflower seed oil containing nominal concentrations of 0, 300 or 900mg DEHP per kilogram of body weight for 3 days and the effects after last injection were assessed in liver, kidney and gill tissues of the exposed organisms. The oxidative stress responses of fish were evaluated by analyzing the level of glutathione (GSH), as well as the activities of antioxidant enzymes such as glutathione S-transferase (GST), glutathione peroxidase (GPx) and glutathione reductase (GR). After exposure to the DEHP, there were significant decrease in GR, GPx activity and GSH content in liver of fish exposed to 900 mg DEHP per kilogram of body weight compared to the control group. Compared with the control group, significant decreases in renal GPx and GR activity were observed in the DEHP treatment groups (900 mg $kg^{-1}$ bw). However, no significant difference was observed in any oxidative stress responses in gills between the DEHP-treated and the untreated group of fish. The findings of the present investigation show that DEHP induce oxidative stress and the liver was the most affected organ followed by the kidney and gills. Furthermore, the changes of GPx and GR activities may be important indicators of oxidative stress responses but additional study is required to confirm the oxidative stress of DEHP.

• Journal of Welding and Joining
• /
• 제12권1호
• /
• pp.102-115
• /
• 1994

This paper is to evaluate the fatigue strength of lap joints of materials applied to LNG carrier cargo containment of GAZ-TRANSPORT(GT) type, which was welded by manual and automatic TIG welding process. The thicknesses of lapped members were 1.5mm/1.5mm or 1.5mm/0.7mm in Invar to Invar joint, and 1.5mm/8.0mm in Invar to stainless steel joint, respectively. These lap joints were mainly applied to the membrance fabrication of GT-LNG carrier. Fatigue tests of Invar/Inar lap joints were conducted under the stress ratio R=0 at room temperature. The effect of mean stress and cumulative fatigue damage on the allowable stress of Invar lap joint was evaluated on the basis of test results. Fatigue test was also conducted on Inver/Stainless steel lap joints welded by automatic TIG process without filler metals. The fatigue test of the joint was carried out under the same conditions as those of Invar/invar lap joints. The fatigue strength of the joint welded without filler metal was comparable to those welded with filler metal quoted from reference. The fatigue strength of Invar/stainless steel lap joint was only dependent on the lap throat thickness, and not on the welding process. Based on test results, the applicability of TIG welding process without filler metal in Invar/stainless steel lap joint was reviewed by controlling welding variables to assure the valid throat thickness of lap joints.

• 대한기계학회논문집A
• /
• 제37권7호
• /
• pp.875-881
• /
• 2013

증기발생기 수직 지지대를 고정하고 있는 고강도 앵커 볼트의 응력부식균열에 대한 건전성 평가는 원자력발전소 기기 건전성 유지와 관련하여 중요한 현안 가운데 하나이다. 이에 따라 미국 EPRI에서는 고강도 앵커 볼트의 건전성 평가를 위한 기준균열계수 개념 기반의 평가 절차를 제시한 바 있으며, 본 연구에서는 EPRI에서 제시한 절차에 입각하여 증기발생기 수직 지지대 고정용 앵커 볼트의 응력부식균열 및 취성 파괴에 대한 건전성 평가를 수행하였다. 이를 위해 볼트 예비하중과 운전하중을 고려한 3차원 유한요소 응력해석을 수행하여 볼트 단면에 작용하는 공칭응력을 결정하였으며, 결정된 볼트 응력과 EPRI 절차를 이용하여 앵커 볼트의 균열 건전성을 평가하였다. 또한 3차원 탄성 유한요소 파괴역학 해석을 수행하여 EPRI에서 제시한 기준균열계수의 정확성을 검증하였다.

• 대한기계학회논문집
• /
• 제9권1호
• /
• pp.1-9
• /
• 1985

본 연구에서는 이러한 점에도 역점을 두어서 초기 피로균열의 발생.거동을 관 찰하기 쉬운 연강을 선택하여 편진인장반복하중을 작용시켜, 연강 평골재의 표면상에 발생.성장하는 미소표면균열의 거동을 전자현미경과 광학현미경을 병용하여 표면과 파 단면을 입체적으로 조사하여, 피로균열의 초기발생상태를 조사하고, 그 성장율을 조사 하여 파괴역학적으로 해석하여 그 특성을 조사한다.

• Steel and Composite Structures
• /
• 제39권4호
• /
• pp.453-469
• /
• 2021

The cracking at the transverse diaphragm cutout is one of the most severe fatigue failures threatening orthotropic steel decks (OSDs), whose mechanisms and crack treatment techniques have not been fully studied. In this paper, full-scale experiments were first performed to investigate the fatigue performance of polished cutouts involving the effect of an artificial geometrical defect. Following this, comparative experimental testing for defective cutouts strengthened with carbon fiber-reinforced polymer (CFRP) was carried out. Numerical finite element analysis was also performed to verify and explain the experimental observations. Results show that the combinative effect of the wheel load and thermal residual stress constitutes the external driving force for the fatigue cracking of the cutout. Initial geometrical defects are confirmed as a critical factor affecting the fatigue cracking. The principal stress 6 mm away from the free edge of the cutout can be adopted as the nominal stress of the cutout during fatigue evaluation, and the fatigue resistance of polished cutouts is higher than Grade A in AASHTO specification. The bonded CFRP system is highly effective in extending the fatigue life of the defective cutouts. The present study provides some new insights into the fatigue evaluation and repair of OSDs.

• 소성∙가공
• /
• 제33권1호
• /
• pp.18-35
• /
• 2024

In the present work, the evolution rules for the internal variables including continuum damage factors are obtained using the thermodynamic framework, which are in turn facilitated to derive the elastic-plastic constitutive relation for the particulate composites. Using the Mori-Tanaka scheme, the homogenization on state and internal variables such as back-stress and damage factors is carried out to procure the rate independent plasticity relations. Moreover, the degradation of mechanical properties of constituents is depicted by the distinctive damages such that the phase and interfacial damages are treated individually accordingly, whereas the kinematic hardening is depicted by combining the Armstrong-Frederick and Phillips' back-stress evolutions. On the other hand, the present constitutive relation for each phase is expressed in terms of the respective damage-free effective quantities, then, followed by transformation into the damage affected overall nominal relations using the aforementioned homogenization concentration factors. An emphasis is placed on the qualitative analyses for strain localization by observing the perturbation growth instead of the conventional bifurcation analyses. It turns out that the proposed constitutive model offers a wide range of strain localization behavior depending on the evolution of various internal variable descriptions.