• Journal of Advanced Marine Engineering and Technology
• /
• v.40 no.6
• /
• pp.504-509
• /
• 2016

Production processes of double wall bellows can be roughly categorized into two steps. In the first step, inner and outer bellows are made of STS316L in austenite stainless steel due to their excellent formability and corrosion resistance. In the second step, the double wall bellows are manufactured using the welding method with both the inner and outer bellows. The microstructure and defects of each weldment are observed to ensure the reliability of bellows since weldment is a highly vulnerable part, which can crack and fracture when bellows are formed or used. In this study, optimum welding conditions were derived from the analysis of microstructure and inspection of weldment of bellows that were produced using various welding procedure. Moreover, the mechanical properties were evaluated through hardness measurement of substrate, weldment and the heat-affected zone.

• Computational Structural Engineering
• /
• v.10 no.4
• /
• pp.155-164
• /
• 1997

A reactor pressure vessel, which contains fuel assemblies and reactor vessel internals, has the thermal stress resulting from the cool-down and heat-up of the vessel wall in combination with the pressure stress from system pressure resulting in large stresses. The combination of the pressure stress and thermal stress along with a decrease in fracture toughness may cause through-wall propagation of a relatively small crack. Therefore, it is necessary to define the relations between operating pressure and temperature during cool-down and heat-up. In this study, theory of fracture mechanics for a pressure/temperature limit curve is investigated and a numerical procedure for generating it is developed. Plant-specific limit curves for the Kori unit 1 plant, the oldest nuclear power plant in Korea, have been obtained for several cooling and heating rates and their results are discussed.

• Proceedings of the Korean Institute of Interior Design Conference
• /
• 2005.05a
• /
• pp.271-272
• /
• 2005

As regards of designing, I chose a simple wall design of repeating pattern of vertical windows, rather than making the building as a glamourous obzet. This kind of approach was intended to pursue strong image of construction company, interchanging and communicating with its confused surrounding. Therefore, I boldly removed parts that I considered needless from the facade, and used simple and easy words clearly implying the organization. Lobby is the face of the building, but since the space is deep and narrow and the reality of lease should be considered, there was limit to give original image to the lobby. Instead, high ceiling is the biggest feature of this space. Doorae Engineering-Construction Corp. is young and energetic company. I wanted to highlight the young and energetic image of the company by crossing tore oblique piece of boards. This doesn't just has a simple function as ceiling, but also work as a major subject in the space. In addition of this powerful space of oblique lines, indirect lighting is used to emphasize the character of territory, continuity and deepness of the space. Character of territory that divides main and supplementary function and main and supplementary moving line is expressed by flow of dimension, and continuity and deepness of space is emphasized by indirect lighting flowing linearly through the crack between the ceiling and the wall.

• Transactions of the Korean Society of Mechanical Engineers A
• /
• v.39 no.7
• /
• pp.645-652
• /
• 2015

In this study, a method for determining Ramberg-Osgood constants for leak-before-break evaluation was investigated. The Ramberg-Osgood constants were calculated for SA312, TP316, and SA-508 Gr.1a in an operating temperature of $316^{\circ}C$. Incremental plasticity, using stress-strain data obtained from experiment, and deformation plasticity, using the Ramberg-Osgood constants, were considered in a finite element analysis. Using incremental plasticity and deformation plasticity, J-integrals and crack opening displacement values were calculated and compared. By comparing the results of incremental plasticity and deformation plasticity, a suitable method for determining Ramberg-Osgood constants for leak-before-break evaluation was confirmed.

• Journal of Welding and Joining
• /
• v.6 no.4
• /
• pp.44-53
• /
• 1988

The mechanical strengths of buried lamellar tears located near the weld toe in the welded tee joints were evaluated in terms of the loss of load carrying capacity as a function of tear area. In static loading, the load carrying capacity was significantly reduced when tear intercepted over 10% of the cross-sectional area of the welded joints. However, the welded joints containing buried tears still failed at stresses over the yield strength of the base metal in the through-thickness direction in spite of the presence of tears up to 20-25% of the area. Fatigue strength of welded joints containing tears markedly reduced with increasing tear areas. Lehigh lamellar tearing test used in this study to produce speicmens was described in detail. The load carrying cpapacity in static loading was influenced by the reduction of supporting area whereas that in fatigue loading was influenced by the stress-concentration effects of lamellar tears and the reduction of supporting area. In bend tests, the pre-existing lamellar tears always grew up toward the weld toe. However, in fatigue loading, cracks grew up and down simultaneously form both the weld toe and the top of lamellar tears because of stress concentration. In fatigue loading, delaminations and decohesion of inclusion/matrix interface generated in multipass welds provided crack propagation paths and enhanced crack propagation because the tips of delaminations and deconhesios acted as stress raisers.

• Transactions of the Korean Society for Noise and Vibration Engineering
• /
• v.13 no.5
• /
• pp.400-408
• /
• 2003

This paper investigates the vibration characteristics of steam generator (SG) U-tubes with defect. The operating SG shell-side flow field conditions for determining the fluidelastic instability parameters such as added mass are obtained from three-dimensional SG flow calculation. Modal analyses are performed for the U-tubes either with axial or circumferential flaw with different sizes. Special emphases are on the effects of flaw orientation and size on the modal and instability characteristics of tubes, which are expressed in terms of the natural frequency, corresponding mode shape and stability ratio. Also, addressed is the effect of the internal pressure on the vibration characteristics of the tube.

• Transactions of the Korean Society of Mechanical Engineers
• /
• v.19 no.3
• /
• pp.731-740
• /
• 1995

The objective of this paper is to develop defect assessment technology for integrity evaluation of CANDU pressure tubes. In fracture mechanics analysis, three-dimensional and two-dimensional (line-spring model) finite element analyses were performed to obtain the stress intensity factor for axial and circumferential surface cracks. In leak before break (LBB) analysis, heat transfer analyses for through-wall cracks were performed by considering the cooling effect and the LBB application time was computed. It was shown that the analytical results obtained in this study provide less-conservative but accurate solution for defect assessment of CANDU pressure tubes.

• Computers and Concrete
• /
• v.5 no.3
• /
• pp.195-216
• /
• 2008

This paper presents a new hypoelasticity model which was implemented in a nonlinear finite element formulation to analyze reinforced concrete (RC) structures. The model includes a new hypoelasticity constitutive relationship utilizing the rotation of material axis through successive iterations. The model can account for high nonlinearity of the stress-strain behavior of the concrete in the pre-peak regime, the softening behavior of the concrete in the post-peak regime and the irrecoverable volume dilatation at high levels of compressive load. This research introduces the modified version of the common application orthotropic stress-strain relation developed by Darwin and Pecknold. It is endeavored not to violate the principal of "simplicity" by improvement of the "capability" The results of analyses of experimental reinforced concrete walls are presented to confirm the abilities of the proposed relationships.

• Proceedings of the Korean Institute of Building Construction Conference
• /
• 2006.11a
• /
• pp.43-46
• /
• 2006

The Hwangtoh is one of the traditional construction material used in wall, plastering material, and ondol (Korean underfloor heating system) with stone and wood. It is an important greenness material and it has much advantages such as; high storage of heat, auto-purification, antibiotic ability, and emission of far infrared rays. But, it is not developed and not used in modern construction because of its low strength and properties of dry shrinkage crack. According to the recent researches and studies, it is evaluated for natural pozzolanic material like flyash or pozzolan. It's possibility on construction material is high because it's chemical and mineralogical proportion is like as Metakaolin and Kaolinite. In this point of view, this study aims to analyze the physical properties on Hwangtoh mortar through an experiment with various activation condition of Hwangtoh, which is natural pozzolanic material, for the purpose of increase the using possibility in construction material.

• Journal of Ocean Engineering and Technology
• /
• v.17 no.2
• /
• pp.34-39
• /
• 2003

Recent deepwater offshore structures in the Gulf of Mexico utilize butt welded tubular joints. Application of a welded tubular joint includes tendons, production risers, and steel catenary risers. Fatigue life assessment of these joints becomes more critical, as the structures to which they are attached are allowed to undergo cyclic and sometimes large displacements around an anchored position. Estimation of the fatigue behavior of these tubular members in the design stage is generally condrcted by using S-N curves, as specified in the codeds and standards. Applying the stress concentration factor of the welded structure to the S-N approach often results in a very conservative assessment, because the stress field acting on the tubular has a non-uniform distribution through the thickness. Fatigue life analysis using fracture mechanics has been applied in the design of the catenary risers. This technology enables the engineer to establish proper requirements on weld quality and inspection acceptance criteria to assure satisfactory structural integrity during its design life. It also provides guidance on proper design curves and a methodology for accounting for the effects of non-uniform stress distribution through the wall thickness. Still, there is inconsistency when designing tubular joints using a conventional S-N approach and when specifying weld flaw acceptance criteria using fracture mechanics approach. This study developed fatigue curves that are consistent with both the S-N approach and the fracture mechanics approach. Accounting for non-uniform stress distribution and threshold stress intensity factor were key parameters in relating both approaches. A series of S-N curves, generated from the fracture mechanics approach, were compared to the existing S-N curves. For flat plate butt joint, the S-N curve generated from fracture mechanics matches with the IIW class 100 curve when initial crack depth was 0.5 mm (0.02 ). The new curves for tubular joint agree very well with the experimental results. The comparison also indicated the degree of conservatism built into the API X design curve.