• Korean Journal of Metals and Materials
• /
• v.46 no.10
• /
• pp.652-661
• /
• 2008

Reduction of NOx in emission gas, improvement of engine efficiency, and extension of warranty period has made demands for developing materials more corrosively resistant to the inner-muffler environments or predicting the lifetime of materials used in muffler more precisely. The corrosion inside muffler has been explained with condensate corrosion mainly though thermal oxidation experiences prior to condensate corrosion. Hence, the aim of this study is to describe how the thermal oxidation affects the corrosion of stainless steel exposed to the inner-muffler environments. Auger electron spectroscopy and electrochemical tests were employed to analyze oxide scale and to evaluate corrosion resistance, respectively. Thermal oxidation has different role of condensate corrosion depending on the temperature: inhibiting condensate corrosion below $380^{\circ}C$ and enhancing condensate corrosion above $380^{\circ}C$. The low temperature oxidation causes to form compact oxide layer functioning a barrier for penetrating condensate into a matrix. Although though thermal oxidation caused chromium-depleted layer between oxide layer and matrix, the enhancement of the condensate corrosion in high temperature oxidation resulted from corrosion-induced crevice formed by oxide scale rather than corrosion in chromium-depleted layer. It was proved by aids of anodic polarization tests and measurements of pitting corrosion potentials. By the study, the role of high temperature oxidation layer affecting the condensate corrosion of stainless steels used as muffler materials was well understood.

• Journal of Korea Foundry Society
• /
• v.12 no.4
• /
• pp.305-316
• /
• 1992

Steel and iron castings made with expandable polystylene (referred to hereafter as EPS) patterns are often affected by distinctive defects associated with incomplete decomposition of the EPS as the molds are filled with metal. The effects of practical factors on carbon pick-up were investigated on the specimens, by taking successive layers of swarf and analysis, whereas the lustrous carbon is determined by using combustion analysis. The quality of the castings, with particular reference to carbon pick-up in low carbon steel and lustrous carbon on gray iron, is further influenced to a significant extent by such practical factors as reduced pressure, the pouring temperature, the density of EPS pattern, the additive in coating and in pattern and the casting thickness. The rate at which carbon pick-up and lustrous carbon deposites are formed can be reduced by reducing the density of the pattern and also reducing pressure, especially by adding $Na_2CO_3$ in coating and in pattern to promote $CO_2$ evolution. The upper parts of castings obtained using EPS patterns are slightly higher in carbon pick-up and in lustrous carbon than other parts.

• Transactions of Materials Processing
• /
• v.26 no.1
• /
• pp.48-54
• /
• 2017

The dissolution and precipitation of Nb, which has been known as strong carbide-forming element, play a key role in controlling phase transformation kinetics of microalloyed steels. In this study, we analyzed both numerically and experimentally the precipitation behavior of Nb-microalloyed steel and its effect on the austenite decomposition during cooling. Nb precipitation in austenite matrix could be predicted by the thermo-kinetic software MatCalc, in which interfacial energy between precipitate and matrix is calculated. The simulated precipitation kinetics fairly well agrees with the experimental observations by TEM. Austenite decomposition, which is strongly affected by Nb precipitation during cooling, was measured by dilatometry and was modeled on the basis of a Johnson-Mehl-Avrami-Kolmorgorov(JMAK) equation. It was confirmed that the dissolved Nb delays the austenite decomposition, whereas, the precipitated Nb accelerates phase transformation during the austenite decomposition.

• Journal of Korean Clinical Nursing Research
• /
• v.21 no.3
• /
• pp.309-318
• /
• 2015

Purpose: The purpose of this study was to examine the effects of foot mats on reducing levels of fatigue, discomfort, lower extremity edema and skin temperature in scrub nurses during surgery. Methods: This study employed one group repeated measures design in which 16 scrub nurses (ages 22-38) stood on steel footstools (SF) during scrub as the conventional test and stood on SF with foot mats as the experimental test. Levels of fatigue, discomfort, lower extremity edema and skin temperature were measured before the first surgical hand scrub and right after the first surgery of the day for 3 consecutive days in both tests. Results: The changes in levels of fatigue and discomfort were significantly different between tests (p<.001~.033). Edema, determined by the differences in circumferences of the ankles and calves before and after the surgery was also significantly different between groups (p=.001~.011). However, the change in skin temperature on the foot tops of both feet was not different between tests (p=.351~.467). Conclusion: The results of this study show that using foot mats on top of the steel footstool is effective in reducing the levels of fatigue, discomfort and lower extremity edema in scrub nurses during surgery.

• Proceedings of the Korean Society of Tribologists and Lubrication Engineers Conference
• /
• 1999.11a
• /
• pp.257-262
• /
• 1999

The economic loss arisen from the abrasion wear have been increasing at every industrial field. To reduce the economic loss we developed a new process, which is named MAHa process(Metallic Adhesives for HArdening). MAHa process is a process to weld tungsten carbide(WC) to the surface of a plain carbon steel so that it may stay longer under the severe abrasive environment. The depth of the WC layer ranges from 0.5 mm to 5 m. Compared with the conventional technology, arc-augmented welding which bonds WC on the flat surface only, MAHa process has the merits that it can make a robust WC layer on the round or wave- shaped surface also. How to turn the WC powder into a flexible mat is the key technology of the MAHa process. We invented new polymer materials to accomplish such a goal and both the MAHa process and the invented materials were applied for patents. For the application, the inner wall of elbow of Concrete Pump Truck(CPT) was maharized(MAHa process-treated) and the new WC layer on the inner wall was made successfully. The elbow was equipped to a CPT.

• Journal of the Korea Institute of Building Construction
• /
• v.9 no.2
• /
• pp.39-46
• /
• 2009

The erection bar is defined as the assistant bar used to fix the position of the reinforcing steel as the reinforcing steel is placed on site. As the erection bar do not bear the structural load and is not showed in the structural drawings, it is not managed importantly. But as chair bars in mat footing is used in large quantities to support the upper main bars, the detailing standards need to be suggested. and some erection bar is placed by experience of the fabricator and placer. Therefore, in this study, a survey about the erection bars was conducted to the reinforcement detailer, the fabricator and placer of domestic construction industry. 11 placing drawings is analyzed to find out the problems of detailing and the quantities of the erection bars. According to the analysis of the survey, the erection bar details in placing drawings were not standardized, and some erection bars are omitted in placing drawings. The improvement in the erection bar detailing was sought by analyzing the results of the survey.

• Steel and Composite Structures
• /
• v.44 no.1
• /
• pp.105-117
• /
• 2022

Impact resistance efficiency of the newly designed sandwich beam with a laterally arched core as bio-inspired by the woodpecker is numerically investigated. The principal components of the beam comprise a dual-core system sandwiched by the top and bottom laminated CFRP skins. Different materials, including hot melt adhesive, high-density polyethylene (HDPE), acrylonitrile butadiene styrene (ABS), epoxy resin (EPON862), aluminum (Al6061), and mild carbon steel (AISI1018), are considered for the side-arched core layer of the beam for impact efficiency assessment. The aluminum honeycomb takes the role of the second core. Contact force, stress, damage formation, and impact energy for beams equipped with different materials are examined. A diversity in performance superiority is noticed in each of these indicators for different core materials. Therefore, for overall performance appraisal, the impact resistance efficiency index, which covers several chief impact performance parameters, of each sandwich beam is computed and compared. The impact resistance efficiency index of the structure equipped with the AISI1018 core is found to be the highest, about 3-10 times greater than other specimens, thus demonstrating its efficacy as the optimal material for the bio-inspired dual-core sandwich beam system.

• Journal of the Korean Geosynthetics Society
• /
• v.13 no.4
• /
• pp.97-107
• /
• 2014

Finite element modelling and analysis were conducted for the roll-type steel mats which were placed on loose sand and subjected to a standard truck wheel load in this study. The roll-type steel mats mean that the steel mats can be folded as a circle shape for the carrying to fields in cold regions where workability is limited and are developed for a rapid rehabilitation method for roadway across soft ground which is caused by thawing during the summer season in cold regions. The model is composed of link elements to simulate nonlinear behavior of connections between steel mats, thick shell elements to have flexural stiffness of the steel mats, and springs to simulate characteristics of foundation soils. The structural behaviors of the shell, link elements, and springs were verified at each modelling step through experiment and analysis. Beam and shell analysis without the link elements were conducted and compared to results obtained from the model presented in this study. Significant vertical displacement is shown in the shell model with hinge connections. Therefore, the results demonstrate that the analysis model for the roll-type steel mats on loose sand needs further detail parametric studies.

• Proceedings of the Korea Concrete Institute Conference
• /
• 1999.10a
• /
• pp.333-336
• /
• 1999

The crack of concrete induced by the heat of hydration is a serious problem, particularly in concrete structures such as mat-slab of nuclear reactor buildings, dams or large footings, foundations of high rise buildings, etc.. As a result of the temperature rise and restriction condition of foundation, the thermal stress which may induce the cracks can occur. Therefore the various techniques of the thermal stress control in massive concrete have been widely used. One of them is prediction of the thermal stress, besides low-heat cement which mitigates the temperature rise, pre-cooling which lowers the initial temperature of fresh concrete with ice flake, pipe cooling which cools the temperature of concrete with flowing water, design change which considers steel bar reinforcement, operation control and so on. The Aim of this paper is to verify the effect of low heat blended cement in reducing thermal stress in slab type's mass concrete such as container harbor structures.

• Proceedings of the Korea Concrete Institute Conference
• /
• 2000.04a
• /
• pp.291-296
• /
• 2000

The crack of concrete induced by the heat of hydration is s serious problem, particularly in concrete structures such as bridge piers. thick walls, box type walls, mat-slab of nuclear reactor building, dams of foundations of high rise buildings, etc. As a result of the temperature rise and restriction condition of foundation, the thermal stress which way induce the cracks can occur. Therefore the various techniques of the thermal stress control in massive concrete have been widely used. One of them is prediction of the thermal stress, besides low-heat cement which mitigates the temperature rise, design change which consider steel bar reinforcement, operation control and so on. In this study, firstly it introduce the thermal cracks control technique by employing low-heat cement concrete, thermal stress analysis, Secondly it shows the application of the cracks control technique like the bottom of No.15,16 Underground LNG Tank in Inchon.