• Transactions of the Korean Society of Mechanical Engineers A
• /
• v.34 no.9
• /
• pp.1257-1263
• /
• 2010

The naval structure exposes to environmental vibration of shafted propeller propulsion and engine vibration. The shipboard equipments are developed compliance to MIL-STD-167-1A. For this purpose, vibration fatigue life of shipboard equipment for long lives should be estimate via an analytical approach and vibration test. In this paper, High cycle fatigue strength of cast aluminum alloy A356 using shipboard equipment was evaluated by 14 S-N method. The stress applied on the structure is evaluated by an analytical method(frequency response analysis with sinusoidal input and a fatigue evaluation) to simulate a MIL-STD-167-1A test. The frequency with the maximum equivalent stress is shown by Max. test frequency and the vibration fatigue life of shipboard equipment was estimated by Miner's rule.

• Environmental Analysis Health and Toxicology
• /
• v.13 no.3_4
• /
• pp.133-142
• /
• 1998

Effects of phosphorous (P) and methylglyoxal (MG) on the cell number, dry weight, chlorophyll content, photosynthetic and respiratory rate, phosphate uptake and protein content of green algae (Scenedesrnus obliquus) were studied. The algal cell number from the medium treated with 0.5-1.0 mM of MG at 1/2 P or 1/4 P concentration was significantly lower than those of algae treated :with full strength of phosphrous in medium. The inhibitory effect of MG on algal cell division was enhenced at low concentration of phosphorous in medium. At the beginning of logrithmic phase of algal growth, the mean dry weight of algae from the medium without MG-treatment in 1/2 P media was significantly higher than that of algae treated with MG. After logrithmic phase of growth cycle, the mean dry weight of algae from the medium with 1.0 mM of MG-treatment in 1/4 P media was significantly lower than that of algae treated with or without MG. At logrithmic phase of algal growth, there were significant differences in the chlorophyll content among all groups of tested algae with various concentrations of P and MG. At 15 days after inoculation, the mean chlorophyll content per algal cell from the media without MG-treatment in 1/2P was significantly higher than that of other cells from MG-treated media. The adverse effect of MG at concentration of 0.5-1.0mM in 1/2 and 1/4 P media on photosynthetic rate was observed. The mean photosynthetic rate of algal cell without P and MG treatment at 15 days after inoculation was significantly higher than that of MGtreated algae. After logarithmic phase, the algal cell treated with 0.5mM of MG with full strength of phosphorous showed significantly high respiratory rate than that of other cell groups. There were significant differences in mean phosphate uptake rate among all groups of Scenedesmus obliquus at logarithmic phase. At 12 days after inoculation, phosphate uptake rate per each algal cell from the basic media without MG and P treatment was rapidly reduced which shows early introduction to stationary phase.

• Transactions of the Korean Society of Mechanical Engineers A
• /
• v.33 no.7
• /
• pp.629-636
• /
• 2009

Mechanical stimulation is known to play a vital role on the differentiation of mesenchymal stem cells (MSCs) to pre-osteoblasts. In this research, we developed a tensile cell stimulator, composed of a DC motor-driven actuator and LVDT sensor for measuring linear displacement, to study the effects of tensile stress on osteogenic differentiation of MSCs. First, we demonstrated the reliability of this device by showing the uniform strain field in the silicon substrate. Secondly, we investigated the effects of tensile stretching on osteogenic differentiation. We imposed a pre-set cyclic strain at a fixed frequency on cell monolayer cultured on a flexible silicon substrate while varying its amplitude and duration. 60 min of resting period was allowed between 30 min of cyclic stretching and this cycle is repeated up to 7 days. Under the combined stimulation with osteogenic media and mechanical stretching, the osteogenic markers such as alkaline phosphatase (ALP), osterix, and osteopontin began to get expressed as early as 4 days of stimulation, which is much shorter than what is typically required for osteogenic media induced differentiation. Moreover, different markers were induced at different magnitudes of the applied strains. Lastly, for the case of ALP, we observed the antagonistic effects of osteogenic media when combined with mechanical stretching.

• Journal of the Korean Solar Energy Society
• /
• v.38 no.1
• /
• pp.45-55
• /
• 2018

Environmentally benign lead-free solder coated ribbon (e. g. SnCu, SnZn, SnBi${\cdots}$) has been intensively studied to interconnect cells without lead mixed ribbon (e. g. SnPb) in the crystalline silicon(c-Si) photovoltaic modules. However, high melting point (> $200^{\circ}C$) of non-lead based solder provokes increased thermo-mechanical stress during its soldering process, which causes early degradation of PV module with it. Hence, we proposed low-temperature conductive paste (CP) based tabbing method for lead-free ribbon. Modules, interconnected by the lead-free solder (SnCu) employing CP approach, exhibits similar output without increased resistivity losses at initial condition, in comparison with traditional high temperature soldering method. Moreover, 400 cycles (2,000 hour) of thermal cycle test reveals that the module integrated by CP approach withstands thermo-mechanical stress. Furthermore, this approach guarantees strong mechanical adhesion (peel strength of ~ 2 N) between cell and lead-free ribbons. Therefore, the CP based tabbing process for lead free ribbons enables to interconnect cells in c-Si PV module, without deteriorating its performance.

• Transactions of the Korean hydrogen and new energy society
• /
• v.30 no.6
• /
• pp.531-539
• /
• 2019

The development of cost-effective electrocatalysts with high durability is one of the most important challenges for the commercialization of polymer electrolyte fuel cells (PEFCs). The durability of the electrocatalyst has been studied in terms of structural change in the active metal and the support. In particular, in fuel cell vehicles, degradation of the carbon-based support is known to have a significant effect on the electrocatalyst deterioration since the start-up/shut-down cycle is frequently repeated. The requirements for the support of the electrocatalyst include high surface area, electrical conductivity, chemical stability, and so on. In this study, we propose the evaluation methods for choosing better support materials and present the physicochemical properties that promising carbon supports should have. Three kinds of carbon materials with different crystallinity are compared. From in-depth study using X-ray diffraction, Raman spectroscopy, thermogravimetric analysis, and accelerated stress test, it is clearly confirmed that the durability of carbon-supported electrocatalysts is closely related to the physicochemical properties of the carbon supports.

• Korean Chemical Engineering Research
• /
• v.56 no.2
• /
• pp.151-155
• /
• 2018

Degree of membrane degradation in Proton Exchange Membrane Fuel Cells (PEMFC) is mainly evaluated by the hydrogen crossover current density. The hydrogen crossover current density is measured by linear sweep voltammetry (LSV), which differs from the DOE protocol and the NEDO protocol. In this study, two protocols were compared during PEMFC operation and accelerated stress test. In the LSV method by the DOE method, the scan rate change affects the hydrogen crossover current density, but the NEDO method does not affect the hydrogen crossover current density. In the course of 15,000 cycles of polymer membrane wet/dry cycle, the DOE method was sensitive to membrane degradation, but the NEDO method was less sensitive to membrane degradation than the DOE method.

• Journal of the Korean Society of Safety
• /
• v.29 no.4
• /
• pp.9-14
• /
• 2014

Self-piercing riveting(SPR) is a mechanical fastening technique which is put pressure on the rivet for joining the sheets. Unlike a spot welding, SPR joining does not make the harmful gas and $CO_2$ and needs less energy consumption. In this study, static and fatigue tests were conducted using tensile-shear specimens with Al-5052 plates for evaluation of fatigue strength of the SPR joints. During SPR joining process for the specimen, using the current sheet thickness and a rivet, the optimal applied punching force was found to be 21 kN. And, the maximum static strength of the specimen produced at the optimal punching force was 3430 N. During the fatigue tests for the specimens, interface failure mode occurred on the top substrate close to the rivet head in the most high-loading range region, but on the bottom substrate close to the rivet tail in the low -loading range region. There was a relationship between applied load amplitude $P_{amp}$ and lifetime of cycle N for the tensile-shear, $P_{amp}=3395.5{\times}N^{-0.078}$. Using the stress-strain curve of the Al-5052 from tensile test, the simulations for fatigue specimens have been carried out using the implicit finite element code ABAQUS. The relation between von-Mises equivalent stress amplitude and number of cycles was found to be ${\sigma}_{eq}=514.7{\times}N^{-0.033}$.

• Journal of Korean Tunnelling and Underground Space Association
• /
• v.12 no.5
• /
• pp.399-405
• /
• 2010

The accumulated displacements and fatigues of rock are increased by the stress-hysteresis, induced from repeated frost-thawing. Also the shear strength is decreased by them continuously. The stress-hysteresis is affected by the atmospheric temperature changes, whose behavior is visco-elasticity, usually. Therefore, to do ideal body analysis, Kelvin model could be used to analyze the frost-thawing behavior in winter. In general, rock slope failure occurs by the deterioration of rocks, which is caused by the repetition of freezing-thawing process. In order to keep the safety of such rock mass structures the deterioration process of rock needs to be described quantitatively using some meaningful parameters. In this work, the deterioration process in freezing-thawing cycle of tuff, which is a famous soft porous rock, is investigated through laboratory tests and successfully described as a differential equation for the change of porosity. And then, the deterioration of the mechanical properties of rock, such as Young's modulus and uniaxial compressive strength, are quantitatively described as a function of the porosity.

• Journal of Korean Society on Water Environment
• /
• v.39 no.6
• /
• pp.433-438
• /
• 2023

This study investigated the growth and metabolic characteristics of Arthrospira platensis (A. platensis) according to pH, which has an alkaline optimal pH. The intake of inorganic carbon was expected to be the highest at the optimum pH 9, but it was different from the expectation, so the cause of the excessive intake of inorganic carbon at pH 7 was investigated. We tried to verify the triacylglycerol (TAG) synthesis metabolic mechanism because it was assumedthat the inorganic carbon intake of A. platensis according to pH is closely related to lipid production inside the cell. To verify this, the effects of pH on inorganic carbon intake were examined through lipid analysis inthe cell of A. platensis according to pH. As a result, in the case of the effect of inorganic carbon intake of A. platensis according to pH on TAG content, pH 9 and pH 11 showed no significant difference in TAG content, but at pH 7, it was two times higher compared to pH 9 and pH 11. It was assumed that the reason why A. platensis excessively consumed inorganic carbon at pH 7 was because itincreased the TAG content in proportion to the intake of inorganic carbon to protect cells from external pH stress. In addition, it is considered that the TAG content produced in proportion to the intake of inorganic carbon is because acetyl-CoA produced in the Calvin cycle is required for the synthesis of TAG.

• Journal of the Microelectronics and Packaging Society
• /
• v.10 no.4
• /
• pp.1-8
• /
• 2003

Thermo-mechanical behavior of a ceramic ball grid array (CBGA) package assembly are characterized by high sensitive moire interferometry. Moir fringe patterns are recorded and analyzed at various temperatures in a temperature cycle. Thermal-history dependent analyses of global and local deformations are presented, and bending deformation (warpage) of the package and shear strain in the rightmost solder ball are discussed. A significant non-linear global behavior is documented due to stress relaxation at high temperature. Analysis of the solder interconnections reveals that inelastic deformation accumulates on only eutectic solder fillet region at high temperatures.