• Transactions of the Korean Society of Mechanical Engineers A
• /
• v.35 no.10
• /
• pp.1179-1185
• /
• 2011

Cold and hot-rolled carbon steel sheets are commonly used in railroad cars or commercial vehicles such as the automobile. The sheets used in these applications are mainly fabricated by spot welding, which is a type of electric resistance welding. However, the fatigue strength of a spot-welded joint is lower than that of the base metal because of high stress concentration at the nugget edge of the spot-welded part. In particular, the fatigue strength of the joint is influenced by not only geometrical and mechanical factors but also the welding conditions for the spot-welded joint. Therefore, there is a need for establishing a reasonable criterion for a long-life design for spot-welded structures. In this thesis, ${\Delta}P-N_f$ relation curves have been used to determine a long-life fatigue-design criterion for thin-sheet structures. However, as these curves vary under the influence of welding conditions, mechanical conditions, geometrical factors, etc. It is very difficult to systematically determine a fatigue-design criterion on the basis of these curves. Therefore, in order to eliminate such problems, the welding residual stresses generated during welding and the stress distributions around the weld generated by external forces were numerically and experimentally analyzed on the basis of the results, reassessed fatigue strength of gas welded joints.

• Journal of Energy Engineering
• /
• v.25 no.4
• /
• pp.198-206
• /
• 2016

Fuel economy label will be used as a national indicator in energy management, leading to the development of car technology manufacturer and plays a role in providing consumer vehicle purchase information. But the government's fuel economy label is continued consumer complaint is different and diminishing fuel economy were introduced by the government to measure the exact fuel economy label than resetting the 5-cycle test method in the US for the domestic vehicle standards. Originally two test mode in order to reduce the impact of the sharp increase in the resources required but methods of calculating a measured result value by driving all of the five test mode a variety of environmental conditions and the running pattern is reflected to the fuel economy label (city( FTP-75 mode), highway(HWFET mode)) and using 5-cycle correction formula for calculating a fuel consumption value and the equivalent value to calculate the result of the 5-cycle test. The compensation was calculated expression 30s, 5-Cycle Test Method of vehicles in 2011 was considered necessary to review the existing 5-cycle correction formula for the New Type car due to the recent rapid development of automotive technology. In this study, recent technology is targeting 14 units New Type car applied over the same test method and the existing check test mode specific fuel economy properties and, as a result of analyzing the corrected expression differences that have already been developed with the existing test vehicle resulting large did not show the difference was found to correction formula also not getting the existing fuel correction expression significant effect on the improvement of the current automobile technology as a maximum error of less than 1.5%.

• Journal of the Korean Society for Nondestructive Testing
• /
• v.24 no.3
• /
• pp.259-267
• /
• 2004

A finite element method is used to simulate interaction of laser-based ultrasounds with surface breaking tracks in elastic media. The laser line source focused on the surface of semi-infinite medium is modeled as a shear dipole in 2-D plane strain finite elements. The shear dipole-finite clement model is found to give correct directivity patterns for generated longitudinal and shear waves. The interaction of surface waves with surface breaking cracks (2-D machined slot) is considered in two ways. Both the source and receiver are fixed with respect to the cracks in the first case, while the source is moving in another case. It is shown that the crack depth tested in the range of 0.3-5.0mm $({\lambda}_R/d=0.21{\sim}3.45)$ can be measured using the corner reflected waves produced by the fixed laser source. The moving laser source is found to cause a large amplitude change of reflected waves near crack, and the crack whose depth is one order lower than the wavelength ran be detected from this change.

• Journal of environmental and Sanitary engineering
• /
• v.7 no.2
• /
• pp.95-110
• /
• 1992

Much progress has been made in understanding the subcellular events of the human lung injuries after acute exposure to environmental air pollutants. Host of those events represent oxidative damages mediated by reactive oxygen species such as superoxide, hydrogen peroxide, and the hydroxy, free radical. Recently, nitric oxide (NO) was found to be endogenously produced by endothelial cells and cells of the reticulo-endothelial system as endothelialderived relaxation factor (EDRF) which is a vasoactive and neurotransmitter substance. Together with superoxide, NO can form another strong oxidant, peroxonitrite. The relative importance of exogenous sources of $N0/N0_2$ and endogenous production of NO by the EDRF producing enzymes in the oxidative stresses to the heman lung has to be elucidated. The exact events leading to chronic irreversible damage are still yet to be known. From chronic exposure to oxidant gases, progressive epithelial and interstitial damages develop. Type I epithelial cells become thicker and cover a smaller average alveolar surface area while thee II cells proliferate instead. Under acute damages, the extent of loss of the alveolar epithelial cell lining, especially type II cells appears to be a good predictor of the ensuing irreversible damage to alveolar compartment. Interstitial matrix undergo remodeling during chronic exposure with increased collagen fibers and interstitial fibroblasts. However, Inany of these changes can be reversed after cessation of exposure. Among chronic lung injuries, genetic damages and repair responses received particular attention in view of the known increased lung cancer risks from exposure to several air pollutants. Heavy metals from foundry emission, automobile traffics, and total suspended particulate, especially polycystic aromatic hydrocarbons have been positively linked with the development of lung cancer. Asbestos in another air pollutant with known risk of lung cancer and mesothelioma, but asbestos fibers are nonauthentic in most bioassays. Studies using the electron spin resonance spin trapping method show that the presence of iron in asbestos accelerates the production of the hydroxy, radical in vitro. Interactions of these reactive oxygen species with particular cellular components and disruption of cell defense mechanisms still await further studies to elucidate the carcinogenic potential of asbestos fibers of different size and chemical composition. The distribution of inhaled pollutants and the magnitude of their eventual effects on the respiratory tract are determined by pollutant-independent physical factors such as anatomy of the respiratory tract and level and pattern of breathing, as well as by pollutant-specific phyco-chemical factors such as the reactivity, solubility, and diffusivity of the foreign gas in mucus, blood and tissue. Many of these individual factors determining dose can be quantified in vitro. However, mathematical models based on these factors should be validated for its integrity by using data from intact human lungs.

• Transactions of the Korean Society of Mechanical Engineers A
• /
• v.34 no.9
• /
• pp.1137-1143
• /
• 2010

This paper presents a fatigue design method for plug- and ring-type gas-welded joints, which takes into account the effects of welding residual stress. To develop this method, we simulated the gas-welding process by performing nonlinear finite element analysis (FEA) To validate the FEA results, numerically calculated residual stresses in the gas welds were then compared with experimental results obtained by the hole-drilling method. To evaluate the fatigue strength of plug- and ring-type gas-welded joints influenced by welding residual stresses, the use of stress amplitude $(\sigma_a)_R$, which includes the welding residual stress in gas welds, is proposed $(\sigma_a)_R$ on the basis of a modified Goodman equation that includes the residual stress effects. Using the stress amplitude $(\sigma_a)_R$ at the hot spot point of gas weld, the relations obtained as the fatigue test results for plug and ring type gas welded joints having various dimensions and shapes were systematically rearranged to obtain the $(\sigma_a)_R-N_f$ relationship. It was found that more systematic and accurate evaluation of the fatigue strength of plug- and ring-type gas-welded joints can be achieved by using $(\sigma_a)_R$.

• Journal of the Korea Academia-Industrial cooperation Society
• /
• v.17 no.8
• /
• pp.62-68
• /
• 2016

The feeder cable assembly is an automotive part used for telecommunication. If it malfunctions, the control and safety of the automobile can be put at risk. ALT (Accelerated Life Testing) is a testing process for products in which they are subjected to conditions (stress, strain, temperatures, etc.) in excess of their normal service parameters in an attempt to uncover faults and potential modes of failure in a short amount of time. Failure is caused by defects in the design, process, quality, or application of the part, and these defects are the underlying causes of failure or which initiate a process leading to failure. Thermal shock occurs when a thermal gradient causes different parts of an object to expand by different amounts. Thermal shock testing is performed to determine the ability of parts and components to withstand sudden changes in temperature. In this research, the main causes of failure of the feeder cable assembly were snapping, shorting and electro-pressure resistance failure. Using the Coffin-Manson model for ALT, the normal conditions were from Tmax = $80^{\circ}C$ to Tmin = $-40^{\circ}C$, the accelerated testing conditions were from Tmax = $120^{\circ}C$ to Tmin = $-60^{\circ}C$, the AF (Acceleration Factor) was 2.25 and the testing time was reduced from 1,000 cycles to 444 cycles. Using the Bxlife test, the number of samples was 5, the required life was B0.04%.10years, in the acceleration condition, 747 cycles were obtained. After the thermal shock test under different conditions, the feeder cable assembly was examined by a network analyzer and compared with the Weibull distribution modulus parameter. The results obtained showed good results in acceleration life test mode. For the same reliability rate, the testing time was decreased by a quarter using ALT.

• Journal of the Korea Academia-Industrial cooperation Society
• /
• v.21 no.9
• /
• pp.405-413
• /
• 2020

The normal stress of cement paste measured under squeeze flow is divided into an elastic solid region at strains between 0.0003 and 0.003 and a strain-hardening region at strains of 0.003 and 0.8. A modeling equation at the strain-hardening region was proposed. First, from the viewpoint of fluid behavior, the power-law non-Newtonian fluid model, with a power-law consistency (m) of 700 and a power index (n) of 0.2, was applied. The results showed good agreement with the experimental results except for an elastic solid region. Second, from the viewpoint of ductile yielding solid behavior, the force balance model was applied, and the friction coefficient between the sensor part measuring the load and the surface of the cement paste was derived as a polynomial of the normal strain by applying the half-interval search method to the experimental data. The results showed good agreement with the experimental results only in the middle normal strain region at strains between 0.003 and 0.3. The rheological behavior of the cement paste under squeeze flow was more consistent with the experimental results from the viewpoint of power-law non-Newtonian fluid behavior than from the viewpoint of ductile yielding solid behavior in the strain-hardening region.

• Journal of the Korea institute for structural maintenance and inspection
• /
• v.21 no.6
• /
• pp.44-51
• /
• 2017

Recently, the parking in downtown area has caused severe problem due to the dramatic increase of possessing automobile in the country. A parking structure has been on the spotlight to solve the parking problem in downtown area. However, the overall height of parking structure is stipulated less than 8 m. Therefore, in this research, 'wide composite beam', which is possible for reducing story height and having long span, is developed and the flexural capacity of the wide composite beam is evaluated. Based on the result of the flexural test, the flexural strength of wide composite beam increased by 20% as the thickness of steel beam increased by 3 mm ($6mm{\rightarrow}9mm$) The shapes of rebar (whether it is triangle or rectangular shape) in the wide composite beam did not affect its flexural strength. The flexural strength of wide composite beam without rebar decreased by 10% compared to that of wide composite beam with rebar. In addition, the neutral axis moved upward as a load increased, but the neutral axis moved downward, when the load exceeded a certain level of load.

• Journal of the Korean Applied Science and Technology
• /
• v.33 no.4
• /
• pp.824-835
• /
• 2016

Although the number of registered cars in South Korea is above 21million and one family has about 1.07 cars, there is no national standard for automobile reference fuel in South Korea. Reference fuel is the fuel used for certificating vehicle performance, emissions and fuel economy. Now, domestic market fuels are used as reference fuel. However, the quality of domestic market fuel is constantly changing by seasonal and fuel manufacturers. It may effect vehicle performance, emissions and fuel efficiency test result. On this study, market fuel quality was monitored and reference fuel standard(draft) was set by reflecting market fuel monitoring result. Reference fuel standard(draft) was applied to GDI and MPI engine. As a result, the difference of fuel economy between fuels meeting the reference fuel standards(draft) was reduced to 1.1% while the difference of fuel economy between market fuels was 3.8%.

• Journal of the Korean Association of Geographic Information Studies
• /
• v.16 no.2
• /
• pp.1-15
• /
• 2013

It is important to empirically investigate the typological characteristics of subway station areas considering the comprehensive elements of transit-oriented development (TOD) planning so that its implementation can be effective in attaining both increase in transit ridership and decrease in inordinate automobile dependence. This article aims to identify diverse features of subway station areas in Seoul known for good public transit system. After collecting and manipulating the measures on planning elements such as density, diversity and accessibility for TOD planning by distance-based buffer from a subway station, the article tried to interpret analysis results on their typological characteristics. They can be summarized with two conclusions. First, characteristics of landuse and public transit system can be distinctly differentiated in the Seoul subway station areas. It implies that both planning elements should have not been integrated for now. Second, the characteristics of public transit system can be divided by modes. They provide us that public transit system in Seoul needs to be more strongly integrated than current system.