• International Journal of Automotive Technology
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• v.5 no.3
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• pp.215-219
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• 2004

A vehicle structure needs to be more precisely analyzed because of complexities and varieties. Structural fatigue which is generated by fluctuations of stresses during the service life of a mechanical system is the primary concern in the structural design for safety. A fatigue life is difficult to obtain in structural components during the service life of mechanical systems since the fluctuating stress contributes to fatigue. This study introduces new procedures to measure the lethargy coefficient and to predict the fatigue life of a mechanical structure by using molecular dynamic simulation. A lethargy coefficient is the total defect-estimating coefficient, which was obtained by using the results of a simple tensile test in this study. With this lethargy coefficient, fatigue life was estimated. The proposed method will be useful in predicting the fatigue life of a structurally-modified vehicle design. The effectiveness of the proposed method using lethargy coefficient measurement to predict the fatigue life of a structure was examined by applying this method to predict the fatigue life of SS41 steel, used extensively as material of vehicle structures. Two types of specimen such as pre-cracked plate and simple plate is discussed. equation of fatigue life using the lethargy coefficient and failure time, both obtained from a simple tensile test, will be useful in engineering. This measurement and prediction technology will be extended for use in analysis of any geometric shapes of modified automotive structures.

• Journal of Families and Better Life
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• v.33 no.5
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• pp.1-24
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• 2015

The purpose of this study was to investigate the effects of Engel coefficient, Angel coefficient and Schwabe index influencing Household head's life satisfaction. For this study, the data from the 8th analysis of the 2013 Korea Welfare Panel Survey conducted by Korea Institute for Health and Social Affairs were used. For the sample, 903 male Household heads with children under the age of 18, were selected. For statistical analysis, SPSS program (Ver. 21.0) was used. And for statistical methods, frequency and percentile, mean and standard deviation, Pearson's correlation, one way analysis of variance, Duncan's multiple range tests, multiple regression analysis were used. The findings are as follows. First, as a results of analyzing the food costs, education costs and housing costs depending on Income Quintile, the food costs and education costs in the 5th Income Quintile compared with other Income Quintile, were highest. Also, the highest housing cost was in the 2nd Income Quintile, while the least housing cost was in the 1st Income Quintile. Second, by analyzing the differences of Engel coefficient, Angel coefficient and Schwabe index according to Income Quintile, the results show that Engel coefficient and Schwabe index decreases as Income Quintile increases, and Angel coefficient increases as Income Quintile becomes higher. Third, the level of HH's life satisfaction according to Income Quintile, 1st Income Quintile, 2nd Income Quintile, 4th Income Quintile, 3rd Income Quintile, 5th Income Quintile in order, increased. Fourth, as the result of analyzing the influence of Variables related to household and demographics about Engel coefficient, Angel coefficient and Schwabe index, it was shown that the variables effecting Engel coefficient, Angel coefficient, and Schwabe index are age, occupations, Number of workers, House ownership, Income Quintile. Fifth, As a result of analyzing the Variables effecting life satisfaction, especially while Schwabe index is not that significant, Engel coefficient and Angel coefficient are shown to have a significant influence. Therefore, the influence of Food costs and education costs can be confirmed.

• Journal of the Korean Society for Precision Engineering
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• v.20 no.7
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• pp.26-35
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• 2003

This study explains the effects of lubricant and surface treatment on hot forging die life. The mechanical and thermal load, and thermal softening which is happened by the high temperature of die, in hot and warm forging, cause die wear, heat checking and plastic deformation, etc. This study is fur the effects of solid lubricants and surface treatment condition for hot forging die. Because cooling effect and low friction are essential to the long life of dies, optimal surface treatment and lubricant are very important to improve die life for hot forging process. The main factors, which affect die hardness and heat transfer, are surface treatments and lubricants, which are related to thermal diffusion coefficient and heat transfer coefficient, etc. For verifying these effects, experiments are performed for hot ring compression test and heat transfer coefficient in various conditions as like different initial billet temperatures and different loads. The effects of lubricant and surface treatment for hot forging die life are explained by their thermal characteristics. The new developed technique in this study for predicting tool life can give more feasible means to improve the tool life in hot forging process.

• Transactions of the Korean Society of Machine Tool Engineers
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• v.12 no.1
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• pp.32-37
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• 2003

Evaluation of fatigue strength on the spot welded part is very important for strength design of spot welded steel structures. In this paper, we could get the life cycle of the spot welded part using the lethargy coefficient obtained through the quasi-static tensile shear test for the specimen welded by current 10kA. The reliability evaluation of the life cycle is completed by comparing the life cycle calculated under the constant loading rate with the life cycle obtained by dynamic fatigue test. And then the result calculated by the lethargy coefficient is verified through the lift cycle calculated using the dynamic final tensile stress formula under the increased loading speed. This way can make save the time and cost in processing of predicting the life cycle of a structure.

• Proceedings of the Korean Institute of Building Construction Conference
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• 2017.05a
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• pp.15-16
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• 2017

The properties of concrete damaged by fire change according to the temperature. Diffusion coefficient of chloride ion also can change which affect the life expectation under salt circumstance. Diffusion coefficient was measured by NT BUILD 492 using the concrete specimen damaged by high temperature. FEM analysis was performed to predict the life expectancy which can help to diagnose the concrete diagnose and to design maintenance strategy.

• Journal of the Society of Disaster Information
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• v.11 no.4
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• pp.548-555
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• 2015

This paper aims to estimate the service life of the target bridge structures subjected to chloride ingress from de-icer, which is used for safety of vehicles in winter, by investigating the chloride ingress into concrete. In this study, the 10-year-old bridge structures were investigated by measuring the chloride along the depth from the exposed surface to derive the surface chloride concentration and the diffusion coefficient for the prediction of service life. The service life of each measured point on the structures were estimated with the surface chloride concentration and the diffusion coefficient by using Life-365 software. As a result, it was estimated for all measured points to have over 100-year service life. Furthermore, the diffusion coefficient and the service life from the measured data were compared to another method calculated with the concrete mix, considering the time dependency of diffusion coefficient.

• Tribology and Lubricants
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• v.14 no.2
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• pp.35-41
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• 1998

The $WS_2$ solid lubricant synthesized through the vapour phase transport method was coated on the commercial bearing steel (SUJ 2) substrate, and the tribological behaviour of the lubricant was investigated using a ball-on-disk type tester. The $WS_2$ powder was spray-coated at room temperature using compressed air, and the change of friction coefficient was examined in various conditions, i.e., specimen configuration, atmosphere (air and nitrogen), applied load and rotating speed. $WS_2$ coated ball and disk showed the optimum friction coefficient of 0.07 and wear life of 45,000 cycles in the nitrogen atmosphere under 0.3 kgf and 100 rpm, whereas relatively high coefficient of 0.13 and reduced wear life of 4,000 cycles were observed in air atmosphere. The effect of rotating speed on the friction coefficient was not observed both in nitrogen and in air atmospheres. This confirmed that the spray-coated $WS_2$ solid lubricant was effective in reducing the friction coefficient and improving wear life in nitrogen atmosphere, and the oxygen and moisture existing in air could seriously deteriorate the lubrication effect of $WS_2$ coating layer.

• Journal of the Korea Concrete Institute
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• v.21 no.3
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• pp.377-386
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• 2009

A reference diffusion coefficient model from ACI life-365 is drawn from test results by NT build 443. This test method gives a time-averaged diffusion coefficient during immersion period, thus the ACI model uses the time-averaged diffusion coefficient as a reference value. ACI model needs to be revised, considering the difference between the time-average value and reference value at specified time. In this study, firstly the analytic solutions of diffusion equation are derived considering the initiation time and period of exposure to chloride, and secondly the time-averaged diffusion coefficient from NT build 443 is converted into the diffusion coefficient at reference time. From this study, the reference diffusion coefficient of ACI model should be modified to be about 10% larger values than those of present ACI model. For convenient design of service life, previous relationship between the chloride diffusion coefficient from NT build 443 and that from NT build 492 is also modified. To compare the chloride diffusion coefficients of ACI and JCI models, the reference chloride diffusion coefficient with respect to the JCI model is drawn in the similar form of ACI model's, and service life prediction by ACI life-365 method is confirmed to give a conservative result.

• Journal of the Korean Recycled Construction Resources Institute
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• v.4 no.3
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• pp.259-268
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• 2016

The service life evaluation in RC(Reinforced Concrete) structure exposed to chloride attack can be classified into deterministic and probabilistic method, and it significantly varies with design parameters. The present work derives PDF (Probability of Durability Failure) and the related service life considering time-dependent diffusion coefficient and internal parameters such as reference diffusion coefficient, critical chloride content, and time-exponent. When critical chloride content increases to 133.3%, the changing ratios of service life are 134.0~145.4% for deterministic method and 149.2%~152.5% for probabilistic method, respectively. In the case of increasing time-exponent to 200%, they increase to 323.8% for deterministic method and 346.0% for probabilistic method. Through adopting time-diffusion coefficient for probabilistic method, reasonable service life evaluation can be achieved, and it is also verified that increasing time-exponent through mineral admixture is very effective to extension of service life in RC structure.

• Computers and Concrete
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• v.15 no.3
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• pp.461-471
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• 2015

The permeability is the most direct indicator to reflect the durability of concrete, and the testing methods based on external electric field can be used to evaluate concrete permeability rapidly. This study aims to use an experiment method to accurately predict the permeability of concrete box beam during service. The ion migration experiments and concrete surface resistivity are measured to evaluate permeability of five concrete box beams, and the relations between these results in service concrete and electric flux after 6 hours by ASTM C1202 in the laboratory are analyzed. The chloride diffusion coefficient of concrete, concrete surface resistivity and concrete 6 hours charge have good correlation relationship, which denote that the chloride diffusion coefficient and the surface resistivity of concrete are effective for evaluating the durability of concrete structures. The chloride diffusion coefficient of concrete is directly evaluated permeability of concrete box beam in service and may be used to predict the service life, which is fit to engineering applications and the concrete box beam is non-destructive. The concrete surface resistivity is easier available than the chloride diffusion coefficient, but it is directly not used to calculate the service life. Therefore the mathematical relation of the concrete surface resistivity and the concrete chloride diffusion coefficient need to be found, which the service life of reinforced concrete is obtained by the concrete surface resistivity.