• 반도체디스플레이기술학회지
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• 제12권4호
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• pp.9-13
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• 2013

Lapping is a very complicated and random process resulting from the variation of abrasive grains in its sizes and shapes and from the numerous factors having an effect on the process quality. This paper presents a study of a $2^4$ full factorial experimental design and analysis to optimize surface quality in lapping operation. The optimization of the factors to obtain minimum surface roughness was carried out by incorporating effect plots, main effect plots, interaction plots, analysis of variance(ANOVA), surface plots, and contour plots. The statistical design experiments, designed to reduce the total number of experiments required, indicated that, within the selected conditions, all the parameters influenced at a significance level of 5%. In addition, some of the possible interactions between these parameters also influenced the lapping process, especially those that were of third order. A regression model was suggested and fitted the experimental data very well.

• Archives of Pharmacal Research
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• 제5권2호
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• pp.53-60
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• 1982

The mixing of salicylic acid and wheat starch powders was studied using a V-type mixer. After the optimum operating conditions of the mixer were examined, the mixing characteristics relating to dilution ratio, particle size of active ingradient and addition ratio of lubricants were investigated. The coefficient of variation was expressed by a power law relating to the dilution ratio and the particle size of active ingredient. Furthermore, the comparison of results with the theoretically estimated value of mixing index suggested that the mixing of cohesive pharmacceutical powders is a complex stochastic process and cannot be explained fully by a simple theory based on a complete random mixing.

• Structural Engineering and Mechanics
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• 제8권5호
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• pp.477-490
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• 1999

The uncertainties associated with structural parameters and dynamic loading are identified and discussed. Structural parametric uncertainties are treated as random variables and dynamic wind load is simulated as a random process. Dynamic wind-induced responses of structures with parametric uncertainties are investigated by using stochastic finite element method. The formulas for structural dynamic reliability analysis considering the randomness of structural resistance and loading are proposed. Two numerical examples of high-rise structures are presented to illustrate the proposed methodology. The calculated results demonstrate that the variation in structural parameters indeed influences the dynamic response and the first passage probability evaluation of structures.

• 한국해양공학회지
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• 제8권2호
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• pp.115-123
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• 1994

Under variable amplitude loading conditions, retardation or accelerated condition of fatigue crack growth occurs with every cycle, Because fatigue crack growth behavior varied depend on load time history. The modeling of stress amplitude with storm loading acted to ships and offshore structures applied this paper. The crack closure behavior examine by recording the variation in load-strain relationship. By taking process mentioned above, fatigue crack growth rate, crack length, stress intensity factor, and crack closure stress intensity factor were obtained from the stress cycles of each type of storm ; A(6m), B(7m), C(8m), D(9m), E(11m) and F(15m) which was wave height. It showed that the good agreement with between the experiment results and simulation of storm loads. So this estimated method of crack propagtion rate gives a good criterion for the safe design of vessels and marine structure.

• 품질경영학회지
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• 제26권4호
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• pp.51-64
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• 1998

Mean shifts may be found in tool wear in machining, drawing, stamping and moulding operations, which make the process quality level deteriorate over time. In such situations, it is necessary to reset or readjust the manufacturing process at regular time basis or by inspection to prevent defective items produced. Although the deterioration rate may be assumed to be linear in a production cycle, there are many cases where the rate varies after resetting due to the variation of tool characteristics or by using the resharpened tools. In such cases, the deterioration rate should not be assumed to be a deterministic constant but a random variable. This paper is to find an optimal resetting period and quality level for such production processes.

• Communications for Statistical Applications and Methods
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• 제2권1호
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• pp.201-208
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• 1995

In the last years there has been growing interest in concepts of positive dependence for families of random variables such that concepts are considerable us in deriving inequalities in probability and statistics. Lehman introdued various concepts of positive dependence for bivariate random variables. A much stronger notions of positive dependence were later considered by Esary, Proschan, and Walkup. Ahmed et al and Ebrahimi and Ghosh also obtained multivariate versions of various bivariate positive dependence as descrived by Lehman. See also Block al. Glaz and Johnson an Barlow and Proschan and the references there. Multivariate processes arise when instead of observing a single process we observe several processes, say $X_19t), \cdots, X_n(t)$ simultaneously. For example, in an engineering context we may want to study the simultaneous variation of current and voltage, or temperature, pressure and volume over time. In economics we may be interested in studying inflation rates and money supply, unemployment and interest rates. We could of course, study each quantity on its own and treat each as a separate univariate process. Although this would give us some information about each quantity it could never give information about the interrelationship between various quantities. This leads us to introduce some concepts of positive and for multivariate stochastic processes. The concepts of positive dependence have subsequently been extended to stochastic processes in different directions by many authors.

• 대한기계학회논문집
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• 제17권10호
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• pp.2509-2517
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• 1993

Lapping is a very complicated and random process resulting from the variation of abrasive grains in its sizes and shapes and from the numerous factors having an effect on the process quality. Thus it needs to be analyzed by experimental method rather than by theoretical method to obtain the relative effects of factors quantitatively. In this study, cylindrical lapping experiment designed by Taguchi's L8 orthogonal array was performed and analyzed by Yates' ANOVA table. As a result, effective factors and interaction effects were identified and discussed. Also the optimal factor combination to obtain the largest improvement of surface roughness was selected and confirmatory experiments were peformed.

• 대한산업공학회지
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• 제31권2호
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• pp.164-172
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• 2005

A loss function approach to a multiresponse problem is considered, when process parameters are regarded as random variables. The variation of each response may be amplified through so called propagation of error (POE), which is defined as the standard deviation of the transmitted variability in the response as a function of process parameters. The forms of POE for each response and for a pair of responses are proposed and they are reflected in our loss function approach to determine the optimal condition. The proposed method is illustrated using a polymer case. The result is compared with the case where parameter fluctuation is not considered.

• Computers and Concrete
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• 제22권1호
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• pp.53-62
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• 2018

Cracking of concrete cover induced by reinforcement corrosion is a critical issue for life-cycle design and maintenance of reinforced concrete structures. However, the critical degree of corrosion, based on when the concrete surface cracks, is usually hard to predict accurately due to the heterogeneity inherent in concrete. To investigate the influence of concrete heterogeneity, a modified rigid-body-spring model, which could generate concrete sections with randomly distributed coarse aggregates, has been developed to study the corrosion-induced cracking process of the concrete cover and the corresponding critical degree of corrosion. In this model, concrete is assumed to be a three-phase composite composed of coarse aggregate, mortar and an interfacial transition zone (ITZ), and the uniform corrosion of a steel bar is simulated by applying uniform radial displacement. Once the relationship between radial displacement and degree of corrosion is derived, the critical degree of corrosion can be obtained. The mesoscale model demonstrated its validity as it predicted the critical degree of corrosion and cracking patterns in good agreement with analytical solutions and experimental results. The model demonstrates how the random distribution of coarse aggregate results in a variation of critical degrees of corrosion, which follows a normal distribution. A parametric study was conducted, which indicates that both the mean and variation of critical degree of corrosion increased with the increase of concrete cover thickness, coarse aggregates volume fraction and decrease of coarse aggregate size. In addition, as tensile strength of concrete increased, the average critical degree of corrosion increased while its variation almost remained unchanged.

• 대한기계학회논문집A
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• 제23권7호
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• pp.1139-1146
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• 1999

Reliability analysis of structures based on fracture mechanics requires knowledge on statistical characteristics of the parameter C and m in the fatigue crack growth law, $da/dN=C({\Delta}K)^m$. The purpose of the present study is to investigate if it is possible to predict fatigue crack growth rate by only the fluctuation of the parameter C. In this study, Paris-Erdogan law is adopted, where the author treat the parameter C as random and m as constant. The fluctuation of crack growth rate is assumed only due to the parameter C. The growth resistance coefficient of material to fatigue crack growth (Z=1/C) was treated as a spatial stochastic process, which varies randomly on the crack path. The theoretical crack growth rates at various stress intensity factor range are discussed. Constant ${\Delta}K$ fatigue crack growth tests were performed on the structural steel, SM45C. The experimental data were analyzed to determine the autocorrelation function and Weibull distributions of the fatigue crack growth resistance. And also, the effect of the parameter m of Paris' law due to variation of fatigue crack growth resistance was discussed.