• Fibers and Polymers
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• v.5 no.3
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• pp.209-212
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• 2004

A nonsteady axi-symmetric ideal flow solution is obtained here. It is based on the rigid perfect-plastic constitutive law with the Tresca yield condition and its associated flow rule. The process is to deform a circular solid disk into a spherical shell of prescribed geometry. It is assumed that there are no rigid zones and friction stresses. The solution obtained provides the distribution of kinematic variables and involves one undetermined function of the time. This function can be in general found by superimposing an optimality criterion.

• Transactions of Materials Processing
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• v.31 no.4
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• pp.214-228
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• 2022

The yield criterion, or called yield function, plays an important role in the study of plastic working of a sheet because it governs the plastic deformation properties of the sheet during plastic forming process. In this paper, we propose a novel anisotropic yield function useful for describing the plastic behavior of various anisotropic sheets. The proposed yield function includes the anisotropic version of the second stress invariant J₂ and the third stress invariant J₃. The anisotropic yield function newly proposed in this study is as follows. F(J₂)+ αG(J₃)+ βH (J₂ × J₃) = k^m The proposed yield function well explains the anisotropic plastic behavior of various sheets by introducing the parameters α and β, and also exhibits both symmetrical and asymmetrical yield surfaces. The parameters included in the proposed model are determined through an optimization algorithm from uniaxial and biaxial experimental data under proportional loading path. In this study, the validity of the proposed anisotropic yield function was verified by comparing the yield surface shape, normalized uniaxial yield stress value, and Lankford's anisotropic coefficient R-value derived with the experimental results. Application for the proposed anisotropic yield function to aluminum sheet shows symmetrical yielding behavior and to pure titanium sheet shows asymmetric yielding behavior, it was shown that the yield curve and yield behavior of various types of sheet materials can be predicted reasonably by using the proposed new yield anisotropic function.

• Fibers and Polymers
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• v.7 no.3
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• pp.276-285
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• 2006

Development and numerical implementation for an elastoplastic constitutive model for anisotropic and asymmetric materials are presented in this paper. The Coulomb-Mohr yield criterion was modified to consider both the anisotropic and asymmetric properties. The modified yield criterion is an isotropic function of the principal values of a symmetric matrix which is linearly transformed from the Cauchy stress space. In addition to the constitutive equation, the numerical treatment for the singularity in the vertex region of yield surface and stress integration algorithm based on elastoplasticity were presented. In order to assess the accuracy of numerical algorithm, isoerror maps were considered. Also, extension of a strip with a circular hole was simulated and results compared with those obtained using the (smooth) Mises yield criterion to validate stress output for a complex stress state.

• Bulletin of the Korean Chemical Society
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• v.19 no.7
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• pp.747-753
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• 1998

The phoisomerization process of symmetric carbocyanine dyes such as 3,3'-diethyloxadicarbocyanine iodide (DODCI), 3,3'-diethylthiadicarbocyanine iodide (DfDCI), 1,1'-diethyl-2,2'-dicarbocyanine iodide (DDI), 1,1'-diethyl-2,2'-carbocyanine iodide (DCI), and cryptocyanine (1,1'-diethyl-4,4'-carbocyanine) iodide (CCI) have been studied by measuring the steady state and time resolved fluorescence spectra and the ground-state recovery profiles. The steady-state fluorescence spectrum of photoisomer as a function of concentration and excitation wavelength provides the evidence that the fluorescence of photoisomer is formed by the radiative energy transfer from the normal form and the quantum yield for the formation of photoisomer is increased by decreasing the excitation wavelength. The fluorescence decay profiles have been measured by using the time correlated single photon counting (TCSPC) technique, showing a strong dependence on the concentration and the detection wavelength, which is due to the formation of excited photoisomers produced either by the radiative energy transfer from the non-nal form or by absorbing the 590 nm laser pulse. We first report the fluorescence decay time of photoisomers for these cyanine dyes. The experimental results are explained by introducing the semiempirical calculations. The ground state recovery profiles of DTDCI, DDI, and CCI normal forms have been measured, showing that the recovery time from the singlet excited state is similar with the fluorescence decay time.

• Advances in nano research
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• v.13 no.1
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• pp.77-86
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• 2022

This paper studied the peristaltic transport of upper convected Maxwell nanofluid through a porous medium in a heated (isothermal) symmetric vertical channel. The nanofluid is assumed to be electrically conducting in the presence of a uniform magnetic field. These phenomena are modeled mathematically by a differential equations system by taking low Reynolds number and long-wavelength approximation, the yield differential equations have solved analytically. A suggested new technique to display and discuss the trapping phenomenon is presented. We discussed and analyzed the pumping characteristics, heat function, flow velocity and trapping phenomena which were illustrated graphically through a set of figures for various values of parameters of the problem. The numerical results show that, there are remarkable effects on the vertical velocity, pressure gradient and trapping phenomena with the thermal change of the walls.

• KDI Journal of Economic Policy
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• v.12 no.2
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• pp.51-79
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• 1990

Research on technical efficiency, an important dimension of market performance, had received little attention until recently by most industrial organization empiricists, the reason being that traditional microeconomic theory simply assumed away any form of inefficiency in production. Recently, however, an increasing number of research efforts have been conducted to answer questions such as: To what extent do technical ineffciencies exist in the production activities of firms and plants? What are the factors accounting for the level of inefficiency found and those explaining the interindustry difference in technical inefficiency? Are there any significant international differences in the levels of technical efficiency and, if so, how can we reconcile these results with the observed pattern of international trade, etc? As the first in a series of studies on the technical efficiency of Korea's manufacturing industries, this paper attempts to answer some of these questions. Since the estimation of technical efficiency requires the use of plant-level data for each of the five-digit KSIC industries available from the Census of Manufactures, one may consture the findings of this paper as empirical evidence of technical efficiency in Korea's manufacturing industries at the most disaggregated level. We start by clarifying the relationship among the various concepts of efficiency-allocative effciency, factor-price efficiency, technical efficiency, Leibenstein's X-efficiency, and scale efficiency. It then becomes clear that unless certain ceteris paribus assumptions are satisfied, our estimates of technical inefficiency are in fact related to factor price inefficiency as well. The empirical model employed is, what is called, a stochastic frontier production function which divides the stochastic term into two different components-one with a symmetric distribution for pure white noise and the other for technical inefficiency with an asymmetric distribution. A translog production function is assumed for the functional relationship between inputs and output, and was estimated by the corrected ordinary least squares method. The second and third sample moments of the regression residuals are then used to yield estimates of four different types of measures for technical (in) efficiency. The entire range of manufacturing industries can be divided into two groups, depending on whether or not the distribution of estimated regression residuals allows a successful estimation of technical efficiency. The regression equation employing value added as the dependent variable gives a greater number of "successful" industries than the one using gross output. The correlation among estimates of the different measures of efficiency appears to be high, while the estimates of efficiency based on different regression equations seem almost uncorrelated. Thus, in the subsequent analysis of the determinants of interindustry variations in technical efficiency, the choice of the regression equation in the previous stage will affect the outcome significantly.