• Transactions of the Korean Society of Mechanical Engineers A
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• v.27 no.9
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• pp.1579-1588
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• 2003

In this paper, the finite element equations for the transient linear viscoelastic stress analysis are presented in time domain, whose variational formulation is derived by using the Galerkin's method based on the equations of motion in time integral. Since the inertia terms are not included in the variational formulation, the time integration schemes such as the Newmark's method widely used in the classical dynamic analysis based on the equations of motion in time differential are not required in the development of that formulation, resulting in a computationally simple and stable numerical algorithm. The viscoelastic material is assumed to behave as a standard linear solid in shear and an elastic solid in dilatation. To show the validity of the presented method, two numerical examples are solved nuder plane strain and plane stress conditions and good results are obtained.

• International Journal of Advanced Culture Technology
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• v.9 no.3
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• pp.367-372
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• 2021

The purpose of this study is to suggest that the movement expression activity of intellectually disabled people is effective in the learning process of LMA motion recognition based on Kinect sensor. We performed an ICT motion recognition games for intellectually disabled based on movement learning of LMA. The characteristics of the movement through Laban's LMA include the change of time in which movement occurs through the human body that recognizes space and the tension or relaxation of emotion expression. The design and implementation of the motion recognition model will be described, and the possibility of using the proposed motion recognition model is verified through a simple experiment. As a result of the experiment, 24 movement expression activities conducted through 10 learning sessions of 5 participants showed a concordance rate of 53.4% or more of the total average. Learning motion games that appear in response to changes in motion had a good effect on positive learning emotions. As a result of study, learning motion games that appear in response to changes in motion had a good effect on positive learning emotions

• Korea-Australia Rheology Journal
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• v.13 no.4
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• pp.205-217
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• 2001

This review article summarizes results of recent viscoelastic and dielectric studies for entangled cis-polyisoprene (PI) chains. The PI chains have the so-called type-A dipoles parallel along the chain backbone, and their slow viscoelastic and dielectric relaxation processes reflect the same global chain motion. However, this motion is differently averaged in the viscoelastic and dielectric properties, the former representing the isochronal orientational anisotropy of individual entanglement segments while the latter detecting the orientational correlation of the segments at two separate times (0 and t). On the basis of this difference, the viscoelastic and dielectric data of the entangled PI chains were compared to elucidate detailed features of the chain dynamics. Specifically, the molecular picture of dynamic tube dilation (DTD) incorporated in recent models was tested for linear and star PI chain. The comparison revealed that the DTD picture was valid for linear PI chains but failed for the star PI chains in the dominant part of the terminal relaxation. The failure for the star chains was related to the pre-requisite for the DTD process, rapid equilibration of successive entanglement segments through their constraint release (CR) motion: For the star chains, the dilated tube diameter expected in the terminal regime was considerably large because of a broad distribution of motional modes of the chains, so that the CR-equilibration required for DTD could not occur in time. The terminal relaxation of the star chain appeared to occur through the CR process before the expected DTD process was completed. The situation was different for the linear chain exhibiting narrowly distributed motional modes. The dilated tube expected for the linear chain was rather thin and the required CR-equilibration occurred in time, resulting in the success of the DTD picture. These detailed features of the chain dynamics was revealed only when the viscoelastic and dielectric properties were compared, demonstrating the importance of this comparison.

• Bulletin of the Korean Chemical Society
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• v.15 no.2
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• pp.118-122
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• 1994

Molecular dynamics simulation was carried out to study density effects on vibrational dephasing. Because of difficulty due to large time scale difference between vibrational motion and vibrational relaxation, we adopt adiabatic approximation in which the vibrational motion is assumed to be much faster than translational and rotational motion. As a result, we are able to study vibrational dephasing by simulating motion of rigid molecules. It is shown that the dephasing time is decreased as density increases and the contribution to this result is mainly due to the mean-squared frequency fluctuation.

• Proceedings of the KIEE Conference
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• 1993.07b
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• pp.1162-1164
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• 1993

The Thermally Stimulated Current(TSC) spectroscopy has been applied to study the influence of the structual cahange and interface on the electrical properties of epoxy composites. Three DGEBA-MeTHPA matrix model samples mixed different ratios and silica($SiO_2$) filled sample and silaln treating-filled sample has been studied. Above room temperature, the relaxation mode $\alpha$ peak associated with Tg has been located at $110^{\circ}C$. Below glass transition temperature(Tg), three relaxation modes are observed in all samples: a $\beta$ mode situated at $10^{\circ}C$, a $\gamma$ mode located at $-40^{\circ}C$ and a $\delta$ mode appeared in $-120^{\circ}C$. The analysis of its fine structure indicates that constitution of elementary processes is characterized by the activation energy and relaxation time. Also the dielectric relaxation properties have been investigated to compare the the change of the molecular structure and motion to the relaxation properties and conduction mechanism in TSC spectra.

• Journal of Magnetics
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• v.5 no.4
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• pp.116-119
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• 2000

Magnetic field dependence of magnetization reversal in Co/Pt multilayers was quantitatively investigated. Serial samples of Co/Pt multilayers were prepared by dc-magnetron sputtering under various Ar pressures. Magnetization reversal was monitored by magnetization viscosity measurement and direct domain observation using a magneto-optical microscope system, and the wall-motion speed V and the nucleation rate R were determined using a domain reversal model based on time-resolved domain reversal patterns. Both V and R were found to be exponentially dependent on the applied reversing field. From the exponential dependencies, the activation volumes for wall motion and nucleation could be determined, based on a thermally activated relaxation model, and the wall-motion activation volume was found to be slightly larger than the nucleation activation volume.

• Geotechnical Engineering
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• v.10 no.4
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• pp.103-118
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• 1994

The rapid motion of granular material is microscopically observed, and investigated by continuum theory. From the binary collision phenomenon two different times are introduced : flying time and contact time. The former says the non -stationary motion and at a same time the variation of bulk volume. The latter is operative by a delayed time during the contact and describes the elastic properties of granular material. With both times a dynamic constitutive equation is postulated for four state variables : dispersive pressure, viscosity, thermal diffusivity and energy annihilation rate. The balance laws of mass, momentum and energy which are represented through above four variabls, are applied to the model, in which due to the elastic property the relaxation and energy absorption are explained.

• Proceedings of the Korean Magnestics Society Conference
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• 2000.09a
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• pp.279-286
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• 2000

Magnetic field dependence of magnetization reversal in Co/Pt multilayers has been quantitatively investigated. Serial samples of Co/Pt multilayers have been prepared by dc-magnetron sputtering under various Ar pressure. Magnetization reversal was monitored by magnetization viscosity measurement and direct domain observation using a magneto-optical microscope system, and the wall-motion speed and the nucleation rate R were determined using a domain reversal model based on time-resolved domain reversal patterns. Both and R were found to be exponentially dependent on the reversing applied field. From the exponential dependencies, the activation volumes of the wall motion and nucleation could be determined based on a thermally activated relaxation model, and the wall-motion activation volume was revealed to be slightly larger than the nucleation activation volume.

• Korean Membrane Journal
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• v.1 no.1
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• pp.8-24
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• 1999

free volume in polymers is defined as the difference of the specific volume and the volume which is not available for the particular molecular motion which is responsible or the process that is considered . Relations between free volume and viscosity free volume and diffusion coefficient are pre-sented both in the case of simple low molecular weight liquids and in the case of polymers. Molecular models and free volume models are reminded starting from the equilibrium state equation of Simha and Somcynski. The non equilibrium situations of specific volume of glass polymers below Tg are shown introducing different relaxation volume equations which involve different material's parameters and con-cept of the fictitious temperature. The diffusivity equations of Vrentas and Duda are introduced both for the glassy and rubbery states. The possibility of introducing time relaxation functions is also suggested. The importance of finding experimental evidences of the free volume is stressed. highlights of the free volume measurement methods are given in particular as to dilatometry photocromy fluorescence electron spin resonance small angle X-ray scattering positron annihilation spectroscopy.

• Bulletin of the Korean Chemical Society
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• v.20 no.11
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• pp.1329-1334
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• 1999

The curing characteristics of diglycidyl ether of bisphenol A (DGEBA) with diaminodiphenylmethane (DDM) as a curing agent were studied using differential scanning calorimetry (DSC), rheometrics mechanical spectrometry (RMS), and dielectric analysis (DEA). The isothermal curing kinetics measured by DSC were well represented with the generalized auto-catalytic reaction model. With the temperature sweep, the inverse relationship between complex viscosity measured by RMS and ionic conductivity obtained from DEA was established indicating that the mobility of free ions represented by the ionic conductivity in DEA measurement and the chain segment motion as revealed by the complex viscosity measured from RMS are equivalent. From isothermal curing measurements at several different temperatures, the ionic conductivity contribution was shown to be dominant in the dielectric loss factor at the early stage of cure. The contribution of the dipole relaxation in dielectric loss factor became larger as the curing further proceeded. The critical degrees of cure, at which the dipolar contribution in the dielectric loss factor starts to appear, increases as isothermal curing temperature is increased. The dielectric relaxation time at the same degree of cure was shorter for a sample cured at higher curing temperature.