• 한국소성가공학회:학술대회논문집
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• 한국소성가공학회 1996년도 추계학술대회논문집
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• pp.139-146
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• 1996

The torsion tests in the range of 900~1100$^{\circ}C$ and 5.0X10-2~5.0X100/sec were performed to study the high temperasture deformation behavior kinetics of 304 stainless steels. The flow curves and microstructures exhibited the characteristic of dynamic recrystallization(DRX). The relationship between the critical strain($\varepsilon$c) for the initiation of dynamic recrystallization and the peak strain($\varepsilon$p) could be expressed as $\varepsilon$c=0.73$\varepsilon$p. The dependence of the flow stress on temperature(T) and stain rate($\varepsilon$) was expressed by hyperbolic sine law, $\varepsilon$=2.75X1014 (sinh 0.076$\sigma$)5.26 exp(-379.55kJ/mol). Under the Zener-Hollomon parameter, Z value of 1013 order, it was found that the grain size was 20${\mu}$m. The relationship between the grain size, dDRX and Z parameter was expressed as dDRX =139.48-7.33 log Z.

• 한국주조공학회지
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• 제22권1호
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• pp.11-16
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• 2002

Hot deformation behavior of GCD-50 cast iron has been investigated by employing the compressive test. Phenomenological deformation behaviors, which were modeled based on the dynamic materials model and the kinetic model, have been correlated with the microstructural change taken place during compression. Microstructural investigation revealed that the adiabatic shear band caused by the locallized deformation was taken place in low temperature and high strain rate. On the other hand, the wavy and curved grain boundaries, which repersent the occurrence of dynamic microstructure change such as dynamic recovery and dynamic recrystallization, were observed in high temperature and low strain rate. Deformation model based on hyperbolic sine law has also been suggested.

• 제어로봇시스템학회논문지
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• 제9권1호
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• pp.1-9
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• 2003

An active control of the lateral vibration of a translating tensioned Euler-Bemoulli beam is investigated. The dynamics of the translating tensioned beam is represented by a non-linear hyperbolic partial differential equation. A right boundary control law based upon the Lyapunov's second method is derived. The transverse motion of the translating tensioned beam is controlled by a time-varying external force besides a passive damping applied at the right boundary. Exponential stability of the closed loop system is proved. Simulation results demonstrate the effectiveness of the proposed controller.

• Wind and Structures
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• 제23권1호
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• pp.59-73
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• 2016

In this paper, a hyperbolic shear deformation beam theory is developed for free vibration analysis of functionally graded (FG) sandwich beams. The theory account for higher-order variation of transverse shear strain through the depth of the beam and satisfies the zero traction boundary conditions on the surfaces of the beam without using shear correction factors. The material properties of the functionally graded sandwich beam are assumed to vary according to power law distribution of the volume fraction of the constituents. The core layer is still homogeneous and made of an isotropic material. Based on the present refined beam theory, the equations of motion are derived from Hamilton's principle. Navier type solution method was used to obtain frequencies. Illustrative examples are given to show the effects of varying gradients and thickness to length ratios on free vibration of functionally graded sandwich beams.

• Bulletin of the Korean Chemical Society
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• 제13권4호
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• pp.413-419
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• 1992

The theoretical equation for the relaxation spectrum of nonlinear viscoelastic polymeric material was derived from the Ree-Eyring and Maxwell non-Newtonian model. This model consists of infinite number of hyperbolic sine law Maxwell elements coupled in parallel plus a spring without a dashpot. Infinite number of nonlinear viscoelastic Maxwell elements can be used by specifying distribution of relaxation times, hole volumes, molecular weights, crystallite size and conformational size, etc. The experimentals of stress relaxation were carried out using the tensile tester with the solvent chamber. The relaxation spectra of nylon 6 filament fibers in various electrolytic solutions were obtained by applying the experimental stress relaxation curves to the theoretical equation of relaxation spectrum. The determination of relaxation spectra was performed from computer calculation.

• Bulletin of the Korean Chemical Society
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• 제12권5호
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• pp.468-473
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• 1991

Viscoelastic properties of PET filament fibers on stress relaxation were investigated in the solvents of $H_2$O, 0.05% NaOH and 50% DMF using an Instron (UTM4-100 Tensilon) with solvent chamber. The theoretical stress relaxation equation derived by applying the Ree-Eyring's hyperbolic sine law to dashpot of three element non-Newtonian model was applied to the experimental stress relaxation curves, and the model parameters $G_1,G_2$, ${\alpha}$ and ${\beta}$ were obtained. By analyzing temperature dependency of the relaxation time, the values of activation entropy, activation enthalpy and activation free energy for flow in PET filament fiber were evaluated, the activation free energy being about 25.7 kcal/mol. The self diffusion coefficient and hole distance were obtained from parameters ${\alpha}$, ${\beta}$ and crystallite size in order to study the self diffusion and the orientation of crystallites in amorphous region and the effect of solvent.

• Structural Engineering and Mechanics
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• 제75권2호
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• pp.193-209
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• 2020

This paper presents a new hyperbolic shear deformation plate theory including the stretching effect for free vibration of the simply supported functionally graded plates in thermal environments. The theory accounts for parabolic distribution of the transverse shear strains and satisfies the zero traction boundary conditions on the surfaces of the plate without using shear correction factors. This theory has only five unknowns, which is even less than the other shear and normal deformation theories. The present one has a new displacement field which introduces undetermined integral variables. Material properties are assumed to be temperature-dependent, and graded in the thickness direction according to a simple power law distribution in terms of the volume power laws of the constituents. The equation of motion of the vibrated plate obtained via the classical Hamilton's principle and solved using Navier's steps. The accuracy of the proposed solution is checked by comparing the present results with those available in existing literature. The effects of the temperature field, volume fraction index of functionally graded material, side-to-thickness ratio on free vibration responses of the functionally graded plates are investigated. It can be concluded that the present theory is not only accurate but also simple in predicting the natural frequencies of functionally graded plates with stretching effect in thermal environments.

• Structural Engineering and Mechanics
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• 제66권3호
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• pp.353-368
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• 2018

In this work, a high order hyperbolic shear deformation theory with four variables is presented to study the vibratory behavior of functionally graduated plates. The field of displacement of the theory used in this work is introduced indeterminate integral variables. In addition, the effect of porosity is studied. It is assumed that the material characteristics of the porous FGM plate, varies continuously in the direction of thickness as a function of the power law model in terms of volume fractions of constituents taken into account the homogeneous distribution of porosity. The equations of motion are obtained using the principle of virtual work. An analytical solution of the Navier type for free vibration analysis is obtained for a FGM plate for simply supported boundary conditions. A comparison of the results obtained with those of the literature is made to verify the accuracy and efficiency of the present theory. It can be concluded from his results that the current theory is not only accurate but also simple for the presentation of the response of free vibration and the effect of porosity on the latter.

• 한국지반공학회논문집
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• 제24권7호
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• pp.37-42
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• 2008

인천시 소재 OO지역 비위생 매립지를 대상으로 선행하중(pre-loading) 공법에 의한 성토시 폐기물층의 침하 계측을 바탕으로 기존에 제시된 경험적 침하 모델을 적용하여 침하 모델의 적용성과 타당성을 분석하였다. 매립 연한이 20년이 지난 비위생 매립에서의 1년간의 성토기간 동안에 9개 지점의 지표면 침하판, 2개의 층별 침하계를 설치하고 약 300일간의 계측을 통해 비위생 매립지의 침하량을 측정하였다. 초기 침하 부분에서 기존의 침하 예측 모델과 본 현장의 침하량을 비교 분석한 결과 PCL(Power Creep Law)모델의 경우 실측 범위내에서 근접한 결과를 보였으나 쌍곡선(hyperbolic) 모델과 Bjarngard와 Edgers 모델의 경우 초기 실측 범위인 약 $50{\sim}70$일부터 300일까지 실측치와 근접하게 예측되었다.

• Structural Engineering and Mechanics
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• 제89권3호
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• pp.225-238
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• 2024

In this paper, a quasi-3D hyperbolic shear deformation theory for the bending responses of a functionally graded (FG) porous micro-beam is based on a modified couple stress theory requiring only one material length scale parameter that can capture the size influence. The model proposed accounts for both shear and normal deformation effects through an illustrative variation of all displacements across the thickness and satisfies the zero traction boundary conditions on the top and bottom surfaces of the micro-beam. The effective material properties of the functionally graded micro-beam are assumed to vary in the thickness direction and are estimated using the homogenization method of power law distribution, which is modified to approximate the porous material properties with even and uneven distributions of porosity phases. The equilibrium equations are obtained using the virtual work principle and solved using Navier's technique. The validity of the derived formulation is established by comparing it with the ones available in the literature. Numerical examples are presented to investigate the influences of the power law index, material length scale parameter, beam thickness, and shear and normal deformation effects on the mechanical characteristics of the FG micro-beam. The results demonstrate that the inclusion of the size effects increases the microbeams stiffness, which consequently leads to a reduction in deflections. In contrast, the shear and normal deformation effects are just the opposite.