• Journal of the Korean Wood Science and Technology
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• v.33 no.5 s.133
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• pp.57-65
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• 2005

Following our previous reports for finger-jointed woods with various finger profiles studied for the efficient use of small diameter logs and woods containing various defects, twelve types of finger-jointed woods glued with three kinds of adhesives and with two sizes of finger pitches were made with sitka spruce and red pine. The effects of the adhesives and finger pitches on bending creep performances of finger-jointed woods were investigated. The shape of creep curves differed among the used adhesives and finger pitches of finger-jointed woods for both tested species. Their creep curves showed a linear behavior beyond about one hour, and the N values fitted to power law increased with increasing finger pitches. The initial deformation increased with increasing finger pitches, regardless of the tested species and kinds of adhesives, whereas the effect of finger pitches on the creep deformation was not clear. For finger-jointed woods glued with polyvinyl acetate (PVAc) resin, creep failure occurred in 106 hours after the load was applied. And the difference of the creep compliance between finger-jointed woods glued with resorcinol-phenol formaldehyde (RPF) resin and aqueous vinyl urethane (AVU) resin was small. The ratios for creep performances of finger-jointed woods glued with RPF resin and AVU resin versus solid wood were higher in creep deformation than initial deformation for both species, and the difference between both adhesives was not found. The relative creep decreased with increasing finger pitches, and the marked differences was not found between RPF resin and AVU resin.

• Steel and Composite Structures
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• v.29 no.3
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• pp.349-362
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• 2018

Thermal buckling behavior of porous functionally graded nanobeam integrated with piezoelectric sensor and actuator based on the nonlocal higher-order shear deformation beam theory is investigated for the first time. Its material properties are assumed to be temperature-dependent and varying along the thickness direction according to the modified power-law rule. Note that the porosity with even type is considered herein. The equations of motion are obtained through Hamilton's principle. The influences of several parameters (such as type of temperature distribution, external electric voltage, material composition, porosity, small-scale effect, Ker foundation parameters, and beam thickness) on the thermal buckling of FG nanobeam are investigated in detail.

• Tunnel and Underground Space
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• v.7 no.1
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• pp.20-30
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• 1997

A discrete joint finite element with joint surface degradation was developed to investigate the shear behavior of rough rock joint. Isoparametric formulation was used for facilitating the implementation of the element in existing Finite Element Codes. The elasto-plastic joint deformation model with the discontinuity constitutive law proposed by Plesha was applied to the element. The reliability of the developed finite element code was successfully testified through numerical direct shear tests conducted under both constant normal stress and constant normal displacement conditions. The result of the numerical direct shear test showed that the code can capture characteristic deformation features envisaged in the direct shear test of rough rock joint.

• Transactions of Materials Processing
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• v.16 no.2 s.92
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• pp.101-106
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• 2007

Uniaxial displacement controlled tests were performed on annealed Type 304 stainless steel at room temperature. A servo-controlled testing machine and strain measurement on the gage length were employed to measure the response to a given input. The test results exhibit that the flow stress increases nonlinearly with the strain rate and the relaxed stress at the end of the relaxation periods depends strongly on the strain rate preceding the relaxation test. The rate-dependent inelastic deformation behavior is simulated using a new unified viscoplasticity model that has the rate-dependent format of nonlinear kinematic hardening rule, which plays a key role in modeling the rate dependence of relaxation behavior. The model does not employ yield or loading/unloading criteria and consists of a flow law and the evolution laws of two tensor and one scalar-valued state variables.

• Proceedings of the KSME Conference
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• 2007.05a
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• pp.566-571
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• 2007

In this study, it is investigated the thermal post-buckling characteristics of step-formed FG panel under the heat and supersonic flow. Material properties are assumed to be temperature dependent as well as continuously varying in the thickness direction of the panel according to a simple power law distribution in terms of the volume fraction of the constituent. First-order shear deformation theory(FSDT) of plate is applied to model the panel, and the von Karman strain-displacement relations are adopted to consider the geometric nonlinearity due to large deformation. Also, the first-order piston theory is used to model the supersonic aerodynamic load acting on a panel. Numerical results are summarized to reveal the thermal post-buckling behaviors of FG panels with various volume fractions, temperature conditions and aerodynamic pressures in detail.

• Steel and Composite Structures
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• v.15 no.2
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• pp.221-245
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• 2013

This paper presents an analytical solution to the thermomechanical bending analysis of functionally graded sandwich plates by using a new hyperbolic shear deformation theory in which the stretching effect is included. The modulus of elasticity of plates is assumed to vary according to a power law distribution in terms of the volume fractions of the constituents. The core layer is still homogeneous and made of an isotropic ceramic material. The effects of functionally graded material (FGM) layer thickness, volume fraction index, layer thickness ratio, thickness ratio and aspect ratio on the deflections and stresses of functionally graded sandwich plates are investigated.

• Wind and Structures
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• v.23 no.6
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• pp.543-558
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• 2016

The response of functionally graded ceramic-metal plates is investigated using theoretical formulation, Navier's solutions, and a new displacement based on the high-order shear deformation theory are presented for static analysis of functionally graded plates. The theory accounts for a quadratic variation of the transverse shear strains across the thickness, and satisfies the zero traction boundary conditions on the top and bottom surfaces of the plate without using shear correction factors. The plates are assumed to have isotropic, two-constituent material distribution through the thickness, and the modulus of elasticity of the plate is assumed to vary according to a power-law distribution in terms of the volume fractions of the constituents. Numerical results of the new refined plate theory are presented to show the effect of the material distribution on the deflections, stresses and fundamental frequencies. It can be concluded that the proposed theory is accurate and simple in solving the static and free vibration behavior of functionally graded plates.

• Proceedings of the Korean Society of Tribologists and Lubrication Engineers Conference
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• 1998.04a
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• pp.212-217
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• 1998

Reynolds equation, which describes behavior of fluid film in journal bearing, basically satisfies mass conservation. But, boundary conditions usually used with this equation, e.g. half Sommerfeld or Reynolds boundary conditions, cannot fulfill this natural law of conservation. In the case of connecting rod bearing, where applied load is dynamic and its magnitude is relatively large, such unrealistic boundary conditions have serious influence on calculation results, especially on lubricant flow rate or power dissipation which are important parameters in thermal analysis. Another important factor in the analysis of connecting rod bearing is elastic deformation of bearing support structure which is relatively flexible. In this paper, EHL analysis of connecting rod beating is performed using mass-conserving boundary condition. Elastic deformation of bearing support structure and application of mass-conserving boundary condition have significant effects on the performances of connecting rod bearing.

• Proceedings of the Korean Society for Technology of Plasticity Conference
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• 1997.03a
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• pp.98-105
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• 1997

The behaviour of alloys in the semi-solid state strongly depends on the imposed stress state and on the morphology of the phase which can very from dendritic to globular. The estimation of behaviour characteristic in the compression simulation with seim-solid materials are calculated by finite element method with proposed algorithm. The proposed theoretical model and a various boundary conditions for compression process is investigated with the coupling calculation between the liquid phase flow and the solid phase deformation. The simulation process considering soldification phenomena is performed to the isothermal conditions of two dimensional problems. To analysis of compression process by using semi-solid materials, a new stress-strain relationship is described, and compression analysis is performed by viscoelastic model for the solid phase and the Darcy's law for the liquid flow. The calculated results for compression force and ram displacement will be compared to experimental data.

• Proceedings of the Korean Society for Technology of Plasticity Conference
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• 1996.10a
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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.