• Proceedings of the Korean Society for Technology of Plasticity Conference
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• 2009.05a
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• pp.70-73
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• 2009

The aim of this research is to obtain a numerical material model for an amorphous glassy polymer, polycarbonate (PC), which can be used in finite element analysis (FEA) of the micro thermal imprint process near the glass transition temperature. An understanding of the deformation behavior of the PC specimens was acquired by performing tensile stress relaxation tests. The viscoelastic material model based on generalized Maxwell model was introduced for the material near Tg to establish the FE model based on the commercial FEA code ABAQUS/Standard with a suitable set of parameters obtained for this material model from the test data. Further validation of the model and parameters was performed by comparing the analysis of FE model results to the experimental data.

• Journal of Biomedical Engineering Research
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• v.28 no.2
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• pp.169-173
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• 2007

During laser irradiation, mechanically deformed cartilage undergoes a temperature dependent phase transformation resulting in accelerated stress relaxation. Clinically, laser-assisted cartilage reshaping may be used to recreate the underlying cartilaginous framework in structures such as ear, larynx, trachea, and nose. Therefore, research and identification of the biophysical transformations in cartilage accompanying laser heating are valuable to identify critical laser dosimetry and phase transformation of cartilage for many clinical applications. quasi-elastic light scattering was investigated using Ho : YAG laser $(\lambda=2.12{\mu}m\;;\;t_p\sim450{\mu}s)$ and Nd:YAG Laser $(\lambda=1.32{\mu}m\;;\;t_p\sim700{\mu}s)$ for heating sources and He : Ne $(\lambda=632.8nm)$ laser, high-power diode pumped laser $(\lambda=532nm)$, and Ti : $Al_2O_3$ femtosecond laser $(\lambda=850nm)$ for light scattering sources. A spectrometer and infrared radiometric sensor were used to monitor the backscattered light spectrum and transient temperature changes from cartilage following laser irradiation. Analysis of the optical, thermal, and quasi-elastic light scattering properties may indicate internal dynamics of proteoglycan movement within the cartilage framework during laser irradiation.

• Proceedings of the Korean Powder Metallurgy Institute Conference
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• 1993.11a
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• pp.2-2
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• 1993

The present status of the thennomechanica1 evaluation of functionally gradient materials(FGMs) for space plane application was reviewed, in which research activities and the cooperation of the national project team organized to study FGM science were demonstrated. The project team was divided into three working groups; de singing, processing and evaluation, each of which had their own tasks in the project cooperation. The testings details of the various thennomechanical tests for the FGM samples fabricated by the processing groups were described, along with their corresponding heating conditions of the real environments in the space plane application. For small-sized samples, laser beam heating test and burner heating test were well applied to study the heat shielding and heat resisting properties. Arc-heated wind tunnel test and high temperature!high velocity gas flow test were used for large-sized panel assemblies having cooling structures. The criteria for the evaluation of the heat shielding and heat resisting properties of the FGMs, as well as a crack activation mechanism in their differential temperature heating, were proposed on the basis of the observation in the burner heating test.

• Transactions of the Korean Society of Automotive Engineers
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• v.6 no.2
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• pp.144-154
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• 1998

A functionally graded material is a nonhomogeneous material, which is composed of several different materials to maintain structural rigidity and endure high temperature loads. An analytical method is presenter to solve the unsteady heat conduction equation for nonhomogeneous materials. A one-dimensional infinite plate made of functionally graded material is considered. The approximate Green's function solution is derived and to be used to obtain the temperature distribution them the stress distributions may be obtained. The volume fraction, the porosity, the stress difference, and the stress ratio are the design parameters and are to be used to set up a systematic design procedure.

• Earthquakes and Structures
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• v.9 no.3
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• pp.577-601
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• 2015

The thermomagnetic effect on plane wave propagation at the liquid-solid interface with nonclassical thermoelasticity is investigated. It is assumed that liquid-solid half-space is under initial stress. Numerical computations are performed for the developed amplitude ratios of P, SV and thermal waves under Cattaneo-Lord-Shulman theory, Green-Lindsay theory and classical thermoelasticity. The system of developed equations is solved by the application of the MATLAB software at different angles of incidence for Green and Lindsay model. The effect of initial stress and magnetic field in the lower half-space are discussed and comparison is made in LS, GL and CT models of thermoelasticity. In the absence of magnetic field, the obtained results are in agreement with the same results obtained by the relevant authors. This study would be useful for magneto-thermoelastic acoustic device field.

• Geomechanics and Engineering
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• v.21 no.1
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• pp.1-9
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• 2020

In this article, an analytical solution for the effect of the rotation on thermo-viscoelastic non-homogeneous medium with a spherical cavity subjected to periodic loading is studied. The distribution of displacements, temperature, redial stress, and hoop stress in non-homogeneous medium, in the context of generalized thermo-viscoelasticity using the GL theory, is discussed and obtained. The results are displayed graphically to illustrate the effect of the rotation. Comparisons with the previous work in the absence of rotation and viscosity are made.

• Proceedings of the KSR Conference
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• 2003.10c
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• pp.73-78
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• 2003

The residual stresses and. distortions of structures by welding exert negative effect on the safety of railroad structures. This investigation performs a thermal elasto-plastic analysis using finite element techniques to evaluate residual stresses in butted-welded joint. Considering this initial residual stresses, local stress and strain at the critical location (weld toe) during the loading were analyzed by elastic plastic finite element analysis. Fatigue crack initiation life and fatigue crack propagation life of butt-welded specimen were predicted by local strain approach and Neuber's role and Paris law. It is demonstrated that fatigue life estimates by local strain approach closely approximate the experimental results.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.31 no.10
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• pp.73-78
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• 2003

MEMS technology in the field of aerospace engineering is more important with light weight and high resolution. Therefore the investigation of thin films properties is issued and the residual stress of thin filrns is one of the important problems to solve. Ion implantation without thermal annealing is applied for the stress gradient relaxation of LPCVD polysilicon films used as the structural part in MEMS. He+ and Ar+ ion implantations reduce the stress gradient of polysilicon films. The property modification of polysilicon films by ion implantation is also investigated. The elastic modulus and hardness of polysilicon films with ion implantation is studied by CSM method which is an advanced nano-indentation method. Ion implantation decreases the elastic modulus and hardness of polysilicon films. However, they are improved with increasing ion dose.

• Journal of the Korean Society of Manufacturing Technology Engineers
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• v.7 no.6
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• pp.117-125
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• 1998

The paper attempts to estimate the incubation time of a cavity in the interface between a power law creep particle and an elastic matrix subjected to a uniaxial stress. Since the power law creep particle is time dependent, the stresses in the interface relax. The volume free energy associated with Helmholtz free energy includes strain energies caused by applied stress and dislocations piled up in interface(DPI). The energy due to DPI is found by modifying the result of Dundurs and Mura[4]. The volume free energies caused by both applied stress and DPI are a function of the cavity size(r) and elapsed time(t) and arise from stress relaxation in the interface. Critical radius $r^*$ and incubation time $t^*$ to maximise Helmholtz free energy is found in present analysis. Also, kinetics of cavity formation are investigated using the results obtained by Riede [7]. The incubation time is defined in the analysis as the time required to satisfy both the thermodynamic and kinetic conditions. Through the analysis it is found that 1) strain energy caused by the applied stress does not contribute significantly to the thermodynamic and kinetic conditions of a cavity formation, 2) in order to satisfy both thermodynamic and kinetic conditions, critical radius $r^*$ decreases or holds constant with increase of the time until the kinetic condition(eq. 2.3) is satisfied. there for the cavity may not grow right after it is formed, as postulated by Harris [15], and Ishida and Mclean [16], 3) the effects of strain rate exponent (m), material constant $\sigma$0, volume fraction of the particle to matrix(f)and particle size on the incubation time are estimated using material constants of the copper as matrix.

• Journal of the Korean Society for Heat Treatment
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• v.24 no.3
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• pp.149-155
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• 2011

Residual stress relief by pulse magnetic treatment is attractive because the process is carried out at room temperature and magnetic fields that are easy to produce and control can be used. This study shows that strong pulse magnetic treatment can lead to stress relaxation of structural steels instead of a conventional heat treatment process. And it makes a comparative study about pulse magnetic treatment and tempering by using Larson-Miller equation. When the specimen was subjected to a pulse magnetic treatment process the residual stress in the specimen was reduced by about 13.8%. It could be compared with tempering at $200^{\circ}C$ for 2hours by using thermal effect of Larson-Miller equation. As a result, it is considered that the pulsed magnetic treatment have an effect of the stress relation by tempering at $200^{\circ}C$ for 2 hours.