• Transactions of the Korean Society of Mechanical Engineers
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• v.14 no.2
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• pp.269-275
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• 1990

Nonaxisymmetric bifurcation behaviours of composite tubes two different materials subjected to uniform radial shrinkage at the external surface have been investigated and compared with those of single tube. The effect of material parameters normalized with respect to those of outer tube upon the bifurcation point and corresponding mode has been clarified. The parameters substantially affect the bifurcation mode with long-wavelength so that the composite tube with low hardening exponent or with high yield stress of inner tube destabilizes the overall deformation of the tube. However surface type bifurcation, short-wavelength mode, shown on the traction-free inner surface is hardly affected by the material parameters. The surface type bifurcation completely depends on the material characteristics of inner tube and the bifurcation point of composite tube almost coincides with the of single tube.

• Steel and Composite Structures
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• v.24 no.5
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• pp.579-589
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• 2017

The objective of this work is to analyze post-buckling of functionally graded (FG) beams with porosity effect under compression load. Material properties of the beam change in the thickness direction according to power-law distributions with different porosity models. It is known that post-buckling problems are geometrically nonlinear problems. In the nonlinear kinematic model of the beam, total Lagrangian finite element model of two dimensional (2-D) continuum is used in conjunction with the Newton-Raphson method. In the study, the effects of material distribution, porosity parameters, compression loads on the post-buckling behavior of FG beams are investigated and discussed with porosity effects. Also, the effects of the different porosity models on the FG beams are investigated in post-buckling case.

• Wind and Structures
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• v.27 no.1
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• pp.59-70
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• 2018

In this paper, geometrically non-linear analysis of a functionally graded simple supported beam is investigated with porosity effect. The material properties of the beam are assumed to vary though height direction according to a prescribed power-law distributions with different porosity models. In the nonlinear kinematic model of the beam, the total Lagrangian approach is used within Timoshenko beam theory. In the solution of the nonlinear problem, the finite element method is used in conjunction with the Newton-Raphson method. In the study, the effects of material distribution such as power-law exponents, porosity coefficients, nonlinear effects on the static behavior of functionally graded beams are examined and discussed with porosity effects. The difference between the geometrically linear and nonlinear analysis of functionally graded porous beam is investigated in detail. Also, the effects of the different porosity models on the functionally graded beams are investigated both linear and nonlinear cases.

• Progress in Superconductivity and Cryogenics
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• v.15 no.2
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• pp.39-43
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• 2013

$MgB_2$ bulk samples are synthesized through solid state reaction route using Mg precursors with different particle size by keeping the boron precursor unchanged. Scanning electron microscopy study of the fractured surface for all the samples depicts quite distinct structure depending on the Mg precursor. Big size of Mg precursor resulted in to largely elongated and deep pores while smaller one gave roughly ellipsoidal and shallow pore structure. Influence of the Mg particle size on the grain to grain connectivity reflected in the critical current density value which was greater for samples with smaller Mg precursor. All the synthesized samples undergo a superconducting transition at around 36.5 K irrespective of different Mg precursor particle size.

• The Journal of Korean Academy of Prosthodontics
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• v.29 no.2
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• pp.59-66
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• 1991

This study was designed to investigate the marginal accuracy of resin temporary crown with different matrix in indirect technique. Matrices were made from irreversible hydrocolloid impression material, putty type of vinyl polysiloxane silicone rubber and vacuum formed plastic sheet. The marginal discrepancies of the temporary crowns were measured using a measuring microscope. The obtained results were as follows 1. The marginal accuracy temporary crown using vinyl polysiloxane silicone rubber or vacuum formed plastic form was better than that of the temporary crown using irreversible hydrocolloid impression material. 2. The marginal accuracies of the temporary crown using the irreversible hydrocolloid impression material and putty type of the vinyl polysiloxane silicone rubber obtained the best results at the distal measuring point. 3. The vacuum formed plastic form was recorded a more acceptable marginal accuracy at the distal and mesial measuring points.

• Proceedings of the Acoustical Society of Korea Conference
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• autumn
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• pp.219-222
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• 2001

Nondestructive nonlinear acoustic method in two dimensions is suggested as a useful tool for detecting defects in a composite layer-structured material. Spectrum level changes in fundamental and harmonic frequencies are observed in the presence of a layer type defect compared with in the absence of such a defect. It is proposed in this study that such spectrum changes we due to the mode conversion. The layer type defect makes different normal modes due to different boundary conditions in the thickness direction for the Lamb waves propagating in a layer-structured material. Specifically, the normal mode with the fundamental frequency in the case of the water-layer gap is converted to the normal mode with the second harmonic frequency in the case of the air-layer gap.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 1996.11a
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• pp.903-907
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• 1996

Under two level block loading, the carbornitrizing specimen can be expected to show different behavior from other uniform material because the properties of surface layer and inner material are different from each other. In this research, the modified Marco-Starkey cumulative theory, which considers load interaction effect, can predict the life of SCM415 carbornitrizing and original notched and smooth specimen, In the low-high test of carbornitrizing specimen which has long life, however, we may additionally consider the increase of life by means of the stress hardening of inner original material.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 1996.11a
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• pp.3-8
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• 1996

To enhance the cutting performance of the tool, single or multilayer coating is applied on the substrate of the tool. Coating material reduces cutting force and heat generation in tool-chip contact zone and enhances resistance against abrasive wear. This paper presents that the effect of different coatings on abrasive wear resistance varies with work material and the flank wear rate is different with depth of cut. Crater wear rate is also found to decrease with higher thermal diffusivity of coating material. It is verified that the estimated thermal diffusivity of multilayer coating has consistent effect on the crater wear.

• Proceedings of the Korean Vacuum Society Conference
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• 2012.02a
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• pp.384-384
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• 2012

PRAM switching device by using current pulse modulation was investigated to verify its possibility for 3D architecture. In this work, two phase change materials connected in series having a different crystallization temperature are used. Its structural for different phase change material was evaluated by electrical resistance. We confirmed that Germanium-Antimony-Tellurium (GST) alloy and Germanium- Copper-Tellurium (GCT) alloy material were selected according to crystallization temperature, ${\sim}180^{\circ}C$ for switching and ${\sim}240^{\circ}C$ for memory devices, respectively. From this research, it is expected that phase change switching device could have advantages of process in terms of material similarity and structural simplification.

• Journal of Welding and Joining
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• v.31 no.2
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• pp.37-42
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• 2013

Different microstructures in the weld zone of a metal structure such as a fusion zone or heat affected zone are formed as compared to the parent material. Thus, the mechanical properties in the weld zone are different from those in the parent material. As the basic data for reliably understanding the structural characteristics of welded PCHE prototype made of SUS316L, the mechanical properties in the weld zone and parent material for a SUS316L plate are measured using an the instrumented indentation technique in this study.