• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2001.07a
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• pp.161-164
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• 2001

In this paper, we investigated the dielectric and piezoelectric properties of Pb(Sb, Nb)O$_3$-Pb(Zr, Ti)O$_3$ ceramic(PSN) for piezoelectric transformer and actuator etc. Effect of MnO$_2$ addition on the PSN ceramic was investigated. Anisotropic properties of electromechanical coupling factor and piezoelectric properties proved to be varied with amount of MnO$_2$ impurity and sintering temperature. The electromechanical coupling factor k$_{p}$ of 0.38 and the mechanical quality factor Q$_{m}$ of 1944 were obtained from the specimen with 0.4 wt% MnO$_2$ sintered at 115$0^{\circ}C$ addition. Experimental results indicated that the PSN ceramic with MnO$_2$ impurity can be effectively used for piezoelectric transformer and actuator.tor.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.24 no.2
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• pp.131-135
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• 2011

We have been studied the effects of oxidant on the properties of Sr-ferrite magnets using mill scale for motor. The small-added (0.5 wt%) $NaNO_3$ oxidant improved significantly the degree of oxidation and the grindability of mill scale, and then highly enhanced the magnetic properties of anisotropic Sr-ferrite sintered magnets; such as the remanent flux density from 3.55 to 3.80 kG, the intrinsic coercivity from 2.75 to 3.22 kOe, and the maximum energy product from 2.90 to 3.45 MGOe.

• Proceeding of EDISON Challenge
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• 2015.03a
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• pp.285-291
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• 2015

In this paper, a composite material analysis program based on the finite element method(FEM) is used. The purpose of this study was to verify whether the composite material analysis program which developed as part of a project of development of softwares and educational contents for structural vibration and composite material analysis that can calculate how similar the macroscopic mechanical behavior of the composite materials actually. Because composite materials are generally anisotropic, analysis of composite laminate is used for the constitutive equations of orthotropic material. For convenience, the unit is ommited in all calculations. To verify the accuracy of the finite element method based program, the deflection and stress distribution of the simply supported composite material laminated plate subjected to a uniform load distribution is compared with exact solution. Size and properties of the composite material laminate used for analysis are fixed variables, and by changing the number of elements and the total thickness of the laminate is compared with the exact solution to the resulting value, respectively.

• Journal of the Microelectronics and Packaging Society
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• v.15 no.2
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• pp.7-15
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• 2008

In this paper, the Chip-On-Flex (COF) assembly process using anisotropic conductive films (ACFs) was investigated and the reliability of COF assemblies using ACFs was evaluated. Thermo-mechanical properties of ACFs such as coefficient of thermal expansion (CTE), storage modulus (E'), and glass transition temperature $(T_g)$ were measured to investigate the effects of ACF material properties on the reliability of COF assemblies using ACFs. In addition, the bonding conditions for COF assemblies using ACFs such as time, temperature, and pressure were optimized. After the COF assemblies using ACFs were fabricated with optimized bonding conditions, reliability tests were then carried out. According to the reliability test results, COF assemblies using the ACF which had lower CTE and higher $T_g$ showed better thermal cycling reliability. Consequently, thermo-mechanical properties of ACFs, especially $T_g$, should be improved for high thermal cycling reliability of COF assemblies using ACFs for compact camera module (CCM) applications.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.11 no.4
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• pp.274-280
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• 1998

Polycrystalline $Sr_2Nb_2O_7$ ceramics with very high Curie temperature were sintered using the powder derived by the chemical coprecipitation method (CCP). The phase evolution and grain-orientation of sintered samples were examined by XRD, while sintering behavior, dielectric properties and polarization were studied by SEM and ferroelectric tester. Extremely high degree of grain-orientation was observed along the (0k0) direction, which resulted in anisotropic dielectric properties of the sintered samples, with the dielectric constant values approaching those for single crystal. Thin film fabrication of $Sr_2Nb_2O_7$ in the pyroniobate family was also attempted on $SiO_2$/Si(100), Pt/$SiO_2$/Si(100), Pt/Ti/$SiO_2$/Si(100) and Pt/$ZrO_2/SiO_2/Si_2(100)$ substrates, using metalorganic decomposition (MOD) process. Neodecanoate precursor solution was prepared by mixing strontium neodecanoate with niobium neodecanoate synthesized from niobium ethoxide. It was found that $Sr_2Nb_2O_7$ single phase appeared in XRD patterns the samples annealed above $950^{\circ}C$. The effect of substrate type on film microstructure and dielectric properties was observed.

• Structural Engineering and Mechanics
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• v.59 no.6
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• pp.951-972
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• 2016

The purpose of this study is to illustrate the propagation of the shear waves (SH-waves) in a prestressed hetrogeneous orthotropic media overlying a pre-stressed anisotropic porous half-space with self weight. It is considered that the compressive initial stress, mass density and moduli of rigidity of the upper layer are space dependent. The proposed model is solved to obtain the different dispersion relations for the SH-wave in the elastic-porous medium of different properties. The effects of compressive and tensile stresses along with the heterogeneity, porosity, Biot's gravity parameter on the dispersion of SH-wave are shown numerically. The wave analysis further indicates that the technical parameters of upper and lower half-space affect the wave velocity significantly. The results may be useful to understand the nature of seismic wave propagation in geophysical applications and in the field of earthquake and material science engineering.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.27 no.1
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• pp.94-101
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• 2003

The pressure tubes made of cold-worked Zr-2.5Nb alloy are subjected to creep deformation during service period resulting in changes to their geometry such as longitudinal elongation, diameter increase and sagging. To evaluate integrity of them, information on the material creep property of the serviced tubes is essential. As one of the methods with which the creep property is directly measured from the serviced components, small punch(SP) creep testing has been considered as a substitute for the conventional uniaxial creep testing. In this study, applicability of the SP creep testing to Zr-2.5Nb pressure tube alloy was studied particularly by measuring the power law creep constants, A, n. The SP creep test has been successfully applied fur other high temperature materials which have isotropic behavior. Since the Zr-2.5Nb alloy has anisotropic property, applicability of the SP creep testing can be limited. Uniaxial creep tests and small punch creep tests were conducted with Zr-2.5Nb pressure tube alloy along with finite element analyses. Creep constants obtained by each test method are compared. It was argued that the SP creep test result gave results reflecting material properties of both directions. But the equations derived in the previous study for isotropic materials need to be modified. Discussions were made fur future research directions for application of the SP creep testing to Zr-2.5Nb tube alloy.

• Journal of the Korea Institute of Military Science and Technology
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• v.22 no.4
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• pp.492-500
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• 2019

Equal channel angular pressing(ECAP) is a severe plastic deformation technique capable of introducing large shear strain in bulk metal materials. However, if an ECAPed material has an inhomogeneous microstructure and anisotropic mechanical properties, this material is difficult to apply as structural components subjected to multi-axial stress during use. In this study, extruded oxygen-free copper(OFC) rods with a large diameter of 42 mm are extruded through ECAP by route Bc up to 12 passes. The variations in the microstructure, hardness, tensile properties, and microstructural and mechanical homogeneity of the ECAPed samples are systematically analyzed. High-strength OFC rods with a homogeneous and equiaxed-ultrafine grain structure are obtained by the repeated application of ECAP up to 8 and 12 passes. ECAPed samples with 4 and 8 passes exhibit much smaller differences in terms of the average grain sizes on the cross-sectional area and the tensile strengths along the axial and circumferential directions, as compared to the samples with 1 and 2 passes. Therefore, it is considered that the OFC materials, which are fabricated via the ECAP process with pass numbers of a multiple of 4, are suitable to be applied as high-strength structural parts used under multi-axial stress conditions.

• Journal of the Computational Structural Engineering Institute of Korea
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• v.37 no.5
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• pp.309-316
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• 2024

In this paper, additive manufacturing (AM)-structural coupled analysis was proposed to accurately predict the mechanical behavior of 3D printed short-fiber reinforced composite structures. Tensile specimens were printed using a composite 3D printer (Mark Two, Markforged), and tensile tests were conducted on specimens manufactured with various nozzle paths. In addition, a reverse engineering scheme was applied to the experimental data to reasonably derive local anisotropic material properties according to the nozzle paths. Consequently, AM-structural coupled analysis was performed using the enhanced finite element model with mapped local materials properties, and the mechanical behavior of the 3D printed short-fiber reinforced composite was accurately described. To demonstrate the effectiveness of the proposed AM-structural coupled analysis model, the computational results obtained were compared with experimental results.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.23 no.7 s.166
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• pp.1075-1084
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• 1999

The family of unidirectional continuous fiber reinforced polymeric composites are currently used in automotive bumper beams and load floors. The material properties and mechanical characteristics of the compression molded parts are determined by the curing behavior, fiber orientation and formation of knit lines, which are in turn determined by the mold filling parameters. In this paper, a new model is presented which can be used to predict the 3-dimensional flow under consideration of the slip of mold-composites and anisotropic viscosity of composites during compression molding of unidirectional fiber reinforced thermoplastics for isothermal state. The composites is treated as an incompressible Newtonian fluid. The effects of longitudinal/transverse viscosity ratio A and slip parameter $\alpha$ on the buldging phenomenon and mold filling patterns are also discussed.