• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2000.06a
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• pp.831-836
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• 2000

In this study, the Rayleigh inextensional theory and extensional theory for thin shells was employed to predict the natural frequencies of the hemi-spherical shell with free and simply. supported boundary condition. The frequencies and mode shapes from theoretical calculation were compared with those of commercial finite element code, ANSYS. In order to validate the theory, modal test was also performed by impact test and FFT analysis. Modal test and FEM analysis of the free, simply supported and clamped boundary condition was also carried out.

• Proceedings of the KIEE Conference
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• 1990.07a
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• pp.243-246
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• 1990

The theory was analyzed and the computer program was developed for simulation about ceramic filter in the state of the one-strip electrode using the energy trapping effect. They were fabricated using the PZT-4 specimen. Each of the average differances of the resonant point and bandwidth between by the theoretical calculations and by experiment results was 5.6[%] and 3.72[%], and it is considered that this differance is originated from the high temperature and stress during the process that the ceramic filter was fabricated It is considered that the one-strip ceramic filter having a wanted characteristics and the lowest differance is fabricated easily by means of the simulation developed in this paper and the fabrication methods.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 1999.05a
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• pp.630-633
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• 1999

This paper presents a new sort of multilayer piezoelectric ceramice transformer for switching regulatied power supplies. And this paper presents the study and development of a DC-DC converter with a transformer made from piezoelectric materials. This piezoelectric transformer operate, in the second thickness extensional vibration mode. Its resonant frequency is higher than 1MHz, This piezoelectric transformer was used the PbTiO$_3$ family ceramics because it was a material large anisotropy between electromechanical coupling factors k$_{t}$ and k$_{p}$. The input and output layer consists of two piezoelectric ceramic layer for eleivater of outpur power.wer.

• Composites Research
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• v.29 no.6
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• pp.347-352
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• 2016

This work presents the free vibration characteristics of laminated composite corrugated rectangular plates using the analytical method. Because it is very difficult to determine its mechanical behavior of 3-dimensional corrugated structures analytically, the equivalent homogenization model is adapted to investigate the overall mechanical behavior of corrugated structures. The corrugated element can be homogenized as an orthotropic material. Both the effective extensional and flexural stiffness of this homogenized equivalent orthotropic material are considered in the analysis. The present analytical results are validated by those obtained from 3D finite element analysis based on shell elements. The natural frequencies and global vibration mode shapes obtained from present analytical and finite element analysis are presented. Some numerical results are presented to check the effect of the geometric properties.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.27 no.1
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• pp.27-32
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• 2014

In this paper, PZT piezoelectric ceramic specimens with 4 compositions (Zr/Ti=50/50, 53/47, 56/44, 58/42) in $Pb(Zr,Ti)O_3$ system were fabricated. We studied effects of poling strength and thermal aging on the temperature characteristics of eletromechanical coupling factor k31 of the specimens, which were poled with the DC electric fields, 1.5, 2.5 and 3.5 kV/mm respectively and thermally aged for an hour at $200^{\circ}C$. The eletromechanical coupling factor k31 of the specimen with the composition Zr/Ti= 53/47, nearest to the morphotropic phase boundary decreased the most greatly, irrelevant to the intensity of poling field, due to 1st thermal aging. And the temperature coefficient of eletromechanical coupling factor k31 was (-) in the tetragonal phase composition and (+) in the rhombohedral phase composition, which is reverse in the temperature coefficient of resonance frequency. It is interesting that eletromechanical coupling factor k31 of PZT ceramics is shown to be able to increase as temperature increase in the interval $-20{\sim}80^{\circ}C$.

• Structural Engineering and Mechanics
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• v.37 no.2
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• pp.149-162
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• 2011

The aim of this research is a comprehensive review and evaluation of beam theories resting on elastic foundations that used to model mode-I delamination in multidirectional laminated composite by DCB specimen. A compliance based approach is used to calculate critical strain energy release rate (SERR). Two well-known beam theories, i.e. Euler-Bernoulli (EB) and Timoshenko beams (TB), on Winkler and Pasternak elastic foundations (WEF and PEF) are considered. In each case, a closed-form solution is presented for compliance versus crack length, effective material properties and geometrical dimensions. Effective flexural modulus ($E_{fx}$) and out-of-plane extensional stiffness ($E_z$) are used in all models instead of transversely isotropic assumption in composite laminates. Eventually, the analytical solutions are compared with experimental results available in the literature for unidirectional ($[0^{\circ}]_6$) and antisymmetric angle-ply ($[{\pm}30^{\circ}]_5$, and $[{\pm}45^{\circ}]_5$) lay-ups. TB on WEF is a simple model that predicts more accurate results for compliance and SERR in unidirectional laminates in comparison to other models. TB on PEF, in accordance with Williams (1989) assumptions, is too stiff for unidirectional DCB specimens, whereas in angle-ply DCB specimens it gives more reliable results. That it shows the effects of transverse shear deformation and root rotation on SERR value in composite DCB specimens.

• The Journal of Engineering Geology
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• v.19 no.3
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• pp.351-363
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• 2009

Two orthogonal joint sets develop well only in sandstone beds in the sandstone-mudstone sequences of Gumi and Dasa outcrops within Cretaceous Gyeongsang Basin. And various joint data are similar in the beds of the same thickness in both outcrops, meaning that the joint sets were homogeneously produced by extensional deformation in the same regional stress field. Most of joints in the sandstone beds are orthogonal to, and confined by bed boundaries, which are believed to be formed by hydrofracturing during consolidation after burial. Two orthogonal joint sets are considered to be almost coeval on the basis of mutual abutting relationship which makes up fracture grid-lock and a product of rapid switching of ${\sigma}_2$ and ${\sigma}_3$ axes with constant ${\sigma}_1$ direction oriented to vertical. The joint sets in the sandstone beds show planar surfaces, parallel orientations and regular spacing, with joint spacing linearly proportional to bed thickness. The spacing distributions of the joints seem to correspond to log-normal to almost normal distribution in most of the beds. But multilayer joints do not display regular spacing and dominant size. Either joint set in this study is characterized by a high level of joint density and a saturated spacing distribution as indicated by the mode/mean ratio values and the Cv(coefficient of variance) values. Joint aperture tends to increase with the vertical length of the joints controlled by bed thickness.

• Tunnel and Underground Space
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• v.13 no.1
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• pp.44-51
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• 2003

Changes of the hydraulic conductivity resulting from the redistribution of stresses by underground excavation are examined using the strain-dependent hydraulic conductivity modification relation, where the modulus reduction ratio and induced strain are the major parameters. The modulus reduction ratio is defined in terms of RMR(Rock Mass Rating) to represent the full gamut of rock mass condition. Though shear dilation has the effect on the modification of hydraulic conductivity, the extent of it depends on RMR When the extensional strain is applied to a fracture, the hydraulic conductivity increases with the decrease of RMR Loading configuration has the effect on the modification of hydraulic conductivity, where the differential stress mode with a magnitude of the minimum principal stress $($\sigma$_x)$ fixed and a magnitude of the maximum principal stress $($\sigma$_y)$ varied is found to exert the greatest effect on the change of hydraulic conductivity.

• Composites Research
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• v.14 no.3
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• pp.1-9
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• 2001

A new non-destructive fatigue prediction model of the composite laminates is developed. The natural frequencies of fatigue-damaged laminates under extensional loading are related to the fatigue life of the laminates by establishing the equivalent flexural stiffness reduction as a function of the elastic properties of sublaminates. The flexural stiffness is derived by relating the 90-ply elastic modulus reduction, and using the laminate plate theory to the degraded elastic modulus and the intact elastic modulus of other laminates. The natural frequency reduction model, in which the dominant fatigue mode can be identified from the sensitivity scale factors of sublaminate elastic properties, provides natural frequency vs. fatigue cycle curves for the composite laminates. Vibration tests were also conducted on $[{90}_2/0_2]_s$ carbon/epoxy laminates to verify the natural frequency reduction model. Correlations between the predictions of the model and experimental results are good.