• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.30 no.1
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• pp.36-43
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• 2002

Thermopiezoelastic snap-through phenomena of piezolaminated plates are investigated by applying an are-length scheme to Newton-Raphson method. Based on the layerwise displacement theory and von Karman strain-displacement relationships, nonlinear finite element formulations are derived for the thermopiezoelastic composite plates. From the static and dynamic viewpoint, nonlinear thermopierzoelastic behavior and vibration characteristicx are stuied for symmetric and eccentric structural models with various piezoelestric actuation modes. Present results show the possibility to enhance the performance, namely thermopiezoelastic snapping, induced by the excessive piezoelectric actuation in the active suppression of thermally buckled large deflection piezolaminated paltes.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.31 no.1
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• pp.34-41
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• 2003

A Green's function approach is adopted for analyzing the thermoelastic deformation and stress analysis of a plate made of functionally graded materials (FGMs). The solution to the 3-dimensional steady temperature is obtained by using the laminate theory. The fundamental equations for thermoelastic problems are derived in terms of out-plane deformation and in-plane force, separately. The thermoelastic deformation and the stress distributions due to the bending and in-plane forces are analyzed by using a Green’Às function based on the Galerkin method. The eigenfunctions of the Galerkin Green's function for the thermoelastic deformation and the stress distributions are approximated in terms of a series of admissible functions that satisfy the homogeneous boundary conditions of the rectangular plate. Numerical examples are carried out and effects of material properties on thermoelastic behaviors are discussed.

• Journal of the Korean Society for Nondestructive Testing
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• v.30 no.2
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• pp.146-154
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• 2010

The effects of severe plastic deformation, equal channel angular pressing, and annealing of Al 5052 alloy on elastic modulus have been studied. The AI 5052 alloy was plastically deformed by ECAP method after solution treatment, and then finally annealing heat treated. Elastic modulus was measured by conventional tensile and nano-indentation test, and also measured on the surface of the specimen using acoustic material signature of the acoustic microscope. The variation in the elastic modulus influenced by plastic deformation and heat treatment, inaccessible by the conventional techniques, was successfully measured by acoustic material signature and obtained the elastic modulus depending on crystal orientation at each grain.

• Journal of the Korean Society of Propulsion Engineers
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• v.23 no.1
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• pp.108-115
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• 2019

The thermal response of elastomeric insulators used as protection against high-temperature and high-pressure combustion gases varies depending on their composition and thermal environment conditions. In this paper, the thermal response characteristics of elastomeric insulators in different mixing environments were compared. Tests to determine thermal protection performance were carried out using a thermal protection rubber evaluation motor(TPREM), combustion gas velocities of 20 m/s and 100 m/s were tested at a chamber pressure of 1,000 psig. The pressure time curve of the chamber, the temperature time curve of the internal materials, the residual thickness and the thermal destruction depth of the test specimens were obtained. The results showed that the thermal protection performance of elastomeric insulators in different mixing environments was similar.

• Journal of the Korean Geotechnical Society
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• v.31 no.3
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• pp.63-72
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• 2015

This paper describes the correlation and relationship between elastic moduli measured by three stiffness measurement methods with different mechanical characteristics to evaluate the compaction characteristics of subgrade soils. The Soil Stiffness Gauge (SSG) with very small strain (${\approx}0.001%$) ranges, static Plate Loading Test (PLT) with mid-level strain (${\approx}0.01{\sim}0.1%$) ranges, and Dynamic Cone Penetrometer (DCP) using penetration resistance were implemented to measure the elastic modulus. To use the elastic modulus measured by different measurement methods with a wide range of strain in practice, it is required to identify the correlation and relationship of measured values in advance. The comparison results of the measured elastic moduli ($E_{SSG}$, $E_{PLT}$, $E_{DCP}$) using the three measurement methods for domestic and overseas subgrade soils under various conditions indicate that the evaluated elastic modulus relies on the types of soils and the level of stress condition. The correlation analysis of the measured elastic moduli except the data of cement treated soils indicates that the static elastic modulus ($E_{PLT}$) is evaluated as about 60 to 80% of the dynamic elastic modulus ($E_{SSG}$). Unusual soils such as cement treated soils are required to be corrected by the stress correction during the correlation analysis with typical soils, because these types of soils are sensitive to the stress condition when measuring the static elastic modulus ($E_{PLT}$) of soils. In addition, when considering the use of DCP data for the evaluation of the elastic modulus ($E_{DCP}$), the measured data of the elastic modulus less than 200 MPa show more reliable correlation.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 1993.10a
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• pp.151-156
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• 1993

본 논문에서는 탄성바닥 위에서의 세개의 질량과 두개의 방지재로 구성된 지지계에 의한 진동절연의 이론적 고찰과 실험에 의한 검증을 하였다. 효과 적인 진동절연은 본 논문에서 기본적으로 관심을 가지는 탄성바닥에서의 진 동전달률을 감소시키는 것이며, 단순한 수학적 형태로 표현되는 진동전달률 공식은 영향계수법(Receptance Method)을 이용하여 유도된다.

• Elastomers and Composites
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• v.37 no.3
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• pp.183-191
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• 2002

Rubber materials with excellent damping property are widely applied for vibration isolators. The dynamic characteristics of the rubber materials for vibration isolators were investigated. Dynamic tests for rubber materials with five different hardness were performed. In dynamic tests for test specimen, non-resonance method was used to obtain the dynamic storage modulus and loss factor. Moreover, the effect of dynamic vibration frequency, strain amplitude and temperature were investigated. As results, the storage modulus and loss factor generally increase when the hardness and frequency increase, and the glass transition temperature is $-50^{\circ}C$ by a large change in modulus and loss factor.

• Journal of Korean Society of Disaster and Security
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• v.10 no.1
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• pp.35-42
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• 2017

This is a comparative study on the characteristics of excavated soils, which is proceeded using soil strength parameter by literature, geotechnical investigation, standard penetration test by drilling, and downhole test by borehole at six sites in urban areas. The results of these site surveys are used as basic data for the evaluation and development of prediction of ground subsidence risk. Geotechnical properties are estimated with the result of standard penetration test-N value and literature. The dynamic geotechnical characteristics are also estimated with top-down seismic exploration at borehole.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.38 no.6
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• pp.612-619
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• 2010

In this paper, an elastomeric bearing for a helicopter rotor hub is designed using nonlinear finite element method. The elastomeric bearing is the main component of the helicopter rotor hub that acts as a hinge to three motions(flapping, lagging and pitching) of rotor blade. The elastomeric bearing consists of rubber and metal plates. The stiffness design of the elastomeric bearing is important because elastic deformation of rubber is served to hinge. Accordingly, the elastomeric bearing is designed to satisfy the stiffness requirements for rotor hub bearing. In this study, a FE model generation algorithm is developed and stiffness characteristic of a rubber plate is analyzed for an efficient design of the spherical elastomeric bearing. It is proven that the elastomeric bearing satisfies stiffness requirements of the spherical bearing for a helicopter rotor hub.

• Journal of the Korean earth science society
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• v.27 no.5
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• pp.539-547
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• 2006

The activity of the seismic wave propagation around the cavity is investigated for the exact inversion of the crosshole tomography data, in order to understand the possibility of the existence inside the underground cavity. It is found that the adequate frequency range for the tunnel investigation is about 2 kHz to 5 kHz, and the grid space should be set up to 1/10 of the wavelength. The propagation of the seismic wave near the cavity may go through or detour the cavity according to the seismic velocity inside the cavity. The detouring wave propagates with the seismic velocity of mother rock in spite of the velocity of inside of the cavity. The smaller the velocity difference is between the mother rock and cavity, the more frequent penetration of the seismic wave through the cavity appears.