• The Journal of Engineering Geology
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• v.13 no.2
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• pp.227-238
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• 2003

Understanding of a creep behavior in rocks under a constant load, due to visco-elastic properties of rock, is an essential element to predict a long term ground deformation. In order to clarify the creep characteristics of the mudstone in Duho formation at Pohang basin, deposited during Tertiary, a series of laboratory tests including physical properties, unconfined compressive strength and uniaxial creep tests, was performed. The mudstone showed a higher creep potential due to 26% of clay minerals such as illite and chlorite. The unconfined compressive strength of the rock was $462{\;}kg/\textrm{cm}^2$ in average, and four creep tests were performed under constant stress of 40 to 70 % of the strength. The creep constants in the empirical and theoretical equations were deduced from the time-strain curves obtained from the tests. Among the several equations, the empirical equation proposed by Griggs and theoretical equation of Burger’s model are appreciated as the best one to express the creep behavior of the mudstone. Instantaneous elastic strain was linearly increased with stress level but strain velocity during the first creep is decreased with a similar pattern by time lapse regardless the stress level.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2002.11b
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• pp.244-249
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• 2002

Rubber seat is extensively used to reduce the vibration of machine or structure. Over the years an enormous effort has been put into developing procedures to provide properties of rubber material for design function. However, there are still a lot of difficulties to analyze static characteristics of rubber components with hyper elasticity and nonlinear large deformation. In this paper material property is obtained by strain-stress curve using a tension test. Mooney-Rivlin Coefficients are gotten by fitting strain-stress curve. The visco-elastic characteristics of refrigerator rubber mount is determined by using ANSYS. And to minimize the rubber stiffness, the rubber seat shape optimization is performed.

• The Journal of the Acoustical Society of Korea
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• v.8 no.1
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• pp.31-37
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• 1989

The effectiveness of using a composite beam with constrained visco-elastic layer as a dynamic vibration absorber is investigated. The performance of this absorber is evaluated in terms of displacement transmissibility when to a primary beam with built-in ends and compared to that of the uniform beam absorber. The results of analysis and design show that it is possible to suppress simultaneoulsy the peak transmissibilities at two or more resonance frequencies and the optimal parameters are located within the available viscoelastic material properties.

• Proceedings of the Earthquake Engineering Society of Korea Conference
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• 2001.04a
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• pp.379-386
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• 2001

Fluid viscous dampers have been used as energy dissipators or STU's (Shock Transmission Unit) in earthquake resistant designs for bridges. Viscous dampers have many advantages compared to other friction type or visco-elastic type of dampers. They do neither increase internal pier forces due to their out of phase response, nor produce reaction forces at the low velocities associated with thermal movements. Therefore, they anable the super structure to restore itself perfectly after a severe movement dut to seismic excitations. This paper investigates the response of bridges designed with viscous dampers in regard to damping coefficients, properties of dampers, and arrangements of dampers. For this purpose, time-history dynamic analyses have been performed using a very simple model relevant to a typical bridge example. Based on the results, it presents some design duidelines on how to determine a proper damping ratio and on how to arrange dampers. In usual cases, damping coefficients corresponding to about 0.2-0.3 of damping ratios seem to be very effective in bridge designs.

• Advances in aircraft and spacecraft science
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• v.7 no.2
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• pp.169-186
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• 2020

Based upon differential quadrature method (DQM) and nonlocal strain gradient theory (NSGT), mechanical-hygro-thermal vibrational analyzes of shear deformable porous functionally graded (FG) nanoplate on visco-elastic medium has been performed. The presented formulation incorporates two scale factors for examining vibrational behaviors of nano-dimension plates more accurately. The material properties for FG plate are porosity-dependent and defined employing a modified power-law form. It is supposed that the nano-size plate is exposed to hygro-thermal and variable compressive mechanical loadings. The governing equations achieved by Hamilton's principle are solved implementing DQM. Presented results indicate the prominence of moisture/temperature variation, damping factor, material gradient index, nonlocal coefficient, strain gradient coefficient and porosities on vibrational frequencies of FG nano-size plate.

• Journal of the Korean Wood Science and Technology
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• v.37 no.4
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• pp.310-319
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• 2009

The representative eco-friendly materials, or bio-composites, were made by incorporating biodegradable polymer of polybutylene succinate (PBS) as the matrix and bamboo flour (BF) as the natural filler. In present study, the effects of content and particle size of natural filler on the bio-composites were carried out around their mechanical, visco-elastic, and thermal properties. By the incorporation of BF, the tensile properties decreased but the viscoelastic and thermal properties revealed positive effect through interaction between the polymer and natural filler. Also, the vulnerability of interfacial adhesion between hydrophobic PBS and hydrophilic BF appeared to adversely affect the properties of bio-composites.

• Fashion & Textile Research Journal
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• v.15 no.6
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• pp.985-992
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• 2013

Polytrimethylene terephthalate(PTT) offers several advantageous properties such as good tensile strength, uniformity, stiffness, toughness, UV stability, resilience, stain resistance, outstanding elastic recovery, and dyeability. The effects of annealing temperature on physical properties and the structure of PTT filaments and yarn were investigated by measuring wide-angle X-ray diffraction (WAXD), density, optical birefringence, dynamic visco elasticity, and tensile testing. The intensity of maximum tan ${\delta}$ decreased and the temperature of maximum tan ${\delta}$ shifted to a higher temperature as the annealing temperature of filaments increased; however, it shifted to a lower temperature when the annealing temperature exceeded $130^{\circ}C$. In addition, crystallinity, density and D-spacing of (010) crystal face increased as the annealing temperature increased. Optical birefringence and specific stress were almost constant up to $100^{\circ}C$ and then decreased above $130^{\circ}C$. The shrinkage of PTT filament is 0 in boiling water when annealed above $130^{\circ}C$; consequently, the use of annealed fiber above $130^{\circ}C$ can remove thermal instability when dyeing PTT fiber. In the case of yarns, the thermal stability and physical properties of yarns showed the best effect when the ply number is less than 5, twist number is less than 400tpm, and the annealing time is 20minutes.

• Applied Chemistry for Engineering
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• v.23 no.5
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• pp.480-484
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• 2012

Concrete, the mixture of cement, sand, gravel and water, is a suspension substance extensively used to construct building materials. When a concrete mortar is applied to the underwater construction, the rheology of concrete is of great importance to its flow performance, placement, anti-washout and consolidation. In this research, the anti-washout and rheological properties of concrete have been investigated with concrete admixtures prepared by adding anionic surfactants, cationic surfactants, and polymeric thickeners. The concrete mortar formulated by pseudo-polymeric systems with the electrostatic association of anionic and cationic surfactants, showed high viscosities and suitable anti-washout properties, but poor pumpabilities. The addition of poly methyl vinyl ether to the mixed surfactant system exhibits synergistic effects by improving the concrete mortar properties of the concrete mortar such as fluidity, visco-elastic property, self-leveling, and anti-washout.

• Structural Engineering and Mechanics
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• v.52 no.3
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• pp.573-593
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• 2014

Pounding between adjacent buildings is a significant challenge in metropolitan areas because buildings of different heights collide during earthquake excitations due to varying dynamic properties and narrow separation gaps. The seismic responses of adjacent buildings of varying height, coupled through soil subjected to earthquake-induced pounding, are evaluated in this paper. The lumped mass model is used to simulate the buildings and soil, while the linear visco-elastic contact force model is used to simulate pounding forces. The results indicate while the taller building is almost unaffected when the shorter building is very short, it suffers more from pounding with increasing height of the shorter building. The shorter building suffers more from the pounding with decreasing height and when its height differs substantially from that of the taller building. The minimum required separation gap to prevent pounding is increased with increasing height of the shorter building until the buildings become almost in-phase. Considering the soil effect; pounding forces are reduced, displacements and story shears are increased after pounding, and also, minimum separation gap required to prevent pounding is increased.

• Steel and Composite Structures
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• v.23 no.6
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• pp.691-714
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• 2017

Rotating fluid induced vibration and instability of embedded piezoelectric nano-composite separators subjected to magnetic and electric fields is the main contribution of present work. The separator is modeled with cylindrical shell element and the structural damping effects are considered by Kelvin-Voigt model. Single-walled carbon nanotubes (SWCNTs) are used as reinforcement and effective material properties are obtained by mixture rule. The perturbation velocity potential in conjunction with the linearized Bernoulli formula is used for describing the rotating fluid motion. The orthotropic surrounding elastic medium is considered by spring, damper and shear constants. The governing equations are derived on the bases of classical shell theory (CST), first order shear deformation theory (FSDT) and sinusoidal shear deformation theory (SSDT). The nonlinear frequency and critical angular fluid velocity are calculated by differential quadrature method (DQM). The detailed parametric study is conducted, focusing on the combined effects of the external voltage, magnetic field, visco-Pasternak foundation, structural damping and volume percent of SWCNTs on the stability of structure. The numerical results are validated with other published works as well as comparing results obtained by three theories. Numerical results indicate that with increasing volume fraction of SWCNTs, the frequency and critical angular fluid velocity are increased.