• Composites Research
• /
• v.27 no.1
• /
• pp.31-36
• /
• 2014

This paper presents the slip behavior of composite fabrics by high speed resin flow in high pressure resin transfer molding. In order to observe the fiber deformation behavior, we constructed the measuring equipment for friction coefficient between fiber and mold, and the monitoring system for deformation of fiber preform in high-pressure RTM process. Coulomb friction coefficient and hydrodynamic friction coefficient between fiber preform and mold were measured and the external force induced by fluid flow causing the deformation of fiber preform was measured. Friction force calculated by friction coefficient and the external force upon fiber deformation were compared, which showed that preform deformation occurred when the external force was bigger than the friction force. The slip behavior of the fiber preform was mainly influenced by the volume fraction of fiber preform and the friction coefficient.

• Journal of the Earthquake Engineering Society of Korea
• /
• v.15 no.2
• /
• pp.61-69
• /
• 2011

In this paper, the factors affecting the dynamic characteristics of a polyurethane spring restoring disk bearing are analysed to predict the dynamic behavior of the bearing. The prediction results and the test results are compared. The Young's modulus of the polyurethane spring, which varies according to strain of spring and the friction coefficient, of PTFE (PolyTetraFluoroEthylene), which varies according to the velocity and pressure of PTFE, are considered as the factors influencing the dynamic characteristics. W-PTFE virgin products are used and polyurethane springs are produced for the tests. The equation related to changing the friction coefficient and the modulus of elasticity are obtained through an inverse estimation of the test results. The estimation results, considering the factors affecting the dynamic characteristics, simulate the test results more appropriately than the estimation without the consideration of those factors.

• Tunnel and Underground Space
• /
• v.33 no.1
• /
• pp.42-56
• /
• 2023

In deep geological disposal of high-level radioactive waste (HLW), the natural barrier must physically support the disposal facility and delay the movement of radionuclides for at least hundreds of thousands of years. To evaluate the long-term geological evolution of the natural barriers, it is essential to analyze the long-term behavior of rock joints, including the frictional healing behavior. This study aimed to experimentally analyze the frictional healing behavior of rock joints under hydro-mechanical (H-M) conditions through the slide-hold-slide (SHS) test. The SHS tests were performed under mechanical and H-M conditions for joint specimens of different roughness. In the H-M conditions, the frictional healing rate tended to increase, which was more evident in the specimens with large roughness. In addition, it was confirmed that the effect of the hydro-mechanical conditions was more significant when the effective normal stress acting on the joint surface was small. These results are expected to be used as fundamental data to understand the frictional healing behavior of rock joints in the natural barriers.

• Journal of the Korea Academia-Industrial cooperation Society
• /
• v.15 no.1
• /
• pp.488-494
• /
• 2014

Although friction pendulum system has various advantages it is difficult to estimate the behavior because of velocity, bearing pressure, and temperature dependent characteristics of coefficient of friction. This research focuses on evaluating the conservatism of each method used and the effects of bearing pressure on the behavior of the system by conducting comprehensive examination on design and analytic procedure of friction pendulum system, as is proposed in standard, code and literature. In addition, this study provides comparative analysis on general behavior characteristics of friction pendulum system by comparing the result with that of the analysis on lead rubber bearing which possesses the same dynamic properties.

• Journal of the Korean Geotechnical Society
• /
• v.21 no.1
• /
• pp.93-103
• /
• 2005

Both static pile load test with load transfer measuring system and the pile dynamic load test are performed to estimate the skin friction and behavior characteristics of a large drilled shaft. And the numerical modeling of large drilled shaft is performed by applying the FDM program. Since the magnitude of friction resistance depends on the relative displacement between soil and shaft, load and displacement at the arbitrary depth along the large drilled shaft are estimated to analyze the correlation. According to the measuring results of load transfer, unit skin friction along the large drilled shaft was fully mobilized at gravel layer in the middle of shaft and the frictional resistance transmitted to bedrock was relatively small. Also, even for the same drilled shaft, the results of PDA and static load test are different with each other and the difference is discussed.

• Applied Chemistry for Engineering
• /
• v.9 no.1
• /
• pp.149-154
• /
• 1998

The characteristics of drag reduction and rheological behaviors were investigated using cationic surfactants, whose microstructures are known to change when concentration of the surfactant exceeds CMC. The firstly formed spherical micelles change to rodlike or disklike micelles because of packing between surfactants micells, and of thermodynamic perference. The drag reduction becomes significant when the concentration increases over this micellar transient point. Drag reductions were measured as a function of concentration, and rheological characteristics of the surfactant were further investigated to understand the correlation between their rheological properties and drag reduction. Micelles show the non-Newtonian behavior, and shear thickening behaviors were observed due to the structural development. In addition, structural developments were determined by adding the counter-ion in case of DOBON-G.

• KSCE Journal of Civil and Environmental Engineering Research
• /
• v.33 no.4
• /
• pp.1281-1293
• /
• 2013

A sophisticated finite element model is illustrated to analyze the behavior of Prefabricated Parallel Wire Strand(PPWS) sockets for main cables of suspension bridges. An orthotropic model is proposed for the casting material by considering both effects of individual wires and a casting alloy, and the contact between surfaces of a socket and a casting alloy is idealized by using the Coulomb friction and the surface-based contact model. The proposed FE model is verified by comparing the strain distributions obtained from the tensile test and FE analysis. The mechanical behavior of a socket is investigated with respect to the variation of the frictional coefficient. The result shows that the friction between surfaces significantly diminishes the stress concentration of a socket and a casting alloy, and the normal stress from the design equation represents the averaged value of the upper and lower quartiles in the distribution of contact stresses between a socket and a casting alloy.

• Journal of the Korean Society of Propulsion Engineers
• /
• v.9 no.4
• /
• pp.89-95
• /
• 2005

Thrust cut off(TCO) system is installed at the port of a rocket motor case forward dome. The snap ring and the closure are escaped sequentially by pulling out a wedge under internal pressure. The hydraulic structural tests of TCO and numerical simulations were performed, and both results were compared to understand the deformation behavior of TCO. By increasing splines symmetrically, the sealing capacity of TCO can be improved significantly. The escape pressure of TCO increases according to the increase of friction coefficient and there is a critical friction coefficient beyond which the snap ring can not be nearly escaped even after forced escape of wedge. Under low friction coefficient the snap ring is contracted to radial direction and easily escaped. But, under high friction coefficient, the snap ring can not be escaped from the port even after severe plastic deformation.

• Journal of the Korean Geotechnical Society
• /
• v.29 no.1
• /
• pp.161-170
• /
• 2013

In this paper, numerical pile segment analysis is conducted with an advanced soil elastoplastic model to investigate the diameter effects on skin friction behaviour of a drilled shaft in sand. Ultimate skin friction and 't-z' behavior from the pile segment analyses for drilled shafts show good agreement with those from design methods. Higher ultimate skin friction for the smaller diameter pile is related to the greater increase in the effective radial stress at the interface due to the localized dilation at and near the pile interface. Stiffer t-z curve for the smaller diameter pile is related to the early occurrence of three shear stages (early, dilation, constant volume shear stages). The diameter effects on ultimate skin friction of drilled shafts are more prominent for denser sand and lower confining pressure.

• Transactions of the Korean Society of Mechanical Engineers A
• /
• v.37 no.6
• /
• pp.775-782
• /
• 2013

In this study, as a series of studies aimed at investigating the spatial randomness of fatigue crack growth for friction stir welded (FSWed) 7075-T651 aluminum alloy joints, the fatigue crack growth behavior of FSWed 7075-T651 aluminum alloy joints was investigated for LT orientation specimens. Fatigue crack growth tests were conducted under constant stress intensity factor range (SIFR) control for 5 specimens of the FSWed 7075-T651 aluminum alloy, including base metal (BM), heat affected zone (HAZ), and weld metal (WM) specimens. The mean fatigue crack growth rate of WM specimens was found to be the highest, whereas that of HAZ and WM specimens was the lowest. Furthermore, the variability of fatigue crack growth rate was found to be the highest in WM specimens and lowest in BM specimens.