• Tunnel and Underground Space
• /
• v.4 no.3
• /
• pp.261-273
• /
• 1994

Direct shear tests were carried out on the rock joints and artificial discontinuities to investigate the influence of joint roughness on the shear strength and deformation behaviour. Single direct shear testing apparatus used in experiment was designed and manufactured. Its capacity is 200 tons of shear load, 20 tons of normal load and 50$\textrm{cm}^2$ of maximum shear area. Test samples were cement mortar with artificial discontinuity and sandstone with natural joint. Peak shear strength was increased as joint roughness or normal stress was increased, especially, linearly increased with roughness angle in cement mortar. If joint roughness angle was constant at low normal stress, shear strength was not affected by width and height of joint roughness in cement mortar. Peak shear strengths obtained from tests were larger than the values calculated by Barton's equation, and shear stiffness was increased with joint roughness coefficient.

• Transactions of the Korean Society of Automotive Engineers
• /
• v.4 no.5
• /
• pp.26-36
• /
• 1996

The fully developed turbulent momentum and heat transfer induced by the square-ribbed roughness elements on both the inner and outer wall surfaces in concentric annuli are studied analytically based on a modified turbulence model. The analytical results of the fuid flow are verified by experiment. The experiment is done with a pitot tube and a X-type hot wire anemometer to measure the time mean velocity profiles, zero shear stress positions, maximum velocity positions and friction factors, and etc. shown in Fig.1. The resulting momentum and heat transfer are discussed in terms of various parameters, such as the radius ratio, the relative roughness, the roughness density, Reynolds number, Nusselt bumber and Prand시 number. The study demonstrates that certain artificial roughness elements may be used to enhance heat transfer rates with advantage from the overall efficiency point of view by investigating turbulent flows and heat transfer in Fig.1.

• Wind and Structures
• /
• v.12 no.3
• /
• pp.179-204
• /
• 2009

A physical and numerical steady flow impinging jet has been used to simulate the bulk characteristics of a downburst-like wind field. The influence of downdraft tilt and surface roughness on the ensuing wall jet flow has been investigated. It was found that a simulated downdraft impinging the surface at a non-normal angle has the potential for causing larger structural loads than the normal impingement case. It was also found that for the current impinging jet simulations, surface roughness played a minor role in determining the storm maximum wind structure, but this influence increased as the wall jet diverged. However, through comparison with previous research it was found that the influence of surface roughness is Reynolds number dependent and therefore may differ from that reported herein for full-scale downburst cases. Using the current experimental results an empirical model has been developed for laboratory-scale impinging jet velocity structure that includes the influence of both jet tilt and surface roughness.

• Proceedings of the Korean Society of Precision Engineering Conference
• /
• 2005.10a
• /
• pp.1033-1036
• /
• 2005

The effect of surface roughness on the contact fatigue was investigated in this study. To accomplish this goal, contact analysis based on the influence functions and the rectangular patch solution was performed to obtain the subsurface stress. Mesoscopic multiaxial fatigue criterion is then applied to predict fatigue damage. Suitable counting method and damage rule were used to evaluate the fatigue life of random loading caused by rough surface. As a result of the analysis, relationship between the life and roughness as well as the creack initiation depth was revealed. Below the critical roughness, It is observed that the fatigue life has hardly changed and creack is initiated around the depth at which the maximum shear stress occurs. Different behavior, however, is observed in case that the roughness is above the critical value.

• Journal of the Korean Society of Manufacturing Technology Engineers
• /
• v.8 no.5
• /
• pp.63-69
• /
• 1999

In tis study the effects of the maximum grit depth of cut on the grinding characteristics were investigated. They are AE signals produced during grinding processes have been studied to find out the appropriate AE parameters for assessing grinding processes. SM45C steel has been ground under the conditions yielding removal rate of workpiece 100, 200,300, and 400m{{{{ {m }^{3 } }}}}/min which was achieved by altering workpiece velocity(v) and apparent depth of cut(Z). According to the experimental result the value of surface roughness increases but grinding power energy rate of AE signal(AErmas2) and specific grinding energy consumed decrease as increasing the maximum grit depth of cut.

• Proceedings of the Korean Society of Machine Tool Engineers Conference
• /
• 1999.05a
• /
• pp.15-20
• /
• 1999

In this study, the effects of the maximum grit depth of cut on the grinding characteristics were investigated. And AE signals produced during grinding processes have been studied to find out the appropriate AE parameters for assessing grinding processes. S45C steel has been ground under the conditions yielding removal rate of workpiece, 100, 200, 300 and 400rnm$^3$/min which was achived by altering workpiece velocity($\upsilon$) and apparent depth of cut(Z). According to the experimental results, the value of surface roughness increases but grinding power, energy rate of AE signal(AErms$^2$) and specific grinding energy consumed decrease with increase of the maximum grit depth of cut.

• Proceedings of the Korean Society of Precision Engineering Conference
• /
• 1997.04a
• /
• pp.827-831
• /
• 1997

Conductive veramic matrix composite(CMC) workpiece of TiC 33%/Al /sab 2/O /sab 3/ 66% Y /sab 2/ O /sab 3/ was machined by die sinking electrical discharge machining(EDM) according to different pulse duration and suty factor for reverse polarity of electrode. Material removal rate(MRR) was examined by process under various operating conditions. The surface morphology was evaluated by surface roughness values and scanning electron microscopy(SEM) research. The more MRR was obtained according to increase pulse duration and duty factor. Also the maximum surface roughness(Rmax) of EDMed surface was slightly changed with increased pulse duration and duty factor. The SEM photographs of EDMed surface showed wide recast wide recast distribution region of melting materials in purse duration 0.130(ms) than 0.048(ms).

• Proceedings of the Korean Society of Precision Engineering Conference
• /
• 2000.11a
• /
• pp.489-493
• /
• 2000

Turbine blade has trouble of cracking at root region. Fracture surface of blade root is surveyed by SEM and AFM to clear relation between fracture mechanical parameter and surface parameter (striation width and surface roughness). Service stress is predicted by maximum height roughness $R_{max}$, on fractured surface and stress analysis on turbine blade. It is to thought that turbine blade is fractured by abnormal condition such as incorrect fittings between pin and pin hole but isn't fractured by normal service conditions such as steam pressure, centrifugal force and torsional force.

• Journal of Power System Engineering
• /
• v.18 no.6
• /
• pp.207-214
• /
• 2014

Mass and flow resistance in a square ribbed microchannel have been studied numerically using the Lattice Boltzmann Method. It has been build up on two dimensional nine velocity vectors model with single relaxation time method called the Lattice Bhatnagor-Gross-Krook model. To analyze the roughness effect on the flow resistance namely the friction factor and mass flow has been discussed at the slip flow regime, $0.01{\leq}Kn{\leq}0.10$, where Kn is the Knudsen number. The wall roughness is considered by square microelements with a relative roughness height up to maximum 10% of channel height. The velocity profiles in terms of streamlines near the riblets are demonstrated to be responsible for the roughness effect. It is found that the roughness effect leads to increase the flow resistance with roughness height but it is decreased significantly with increasing the space between two roughness elements as well as the Knudsen number. In addition, the mass flow decreased linearly with increasing both roughness height and gap but significantly changed at the slip flow regime.

• Journal of the Semiconductor & Display Technology
• /
• v.9 no.2
• /
• pp.103-109
• /
• 2010

An ink transfer is modeled and experimentally verified using roll-to-roll electric direct gravure printing process. The ink transfer model based on the physical mechanism for the maximum ink transfer rate is proposed, and experimented by the electric printing machine in FDRC for the relations of the maximum ink transfer rates to the printing pressure, the operating speed, the operating tension, the surface roughness of substrates, and the contact angle between substrate and silver ink. The free ink split coefficient and immobilized ink under the maximum ink transfer rate are calculated by the physical parameter in a printing process and contact angle between substrates and ink. Numerical simulations and experimental studies were carried out to verify performances of the proposed ink transfer model. Results showed that the proposed ink transfer model was effective for the prediction of the amount of transferred ink to the substrate in a direct gravure printing systems.