• Transactions of the Korean Society of Automotive Engineers
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• v.15 no.5
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• pp.174-179
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• 2007

The transient brake time or distance is one of very important factors to guess the vehicle speed to inspect an automobile accident. But, it is usual that the vehicle speed is estimated by using only skid mark without considering the transient brake distance. Deceleration and the friction coefficients of tire and road surface play an important role in calculating the brake distance. In this paper, a scheme is presented to estimate more accurate automobile speed. The scheme contains the effect of the transient brake distance on the speed. Experiment was carried out on the asphalt, unpacked road to get relationships between the speeds and the skid mark distances, and to get the transient brake time. The experimental results were utilized to construct the equation to approximate more realistic vehicle speeds.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.11 no.6
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• pp.465-471
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• 1998

Diamond-like carbon (DLC) films have been prepared by means of the plasma enhanced chemical vapor deposition (PECVD) method using vertical-capacitor electrodes. The deposition rata in our experiment is relatively small compared with that in the conventional PECVD methods, which implies that the accumulation of the neutral $CH_n$ radicals on the substrates due to the gravitational movement may not contribute to the deposition of DLC films. The hardness and the transparency were measured as a function of the ratio of the partial pressure of $CH_4-H_2$ mixtures or the hydrogen contents of specimens. The coefficients of friction between DLC films and a $Si_3N_4$ tip measured by using a lateral force microscope are in the range of 0.024 to 0.033 which depend on the hydrogen contents in DLC, and the surface roughness depends mainly on the deposition rate. The optical gaps increase with increasing the hydrogen contents. DCL films deposited on Pt-coated Si wafers show the stable emission characteristics, and the turn-on fields are in the range of 11 to 20 $V/\mu$m.

• Special Issue of the Society of Naval Architects of Korea
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• 2013.12a
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• pp.66-72
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• 2013

The demand for an ice class ship is rising expected to rise according to the increase of energy consumption and the opening of arctic sea routes. Ice class ship should be designed to cope with the severe environmental conditions of arctic sea such as a high mechanical impact and abrasion damage, caused by pack ice, ice bergs and low temperature. The ice class ship hulls are coated with an anti-abrasion and low friction coating such as a solvent free epoxy or high solid-volume epoxy. These coatings require two-component heating pump and a high grade surface preparation. In this study, the coating performances for the arctic vessels, such as puncture absorbed energy, abrasive wear loss, friction coefficients and impact absorbed energy were evaluated. Based on this study, a proper coating performance specification for the arctic vessels was proposed and coating selection guideline in terms of coating performance and workability was also established.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.41 no.7
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• pp.585-590
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• 2017

Vehicle behavior is determined by forces and a torques generated at the ground contact surface of the tire. Various tire models are used to calculate the forces and torques acting on the tire. The brush model calculates the forces and torques with fewer coefficients than other tire models. However, owing to fewer degrees of freedom in calculating the forces, this model has limitations in precisely expressing measured data. In this study, this problem was addressed by adding the least parameters to the friction coefficient and tire properties of the brush model, and the proposed model was validated.

• Polymer(Korea)
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• v.36 no.2
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• pp.190-195
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• 2012

Interfacial and rheological properties of selected hydrogel formulations were studied to understand the contact-lens comfort in end use. It was concluded that protein adsorption from aqueous solution decreased monotonically with increasing surface energy (water wettability) of tested hydrogels. Also, it has revealed that friction coefficient of polydimethylsiloxane-polyvinylpyrrolidone (PDMS-PVP) was significantly larger that 2-hydroxyethyl methacrylate (HEMA) based hydrogels. Interestingly, in artificial tear solution, friction coefficients of HEMA based hydrogels were larger than silicone hydrogels.

• Proceedings of the KSME Conference
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• 2007.05b
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• pp.2384-2389
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• 2007

The 2nd order response surface method (RSM) has been carried out to get optimum thermal design for enhanced heat transfer on square channel with bleed holes. The RSM was used as an optimization technique with Reynolds-averaged navier-stokes equation. Turbulence model for heat transfer analysis used RNG k-epsilon model. The wall function used enhanced wall function. Numerical local heat transfer coefficients were similar to the experimental tendency. Two design variables such as attack angle of rib (${\alpha}$), rib pitch-to-rib height ratio (p/e) were chosen. Operation condition considered bleeding ratio per bleed hole ($BR_{hole}$). A response surface were constructed by the design variables and operation condition. As a result, adjusted $R^2$ was more than 0.9. Optimization results of various objective function were similar to heat transfer in channel with and without bleed flow. But friction factor was lower than channel without bleed flow.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.28 no.7
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• pp.879-886
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• 2004

A numerical optimization has been carried out to determine the shape of the three-dimensional channel with oblique ribs attached on both walls to enhance turbulent heat transfer. The response surface based optimization is used as an optimization technique with Reynolds-averaged Navier-Stokes analysis of fluid flow and heat transfer. Shear stress transport (SST) turbulence model is used as a turbulence closure. Numerical results fur heat transfer rate show good agreements with experimental data. four dimensionless variables such as, rib pitch-to-rib height ratio, rib height-to-channel height ratio, streamwise rib distance on opposite wall to rib pitch ratio, and the attack angle of the rib are chosen as design variables. The objective function is defined as a linear combination of heat-transfer and friction-loss related coefficients with a weighting factor. D-optimal method is used to determine the training points as a means of design of experiment. Sensitivity of the objective parameters to each design variable has been analyzed. And, optimal values of the design variables have been obtained in a range of the weighting factor.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.32 no.4
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• pp.362-370
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• 2008

In this paper, we propose a 2D-FE model in single impact with combined physical factors to obtain a unique residual stress by shot peening. Applied physical parameters consist of elastic-plastic deformation of shot ball, material damping coefficients, strain rate, dynamic friction coefficients. As a kinematical parameter, there is impact velocity. Single impact FE model consists of 2D axisymmetric elements. The FE model with combined factors showed converged and unique distributions of surface stress, maximum compressive residual stress and deformation depth. Further, in contrast to the FE models with rigid shot and elastic deformable shot, FE model with plastic deformable shot produces residual stresses very close to experimental solutions by X-ray diffraction. We therefore validated the 2D FE model with combined peening factors and plastic deformable shot. This FE model will be a base of the 3D FE model for residual stresses by multi-impact shot peening.

• Journal of Korean Society of Transportation
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• v.27 no.1
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• pp.43-51
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• 2009

This paper investigates the accuracy of vehicle pre-braking speed estimates based upon tire/roadway coefficient of friction (drag factor) measurements and skid mark measurements Data for pre-braking and pre-skidding speeds were collected to determine if there were any correlations between pre-braking speeds and pre-skidding speeds. Braking tests were performed on two vehicles using various measurement devices including a fifth wheel, a speed gun, and a vericom 2000. The vehicle speeds, braking distances, skid mark distances, and deceleration histories were recorded. From these data. coefficients of friction and vehicle pre-skidding speeds for the tested road surface were calculated. The pre-skidding speeds were then compared to the actual pre-braking speeds of the vehicles in order to establish relationships between pre-skidding and pre-braking speed. A correlation between the Pre-skidding speed and the actual pre-braking speed was established for the study data.

• Korean Journal of Materials Research
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• v.25 no.9
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• pp.442-449
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• 2015

The effects of coating parameters were investigated in wear resistance coatings of Diamalloy-406 on Inconel 718 to obtain an optimum coating condition by high velocity oxy-fuel spraying. The coating parameters, the flow rates of source gases (hydrogen and oxygen), the powder feed rate, and the spray distance, were designed by the Taguchi method. The optimal conditions were determined: oxygen flow rate 34 FRM, hydrogen flow rate 57 FRM, powder feed rate 35 g/min, and spray distance 7 inch. Friction coefficients of the coating and the substrate decreased with an increasing sliding surface temperature from $25^{\circ}C$ to $450^{\circ}C$. The friction coefficient of Diamalloy-4006 coating decreased as the sliding surface temperature increased from $0.43{\pm}0.01$ at $25^{\circ}C$ to $0.29{\pm}0.01$ at $450^{\circ}C$. The wear trace and wear depth of the coating were smaller than the substrate at all temperatures tested. The relationship between spray parameters and wear resistance was discussed extensively, based on the measured roughness, hardness, and porosity in each coating.