• 한국정밀공학회지
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• 제14권1호
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• pp.126-141
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• 1997

The purpose of this research is to develope a FEM program for analyzing solidification processes of axisymmetric casting, considering phase changes and the contact between the metal and mold. Tempera- ture recovery method is employed fro considering the phase changes releasing the latent heat and the coin- cident node method is used for calculating the amount of heat transfer between the metal and mold. Tan- gent modulus algorithm is adopted for calculating flow stress and a gap element is employed for modeling the interface between the mold and metal in finding deformed shapes. In order to verify the developed program, axisymmetric aluminum and steel casting processes are simulated. Temperature distribution, phase front position, and shrinkage and porosity creation are compared with measurements, FIDAP results, and good agreements are examined.

• 한국소성가공학회:학술대회논문집
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• 한국소성가공학회 1997년도 춘계학술대회논문집
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• pp.140-143
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• 1997

The present study is concerned with the hydrostatic extrusion process of copper-clad aluminium bar to investigate the basic flow characteristics. Considering the bonding mechanism of bi-metal contact surface as cold pressure welding, the normal pressure and the contact surface expansion are selected as process parameters governing the bonding condition. The critical pressure required for the bonding at the interface is obtained by solving a "local extrusion" using a slip line meyhod. A viscoplastic finite element method is used to analyze the steady state extrusion process. The boundary profile of bi-metal rod is predicted by tracking a particle path adjacent to interface surface. The variations of contact surface area and the normal pressure along the interface profile are predicted and compared to those by experiments.

• 한국진공학회:학술대회논문집
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• 한국진공학회 2014년도 제46회 동계 정기학술대회 초록집
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• pp.179.2-179.2
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• 2014

Carbon nanotubes (CNT)-metal contacts play an important role in nanoelectronics applications such as field-effect transistor (FET) devices. Using Al and (10,0) CNT, we have recently showed that the CNT-metal contacts mediated via topological defects within CNT exhibits intrinsically low contact resistance, thanks to the preservation of the sp2 bonding network at the metal-CNT contacts.[1] It is well-established that metals with good wetting property such as Pd consistently yield good contacts to both metallic and semiconducting CNTs. In this work, the electronic and charge transport properties of the interfaces between capped CNT and Pd will be investigated based on first-principles computations and compared with previous results obtained for the Al electrodes.

• 한국기계가공학회지
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• 제9권1호
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• pp.93-98
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• 2010

The metal fastening method is the new technology to repair cracks in the casting material using specially designed reverse screws. In this study, we conduct the finite element analysis to analyze the pulling force characteristic of a reverse screw, the core component of the metal fastening method, with respect to the change of the applying torque, frictional coefficient and front screw angle. The simplified analysis model with single screw pitch is proposed for convergency of the non-linear contact analysis. As a results, the pulling force of a reverse screw increase in proportion to the applying torque but exponentially decrease according to frictional coefficient. And also we can find the optimum front screw angle with the largest pulling force is $20^{\circ}$.

• 전기학회논문지
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• 제59권1호
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• pp.130-133
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• 2010

Although many structures based on $SnO_2$ nanowires have been demonstrated, there is a limitation towards practical application due to the unwanted contact potential between the metal electrode and the $SnO_2$ nanowire. This is mostly due to the presence of the native oxide layer that acts as an insulator between the metal contact and the nanowire. In this study the contact properties between Ti/Au contacts and a single $SnO_2$ nanowire was compared to the electrical properties of a contact without the oxide layer. RIE(Reactive Ion Etching) is used to selectively remove the oxide layer from the contact area. The $SnO_2$ nanowires were synthesized by chemical vapor deposition (CVD) and dispersed on a $Si/Si_3N_4$ substrate. The Ti/Au (20nm/100nm) electrodes were formed bye-beam lithography, e-beam evaporation and a lift-off process.

• Transactions on Electrical and Electronic Materials
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• 제9권4호
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• pp.137-142
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• 2008

The parasitic resistance is studied to silicon/metal contact junction for improving device performance and to lower contact/serial resistance silicide in natural sequence. In this paper constructs the stepwise Ni silicide process for parasitic resistance reduction for silicon/metal contact junction. We have investigated multi-step Ni silicide on SiGe substrate with stepwise annealing method as an alternative to compose more thermally reliable Ni silicide layer. Stepwise annealing for silicide formation is exposed to heating environment with $5^{\circ}C/sec$ for 10 seconds and a dwelling for both 10 and 30 seconds, and ramping-up and the dwelling was repeated until the final annealing temperature of $700\;^{\circ}C$ is achieved. Finally a direct comparison for single step and stepwise annealing process is obtained for 20 nm nickel silicide through stepwise annealing is $5.64\;{\Omega}/square$ at $600\;^{\circ}C$, and it is 42 % lower than that of as nickel sputtered. The proposed stepwise annealing for Ni silicidation can provide the least amount of NiSi at the interface of nickel silicide and silicon, and it provides lower resistance, higher thermal-stability, and superior morphology than other thermal treatment.

• Journal of Mechanical Science and Technology
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• 제19권spc1호
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• pp.437-443
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• 2005

Controlling the friction between wheel and rail is direct and very effective measures to improve the curving performances of railway trucks, because the curving performances depend much on friction characteristics. Authors have proposed a method, 'friction control', which utilizes friction modifier ($KELTRACK^{TM}$ HPF) with onboard spraying system. With the method, not only friction coefficient, but also friction characteristics can be controlled as expected. In this study, MBD simulation is very valuable tool to foresee the effect of the control in advance of experiment with real car. And the creep characteristics of wheel/rail contact with the friction modifier takes very important role in the simulation. In this paper, authors propose a theoretical model of wheel/rail contact condition considering the creep characteristics of friction modifier, which is derived the application of principle tribological theories.

• 소성∙가공
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• 제19권6호
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• pp.378-386
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• 2010

Nowadays there has been great interest in using heat treated cast material for press dies due to several advantages like reduction in die production costs. However, in hot press forming processes H13 forged tool steel is mostly used. Cooling performance of dies in hot press forming processes is considered as an important factor of study and also the IHTC parameter between cast material die and sheet metal should be considered as an essential. In the present study, the IHTC was calculated for the sheet metal in the hot press forming process with cast and forged material dies. The temperature measurements were performed for the sheet metal, casting and forged material dies by applying various contact pressure in hot press forming. IHTC was calculated and studied by adopting the inverse heat convection method in DEFORM-2D. Each IHTC was considered as a function of contact time and contact pressure. The experimental data were compared with calculated data obtained from the proposed equation and references.

• 대한기계학회논문집
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• 제19권1호
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• pp.193-201
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• 1995

The role of thermal contact resistance between a casting and a metal mold as well as natural convection in the melt during solidification of a pure metal is numerically studied. Numerical simulation is performed for a rectangular cavity using the coordinate transformation by boundary-fitted coordinate and pure aluminum is used as the phase- change material. The influences of thermal contact resistance on the interface shape and position, solidified volume fraction, temperature field and local heat transfer are investigated.

• 한국복합재료학회:학술대회논문집
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• 한국복합재료학회 2000년도 추계학술발표대회 논문집
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• pp.71-74
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• 2000

In this study, the optimal condition of surface treatment for aluminum panel was determined by measuring the contact angle and T-peel strength. The contact angle was measured for various mixture ratios of acetylene gas and nitrogen gas. The mixture (acetylene gas to nitrogen gas) ratios used were 1:9, 3:7, 5:5, 7:3, and 9:1. The contact angle was also measured as a function of time of surface treatment. The results showed that the contact angle was a minimum for mixture ratio of 5:5. T-peel strength was a maximum for the treatment time of 30 second.