• 한국진공학회:학술대회논문집
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• 한국진공학회 1999년도 제17회 학술발표회 논문개요집
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• pp.202-202
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• 1999

The Polyethylene (PE), Polystyrene (PS) and Polytetrafluoroethylene (PTFE) surface modification was investigated by hydrogen io assisted reaction (H-IAR) in oxygen environment. The IAR is a kind of surface modification techniques using ion beam irradiation in reactive gas environment. The energy of hydrogen ion beam was fixed at 1keV, io dose was varied from 5$\times$1014 to 1$\times$1017 ions/$\textrm{cm}^2$, and amount of oxygen blowing gas was fixed 4ml/min. Wettability was measured by water contact angles measurement, and the surface functionality was analyzed by x-ray photoelectron spectroscopy. The contact angle of water on PE modified by argon ion beam only decrease from 95$^{\circ}$ to 52$^{\circ}$, and surface energy was not changed significantly. But, the contact angle using hydrogen ion beam with flowing 4ml/min oxygen stiffly decreased to 8$^{\circ}$ and surface energy to 65 ergs/cm. In case of PS, the contact angle and surface energy changes were similar results of PE, but the contact angle of PTEE samples decreased with ion dose up to 1$\times$1015 ions/$\textrm{cm}^2$, increased at higher dose, and finally increased to the extent that no wetting was appeared at 1$\times$1017 ions/$\textrm{cm}^2$. These results must be due to the hydrogen ion beam that cleans the surface removing the impurities on polymer surfaces, then hydrogen ion beam was activated with C-H bonding to make some functional groups in order to react with the oxygen gases. Finally, unstable polymer surface can be changed from hydrophobic to hydrophilic formation such as C-O and C=O that were confirmed by the XPS analysis, conclusionally, the ion assisted reaction is very effective tools to attach reactive ion species to form functional groups on C-C bond chains of PE, PS and PTFE.

• Transactions on Electrical and Electronic Materials
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• 제16권3호
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• pp.112-116
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• 2015

This work studied the thickness and contact angle of solder joints between SAC 305 lead-free solder alloy and a Copper (Cu) substrate. Intermetallic compound (IMC) thickness and contact angle of 3Sn-Ag-0.5Cu (SAC 305) leadfree solder were measured using varying aging times, at a fixed temperature at 30℃. The thickness of IMC and contact angle depend on the aging time. IMC thickness increases as the aging increases. The contact angle gradually decreased from 39.49° to 27.59° as aging time increased from zero to 24 hours for big solder sample. Meanwhile, for small solder sample, the contact angle increased from 32.00° to 40.53° from zero to 24 hours. The IMC thickness sharply increased from 0.007 mm to 0.011 mm from zero to 24 hours aging time for big solder. In spite of that, for small solder the IMC thickness gradually increased from 0.009 mm to 0.017 mm. XRD analysis was used to confirm the intermetallic formation inside the sample. Cu₆Sn₅, Cu₃Sn, Ni₃Sn and Ni₃Sn₂ IMC layers were formed between the solder and the copper substrate. As the aging time increased, the strength of the solder joint mproved due to reduced contact angle.

• 대한기계학회논문집A
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• 제31권2호
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• pp.197-204
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• 2007

Fretting is a contact damage process that occurs between two contact surfaces. Fretting fatigue reduces fatigue strength of the material due to low amplitude oscillatory sliding and changes in the contact surfaces of strongly connected machine and structure such as bolt, key, pin, fixed rivet and connected shaft, which have relative slip of repeatedly extreme low frequency amplitude. In this research, the fretting fatigue behavior of 2024-T3511 and 7050-T7451 aluminum alloys used mainly in aircraft and automobile industry were experimentally estimated. Based on this experimental wort the following results were obtained: (1) A significant decrease of fatigue lift was observed in the fretting fatigue compared to the plain fatigue. The fatigue limit of 2024-T3511 aluminum alloy decreased about 59% while 7050-T7451 aluminum alloy decreased about 75%. (2) In 7050-T7451 specimen using ATSI4030 contact pad, crack was initiated more early stage than using 2024-T3511 contact pad. (3) In all specimens, oblique cracks were initiated at contact edge. (4) Tire tracks and rubbed scars were observed in the oblique crack region of fracture surface.

• 한국윤활학회:학술대회논문집
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• 한국윤활학회 1999년도 제29회 춘계학술대회
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• pp.297-302
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• 1999

Finite element analysis is peformed about the crack propagation in half-space due to sliding contact. The analysis is based on linear elastic fracture mechanics and stress intensity factor concept. The crack location is fixed and the friction coefficient between asperity and half-space is varied to analyze the effect of surface friction on stress Intensity factor for horizontal crack. The crack propagation direction is predicted based on the maximum range of shear and tensile stress intensity factor.

• Tribology and Lubricants
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• 제16권5호
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• pp.373-380
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• 2000

Finite element analysis is performed on the subsurface crack propagation in brittle materials due to sliding contact. The sliding contact is simulated by a rigid asperity moving across the surface of an elastic half-surface containing single and multiple cracks. The single crack, coplanar cracks and parallel cracks are modeled to investigate the interaction effects on the crack growth in contact fatigue. The crack location is fixed and the friction coefficients between asperity and half-space are varied to analyze the effect of surface friction on stress intensity factor for horizontal cracks. The crack propagation direction is predicted based on the maximum range of shear and tensile stress intensity factors. With a coplanar crack, the stress intensity factor was increased. However, with a parallel crack, the stress intensity factor was decreased. These results indicate that the interaction of a coplanar crack increases fatigue crack propagation, whereas that of a parallel crack decreases it.

• 한국소성가공학회:학술대회논문집
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• 한국소성가공학회 1995년도 추계학술대회논문집
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• pp.76-85
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• 1995

The general equation of homogeneous strin for tube drawing has been derived. This can be applied to the general tube drawing method for non-zero plug angle. Also, the derived equation can represent Blazynski's equations for the sinking and tube drawing with a constant plug diameter. The general tube drawing was divided into two steps, sinking and contact drawing zones. The derived equation can calculate the homogeneous strains of the two steps. The various tube drawing methods such as fixed tapered plug, fixed mandrel, fixed back tapered plug, and floating plug have been analysed by the equation and finite element analysis. From the FEM calculations, the total strains and drawing stresses are obtained and consequently the redundancy factor of various drawing methods was analysed. The fixed back tapered plug method showed the largest redundancy factor and the floating plug method had the largest drawing stress.

• 한국정밀공학회지
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• 제34권3호
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• pp.167-172
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• 2017

This study proposes a method for identifying correlations between tension and drop height for sessile droplets in a roll-to-roll processing system. The effect of tension and drop height on the contact angle of a sessile droplet is presented. Design of experiment (DOE) methodology and statistical analysis are used to define a correlation between the process parameters. The contact angle is decreased while increasing tension and drop height. The influence of the tension is less significant on the contact angle compared with the effect of the drop height. However, tension should be considered as a major parameter because it is not easy to fix with roll eccentricity and compensating speed of the driven roll. The results of this study show that the effect of tension on the contact angle of a sessile droplet is more important than drop height because the drop height is fixed when the process systems are determined.

• Structural Engineering and Mechanics
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• 제37권5호
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• pp.489-507
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• 2011

The dynamic response of a Timoshenko beam on a tensionless Pasternak foundation is investigated by assuming that the beam is subjected to a concentrated harmonic load at its middle. This action results in the creation of lift-off regions between the beam and the foundation that effect the character of the response. Although small displacements for the beam and the foundation are assumed, the problem becomes nonlinear since the contact/lift-off regions are not known at the outset. The governing equations of the beam, which are coupled in deflection and rotation, are obtained in both the contact and lift-off regions. After removing the coupling, the essentials of the problem (the contact regions) are determined by using an analytical-numerical method. The results are presented in figures to demonstrate the effects of some parameters on the extent of the contact lengths and displacements. The results are also compared with those of Bernoulli-Euler, shear, and Rayleigh beams. It is observed that the solution is not unique; for a fixed value of the frequency parameter, more than one solution (contact length) exists. The contact length of the beam increases with the increase of the frequency and rotary-inertia parameters, whereas it decreases with increasing shear foundation parameter.

• 대한전기학회:학술대회논문집
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• 대한전기학회 1994년도 추계학술대회 논문집 학회본부
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• pp.270-273
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• 1994

The capacitive current breaking capability as well as the short circuit current breaking capability is a very important factor in the performance of a circuit breaker. The dielectric recovery capability between poles should be considered in the desist of a circuit breaker because approximately two times of the maximum power system voltage might be applied between poles after the capacitive current be interrupted. The electric field and flow field analyses were utilized in the calculation of dielectric recovery characteristics between poles of 800kV model interrupter. The results show that the separation between moving main contact and moving arcing contact will affect to decrease significantly the electric field strength of a moving arcing contact and an insulation cover, to increase slightly the electric field strength of a fixed arcing contact and to decrease consequently the dielectric recovery capability between poles of the interrupter.

• International Journal of Naval Architecture and Ocean Engineering
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• 제11권1호
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• pp.59-69
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• 2019

This paper focuses on the numerical simulation of ice abrasion induced by unbreakable ice floe. Under the assumption that unbreakable floes behave as rigid body, the Discrete Element Method (DEM) was applied to simulate the interaction between a fixed structure and ice floes. DEM is a numerical technique which is eligible for computing the motion and effect of a large number of particles. In DEM simulation, individual ice floe was treated as single rigid element which interacts with each other following the given interaction rules. Interactions between the ice floes and structure were defined by soft contact and viscous Coulomb friction laws. To derive the details of the interactions in terms of interaction parameters, the Finite Element Method (FEM) was employed. An abrasion process between a structure and an ice floe was simulated by FEM, and the parameters in DEM such as contact stiffness, contact damping coefficient, etc. were calibrated based on the FEM result. Resultantly, contact length and contact path length, which are the most important factors in ice abrasion prediction, were calculated from both DEM and FEM and compared with each other. The results showed good correspondence between the two results, providing superior numerical efficiency of DEM.