• 비파괴검사학회지
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• 제35권6호
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• pp.407-413
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• 2015

Ultrasonic infrared thermography is an active thermography methods. In this method, mechanical energy is introduced to a structure, it is converted into heat energy at the defects, and an infrared camera detects the heat for inspection. The heat generation mechanisms are dependent on many factors such as structure characteristics, defect type, excitation method and contact condition, which make it difficult to predict heat distribution in ultrasonic infrared thermography. In this paper, a method to simulate frictional heating, known to be one of the main heat generation mechanisms at the closed defects in metal structures, is proposed for ultrasonic infrared thermography. This method uses linear vibration analysis results without considering the contact boundary condition at the defect so that it is intuitive and simple to implement. Its advantages and disadvantages are also discussed. The simulation results show good agreement with the modal analysis and experiment result.

• 대한기계학회논문집A
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• 제20권10호
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• pp.3126-3134
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• 1996

In this paper, to examine the propagation of inclined surface crack due to frictional heating, analytic model is considered as the semi-infinite elastic body subjected to the thermo-mechanical loading of an asperity moving with a high speed. Considering the moving of frictional heat source and convection on a semi-infinite surface having inclined crack, theoretical analysis was carried out to estimate the propagation characteristics of thermo-mechanical crack. Numerical results showed that stress intensity factor $K_\prod/P_0\sqrt{c}$ is increasing with increasing velocity and frictional coefficient, inclined degree, decreasing crack length and the maximum value of it is positioned at the trailing edge. So it is shown that the propagation probability of surface crack is high at the trailing edge of contact area as increasing velocity and frictional coefficient, inclined degree, as decreasing crack length.

• 한국윤활학회:학술대회논문집
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• 한국윤활학회 1987년도 제5회 학술강연회초록집
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• pp.50-56
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• 1987

A mechanical face seal is most commonly used to seal liquids and gases at various speeds, pressures and temperatures. The primary seal ring is in sliding contact with the seal seat and as a result heat in the vicinity of the interface is generated. Local temperatures at points along the circumferential direction will fluctuate as asperities on the surfaces pass. This kind of fluctuation of temperature has been investigated to take place. This may lead to the hot spots phenomenon between the contacting asperities. Sibley and Allen showed photographic evidence of systemically moving hot spots in the contact zone. The appearance of such a temperature disturbance has been attributed to a kind of thermoelastic instabilities between two surfaces: This involves a feedback loop which comprises localized elevation of frictional heating, resultant localized thermal bulding, localized pressure increase as the result of the bulging and futher elevation of frictional heating as the result of the pressure increase. The heating of hot spots will be continued until the expanded material due to the frictional heating is worn off. Therefore to predict the speed of temperature propagation into the body is essential to the analysis of heat transfer on the edge of the seal.

• 한국기계가공학회지
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• 제21권8호
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• pp.99-109
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• 2022

In this study, an electric resistance-heated surface friction spot-welding process was proposed and tested for the spot-welding ability of copper and aluminum dissimilar metal sheets using electric resistance heating and surface friction heating. This process has welding variables, such as the current value, energizing cycles, rotational speed, and friction time. The current value and energizing cycle can affect the resistance heat, and the rotational speed of the rotating pin and friction time influence frictional heat generation. Resistance heating before friction heating has a preheating effect on the Cu-Al contact interface and a positive effect on preventing friction heat loss during the friction stage. However, because resistance preheating can soften the copper sheet and affect the contact stress and friction coefficient, it has difficulties that may adversely affect frictional heat generation. Therefore, the optimal combination of welding variables should be determined through simulations and experiments of the spot-welding process to determine the effects of electric resistance preheating on the suggested process. Through this procedure, it is known that the proposed spot-welding process can improve the welding quality during the spot welding of Cu-Al sheets.

• 대한기계학회논문집
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• 제18권7호
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• pp.1730-1737
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• 1994

Theoretical equations for an influence of fiber breaks on the frictional heating phenomenon in a uniaxially fiber-reinforced ceramic matrix composite are formulated. The microslip and gross slip phases are considered for deriving the equations. During a complete loading/unloading cycle, the work done against friction is derived. In order to estimate interfacial shear in a unidirectionally reinforced ceramic matrix composite which has fiber fractures as well as matrix cracks, parametric studies using the derived equations are done. In a case of less than 10% fiber fractures, additional frictional work due to fiber breaks can be neglected compared to the rest.

• 한국윤활학회:학술대회논문집
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• 한국윤활학회 1997년도 제25회 춘계학술대회
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• pp.232-241
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• 1997

The tribological behavior for MoS$_2$ bonded films is evaluated according to the international standard testing methods, such as ASTM D 2625(Falex tester) and ASTM D 2714(LFW-1 tester). It has been well known that the tribological behavior for MoS$_2$ bonded films is affected by several factors. However, in this work, the wear life for MoS$_2$ bonded films is mainly experimentally measured with different contact geometry, and evaluated in terms of the frictional heating according to the contact geometry of tribotester. The test results show that the wear life of MoS$_2$ bonded films is significantly affected not only by the frictional heating, but also by the contact pressure, test running-in conditions, and the contact conformity.

• Tribology and Lubricants
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• 제13권3호
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• pp.20-27
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• 1997

The tribological behavior for $MoS_2$ bonded films is evaluated according to the international standard testing methods, such as ASTM D 2625 (Falex tester) and ASTM D 2714 (LFW1 tester). It has been well known that the tribological behavior for $MoS_2$ bonded films is affected by several factors. However, in this work, the wear life for $MoS_2$ bonded films is mainly experimentally measured with different contact geometry, and evaluated in terms of the frictional heating according to the contact geometry of tribotester. The test results show that the wear life of $MoS_2$ bonded films is significantly affected not only by the frictional heating, but also by the contact pressure, test running-in conditions, and the contact conformity.

• 대한기계학회논문집A
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• 제32권12호
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• pp.1107-1114
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• 2008

This paper is aimed to understand the effect of different galvannealing temperatures on the frictional properties and Fe-Zn intermetallic phases of the galvannealed (GA) coatings on steel sheets. Their galvannealing treatments were conducted at 465, 505, 515 and $540^{\circ}C$ for about 10s in the additional heating furnace of an industrial continuous hot-dip galvanizing line. The mechanical and the frictional properties of the coatings were estimated using nanoindentation, nanoscratch, micro vickers hardness tests and flat friction tests, which were performed at contact pressures of 4, 20 and 80MPa. Also, the correlation between the microstructure and the frictional properties of the GA coatings were investigated by SEM observation for the cross-section of the GA coating after and before flat friction tests. The results showed that the mechanical and the frictional properties of the coatings are strongly dependent on their phase distributions and microstructure. Especially, in low contact pressure of 4MPa the frictional properties of the coatings were dependent on the surface phases and morphology, while in high contact pressure of 80MPa it was influenced by their mechanical properties based on the dominant phase distributions.

• Journal of the Korean Physical Society
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• 제73권9호
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• pp.1303-1309
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• 2018

In the present paper, we study the entropy analysis of boundary layer flow over a slender stretching sheet under the action of a non uniform magnetic field that is acting perpendicular to the flow direction. The effects of viscous dissipation and Joule heating are included in the energy equation. Using similarity transformation technique the momentum and thermal boundary layer equations to a system of nonlinear differential equations. Numerical solutions are obtained using the shooting and fourth-order Runge-Kutta method. The expressions for the entropy generation number and Bejan number are also obtained using a suggested similarity transformation. The main objective of this article is to investigate the effects of different governing parameters such as the magnetic parameter ($M^2$), Prandtl number (Pr), Eckert number (Ec), velocity index parameter (m), wall thickness parameter (${\alpha}$), temperature difference parameter (${\Omega}$), entropy generation number (Ns) and Bejan number (Be). All these effects are portrayed graphically and discussed in detail. The analysis reveals that entropy generation reduces with decreasing wall thickness parameter and increasing temperature difference between the stretching sheet and the fluid outside the boundary layer. The viscous and magnetic irreversibilities are dominant in the vicinity of the stretching surface.

• Journal of Biosystems Engineering
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• 제26권3호
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• pp.263-270
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• 2001

This study was conducted in order to develop wind-water heating system where frictional heat is creased between the rotor and working fluid when they are rotating in the cylindrical heat generator. The wind-water heating system is composed of rotor, stator, working fluid, motor, inverter and heat generation tank. Instead of wind turbine, we have used an electrical motor of 30㎾ to rotate the rotor in this system. Two working fluids and six levels of rotor rpm were tested to quantify heat amounts generated by the system. Generally, as motor rpm goes up heat amount increases that we have expected. At the same rpm, viscous fluid showed up better performance than the water, generating more heat by 10$\^{C}$ difference. The greatest heat amount of 31,500kJ/h was obtained when the system constantly drained out the hot water of at the flow rate of 500ℓ/h. Power consumption rate of the motor was measured by thee phase electric power meter where the largest power consumption rate was 14㎾ when motor rpm was 600 and gained heat was 31,500kJ/h, that indicated total thermal efficiency of the wind power water heating system was 62%.