• Korea-Australia Rheology Journal
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• 제20권3호
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• pp.117-125
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• 2008

Viscoelastic instabilities are of fundamental importance to understanding the physics of complex fluids and of practical importance to materials processing and fluid characterization. Significant progress has been made over the past 15 years in understanding instabilities in viscoelastic flows with curved streamlines and is reviewed here. Taylor-Couette flow, torsional flow between a cone and plate, and torsional flow between parallel plates have received special attention due to both the basic significance of these flows and their critical role in rheometry. First, we review the criteria for determining when these flows become unstable due to elasticity in the absence of inertia, and discuss the generalization of these criteria to more complex flows with curved streamlines. Then, focusing on experiments and simulations in the Taylor-Couette problem, we review how thermal sensitivity (i.e., the dependence of fluid viscosity and elasticity on temperature) and inertia affect the stability of viscoelastic flows. Finally, we conclude with some general thoughts on unresolved issues and remaining challenges related to viscoelastic instabilities.

• 한국윤활학회:학술대회논문집
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• 한국윤활학회 2000년도 제31회 춘계학술대회
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• pp.211-218
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• 2000

Hot spot behaviors on the disk-pad contact surface during a braking operation have been analyzed for a ventilated disk brake using the finite element method. Hot spots which were studied using a coupled thermal-mechanical analysis technique are influenced by all of the mechanical, thermal, elastic and plastic processes that are involved in braking cycles, but their temperature gradients are most affected by rubbing speeds, braking forces, and design parameters between the disk and the pad. Undesirable hot spots that are generated by local thermoelastic instabilities are intended to be removed by optimized design parameters and material properties. In this study, a three-dimensional numerical method for the demonstration of hot spot behaviors has been applied to the rubbing surfaces between the disk and the pad.

• 한국생산제조학회지
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• 제23권3호
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• pp.259-265
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• 2014

When the brakes of a vehicle are applied, large amounts of heat are generated on the surfaces of the brake discs owing to friction between the discs and the brake pads. A high temperature gradient on the disc surfaces leads to thermal deformation and severe disc abrasion. Ultimately, the thermal deformation and disc wear give rise to a thermal judder phenomenon, which has a major effect on the stability of the vehicle. To investigate and propose a solution to these problems, thermoelastic instabilities under applied thermal and mechanical loads were analyzed using the commercial finite element package ANSYS by considering the contact surfaces between the discs and pads. Direct-contact three-dimensional finite elements between the discs and pads were applied to investigate the disc friction temperature, thermal deformation, and contact stress so that the thermal judder phenomenon on the surface of the disc could be predicted.

• 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.