Date of Award

3-2024

Document Type

Dissertation

Degree Name

Ph.D.

Organizational Unit

Daniel Felix Ritchie School of Engineering and Computer Science, Mechanical and Materials Engineering

First Advisor

Yun-Bo Yi

Keywords

Thermal-mechanical instability (TMI), Sliding systems, Brakes, Friction

Abstract

Thermal-mechanical instability (TMI) has been a research topic of interest as it focuses a lot on transportation systems. Thermal-mechanical instability was first noticed in railway and experimentally studied with a pin-to-pin or pin-to-surface setup of sliding contact. The topic has been extended into brakes and clutches which are two of the most common sliding systems most susceptible to thermal buckling and thermoelastic instability (TEI), where thermal buckling and thermoelastic instability are two sub-categories of thermal-mechanical instability. Thermal-mechanical instability is an ongoing research to better understand the phenomenon and the limits at which such instability occurs. This work delved into the thermal-mechanical instability in automotive systems (brakes and clutches), studying the point of occurrence of this instability.

Coupling analysis such as vibration coupled with thermal buckling and thermal buckling coupled with thermoelastic instability was performed. The idea behind the coupling studies was to find out if the temperature gradient alone can induce instability in brakes or clutches, or the occurrence of one TMI can cancel out or induce the occurrence of another TMI to reduce or increase the chance of failure.

It was found that vibration during braking can induce uneven temperature gradient and internal stress in brakes to increase the chance of thermal buckling to occur but the increase in gradient temperature does not induce vibration. Also, thermal buckling modes tend to induce vibration in brakes. Thermal buckling and thermoelastic instability induce the occurrence of one another. In instances of TEI which creates hotspots due to uneven contact surface area during sliding, which increases the thermally induced stress in the brake or clutch to cause thermal buckling.

Alternate non-metallic friction material and the effect of anisotropy in friction materials was also investigated to determine the limits of brakes and clutches at which thermal-mechanical instability can occur. Carbon-carbon silicon carbide as a replacement for metallic friction material proved to minimize the occurrence of thermal-mechanical instability in brakes and clutches. The arrangement of reinforced fiber in the composite material also affects the limit of thermal buckling and thermoelastic instability. A composite with randomly distributed reinforced fiber evenly distributes the internal stress better than uniformly aligned reinforced fibers and hence the randomly distributed composite used in brake and clutch production significantly increases the point of thermal buckling or thermoelastic instability to occur. The ideal composition for a carbon-carbon silicon carbide composite material with fiber aspect ratio of 1 to produce a clutch to withstand high temperatures without TMI occurring is 35% carbon fiber volume and 20% silicon carbide volume.

Copyright Date

3-2024

Copyright Statement / License for Reuse

All Rights Reserved
All Rights Reserved.

Publication Statement

Copyright is held by the author. User is responsible for all copyright compliance.

Rights Holder

Joseph-shaahu Shaahu

Provenance

Received from ProQuest

File Format

application/pdf

Language

English (eng)

Extent

132 pgs

File Size

2.7 MB

Discipline

Automotive engineering, Commerce-business

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