Operating temperature range is one of the primary design considerations for
developing effective disc brake system performance. Very high braking
temperatures can introduce effects detrimental to performance such as
brake fade, premature wear, brake fluid vaporization, bearing failure, thermal
cracks, and thermally-excited vibration [2].
This project is concerned with investigating deficiencies and proposing
improvements in brake system Finite Element (FE) models in order to
provide high quality descriptions of thermal behaviour during braking events.
The work focuses on brake disc/pad models and the degree of rotational
freedom allowed for the pad. Conventional models [10] allow no motion/or
free motion of the pad. The present work investigates the effect on disc/pad
interface temperature and pressure distributions of limited relaxations of this
rotational restriction. Models are proposed, developed and validated that
facilitate different rotational degrees of freedom (DoF) of the pad.
An important influencing factor in friction brake performance is the
development of an interface tribo-layer (ITL). It is reasonable to assume that
allowing limited rotational motion of the pad will impact the development of
the ITL (e.g. due to different friction force distributions) and hence influence
temperature. Here the ITL is modelled in the numerical simulations as a
function of its thickness distribution and thermal conductivity. Different levels
of ITL thermal conductivity are defined in this work and results show that
conductivity significantly a1qwffects interface temperature and heat partition
ratio.
The work is based around a set of test-rig experiments and FE model
developments and simulations. For the experimental work, a small-scale test
rig is used to investigate the friction induced bending moment effect on the
pad/disc temperature. Significant non-uniform wear is observed across the
friction surface of the pad, and reasons for the different wear rates are
proposed and analyzed together with their effect on surface temperature.
Following on from experiment a suite of models is developed in order to
evidence the importance of limited pad motion and ITL behaviours.
A 2D coupled temperature-displacement FE model is used to quantify the
influence of different pad rotational degrees of freedom and so provide
evidence for proposing realistic pad boundary settings for 3D models.
Normal and high interface thermal conductance is used in 2D models and
results show that the ITL thermal conductivity is an important factor
influencing the maximum temperature of contact surfaces and therefore
brake performance. The interface heat partition ratio is calculated by using
the heat flux results and it is confirmed that this value is neither constant nor
uniform across the interface surfaces.
Key conclusions from the work are (i) that ITL thermal conductivity is an
important factor influencing the interface temperature/heat flux distribution
and their maximum values, (ii) that allowed motion of the pad significantly
affects the interface pressure distribution and subsequently the temperature
distribution, (iii) that the transient heat partition in friction braking is clearly
quite different to the conventional friction-pair steady heat partition (the heat
partition ratio is not uniformly distributed along the interface) and (iv) that the
thickness of the ITL increases through braking events, reducing the heat
transfer to the disc, and so providing a possible explanation for increasing
pad temperature observed over the life time of a brake pad.
| Identifer | oai:union.ndltd.org:BRADFORD/oai:bradscholars.brad.ac.uk:10454/18666 |
| Date | January 2018 |
| Creators | Qui, Le |
| Contributors | Qi, Hong Sheng, Wood, Alastair S. |
| Publisher | University of Bradford, Faculty of Engineering and Informatics |
| Source Sets | Bradford Scholars |
| Language | English |
| Detected Language | English |
| Type | Thesis, doctoral, PhD |
| Rights | <a rel="license" href="http://creativecommons.org/licenses/by-nc-nd/3.0/"><img alt="Creative Commons License" style="border-width:0" src="http://i.creativecommons.org/l/by-nc-nd/3.0/88x31.png" /></a><br />The University of Bradford theses are licenced under a <a rel="license" href="http://creativecommons.org/licenses/by-nc-nd/3.0/">Creative Commons Licence</a>. |
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