Mechanical braking systems for trains: A study of temperatures, fatigue and wear by experiments and simulations
Increased demand for shorter travel times, higher axle loads, increased
volumes and increased punctuality of railway traffic calls for a better design
and management of the railway subsystems. The present thesis deals with
aspects of mechanical friction brakes, in the form of tread brakes and disc
brakes. These are critical for reliable, safe and economical operation of trains.
The thesis establishes models and simulation tools for frictional braking
systems that may operate in parallel with an electrodynamic braking system.
A main focus is the influence of thermal loading on rolling contact fatigue from
tread brakes at stop braking. A simulation methodology for thermomechanical
cracking of railway wheel treads due to rolling contact and repeated stop
braking by tread brakes, is established based on full-scale brake rig
experiments. Building on the same approach, plastic deformation of the tread
is also investigated. The results indicate that tread damage increases
drastically for frictional temperatures above some 450 ºC.
Another focus is temperatures and wear of tread brakes and disc brakes
under operational loading. In two field test campaigns, detailed
instrumentation and continuous measurements of relevant temperatures
and braking parameters are combined with intermittent measurement of
wear of friction brake components. Wear of brake blocks and wheel treads
is quantified. It is found that the tread wear introduced by the block contact
dominates for trailing wheelsets, whereas for powered wheelsets wear from
tractive forces in the wheel–rail contact can be of equal importance. In a
study on disc brakes, temperatures and wear performance are compared
for two friction pairs: one new segmented disc with sintered pads and a
traditional disc with an undivided friction ring combined with organic pads.
It is found that the discs have similar braking temperatures, but that the
wear of disc and pads is substantially lower for the segmented disc.
A numerical investigation of thermomechanical fatigue damage of the two
disc types indicates that the segmented disc also has a substantially
longer fatigue life.
KS101, Kemigården 4, Chalmers
Opponent: Prof. Paul Allen, Department of Engineering and Technology, University of Huddersfield, United Kingdom