Mechanical braking systems for trains: A study of temperatures, fatigue and wear by experiments and simulations

Abstract: 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.