Dr. Gérard Degallaix is a Professor of Mechanical Engineering in the Centrale Graduate Engineering School in Lille (France). He is a member of the Laboratory of Mechanics of Lille (UMR CNRS 8107). He is known internationally for his contributions in the areas of fatigue, failure analysis and damage mechanics of advanced and structural materials, and friction and wear of friction materials as well as brake discs fatigue resistance in particular for railway applications. He has worked in his lab with Yannick Desplanques on the development of braking Tribometers and characterization of various friction materials. He has published or deliverered over than 180 papers and contributions. In Ecole Centrale de Lille, he directed the "Advanced Mechanics" course during 1989-07 and serves currently as the Dean for Research.

Title- “Tribological mechanisms activated during localized thermal phenomena induced in railway braking”.

Abstract: -In the field of railway braking, improving the performance of friction brake systems requires deeper knowledge of the tribological behaviour of pad-disc contact under near-realistic braking conditions. During railway braking, dissipation of highenergy due to friction leads to transient and localized thermal phenomena such as hot bands and hot spots. These thermal phenomena interact with third body flows and friction mechanisms activated in the contact. The talk presents the experimental approach used to study these physical mechanisms of friction and wear in railway braking.
The design of an original braking tribometer developed as an inertial test bench is based on similitude rules between reduced-scale and full-scale. This enables to reproduce high thermo- mechanical brake-disc loadings, such as hot-spots and hot-bands, as a function of braking severity. The selection of the most representative test conditions is discussed, particularly from the thermal point of view.
This talk deals with the correlation between the physical mechanisms of friction and the localized thermal phenomena involved during severe railway braking using non-asbestos organic matrix composites. Post-mortem analyses of the samples allow identification of the main friction mechanisms and the associated flows of the third body. They are completed by in-situ observations  of the disc friction track in the infrared and visible wavelengths,in order to take into account the transient nature of braking. Local and transient aspects of thermal phenomena are observed by infrared thermography on the disc track while rubbing surfaces are observed and analysed in correlation with the corresponding disc-track thermograms. To obtain more information on the dynamics of the third body during braking, a high speed video device was developed to observe the disc friction track. It permitted monitoring of specific  zones of the disc friction track during the test and thus monitoring the recirculation flow during braking. The localization phenomena observed by thermography are correlated with the physical mechanisms activated in the contact during braking.