Abstract
KEYWORDS – Hot spots, TEI, Hertz contact, Thermomechanics, SEHB
ABSTRACT
The emergency braking distance of a high-speed train at 320 km/h is almost 3000 m. Dry running brakes are reliable due to their predictable response to external stresses and are thus used in such applications. The kinetic energy is dissipated proportionally between the brake disc and the brake pad. This induced dissipation of energy and the high frequency of the brake application cause high temperatures. During the brake application at relatively high energy levels, the occurrence of the hot-spot phenomena can be observed.
Generally, hot spotting describes the development of thermal localizations and can lead to fading, early damage, early wear, pad performance loss, hot judder and squeal noise. These immense temperature changes could cause macroscopic cracks leading to the failure of discs and accidents. Several theories have been developed explaining these localizations: Thermoelastic instabilities (TEI), buckling, progressive waviness distortion (PWD), etc.
In the present work, a coupled thermomechanical model in combination with a Hertz contact formulation is proposed to explain and quantitatively predict hot spotting in disc brakes. The model is implemented into a finite element framework and used to simulate the evolution of the temperature distribution of the hot spots depending on the local contact pressure variation and physically sound boundary conditions. In a first step the simulation results are then compared to data reported in the related literature. For further validation, a full-scale brake test rig for railway applications is modified to detect the occurrence of hot spots and their influence on the dynamic brake performance of a self-energizing electro-hydraulic brake (SEHB) developed at RWTH Aachen University.