Abstract
The tribological behaviour is crucial for questions of performance, comfort and ecological behaviour of wheel brakes. It is possible to identify reasons for phenomena and moreover to define more efficient countermeasures by describing it.
Traditional approaches consider the global determination of relevant parameters such as applied brake pressure, temperature of disc and brake lining or the brake torque. Using a transparent friction partner (complete or segmented), local processes within the friction zone including their dynamic changes should be visualised as well as generated friction layers. Furthermore it is intended to show that the obtained results are transferable to the conventional friction couple cast iron brake disc – organic brake lining.
Base of the work is represented by a modular test rig concept which is in its functionality comparable to a tribometer. Though, several measures have been realised to ensure the visualisation of the friction zone.
The used brake pads have not been modified in size or geometry compared to conventional linings.
For the analysis of the friction behaviour and the characterization of the friction partners respectively, amongst conventional transducers most of all visualisation devices are used. They comprehend several camera systems like a high speed camera, a digital single-lens reflex camera and a microscope camera. Alongside intensive physical and chemical analysis were done.
As a first result it is confirmed that friction films also on the surface of glass discs can be found. This in combination with the results of friction behaviour analysis let the authors conclude that for certain phenomena the comparison between cast iron and glass discs is feasible.
Using this approach it is possible to examine the phenomenon of “hot spots” regarding their creation and time dependant behaviour. Beside the visualisation, physical and chemical investigations (by the use of REM / EDX) were done to characterize the areas of local hot spots (showing flash temperatures)
The presented method shows potential to investigate also other phenomena (such as friction induced vibrations or the behaviour under wet conditions) more in detail and to understand their working mechanisms better.
KEYWORDS – visualisation, friction zone, friction layer, transfer film, hot spots