Influence of various metallic fillers in friction materials on hot-spot appearance during stop braking

The heat generated between friction couple during high speed braking induces thermal distortion in the disc and leads to appearance of hot spots. The nature and extent of intensity of this phenomenon are highly influenced by the mechanical and thermal properties of materials. In the present work, three non-asbestos organic (NAO) friction composites with three metallic particulate fillers (iron, copper and brass) were developed. They were evaluated on a specially designed tribometer for enabling the studies of hot spots and thermal localization phenomenon under braking conditions. Overall, composite with iron powder proved best by showing least tendency for hot-spot generation.

Research highlights▶ This article emphasizes on the various metallic ingredient in friction composites on counter-face friendliness in terms of thermal localization phenomenon and tendency of hot spot generation when evaluated on special tribometer. ▶ A well set article and a valuable work on the correlation between thermo-physics and mechanics of a disc brake system. ▶ Inclusions of metallic contents improved the overall thermal-localization performance of friction material. The best results were obtained with iron powder while the performance of composites with brass and copper was almost similar and moderate. ▶ The progressiveness of hot-spot appearance during braking confirmed that the origin of hot spots lies in a progressive waviness distortion of the disc. ▶ Interesting correlations were observed between thermal effusivity and compressibility of composites. Higher the effusivity and the compressibility, lower was the tendency to produce hot spots and higher was the counterface friendliness. ▶ The number of excited harmonic frequencies of the disc rotation exactly matched with the number of dominant hot spots observed by infrared thermography.