Harjeet S. Jaggi

Dynamic mechanical response and fade–recovery performance of friction composites: effect of flyash and resin combination

Flyash-filled and glass fibre-reinforced phenolic composites have been fabricated by compression molding. The composites were characterized for their mechanical, thermo-mechanical, tribological and morphological attributes. Temperature dependence of mechanical properties has been investigated using dynamic mechanical analyzer. Tribological properties of the composites were evaluated by chase friction tester conforming to SAE J661a standard. An inverse relation between the storage modulus and wear has emerged, indicating wear to be mainly controlled by the fibre/filler matrix interfacial characteristics. Tribo-analysis reveals improvement in the friction fluctuations, whereas wear resistance deteriorates with increase in the ratio of flyash to resin content. Temperature-dependent reduction and revival of friction coefficient revealed the improvement in the average friction–recovery performance although the friction–fade response was found to be mostly unaffected due to compositional variation. SEM analysis is carried out to study the topography of the contact patches/friction film and associated wear mechanism of the phenolic-based composites, which has further revealed more of the secondary plateaus for composites containing more of the phenolic content. Disc rubbing intensity, as obvious from the energy-dispersive X-ray analysis (Fe content), becomes less prominent with increase in the ratio of flyash to resin content.

Temperature dependence of friction and wear performance and thermomechanical response of flyash-filled brake composites

Flyash-filled glass fibre reinforced composites have been fabricated and evaluated for drag braking performance on a chase friction testing machine following SAE J 661a standard. The friction build-up and decay phenomena in the drag braking mode as a function of drum temperature have consistently been found to be in the composites with ∼5−7.5 wt% of glass fibres, whereas the absolute friction effectiveness remained higher in the composites with maximum flyash/maximum glass fibre contents. Temperature-dependent friction performance remained broadly composition specific and qualitative correlations of performance to compositional attributes have been found to be complex. Topographical variations and their possible roles in controlling the tribological performance have been characterized by worn surface morphology. Scanning electron microscopy–energy dispersive X-ray combined analysis have revealed that at higher amount of glass fibre content in combination with flyash, the composite exhibited enhanced noise and judder propensity apart from higher Fe-content deposition on friction film. The energy dissipation ability modes as revealed from dynamic mechanical analysis showed not only a correspondence between the damping ability of the composites and compositional variations but also qualitatively established a correlation between wear and storage moduli.