Friction hysteresis and subsequent wear mechanism of clay-based phenolic composites under cyclic load

Abstract

Abstract Friction composites based on different allumino-silicate (i.e. halloysite, montmorillonite and wollastonite) have been developed for automotive brakes to investigate the relative contribution of the clay-minerals as a replacement of MgO and BaSO4 separately. The effect of the cyclic load on friction-hysteresis and wear behavior of the composites are comparatively evaluated with clay free compositions (with and without MgO and BaSO4). The general characteristics of the friction hysteresis under cyclic load reveal three distinct phases i.e. μ build-up, μ-decay, and μ-unloading. It is found that halloysite being less effective in debris compaction manifests minimum friction hysteresis loss, whereas the montmorillonite based composites are characterised with maximum hysteresis loss due to the difference between μ-level during loading and unloading in presence of MgO as an abrasive. Wollastonite with the relatively minimum area to volume ratio manifests inefficient reinforcement in the tribo-film thus debris formation and subsequent third body abrasion demonstrates undulating μ-level with maximised μ-average. Worn surface morphology illustrates the presence of plastically deformed distorted surface with fiber dislodging and pit formation for composites containing halloysite, suggesting extensive abrasion. Soft regimes over the worn surface as a result of debris compaction and smooth morphology is the characteristics of montmorillonite based worn surfaces. Easy removal of the tribo-layer due to shear and heat accumulation results in discontinuous transfer film over the worn surface in presence of wollastinite, where MgO is effective in debris compaction. An almost similar level of volumetric wear for all the composites with circular and transverse cracks over the surface is due to the persistence of fatigue wear-mechanism under cyclic load.