Comparative performance assessment of cenosphere and barium sulphate based friction composites Avinash Tiwari a , Harjeet S. Jaggi a , Rakesh K. Kachhap a , Bhabani K. Satapathy a,n , Saurindra N. Maiti a , Bharat S. Tomar b a Centre for Polymer Science and Engineering, Indian Institute of Technology Delhi, Hauz Khas, New Delhi 110016, India b Allied-Nippon Industries Limited, Sahibabad 201010, UP, India article info Article history: Received 20 August 2013 Received in revised form 26 November 2013 Accepted 2 December 2013 Available online 7 December 2013 Keywords: Sliding wear Polymers Brakes Electron microscopy Wear modelling abstract Friction composites utilising cenosphere and barium sulphate as major fillers were fabricated both separately and in combination. Thermal analysis revealed initial degradation temperature 4500 1C irrespective of the composition. Mechanical properties viz. hardness, compressibility and shear strength were found to be well above the standard values as per the industrial practice. Dynamic mechanical response demonstrated improved storage and loss moduli for barium sulphate based composites. Tribological assessment conforming to the regulation-90 as per the Economic Commission for Europe (ECE) norms revealed improved wear resistance, enhanced recovery, lower disc temperature rise and reduced friction fluctuation for cenospheres based composites. Composites containing both fillers showed cenospheres dominated tribological response. Empirical correlation between wear, friction coefficients and dynamic mechanical properties as temperature controlled parameters was developed to predict wear. Worn surface analysis of the brake pads was carried out by scanning electron microscope (SEM) to visually analyse the associated wear mechanism at the braking interface through various topographical attributes viz. primary and secondary contact plateaus. & 2013 Elsevier B.V. All rights reserved. 1. Introduction Increasing attention on the use of sustainable and environ- mental friendly resources, without depleting mineral resources has caused a paradigm shift in research and developmental activities towards providing solutions which meet the sustainability and techno-commercial viability objective. Friction materials such as brake pads, brake linings and brake shoes are comprised of four basic ingredients viz. binder (usually phenolic resin and its modified forms), fillers (barium sulphate, vermiculite, mica etc.), fibres (glass fibres, kevlar fibres, lapinus fibres etc.) and friction modifiers (abrasives and solid lubricants). Among these prime ingredients, fillers occupying large volume fractions in friction material formu- lation are important as they reduce cost and facilitate processing of the composites [1]. Designing friction materials meeting the sus- tainability objective requires replacement of rapidly depleting mineral resource based ingredients in friction material formulation with alternative resources which are sustainable and cheap. Conventionally, mineral fillers such as barium sulphate, calcium carbonate, mica etc. are widely used as functional fillers in friction materials for manufacturing automotive brake pads. On the other hand, flyash, a coal combustion by-product and its refined form i.e. cenospheres have emerged as potential fillers for brake applications [2–8] not only because of good mechanical and tribological proper- ties obtained but also due to the fact that there is a value addition aspect associated to the otherwise costly and improper disposal of this industrial byproduct. A recent study pertaining to the com- parative assessment of flyash and cenospheres filled composites has revealed enhanced wear resistance and improved recovery char- acteristics accompanied with optimum friction performance for cenospheres based brake composites [8]. Apart from benchmarking studies of propriety nature carried out in industries, there is a dearth of studies pertaining to comparative performance evaluation in open literature. Cenospheres with its many associated advan- tages such as low bulk density (0.26–0.45 g/cc), low thermal conductivity (0.11 W/mK), high hardness (5–7 Mohs scale) and hollow spherical morphology will provide a suitable and cheaper alternative to costlier fillers used in the industries [9,10]. Friction materials usually contain multiple and often functionally disparate ingredients and hence developing a formulation based on opti- mised tribological performance characteristics is a tough task faced by development engineers. Dadkar et al. [4], Jaggi et al. [5] and Satapathy et al. [6] utilised sequential dilution of the resin with the numerous ingredients one by one with flyash as major constituent Contents lists available at ScienceDirect journal homepage: www.elsevier.com/locate/wear Wear 0043-1648/$ - see front matter & 2013 Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.wear.2013.12.001 n Corresponding author. Tel.: þ91 11 26596043. E-mail address: bhabaniks@gmail.com (B.K. Satapathy). Wear 309 (2014) 259–268