Impact of Phenolic Resin Type on the Performance of Newly Developed Friction Materials for Vehicles with Regenerative Braking

Automotive industry is undergoing a paradigm shift towards vehicles with alternative power. The sales of electric vehicles have increased by over 165% over the past 2 years in the United States [1]. With government incentives coupled with the decrease in battery cost, the trend seems to continue. As the friction brake accounts for about 5 to 30% of total braking in electric/hybrid vehicles, this also warrants for more research into the development of new lightweight, wear resistant, and sustainable friction materials also for reviewing the existing testing procedures. Phenolic resin is typically used as binding material in majority of the current brake friction materials. Numerous authors demonstrated that the type of phenolic resin has effect on properties of brake pads [2]. In this study, laboratory developed Non-Asbestos Organic (NAO) brake pads with identical composition but formulated with two different resin types, respectively, one with unmodified standard resin and another with a silicon modified resin, were subjected to series of standardized tests. The goal was to compare the impact of used resin on the friction performance and the physical properties of pads. The density, Shore D hardness, thermal stability at 300?C and 500?C (using TGA Q50 by TA instruments), storage and loss moduli (in temperature range from 0?C to 300?C using DMA Q800 by TA instruments) of these pads were measured. Pads were tested against commercially available rotors (ASTM A48 C30 gray cast iron) coated with ceramic material [3]. Friction tests were performed using Universal Mechanical Tester (Tribolab by Bruker) and the scaled-down ISO SAE J 2522 procedure. Scaling philosophy was based on characteristic dimensions (length, area, and volume) of real pads and scaled down samples. Scanning Electron Microscopy (FEI, Quanta FEG450) equipped with energy dispersive X-ray microanalysis (EDX, Oxford Instruments) was used to analyze the friction surfaces of pads and rotors in order to understand their surface chemistry and morphology, as well as their impact of on performance of the tested friction material. Both the sample types prepared with different resins were gentle on the coated rotors. Good friction layer is developed on coated rotors tested against both the set of samples, protecting the friction surface and stabilizing friction. Sample with silicon modified resin exhibited higher level of friction, was more stable at higher temperatures, and had better pressure and fade characteristics when compared to sample with unmodified standard resin. DMA results indicate that sample with Si modified resin has higher damping capacity, which is favorable when NVH characteristics are concerned.