Performance Evaluation of New Series of Kevlar Fiber Based Nano Composite Friction Material Tested on Coated Rotors
Regenerative braking is an important system of an electric/hybrid vehicle as it enables to recover the considerable part of its kinetic energy. Since the braking torque demand could often be higher than the torque provided by the electric motor, a ??blended?? approach of friction and regenerative braking is used . This provides an opportunity for development of advanced new designs of regenerative brakes and a new series of advanced lightweight, low wear, high strength, corrosion mitigating and sustainable friction materials. This study focuses on the performance of a newly patented polyimide matrix composites reinforced with Kevlar fabric and further modified with carbon nanoadditives. These alternative friction materials are very light and are free of not only asbestos and copper, but also of other environmentally challenging constituents potentially used in friction materials. The new advanced pad materials with dimensions of 10.9 x 10.9 x 5 mm3 (by Tribco Inc.) were tested in a scaled-down ISO SAE J2522 test using the ??bench-top?? Universal Mechanical Tester (UMT, Tribolab by Bruker) also equipped with accelerometer (PCB Electronics, Model = 356A45), microphone (PCB Electronics, Model = 377C01) and a custom-made heating chamber, allowing for heating up to 550?aC, and designed by Bruker. The polyimide matrix pads were rubbed against commercially available gray cast iron rotors (C30, ASTM A48, diameter of 95.5 mm) coated with ceramic material in accord with a patented process . Scaling philosophy was based on the characteristic dimensions of length, area, and volume. Density, porosity (Archimedes principle in distilled water and AWS ALX -310 precision balance), and shore D hardness (using CV Instruments Durometer - ASTM 2240) were compared to the selected currently available commercial non-asbestos organic brake pad materials. Surfaces of tested pads and rotors were analyzed using Scanning Electron Microscopy (FEI, Quanta FEG450) equipped with the energy dispersive X-ray microanalysis (EDX, Oxford Instruments). A stable and sufficiently high coefficient of friction was observed during the increased temperature, speed or pressure sections. Wear of pads and rotors was extremely low. Importantly, the friction tests revealed that the polyimide matrix composite samples were very gentle on the rotor. The pad material does not remove the ceramic coating and the material is deposited on the rotor surface creating a chemically stable and strong friction layer reinforced by nanoadditives and Kevlar fiber. No noise or excessive vibrations were detected during the tests. Extremely low wear of pads and rotors alongside with the capacity of the pad material acting gently on rotor coating, combined with interesting physical properties, would make this type of friction materials attractive, especially for regenerative braking scenarios where corrosion ??could also be an issue.?? Further full-scale brake dynamometer as well as field testing in accord with the currently adopted standards is suggested in order to understand the full potential of the polyimide matrix, Kevlar reinforced and nano-carbon modified pad materials.