Optimization of brass contents for best combination of tribo-performance and thermal conductivity of non-asbestos organic (NAO) friction composites

Thermal conductivity (TC) of composites especially friction composites plays a vital role in the performance during braking. Low TC renders the tribo-surface vulnerable for degradation of organic ingredients affecting the braking capability adversely while too high TC on the other hand, results in adverse effect on brake-fluid. Simultaneously it is also required that the composite should exhibit best possible combination of performance properties as a friction material. The optimum combination of various properties hence is to be tailored with right contents of metallic fillers. In this paper the effect of brass fibers in increasing amount on friction and wear performance of non-asbestos organic (NAO) friction composites was studied. Four friction materials based on parent composition and with varying amount of brass (0, 4, 8 and 12 wt%) and barite (35, 31, 27, and 23 wt%) in a complementary manner were developed as brake pads and were characterized for physical, chemical and mechanical properties. These were further tested for their friction and wear behavior in fade and recovery (F & R) mode on a Krauss machine as per ECE R 90 schedule. Moreover, the small specimens (24 mm × 24 mm) of the brake pad were evaluated for studying their friction sensitivity for loads and speeds in simulated braking conditions against a commercial disc on a reduced scale prototype (RSP). Composite with 8% brass fibers (where TC was not highest) proved to exhibit best combination of performance parameters related to friction and wear in both the testing modes. Scanning electron microscopy (SEM) and energy dispersive X-ray analysis (EDAX) were employed to understand wear mechanisms.