EFFECT OF HUMIDITY ON FRICTION PERFORMANCE OF AUTOMOTIVE BRAKE MATERIALS CONTAINING SOLID LUBRICANTS

Author

Mohammed Gamal Saleh Ali, Southern Illinois University CarbondaleFollow

Date of Award

5-1-2017

Degree Name

Master of Science

Department

Mechanical Engineering

First Advisor

Filip, Peter

Abstract

During the braking process, heat is generated between the contact surfaces of the rotors and pads. These elevated temperatures impact the brake pads performance and therefore solid lubricants are used to stabilize the coefficient of friction. However, solid lubricants are very reactive when they expose to high temperatures resulting in a change in the tribological properties. Generally, the presence of liquid films increases the adhesion between solid bodies. The most common solid lubricants in friction materials formulation are Graphite, Molybdenum Disulfide (MoS2) and Antimony Trisulfide (‎Sb2S3). Solid lubricants are efficient because of their lamellar structure. The lamellas have a parallel orientation to the surface with respect to the direction of motion. These lamellas results in low friction because they have the capability to shear over each other. Different types of materials including materials with solid lubricant additives have been investigated experimentally to determine the variation of coefficient of friction and investigate the brake pads in the presence of relative humidity using the Universal Mechanical Tester (UMT). The chemistry analyses were studied using the energy dispersive X-ray microanalysis to investigate any chemistry differences on the contact surface area of these materials. It is concluded that the friction level increases with an increase of relative humidity level due to the consequence of a stronger adhesion. The addition of used solid lubricants did not have any positive impact under the effect of humidity on frictional performance. The chemistry of the friction surface/layer also is playing important role when humidity adsorption is concerned.