Effects of Steel fibers and Cu Powder on wear and friction characteristics of brake pads

Brake pads are critical components in any vehicle s braking system, providing the friction necessary to convert kinetic energy into heat and bring the vehicle to a safe stop. Their reliability and performance directly impact the driver s ability to maintain control and prevent accidents, underscoring their paramount importance in road safety. Generally, pad friction materials of brake systems are composed of a mixture of ingredients grouped into four material categories: fillers, abrasives, lubricants, and reinforcing. Cu has proved to be one of the most important ingredients in brake pads. Indeed, it improves the thermal conductivity of brake pads and helps to build up a compact friction layer, in such a way as to avoid the thermal fade and decrease the wear rate of brake pads. Although Cu has a multifunctional contribution to brake performance, its usage in brake pads has recently become a subject of debate due to its potential toxicity to aquatic species. For this reason, potential alternatives for the production of Cu-free brake pads have recently been evaluated. In this study, steel fibers with a particle size range of 300-600 µm were prepared instead of Cu powder in proportions of 8, 6, 4, 2, and 0 %. Cylindrical samples with a diameter of 25 mm and a height between 8 and 11 mm were produced by the following steps: 1. Single ingredient raw powders/fibers and phenolic resin were mixed for 30 min; 2. A cylindrical mold was filled with the achieved mixtures; 3. Hot pressing with a uniaxial hydraulic press under 20 MPa pressure and 160℃ temperature for 5 min. 4. hot-pressed samples were initially heat treated for 1 hour at 100°C, followed by 2 hours at 130°C, and finally, 2 hours at 180°C. A pin-on-disk tribometer was used to measure the specific wear rate of the samples by applying a force of 29N at a rotation of 240rpm, based on Archard s law. The optimal wear rate was reported based on the ISIRI 586 standard for samples containing 4% Cu and 4% steel fibers with a specific wear rate of 0.8118 ×10^(-6) gr/m . In order to check the actual braking conditions and changes in morphology and material interaction, the wear test was also evaluated at 300℃. The samples containing 2% Cu and 6% steel fibers with a specific wear rate 10.153×10^(-6) gr/m had the lowest wear rate. Finally, the changes in the friction coefficient of the samples during different heating and fade stages were compared. It was found that samples with a constant and stable friction coefficient of 0.25 to 0.6 have favorable wear properties.