Relationship Between Mechanical Behavior and Microstructure Evolution of Sintered Metallic Brake Pad Under the Impact of Thermomechanical Stress

Abstract

It is well known that on the brake pad material, the triptych microstructure-properties-solicitations is the key to better understand the phenomena caused by braking stress. The challenging issues are the evolution of this triptych, i.e., the impact of thermal stress and mechanical stress on the microstructure which undoubtedly induces changes in properties. In order to solve the issues without tackling them in all their complexity, this study proposes an experimental approach where physics is decoupled but inspired by the braking sequence in terms of applied temperature gradient and braking loads. Two experimental tests were carried out. The first one is the thermal solicitation test where a temperature gradient from 400°C to 540°C was applied to the material. The second one is the thermomechanical test where a compressive load at 20 MPa was applied under the same thermal gradient. The experiment time is fixed for two minutes, equivalent to the time of one braking stroke. The referred material is sintered metallic composite, which is widely used as brake pad material for high-energy railways. As result, it shows that coupled thermomechanical stress has a greater impact on the material properties than decoupled one. This impact is related to the microstructure where graphite inclusions play an important role.

Sintered Brake Pads Failure in High-Energy Dissipation Braking Tests: A Post-Mortem Mechanical and Microstructural Analysis

“…Since graphite particles in the pad can reach several millimetres, the volume of the samples may seem slightly small to be truly representative of the heterogeneity of the pad. Nonetheless, several tests were performed on samples extracted in different areas of the pads, showing a great consistency in the results [32].…”