Residual stress development and thermo-elasto-plastic distortion in brake discs

Abstract

The relationship between thermo–elasto–plastic deformation during braking and the residual stress in brake discs is investigated experimentally in this study. X-ray diffraction is conducted to validate the residual stress distribution in the depth direction, whereas the cut/sectioning method is used to quantitatively measure the residual stress across a broader disc area. In addition, thermo–elastic distortion is quantified using thermal strain measured using a dynamometer. The compressive residual stress is distributed on both the circumferential and radial surfaces of unused brake discs with a magnitude of approximately 30 MPa, which transforms into a tensile stress exceeding 50 MPa in the circumferential direction after continuous braking tests, thus resulting in thermo–elastic distortion. This distortion is proportional to the tensile stress developed along the braking direction, which is primarily caused by plastic deformation due to external force and temperature gradient from the disc surface and core. The distortion magnitude ranges from 60 to 140 µm, depending on the type of pad material. Thermo–elastic disc distortion can be reduced by releasing tensile stress on the plastically deformed disc surface through abrasive wear using frictional pads. However, the magnitude of the initial compressive stress has minor effect on the distortion. The present experimental study provides insights into factors that affect thermo–elasto–plastic distortion in brake discs as well as methods that can reduce the distortion of brake discs in the design stage.