Cracks (Stress-Relief Microstructure) In The Brake Disc Friction Surface

Cracks in the brake disc friction surfaces must be regarded differently to cracks in grey cast-iron brake discs. These cracks are not regarded as wear criteria for PCCB brake discs and may even be present on new brake discs, depending on the manufacturer.

Fig 1: Identifying PCCB Brake Disc Friction Surfaces Area - Stress-Relief Microstructure

Courtesy of PORSCHE CARS NORTH AMERICA, INC.

Information 

• Due to the composition of different materials in the friction layer and support body, the friction surfaces (even when new) are coated with an uncritical crack pattern (stress-relief microstructure). Individual relaxation cracks sometimes run along the perforated bores  .
• The stress-relief microstructure results from the way in which the brake disc surface is manufactured and does not pose a risk to safety. There is also no danger of the friction layers flaking off from the support body, since the friction layers are almost free of internal stresses as a result of the stress-relief microstructure  .
• The stress-relief microstructure is sometimes clearly visible in new brake discs and the brake disc chamber side and the side that is opposite to the chamber can differ significantly from one another  .