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

Cracks in brake disc friction surfaces are viewed differently to cracks in grey cast-iron brake discs. Cracks in PCCB brake discs do not constitute a wear criterion but exist already in new brake discs because of the way in which they are manufactured.

Courtesy of PORSCHE CARS NORTH AMERICA, INC.

Stress-relief microstructure in PCCB brake disc friction surfaces

Information 

• Due to the composition of different materials in the friction layer and support body, the friction surfaces have an non-critical 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 because the friction layers are virtually 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 can be significantly different on the brake disc hub side and the side opposite the hub.