Radial, close lying and mostly shallow cracks in the sliding face. Thermal stress cracks are always caused by thermal overloading of the face material surface. Brief contact between solids results in brief local temperature peaks of several 100 °C, causing great stresses. Local overstepping of the material strength causes the surface to tear open. Contact between solids can arise due to warping, lack of lubrication ending with dry running, solid inclusions in the sealing gap or deposits on the sliding faces.