Transmission topographs of two cracks introduced from a 50 N indentation at the wafer edge, 90° from the notch: Tc indicates the shadow of a thermocouple, P1 the position where crack C3 originates (room temperature, view from the back side through the sample). (a) Before the first heating sequence. The left crack C1 is short and shows a substantial strain field at the tip of the crack for which κ = 20. The more dangerous crack C2 is almost four times longer and has a sharp contrast at the tip; no strain field is visible which results in κ = 167. (b) After the first heat treatment. The new horizontal crack C3 is generated. Around the crack tips dense dislocations and slip bands were produced, visible from the black contrasts.