Beschreibung:
For failure assessment of natural cracks caused by surface treatment, the crack resistance for very small crack extensions is necessary. In ceramics with strongly rising R curves, the initial part of a few micrometer crack propagation is of special interest. For this purpose, the use of very small sharp starter notches introduced by a focused ion beam is recommended. As an example, the initial R curve for gas‐pressure‐sintered silicon nitride at high temperature will be estimated. Whereas for V‐notched bending bars a fracture toughness of about 6–6.3 MPa·m1/2 was determined, the toughness for small strength‐relevant cracks was found to be KIc≅5.1 MPa·m1/2.