Crack-Face Interaction

In the classical analysis of Griffith (line) cracks, the crack faces do not interact with each other. But for real cracks, various kinds of mechanical crack face interaction can occur. In particular, protrusion interference during biaxial loading of a bumpy Griffith crack is discussed. The influence of this interference on the stress required to produce fast fracture in a brittle material is analyzed using the Griffith fracture criterion for biaxial stress. The dependence of the fracture stress on the orientation, magnitude and biaxiality of the remote stress is described quantitatively. It is shown that the stress required to produce fracture is slightly altered by a single interference site, but significantly altered when many sites are present. It is also shown that for all cracks whose length is less than about one-tenth of a millimeter in silicon carbide or 1 mm in silicon nitride, any interference that exists influences fracture.