 Therefore, these cannot necessarily be qualified as Mode II or III fractures.An additional, important characteristic of shear-mode fractures is the process by which they spawn "wing cracks", which are tensile cracks that form at the propagation tip of the shear fractures.As the faces slide in opposite directions, tension is created at the tip, and a mode I fracture is created in the direction of the "σh-max", which is the direction of maximum principal stress.