Fracture of single crystals having layered morphology

The mechanism for relaxation of elastic energy in layered crystals (where interlayer glide is possible) under a point load is discussed. Titanium dichalcogenides are chosen as materials with covalent interatomic bonds, while the Ir-Sn compound is a metallic single crystal. All studied samples have layered morphology with similar parameters, such as the thickness of the sample and the thickness of a single layer. It was found that penetration of a diamond pyramid induces mechanical twins around the indent, whereas the appearance of cracks is a very rare phenomenon. In contrast with bulk samples, cracks in layered crystals move on complicated trajectories, which do not coincide with low-index crystallographic directions. Besides, their growth is limited by the surface single layer. Gliding between neighbouring layers effectively suppresses the propagation of cracks via the interlayer boundary. Glide may be considered an irreversible shift, which prevents the fracture of a material.