ABSTRACT
Fracture is caused by the internal stress-state of the sample. Two ways of destroying is observed: if the friction at the loaded bottom and top faces is high, shearing planes develope; if the friction is low, tensional cracks will open because of crosswise strains - Everling(1961). Both mechanisms show that the material cannot be assumed homogeneous at fracture: merging craks form fracture planes with intact parts between them.
