Fracture is the failure surface of a product or the whole piece of metall. According to cracks fracture cracks, holes, blowholes, stratifications, gaps, large slag inclusions and other defects are well identified.
The fracture contains information on features and causes of failure, which can be fragile, viscous and mixed – fatigue. The viscous fracture is common to the high strength fine grained metal with high mechanical properties; the fragile fracture is common to the coarse-grained metal with low dynamic resistance (toughness).
For the uniform determination of destruction nature, the successful prevention of premature and catastrophic destructions and, therefore, for the systematic increase in operational reliability of machines and designs, the unified fractures classification and common terminology for their description are created. The main fracture type’s classification is made on the whole range of features:
by the nature of force impact it is distinguish the short-term fractures (static, dynamic) and long term loading: the creep fractures, the corrosion on stress, the fatigue failure, the thermal fatigue and others;
by the fractures’ orientation – a straight, slanting, straight with bevels (cup), the surface of straight fracture is perpendicular to the sample axis and to the direction of the greatest extending forces that is common to macro fragile destruction; the surface of the slanting fracture is inclined at an angle to the sample axis or the detail that is common to macro viscous destruction;
by the macro geometry of fracture – the uniform, non-uniform, star-shaped, chevron (pine-tree), irregular shape;
by the surface, shine and color there are fractures:
crystal (fragile) and fibrous (viscous); stone like, silky (in coarse-grained, overheated steel); porcelain, dull (at the short-grained, tempered steel); brilliant (fragile), light (at steel and iron with cementite Fe3C); gray, dark (black – at steel and iron with graphite) and other.