As mentioned earlier in Part 1 of this article, 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 energy efficiency and degree of the plastic deformation in the process of destruction – a fragile, quasi-brittle, ductile, where the energy to failure A and relative reduction y of cross-sectional area is suitably: А < 0,5 kilogram-meter, ψ ≤ 1,5 %; А= 0,5–2,0 kilogram-meter, ψ ≤ 15 %; А > 2,0 kilogram-meter, ψ > 15 %;
by the destructions micro mechanism – fragile, quasi-brittle, viscous, fatigue;
by communications with the structure element – intracrystalline; intracrystalline, intersubcrystalline.
The terms for the fractures macro relief description:
The crystal fracture – brilliant, brittle; occurs by the separation on the cleavage faces without considerable plastic deformation therefore, the grains aren’t distorted and well defined in the fracture.
The fiber fracture – viscous; is formed at significant plastic deformation in the fracture; the grains strongly distorted and do not defined in the fracture.
The cup fracture is in conic frustum form and is common to the three dimensional state of stress, at the fracture nucleation time.
The chevron (pine-tree) fracture – is the indication of low plastic deformation at the fracture.
The fatigue fracture – on the structure is mixed and always has two zones of destruction: fatigue with the fine-grained, deformed, often step slate structure, sometimes with the brilliant, fibrous sites, as if a polished surface; and the final zone is more often than fragile destruction (doloma).
The naphthalene fracture – intracrystalline, coarse-grained; scaly, as naphthalene; brilliant, fragile; meets in instrumental, mainly, high speed steel, at overheat and existence of the intracrystalline orientation – textures; disappears together with the coarseness and texture disappearance when annealing.
The stone like fracture is fully or partially i intracrystalline; with lumpy, coarse-grained structure, brittle; grain without metallic luster, as if melted; occurs in strongly superheated steel, is quite stable; eliminating lengthy gamogenesis annealing or normalization with the short-term heating to 1050 – 1100 0С.
The flaky fracture – the flakes in the longitudinal fracture are brilliant bright spots round and oval-shaped with a diameter from fractions of mm up to 100 mm, and in the transverse failure is fracture is formed by rapid cooling of steel with a high content of hydrogen in the temperature range from ≈ от 200 до 20 0С.
The burnout fracture occurs when a strong homogenizing annealing temperature exceeds molding and is characterized by the presence of large dendrites of the oriented position, acquiring a dark color due to the high temperature oxidation; the fracture is defective, incorrigible.
The slate facture is layered, with a treelike arrangement of the coarse fibers, is common to intermediate-carbon, hot-wrought steel. The slate indicates the presence of extremely intense segregation, gas and slag inclusions; the fracture is defective, and is not corrected by the heat treatment.
