Fractography - Break morphology

Any fracture of a machine component or steel structure simultaneously implies local tensile stresses and at least momentary weakness of the metal. Fracture begins with a crack that propagates from an incipient crack at a highly variable rate, ranging from a very sudden break to cracking over several months. The fractures bear the imprint of both fracture conditions.

The link between mechanics and metallurgy couldn't have escaped the attention of our clever ancestors: probably already in the search for minerals that could be transformed into cutting tools (flint), then in the "mechanical testing" of swords cited by Greek authors.

Such observations were later specified in writing: G. Agricola (Bauer) (1556 Bale), L. Ercker (1574 Prague), R. Réaumur (1722 Paris), A. Martens (1878 Berlin), C. Zapffe (1939 ASM).

Careful observation of fracture morphology enables us to detect two fundamental characteristics: firstly, the initiation of cracks and secondly, their mode of propagation. It allows us to trace the cause(s) of the fracture: the actual intensity and distribution of stresses, and their metallurgical uniformity. As a result, we can improve the design, production and working conditions of mechanical assemblies.

The complete study of the subject includes the articles :

• M 4 120 – Fractography. Physical basics ;

• M 4 121 – Fractography. Fracture morphology (this article) ;

• Form. M 4 122 – Fractography. Macrography and micrography;

• Doc. M 4 123 – Fractography.