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Figure 5.7 Ductile failure: ‐one piece ‐large deformation (after some amount of plastic deformation).

Source: Colangelo, Vito J. and Heiser, Francis A. (1987). Analysis of Metallurgical Failures. 2e. Wiley.

Figure 5.8 Brittle failure: ‐many pieces ‐small deformation, (even when the stress is within the elastic range).

Depending on the ability of material to undergo plastic deformation before the fracture two fracture modes can be defined – ductile or brittle. Ductile fracture is characterized by large amounts of plastic deformation. Proportionally large amounts of energy will therefore be required to induce this fracture. When designing a structure, it is usually preferable for the material to fail in a ductile manner as there will be sufficient warning (evidence of deformation) before the final failure occurs. In a brittle fracture, little plastic deformation and low energy absorption before fracture take place.

Ductile fracture‐ most metals (not too cold):

 Extensive plastic deformation ahead of crack.

 Crack is “stable”.

 Resists further extension unless applied stress is increased.