Brittle Fracture Mechanism:

Metals could fail through brittle or ductile fracture. Metals which could sustain substantial plastic strain or deformation before fracturing exhibit ductile fracture. Commonly a huge part of the plastic flow is concentrated near the fracture faces.

Metals which fracture along with an associatively small or negligible amount of plastic strain exhibit brittle fracture. Cracks propagate quickly.  Brittle failure output from cleavage (splitting along definite planes). Ductile fracture is better than brittle fracture, since  ductile fracture occurs over a period of time, whereas brittle fracture is fast, and could occur (along with flaws) at lower stress levels than a ductile fracture. The given figure displays the basic categories of fracture.