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Brittle vs Ductile Fracture

Brittle fracture

Stress (MPa) Strain

Ductile fracture

Stress (MPa) Strain

Mouse over the graphs to compare the area underneath which is the energy absorbed before fracture i.e. toughness.

Nucleation of voids

Once a neck has formed, plastic deformation is concentrated and voids form.

Void growth

The formation of voids causes higher stresses and there is further deformation under the effect of shear.

Void coalescence to form a crack

The voids concentrate stresses themselves, such that the stresses in the ligaments between them become higher and these fail by shear. The voids will link up ahead of the crack tip.

Fracture

The crack grows and final failure occurs by shear at 45° at the edges.