Brittle vs Ductile Fracture
Mouse over the graphs to compare the area underneath which is the energy absorbed before fracture i.e. toughness.
Once a neck has formed, plastic deformation is concentrated and voids form.
The formation of voids causes higher stresses and there is further deformation under the effect of shear.
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.
The crack grows and final failure occurs by shear at 45° at the edges.