Malleability vs. Brittlenes vs. Ductility

Malleability

• whereby a material can be plastic deformed and shaped when cold

A malleable material can be plastic shaped with hammering or rolling without fracture.

Typical malleable materials:

• mild steel, gold, lead

Brittleness

• whereby a material will fracture without appreciable prior plastic deformation

Brittleness is lack of ductility and for a brittle material there is no plastic deformation. The elastic stage is followed by immediate fracture.

Typical brittle materials:

• glass, concrete, ceramics, stone, gray cast iron

Ductility

• whereby a material can be plastic deformed by elongation without fracture

Ductile materials can typically be plastic elongated with more than 15% before they fracture.

Typical ductile materials:

• copper, mild steel, thermoplastics

Specification of Ductility

Ductility can be specified as percent elongation before rupture as

D_L = 100% (L_f - L₀) / L₀                        (1)

where

D_L = ductility related to elongation (%)

L_f = final length of specimen at fracture  (m, mm, in...)

L₀ = original length of specimen (m, mm, in...)

Alternatively ductility can be specified as percent reduction of area as

D_A = 100% (A₀ - A_f) / A₀                        (2)

where

D_A = ductility related to reduction of area (%)

A_f = final area of specimen at fracture  (m, mm, in...)

A₀ = original area of specimen (m, mm, in...)