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Malleability vs. Brittlenes vs. Ductility

Plastic deformation properties.

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

DL = 100% (Lf - L0) / L0                        (1)

where

DL = ductility related to elongation (%)

Lf = 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

DA = 100% (A0 - Af) / A0                        (2)

where

DA = ductility related to reduction of area (%)

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

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

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