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Ductility and brittleness

A ductile material, like copper or structural steel, deforms plastically a lot before fracture, while a brittle material, like glass or cast iron, breaks with little or no plastic deformation. Toughness (the ability to absorb energy before fracture) is often measured with a Charpy impact test, where a pendulum strikes a notched test bar.

ductile: much plastic deformationbrittle: little/none\text{ductile: much plastic deformation} \quad \text{brittle: little/none}the main difference before fracture

Example

The Charpy test measures the impact energy used to break the test bar — low energy suggests brittle fracture, high energy suggests ductile.

Brittleness often increases at low temperature — many steels have a ductile-to-brittle transition temperature.
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Part of Materials Technology: Mechanical properties.