How is the toughness of a metal defined?

metal toughness
CVN specimen before and after impact testing. Photo &copy

Definition of Toughness:

Toughness is a measure of how much energy a metal can absorb before rupturing.

While not technically a toughness test, material toughness is most commonly measured by an impact test known as a Charpy V-notch test (CVN).

In standard CVN testing, a 10 mm x 10 mm square bar has a small "V"-shaped notch machined on one face. A hammer swung from a large pendulum will strike the side opposite the notch.

If the metal does not break, the level of energy is increased until the metal breaks. Once the Charpy impact machine breaks the bar, the amount of energy required to cause the rupture is recorded, giving a measurement of toughness in pound-feet.

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