Engineering Reference

Elongation

The strain at fracture, expressed as a percentage of the original length.

Definition

Elongation is the standard measure of ductility. High elongation means the material deforms before it breaks; low elongation means it fails suddenly.

It is a strong indicator of machinability and of toughness, and it falls as strength rises — the two trade off directly. A hardened tool steel at 1,930 MPa tensile has 2% elongation; low-carbon steel at 440 MPa has 25%.

Common misuse

Reading elongation as a measure of toughness. A high-strength material with low elongation can still be tough, though usually at low strength levels.

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