Elongation at Break

Elongation at break quantifies ductility: how much tensile strain a material sustains before fracture. It is measured by comparing the final gauge length after specimen halves are fitted together to the original gauge length L0, expressed as a percentage.

Because necking concentrates strain locally, reported elongation is not a material constant—it scales with L0 relative to cross-section (longer proportional gauges average more lightly deformed material outside the neck and show higher A). Standards therefore mandate proportional specimens such as L0 = 5.65√S0 for round bars.

Uniform elongation (strain at onset of necking) better reflects the microstructural capacity for stable plastic flow before localization, but it requires extensometry or digital image correlation rather than post-fracture length measurement alone.

For polymers per ISO 527, thickness and testing speed dominate elongation results; metals and plastics values must never be compared directly without matching standards.

Quality departments use A alongside Rm and Rp0.2 to detect embrittlement from improper heat treatment, contamination, or hydrogen exposure.