---
term: "Elongation at Break"
category: "material-testing"
shortDefinition: "Permanent tensile strain after fracture, usually reported as percentage elongation A using original gauge length L0; depends strongly on L0/specimen proportionality."
formula: "A = ((Lu − L0) / L0) × 100%"
relatedStandards: ["ISO 6892-1","ISO 527-1","ASTM E8"]
url: "https://vectorbtc.com.tr/resources/glossary/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.