Ductility is a mechanical property that describes a material’s ability to undergo significant plastic deformation before fracture. Ductile materials can stretch, bend, or elongate without breaking, making them essential for applications requiring formability, toughness, and energy absorption.
Measures of Ductility
Ductility is typically quantified using two common tensile test measurements:
- Elongation (%) – The percentage increase in a material’s gauge length before fracture, calculated as:
elongation (%) = (final length – original length) / original length × 100- Higher elongation values indicate greater ductility.
- Common ductile materials like mild steel or copper exhibit elongation values between 20-50%, while brittle materials like ceramics have near-zero elongation.
- Reduction of Area (%) – The percentage decrease in the cross-sectional area at the fracture point, calculated as:
reduction of area (%) = (original area – final area) / original area × 100- This measure accounts for necking, a key characteristic of ductile fracture.
Ductile Fracture Characteristics
- High plastic deformation before failure – Ductile materials stretch significantly before breaking.
- Necking occurs – A localized reduction in cross-sectional area precedes fracture.
- Cup-and-cone fracture – The material fails with a rough, fibrous interior and a slanted shear lip, typical in metals like steel and aluminum.
- Absorbs more energy before failure – Ductile materials can withstand high impact loads, making them useful in structural applications.
Ductility vs. Malleability
- Ductility refers to the ability to undergo tensile deformation (stretching into a wire).
- Malleability refers to the ability to undergo compressive deformation (hammering into a thin sheet).
- While related, materials like gold and lead are highly malleable but not necessarily highly ductile, whereas copper and aluminum exhibit both high ductility and malleability.