Ductility
Ductility is a mechanical property that describes a material's ability to undergo significant plastic (permanent) deformation before fracture under tensile stress. It is quantified as the percentage elongation or percentage reduction in area measured in a tensile test. Ductile materials such as mild steel and copper provide engineers with warning before failure (through visible deformation and "necking"), making them safer choices for structures subjected to overload or impact loading.
Key Formula
% Elongation = ((Lf - L0) / L0) × 100%
LaTeX: \%\,\text{Elongation} = \frac{L_f - L_0}{L_0} \times 100\%
| Symbol | Meaning | Unit |
|---|---|---|
| Lf | Final gauge length after fracture | mm |
| L₀ | Original gauge length | mm |
Worked Example
Problem
A tensile specimen of copper with an original gauge length of 50 mm fractures at a final length of 68 mm. Calculate the percentage elongation.
Solution
Step 1: Identify values. Lf = 68 mm, L₀ = 50 mm Step 2: Apply percentage elongation formula. % Elongation = ((68 − 50) / 50) × 100% % Elongation = (18 / 50) × 100% % Elongation = 36%
Answer
% Elongation = 36% (copper is highly ductile)
Ductility Comparison of Engineering Materials (% Elongation at Fracture)
| Material | % Elongation | Classification | Engineering Implication |
|---|---|---|---|
| Low-carbon steel (A36) | 20–30 | Highly ductile | Large plastic warning before failure |
| Aluminium alloy 6061-T6 | 12–17 | Moderately ductile | Suitable for forming |
| Copper (annealed) | 30–40 | Highly ductile | Excellent for cold working |
| Cast iron (grey) | < 1 | Brittle | Fails suddenly without warning |
| High-strength steel | 5–10 | Low ductility | Limited cold formability |
| Titanium alloy Ti-6Al-4V | 10–14 | Moderately ductile | Aerospace applications |
Interactive Tools
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Related Terms
Brittleness
Brittleness is a material property characterised by the tendency to fracture suddenly under stress with little or no prior plastic (permanent) deformation, typically showing less than 2–5% elongation at fracture in a tensile test. Brittle materials store elastic energy and release it catastrophically at fracture, giving virtually no warning of impending failure. Materials such as cast iron, glass, ceramics, and concrete exhibit brittle behaviour, and engineering designs using them must account for the absence of ductile redistribution of stress.
Engineering Strain
Engineering strain is the ratio of the change in length of a specimen to its original length when subjected to axial loading, expressed as a dimensionless number or percentage. It quantifies how much a material deforms relative to its initial size and is the conventional measure plotted alongside engineering stress to produce stress-strain curves. Engineering strain assumes uniform deformation and uses the original gauge length, making it straightforward to measure experimentally.
Material Hardness
Material hardness is the resistance of a material's surface to permanent plastic deformation, typically measured by pressing a standardised indenter into the surface under a controlled load and measuring the size or depth of the resulting indentation. It is a surface property that correlates with wear resistance, machinability, and (for steels) approximate tensile strength. Common hardness scales include Vickers (HV), Brinell (HB), and Rockwell (HR), each suited to different materials and applications.
From Latin "ductilis" (that may be led or drawn), derived from "ducere" (to lead or draw). The term entered scientific usage in the 17th century to describe metals that could be drawn into wire — gold being the classic example. It was formalised as a quantitative mechanical property in the 19th century through tensile testing.