The materials which can be elastically stretched to large values of strain are called elastomers. For example, rubber can be stretched to several times its original length but still it can regain its original length when the applied force is removed.
There is no well-defined plastic region, rubber just breaks when pulled beyond a certain limit. Its Young’s modulus is very small, about 3× 105 Nm-2 at slow strains. Elastic region in such cases is very large, but the material does not obey Hooke’s law.
In our body, the elastic tissue of aorta (the large blood vessel carrying blood from the heart) is an elastomer, for which the stress-strain curve is shown in figure below.
Table: Young’s moduli, ultimate strengths and yield strengths of some materials
| Substance | Density 𝛒 (kgm-3) | Young’s modulus Y (109Nm-2) | Ultimate strength Su (106Nm-2) | Yield strength Sy (106Nm-2) |
| Aluminium | 2710 | 70 | 110 | 95 |
| Copper | 8890 | 110 | 400 | 200 |
| Iron (wrought) | 7800-7900 | 190 | 330 | 170 |
| Steel | 7860 | 200 | 400 | 250 |
| Glass | 2190 | 65 | 50 | – |
| Concrete | 2320 | 30 | 40 | – |
| Wood | 525 | 13 | 50 | – |
| Bone | 1900 | 9 | 170 | – |
| Polystyrene | 1050 | 3 | 48 | – |
The above table shows that metals have large Young’s moduli. Such materials require large forces to produce small changes in length i.e., they are highly elastic. Thus, steel is more elastic than copper, brass and aluminium. That is why steel is preferred for making heavy-duty machines and structural designs.
On the other hand, the materials like wood, bone, concrete and glass have small Young’s moduli.