Rubber exhibits the highest Poisson's ratio among commonly listed materials, approaching the theoretical maximum for incompressible substances.
Understanding Poisson's Ratio
Poisson's ratio (μ) is a fundamental material property that quantifies the deformation of a material when subjected to axial strain. Specifically, it is defined as the negative ratio of transverse strain to axial strain.
- Positive Poisson's Ratio: When a material is stretched (positive axial strain), it tends to become thinner in the perpendicular direction (negative transverse strain), resulting in a positive Poisson's ratio. Most conventional materials have a positive Poisson's ratio between 0 and 0.5.
- Zero Poisson's Ratio: If a material's width remains unchanged when stretched, its Poisson's ratio is zero (e.g., cork).
- Negative Poisson's Ratio (Auxetic Materials): Some rare, specially engineered materials, known as auxetic materials, expand laterally when stretched, resulting in a negative Poisson's ratio.
- Maximum Poisson's Ratio: For an isotropic elastic material, the theoretical maximum Poisson's ratio is 0.5. This value indicates that the material is perfectly incompressible; its volume remains constant under deformation.
Materials and Their Poisson's Ratios
Based on common material properties, here's a comparison of Poisson's ratios for various substances:
| Material | Poisson's Ratio (μ) |
|---|---|
| Rubber | 0.4999 |
| Gold | 0.43 |
| Bronze | 0.34 |
| Copper | 0.33 |
| Steel | 0.27 - 0.30 |
| Aluminum | 0.33 |
| Cork | ≈ 0.0 |
As evident from the table, rubber stands out with a Poisson's ratio extremely close to 0.5. This high value explains why rubber materials are so effective in applications requiring significant deformation without significant volume change, such as seals, O-rings, and shock absorbers. Its near-incompressibility under elastic deformation is a key characteristic.
