Specific strength
The specific strength is a material's strength per unit area divided by its density. It is expressed in newton metres per kilogram, and is used for tensile strength as for compressive strength. It is sometimes known as the strength-to-weight ratio. Materials with very high specific strengths are widely used in aerospace applications where weight savings are more important than material costs. Materials such a titanium alloys and carbon fiber are widely used in these applications for this reason.
Another way to quote specific strength is breaking length, also known as self support length: the maximum length of a vertical column of the material (assuming a fixed cross-section) that could suspend its own weight when supported only at the top. For this measurement, the definition of weight is the force of gravity at the earth's surface applying to the entire length of the material, not diminishing with height.
Examples
| Material | Strength (MPa) |
Density (g/cm³) |
Specific Strength (kN·m/kg) |
Breaking length (km) |
source |
|---|---|---|---|---|---|
| Scifer steel wire | 5,500 | ? | ? | ? | [1] |
| Bainite | 2,500 | ? | ? | ? | [1] |
| 1 μm iron whiskers | 14,000 | 7.87 | ? | ? | [1] |
| Concrete | 10 | 2.30 | 4.34 | 0.44 | [2] |
| Rubber | 15 | 0.92 | 16.3 | 1.66 | [2] |
| Brass | 580 | 8.55 | 67.8 | 6.91 | [3] |
| Oak | 60 | 0.69 | 86.95 | 8.86 | [4] |
| Polypropylene | 80 | 0.90 | 88.88 | 9.06 | [5] |
| Nylon | 78 | 1.13 | 69.0 | 7.04 | [6] |
| Magnesium | 275 | 1.74 | 158 | 16.11 | [7] |
| Aluminium (alloy) | 600 | 2.70 | 222 | 22.65 | [8] |
| Steel | 2000 | 7.86 | 254 | 25.93 | [8] |
| Titanium (alloy) | 1300 | 4.51 | 288 | 29.38 | [8] |
| Silicon carbide | 3440 | 3.16 | 1088 | 110 | [9] |
| Glass fiber | 3400 | 2.60 | 1307 | 133 | [8] |
| Vectran | 2900 | 1.40 | 2071 | 211 | [8] |
| Graphite | 4300 | 1.75 | 2457 | 250 | [8] |
| Kevlar | 3620 | 1.44 | 2514 | 256 | [10] |
| Spectra fiber | 3510 | 0.97 | 3619 | 369 | [11] |
| Carbon nanotube | 62000 | 1.34 | 46268 | 4716 | [2] |
The data of this table is from best cases, and has been established for giving a rough figure.
Specific strength for construction of a Space elevator
 | It has been suggested that Space_elevator_safety#Cable_strength be merged into this article. (Discuss) Proposed since January 2009. |
| It has been suggested that Space_elevator#Cable be merged into this article. (Discuss) Proposed since January 2009. |
A space elevator would need a material capable of sustaining 4,960 kilometers of its own weight at sea level to reach a geostationary altitude of 36,000 km without tapering.[12] Individual carbon nanotubes have achieved this strength, however only on a microscopic scale to date. A lower specific strength can be usable however if the cable tapered down towards the Earth's surface and past the geostationary altitude, however the mass and costs of material would be prohibitive for low specific strengths such as provided by Kevlar.
See also
Footnotes
- ^ a b c 52nd Hatfield Memorial Lecture: "Large Chunks of Very Strong Steel" by H. K. D. H. Bhadeshia 2005
- ^ a b c tensile strength
- ^ RoyMech: Copper Alloys
- ^ Delft University of technology: Oak wood
- ^ Goodfellow: Polypropylene
- ^ Goodfellow: Polyamide - Nylon 6
- ^ eFunda: Magnesium Alloys
- ^ a b c d e f Vectran fiber: specific strength
- ^ Specialty Materials, Inc SCS Silicon Carbide Fibers
- ^ Network Group for Composites in Construction: Introduction to Fibre Reinforced Polymer Composites
- ^ Spectra Fiber - Honeywell Advanced Fibers and Composites
- ^ This 4,960 km "escape length" (calculated by Arthur C. Clarke in 1979) is much shorter than the actual distance spanned because centrifugal forces increase (and gravity decreases) dramatically with height: Clarke, A.C. (1979). "The space elevator: 'thought experiment', or key to the universe?".
External links
Specific stiffness - Specific strength chart, University of Cambridge, Department of EngineeringCluebot sucks. It won't detect this kind of vandalism. Fuck you all. FEF