Specific strength

From Wikipedia, the free encyclopedia

The specific strength is a material strength 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: the length of the material (in km) that could suspend its own weight (with a fixed cross-section). 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. (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.[1] Individual carbon nanotubes have achieved this strength, however only on a microscopic scale to date.)

Specific tensile strength of various materials
Material Strength
(MPa)		 Density
(g/cm³)		 Specific Strength
(kN·m/kg)		 Breaking length
(km)		 source
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 600 2.70 222 22.65 [8]
Steel 2000 7.86 254 25.93 [8]
Titanium 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.

[edit] See also

[edit] Footnotes

  1. ^ 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?.
  2. ^ a b c tensile strength
  3. ^ RoyMech: Copper Alloys
  4. ^ Delft University of technology: Oak wood
  5. ^ Goodfellow: Polypropylene
  6. ^ Goodfellow: Polyamide - Nylon 6
  7. ^ eFunda: Magnesium Alloys
  8. ^ a b c d e f Vectran fiber: specific strength
  9. ^ Specialty Materials, Inc SCS Silicon Carbide Fibers
  10. ^ Network Group for Composites in Construction: Introduction to Fibre Reinforced Polymer Composites
  11. ^ Spectra Fiber - Honeywell Advanced Fibers and Composites

[edit] External links

Languages