The specific strength is a material's strength (force per unit area at failure)

Strength of materials

In materials science, the strength of a material is its ability to withstand an applied stress without failure. The applied stress may be tensile, compressive, or shear. Strength of materials is a subject which deals with loads, deformations and the forces acting on a material. A load applied to a...

 divided by its density

Density

The mass density or density of a material is defined as its mass per unit volume. The symbol most often used for density is ρ . In some cases , density is also defined as its weight per unit volume; although, this quantity is more properly called specific weight...

. It is also known as the strength-to-weight ratio or strength/weight ratio. In fiber or textile applications, tenacity

Tenacity

Tenacity is the customary measure of strength of a fiber or yarn. In the U.S. it is usually defined as the ultimate strength of the fiber divided by the denier....

 is the usual measure of specific strength. The SI unit for specific strength is (N/m²)/(kg/m³) or more commonly N·m/kg.

Another way to describe 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

Weight

In science and engineering, the weight of an object is the force on the object due to gravity. Its magnitude , often denoted by an italic letter W, is the product of the mass m of the object and the magnitude of the local gravitational acceleration g; thus:...

 is the force of gravity at the Earth's surface applying to the entire length of the material, not diminishing with height. This usage is more common with certain specialty fiber or textile applications.

The materials with the highest specific strengths are typically fibers such as carbon fiber

Carbon fiber

Carbon fiber, alternatively graphite fiber, carbon graphite or CF, is a material consisting of fibers about 5–10 μm in diameter and composed mostly of carbon atoms. The carbon atoms are bonded together in crystals that are more or less aligned parallel to the long axis of the fiber...

, glass fiber and various polymers, and these are frequently used to make composite material

Composite material

Composite materials, often shortened to composites or called composition materials, are engineered or naturally occurring materials made from two or more constituent materials with significantly different physical or chemical properties which remain separate and distinct at the macroscopic or...

s (e.g. carbon fiber-epoxy

Carbon fiber-reinforced polymer

Carbon-fiber-reinforced polymer or carbon-fiber-reinforced plastic , is a very strong and light fiber-reinforced polymer which contains carbon fibers. The polymer is most often epoxy, but other polymers, such as polyester, vinyl ester or nylon, are sometimes used...

). These materials and others such as titanium

Titanium

Titanium is a chemical element with the symbol Ti and atomic number 22. It has a low density and is a strong, lustrous, corrosion-resistant transition metal with a silver color....

, aluminium

Aluminium

Aluminium or aluminum is a silvery white member of the boron group of chemical elements. It has the symbol Al, and its atomic number is 13. It is not soluble in water under normal circumstances....

, magnesium

Magnesium

Magnesium is a chemical element with the symbol Mg, atomic number 12, and common oxidation number +2. It is an alkaline earth metal and the eighth most abundant element in the Earth's crust and ninth in the known universe as a whole...

 and high strength steel alloys are widely used in aerospace

Aerospace

Aerospace comprises the atmosphere of Earth and surrounding space. Typically the term is used to refer to the industry that researches, designs, manufactures, operates, and maintains vehicles moving through air and space...

 and other applications where weight savings are worth the higher material cost.

Note that strength and stiffness are distinct. Both are important in design of efficient and safe structures.

Examples

Specific tensile strength of various materials

Material Material Material is anything made of matter, constituted of one or more substances. Wood, cement, hydrogen, air and water are all examples of materials. Sometimes the term "material" is used more narrowly to refer to substances or components with certain physical properties that are used as inputs to...	Strength (MPa)	Density (g/cm³ Density The mass density or density of a material is defined as its mass per unit volume. The symbol most often used for density is ρ . In some cases , density is also defined as its weight per unit volume; although, this quantity is more properly called specific weight... )	Specific Strength (kN·m/kg)	Breaking length (km)	source
Scifer steel wire	5,500	7.87	706	71.2
Bainite Bainite Bainite is an acicular microstructure that forms in steels at temperatures from approximately 250-550°C . First described by E. S. Davenport and Edgar Bain, it is one of the decomposition products that may form when austenite is cooled past a critical temperature of 727 °C...	2,500	7.87	321	32.4
1 μm iron Iron Iron is a chemical element with the symbol Fe and atomic number 26. It is a metal in the first transition series. It is the most common element forming the planet Earth as a whole, forming much of Earth's outer and inner core. It is the fourth most common element in the Earth's crust...  whiskers Whisker (metallurgy) Metal whiskering is a crystalline metallurgical phenomenon involving the spontaneous growth of tiny, filiform hairs from a metallic surface. The effect is primarily seen on elemental metals but also occurs with alloys....	14,000	7.87	1800	183
Concrete Concrete Concrete is a composite construction material, composed of cement and other cementitious materials such as fly ash and slag cement, aggregate , water and chemical admixtures.The word concrete comes from the Latin word...	10	2.30	4.35	0.44
Rubber Rubber Natural rubber, also called India rubber or caoutchouc, is an elastomer that was originally derived from latex, a milky colloid produced by some plants. The plants would be ‘tapped’, that is, an incision made into the bark of the tree and the sticky, milk colored latex sap collected and refined...	15	0.92	16.3	1.66
Brass Brass Brass is an alloy of copper and zinc; the proportions of zinc and copper can be varied to create a range of brasses with varying properties.In comparison, bronze is principally an alloy of copper and tin...	580	8.55	67.8	6.91
Oak Oak An oak is a tree or shrub in the genus Quercus , of which about 600 species exist. "Oak" may also appear in the names of species in related genera, notably Lithocarpus...	60	0.69	86.95	8.86
Balsa Balsa Ochroma pyramidale, commonly known as the balsa tree , is a species of flowering plant in the mallow family, Malvaceae. It is a large, fast-growing tree that can grow up to tall. It is the source of balsa wood, a very lightweight material with many uses...  (axial load)	73	0.14	521	53.2
Polypropylene Polypropylene Polypropylene , also known as polypropene, is a thermoplastic polymer used in a wide variety of applications including packaging, textiles , stationery, plastic parts and reusable containers of various types, laboratory equipment, loudspeakers, automotive components, and polymer banknotes...	80	0.90	88.88	9.06
Nylon Nylon Nylon is a generic designation for a family of synthetic polymers known generically as polyamides, first produced on February 28, 1935, by Wallace Carothers at DuPont's research facility at the DuPont Experimental Station...	78	1.13	69.0	7.04
Magnesium Magnesium Magnesium is a chemical element with the symbol Mg, atomic number 12, and common oxidation number +2. It is an alkaline earth metal and the eighth most abundant element in the Earth's crust and ninth in the known universe as a whole...	275	1.74	158	16.11
Aluminium alloy Aluminium alloy Aluminium alloys are alloys in which aluminium is the predominant metal. The typical alloying elements are copper, magnesium, manganese, silicon and zinc. There are two principal classifications, namely casting alloys and wrought alloys, both of which are further subdivided into the categories...	600	2.70	222	22.65
Steel alloy	2,000	7.86	254	25.93
Titanium alloy Titanium alloy Titanium alloys are metallic materials which contain a mixture of titanium and other chemical elements. Such alloys have very high tensile strength and toughness , light weight, extraordinary corrosion resistance, and ability to withstand extreme temperatures...	1,300	4.51	288	29.38
carbon-epoxy composite Carbon fiber-reinforced polymer Carbon-fiber-reinforced polymer or carbon-fiber-reinforced plastic , is a very strong and light fiber-reinforced polymer which contains carbon fibers. The polymer is most often epoxy, but other polymers, such as polyester, vinyl ester or nylon, are sometimes used...	1240	1.58	785	80
Silicon carbide Silicon carbide Silicon carbide , also known as carborundum, is a compound of silicon and carbon with chemical formula SiC. It occurs in nature as the extremely rare mineral moissanite. Silicon carbide powder has been mass-produced since 1893 for use as an abrasive...	3,440	3.16	1,088	110
Glass fiber	3,400	2.60	1,307	133
Basalt fiber Basalt fiber Basalt fiber or fibre is a material made from extremely fine fibers of basalt, which is composed of the minerals plagioclase, pyroxene, and olivine. It is similar to carbon fiber and fiberglass, having better physicomechanical properties than fiberglass, but being significantly cheaper than...	4,840	2.70	1,790	182.7
Vectran Vectran Vectran is a manufactured fibre, spun from a liquid crystal polymer created by Celanese Acetate LLC and now manufactured by Kuraray Co., Ltd. Chemically it is an aromatic polyester produced by the polycondensation of 4-hydroxybenzoic acid and 6-hydroxynaphthalene-2-carboxylic acid.- Properties...	2,900	1.40	2,071	211
Carbon fiber Carbon fiber Carbon fiber, alternatively graphite fiber, carbon graphite or CF, is a material consisting of fibers about 5–10 μm in diameter and composed mostly of carbon atoms. The carbon atoms are bonded together in crystals that are more or less aligned parallel to the long axis of the fiber...  (AS4)	4,300	1.75	2,457	250
Kevlar Kevlar Kevlar is the registered trademark for a para-aramid synthetic fiber, related to other aramids such as Nomex and Technora. Developed at DuPont in 1965, this high strength material was first commercially used in the early 1970s as a replacement for steel in racing tires...	3,620	1.44	2,514	256
Spectra fiber Ultra high molecular weight polyethylene Ultra-high-molecular-weight polyethylene , also known as high-modulus polyethylene or high-performance polyethylene , is a subset of the thermoplastic polyethylene. It has extremely long chains, with molecular weight numbering in the millions, usually between 2 and 6 million...	3,510	0.97	3,619	369
Zylon Zylon Zylon is a trademarked name for a range of thermoset liquid crystalline polyoxazole...	5,800	1.54	3,766	384
Colossal carbon tube Colossal carbon tube Colossal carbon tubes are a tubular form of carbon. In contrast to the carbon nanotubes , colossal carbon tubes have much larger diameters ranging between 40 and 100 μm...	6,900	.116	59,483	6,066
Carbon nanotube Carbon nanotube Carbon nanotubes are allotropes of carbon with a cylindrical nanostructure. Nanotubes have been constructed with length-to-diameter ratio of up to 132,000,000:1, significantly larger than for any other material...  (see note below)	62,000	.037-1.34	46,268-N/A	4,716-N/A
spider silk Spider silk Spider silk is a protein fiber spun by spiders. Spiders use their silk to make webs or other structures, which function as nets to catch other animals, or as nests or cocoons for protection for their offspring...	1,400	1.31	1,069	109

The data of this table is from best cases, and has been established for giving a rough figure.

• Note: Multiwalled carbon nanotubes have the highest tensile strength of any material yet measured, with labs producing them at a tensile strength of 63 GPa, still well below their theoretical limit of 300 GPa. The first nanotube ropes (20 mm long) whose tensile strength was published (in 2000) had a strength of 3.6 GPa, still well below their theoretical limit. The density is different depending on the manufacturing method, and the lowest value is 0.037 or 0.55(solid).

Relation to velocity

Since N·m/kg (the unit of specific strength) expands to (kg·m/s²)·m/kg or (m/s)², a specific strength can also be understood as the square of a speed, hence represented by it square root, a speed.
Further, the structural analysis for whether a particular material is strong enough for some purpose can sometimes be expressed in terms of comparing this speed to the speed of a relevant part of the structure.
For example, a spinning cylindrical shell (as in an idealized flywheel or an idealized cylinder space ship) is only feasible if built of a material whose square root of specific strength is at least the speed at which the spinning shell moves.

External links

• Specific stiffness - Specific strength chart, University of Cambridge, Department of Engineering