Mechanical property that measures stiffness of a solid material
Young's modulus is the slope of the linear part of thestress–strain curve for a material under tension or compression.
Young's modulus (or theYoung modulus) is a mechanical property of solid materials that measures the tensile or compressivestiffness when the force is applied lengthwise. It is theelastic modulus fortension or axialcompression. Young's modulus is defined as the quotient of thestress (force per unit area) applied to the object and the resulting axialstrain (a dimensionless quantity that quantifies relative deformation) in thelinear elastic region of the material. As such, Young's modulus is similar to and proportional to the spring constant inHooke's law, but with dimensions of pressure instead of force per distance.
Although Young's modulus is named after the 19th-century British scientistThomas Young, the concept was developed in 1727 byLeonhard Euler. The first experiments that used the concept of Young's modulus in its modern form were performed by the Italian scientistGiordano Riccati in 1782, pre-dating Young's work by 25 years.[1] The term modulus is derived from theLatinroot termmodus, which meansmeasure.
Young's modulus,, quantifies the relationship between tensile or compressivestress (force per unit area) and axialstrain (proportional deformation) in thelinear elastic region of a material:[2]
A solid material undergoeselastic deformation when a small load is applied to it in compression or extension. Elastic deformation is reversible, meaning that the material returns to its original shape after the load is removed.
At near-zero stress and strain, the stress–strain curve islinear, and the relationship between stress and strain is described byHooke's law that states stress is proportional to strain. The coefficient of proportionality is Young's modulus. The higher the modulus, the more stress is needed to create the same amount of strain; an idealizedrigid body would have an infinite Young's modulus. Conversely, a very soft material (such as a fluid) would deform without force, and would have zero Young's modulus.
Material stiffness is a distinct property from the following:
Strength: maximum amount of stress that material can withstand while staying in the elastic (reversible) deformation regime;
Geometric stiffness: a global characteristic of the body that depends on its shape, and not only on the local properties of the material; for instance, anI-beam has a higher bending stiffness than a rod of the same material for a given mass per length;
Hardness: relative resistance of the material's surface to penetration by a harder body;
Toughness: amount of energy that a material can absorb before fracture.
The point E is the elastic limit or the yield point of the material within which the stress is proportional to strain and the material regains its original shape after removal of the external force.
Young's modulus enables the calculation of the change in the dimension of a bar made of anisotropic elastic material under tensile or compressive loads. For instance, it predicts how much a material sample extends under tension or shortens under compression. The Young's modulus directly applies to cases of uniaxial stress; that is, tensile or compressive stress in one direction and no stress in the other directions. Young's modulus is also used in order to predict thedeflection that will occur in astatically determinatebeam when a load is applied at a point in between the beam's supports.
Other elastic calculations usually require the use of one additional elastic property, such as theshear modulus,bulk modulus, andPoisson's ratio. Any two of these parameters are sufficient to fully describe elasticity in an isotropic material. For example, calculating physical properties of cancerous skin tissue, has been measured and found to be a Poisson's ratio of 0.43±0.12 and an average Young's modulus of 52 KPa. Defining the elastic properties of skin may become the first step in turning elasticity into a clinical tool.[3] For homogeneous isotropic materialssimple relations exist between elastic constants that allow calculating them all as long as two are known:
Young's modulus represents the factor of proportionality inHooke's law, which relates the stress and the strain. However, Hooke's law is only valid under the assumption of anelastic andlinear response. Any real material will eventually fail and break when stretched over a very large distance or with a very large force; however, all solid materials exhibit nearly Hookean behavior for small enough strains or stresses. If the range over which Hooke's law is valid is large enough compared to the typical stress that one expects to apply to the material, the material is said to be linear. Otherwise (if the typical stress one would apply is outside the linear range), the material is said to be non-linear.
Steel,carbon fiber andglass among others are usually considered linear materials, while other materials such asrubber andsoils are non-linear. However, this is not an absolute classification: if very small stresses or strains are applied to a non-linear material, the response will be linear, but if very high stress or strain is applied to a linear material, the linear theory will not be enough. For example, as the linear theory impliesreversibility, it would be absurd to use the linear theory to describe the failure of a steel bridge under a high load; although steel is a linear material for most applications, it is not in such a case of catastrophic failure.
Young's modulus is not always the same in all orientations of a material. Most metals and ceramics, along with many other materials, areisotropic, and their mechanical properties are the same in all orientations. However, metals and ceramics can be treated with certain impurities, and metals can be mechanically worked to make their grain structures directional. These materials then becomeanisotropic, and Young's modulus will change depending on the direction of the force vector.[4] Anisotropy can be seen in many composites as well. For example,carbon fiber has a much higher Young's modulus (is much stiffer) when force is loaded parallel to the fibers (along the grain). Other such materials includewood andreinforced concrete. Engineers can use this directional phenomenon to their advantage in creating structures.
Young's modulus of a material can be used to calculate the force it exerts under specific strain.
where is the force exerted by the material when contracted or stretched by.
Hooke's law for a stretched wire can be derived from this formula:
where it comes in saturation
and
Note that the elasticity of coiled springs comes fromshear modulus, not Young's modulus. When a spring is stretched, its wire's length doesn't change, but its shape does. This is why only the shear modulus of elasticity is involved in the stretching of a spring.[citation needed]
Theelastic potential energy stored in a linear elastic material is given by the integral of the Hooke's law:
now by explicating the intensive variables:
This means that the elastic potential energy density (that is, per unit volume) is given by:
or, in simple notation, for a linear elastic material:, since the strain is defined.
In a nonlinear elastic material the Young's modulus is a function of the strain, so the second equivalence no longer holds, and the elastic energy is not aquadratic function of the strain:
Influences of selected glass component additions on Young's modulus of a specific base glass
Young's modulus can vary somewhat due to differences in sample composition and test method. The rate of deformation has the greatest impact on the data collected, especially inpolymers. The values here are approximate and only meant for relative comparison.
^The Rational mechanics of Flexible or Elastic Bodies, 1638–1788: Introduction to Leonhardi Euleri Opera Omnia, vol. X and XI, Seriei Secundae. Orell Fussli.
^Jastrzebski, D. (1959).Nature and Properties of Engineering Materials (Wiley International ed.).John Wiley & Sons, Inc.
^abcdefgLide, David R., ed. (1999). "Commercial Metals and Alloys".CRC Handbook of Chemistry and Physics (80th ed.). Boca Raton, FL:CRC Press.ISBN978-0-84-930480-4.
^Foley, James C.; Abeln, Stephen P.; Stanek, Paul W.; et al. (2010). "An Overview of Current Research and Industrial Practices of be Powder Metallurgy". In Marquis, Fernand D. S. (ed.).Powder Materials: Current Research and Industrial Practices III. Hoboken, NJ:John Wiley & Sons, Inc. p. 263.doi:10.1002/9781118984239.ch32.ISBN978-1-11-898423-9.
^Chou, Hung-Ming; Case, E. D. (November 1988). "Characterization of some mechanical properties of polycrystalline yttrium iron garnet (YIG) by non-destructive methods".Journal of Materials Science Letters.7 (11):1217–1220.doi:10.1007/BF00722341.S2CID135957639 – viaSpringerLink.
^"Yttrium Iron Garnet".Deltronic Crystal Industries, Inc. December 28, 2012. RetrievedMay 7, 2021.
Homogeneous isotropic linear elastic materials have their elastic properties uniquely determined by any two moduli among these; thus, given any two, any other of the elastic moduli can be calculated according to these formulas, provided both for 3D materials (first part of the table) and for 2D materials (second part).
3D formulae
Notes
There are two valid solutions. The plus sign leads to.