Kimmoisuus

Kimmoisuus, in physics and engineering, is the property of a material to return to its original shape and size after the removal of deforming stress. When a material deforms within its elastic range, the deformation is reversible; beyond the elastic limit, plastic deformation occurs and the original shape is not fully recovered.

In linear elasticity, stress is proportional to strain (Hooke's law). The proportionality constant is the elastic modulus, such as Young's modulus (E) for uniaxial tension, shear modulus (G), and Poisson's ratio (ν). The area under the stress-strain curve up to the yield point is the material's resilience; the peak elastic deformation is the elastic limit.

Real materials often show viscoelastic behavior, where deformation depends on time and loading rate, and energy is dissipated as heat (hysteresis). Temperature, strain rate, and microstructure influence kimmoisuus.

Measurement: standard tensile tests, dynamic mechanical analysis; note that different loading conditions yield different moduli (e.g., bulk vs. shear).

Applications: design of structures, components, protective gear, biomedical devices rely on sufficient kimmoisuus to absorb shocks and recover shape. Metals tend to have high elastic limits; polymers may be highly elastic at certain temperatures; composites tailor elastic properties.

Biological tissues and skin also display elastic properties, allowing joints and muscles to restore form after movement; however, many tissues are viscoelastic and subject to fatigue.

See also: elasticity, Young's modulus, Hooke's law, viscoelasticity, plasticity.