Viskoosiset

Viskoosiset are materials that exhibit both viscous flow and elastic deformation when subjected to stress, i.e., viscoelastic materials. They are not purely viscous liquids nor purely elastic solids; their response depends on time and the rate of loading. At short times or high frequencies they behave more elastically, while at long times or low frequencies viscous flow can dominate.

Key properties of viscoelastic materials include creep under constant stress, stress relaxation under constant strain, and hysteresis under cyclic loading. They are commonly described using rheological models such as the Maxwell model, the Kelvin–Voigt model, or the Standard Linear Solid model. In oscillatory tests, the material is characterized by the storage modulus G' and the loss modulus G'', and by the loss tangent tan δ, which indicates the balance between elastic and viscous behavior.

Characterization is typically performed with rheometry or dynamic mechanical analysis. Experiments measure G', G'', relaxation times, and viscosity as functions of temperature and frequency, as well as composition. Temperature changes can shift viscoelastic behavior according to established temperature–dependence relations.

Viskoosiset appear in a wide range of materials, including polymers, gels, asphalt, foams, food products, lubricants, and biological tissues. They are exploited in damping and vibration isolation, coatings, tissue engineering, and soft robotics, among other applications. Understanding their time- and rate-dependent responses is essential for design and performance prediction in engineering and materials science.