viskoelastik

Viscoelasticity, often referred to as viskoelastik in some languages, describes materials that exhibit both viscous flow and elastic deformation. These materials respond to stress with a combination of immediate elastic strain and time-dependent viscous flow, making their deformation history-dependent. The behavior is temperature- and rate-dependent, and the relative contribution of the viscous and elastic components can vary with time.

In linear viscoelasticity, constitutive relations relate stress and strain through a relaxation modulus G(t) or a creep compliance J(t). Equivalently, the response can be described as a convolution of the strain history with G(t) or of the stress history with J(t). Common mechanical representations include the Maxwell model (spring and dashpot in series), the Kelvin-Voigt model (spring and dashpot in parallel), and the Standard Linear Solid (a spring-dashpot-spring arrangement). Real materials often exhibit a spectrum of relaxation times and may require more sophisticated or fractional models to capture complex behavior.

Phenomena and testing: Creep under constant load and stress relaxation under constant strain are hallmark viscoelastic effects. Under cyclic loading, energy is dissipated, producing hysteresis. Dynamic mechanical analysis and rheometry measure storage modulus G' (elastic energy storage) and loss modulus G'' (energy dissipation); the ratio tan δ = G''/G' characterizes damping. The response depends on frequency and temperature, and time-temperature superposition allows data to be shifted to predict behavior across conditions.

Applications include polymers and polymer composites, gels and biological tissues, asphalt and soils, damping and vibration control, adhesives, and medical devices. Molecular or microstructural factors—such as chain mobility, crosslinks, entanglements, and solvent content—determine viscoelastic properties.