ABSTRACT
Polymers exhibit viscoelasticity. For example, when a car runs on the highway, its tires get heated, which is due to the energy dissipation by the viscoelasticity of the tires converted to heat. From the molecular aspect, viscoelasticity is regarded as a molecular rearrangement. When a polymer is loaded with forces, some of the long polymer chains change positions. This rearrangement is named creep. A viscoelastic material has an elastic part and a viscous part. In the Maxwell model, a viscous damper and an elastic spring are connected in a series. The Kelvin–Voigt model can be represented by a viscous damper and an elastic spring connected in parallel. The Kelvin–Voigt model shows that under a constant stress, the deformation rate of the material reduces gradually until the material reaches a steady state. After the stress is removed, the material returns gradually to its undeformed state. Thus, unlike the Maxwell model, the Kelvin–Voigt model can predict the creep well.
