MSR/ressources/Viscoelasticity.md

Viscous materials, like water, resist both shear flow and strain linearly with
time when a stress is applied. Elastic materials strain when stretched and
immediately return to their original state once the stress is removed.

A viscoelastic material has the following properties:

[Hysteresis](Hysteresis.md) is seen in the stress–strain curve
stress relaxation occurs: step constant strain causes decreasing stress
creep occurs: step constant stress causes increasing strain
its stiffness depends on the strain rate 

A viscoelastic substance dissipates energy when a load is applied, then removed.

In most of the analyses, extensional/compressional strains of the viscoelastic layer are not taken into account since the damping comes mostly from the shear strain.

### Nota Bene
The properties of a viscoelastic layer change with the frequency of excitation .