VISCOELASTICITY

The simplest model for viscoelastic materials is Kelvin-Voigt model which consists of a spring and a dashpot. These two elements are shown below right. 

The behavior of the system is dependent on the stiffness of the spring and damping coefficient of the dashpot. Another simple model presented by Maxwell is shown below left.

In linear viscoelasticity, the characteristic of the material is interpreted by creep and relaxation behaviors. Each of the abovementioned models complies with one of the behaviors. Kelvin-Voigt model demonstrates creep and fails to show relaxation behavior while Maxwell model demonstrates relaxation and fails to show creep behavior.

Thus a nonlinear approach is required to analyze a viscoelastic material. Since the material should be subjected to large deformation to show their time dependent behavior, a hyperelastic material have to be included in its model in addition to a viscous media which could be a fluid or a semi solid material. In another word, a viscoelastic material consists of a hyperealstic element, which is time independent and absorbs the energy to deform and releases it by removing the force, and a dissipating media, which absorbs energy by internal friction and wastes it through heat loss or increase of internal energy.

In order to better understand the behavior of viscous media, fluid mechanics analysis in three dimensional is essential. For more information refer to “Method and system for real time characterization of soft materials and biological tissues based on nonlinear properties, Patent No. 10126219”.