Figure 4. Relaxation and creep function of (A) Maxwell, (B) Voigt, and (C) Kelvin model (standard linear solid). Maxwell’s model and Voigt’s model consist of only two elements, which are a linear spring with a spring constant µ and a dashpot with a coefficient of viscosity , whereas Kelvin’s model is composed of a combination of two springs and a dashpot. A linear spring produces an instantaneous deformation proportional to the stress. A dashpot produces a velocity proportional to the stress at any instant.