Figure 15.

Schematic model of a viscoelastic material. The total stress $\mathbf{S}$ decomposes according to Equation (45). The spring in the first row represents the elastic stress, while the Maxwell elements contribute the non-equilibrium stresses ${\mathbf{Q}}_n$,$n=1,...,m$. The mechanical properties of the springs and dashpots of Maxwell elements are defined by the free-energy parameters θ and the relaxation times τ, respectively.