Figure 2.

Basis functions ${\phi }_i\left(t\right)$ (17), $i=1,\dots ,5$, of the relaxation modulus model ${\overline{G}}_N\left(t\right)$ (16) for time sampling instants: (a) $t_i=10, 30, 50, 70, 90 \mathrm{s}$ and (b) $t_i=0.1, 0.5, 1, 1.5, 2 \mathrm{s}$.