add properties 'eps_c_interpolated_smoothed' and
'sig_c_interpolated_smoothed' using 'np.smooth' for 'eps_c' AND 'sig_c'
values
plot sigc-epsc or sigtex-epstex for comparison between 'TT-SH2-6cm' and
'TT-SH3-4cm'; evaluate experimental stiffness in tensile test;
change order in plot; minor change;