{n}>\delta_{n}^{res}$):
%
% $$F_{n}^{e} = K_{n}^{U} \left ( \delta_{n}-\delta_{n}^{res} \right )$$
%
% * *Unloading (after detachment)* ($\dot{\delta_{n}}<0, \delta_{n}\leq\delta_{n}^{res}$):
%
% $$F_{n}^{e} = 0$$
%
% The loading stiffness coefficient $K_{n}^{L}$ can be computed by 3
% different formulas, if its value is not provided:
%
% * *Equivalent energy*:
%
% $$K_{n} = 1.053 \left ( \dot{\delta}_{n}^{0}R_{eff}E_{eff}^{2}\sqrt{m_{eff}} \right )^{2/5}$$
%
% * *Equivalent overlap*:
%
% $$K_{n} = 1.053 \l