A large number of rheological models can be covered by the existence and un
iqueness theory for maximal monotone operators. Numerical simulations displ
ay hysteresis cycles when the forcing is periodic. A given shape of hystere
sis cycle in an appropriate class of polygonal cycles can always be realize
d by adjusting the physical parameters of the rheological model. (C) 2000 E
ditions scientifiques at medicales Elsevier SAS.