Constrained FSM Model
The constrained FSM model is a reduction of the regular FSM model, therefore it handles the plate elements as plates, i. e. together with the Poisson effect. However, the transverse strains as well as transverse flexure is completely eliminated, consequently a constrained FSM model behaves more rigidly than a regular FSM model. At the same time it differs from beam models, too, as already demonstrated via Eqs. (14) and (16), because it is not possible to simultaneously enforce zero transverse strains (which is a requirement from the basic GBT assumptions) and zero transverse stresses (which is the assumption of beam models). Since the constrained FSM satisfies the zero transverse strain condition, it gives larger rigidity, consequently higher critical forces than the beam models, as presented in Figure 7a.