Numerical analysis of the counterintuitive dynamic behavior of the elastic-plastic fully-clamped beams under impulsive loading

The Counterintuitive behavior, i.e. the permanent deflection of the elastic-plastic beam which rests in opposite direction of the impulsive loading, normally appears and disappears abruptly in certain small ranges of the loading and structural parameters. One of the most important issues in the study of this phenomenon is the determination of the region within which the counter-intuitive response occurs. In the present study, the counterintuitive dynamic behavior of the elastic-plastic fully-clamped beams, formerly used by researchers during an experiment, is numerically simulated. Finite element code ANSYS/LS-DYNA and Galerkin's method are applied to study this phenomenon. Displacement-time history curves of mid-span of the beams are investigated in detail and the region of the occurrence of the counterintuitive behavior is determined as well. Furthermore, using finite element code, the energy diagrams of the beams are also studied. The computations, which were carried out by the two applied numerical methods showed that as long as the initial deflection of the fully-clamped beam lies within a proper range, there is a continuous region for the occurrence of the counterintuitive behavior. The simulation results also indicated that the Galerkin's method demands less computation time than the finite element analysis, and the predicted counterintuitive region by the former has slightly wider band in comparison to the latter. Moreover, the investigations showed that this anomalous behavior will occur for all motions with proper ratio of internal energy to kinetic energy.