On the predictability of elasto-plastic and geometrically non-linear oscillations of beams under harmonic excitation

摘要

Vibrations in one plane of beams with fixed ends, vibrating in the geometrically non-linear and elasto-plastic regimes under the influence of harmonic external forces, are studied. A p-version finite element that considers transverse and longitudinal displacements, as well as shear deformation, is employed. The incremental theory of plasticity with isotropic hardening is followed. Numerical methods are employed to solve the differential equations of motion and to carry out integrals where plastic terms exist. The main interest of this work is that “chaotic-like” behavior—in the sense of unpredictable behavior of an apparently deterministic system—is discovered. This behavior is explained by a buckling phenomenon induced by the plastic strains: no longitudinal external force, other than the boundary forces, exists in the cases investigated. Since the plastic strains depend on the past history, the predictions of the long term behavior are also affected by the different predictions on the brief transition phase. An eigenvalue problem is defined to compute eigenvalues that provide an indication that a bifurcation induced by the plastic strains is likely to occur.