The objective of this project is to study the degradation and buckling of metal beams subjected to cyclic bending into the plastic range of the material. The cross-sectional shapes which will be considered are: tubular (square and circular), I, wide- flange and T. Previous work on cyclic bending of circular tubes has indicated that the interaction of material and geometric nonlinearities causes accumulation of deformation in the beam cross-section. This leads to degradation of the structural response. Persistent cycling results in buckling and catastrophic collapse of the structure. Evidence exists that similar degradation and failure can occur in the other geometries mentioned. The problems will be studied through a combination of experiment and analysis. The cyclic bending experiments will be conducted in a special purpose bending apparatus. In these experiments the curvature, bending moment and deformation of the cross-section will be monitored. The analysis will be conducted using special purpose numerical tools which include appropriate nonlinear kinematics and state-of-the-art cyclic plasticity models. The models which yield good predictions in the cases studied will be identified and used to help establish the cyclic degradation and the onset of failure of the structures.
