DYNAMIC BEHAVIOR OF ELASTIC-PLASTIC FREE-FREE BEAMS SUBJECTED TO IMPULSIVE LOADING

A dynamic analysis of an elastic-plastic free-free beam subjected to i mpact by a projective at the mid-span or to triangularly distributed i mpulsive loading along the span is presented. Attention is focused on the dynamic behaviour of the beam in the early, transient stage of the response. Details of the interactions between the plastic flexural wa ve and the elastic flexural wave reflected from the Free ends are desc ribed, which assist in understanding how the elastic effect modifies t he deformation history of a beam and finally leads to a somewhat diffe rent configuration from that based on a rigid-perfectly plastic model. The partitioning of the energy in the deformed beam is also examined and a rigid-plastic model with a rotational elastic-plastic spring at the midspan of the beam is proposed in order to estimate the proportio ns of elastic energy and plastic dissipation. To verify the theoretica l predictions, a group of high-speed photographs obtained experimental ly for central impact of a free-free beam is presented and compared wi th the numerical results on the instantaneous profiles of the beam. Co pyright (C) 1996 Elsevier Science Ltd.