Dynamic shakedown and degradation of elastic reactions in laterally impacted steel tubes

This paper reports some interesting observations on the response of laterally impacted steel tubes which in some respects have been considered to undergo an elastic shakedown. In an experimental study on the behaviour of axially compressed tubes under lateral impacts, it has been noticed that, after full development of plastic deformations in the impacted bodies, the structural system ceases to exhibit additional plastic responses. The impacted tubes then exhibit an elastic response. It has also been observed that the amplitude of the elastic excitations in the specimens becomes more restricted as the load configuration moves close to a dynamic failure state. With load conditions quite close to the dynamic failure limit, almost no elastic excitation has been perceived from the impacted specimens. Additional numerical and analytical investigations have been carried out on impacted tubes, frames and non-linear Single Degree of Freedom (SDOF) systems and similar results have been obtained. Despite the non-cyclic nature of the external loads in these impact cases, a phenomenon similar to elastic shakedown has been observed.