On the mechanics of the global bending collapse of circular tubes under dynamic axial load—Dynamic buckling transition

The common features of the deformation of long circular tubes made from different aluminium alloys and subjected to various axial impact loadings are established and used to develop simplified structural models for global bending collapse and progressive buckling. A two-phase deformation model for axially loaded structural elements is proposed, which retains the characteristic features of the initial compression and subsequent bending/buckling phases. It is shown that the velocity histories in the two principal collapse modes of long tubes play an important role for the formation of the particular deformation pattern. The simplified structural models are verified with some numerical finite-element results and their behaviour is shown to be adequate. A parametric analysis of the models is further performed in order to divulge the major factors, which influence the dynamic buckling transition. The analysis reveals that there is a specific impact velocity associated with the particular geometric and material properties of a circular tube, which causes a counter-intuitive response. An empirical criterion for the lower and upper bounds to the critical impact velocity for a buckling transition is proposed. Further, the upper bound to the impact velocity is used to formulate a criterion for the dynamic buckling transition.