CONSIDERATION OF INTERNAL FOLDING AND NONSYMMETRICAL FOLD FORMATION IN AXISYMMETRICAL AXIAL COLLAPSE OF ROUND TUBES

Experiments were performed on short aluminium and steel round tubes to study the nature of their axisymmetric folding and the extent by whic h a tube folds internally. The mean diameter to thickness (D/t) ratios of these tubes varied from 12 to 30. Typical histories of specimen de formation and load-compression curves obtained in these tests are pres ented. It is seen that the fold formation is not symmetric about its m id plane and the extent of internal folding in each tube is dependent on its D/t ratio. Based on the experimental observations and consideri ng the formation of plastic hinges in a perfectly plastic material, a simple analysis is first presented by assuming the fold formation to b e symmetric. The effect of the non-symmetric fold formation is then co nsidered. Various features like the fold length, the mean collapse loa d and the load-compression curve are derived from the analysis and the computer results are compared with the experiments. (C) 1997 Elsevier Science Ltd.