On the axisymmetric progressive crushing of circular tubes under axial compression

Moderately thick circular tubes under compression crush progressively by axisymmetric folding. The paper presents a combined experimental analytical study of the onset of collapse, its localization and the subsequent progressive folding. Results from four displacement controlled crushing experiments are presented on tubes of various radius-to-thickness ratios made of different metal alloys. The experimental results include the crushing response, careful measurements of the geometric characteristics of the folds and the mechanical properties of the alloys. A finite element model of the crushing process has been developed and results from simulations are directly compared with the experiments. The model is found to reproduce the crushing response to a significant degree of accuracy. The mean crushing load is essentially the same as in the experiments; the calculated wavelength of the folds are within a few percent from measured values as are other geometric variables considered. Thus, the crushing energy per unit length of tube is predicted to a very good accuracy. In addition, the model was used to demonstrate that changes in the loading cycles which take place as the number of folds increases, are due to small differences between the inner and outer folds which in turn affect the self contact of the fold walls. Three simpler models taken from the literature in which steady-state folding is modeled by kinematically admissible collapse mechanisms are critically reviewed by comparing predictions of key variables to measured values.