Considerations in straight fold analysis of thin tubes under axial compression

A straight fold model for the analysis of the tubes under axial compression is reconsidered. Based on experiments, the tube is assumed to fold partly inside and partly outside the mean diameter of tube. The model considers the variation of circumferential strain during the formation of a fold, change in thickness of the tube during the deformation, and the influence of change in the yield strength of material in tension and compression. The first fold ends at the mean diameter and all subsequent folds initiate and end at the mean diameter. Some parameters have been introduced for making the expressions valid for first as well as the subsequent folds. The size of fold, load-compression curves, variation of inside and outside fold lengths and mean crushing load have been computed. All the variables involved in the analysis such as, the size of fold, folding parameter, mean crushing load, and the peak load have been obtained analytically. The model developed has been validated with the experiments.