Change in thickness in straight fold models for axial crushing of thin-walled frusta and tubes

The axisymmetric axial crushing of thin metallic frusta has been modeled by straight fold model with partly inside and partly outside folding. The first fold of the model 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 all the folds. The variation of circumferential strain during the formation of a fold has been taken into account for the purpose of computing the variation of crushing load. Change in the thickness of frusta during the formation of fold has been incorporated for explaining the reasons of the inside portion of fold being smaller than the outside. Different values of yield stress of the material in compression and tension have been taken in the analysis. Existing total outside fold model of frusta and partly inside and partly outside fold model of tube can be derived from the present model. The lengths of inside and outside portion of fold in tubes are derived. The results have been compared with experiments and good agreement has been observed.