Curved fold model analysis for axi-symmetric axial crushing of tubes

In the present paper, a plastic curved fold model with partly inside and partly outside folding and variable straight length has been developed. The variation of circumferential strain with change in the hinge angle during the formation of a fold has been taken into account. The size of fold and proportions of inside and outside fold lengths have been determined by minimizing the average crushing load. The mean, as well as the variation of crushing load, have been computed. Most of the earlier straight as well as curved fold models can be easily derived from the present model. The maximum hinge angle and the final radius of curvature of fold have been determined mathematically. The validation with experiments provides reasonably good agreement. The results are of great help in understanding the phenomenon of actual fold formation.