Tube Inversion: A Process for Obtaining Gross Expansions in the Diameter of Thin-Wall Tubes

Circumferential strains much in excess of the instability strains in internally pressurized tubes may be obtained by axially compressing the tube over a radiused die. As the tube walls slide over the curved parts of the die, simultaneous bending, stretching and unbending takes place. The resulting tube is of larger diameter, same wall thickness, and shorter in length. The phenomena associated with the inversion process of strain-hardening tubes are described and load-displacement curves are presented. Experimental results to establish the optimum radial expansion are given and conditions for buckling and tearing are identified. A simple theoretical analysis of the process which allows for strain-hardening is given.