Finite element study of stress and strain state during hot tube necking process

Tube necking is a common process used for manufacturing pressure vessels, for example, compressed natural gas capsules, categorized under general spinning processes. An experimentally validated finite element model suited to the process is incorporated to study the deformation, and state of strain and stress in the contact zone. The in situ variation of stress and strain is illustrated via colored contour plots, and Cartesian and polar diagrams. It is shown that in some areas, there are similarities and differences between flow forming and tube necking; for example, like flow forming, the equivalent plastic strain decreases from the inner and outer layers toward the middle layer, and unlike flow forming, the axial strain at the outer layer is negative all around the tube while at the inner layer, axial strain possesses a maximum positive value at contact position. The state of stress and plastic strain in regions around the contact zone is shown at an instant of process duration, which is not quite similar to postprocess stress and strain distribution.