Stress Analysis of Tubes During Die Expansion Process

In practical applications, the stress status of expanded tubes is a critical parameter to control leakage and stress corrosion cracking. Therefore, it is important to study and analyze the stress distribution generated from tube expansion. Unfortunately, there are only a few theoretical approaches available for estimating the stress distribution of formed tubes, especially for cases where the expansion is achieved with spherical and oval dies. In this study, 3/8 stainless steel and copper tubes were expanded with an oval die in a designed test workbench, and the tangential and longitudinal strains were monitored during the expansion process. A new analytical approach is developed to estimate the stresses and strains in the expanded tube during the expansion process. The different expanded zones are treated using different theories. An axisymmetric finite element model as a numerical approach is used to analyze the stresses based on a multi-linear kinematic hardening behavior to validate the analytical approach. In addition, the stresses in the expanded tube and the push force of the die are also provided by the analytical, numerical and experimental approaches. Finally, the results from the three approaches are in a relatively good agreement.