Influences of generalized loading parameters on FLD predictions for aluminum tube hydroforming

The present study intends to investigate the prediction of forming limit diagrams (FLDs) for tube hydroforming from the perspective of selecting various combinations of loading parameters based on plastic instability. From this perspective, certain related research efforts on plastic instability of thin-walled tubes subjected to internal fluid pressure and axial force are reviewed and six combinations of loading parameters have been identified. There are nine combinations of loading parameters, including six found in the literature, being employed to determine forming limit curves (FLCs) for tube hydroforming in the present study. The predicted FLCs are compared with experimental data obtained in a well-controlled laboratory condition. Comparisons indicate that the combination of the internal pressure p and the resultant axial force Fz+πr2p provides the best predicted right side of FLC among the nine combinations and a reasonably well-predicted left-hand side of FLC. In addition, comparison also demonstrated that the combination of p and the applied axial stress Fz/2πrt can also give a reasonable predicted left-hand side of FLC.