Enhancing tube hydroformability by reducing the local strain gradient at potential necking sites

다국어 초록 (Multilingual Abstract)

Bursting in tube hydroforming is preceded by localized deformation, which is often called necking. The retardation of the initiation ofnecking is a means to enhance hydroformability. Since high strain gradients occur at necking sites, a decrease in local strain gradients isan effective way to retard the initiation of necking. In the current study, the expansion at potential necking sites was intentionally restrictedin order to reduce the strain gradient at potential necking sites. From the strain distribution obtained from FEM, it is possible todetermine strain concentrated zones, which are the potential necking sites. Prior to the hydroforming of a trailing arm, lead patch is attachedto the tube where the strain concentration would occur. Due to the incompressibility of lead, the tube expansion is locally restricted,and the resultant strain extends to adjacent regions of the tube during hydroforming. After the first stage of hydroforming, thelead is removed from the tube, and the hydroforming continues to obtain the targeted shape without the local restriction. This method wassuccessfully used to fabricate a complex shaped automotive trailing arm that had previously failed during traditional hydroforming processing.

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