It is important to elucidate preforming processes such as tube bending and crushing carried out prior to tube hydroforming. Although tube bending affects the formability of the subsequent hydroforming, the study of prebending remains limited. To investigate the deformation behavior of tube bending, experiments and FEM simulations were carried out for rotary draw bending with the mandrel and wiper at three continuous portions for TS390MPa class steel tubes. The results are as follows: (1) Thinning and thickening behaviors in regions outside and inside the bend respectively are markedly affected by a change in the circumferential stress of a tube during the material pass through the mandrel. (2) The shear strain observed from the outside to the inside of the bend results from the difference between the longitudinal strain distributions inside and outside the bend. (3) In multiple bending whose areas are consecutive, the deformation properties of the prior bending affect those of the subsequent bending.
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