Deformation Mechanism of ERW Tubes in Newly Developed Bending Method “PRB”

In the investigation of the strain and stress states both outside and inside the bend, it was found that plastic deformation in PRB was almost completed before the tube material entered the bend area. In rotary draw bending, plastic deformation developed in the bend area.

Regarding the effect of tube reduction in diameter by the pressure die in deformation of tubes, circumferential compressive deformation involving longitudinal tensile deformation is enhanced outside the bend. Protrusion of the bending die toward the tube facilitates longitudinal compressive deformation inside the bend.

In PRB, the tube material inside the bend tends to be compressed along the longitudinal direction in a large area as a result of the protrusion of the bending die toward the tube inside the bend. This eases circumferential compressive stress and reduces wrinkling, even though a mandrel and wiper are not used in PRB.

The stress in the thickness direction is not negligible inside the bend for a detailed investigation of deformation behavior.