Bending Behavior of Rectangular Cross-Sectional Tube Considering Internal Fluid Pressure Effects

The objective of this research is to examine the influence of internal fluid pressure on the development of imperfections when quadrilateral tubes undergo rotary draw bending. Both experimental and numerical methods are utilized to conduct the tests. The experimental setup involved using an aluminum sample with an outer cross section of 35 mm × 35 mm and 1.5 mm thickness. The internal mandrel is replaced with fluid pressure introduced through a connection at one end of the sample while the other end is blocked. Several tests are carried out at various pressures with a bend radius ratio of 3 and a bending angle of 90°. The findings of this research indicate that in the absence of internal pressure, the profiles experienced buckling in the bending area at a 90-degree angle. As the internal pressure increases up to 24 bar, the rupture load is determined. Both experimental tests and simulations confirmed that the impact of internal fluid pressure on tube thinning is much greater than on thickening. Increasing internal fluid pressure caused thinning in the extrados, whereas the intrados thickness is not significantly affected. Instead, thickening is reduced due to material flow direction at higher pressures. The formed tube under pressures of 6 and 10 bar experience wrinkling and cross-sectional distortion of 20% and 10%, respectively. However, samples bent under 20 bar pressure show the best results regarding defects of the bend zone, with less than 1% distortion.