Abstract
3D free bending technology is a fabrication technology that has drawn more and more attention all over the world in recent years. During the free bending process, the relative thickness (t(0)/d(0)) has a great impact on stress-strain distribution and the movement of the neutral layer, thus further affecting the formability and cross-section distortion of the tube. In this study, relative thickness (t(0)/d(0)) were set as 0.033, 0.067, 0.1 and 0.133, respectively. A mechanical analysis model was built to analysis the equivalent stress distribution and the displacement of the strain neutral layer (xi), and the reliability of the theoretical model was verified. The results showed that the equivalent stress is the lowest and its distribution is the most uniform when the relative thickness (t(0)/d(0)) was set as 0.067, which leads to the best formability under all conditions. The peak values of equivalent stress under all conditions appear at the 10 degrees cross-section and the 150 degrees cross-section, respectively, which leads to the thickness of the inner and outer tube changes dramatically. Due to the effect of feeding force which increases the compressive stress of the inner tube and reduces the tensile stress of the outer tube correspondingly, the equivalent stress of the inner tube was higher than the values of the outer tube at the same positions. The displacement of the strain neutral layer (xi) decreases with the increase of the initial thickness of the tube. The lowest values of ellipticity of 3.48% and 2.85% are reached at the two typical cross-sections when the relative thickness is 0.133.