Finite element simulation study on residual cross-sectional ovalization of thin-walled circular steel tubes in continuous rotary straightening process

Abstract

Cross-sectional ovalization of thin-walled circular steel tube caused by large plastic bending usually occurs at initial large bending stage in tube’s continuous rotary straightening process. When the bending loads have been removed, there must be residual ovalization kept on the tube’s cross-section during the whole straightening process, to induce the poor roundness and the reduction of the tube flexural stiffness. In order to clarify the fundamental ovalization characteristics, find out what factors influence the residual flattening (value of ovalization), the ovalization behavior is investigated by the simulation method. Seven groups of the finite element (FE) simulations for the thin-walled tube straightening process are carried out on the stainless steel specimens with different geometric parameters using different working rolls of different bending radii. The residual cross-sectional flattening is obtained periodically along the hoop direction by tracing the x- and y-coordinate values of the nodes on the cross-section during the whole simulation process. From the simulation results, it is observed that the shape of the tube cross-section is not a perfect standard ellipse, and the appearance of the maximum residual flattening is usually found in the direction perpendicular to the tube’s centroid axis. Then, the influences of tube’s outer diameter, thickness, and bending radius on residual flattening are found, i.e., the residual flattening increases with the increase of the outer diameter, but it decreases with the increases of the bending radius and the wall thickness. Meanwhile, the variation of the cross-sectional flattening with the number of bending is also analyzed.