Analysis of Strain Neutral Layer Displacement in Tube-bending Process

Abstract

In the series study of the tube-bending deformation, in order to reveal the deformation mechanism of tube bending and promote the rapid development of accurate tube bending and digital bending technology, the approximate calculation formulae of the strain neutral layer radius and the thickness attenuation of outer-lateral tube-wall are deduced on the basis of the plate-bending theory and under the plane strain conditions, and the changes of the strain neutral layer along radius are analysed with the consideration of the thinning of thickness of outer-lateral tube-wall. Given that the ratio of the strain neutral layer radius and bending radius is smaller than 1, it is proved that the strain neutral layer moves towards the bending center during the process of tube-bending. In addition, it is pointed that the amount of movement towards center of the strain neutral layer is inversely proportional to the relative bending radius. According to the comparison between the tube-bending test and finite element simulation results, the calculation of tube-wall thinning is proved to be relatively accurate, but since it does not include the effects of deformation perpendicular to the direction of the bending plane in material property parameters, the calculated value is on the high side and needs further modification.