National University of Science and Technology (Moscow, Russia):

V. N. Shinkin, Dr. Phys.-Math., Prof., e-mail: shinkin-korolev@yandex.ru

At the up-to-date production of steel thick-walled pipes of large diameter for the main gas-and-oil pipelines, the steel sheet is bent sequentially several times during the technological transitions from one press to another. So, at the production of the steel large-diameter pipes by UOE-technology on TESA 1020, the steel sheet is bent sequentially on the flanging press, pre-shaping press (giving the sheet a U-shape) and final-shaping press (giving the sheet an O-shape). At the deformation of the steel sheet on the O-press, there is a hysteresis of the mechanical properties of the sheet: the excessively curved areas of the sheet are partially unbent by the press, and the insufficiently curved areas receive an additional bending in the original direction. At straightening of steel sheet on the multi-roller sheet-straightening machines (the sighn-alternating bending of the sheet between the working rollers of the machine) also observed a low-cycle hysteresis of the mechanical properties of the sheet. The calculation of the sheet’s curvature at the sighn-alternating bending causes the great difficulties for the metallurgical technologists because of the effect of the Bauschinger’s effect under bending. In this paper, we propose the analytical method for calculating of the final curvature of the thick steel sheet at hysteresis (at sighn-alternating bending). The results of the work can be applied in metallurgy at the production of the thick-walled largediameter steel pipes.

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