Pure Bending Equivalent Principle for Over-bend Straightening and Its Experimental Verification

Abstract

Straightening is the key technology to deal with the curving pipe in the manufacturing processes of large diameter longitudinal submerged arc welded(LSAW) pipes production.The research of forming rules is the theoretical foundation for reasonably determining the process parameter.According to the small deformation feature in the straightening process,the concept of equivalent initial strain is firstly proposed,and based on this concept the relationship is built between initial curvature and strain distribution of the curved beam.Under the basic hypothesis of pure bending engineering theory for elastic-plastic small deformation,the geometrical equation and the springback equation for planar curved beam is deduced.Further the equivalent relation is demonstrated between over-bend straighting of curved beam and pure bending of straight beam,and then the equivalent principle for over-bend straighting is put forward,which is equivalent relation between the bending moment in straight beam bending and curved beam being straightened.The validity of the equivalent principle is verified by three point bending,four point bending and their reverse bending.All these works establish the theoretical and experimental base for over-bend straighting technology and its control strategy.