纯弯曲过弯矫直等价原理及其试验验证

矫直是大口径埋弧直缝焊管生产过程中处理直线度不达标管件的关键性技术,研究矫直过程中的变形规律是合理确定矫直工艺参数的理论基础。根据矫直过程中弯曲小变形的特点,提出初始当量应变的概念,借此建立平面曲梁初始曲率分布与应变分布之间的联系。基于弹塑性小变形纯弯曲工程基本假设,导出平面曲梁小变形反向纯弯曲的几何方程和弹复方程,进而理论上论证曲梁过弯矫直与直梁纯弯曲之间的等价关系,从而给出过弯矫直等价原理,即曲梁矫直所需弯矩载荷与同材质、同形状的直梁弯曲成待矫曲梁形状所需载荷的等价关系。用三点弯曲和四点弯曲及其反向弯曲试验证实过弯矫直等价原理的正确性,为过弯矫直工艺方案和控制策略的确定奠定了理论和试验基础。

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

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.