铜系异质双金属复合管小半径绕弯的界面失效机理与柔性填充研究

The lack of plastic bending process of composite tube is a key factor that hinders the copper/dissimilar material bimetallic (CDB) tube to play its excellent comprehensive properties in machinery manufacturing, marine operations, aerospace and other industries. To solve this problem, this study develops the process of rotary draw bending of small bending radius for CDB tube. The description of interface failure, which is characterized by the problems of interfacial delamination, sectional distortion and excessive wall thinning, is established to give correct assessments for processes and accuracy of tube bending. By using the simulative and experimental methods, the relationships among interface failure problems are researched. It also reveals the interfacial failure mechanism of CDB tube rotary draw bending with small bending radius, which is controlled by the coupling constraints between carrier tube and liner tube. The flexible fillers and their modular forms are researched and designed to apply to different CDB tubes, and by combining which with a global sensitivity analysis of process parameters, the accurate forming of CDB tube rotary draw bending with small bending radius is achieved. This study can contribute to the application of CDB tubes in some key structures and some fields with high-performance material requirement, which has important practical values. It is also helpful to promote the development of secondary processes for bimetallic tubes by providing a certain theoretical basis.

复合管塑性弯曲工艺的缺乏，成为制约铜系异质双金属复合管在机械制造、海洋作业、航空航天等工业领域发挥优秀综合性能的关键因素。为此，本研究提出铜系异质双金属复合管的小半径绕弯成形工艺，并建立以界面分层、畸变和壁厚过度减薄缺陷为特征的界面失效描述，对工艺过程和管件弯曲精度实施正确评估。采用模拟结合实验的方法，研究界面失效问题之间的关联性，揭示基-覆管耦合约束作用下的铜系异质双金属复合管小半径绕弯界面失效机理。研究、设计适用不同铜系异质金属复合管的柔性填充及其组合形式，并结合工艺参数组合的全局敏感性分析，实现铜系异质双金属复合管小半径绕弯的精确成形。本研究能够促进铜系双金属复合管在一些关键结构和一些高性能材料要求的领域中的应用，具有重要的工程实用价值，同时，为促进双金属复合管的二次工艺开发奠定一定的理论基础。

本项目将绕弯成形引入双金属管的弯曲工艺之中。研究成果能够促进铜系异质双金属复合管在高性能材料要求的结构件中的运用，具有重要的工程实用价值。同时，研究成果将丰富管材的塑性弯曲内容，促进精确塑性加工技术的发展，为其它材质的金属复合管的二次塑性成形研究起到抛砖引玉的作用。此外，我国还是一个铜资源缺口量很大的国家，研究推广铜系异质双金属复合弯管可以减少国家对铜的进口量，节约铜资源，具有良好的经济效益。本项目取得的主要研究进展和重要结论如下：.（1）建立了基于库仑摩擦接触的基-覆管界面结合模型。建立了铜钛双金属复合管绕弯-回弹全过程有限元模型，该模型能够可靠地预测回弹和截面变形，可以为后继研究奠定基础。.（2）铜系异质双金属管弯曲过程中，基、覆管相互作用力较小，不存在明显的变形不协调现象，复合管的回弹量是覆管与基管协同回弹的结果。基、覆管的结合提高了复合管的截面刚度。弯曲过程中覆管的最大损伤值大于基管的最大损伤值，覆管的材料流动比基管更容易受到工艺条件影响。.（3）复合管的横截面尺寸越大，弯曲过程中越容易因为中空缺乏支撑而发生变形，基管发生塌陷的情况比覆管严重。截面变形率随着弯曲半径的增大而减小，但弯曲半径增大至一定程度，截面变形率反而因为整体塑性变形区域的增大而增大。芯模填充可以大大降低截面变形率，当弯曲半径较小时，弹性芯模比刚性芯模的填充性更好。刚性芯模填充下，双金属管存在周向应力、切向应力的反复加载和反向加载过程，其反向加载经常保持在塑性范围内。