复杂边界条件下薄壁件塑性成形多模式失稳预测与控制

The precision forming of thin-walled components has been urgently needed in aviation, aerospace and automobile field. An accurate prediction of wrinkling instability, improvement of the forming limit and forming quality in the thin-walled part forming process, are still the challenges and focused issues in precision forming. Solely using analytical solution, implicit finite element method (FEM) or explicit FEM cannot solve this problem. Therefore, by introducing a micro imperfection into the idealized mesh which considering the variation of geometry, material and wall thickness, a numerical simulation method combined with the analytical approach is proposed to accurately predict multiple instability in thin-walled part forming under complicated boundary conditions(CBC). Taking two typical thin-walled plate/tube forming processes as research cases, a systematical investigation on multiple instability prediction in the thin-walled part forming with CBC will be carried out. This project will provide basis for developing precise plastic forming technique of thin-walled part under CBC.

薄壁件是航空、航天和汽车等高端装备领域越来越广泛需要的关键高性能轻量化构件之一。如何准确预测复杂边界条件下的多模式失稳现象，从而实现薄壁件精确塑性成形、并提高其成形极限和成形质量一直是该领域研究的焦点与基础性难题。而现有的理论解析和数值模拟方法均极难解决这一问题。为此，本文研究建立考虑几何、材料和壁厚变化的初始缺陷分析网格模型，引入多阶屈曲模态叠加的解析-有限元数值模拟相结合的预测方法，并以两种典型的复杂边界条件下的起皱预测难题-薄板面内弯曲成形多模式失稳预测和大直径薄壁铝管绕弯成形多模式失稳预测为研究对象，开展对复杂边界条件下薄壁件塑性成形多模式失稳的预测研究，本研究可为发展复杂边界条件下薄壁件精确塑性成形技术提供指导。

随着航空航天、汽车等制造领域对轻量化高强度产品设计的不断深入，失稳起皱是制约金属板材成形性的主要缺陷之一。由于皱纹的萌生与扩展受到多种因素的交互影响,包括几何参数、材料性能参数和边界条件,特别金属薄壁件在塑性形成过程中涉及几何非线性、材料非线性和边界非线性等动态变化时,如何高效和敏感地预测失稳起皱的发生是金属板料成形过程中最基本的和具有挑战性的问题之一。在金属板料成形过程中,以确保没有缺陷变形。本项目以典型的薄壁钛合金管在轴向压缩载荷下失稳起皱和方板对角拉伸下压缩失稳起皱为研究对象，实验探索了不同约束条件下屈曲模态的起皱特性，提出了考虑多阶屈曲模态叠加的解析-有限元数值预测方法。结果表明，在较少约束的边界条件下，失稳的屈曲模态发在在较低阶。而在多约束的边界条件下，失稳的屈曲模态发在较高阶，高阶屈曲同时也会消耗更改多的能量。将线性屈曲分析得到的多个模态叠加到显式有限元模型中，与未引入屈曲模态的完美模型相比，采用多个模态叠加的有限元模型可以对两种成形情况下的起皱提供更敏感的预测。