基于精确几何拟协调技术的金属板材大步长隐式成形及回弹算法研究

With the deterioration of the global environment and energy problems, lightweight research of vehicles has become one of the hottest research directions and eternal topics of today's international automotive industry and academia. Car Body weight accounts for a large proportion of the vehicle weight, so reducing white body weight is one of the most effective measures to reduce fuel consumption and exhaust gases emission. Currently car body manufacturing mainly applies high-strength steel to simultaneously meet the requirements of cars' lightweight and security design, but the spring-back problem of high-strength steel is often more significant than ordinary steel , which becomes one of the most important constraint bottlenecks in the application of high-strength steel. This project will establish a high-level Rotation-Free NURBS degenerated shell element model based on exact-geometry quasi-conforming technique, and study "intermediate configuration technology based on material point mapping" under NURBS condition. It could effectively solve these key problems of efficiency, convergence and stability, which are caused by singular stiffness matrix and the contact nonlinear quality in large step static implicit algorithms of sheet metal forming simulation. Based on this study, spring-back prediction and compensation algorithms under NURBS conditions could be further researched, which would lay a good foundation for the development of commercial high precision sheet metal forming and spring-back simulation software with fully independent intellectual property.

全球环境与能源问题的日趋恶化，使汽车的轻量化研究成为当今国际汽车行业和学术界的最热点的研究方向和永恒的研究主题之一。轿车车身重量占整车重量的相当大比重，减小白车身自重是降油耗及减排放的最有效措施之一。当前在车身制造工艺上主要采用高强钢板同时满足轻量化和安全性方面的需求，但高强钢板的回弹问题往往较之普通钢板更为显著，这成为制约高强钢板应用的最主要瓶颈之一。本项目将基于精确几何拟协调技术建立Rotation-Free的高阶NURBS退化壳单元模型，研究NURBS条件下"基于物质点映射的中间构型技术"，有效解决金属板材冲压成形仿真大步长静力隐式算法中由于刚度矩阵奇异和接触非线性导致的效率、收敛性和求解稳定性等关键问题，在此基础上研究NURBS条件下的回弹预测及补偿算法，为开发具有自主知识产权的高精度金属板材成形和回弹商品化仿真软件包打下良好基础。

全球环境与能源问题的日趋恶化，使汽车的轻量化研究成为当今国际汽车行业和学术界的最热点的研究方向和永恒的研究主题之一。轿车车身重量占整车重量的相当大比重，减小白车身自重是降油耗及减排放的最有效措施之一。当前在车身制造工艺上主要采用高强钢板同时满足轻量化和安全性方面的需求，但高强钢板的回弹问题往往较之普通钢板更为显著，这成为制约高强钢板应用的最主要瓶颈之一。本项目将精确几何技术引入到金属板材冲压成形大步长静力隐式算法中，发展了可处理多个剪裁曲面的基于 RM 理论的等几何壳分析方法；提出了一种新的拟协调方法，从多项式形式的初始假设应力出发，根据本构方程导出应变，经过证明改方法在应变积分过程中不再需要域内函数。在此基础上，提出了两种新的拟协调板单元，无剪切闭锁现象，有效克服大变形迭代过程中由于网格畸变带来的精度变差和求解稳定性问题；提出基于等几何单元的“Cutting-Stitching”初始解预示算法，及基于拟最小面积法的滑移约束面构造方法，有效克服复杂工业零件的卷边问题，是本项目研究成果将来形成的自主CAE软件是否有市场竞争力的关键。在上述理论研究的基础上实现了基于等几何分析的金属板材大步长隐式冲压仿真分析弹塑性算法，为开发自主知识产权的高精度金属板材冲压成形和回弹仿真软件打下良好基础。在上述理论成果基础上，本项目后继计划在2~3年内研发一套计算稳定、鲁棒性强且计算效率高的金属板材冲压成形及回弹高精度仿真软件包，形成一套有特色的自主计算力学CAE软件。

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