柔性轧制差厚板各向异性材料本构模型构建及成形极限理论研究

The plasticity theory for sheet metal forming is established on the uniform thickness assumption, which does not take into account the thickness change and strain hardening variation of Tailor Rolled Blank (TRB). Thus it will not be applicable to the formability analysis for TRB forming. This program focuses on the issue of anisotropy material constitutive modeling and forming limit theory for tailor rolled blank. Based on the principle of equal section area, a novel equal-stress uniaxial tension test sample with variable width is designed. The mechanical tension test will be performed by using Digital Image Correlation (DIC) technique, and the experimental data for material characteristic of TRB will be acquired. By introducing a processes parameter for variable gauge rolling, a general strain hardening model suitable for each region of tailor rolled blank will be developed, which can describe accurately the strain hardening variation for TRB. An anisotropy yield criterion for tailor rolled blank will be constructed. The micro indentation test for three orthogonal directions will be performed in order to indentify the parameters of anisotropy material constitutive model by using the experimental data in conjunction to the inverse method. And the influence of the processes parameter for variable gauge rolling on the mechanical behavior of TRB will be studied. The forming limit theory for tailor rolled blank will be explored. A three-dimension forming limit surface, which can be used to quantitative evaluate the formability of TRB, will be constructed. A M-K model with two nested initial groove assumption will be developed, which can be used to predict the forming limit of tailor rolled blank. A forming limit prediction procedure for tailor rolled blank will be proposed. The research results of this program will have an important theoretical significance to the development of forming limit and serve as a guide to the application of tailor rolled blank.

基于等厚板构建的塑性成形理论未考虑差厚板的厚度变化和加工硬化非均匀性，难以适用于差厚板的成形性能分析。本项目围绕差厚板各向异性本构模型的构建和成形极限理论开展研究工作：基于等截面面积原则，提出新型变宽度等应力单向拉伸试样设计方法，结合DIC技术，开展差厚板力学性能的试验研究，获取差厚板的材料特性试验数据；通过引入柔性轧制工艺参数，建立对差厚板各区域具有统一形式的强化模型，准确描述加工硬化程度的差异，构建各向异性屈服准则，开展沿正交方向的显微压痕试验，结合反求技术，获取差厚板的各向异性材料本构方程参数，阐明柔性轧制工艺参数对差厚板力学行为的影响规律；探索差厚板的成形极限理论，建立适用于差厚板成形性定量评价的三维成形极限曲面，构建差厚板成形极限理论预测的嵌套M-K模型，建立差厚板成形极限的模拟预测方法。本课题研究成果对成形极限理论体系的发展和差厚板的应用具有重要的理论意义和工程价值。

作为一种功能定制变厚度板材，差厚板利用柔性轧制技术按照载荷大小配置板料的厚薄，实现零件各区域的负载优化，为结构轻量化提供了良好的解决方案。然而，厚度差异性和微结构非均匀性使其相较于等厚板呈现出一些新的材料力学行为。本项目围绕差厚板力学性能测试方法、本构模型构建及参数识别和成形极限理论等方面，综合应用理论分析、试验和数值模拟相结合的方法开展了研究工作。项目完成了柔性轧制差厚板等截面单向拉伸试样设计，开展了典型差厚板单向拉伸力学性能试验测试，采用DIC技术获得了单向拉伸变形过程中试样表面的应变分布，结合力传感器采集的试验数据获得了差厚板的真实应力应变试验数据，建立了一种准确获取柔性轧制差厚板力学性能的试验方法；构建了差厚板具有统一形式的流变力学模型和各向异性屈服准则，基于差厚板单向拉伸和显微压痕试验数据，应用反求方法，获得了差厚板的材料本构模型参数，分析了柔性轧制工艺参数对差厚板流变特性和屈服轨迹的影响；建立了适用于差厚板成形性能评价的三维成形极限曲面数学模型，基于M-K模型对差厚板的成形极限曲线进行了预测，拟合得到了三维成形极限曲面的系数，发展了差厚板的成形极限理论；开展了成形极限试验，通过对比数值模拟仿真结果与试验数据，验证了所构建的差厚板材料本构模型和三维成形极限曲面的适用性和准确性。项目所取得的成果为差厚板的成形制造和推广应用提供了理论支持和工艺方法指导，对促进我国先进制造业发展和推动汽车轻量化进程具有重要意义。