基于变形历程与板材后续性能的等效拉深筋模型研究

Equivalent drawbead instead of real drawbead is usually used in numerical simulation technology of sheet drawing. Only the drawbead resistance is considered in the equivalent drawbead model in current commerical FE software. The thinning thickness of sheet resulting from repeated bending deformation and the changes of subsequent properties are negelected, as well as the Bauschinger effect of reverse loading. Then the accuracy and reliability of results from the simulation are low inevitablely. So a equivalent drawbead model considering the loading history and the subsequent properties will be proposed in the study. First, through systemic experimental study of cyclic tension and compression for thin sheet, the evolution of Bauschinger and hardening parameters will be revealed. And the anisotropy of sheet will be took into account too. Based on the above results a constitutive model which can reflect cyclic deformation behaviour will be proposed and be used in FE software. Then a computation model which can reflect actual sheet thickness and compute the drawbead resistance and stain distribution accurately will be establised. At the same time a model predicting subsequent deforming properties from loading path and deformation can be built based on the experimental and simulated results. Finally, a equivalent drawbead model which can reflect the changes of sheet subsequent forming properties and sheet thickness and drawbead resistance will be established. Then the accuracy of simulation of sheet drawing will be improved effectively.

在板材拉深成形数值模拟技术中通常采用等效拉深筋代替真实拉深筋结构。现有通用有限元软件中的等效拉深筋模型只考虑拉深筋阻力，忽略反复弯曲变形后板材厚度减薄、后续性能的变化，以及反向加载时包申格效应的影响，因此整个成形工艺模拟结果的精度和可靠性势必降低。鉴于此，本申请拟建立一种考虑板材变形历程及后续性能的等效拉深筋模型。首先通过对薄板单轴大应变循环拉压试验的系统研究，揭示包申格效应参数与硬化特征参数在循环加载各阶段的演化规律；以此为基础并考虑板材各向异性，提出一种反映循环变形特征的本构模型，嵌入有限元中建立能真实反映板材厚度变化且准确计算拉深筋阻力及应变分布的分析模型；并基于数值模拟与实验，建立根据变形程度及加载路径预测板材后续性能的计算模型；最后依据上述结果建立反映板材后续性能、板厚变化及拉深筋阻力的更完善的等效拉深筋模型，从而有效提高板材拉深成形数值模拟计算精度。

在板材拉深成形数值模拟技术中通常采用等效拉深筋代替真实拉深筋结构。目前常见的等效拉深筋模型主要以提供拉深筋阻力为目的，不考虑板材经过拉深筋反复弯曲时包申格效应的影响以及反复弯曲后的变形特征，因此成形工艺模拟计算的精度有待提高。本项研究提出建立一种考虑变形历程的双线法等效拉深筋模型。首先制作了一套结构简单、灵活适用的金属薄板大应变循环拉伸-压缩试验系统，获取了常用冲压钢板，铝合金板及高强钢板等不同薄板大应变循环拉伸-压缩及压缩-拉伸应力应变曲线，揭示了包申格效应参数及硬化特征参数在不同循环加载分支的变化规律；建立了反映循环变形特征的基于HILL、Barlat各向异性屈服准则及A-F、Chaboche非线性随动强化模型的几种各向异性非线性随动强化本构模型，借助Fortran语言编写了各材料本构模型的ABAQUS软件UMAT子程序，并验证了开发程序的有效性。运用上述本构模型对板材通过拉深筋的循环变形机理进行了分析。在此研究工作基础上，建立了基于HILL各向异性屈服准则及voce与A-F结合的混合强化的材料本构模型，根据板材的循环应力-应变曲线，利用通用全局优化算法，确定了混合强化模型中的材料系数，运用该模型获得了更加准确的拉深筋约束阻力、板材通过拉深筋后板厚及应变分布的分析结果；基于正交回归分析构建了通过拉深筋后板材后续性能的预测模型；建立了一种既反映拉深筋约束阻力，又能反映板材经过拉深筋后变形特征的双线法等效拉深筋模型，将其应用于盒形件和门槛外板前端盖的拉深成形，通过实验对比验证了所建立的等效拉深筋模型可以应用于板材冲压成形问题的模拟分析。.本项研究所获得的各种材料循环拉伸-压缩应力应变曲线不仅可以为各种弹塑性本构模型提供试验验证，又可以为各本构模型中材料参数的优化回归提供直接数据；双线法等效拉深筋模型可以有效提高数值模拟计算精度，所建立的通过拉深筋后板材后续性能的预测模型为冲压模具设计提供可参考依据。