无约束圆柱弯曲成形卸载回弹的数值模拟

FEM simulation and experimental study on springback of unconstrained cylindrical bending benchmark

采用Barlat' 91材料屈服准则准确描述铝合金板料各向异性,通过与其它屈服准则的比较发现,Barlat 91屈服准则能反映在单轴拉伸和等双轴拉伸条件附近屈服面的小曲率半径。引入一种新型的双线性厚壳单元来模拟弯曲型板材的成形与卸载回弹全过程;该单元采用减缩积分方式,可以在不损失计算精度的前提下提高计算效率。模拟中板材本构方程基于更新Lagrangian弹塑性材料模型,适于大位移大变形过程模拟。卸载过程采用模具反运动方式描述,采用修正的Coulomb摩擦模型。通过商品化通用CAE软件MSC/MARC对国际板成形会议(NUMISHEET2002)无约束圆柱弯曲成形卸载回弹Benchmark B进行计算机仿真,把不同阶段的模拟结果与试验数据及其他软件模拟结果进行对比。通过回弹过程模拟与实验结果的对比,验证了相关关键技术的采用可以较好地模拟复杂接触卸载回弹问题。

Barlat＇91 yield criteria account for six stress components is adopted to describe the material constitutive behaviors of aluminum alloys.Comparisons with other yield criteria such as Hill＇48 and Mises show that Barlat＇91 can well reflect the decreasing of the curvature radius of rounded vertices near the uniaxial and balanced biaxial tension ranges of the yield surface.A four-node,thick-shell element with bilinear interpolation is adopted to simulate the forming and springback process.Though the shell element adopts reduced integration scheme,it shows better computational efficiency and uses less memory than other shell elements without sacrificing accuracy.The underlying formulation is based on updated Lagrangian elastoplastic materials model.Sheet unloading is simulated by the tools＇ reverse motion and the modified Coulomb friction model is used.The solutions validated with experimental data of NUMISHEET2002 benchmark B show much accuracy than other commercial software and witness the robustness of MSC/M ARC to simulate complicated unloading process.