基于连续介质损伤力学的7075铝合金高温成形极限理论预测与数值仿真

开展7075铝合金高温单向拉伸试验和成形极限试验，获得了不同温度和应变率的应力-应变曲线和成形极限曲线。结果表明，在较高的温度和应变率时7075铝合金的强度减小、成形性提高。为描述7075铝合金高温损伤演化过程，提出一种改进的连续介质损伤模型，并建立了耦合损伤的多轴统一黏塑性本构模型。基于试验结果，运用NSGAII遗传算法标定了模型中的参数，标定后的本构模型可以很好地预测7075铝合金的高温热力行为和极限应变。通过有限元软件Abaqus的用户材料子程序VUMAT，该本构模型被编入到Abaqus软件中进行数值仿真计算。结果表明，仿真获得的成形极限曲线和应变场分布与试验和理论结果吻合度好，进一步证明了所建立的耦合损伤的多轴本构模型的正确性及其在高温成形极限有限元仿真中的适用性。

Theoretical Prediction and Numerical Simulation Investigation of the Thermal Forming Limit of 7075 Aluminum Alloy Based on Continuum Damage Mechanics

Hot uniaxial tensile tests and forming limit tests of 7075 alloy are conducted. Stress-strain curves and forming limit curves at different temperatures and strain rates are obtained. The results show that reduction of strength and improvement of formability are observed at relatively higher temperatures and strain rates. In order to describe the thermal damage evolution of 7075 alloy, a modified continuum damage model is proposed and incorporated into a set of multi-axial unified visco-plastic constitutive equations. The parameters in equations are calibrated with NSGAII algorithm based on experimental results. The set of calibrated constitutive equations can commendably predict the thermomechanical behavior and forming limit strains of 7075 alloy. Moreover, numerical simulation is carried out in the simulation software Abaqus by implementing the set of constitutive equations via the user material subroutine VUMAT. The results show the forming limit curves and strain field of simulation are in good agreement with experimental and theoretical grades, which proves the established set of mult-axial constitutive equations coupled with damage is valid and appropriate for the numerical simulation of thermal forming limit.