镁合金塑性变形及延性损伤断裂的多尺度建模及应用

由于镁具有特殊的HCP晶格结构，在复杂加载条件下镁合金塑性变形和延性断裂的准确预测还存在困难。本项目拟针对该问题开展多尺度建模研究，包括微观变形和断裂、细观晶体塑性、宏观上的镁合金成形和断裂等三个方面。首先，通过基于SEM-EBSD-DIC的原位变形实验，观察和测量镁合金晶体的变形和延性断裂演变，探究其微观机制。其次，从细观尺度上开展镁合金晶体塑性有限元分析，考虑孪晶在塑性本构中的作用和晶粒间相互滑动，建立合理的晶体塑性本构模型，预测材料各种变形条件下的屈服行为，为建立和完善宏观非关联本构模型提供可靠数据。接着，在宏观本构模型中综合考虑材料拉压非对称屈服、畸变硬化、各向异性和非关联流动等复杂塑性行为，准确预测复杂加载条件下镁合金塑性变形；通过材料变形和断裂实验，建立合理的延性损伤断裂准则。最后，利用所建立的材料本构模型和断裂准则，预测稀土镁合金板料成形和管材弯曲，优化制坯、模具和工艺。

Magnesium has a special hexagonal close-packed (HCP) lattice structure. The prediction accuracy of plastic deformation and ductile fracture of magnesium alloys under complex loading conditions needs to be improved. The present project is aimed to carry out multi-scale modeling research on this issue, including an exploration of microscopic mechanism of plastic deformation and fracture, mesoscale analysis of crystal plastic deformation, macroscopic forming and fracture prediction of magnesium alloy. First, through in-situ deformation experiments based on SEM-EBSD-DIC, the plastic deformation and ductile fracture evolution of magnesium alloy crystals are observed and measured, and the microscopic deformation and fracture mechanism are explored. Secondly, the finite element analysis of magnesium alloy crystal plasticity is carried out. Considering the role of twins in plastic constitutive and mutual sliding between grains, a reasonable crystal plastic constitutive model is established to predict the material under various deformation conditions. These simulations provide reliable data for establishing and perfecting macroscopic non-associated constitutive models. Then, the complex plastic behaviors such as tensile and compression asymmetric yielding, distortion hardening, anisotropy and non-associated flow are comprehensively considered in the macro constitutive model to accurately predict the plastic deformation of the magnesium alloy under complex loading conditions. A reasonable ductile damage fracture criterion is established through material deformation and fracture experiments. Finally, the established material constitutive model and fracture criterion are used to predict sheet forming and tube bending of the rare earth magnesium alloys, and optimize the blank making, die and process.