镁合金板材伪弹性变形机制与细观建模

Magnesium alloy sheet shows special pseudoelastic characteristic under loading-unloading, which brings great challenges to modelling constitutive behavior. It is necessary to establish a constitutive model characterizing the pseudoelastic behavior, so as to accurately predict the cyclic loading/unloading process and solve the pre-failure of structure parts in engineering. Due to the second phase LPSO in rare earth (RE) magnesium alloy sheet, the kink band becomes a potential deformation mechanism contributing to the pseudoelasticity. Constitutive modeling is rather complex for RE magnesium alloy. In this project, both non-RE magnesium alloy sheet (AZ31) and RE magnesium alloy sheet (Mg-Zn-Gd) will be studied. The deformation mechanisms under cyclic loading-unloading will be systematicly studied, then a constitutive model considering slip and twinning/detwinning/retwinning will be established for describing the pseudoelasticity of AZ31 alloy sheet, furthermore, the theoretical model of kink band will be constructed and coupled to the constitutive model, accurately describing the pseudoelasticity of Mg-Zn-Gd alloy sheet. A numerical method for quantitatively evaluating of pseudoelasticity will be presented, and further to predict the chord modulus and hysteresis loop. Finally, the crystal plasticity finite element method for cyclic loading-unloading will be established to predict the draw-bending forming and springback. The influences of various parameters on springback will be analyzed to optimize the draw-bending process. The research results will provide theoretical support for cyclic loading-unloading forming technology of magnesium alloy sheet, and guide the mechanical design in engineering.

伪弹性是镁板加/卸载下的重要变形特征，必须建立合理表征伪弹性变形的本构模型，才能准确预测镁板循环加/卸载成形过程，解决结构件提前失效的工程问题。稀土镁合金由于第二相LPSO的存在使得扭折带成为伪弹性的潜在变形机制，本构建模更加复杂。本项目以AZ31不含稀土镁合金和Mg-Zn-Gd稀土镁合金为研究对象，通过宏-微观表征方法对伪弹性变形机制进行系统研究，首先建立考虑滑移和孪生/反孪生/再孪生的描述AZ31伪弹性的细观本构模型，在此基础上，构建扭折带理论模型，耦合到晶体塑性模型，建立准确描述Mg-Zn-Gd伪弹性的细观本构模型；提出定量评估伪弹性大小的数值方法，准确预测弦线模量和滞后环大小随应变的变化规律；建立循环加/卸载晶体塑性有限元，对镁板拉弯成形回弹进行预测，分析不同参数对回弹量的影响，为拉弯工艺优化提供依据。研究成果将为镁板循环加/卸载成形技术提供理论支撑，为工程力学设计提供依据。

伪弹性是镁板加/卸载下的重要变形特征，必须建立合理表征伪弹性变形的本构模型，才能准确预测镁板循环加/卸载成形过程，解决结构件提前失效的工程问题。本项目以AZ31不含稀土镁合金、Mg-Zn-Gd和ZE10稀土镁合金为研究对象，通过宏-微观表征方法对伪弹性变形机制进行系统研究，建立考虑滑移和孪生/反孪生/再孪生的描述镁合金伪弹性的细观本构模型，在此基础上，耦合晶体塑性模型，建立准确描述稀土镁合金伪弹性的细观本构模型；提出了定量评估伪弹性大小的数值方法，准确预测弦线模量和滞后环大小随应变的变化规律；建立了循环加/卸载晶体塑性有限元，对镁板四点弯曲成形过程进行预测，并进行了实验验证。研究成果将为镁板循环加/卸载成形技术提供理论支撑，为工程力学设计提供依据。