镁合金板材非对称硬化变形行为的细观本构模型及应用

Magnesium alloy sheet shows special asymmetric hardening characteristics during loading-unloading strain path. To establish constitutive model reflecting the asymmetric hardening characteristics is essential for simulation of forming and springback for magnesium alloy sheet. In this project, slip-reverse slip and twinning-detwinning deformation mechanisms and their interactions of AZ31 magnesium alloy sheet will be studied, based on mesoscopic plastic mechanics theory. Then a crystal plasticity constitutive model describing the microscopic nature of asymmetric hardening behavior will be established using theory-simulation-experiment method. By analyzing the polycrystalline uniform and coupling method, a polycrystal constitutive model will be established. Further, polycrystal model is introduced into the large deformation elastic-plastic finite element framework. Thus loading-unloading-reversal loading deformation can be simulated accurately. Finally, the model will be applied to forming and springback simulation of AZ31 alloy and experimental validated. The effect of different texture characteristics on loading-unloading deformation behaviour during forming and springback will be analyzed using this model. This project shows a great theoretical value for revealing deformation mechanisms and developing the plastic deformation theory of magnesium alloy sheet. It also shows important social significance and economic prospects for predicting spingback and developing plastic forming process for magnesium alloy sheet.

镁合金板材在加卸载复杂变形路径下表现出特殊的非对称硬化特性，建立反映其非对称硬化特征的本构模型对于精确模拟镁板冲压成形与回弹至关重要。本项目以AZ31板材为研究对象，基于细观塑性力学理论，采用理论推导、数值模拟与变形实验相结合的方法，研究镁板在加卸载变形路径下滑移-反向滑移、孪生-反孪生等微观变形机制及相互作用，建立能够描述镁板非对称硬化行为微观本质的晶体塑性本构模型；研究多晶体均匀化与宏微观耦合计算方法，将镁板非对称硬化晶体塑性模型引入大变形弹塑性有限元框架，准确模拟镁板加载-卸载-反向加载变形过程，应用于镁板成形与回弹的计算，并通过实验进行验证；利用所建立的模型，研究板材不同织构特性对成形回弹过程中加卸载变形行为的影响规律。本项目研究对于揭示镁合金板材的变形机制、发展镁合金塑性变形理论具有重要的理论价值；对于准确预测镁板回弹、发展镁板塑性成形工艺具有良好的社会意义和经济前景。

镁合金作为工程应用中最轻的金属结构材料，是轻量化选材的重要目标。但是镁合金板材常温冲压成形后回弹较大，严重影响了冲压零件精度，必须精确预测并在成形中加以控制。板材冲压回弹过程包含非线性接触、大变形和弹塑性等多种复杂现象，以及加载、卸载、反向加载等变应变路径。镁板在加卸载复杂路径下表现出特殊的非对称硬化特性，因此建立反映其非对称硬化特征的本构模型对于精确模拟镁板冲压成形与回弹至关重要。本项目以AZ31B镁合金板材为研究对象，主要研究内容有：(1) 实验研究了单一路径下镁板的力学性能及织构演变，以及加载-卸载-反向加载路径下镁板的力学行为，包括拉压不对称性及非对称硬化行为。重点研究了镁板的面内各向异性及对冲压性能的影响，为提高冲压性能提供轧制工艺优化方案。(2) 基于细观塑性力学理论，研究了滑移、孪生、反孪生等微观变形机制及相互作用，建立了耦合滑移、孪生和反孪生的多晶体塑性本构模型，能够反映变应变路径下的非对称硬化行为。(3) 研究了多晶体均匀化方法，建立了弹-粘塑性本构模型，该模型能够反映弹-塑性阶段力学行为。(4) 研究了宏微观耦合计算方法，将镁板非对称硬化晶体塑性模型引入大变形弹塑性有限元框架，准确模拟了镁板加载-卸载-反向加载变形过程，应用于镁板成形与回弹的计算，U形弯曲回弹角度误差在2%左右。