高应变率加载下密排六方金属的拉压非对称行为研究

Uniaxial tension and uniaxial compression tests for titanium and magnesium alloys will be performed under quasi-static and high-rate loadings to investigate the strain-rate dependent strength differential effects. The matching relationship between the tension-compression specimen and the Hopkinson bar system will be studied and the specimen geometry will be determined. Based on the proposed experimental method for dynamic Bauschinger effect of metals, high-rate tension-compression and compression-tension tests will be carried out under single-cycle and multi-cycle loadings to investigate the influences of strain rate, strain history and loading path on the Bauschinger effects of titanium and magnesium alloys and evaluate the relationship between strength differential effect and Bauschinger effect. The rate dependent plastic deformation mechanisms, especially the microscopic mechanism of tension-compression asymmetry, will be studied using microscopic analysis methods. The macroscopic constitutive model incorporating strain-rate dependent strength differential effect will be proposed to describe the dynamic Bauschinger behavior of titanium and magnesium alloys. The polycrystalline microscopic constitutive model in which the strength differential effect is incorporated into the crystal plasticity finite element method will be established to characterize the Bauschinger behavior and microstructure evolution of titanium and magnesium alloys. The aforementioned testing, analyzing and characterizing studies on tension-compression asymmetric responses of titanium and magnesium alloys will give experimental data and theoretical foundation for the designs of forming process and structural strength.

对密排六方结构的钛合金和镁合金实施准静态至高应变率的单向拉伸和单向压缩实验，研究强度差效应的应变率相关性；研究拉压一体试件与霍普金森杆实验系统的匹配关系并确定试件几何参数，形成金属材料动态包辛格效应的测试方法；对钛合金和镁合金实施准静态至高应变率、单循环和多循环的拉伸-压缩和压缩-拉伸加载实验，研究包辛格效应的应变率相关性、应变历史相关性、加载路径相关性以及包辛格效应与强度差效应的关联；结合材料微结构显微分析手段，研究钛合金和镁合金应变率相关的拉压非对称变形行为的细观机制；建立计及应变率相关性和强度差效应的宏观本构模型，建立基于晶体塑性理论的计及强度差效应的多晶细观数值本构模型，表征和分析钛合金和镁合金的动态包辛格行为及其变形机制。上述高应变率加载下拉压非对称行为的测试、分析和表征研究将为钛合金和镁合金的成形工艺设计和结构强度设计等提供实验数据和理论依据。

对密排六方结构的钛合金TA7和镁合金ME20M在较大的应变率和温度范围内实施了单向拉伸和单向压缩加载实验，获得了等温和绝热应力-应变响应，发现其塑性变形行为均具有拉压非对称性且与温度和应变率相关。建立了计及应变率和温度相关性的宏观本构模型，建立了基于晶体塑性理论的多晶细观数值本构模型和粘塑性自洽晶体塑性模型，有效表征了钛合金和镁合金的温度和应变率相关的拉压非对称行为并分析了其塑性变形机制。显微观察和数值模拟表明，孪晶和锥面滑移是TA7和ME20M宏观塑性变形行为出现强度差效应的主要原因。设计了霍普金森杆实验系统加载波吸波装置有效避免了试件的二次塑性变形，形成了金属材料动态包辛格效应的测试方法；对钛合金TA7和镁合金AZ80实施了准静态至高应变率、单循环和多循环的拉伸-压缩和压缩-拉伸加载实验，发现包辛格效应具有应变率相关性、应变历史相关性和加载路径相关性，分析和表征了强度差效应与包辛格效应的关联。上述拉压非对称行为的测试、分析和表征研究为钛合金和镁合金的成形工艺设计和结构强度设计等工程应用提供了实验数据和理论依据。

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