低周疲劳下钛合金的残余孪晶累积机制及弹粘塑性自恰模型研究

低周疲劳下钛合金的滑移、孪生及退孪生机制是诱发疲劳损伤的重要因素。基于晶体塑性模型研究滑移、孪生及退孪生机制与宏观行为的定量关系，是研发高性能钛合金的理论基础，但低周疲劳下钛合金的塑性变形存在残余孪晶累积等复杂行为，使得构建其晶体塑性模型面临严峻挑战。本项目旨在对低周疲劳下钛合金的残余孪晶累积机制及其晶体塑性模型展开攻关，包括：借助原位EBSD系统，阐明循环载荷下钛合金残余孪晶体积分数随循环次数的变化规律，构建残余孪晶体积分数控制准则；将背应力引入现有弹粘塑性自洽模型的本构关系，结合残余孪晶体积分数控制准则，建立考虑循环载荷下钛合金孪晶累积及反向加载应变软化效应的弹粘塑性自洽模型，并开发其数值软件；借助数值方法，研究低周循环载荷下钛合金的塑性变形机制与宏观塑性变形行为的定量关系，揭示滑移、孪生及退孪生机制对包辛格效应、各向异性、加工硬化的作用。研究成果可为高性能钛合金研发提供理论支撑。

The slip, twinning and detwinning mechanisms of titanium alloy under low-cycle fatigue are significant factors to induce fatigue damage. It is the theoretical basis for the development of high performance titanium alloy to study the quantitative relationship between slip, twinning and detwinning mechanisms and macroscopic behavior based on the crystal plasticity model. However, due to the complex behavior of plastic deformation of titanium alloy under low-cycle fatigue (such as, alternating twinning and detwinning), it is a severe challenge to develop crystal plasticity model for titanium alloy. This project aims to study the crystal plasticity model and plastic deformation mechanisms of titanium alloy under low-cycle fatigue, including: Based on the in-situ EBSD system, the variation of the residual twin volume fraction with the fatigue cycles in titanium alloy is clarified, and a control criterion for the residual twin volume fraction is established; Implementing back stress to the constitutive relation, and combining with the residual twin volume fraction control criterion, the elastic viscoplastic self-consistent model considering the twins accumulation and the strain softening effect under reverse loading is established, of which numerical software is also developed; By numerical method, the quantitative relationship between plastic deformation mechanisms and macroscopic plastic deformation behavior of titanium alloy under low-cyclic loading is studied, and the effects of slip, twinning and detwinning mechanisms on Bauschinger effect, anisotropy and work hardening are revealed. The research results can provide theoretical support for the development of high performance titanium alloy.