工业纯钛各向异性循环变形与多尺度疲劳裂纹扩展行为研究

The anisotropic commercial pure titanium has been widely applied in petrochemical industry, nuclear power equipment and other industrial fields. Its fatigue and crack growth behaviors under cyclic loading are concerned with the safety and reliability of titanium pressurized equipment. The anisotropic cyclic deformation and multiscale fatigue crack growth behaviors of commercial pure titanium are systematically studied in this project by experimental research, theoretical analysis, microscopic characterization and molecular dynamics simulation. The effect of tension-compression asymmetry under different orientations, loading modes and levels is quantitatively characterized, the anisotropic twinning and slipping deformation mechanism is revealed, and the fatigue life prediction model applicable for hexagonal close-packed metal materials presenting tension-compression asymmetry is proposed. The anisotropic fatigue crack growth law of commercial pure titanium at different scales is clarified, the anisotropic prediction model of fatigue crack growth rate is established, and the physical nature and law of the anisotropy in fatigue crack growth behavior of hexagonal close-packed metal materials at atomic scale is revealed. The contents of this project reflect the intersection of material science, mechanics, physics and other multidisciplinary fields, which is conducive to refine the theoretical study of fatigue and fracture of hexagonal close-packed metal materials, and provides scientific guidance for the fatigue design and safety assessment of anisotropic titanium pressurized structure. Therefore, it is not only of great academic significance but also has engineering application value.

广泛用于石油化工、核电装备等工业领域中的工业纯钛具有各向异性，其在循环载荷作用下的疲劳与裂纹扩展行为关系到钛制承压设备的安全与可靠性。本项目拟运用试验研究、理论分析、微观表征及分子动力学模拟，对工业纯钛各向异性循环变形与多尺度疲劳裂纹扩展行为展开系统研究。定量描述不同取向、载荷模式及载荷水平下拉压不对称性效应，揭示其各向异性孪晶及滑移变形机制，并提出适用于具有拉压不对称性密排六方金属材料的疲劳寿命预测模型；阐明不同尺度下工业纯钛各向异性疲劳裂纹扩展规律，建立各向异性疲劳裂纹扩展速率预测模型，并从原子尺度层面揭示密排六方金属材料中疲劳裂纹扩展行为各向异性的物理本质与规律。本项目研究内容体现了材料学、力学和物理学等多学科领域的交叉，有利于完善密排六方金属材料的疲劳与断裂理论研究，为各向异性钛金属承压结构的疲劳设计及安全评估提供科学支持，具有重要的学术及工程应用价值。

广泛用于石油化工、核电装备等工业领域中的工业纯钛具有各向异性，其在循环载荷作用下的疲劳与裂纹扩展行为关系到钛制承压设备的安全与可靠性。本项目系统研究了工业纯钛各向异性变形行为、疲劳寿命预测方法及多尺度疲劳裂纹扩展规律。主要研究内容和结果包括：（1）基于晶体塑性模拟及微观表征测试，定量描述了不同滑移系对于拉伸变形贡献，揭示了各向异性滑移机理。（2）基于对称应变/应力控低周疲劳实验，定量分析了拉压不对称性对于工业纯钛各向异性疲劳行为影响，揭示了不同载荷模式下各向异性循环变形机制及断裂机理，建立了适用于具有拉压不对称性密排六方金属材料的疲劳寿命预测模型。（3）基于平面双轴疲劳与棘轮实验，分析了不同双轴加载路径下的疲劳与棘轮变形规律，阐明了不同双轴加载路径下的断裂机理，建立了平面双轴疲劳寿命预测模型。（4）基于跨尺度原位疲劳裂纹扩展实验，构建了微缺陷尺寸与疲劳寿命之间定量关系，揭示了微观结构（晶界及晶体取向）与小裂纹扩展异常行为（裂纹止裂、裂纹偏折）、裂纹扩展速率波动及裂尖塑性变形机制之间内在联系，探明了小裂纹至长裂纹阶段疲劳裂纹扩展规律。（5）开展了不同晶体取向及孪晶界面裂纹扩展行为分子动力学模拟，深入揭示了晶体取向对于裂纹扩展速率、裂尖应力场分布及裂尖塑性变形机制的影响，且模拟结果与线弹性断裂力学理论预测结果及实验现象吻合较好。项目研究成果丰富并完善了密排六方金属材料的疲劳与断裂理论知识体系，为各向异性钛金属承压结构的疲劳设计及安全评估提供了理论依据与应用基础。