基于细观损伤理论的高温构件蠕变疲劳寿命预测方法

An accurate prediction of the in-service lifetime of components at high temperatures is of great importance to the safe, long-term operation of key equipment. The goal of the project is to establish a physical mechanism-based creep-fatigue damage model using a meso-damage theory for polycrystalline metals, and to develop a creep-fatigue lifetime prediction method for components at high temperatures. The following three research tasks will be completed in the study: (1) Based on the theory for grain-boundary cavity growth and deformation and the micromechanical analysis, the transition of physical mechanisms for the creep fracture between high triaxiality and low triaxiality of the stress will be discussed, and a mechanism-based creep-damage model for wide-range stress states will be proposed; (2) By using the digital image correlation method, electron backscatter diffraction technique and crystal plasticity theory, the quantitative correlation between the critical plastic strain and the stress state for high-temperature fatigue will be established, and a multi-axial local critical-strain criterion will be proposed; (3) Based on the analyses of creep damage and fatigue damage at the mesoscale, competing and coupling mechanisms of creep and fatigue will be identified, and a numerical method will be developed to predict the formation and propagation of the micro crack and macro crack. The successful completion of the project will improve the current understanding of the failure mechanisms arising from the creep-fatigue interaction for components at high temperatures. Also, the findings of the project will provide useful guidelines for improving the creep-fatigue lifetime prediction method for components operating at high temperatures.

准确预测蠕变疲劳载荷下高温构件的服役寿命，是重大装置长周期安全运行的重要保证。本项目拟以多晶体金属材料为研究对象，力图建立物理意义清晰的基于细观损伤理论的蠕变疲劳损伤模型，进而发展高温构件蠕变疲劳寿命预测方法。主要内容包括：（1）基于晶界孔洞长大与变形理论和微观力学分析，探索高、低应力三轴度下蠕变断裂物理机制的转变，提出宽范围应力状态下具有明确物理意义的蠕变损伤模型；（2）结合数字图像相关、电子背散射衍射技术和晶体塑性理论，针对高温疲劳模式建立临界塑性应变和应力状态的定量关联，提出多轴局部应变准则；（3）基于蠕变、疲劳损伤在细观尺度上的科学描述，澄清蠕变与疲劳的竞争与耦合效应，发展预测微裂纹与宏观裂纹形成与扩展的数值方法。研究成果有望阐明高温构件蠕变疲劳交互作用下失效的本质和规律，为高温构件蠕变疲劳寿命预测技术水平的提升提供科学支持。

如何准确预测蠕变疲劳载荷下高温构件的服役寿命，从而避免灾难性事故的发生，是结构完整性领域当前最具挑战的问题之一。项目组综合应用损伤力学理论、数值模拟方法和显微测试观察等手段，建立了合理的蠕变疲劳损伤模型，发展了高温构件蠕变疲劳寿命预测方法，较好地完成了项目的预期计划。主要研究工作及成果包括：（1）梳理了高温蠕变失效的物理机制，开展了蠕变表面裂纹扩展分析和焊接接头蠕变损伤分析，发现基于多轴蠕变损伤模型的有限元法预测精度显著优于英国标准推荐的计算方法。（2）建立了考虑负应力三轴度对孔洞长大影响的循环多轴断裂应变能模型，并对超低周疲劳失效进行了预测，发现该模型能很好地预测断裂时的等效塑性应变和循环周次。（3）对现有的蠕变疲劳寿命预测模型进行了对比与评价，发现应变能密度耗散模型和氧化损伤方程的耦合模型表现最佳，不仅寿命误差带最小，而且统计学指标最理想。（4）建立了晶体塑性有限元法与细观损伤机制相结合的多尺度数值计算框架，实现了缺口试样蠕变疲劳裂纹萌生行为的合理预测。研究成果为高温构件蠕变疲劳寿命预测提供了科学支持。项目执行期间，发表期刊论文14篇（其中SCI收录8篇），参编SCTS和机械工程学报专刊各1期，申请发明专利8项、软件著作权5项，培养博士研究生2名、硕士研究生4名。组织国际学术会议3次、全国学术会议1次，并作邀请报告4次。项目负责人获国家自然科学基金优秀青年科学基金项目资助，入选上海市东方学者特聘教授和福建省闽江学者讲座教授，并获中国机械工程学会年度优秀论文奖。项目成员获ISSI2021最佳学生论文奖和中国压力容器优秀青年论文奖。