循环载荷下短裂纹的起裂门槛与扩展不同于长裂纹，但机理研究不足。在超高周范畴，短裂纹起裂与扩展是疲劳总寿命的重要部分。掌握短裂纹的扩展规律对于提升寿命预测水平和完善全寿命设计理论等方面作用突出。本项目用两种代表性金属的超大晶粒试件，采用超声疲劳试验结合原位红外热成像和显微观测，研究预制短裂纹在单个晶体内的低速扩展行为。是综合数字图像相关分析、热耗散分析和微观组织演化分析等方法的实验研究。项目通过对比实验，量化短裂纹近门槛值扩展速率，研究短裂纹的晶内低应力扩展规律；探讨微观组织结构、材料力学性能、缺口长度和应力水平对短裂纹扩展的影响，提出物理意义明确的短裂纹低应力疲劳扩展机理并建立相应的寿命预测模型；分析不同载荷周次下的裂尖变形及温度场变化，阐明短裂纹扩展与裂尖应变和热耗散的关系。本项目的开展对提升工程结构寿命预测的精准度，拓展红外非接触监控技术，支撑多尺度计算细观力学研究有重要现实意义。

Short crack propagation behavior is distinguishing with long crack propagation under cyclic loading. In the very high cycle fatigue (VHCF) regime, the stage of short crack formation and propagation is an important part in the total fatigue life. Understanding the short crack propagation behavior will improve the fatigue life prediction and total life design theory. The project will selecting two representative metal large scale crystalline specimens, employing ultrasonic fatigue plus in-situ microscope observation and infra imaging technology to study artificial short crack propagation behavior in single crystalline by combining Digital Image Correlation technology(DIC), fractographic analysis, thermal dissipation analysis, and microstructure deformation analysis. The project will discuss the role of microstructure, mechanical properties, crack length and fatigue stress to the short crack propagation and propose a short crack propagation mechanism and prediction model. To establishing the relation between crack propagation rate, strain and thermal dissipation by analyzing the deformation and temperature field at crack tip. The study is meaningful for raising the precision of life prediction, extending the IR-NDT inspection technology and supporting multi-scale computational micromechanics.