金属细观疲劳损伤的跨尺度实验表征与机理研究

金属疲劳失效是涉及宏细微多个物理层次的跨尺度损伤演化过程，多尺度方法的引入有力地推动了基于物理机制的疲劳模型的建立，然而目前仍存在跨尺度关联力学理论尚不完善，缺乏有效的跨尺度实验表征方法等不足，制约了多尺度疲劳研究的发展。本项目将基于先进的数字图像相关方法，针对金属疲劳在细观层次的非均匀变形特征，通过全场应变测量与表面微观结构在不同空间尺度的耦合，形成一套从亚晶到多晶的跨尺度实验表征方法，并将该方法直接用于疲劳微裂纹的形核机理研究中。主要研究一种多物理参量跨尺度耦合测量方法及建立考虑跨尺度微结构特征的数字图像相关方法，并在此基础上对非均匀变形模式与微裂纹形核之间的关联机制展开理论与实验研究。本项目的完成将为金属疲劳的研究提供一种在介观尺度上的解决思路，有助于改进现有多尺度疲劳模型的定量表征精度，同时将为跨尺度关联力学的发展提供一种有效的实验表征方法，有望用于工程材料与结构的疲劳设计中。

Metal fatigue failure is a trans-scale damage evolution process involving multiple physical levels from micro- to macroscale. The introduction of multiscale method has effectively impelled the recent development of mechanism-based fatigue models. It has, however, some drawbacks such as the immaturity of the trans-scale correlation mechanics and the absence of effective trans-scale experimental characterization methods, restricting the advance of multiscale fatigue research. Based on the advanced digital image correlation method and in view of the heterogeneous deformation feature of metal fatigue on the mesoscale, this project attempts to establish an experimental characterization method across scales from subgrain to polycrystal through the coupling of full-field strain measurements and surface microstructures at various spatial scales. And this developed method is expected to be applied directly to the study of fatigue microcrack nucleation mechanism. The main research concerns the establishment of a trans-scale multiple physical coupling measurement method and a digital image correlation method considering the microstructure feature across scales. Based on the developed techniques, both theoretical and experimental research on the correlation mechanism between heterogeneous deformation pattern and microcrack nucleation are anticipated. This project will offer a mesoscale solution for the study of metal fatigue, which may contribute to improving the quantitative characterization precision of the current multiscale fatigue models. And it will also provide an effective experimental characterization method for the development of the trans-scale correlation mechanics, which could be hopefully applied to the fatigue design of engineering materials and structures.