金属材料和结构的疲劳损伤是造成机械/机电产品尤其是长寿命高可靠性产品故障的最重要原因之一。本项目将研究建立一种多尺度的疲劳裂纹扩展模型，此模型的最大的优点就是可以在不同的时间和空间尺度下对疲劳损伤进行分析，比如从描述微观裂纹在载荷周期内任意时刻的瞬时行为到估算宏观结构整体的疲劳寿命，从而得到更准确和可信的疲劳寿命预测。本项目基于小时间尺度（Small-Time-Scale）的基本概念，根据扫描电镜（SEM）和光学显微镜下原位疲劳裂纹扩展试验(In-Situ SEM/Optical Microscopy Fatigue Crack Growth Testing)所观测到的微观疲劳裂纹扩展行为和机理，建立小时间尺度下描述疲劳裂纹尖端行为的物理模型，然后在这个微观物理模型的基础上进一步建立多尺度的疲劳裂纹扩展模型，从而实现对疲劳损伤和疲劳寿命准确实时的预测。

Among various damage mechanisms in mechanical/electromechanical products, especially for these long-life and high-reliability products, fatigue damage is one of the most important failure modes of metallic materials and structures. In this project, a fundamentally different and innovative fatigue prognosis methodology based on a small-time-scale concept is proposed. One of the most important advantages is that the proposed fatigue analysis methodology across multiple spatial and temporal scales becomes feasible, such as from material level up to structure level and from a single load cycle to the whole fatigue life. The fatigue crack growth mechanisms and behaviors observed by state-of-the-art experimental techniques (In-Situ SEM/Optical Microscopy Fatigue Crack Growth Testing) are used to establish a small-time-scale fatigue crack growth model. And then, a multi-scale fatigue crack growth methodology is developed for real-time and accurate fatigue life prognosis.