Abstract In this research, the fracture processes in concrete subjected to monotonic and fatigue loadings are characterized and the differences in failure mechanisms are studied using acoustic emission (AE) and digital image correlation (DIC) techniques. Experiments are performed on notched plain concrete beams under three-point bending. The micro and macro structural activities are classified based on acoustic energy levels to differentiate between the formation of a fracture process zone (FPZ) under monotonic and fatigue loadings. It is observed that a FPZ within its conventional definition is formed under monotonic loading. On the contrary, the AE results under fatigue loading indicate isolated and dispersed micro cracks up to 95% of fatigue life. A damage index based on AE energy is proposed for concrete subjected to fatigue loading which could be used in health monitoring of structures.

中文翻译：

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单调和疲劳载荷下混凝土断裂和破坏的微观力学

摘要 本研究表征了混凝土在单调和疲劳载荷作用下的断裂过程，并利用声发射 (AE) 和数字图像相关 (DIC) 技术研究了破坏机制的差异。试验是在三点弯曲下的带缺口的素混凝土梁上进行的。微观和宏观结构活动根据声能水平进行分类，以区分单调载荷和疲劳载荷下断裂过程区 (FPZ) 的形成。据观察，其传统定义内的 FPZ 是在单调载荷下形成的。相反，疲劳载荷下的 AE 结果表明孤立和分散的微裂纹高达疲劳寿命的 95%。