Research

This study investigated the effect of loading frequency on the fatigue damage process in concrete using digital imaging and acoustic emission techniques. It was found that the complex fatigue damage process in heterogeneous concrete is reflected in the amplitude of acoustic energy. The distribution of acoustic energy levels was utilized to classify micro- and macro-structural activities. It was found that fatigue failure at higher frequencies is governed predominantly by microcracks, while at lower frequencies both micro- and macro-cracks contribute to failure. The applied loading frequency had a marked influence on the size of the fracture process zone (FPZ). A fatigue model encapsulating frequency effects in terms of FPZ width is proposed using a unified damage and fracture mechanics approach within the framework of dimensional analysis and similitude concepts

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.

This study investigated the effect of loading frequency on the fatigue damage process in concrete using digital imaging and acoustic emission techniques. It was found that the complex fatigue damage process in heterogeneous concrete is reflected in the amplitude of acoustic energy. The distribution of acoustic energy levels was utilized to classify micro- and macro-structural activities. It was found that fatigue failure at higher frequencies is governed predominantly by microcracks, while at lower frequencies both micro- and macro-cracks contribute to failure. The applied loading frequency had a marked influence on the size of the fracture process zone (FPZ). A fatigue model encapsulating frequency effects in terms of FPZ width is proposed using a unified damage and fracture mechanics approach within the framework of dimensional analysis and similitude concepts