Fractal micro-cracking features in concrete under fatigue and monotonic loading

The fracture process in concrete is a collaborative process among the micro-cracks originating ahead of the crack tip under the applied load, and influenced by the constituent heterogeneity.To understand this interactive phenomenon, statistical physics-based theories are very applicable, and by treating each micro-crack as an energy source, the whole process can be remodeled into a phase space.This study aims to investigate the sparsity of micro-cracking in concrete subjected to fatigue and monotonic loadings by utilizing the fractal signatures of the phase space constructed from the acoustic emission parameters.The correlation dimension of the acoustic emission energy time series generated from concrete for both types of loading is obtained separately using the Grasserberger-Proccacia algorithm.The results indicate that concrete under fatigue has a lower correlation dimension than the monotonic case, explaining that fatigue is a process where one crack causes failure, unlike the monotonic case, where it is a cooperative phenomenon.The correlation dimension can also capture the influence of cycling frequency on the fatigue life, showing an increment with the increase in frequency.The efficiency of this method can be enhanced by choosing the appropriate dimension of the underlying phase space of the time series and, therefore, can preferably employed to estimate the health of a real-life structure over conventional methods like event source localization.