Fractal Stick-Slip Processes and Acoustic Emission Spectra for Analysis of Mode I Fracture in Fibrous Cementitious Composites

This study presents fast Fourier transform (FFT) based spectral analysis of acoustic emission (AE) waveforms to assess damage and fractal stick-slip processes in fiber reinforced composites. Mode I fracture experiments were conducted on plain concrete (PC) and steel fiber reinforced concrete (SFRC). The study aims to enhance real-time nondestructive evaluation of SFRC. The fracture behavior of the SFRC was modeled by analyzing the fiber induced stick-slip behavior using singular fractal functions. The frequencies of all AE waveforms were correlated with the frequency centroid spectrum (FCS) to analyze different fracture mechanisms, such as the initiation of microcracking, coalescence, macrocracking, and fiber bridging. At the initial peak load, the distributed crack growth in PC was found to be about five times higher than SFRC with 2% fiber content, as indicated by the steeper slope of FCS. Based on the experimental results and damage parameter, an optimal steel fiber content of about 1.5% appears to provide a balance between ultimate peak load (Pu) and the damage progression in SFRC.