Fatigue crack propagation monitoring by Acoustic Emission signal analysis

A crucial aspect in damage evaluation of masonry structures is the analysis of long-term behaviour and for this reason fatigue analysis has a great influence on safety assessment of these structures.Acoustic Emission (AE) technique is very effective in identifying micro and macro-defects and their temporal evolution due to fatigue in several materials. This technique permits to estimate the velocity of ultrasonic waves propagation and the amount of energy released during fracture propagation to obtain information on the criticality of the ongoing process.By means of AE monitoring, an experimental analysis on two different sets of reinforced masonry walls under fatigue loading has been carried out. During these tests, the AE signals were recorded. The AE signals were analysed using Fast Fourier Transform (FFT) to examine the frequency distribution during the micro- and macro-cracking process. The evolution of the wavelength of the shear component of the AE signal was evaluated through the two characteristic peaks in the AE signals spectrum and the wave speed of the P or S waves. This wavelength evolution can provide information on the micro-crack and macro-crack progress. This procedure permits to estimate the characteristic fracture dimension in several loading conditions and for different masonry reinforcing methods.