A preliminary study for prefailure indicators in acoustic emissions using wavelets and natural time analysis

Acoustic emission tests were conducted on prismatic Dionysos’ marble specimens subjected to compressive mechanical loading cycles. Two groups of acoustic emission time series were analyzed: one group comprised the number of counts per acoustic emission hit and a second group comprised the RA quantity (RA=rise time/amplitude). Both time series were studied during the load increase period. The investigation of prefailure indicators was carried out using an interdisciplinary approach: using two solid methods from different scientific areas (i.e. cardiology and seismology) we were able to detect failure indicators along before the final collapse. More specific, by means of multiresolution wavelet analysis for the study of temporal variation of the wavelet-coefficients’ standard deviation and natural time analysis using the variance (κ₁) of natural-time transformed time-series, a common pattern for both domains was discovered, clearly showing that it is feasible to estimate if the applied mechanical load has led the specimen in the nonlinear region (σ^* > 70% σ_f) regarding the stress–strain behavior.