Abstract
In this paper we propose a fractal theory for the prediction of the time-effects on the damage evolution in cracking solids. By means of the Acoustic Emission (AE) technique, we have analysed the evolution of damage in several structures by an extensive experimental analysis in time. This technique permits to estimate the amount of energy released during fracture propagation and to obtain information on the criticality of the ongoing process. Theory and experiments agree closely. Moreover, based on fractal concepts, we have formulated a multiscale criterion to predict the damage progress in concrete structural elements. According to this method, the damage level of a structure can be estimated from AE data of a reference specimen extracted from the structure and tested up to failure. By monitoring the fracture propagation by AE, it is therefore possible to evaluate the damage level of a structure as well as the time corresponding to final collapse. Consequently, the life-time predictions of monitored solid structures can be estimated: as an example we have analysed the evolution of damage in two piers supporting a viaduct along an Italian highway built in the 1950s.