Nonlinear phenomena analysis in the ultrasonic wave propagation to detect damage evolution in historical structures

The non-linear behaviour of both virgin and damaged samples is experimentally investigated by means of ultrasonic tests. Generally, the signatures of non linearity in the elastic response of a specimen stressed by an ultrasonic wave is analysed by means of classical Fourier analysis. The main problem is related to the low amplitude responses obtained, often below the noise level. For this reason, in this paper a novel and alternative tool, based on the amplitude dependence of the response of the system, is presented. The sensitivity of the approach to the presence of non linearity is proven experimentally onto several linear and non-linear material and an application on a granite slab is shown.