Papers by Author: Caterina L.E. Bruno

Abstract: One of the signatures of the presence of cracks in a sample is the nonlinearity in its elastic response to an impingent ultrasonic wave. The Fourier analysis is often inadequate to monitor the evolution of nonlinearity, since the signal-to-noise ratio of higher order harmonics is very low. In order to overcome this drawback, we suggest an alternative procedure to extract nonlinearity indicators from a recorded ultrasonic signal, based on the amplitude dependence of the response of the system. The procedure is first described and then used to analyse the evolution of the nonlinearity due to cracks induced by a quasi-static loading in mortar samples. Our approach allows to distinguish the compaction phase from the micro-damage progression and the pre-rupture phases.

Abstract: The presence of damage or cracks modifies the elastic properties of a sample, introducing nonlinear components in the elastic response to an ultrasonic excitation. Among other effects, we discuss here conditioning and memory, i.e. the transition of the sample to a new (non equilibrium) elastic state when perturbed by a strain, even at a relatively low amplitude. A quantification of these phenomena can be the basis for a novel Nondestructive Method to evaluate the integrity of a structural or mechanical component.

Abstract: The evolution of concrete behavior in the proximity of a joint under the effect of varying external pressures is studied by means of a novel nonlinear ultrasonic technique denoted as Scaling Subtraction Method. The results obtained show that the proposed method is effective in describing the occurrence of micro-structural changes near the joint and detect potential conditions for crack opening and damage initiation.