A Novel Ultrasonic Technique to Detect Damage Evolution in Quasi-Brittle Materials

The results of an experimental research on plain concrete are presented. The non-linear behavior of both virgin and damaged samples is investigated by means of ultrasonic tests: recent theoretical models, indeed, have pointed out that mono-frequency ultrasonic excitations bring to light such phenomena as harmonic generation and sidebands production, which are essentially due to the material classical or hysteretic non-linearity. The estimation of the harmonic components parameters (amplitudes and phases) is achieved through a signal processing technique based on MUltiple SIgnal Classification (MUSIC) system, which reveals to be optimal for the specific signal model here considered. The experiments described in this paper show that the material non-linear features increase with increasing level of internal micro-cracking, thus suggesting the possibility to use the ultrasonic signal analysis in the frequency domain as a valuable tool for damage assessment.