Effects of slow dynamics and conditioning on non-linear hysteretic material assessment using impact resonance acoustic spectroscopy

The microstructural features of heterogeneous and porous materials give rise to unique non-linear dynamic behaviour. The purpose of this work is to investigate the dynamic response of thermally damaged concrete specimens measured by two different techniques: Non-linear Impact Resonance Acoustic Spectroscopy (NIRAS) and new Flipped Accumulative Non-linear Single Impact Acoustic Spectroscopy (FANSIRAS). Specimens were characterised in two different dynamic condition states of the material: relaxed and conditioned. The specimen's relaxed state indicates that no previous dynamic excitation event ocurred. The conditioned state denotes that the specimen has been dynamically tested before. The NIRAS results show that the non-linear material parameters, α_f and α_Q, are affected by their previous dynamic history (its conditioning). The recently proposed algorithm, FANSIRAS, extracts from a single resonant signal equivalent results to NIRAS when the specimen is conditioned. In this situation, both parameters α_f and α_Q were equivalent. The results suggest that new NDT parameters based on non-linear hysteretic parameters can quantify the damage level of thermally treated mortar specimens.