Suivi non destructif de l’altération de marbres par méthodes acoustiques

Statue marble characterization by acoustic waves is a well-known non-destructive method. Such investigations through the statues by time of flight method (TOF) point out sound speeds decrease with ageing state by comparing healthy and altered rocks. However for outdoor stored statues as the ones in the gardens of Chateau de Versailles, ageing affects mainly the surface of the Carrara marble. An artificial aging protocol is implemented in the laboratory to simulate the degradation of the marble surface by using heating/cooling thermal cycles on one face of a marble plate. Acoustic waves are generated by contact transducers excited by a voltage pulse placed on both sides of the sample. During ageing, the marble samples are characterized in transmission, along their volume by shear, compressional TOF measurements and along their surface by Rayleigh wave’s measurements. To follow the Rayleigh wave propagation, laser vibrometry method is used. The obtained results, and the associated signal processing, make it possible to extract relevant physical parameters in the monitoring of the degradation state.