Experimental ultrasonic characterization of polyester-based materials for cultural heritage applications

For several years, the Réunion des musées nationaux - Grand-Palais has produced polyester resin reproductions in order to replace marble sculptures that have weakened by outdoor exposure. These objects are made of a complex multilayered polyester composite material including reinforcements to ensure the mechanical strength of the final structure and mineral fillers that allow to imitate the original aesthetics. However, the final structure also weakens because of constant outdoor exposure and ageing. This observation leads today to conduct research related to the structural health monitoring of reproductions for preventive conservation of cultural heritage. This paper presents a nondestructive technique to study the properties of the composite material used to produce reproductions of marble sculptures. Firstly, classical ultrasonic contact measurements were performed to estimate bulk properties and Rayleigh wave velocity. Secondly, experimental Rayleigh wave was measured using contact and laser vibrometry methods. The results show the potential of using ultrasonic surface wave propagation and laser vibrometry method to develop a minimum contact technique to study these polyester-based materials. The maximum relative uncertainty with respect to the expected theoretical Rayleigh wave velocity was close to 12%.