Nicolas Wilkie-Chancellier

Slant-Stack analysis for the estimation of a marble degradation profile

Ultrasonic techniques are increasingly used in various fields such as mining, geotechnical, civil engineering, because they are non-destructive and easy to apply. These techniques are usually employed both in situ and in laboratory conditions to characterize and determine the dynamic and physical properties of rocks. In cultural heritage, the characterization of marble statue by acoustic wave is a wellknown non-destructive method. This paper undertakes a study of the Carrara marble that composes the statues exposed in the Château de Versailles gardens, in order to better understand the processes of deterioration affecting them. For this, a plate of Carrara marble is artificially aged through heating/cooling thermal cycles performed on one face of the samples. A Rayleigh wave is generated by a 1 MHz central frequency contact transducer exited by a voltage pulse. A laser vibrometry method is used to detect the Rayleigh wave propagation on the depth sample. In order to understand how the degradation and nonhomogeneity and Rayleigh velocity vary through depth, Slant Stack (SS) transform was used. This analysis is a particular case of the Radon Transform (TR). The results show a uniform vibration behavior of non-degraded sample and highlight three zones with different state of degradation in the altered marble sample. The extraction of relevant parameters using this analysis is promising for the characterization of marble and following up its weathering.

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

&NA; 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%. HighlightsExisting ultrasonic methods can be used to study new polyester‐based composites.Isotropic homogeneous hypothesis seems adapted to explain surface wave propagation.Mechanical properties are reported for polyester‐marble composites.No significative difference was found between two resin types.Acousto‐optics measurement might be suitable to operate with low contact condition.

New ultrasonic technic for on-line encapsulation monitoring

This presented work shows the ability for this method to monitor the encapsulation process for fragrance delivery. The encapsulation is based on the coacervation principle which consists in the chemical reaction between two water soluble polyelectrolytic polymers with opposite charges. An experimental protocol is performed with precise conditions of temperature and acidity to form, during the process, elastic micro-shells encapsulating the fragrance. Thus, in this paper, the new ultrasonic technic is presented. It is based on the resonance of an AT cut quartz sensor. When the sensor is loaded, using the shear wave propagation in the complex fluid, the mechanical impedance of the material is extracted from the modification of the resonance parameters [1]. A complete on-line monitoring can then be carried out during the encapsulation process. The obtained results allow focusing the different steps of the encapsulation. This new system is inexpensive and easily adaptable to industrial conditions. It is robust in aggressive conditions. The evolution is to make this system remotely controlled.